$NFBK
Northfield Bancorp, Inc. Stock $nfbk

$nfbk Overview Financials Valuation SEC Filings Company Website

2019 Q4 Form 10-K Financial Statement

#000149322521000048 Filed on March 10, 2021

Income Statement

Concept	2019 Q4	2019 Q3	2019 Q2
Revenue	$42.64M	$42.85M	$40.19M
YoY Change	9.47%	13.57%	11.85%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$1.320M	$840.0K	$840.0K
YoY Change	57.14%	3.7%	-1.18%
% of Gross Profit
Operating Expenses
YoY Change
Operating Profit
YoY Change
Interest Expense	$14.16M	$14.03M	$13.03M
YoY Change	29.4%	43.09%	59.63%
% of Operating Profit
Other Income/Expense, Net
YoY Change
Pretax Income	$13.17M	$17.98M	$10.48M
YoY Change	7.45%	47.93%	-16.16%
Income Tax	$3.052M	$4.845M	$2.280M
% Of Pretax Income	23.17%	26.94%	21.75%
Net Earnings	$10.12M	$13.14M	$8.204M
YoY Change	1.76%	44.77%	-22.69%
Net Earnings / Revenue	23.74%	30.66%	20.41%
Basic Earnings Per Share	$0.22	$0.28	$0.18
Diluted Earnings Per Share	$0.21	$0.28	$0.17
COMMON SHARES
Basic Shares Outstanding	49.18M shares	46.63M shares	46.86M shares
Diluted Shares Outstanding		46.98M shares	47.27M shares

Balance Sheet

Concept	2019 Q4	2019 Q3	2019 Q2
SHORT-TERM ASSETS
Cash & Short-Term Investments
YoY Change
Cash & Equivalents	$147.8M	$69.65M	$46.91M
Short-Term Investments
Other Short-Term Assets
YoY Change
Inventory
Prepaid Expenses
Receivables
Other Receivables
Total Short-Term Assets
YoY Change
LONG-TERM ASSETS
Property, Plant & Equipment	$25.66M	$25.97M	$25.70M
YoY Change	0.21%	2.93%	2.56%
Goodwill	$38.41M	$38.41M	$38.41M
YoY Change	0.0%	0.0%	0.0%
Intangibles
YoY Change
Long-Term Investments
YoY Change
Other Assets
YoY Change
Total Long-Term Assets
YoY Change
TOTAL ASSETS
Total Short-Term Assets
Total Long-Term Assets
Total Assets	$5.055B	$4.808B	$4.768B
YoY Change	14.67%	12.18%	13.85%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$20.00M	$18.80M	$20.80M
YoY Change	11.11%	10.59%	15.56%
Accrued Expenses	$74.20M	$71.20M	$71.10M
YoY Change	159.44%	119.08%	146.02%
Deferred Revenue
YoY Change
Short-Term Debt	$81.00M	$75.00M	$75.00M
YoY Change
Long-Term Debt Due
YoY Change
Total Short-Term Liabilities	$94.20M	$90.00M	$91.90M
YoY Change	102.15%	81.82%	95.95%
LONG-TERM LIABILITIES
Long-Term Debt	$776.0M	$616.2M	$620.1M
YoY Change	89.78%	39.66%	18.27%
Other Long-Term Liabilities
YoY Change
Total Long-Term Liabilities	$776.0M	$616.2M	$620.1M
YoY Change	89.78%	39.66%	18.27%
TOTAL LIABILITIES
Total Short-Term Liabilities	$94.20M	$90.00M	$91.90M
Total Long-Term Liabilities	$776.0M	$616.2M	$620.1M
Total Liabilities	$4.359B	$4.118B	$4.087B
YoY Change	16.5%	13.39%	15.51%
SHAREHOLDERS EQUITY
Retained Earnings	$322.6M	$317.6M	$309.6M
YoY Change	6.62%	6.83%	5.7%
Common Stock	$609.0K	$609.0K	$609.0K
YoY Change	0.0%	0.0%	0.0%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$160.8M	$161.0M	$161.0M
YoY Change	5.23%	4.47%	3.94%
Treasury Stock Shares	11.76M shares	11.78M shares	11.82M shares
Shareholders Equity	$695.9M	$689.9M	$681.1M
YoY Change
Total Liabilities & Shareholders Equity	$5.055B	$4.808B	$4.768B
YoY Change	14.67%	12.18%	13.85%

Cashflow Statement

Concept	2019 Q4	2019 Q3	2019 Q2
OPERATING ACTIVITIES
Net Income	$10.12M	$13.14M	$8.204M
YoY Change	1.76%	44.77%	-22.69%
Depreciation, Depletion And Amortization	$1.320M	$840.0K	$840.0K
YoY Change	57.14%	3.7%	-1.18%
Cash From Operating Activities	$17.23M	$17.86M	$6.430M
YoY Change	61.48%	11.07%	-48.31%
INVESTING ACTIVITIES
Capital Expenditures	-$940.0K	-$1.040M	-$1.260M
YoY Change	-17.54%	15.56%	137.74%
Acquisitions
YoY Change
Other Investing Activities	-$171.1M	-$18.95M	-$239.8M
YoY Change	71.23%	-81.19%	81.76%
Cash From Investing Activities	-$172.1M	-$19.99M	-$241.1M
YoY Change	70.26%	-80.33%	81.99%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	233.0M	24.88M	195.7M
YoY Change	112.93%	-70.92%	55.09%
NET CHANGE
Cash From Operating Activities	17.23M	17.86M	6.430M
Cash From Investing Activities	-172.1M	-19.99M	-241.1M
Cash From Financing Activities	233.0M	24.88M	195.7M
Net Change In Cash	78.16M	22.75M	-38.92M
YoY Change	310.72%	-227600.0%	-730.79%
FREE CASH FLOW
Cash From Operating Activities	$17.23M	$17.86M	$6.430M
Capital Expenditures	-$940.0K	-$1.040M	-$1.260M
Free Cash Flow	$18.17M	$18.90M	$7.690M
YoY Change	53.85%	11.31%	-40.71%

Facts In Submission

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CY2019	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	5679000	USD
CY2018	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	5011000	USD
CY2020	us-gaap	Professional Fees ProfessionalFees	4141000	USD
CY2019	us-gaap	Professional Fees ProfessionalFees	3545000	USD
CY2018	us-gaap	Professional Fees ProfessionalFees	3482000	USD
CY2020	us-gaap	Marketing And Advertising Expense MarketingAndAdvertisingExpense	2088000	USD
CY2019	us-gaap	Marketing And Advertising Expense MarketingAndAdvertisingExpense	3442000	USD
CY2018	us-gaap	Marketing And Advertising Expense MarketingAndAdvertisingExpense	2726000	USD
CY2020	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	885000	USD
CY2019	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	563000	USD
CY2018	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	1065000	USD
CY2020	us-gaap	Other Noninterest Expense OtherNoninterestExpense	5168000	USD
CY2019	us-gaap	Other Noninterest Expense OtherNoninterestExpense	5988000	USD
CY2018	us-gaap	Other Noninterest Expense OtherNoninterestExpense	6857000	USD
CY2020	us-gaap	Noninterest Expense NoninterestExpense	78513000	USD
CY2019	us-gaap	Noninterest Expense NoninterestExpense	73549000	USD
CY2018	us-gaap	Noninterest Expense NoninterestExpense	67043000	USD
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	50025000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	53022000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	49711000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	13037000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	12787000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	9632000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	36988000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	40235000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	40079000	USD
CY2020	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.76
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.86
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.87
CY2020	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.76
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.85
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.85
CY2020	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	48721504	shares
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	46783442	shares
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	46319760	shares
CY2020	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	48785963	shares
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	47163804	shares
CY2018	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	47107433	shares
CY2020	us-gaap	Net Income Loss NetIncomeLoss	36988000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	40235000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	40079000	USD
CY2020	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	12077000	USD
CY2019	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	19666000	USD
CY2018	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	-5203000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	327000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	514000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	178000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Before Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax	11750000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Before Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax	19152000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Before Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax	-5381000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	0	USD
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-77000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-240000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Before Tax Portion Attributable To Parent OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent	11750000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Before Tax Portion Attributable To Parent OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent	19229000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Before Tax Portion Attributable To Parent OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent	-5141000	USD
CY2020	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	3380000	USD
CY2019	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	5505000	USD
CY2018	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	-1462000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	91000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	144000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	50000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	0	USD
CY2018	us-gaap	Stock Issued During Period Value Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	0	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-22000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-67000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	8461000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	13846000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-3696000	USD
CY2020	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	45449000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	54081000	USD
CY2018	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	36383000	USD
CY2017Q4	us-gaap	Stockholders Equity StockholdersEquity	638877000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	40079000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-3696000	USD
CY2018	us-gaap	Amortization Of Esop Award AmortizationOfESOPAward	2337000	USD
CY2018	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	5432000	USD
CY2018	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	2088000	USD
CY2018	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	0.40
CY2018	us-gaap	Dividends Common Stock DividendsCommonStock	18673000	USD
CY2018	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	16.85
CY2018	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	5000	USD
CY2018Q4	us-gaap	Stockholders Equity StockholdersEquity	666439000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	40235000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	13846000	USD
CY2019	us-gaap	Amortization Of Esop Award AmortizationOfESOPAward	2340000	USD
CY2019	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	3236000	USD
CY2019	us-gaap	Restricted Stock Award Forfeitures RestrictedStockAwardForfeitures	0	USD
CY2019	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	5770000	USD
CY2019	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	0.43
CY2019	us-gaap	Dividends Common Stock DividendsCommonStock	20198000	USD
CY2019	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	15.26
CY2019	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	15815000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	695853000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	36988000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	753981000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	36988000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	40235000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	8461000	USD
CY2020	us-gaap	Amortization Of Esop Award AmortizationOfESOPAward	1780000	USD
CY2020	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	1432000	USD
CY2020	us-gaap	Stock Issued During Period Value Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	0	USD
CY2020	us-gaap	Restricted Stock Award Forfeitures RestrictedStockAwardForfeitures	0	USD
CY2020	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	175000	USD
CY2020	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	0.44
CY2020	us-gaap	Dividends Common Stock DividendsCommonStock	21476000	USD
CY2020	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	41173000	USD
CY2020	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	11.59
CY2020	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	10405000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	40079000	USD
CY2020	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	12742000	USD
CY2019	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	22000	USD
CY2018	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	2615000	USD
CY2020	us-gaap	Share Based Compensation ShareBasedCompensation	3212000	USD
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	5576000	USD
CY2018	us-gaap	Share Based Compensation ShareBasedCompensation	7769000	USD
CY2020	us-gaap	Depreciation Nonproduction DepreciationNonproduction	3878000	USD
CY2019	us-gaap	Depreciation Nonproduction DepreciationNonproduction	3569000	USD
CY2018	us-gaap	Depreciation Nonproduction DepreciationNonproduction	3020000	USD
CY2020	nfbk	Amortization Of Premiums And Deferred Loan Costs AmortizationOfPremiumsAndDeferredLoanCosts	4073000	USD
CY2019	nfbk	Amortization Of Premiums And Deferred Loan Costs AmortizationOfPremiumsAndDeferredLoanCosts	4344000	USD
CY2018	nfbk	Amortization Of Premiums And Deferred Loan Costs AmortizationOfPremiumsAndDeferredLoanCosts	2441000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	229000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	265000	USD
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	326000	USD
CY2020	nfbk	Operating Lease Right Of Use Asset Amortization OperatingLeaseRightOfUseAssetAmortization	4586000	USD
CY2019	nfbk	Operating Lease Right Of Use Asset Amortization OperatingLeaseRightOfUseAssetAmortization	5069000	USD
CY2018	nfbk	Operating Lease Right Of Use Asset Amortization OperatingLeaseRightOfUseAssetAmortization	0	USD
CY2020	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	3774000	USD
CY2019	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	7023000	USD
CY2018	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	3705000	USD
CY2020	us-gaap	Gain Loss On Sale Of Loans And Leases GainLossOnSaleOfLoansAndLeases	665000	USD
CY2019	us-gaap	Gain Loss On Sale Of Loans And Leases GainLossOnSaleOfLoansAndLeases	0	USD
CY2018	us-gaap	Gain Loss On Sale Of Loans And Leases GainLossOnSaleOfLoansAndLeases	0	USD
CY2020	us-gaap	Debt Securities Available For Sale Gain Loss DebtSecuritiesAvailableForSaleGainLoss	327000	USD
CY2019	us-gaap	Debt Securities Available For Sale Gain Loss DebtSecuritiesAvailableForSaleGainLoss	514000	USD
CY2018	us-gaap	Debt Securities Available For Sale Gain Loss DebtSecuritiesAvailableForSaleGainLoss	178000	USD
CY2020	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	1601000	USD
CY2019	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	1988000	USD
CY2018	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	-879000	USD
CY2020	us-gaap	Increase Decrease In Trading Securities IncreaseDecreaseInTradingSecurities	-532000	USD
CY2019	us-gaap	Increase Decrease In Trading Securities IncreaseDecreaseInTradingSecurities	266000	USD
CY2018	us-gaap	Increase Decrease In Trading Securities IncreaseDecreaseInTradingSecurities	250000	USD
CY2020	us-gaap	Increase Decrease In Accrued Interest Receivable Net IncreaseDecreaseInAccruedInterestReceivableNet	-1334000	USD
CY2019	us-gaap	Increase Decrease In Accrued Interest Receivable Net IncreaseDecreaseInAccruedInterestReceivableNet	1650000	USD
CY2018	us-gaap	Increase Decrease In Accrued Interest Receivable Net IncreaseDecreaseInAccruedInterestReceivableNet	2246000	USD
CY2020	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	-1294000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	-2679000	USD
CY2018	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	-3563000	USD
CY2020	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	3058000	USD
CY2019	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	177000	USD
CY2018	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	893000	USD
CY2020	us-gaap	Increase Decrease In Other Accounts Payable And Accrued Liabilities IncreaseDecreaseInOtherAccountsPayableAndAccruedLiabilities	-4229000	USD
CY2019	us-gaap	Increase Decrease In Other Accounts Payable And Accrued Liabilities IncreaseDecreaseInOtherAccountsPayableAndAccruedLiabilities	1011000	USD
CY2018	us-gaap	Increase Decrease In Other Accounts Payable And Accrued Liabilities IncreaseDecreaseInOtherAccountsPayableAndAccruedLiabilities	-631000	USD
CY2020	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	55214000	USD
CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	51152000	USD
CY2018	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	52789000	USD
CY2020	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	276616000	USD
CY2019	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	147507000	USD
CY2018	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	69270000	USD
CY2020	us-gaap	Payments To Acquire Finance Receivables PaymentsToAcquireFinanceReceivables	0	USD
CY2019	us-gaap	Payments To Acquire Finance Receivables PaymentsToAcquireFinanceReceivables	44918000	USD
CY2018	us-gaap	Payments To Acquire Finance Receivables PaymentsToAcquireFinanceReceivables	37593000	USD
CY2020	us-gaap	Proceeds From Sale Of Finance Receivables ProceedsFromSaleOfFinanceReceivables	48165000	USD
CY2019	us-gaap	Proceeds From Sale Of Finance Receivables ProceedsFromSaleOfFinanceReceivables	0	USD
CY2018	us-gaap	Proceeds From Sale Of Finance Receivables ProceedsFromSaleOfFinanceReceivables	0	USD
CY2020	us-gaap	Payments To Acquire Federal Home Loan Bank Stock PaymentsToAcquireFederalHomeLoanBankStock	10497000	USD
CY2019	us-gaap	Payments To Acquire Federal Home Loan Bank Stock PaymentsToAcquireFederalHomeLoanBankStock	38546000	USD
CY2018	us-gaap	Payments To Acquire Federal Home Loan Bank Stock PaymentsToAcquireFederalHomeLoanBankStock	21557000	USD
CY2020	us-gaap	Proceeds From Sale Of Federal Home Loan Bank Stock ProceedsFromSaleOfFederalHomeLoanBankStock	21735000	USD
CY2019	us-gaap	Proceeds From Sale Of Federal Home Loan Bank Stock ProceedsFromSaleOfFederalHomeLoanBankStock	21488000	USD
CY2018	us-gaap	Proceeds From Sale Of Federal Home Loan Bank Stock ProceedsFromSaleOfFederalHomeLoanBankStock	24086000	USD
CY2020	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	572342000	USD
CY2019	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	635898000	USD
CY2018	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	451174000	USD
CY2020	us-gaap	Payments To Acquire Marketable Securities PaymentsToAcquireMarketableSecurities	27000	USD
CY2019	us-gaap	Payments To Acquire Marketable Securities PaymentsToAcquireMarketableSecurities	2061000	USD
CY2018	us-gaap	Payments To Acquire Marketable Securities PaymentsToAcquireMarketableSecurities	0	USD
CY2020	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	556920000	USD
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	243374000	USD
CY2018	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	118485000	USD
CY2020	us-gaap	Proceeds From Maturities Prepayments And Calls Of Held To Maturity Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities	1462000	USD
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Held To Maturity Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities	709000	USD
CY2018	us-gaap	Proceeds From Maturities Prepayments And Calls Of Held To Maturity Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities	403000	USD
CY2020	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	23628000	USD
CY2019	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	79255000	USD
CY2018	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	32115000	USD
CY2020	nfbk	Proceeds From Sale Of Equity Securities ProceedsFromSaleOfEquitySecurities	3115000	USD
CY2019	nfbk	Proceeds From Sale Of Equity Securities ProceedsFromSaleOfEquitySecurities	0	USD
CY2018	nfbk	Proceeds From Sale Of Equity Securities ProceedsFromSaleOfEquitySecurities	0	USD
CY2020	us-gaap	Proceeds From Life Insurance Policies ProceedsFromLifeInsurancePolicies	2716000	USD
CY2019	us-gaap	Proceeds From Life Insurance Policies ProceedsFromLifeInsurancePolicies	5002000	USD
CY2018	us-gaap	Proceeds From Life Insurance Policies ProceedsFromLifeInsurancePolicies	174000	USD
CY2020	nfbk	Proceeds From Sale Of Premises And Equipment And Other Real Estate Owned ProceedsFromSaleOfPremisesAndEquipmentAndOtherRealEstateOwned	0	USD
CY2019	nfbk	Proceeds From Sale Of Premises And Equipment And Other Real Estate Owned ProceedsFromSaleOfPremisesAndEquipmentAndOtherRealEstateOwned	0	USD
CY2018	nfbk	Proceeds From Sale Of Premises And Equipment And Other Real Estate Owned ProceedsFromSaleOfPremisesAndEquipmentAndOtherRealEstateOwned	850000	USD
CY2020	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	3059000	USD
CY2019	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	3623000	USD
CY2018	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	2879000	USD
CY2020	us-gaap	Cash Acquired From Acquisition CashAcquiredFromAcquisition	72875000	USD
CY2019	us-gaap	Cash Acquired From Acquisition CashAcquiredFromAcquisition	0	USD
CY2018	us-gaap	Cash Acquired From Acquisition CashAcquiredFromAcquisition	0	USD
CY2020	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-131925000	USD
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-522725000	USD
CY2018	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-406360000	USD
CY2020	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	313726000	USD
CY2019	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	121721000	USD
CY2018	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	449533000	USD
CY2020	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	21476000	USD
CY2019	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	20198000	USD
CY2018	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	18673000	USD
CY2020	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	175000	USD
CY2019	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	5770000	USD
CY2018	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	2088000	USD
CY2020	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	10405000	USD
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	15815000	USD
CY2018	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	5000	USD
CY2020	us-gaap	Increase Decrease In Advance Payments By Borrowers For Taxes And Insurance IncreaseDecreaseInAdvancePaymentsByBorrowersForTaxesAndInsurance	-368000	USD
CY2019	us-gaap	Increase Decrease In Advance Payments By Borrowers For Taxes And Insurance IncreaseDecreaseInAdvancePaymentsByBorrowersForTaxesAndInsurance	2038000	USD
CY2018	us-gaap	Increase Decrease In Advance Payments By Borrowers For Taxes And Insurance IncreaseDecreaseInAdvancePaymentsByBorrowersForTaxesAndInsurance	3209000	USD
CY2020	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	0	USD
CY2019	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	44000	USD
CY2018	us-gaap	Repayments Of Long Term Capital Lease Obligations RepaymentsOfLongTermCapitalLeaseObligations	255000	USD
CY2020	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	370785000	USD
CY2019	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	1206659000	USD
CY2018	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	397312000	USD
CY2020	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	636000000	USD
CY2019	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	758502000	USD
CY2018	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	459715000	USD
CY2020	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	16437000	USD
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	541629000	USD
CY2018	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	373494000	USD
CY2020	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-60274000	USD
CY2019	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	70056000	USD
CY2018	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	19923000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	147818000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	77762000	USD
CY2017Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	57839000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	87544000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	147818000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	77762000	USD
CY2020	us-gaap	Interest Paid Net InterestPaidNet	39584000	USD
CY2019	us-gaap	Interest Paid Net InterestPaidNet	51634000	USD
CY2018	nfbk	Operating Lease Liability Initial Recognition Noncash OperatingLeaseLiabilityInitialRecognitionNoncash	0	USD
CY2020	us-gaap	Transfer Of Portfolio Loans And Leases To Held For Sale1 TransferOfPortfolioLoansAndLeasesToHeldForSale1	67395000	USD
CY2019	us-gaap	Transfer Of Portfolio Loans And Leases To Held For Sale1 TransferOfPortfolioLoansAndLeasesToHeldForSale1	0	USD
CY2018	us-gaap	Interest Paid Net InterestPaidNet	35822000	USD
CY2020	us-gaap	Income Taxes Paid IncomeTaxesPaid	15169000	USD
CY2019	us-gaap	Income Taxes Paid IncomeTaxesPaid	11092000	USD
CY2018	us-gaap	Income Taxes Paid IncomeTaxesPaid	10368000	USD
CY2020	us-gaap	Allowance For Loan And Lease Losses Writeoffs Net AllowanceForLoanAndLeaseLossesWriteoffsNet	3842000	USD
CY2019	us-gaap	Allowance For Loan And Lease Losses Writeoffs Net AllowanceForLoanAndLeaseLossesWriteoffsNet	-1189000	USD
CY2018	us-gaap	Allowance For Loan And Lease Losses Writeoffs Net AllowanceForLoanAndLeaseLossesWriteoffsNet	1278000	USD
CY2020	nfbk	Operating Lease Right Of Use Asset Initial Recognition Noncash OperatingLeaseRightOfUseAssetInitialRecognitionNoncash	0	USD
CY2019	nfbk	Operating Lease Right Of Use Asset Initial Recognition Noncash OperatingLeaseRightOfUseAssetInitialRecognitionNoncash	43560000	USD
CY2018	nfbk	Operating Lease Right Of Use Asset Initial Recognition Noncash OperatingLeaseRightOfUseAssetInitialRecognitionNoncash	0	USD
CY2020	nfbk	Operating Lease Liability Initial Recognition Noncash OperatingLeaseLiabilityInitialRecognitionNoncash	0	USD
CY2019	nfbk	Operating Lease Liability Initial Recognition Noncash OperatingLeaseLiabilityInitialRecognitionNoncash	47328000	USD
CY2018	us-gaap	Transfer Of Portfolio Loans And Leases To Held For Sale1 TransferOfPortfolioLoansAndLeasesToHeldForSale1	0	USD
CY2020	us-gaap	Noncash Or Part Noncash Acquisition Investments Acquired1 NoncashOrPartNoncashAcquisitionInvestmentsAcquired1	126931000	USD
CY2020	us-gaap	Noncash Or Part Noncash Acquisition Other Assets Acquired1 NoncashOrPartNoncashAcquisitionOtherAssetsAcquired1	4702000	USD
CY2019	us-gaap	Noncash Or Part Noncash Acquisition Investments Acquired1 NoncashOrPartNoncashAcquisitionInvestmentsAcquired1	0	USD
CY2018	us-gaap	Noncash Or Part Noncash Acquisition Investments Acquired1 NoncashOrPartNoncashAcquisitionInvestmentsAcquired1	0	USD
CY2020	nfbk	Noncashor Part Noncash Acquisition Loansand Leases Receivable Net NoncashorPartNoncashAcquisitionLoansandLeasesReceivableNet	180431000	USD
CY2019	nfbk	Noncashor Part Noncash Acquisition Loansand Leases Receivable Net NoncashorPartNoncashAcquisitionLoansandLeasesReceivableNet	0	USD
CY2018	nfbk	Noncashor Part Noncash Acquisition Loansand Leases Receivable Net NoncashorPartNoncashAcquisitionLoansandLeasesReceivableNet	0	USD
CY2020	nfbk	Non Cash Or Non Cash Acquisition Accrued Interest Receivable NonCashOrNonCashAcquisitionAccruedInterestReceivable	1415000	USD
CY2019	nfbk	Non Cash Or Non Cash Acquisition Accrued Interest Receivable NonCashOrNonCashAcquisitionAccruedInterestReceivable	0	USD
CY2018	nfbk	Non Cash Or Non Cash Acquisition Accrued Interest Receivable NonCashOrNonCashAcquisitionAccruedInterestReceivable	0	USD
CY2020	nfbk	Noncashor Part Noncash Acquisition Bank Owned Life Insurance NoncashorPartNoncashAcquisitionBankOwnedLifeInsurance	5714000	USD
CY2019	nfbk	Noncashor Part Noncash Acquisition Bank Owned Life Insurance NoncashorPartNoncashAcquisitionBankOwnedLifeInsurance	0	USD
CY2018	nfbk	Noncashor Part Noncash Acquisition Bank Owned Life Insurance NoncashorPartNoncashAcquisitionBankOwnedLifeInsurance	0	USD
CY2020	us-gaap	Noncash Or Part Noncash Acquisition Fixed Assets Acquired1 NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1	7789000	USD
CY2019	us-gaap	Noncash Or Part Noncash Acquisition Fixed Assets Acquired1 NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1	0	USD
CY2018	us-gaap	Noncash Or Part Noncash Acquisition Fixed Assets Acquired1 NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1	0	USD
CY2020	nfbk	Noncashor Part Noncash Acquisition Intangible Assetsincluding Goodwill Acquired NoncashorPartNoncashAcquisitionIntangibleAssetsincludingGoodwillAcquired	2909000	USD
CY2019	nfbk	Noncashor Part Noncash Acquisition Intangible Assetsincluding Goodwill Acquired NoncashorPartNoncashAcquisitionIntangibleAssetsincludingGoodwillAcquired	0	USD
CY2018	nfbk	Noncashor Part Noncash Acquisition Intangible Assetsincluding Goodwill Acquired NoncashorPartNoncashAcquisitionIntangibleAssetsincludingGoodwillAcquired	0	USD
CY2019	us-gaap	Noncash Or Part Noncash Acquisition Other Assets Acquired1 NoncashOrPartNoncashAcquisitionOtherAssetsAcquired1	0	USD
CY2018	us-gaap	Noncash Or Part Noncash Acquisition Other Assets Acquired1 NoncashOrPartNoncashAcquisitionOtherAssetsAcquired1	0	USD
CY2020	us-gaap	Noncash Or Part Noncash Acquisition Value Of Assets Acquired1 NoncashOrPartNoncashAcquisitionValueOfAssetsAcquired1	329891000	USD
CY2019	us-gaap	Noncash Or Part Noncash Acquisition Value Of Assets Acquired1 NoncashOrPartNoncashAcquisitionValueOfAssetsAcquired1	0	USD
CY2018	us-gaap	Noncash Or Part Noncash Acquisition Value Of Assets Acquired1 NoncashOrPartNoncashAcquisitionValueOfAssetsAcquired1	0	USD
CY2020	nfbk	Non Cash Or Non Cash Acquisition Deposits Assumed NonCashOrNonCashAcquisitionDepositsAssumed	354592000	USD
CY2019	nfbk	Non Cash Or Non Cash Acquisition Deposits Assumed NonCashOrNonCashAcquisitionDepositsAssumed	0	USD
CY2018	nfbk	Non Cash Or Non Cash Acquisition Deposits Assumed NonCashOrNonCashAcquisitionDepositsAssumed	0	USD
CY2020	us-gaap	Noncash Or Part Noncash Acquisition Other Liabilities Assumed1 NoncashOrPartNoncashAcquisitionOtherLiabilitiesAssumed1	7001000	USD
CY2019	us-gaap	Noncash Or Part Noncash Acquisition Other Liabilities Assumed1 NoncashOrPartNoncashAcquisitionOtherLiabilitiesAssumed1	0	USD
CY2018	us-gaap	Noncash Or Part Noncash Acquisition Other Liabilities Assumed1 NoncashOrPartNoncashAcquisitionOtherLiabilitiesAssumed1	0	USD
CY2020	us-gaap	Noncash Or Part Noncash Acquisition Value Of Liabilities Assumed1 NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumed1	361593000	USD
CY2019	us-gaap	Noncash Or Part Noncash Acquisition Value Of Liabilities Assumed1 NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumed1	0	USD
CY2018	us-gaap	Noncash Or Part Noncash Acquisition Value Of Liabilities Assumed1 NoncashOrPartNoncashAcquisitionValueOfLiabilitiesAssumed1	0	USD
CY2020	us-gaap	Noncash Or Part Noncash Acquisition Net Nonmonetary Assets Acquired Liabilities Assumed1 NoncashOrPartNoncashAcquisitionNetNonmonetaryAssetsAcquiredLiabilitiesAssumed1	-31702000	USD
CY2019	us-gaap	Noncash Or Part Noncash Acquisition Net Nonmonetary Assets Acquired Liabilities Assumed1 NoncashOrPartNoncashAcquisitionNetNonmonetaryAssetsAcquiredLiabilitiesAssumed1	0	USD
CY2018	us-gaap	Noncash Or Part Noncash Acquisition Net Nonmonetary Assets Acquired Liabilities Assumed1 NoncashOrPartNoncashAcquisitionNetNonmonetaryAssetsAcquiredLiabilitiesAssumed1	0	USD
CY2020	nfbk	Cash And Cash Equivalents Acquired Net Of Cash Paid Related To Acquisition CashAndCashEquivalentsAcquiredNetOfCashPaidRelatedToAcquisition	72875000	USD
CY2019	nfbk	Cash And Cash Equivalents Acquired Net Of Cash Paid Related To Acquisition CashAndCashEquivalentsAcquiredNetOfCashPaidRelatedToAcquisition	0	USD
CY2018	nfbk	Cash And Cash Equivalents Acquired Net Of Cash Paid Related To Acquisition CashAndCashEquivalentsAcquiredNetOfCashPaidRelatedToAcquisition	0	USD
CY2020	nfbk	Non Cash Or Part Non Cash Acquisition Non Cash Financial Or Equity Instrument Consideration Shares Issued Value NonCashOrPartNonCashAcquisitionNonCashFinancialOrEquityInstrumentConsiderationSharesIssuedValue	41173000	USD
CY2019	nfbk	Non Cash Or Part Non Cash Acquisition Non Cash Financial Or Equity Instrument Consideration Shares Issued Value NonCashOrPartNonCashAcquisitionNonCashFinancialOrEquityInstrumentConsiderationSharesIssuedValue	0	USD
CY2018	nfbk	Non Cash Or Part Non Cash Acquisition Non Cash Financial Or Equity Instrument Consideration Shares Issued Value NonCashOrPartNonCashAcquisitionNonCashFinancialOrEquityInstrumentConsiderationSharesIssuedValue	0	USD
CY2020	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2020	nfbk	Threshold Of Membership Investment Component Percentage ThresholdOfMembershipInvestmentComponentPercentage	0.00125
CY2020	nfbk	Threshold Of Membership Investment Component ThresholdOfMembershipInvestmentComponent	1000	USD
CY2020	nfbk	Activity Based Investment Component As Percentage Of Outstanding Advances ActivityBasedInvestmentComponentAsPercentageOfOutstandingAdvances	0.045
CY2020Q4	us-gaap	Goodwill Goodwill	41300000	USD
CY2020	nfbk	Employee Stock Ownership Plan Esop Debt Structure Direct Loan Repayment Period EmployeeStockOwnershipPlanEsopDebtStructureDirectLoanRepaymentPeriod	P30Y
CY2020	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	64459	shares
CY2019	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	380362	shares
CY2018	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	787673	shares
CY2019Q1	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	43600000	USD
CY2019Q1	us-gaap	Operating Lease Liability OperatingLeaseLiability	47300000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	1246673000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	18862000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	730000	USD
CY2019Q4	nfbk	Available For Sale Securities Carrying Value AvailableForSaleSecuritiesCarryingValue	730900000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	1264805000	USD
CY2019Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	1131970000	USD
CY2019Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	9374000	USD
CY2019Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	2992000	USD
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	1138352000	USD
CY2020Q4	nfbk	Available For Sale Securities Carrying Value AvailableForSaleSecuritiesCarryingValue	542100000	USD
CY2020	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	23600000	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	350000	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	23000	USD
CY2019	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	79300000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	514000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	0	USD
CY2018	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	32100000	USD
CY2018	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	183000	USD
CY2018	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	5000	USD
CY2020	us-gaap	Debt Securities Trading Realized Gain Loss DebtSecuritiesTradingRealizedGainLoss	1600000	USD
CY2019	us-gaap	Debt Securities Trading Realized Gain Loss DebtSecuritiesTradingRealizedGainLoss	2000000.0	USD
CY2018	us-gaap	Debt Securities Trading Realized Gain Loss DebtSecuritiesTradingRealizedGainLoss	879000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	719000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	242146000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	11000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	459000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	730000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	242605000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	975000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	201038000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	2017000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	125378000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	2992000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	326416000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	7574000	USD
CY2019Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	8762000	USD
CY2018	us-gaap	Other Than Temporary Impairment Loss Debt Securities Available For Sale Recognized In Earnings OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSaleRecognizedInEarnings	0	USD
CY2019	us-gaap	Other Than Temporary Impairment Loss Debt Securities Available For Sale Recognized In Earnings OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSaleRecognizedInEarnings	0	USD
CY2020	us-gaap	Other Than Temporary Impairment Loss Debt Securities Available For Sale Recognized In Earnings OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSaleRecognizedInEarnings	0	USD
CY2020Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	7234000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	340000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	0	USD
CY2019Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	129000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	5000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	8886000	USD
CY2020	us-gaap	Debt Securities Held To Maturity Sold Amount DebtSecuritiesHeldToMaturitySoldAmount	0	USD
CY2018	us-gaap	Debt Securities Held To Maturity Sold Amount DebtSecuritiesHeldToMaturitySoldAmount	0	USD
CY2019	us-gaap	Debt Securities Held To Maturity Sold Amount DebtSecuritiesHeldToMaturitySoldAmount	0	USD
CY2020Q4	nfbk	Heldtomaturity Securities Pledgedas Collateralon Borrowingsand Deposits HeldtomaturitySecuritiesPledgedasCollateralonBorrowingsandDeposits	5900000	USD
CY2019Q4	nfbk	Heldtomaturity Securities Pledgedas Collateralon Borrowingsand Deposits HeldtomaturitySecuritiesPledgedasCollateralonBorrowingsandDeposits	7400000	USD
CY2020Q4	nfbk	Debt Securities Held To Maturity Unrealized Loss Position Number Of Positions DebtSecuritiesHeldToMaturityUnrealizedLossPositionNumberOfPositions	0	security
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	0	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue	0	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	5000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue	378000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss	5000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue	378000	USD
CY2019	us-gaap	Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net Heldtomaturity Securities OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNetHeldtomaturitySecurities	0	USD
CY2018	us-gaap	Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net Heldtomaturity Securities OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNetHeldtomaturitySecurities	0	USD
CY2020	us-gaap	Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net Heldtomaturity Securities OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNetHeldtomaturitySecurities	0	USD
CY2020Q4	us-gaap	Equity Securities Fv Ni And Without Readily Determinable Fair Value EquitySecuritiesFvNiAndWithoutReadilyDeterminableFairValue	253000	USD
CY2019Q4	us-gaap	Equity Securities Fv Ni And Without Readily Determinable Fair Value EquitySecuritiesFvNiAndWithoutReadilyDeterminableFairValue	3300000	USD
CY2020Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3823238000	USD
CY2019Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3437085000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	37607000	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	28707000	USD
CY2020Q4	us-gaap	Notes Receivable Net NotesReceivableNet	3785631000	USD
CY2019Q4	us-gaap	Notes Receivable Net NotesReceivableNet	3408378000	USD
CY2020Q4	us-gaap	Loans Receivable Held For Sale Amount LoansReceivableHeldForSaleAmount	19900000	USD
CY2019Q4	us-gaap	Loans Receivable Held For Sale Amount LoansReceivableHeldForSaleAmount	0	USD
CY2019Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	17086000	USD
CY2018Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	21846000	USD
CY2020	us-gaap	Certain Loans Acquired In Transfer Accounted For As Debt Securities Accretable Yield Additions CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYieldAdditions	599000	USD
CY2019	us-gaap	Certain Loans Acquired In Transfer Accounted For As Debt Securities Accretable Yield Additions CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYieldAdditions	0	USD
CY2020	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Accretion CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion	2856000	USD
CY2019	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Accretion CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion	4142000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	37607000	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	28707000	USD
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	27497000	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	28707000	USD
CY2020	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	4307000	USD
CY2020	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	465000	USD
CY2020	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	12742000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	37607000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses Individually Evaluated For Impairment1 FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1	73000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses Collectively Evaluated For Impairment FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment	37534000	USD
CY2020Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3823238000	USD
CY2020Q4	us-gaap	Financing Receivable Individually Evaluated For Impairment FinancingReceivableIndividuallyEvaluatedForImpairment	13242000	USD
CY2020Q4	us-gaap	Financing Receivable Collectively Evaluated For Impairment FinancingReceivableCollectivelyEvaluatedForImpairment	3809996000	USD
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	27497000	USD
CY2019	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	987000	USD
CY2019	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	2175000	USD
CY2020Q4	nfbk	Originated Loans Held For Investment Net OriginatedLoansHeldForInvestmentNet	3339002000	USD
CY2019	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	22000	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	28707000	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses Individually Evaluated For Impairment1 FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1	142000	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses Collectively Evaluated For Impairment FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment	28565000	USD
CY2019Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3437085000	USD
CY2019Q4	us-gaap	Financing Receivable Individually Evaluated For Impairment FinancingReceivableIndividuallyEvaluatedForImpairment	20957000	USD
CY2019Q4	us-gaap	Financing Receivable Collectively Evaluated For Impairment FinancingReceivableCollectivelyEvaluatedForImpairment	3416128000	USD
CY2019Q4	nfbk	Originated Loans Held For Investment Net OriginatedLoansHeldForInvestmentNet	2987067000	USD
CY2020Q4	nfbk	Investment In Non Accrual Loans InvestmentInNonAccrualLoans	8500000	USD
CY2019Q4	nfbk	Investment In Non Accrual Loans InvestmentInNonAccrualLoans	9400000	USD
CY2020	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2020	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2020Q4	nfbk	Loans Deemed To Be Impaired Non Accrual Amount LoansDeemedToBeImpairedNonAccrualAmount	5500000	USD
CY2019Q4	nfbk	Loans Deemed To Be Impaired Non Accrual Amount LoansDeemedToBeImpairedNonAccrualAmount	6800000	USD
CY2020Q4	nfbk	Principal Balance Threshold For Non Accrual Status PrincipalBalanceThresholdForNonAccrualStatus	2300000	USD
CY2019Q4	nfbk	Principal Balance Threshold For Non Accrual Status PrincipalBalanceThresholdForNonAccrualStatus	2600000	USD
CY2020	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2019	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2020Q4	us-gaap	Financing Receivable Recorded Investment90 Days Past Due And Still Accruing FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing	1100000	USD
CY2019Q4	us-gaap	Financing Receivable Recorded Investment90 Days Past Due And Still Accruing FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing	518000	USD
CY2020Q4	us-gaap	Loans Receivable Held For Sale Amount LoansReceivableHeldForSaleAmount	19900000	USD
CY2019Q4	us-gaap	Loans Receivable Held For Sale Amount LoansReceivableHeldForSaleAmount	0	USD
CY2020	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2019	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2020Q4	us-gaap	Impaired Financing Receivable Recorded Investment ImpairedFinancingReceivableRecordedInvestment	13242000	USD
CY2020Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	15512000	USD
CY2020Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	73000	USD
CY2019Q4	us-gaap	Impaired Financing Receivable Recorded Investment ImpairedFinancingReceivableRecordedInvestment	20957000	USD
CY2019Q4	nfbk	Loans With Carrying Balances Not Written Down LoansWithCarryingBalancesNotWrittenDown	15900000	USD
CY2019Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	23132000	USD
CY2019Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	142000	USD
CY2020Q4	nfbk	Loans With Carrying Balances Not Written Down LoansWithCarryingBalancesNotWrittenDown	7800000	USD
CY2020	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	18817000	USD
CY2020	us-gaap	Impaired Financing Receivable Interest Income Cash Basis Method ImpairedFinancingReceivableInterestIncomeCashBasisMethod	654000	USD
CY2019	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	21641000	USD
CY2020	us-gaap	Certain Loans Acquired In Transfer Accounted For As Debt Securities Accretable Yield Reclassifications From Nonaccretable Difference CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference	-628000	USD
CY2019	us-gaap	Certain Loans Acquired In Transfer Accounted For As Debt Securities Accretable Yield Reclassifications From Nonaccretable Difference CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference	-618000	USD
CY2020Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	14201000	USD
CY2019Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	17086000	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	28707000	USD
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	27497000	USD
CY2017Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	26160000	USD
CY2020	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	12742000	USD
CY2019	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	22000	USD
CY2018	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	2615000	USD
CY2020	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	465000	USD
CY2019	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	2175000	USD
CY2018	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	112000	USD
CY2020	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	4307000	USD
CY2019	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	987000	USD
CY2018	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	1390000	USD
CY2020	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	731000	USD
CY2019	us-gaap	Impaired Financing Receivable Interest Income Cash Basis Method ImpairedFinancingReceivableInterestIncomeCashBasisMethod	778000	USD
CY2020Q4	nfbk	Trouble Debt Restructuring Amount TroubleDebtRestructuringAmount	12100000	USD
CY2019Q4	nfbk	Trouble Debt Restructuring Amount TroubleDebtRestructuringAmount	19200000	USD
CY2020	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	3	loan
CY2020	us-gaap	Financing Receivable Modifications Pre Modification Recorded Investment2 FinancingReceivableModificationsPreModificationRecordedInvestment2	731000	USD
CY2019	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	2	contract
CY2019	us-gaap	Financing Receivable Modifications Pre Modification Recorded Investment2 FinancingReceivableModificationsPreModificationRecordedInvestment2	2836000	USD
CY2019	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	2836000	USD
CY2020Q4	nfbk	Financing Receivable Modification Number Of Borrowers FinancingReceivableModificationNumberOfBorrowers	3	borrower
CY2019	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	0	instrument
CY2020Q4	us-gaap	Deposits Negotiable Order Of Withdrawal Now DepositsNegotiableOrderOfWithdrawalNOW	905208000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	78685000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	71343000	USD
CY2020Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	50497000	USD
CY2019Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	45684000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	28188000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	25659000	USD
CY2020	us-gaap	Depreciation Depreciation	3900000	USD
CY2019	us-gaap	Depreciation Depreciation	3600000	USD
CY2018	us-gaap	Depreciation Depreciation	3000000.0	USD
CY2020	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	0	USD
CY2018	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	0	USD
CY2019	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	0	USD
CY2020Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	1953885000	USD
CY2019Q4	nfbk	Weighted Average Interest Rate Of Time Deposits Interest Bearing Deposit Liabilities WeightedAverageInterestRateOfTimeDepositsInterestBearingDepositLiabilities	0.0102
CY2020Q4	us-gaap	Weighted Average Rate Domestic Deposit Notice Of Withdrawal WeightedAverageRateDomesticDepositNoticeOfWithdrawal	0.0011
CY2019Q4	us-gaap	Deposits Negotiable Order Of Withdrawal Now DepositsNegotiableOrderOfWithdrawalNOW	573927000	USD
CY2019Q4	us-gaap	Weighted Average Rate Domestic Deposit Notice Of Withdrawal WeightedAverageRateDomesticDepositNoticeOfWithdrawal	0.0087
CY2020Q4	us-gaap	Noninterest Bearing Deposit Liabilities NoninterestBearingDepositLiabilities	695831000	USD
CY2019Q4	us-gaap	Noninterest Bearing Deposit Liabilities NoninterestBearingDepositLiabilities	387409000	USD
CY2020Q4	nfbk	Deposits Transactions DepositsTransactions	1601039000	USD
CY2020Q4	nfbk	Weighted Average Rate Domestic Deposit Transaction WeightedAverageRateDomesticDepositTransaction	0.0006
CY2019Q4	nfbk	Deposits Transactions DepositsTransactions	961336000	USD
CY2019Q4	nfbk	Weighted Average Rate Domestic Deposit Transaction WeightedAverageRateDomesticDepositTransaction	0.0052
CY2020Q4	us-gaap	Deposits Money Market Deposits DepositsMoneyMarketDeposits	813168000	USD
CY2020Q4	us-gaap	Weighted Average Rate Domestic Deposit Money Market WeightedAverageRateDomesticDepositMoneyMarket	0.0010
CY2019Q4	us-gaap	Deposits Money Market Deposits DepositsMoneyMarketDeposits	651159000	USD
CY2019Q4	us-gaap	Weighted Average Rate Domestic Deposit Money Market WeightedAverageRateDomesticDepositMoneyMarket	0.0118
CY2020Q4	us-gaap	Interest Bearing Deposit Liabilities InterestBearingDepositLiabilities	1140717000	USD
CY2020Q4	nfbk	Weighted Average Interest Rate Of Time Deposits Interest Bearing Deposit Liabilities WeightedAverageInterestRateOfTimeDepositsInterestBearingDepositLiabilities	0.0019
CY2019Q4	us-gaap	Interest Bearing Deposit Liabilities InterestBearingDepositLiabilities	747186000	USD
CY2020Q4	us-gaap	Weighted Average Rate Domestic Deposit Savings WeightedAverageRateDomesticDepositSavings	0.0015
CY2019Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	1398345000	USD
CY2019Q4	us-gaap	Weighted Average Rate Domestic Deposit Savings WeightedAverageRateDomesticDepositSavings	0.0109
CY2020Q4	us-gaap	Time Deposits Less Than100000 TimeDepositsLessThan100000	241862000	USD
CY2020Q4	nfbk	Weighted Average Interest Rateof Time Deposits Less Than100000 WeightedAverageInterestRateofTimeDepositsLessThan100000	0.0105
CY2019Q4	us-gaap	Time Deposits Less Than100000 TimeDepositsLessThan100000	563303000	USD
CY2019Q4	nfbk	Weighted Average Interest Rateof Time Deposits Less Than100000 WeightedAverageInterestRateofTimeDepositsLessThan100000	0.0186
CY2020Q4	us-gaap	Time Deposits100000 Or More TimeDeposits100000OrMore	279765000	USD
CY2020Q4	us-gaap	Weighted Average Interest Rate Of Time Deposits100000 Or More WeightedAverageInterestRateOfTimeDeposits100000OrMore	0.0071
CY2019Q4	us-gaap	Time Deposits100000 Or More TimeDeposits100000OrMore	485249000	USD
CY2019Q4	us-gaap	Weighted Average Interest Rate Of Time Deposits100000 Or More WeightedAverageInterestRateOfTimeDeposits100000OrMore	0.0198
CY2020Q4	us-gaap	Time Deposits TimeDeposits	521627000	USD
CY2020Q4	us-gaap	Weighted Average Rate Domestic Deposit Time Deposits WeightedAverageRateDomesticDepositTimeDeposits	0.0087
CY2019Q4	us-gaap	Time Deposits TimeDeposits	1048552000	USD
CY2019Q4	us-gaap	Weighted Average Rate Domestic Deposit Time Deposits WeightedAverageRateDomesticDepositTimeDeposits	0.0192
CY2020Q4	us-gaap	Deposits Deposits	4076551000	USD
CY2020Q4	us-gaap	Weighted Average Rate Domestic Deposit WeightedAverageRateDomesticDeposit	0.0021
CY2019Q4	us-gaap	Deposits Deposits	3408233000	USD
CY2019Q4	us-gaap	Weighted Average Rate Domestic Deposit WeightedAverageRateDomesticDeposit	0.0118
CY2020Q4	us-gaap	Time Deposit Maturities Year One TimeDepositMaturitiesYearOne	375248000	USD
CY2020Q4	us-gaap	Time Deposit Maturities Year Two TimeDepositMaturitiesYearTwo	72168000	USD
CY2020Q4	us-gaap	Time Deposit Maturities Year Three TimeDepositMaturitiesYearThree	45447000	USD
CY2020Q4	us-gaap	Time Deposit Maturities Year Four TimeDepositMaturitiesYearFour	14988000	USD
CY2020Q4	us-gaap	Time Deposit Maturities Year Five TimeDepositMaturitiesYearFive	13546000	USD
CY2020Q4	us-gaap	Time Deposit Maturities After Year Five TimeDepositMaturitiesAfterYearFive	230000	USD
CY2020Q4	us-gaap	Time Deposits TimeDeposits	521627000	USD
CY2020	nfbk	Interest Expense Domestic Deposit Liabilities Transaction InterestExpenseDomesticDepositLiabilitiesTransaction	2372000	USD
CY2018	us-gaap	Interest Expense Deposits InterestExpenseDeposits	27741000	USD
CY2019	nfbk	Interest Expense Domestic Deposit Liabilities Transaction InterestExpenseDomesticDepositLiabilitiesTransaction	4623000	USD
CY2018	nfbk	Interest Expense Domestic Deposit Liabilities Transaction InterestExpenseDomesticDepositLiabilitiesTransaction	2175000	USD
CY2020	nfbk	Interest Expense Domestic Deposit Liabilities Savings And Money Market InterestExpenseDomesticDepositLiabilitiesSavingsAndMoneyMarket	7869000	USD
CY2019	nfbk	Interest Expense Domestic Deposit Liabilities Savings And Money Market InterestExpenseDomesticDepositLiabilitiesSavingsAndMoneyMarket	15850000	USD
CY2018	nfbk	Interest Expense Domestic Deposit Liabilities Savings And Money Market InterestExpenseDomesticDepositLiabilitiesSavingsAndMoneyMarket	8878000	USD
CY2020	us-gaap	Interest Expense Domestic Deposit Liabilities Certificates Of Deposit InterestExpenseDomesticDepositLiabilitiesCertificatesOfDeposit	14989000	USD
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Certificates Of Deposit InterestExpenseDomesticDepositLiabilitiesCertificatesOfDeposit	20855000	USD
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Certificates Of Deposit InterestExpenseDomesticDepositLiabilitiesCertificatesOfDeposit	16688000	USD
CY2020	us-gaap	Interest Expense Deposits InterestExpenseDeposits	25230000	USD
CY2019	us-gaap	Interest Expense Deposits InterestExpenseDeposits	41328000	USD
CY2020Q4	nfbk	Repurchase Agreement Included In Overnight Accounts RepurchaseAgreementIncludedInOvernightAccounts	75000000	USD
CY2019Q4	nfbk	Repurchase Agreement Included In Overnight Accounts RepurchaseAgreementIncludedInOvernightAccounts	75000000	USD
CY2020Q4	us-gaap	Federal Home Loan Bank Advances Long Term FederalHomeLoanBankAdvancesLongTerm	510000000	USD
CY2019Q4	us-gaap	Federal Home Loan Bank Advances Long Term FederalHomeLoanBankAdvancesLongTerm	776000000	USD
CY2020Q4	us-gaap	Longterm Debt Percentage Bearing Variable Interest Amount LongtermDebtPercentageBearingVariableInterestAmount	6789000	USD
CY2019Q4	us-gaap	Longterm Debt Percentage Bearing Variable Interest Amount LongtermDebtPercentageBearingVariableInterestAmount	6004000	USD
CY2020Q4	us-gaap	Long Term Debt LongTermDebt	591789000	USD
CY2019Q4	us-gaap	Long Term Debt LongTermDebt	857004000	USD
CY2020Q4	nfbk	Additional Funding Federal Home Loan Bank Advances Long Term AdditionalFundingFederalHomeLoanBankAdvancesLongTerm	1900000000	USD
CY2020Q4	nfbk	Unencumbered Securities UnencumberedSecurities	715100000	USD
CY2020Q4	nfbk	Multifamily Loans Held As Collateral By Federal Home Loan Bank MultifamilyLoansHeldAsCollateralByFederalHomeLoanBank	1200000000	USD
CY2020	us-gaap	Interest Expense Debt InterestExpenseDebt	13107000	USD
CY2019	us-gaap	Interest Expense Debt InterestExpenseDebt	12030000	USD
CY2018	us-gaap	Interest Expense Debt InterestExpenseDebt	8309000	USD
CY2020	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	11270000	USD
CY2019	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	8543000	USD
CY2018	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	8540000	USD
CY2020	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-2391000	USD
CY2019	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	376000	USD
CY2018	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-742000	USD
CY2020	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	8879000	USD
CY2019	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	8919000	USD
CY2018	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	7798000	USD
CY2020	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	4825000	USD
CY2019	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	4067000	USD
CY2018	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	1985000	USD
CY2020	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-667000	USD
CY2019	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-199000	USD
CY2018	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-151000	USD
CY2020	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	4158000	USD
CY2019	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	3868000	USD
CY2018	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	1834000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	13037000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	12787000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	9632000	USD
CY2020	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	10505000	USD
CY2019	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	11135000	USD
CY2018	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	10439000	USD
CY2020	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.21
CY2019	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.21
CY2018	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.21
CY2020	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	3285000	USD
CY2019	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	3056000	USD
CY2018	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	1448000	USD
CY2020	nfbk	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsuranceAmount	793000	USD
CY2019	nfbk	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsuranceAmount	1475000	USD
CY2018	nfbk	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsuranceAmount	778000	USD
CY2020	nfbk	Income Tax Rate Reconciliation Deduction Employee Stock Ownership Plan Fair Market Value Adjustment Amount IncomeTaxRateReconciliationDeductionEmployeeStockOwnershipPlanFairMarketValueAdjustmentAmount	42000	USD
CY2019	nfbk	Income Tax Rate Reconciliation Deduction Employee Stock Ownership Plan Fair Market Value Adjustment Amount IncomeTaxRateReconciliationDeductionEmployeeStockOwnershipPlanFairMarketValueAdjustmentAmount	187000	USD
CY2018	nfbk	Income Tax Rate Reconciliation Deduction Employee Stock Ownership Plan Fair Market Value Adjustment Amount IncomeTaxRateReconciliationDeductionEmployeeStockOwnershipPlanFairMarketValueAdjustmentAmount	196000	USD
CY2020	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	18000	USD
CY2019	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	81000	USD
CY2018	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	146000	USD
CY2020	nfbk	Income Tax Reconciliation Acquisition Related Costs IncomeTaxReconciliationAcquisitionRelatedCosts	-147000	USD
CY2019	nfbk	Income Tax Reconciliation Acquisition Related Costs IncomeTaxReconciliationAcquisitionRelatedCosts	0	USD
CY2018	nfbk	Income Tax Reconciliation Acquisition Related Costs IncomeTaxReconciliationAcquisitionRelatedCosts	0	USD
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Share Based Compensation Excess Tax Benefit Amount EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount	0	USD
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Share Based Compensation Excess Tax Benefit Amount EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount	-110000	USD
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Share Based Compensation Excess Tax Benefit Amount EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount	-1939000	USD
CY2020	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-167000	USD
CY2019	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-87000	USD
CY2018	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	120000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	13037000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	12787000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	9632000	USD
CY2020Q4	nfbk	Deferred Tax Assets Allowance For Credit Losses DeferredTaxAssetsAllowanceForCreditLosses	10348000	USD
CY2019Q4	nfbk	Deferred Tax Assets Allowance For Credit Losses DeferredTaxAssetsAllowanceForCreditLosses	7985000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits	3233000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits	3498000	USD
CY2020Q4	nfbk	Deferred Tax Assets Accrued Salaries And Benefits And Other DeferredTaxAssetsAccruedSalariesAndBenefitsAndOther	775000	USD
CY2019Q4	nfbk	Deferred Tax Assets Accrued Salaries And Benefits And Other DeferredTaxAssetsAccruedSalariesAndBenefitsAndOther	738000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Postretirement Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits	346000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Postretirement Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits	376000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	2170000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	2164000	USD
CY2020Q4	nfbk	Deferred Tax Assets Net Actuarial Loss On Defined Benefit Post Retirement Benefit Plans DeferredTaxAssetsNetActuarialLossOnDefinedBenefitPostRetirementBenefitPlans	-15000	USD
CY2019Q4	nfbk	Deferred Tax Assets Net Actuarial Loss On Defined Benefit Post Retirement Benefit Plans DeferredTaxAssetsNetActuarialLossOnDefinedBenefitPostRetirementBenefitPlans	-21000	USD
CY2020Q4	nfbk	Deferred Tax Assets Straight Line Rent Adjustments DeferredTaxAssetsStraightLineRentAdjustments	1533000	USD
CY2019Q4	nfbk	Deferred Tax Assets Straight Line Rent Adjustments DeferredTaxAssetsStraightLineRentAdjustments	1277000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Asset Retirement Obligations DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAssetRetirementObligations	71000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Asset Retirement Obligations DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAssetRetirementObligations	70000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Returns And Allowances DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsReturnsAndAllowances	675000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Returns And Allowances DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsReturnsAndAllowances	578000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	226000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	216000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Compensation DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeCompensation	647000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Compensation DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeCompensation	615000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	293000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	244000	USD
CY2020Q4	nfbk	Deferred Tax Assets Depreciation DeferredTaxAssetsDepreciation	2798000	USD
CY2019Q4	nfbk	Deferred Tax Assets Depreciation DeferredTaxAssetsDepreciation	2414000	USD
CY2020Q4	nfbk	Deferred Tax Assets Related To Fair Value Adjustments On Business Acquisitions DeferredTaxAssetsRelatedToFairValueAdjustmentsOnBusinessAcquisitions	4967000	USD
CY2019Q4	nfbk	Deferred Tax Assets Related To Fair Value Adjustments On Business Acquisitions DeferredTaxAssetsRelatedToFairValueAdjustmentsOnBusinessAcquisitions	3713000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	140000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	160000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	28207000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	24027000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Unrealized Gains On Trading Securities DeferredTaxLiabilitiesUnrealizedGainsOnTradingSecurities	5083000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Unrealized Gains On Trading Securities DeferredTaxLiabilitiesUnrealizedGainsOnTradingSecurities	1786000	USD
CY2020Q4	nfbk	Deferred Tax Liabilities Adjustment Of Investment Securities DeferredTaxLiabilitiesAdjustmentOfInvestmentSecurities	825000	USD
CY2019Q4	nfbk	Deferred Tax Liabilities Adjustment Of Investment Securities DeferredTaxLiabilitiesAdjustmentOfInvestmentSecurities	20000	USD
CY2020Q4	nfbk	Deferred Tax Liabilities Adjustment Of Deposit Liabilities DeferredTaxLiabilitiesAdjustmentOfDepositLiabilities	3000	USD
CY2019Q4	nfbk	Deferred Tax Liabilities Adjustment Of Deposit Liabilities DeferredTaxLiabilitiesAdjustmentOfDepositLiabilities	219000	USD
CY2020Q4	nfbk	Deferred Tax Liability Deferred Loan Fees DeferredTaxLiabilityDeferredLoanFees	1387000	USD
CY2019Q4	nfbk	Deferred Tax Liability Deferred Loan Fees DeferredTaxLiabilityDeferredLoanFees	2224000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	26000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	30000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	7324000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	4279000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	20883000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	19748000	USD
CY2019	nfbk	Amount Of Bad Debts Reserved For In Current Year AmountOfBadDebtsReservedForInCurrentYear	5900000	USD
CY2020	nfbk	Amount Of Bad Debts Reserved For In Current Year AmountOfBadDebtsReservedForInCurrentYear	5900000	USD
CY2019Q4	nfbk	Federal Tax Bad Debt Deferred Tax Liability FederalTaxBadDebtDeferredTaxLiability	2800000	USD
CY2020Q4	nfbk	Federal Tax Bad Debt Deferred Tax Liability FederalTaxBadDebtDeferredTaxLiability	2800000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	190000	USD
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	530000	USD
CY2017Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	482000	USD
CY2020	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	33000	USD
CY2019	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	530000	USD
CY2018	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	238000	USD
CY2020	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2019	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	190000	USD
CY2018	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	286000	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	157000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	190000	USD
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	530000	USD
CY2020	nfbk	Defined Contribution Plan Requisite Service Period DefinedContributionPlanRequisiteServicePeriod	P3M
CY2020	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent Of Match DefinedContributionPlanEmployerMatchingContributionPercentOfMatch	0.25
CY2020	nfbk	Percentage Contribution From Employees First Base Compensation PercentageContributionFromEmployeesFirstBaseCompensation	0.06
CY2020	nfbk	Defined Contribution Plan Vesting Period DefinedContributionPlanVestingPeriod	P3Y
CY2020	nfbk	Defined Contribution Plan Periodof Participationto Trigger Increasein Employee Contribution Percentage DefinedContributionPlanPeriodofParticipationtoTriggerIncreaseinEmployeeContributionPercentage	P3Y
CY2020	nfbk	Percentage Contribution From Employees First Base Compensation PercentageContributionFromEmployeesFirstBaseCompensation	0.06
CY2020	nfbk	Defined Contribution Plan Requisite Service Periodto Become Fully Vested DefinedContributionPlanRequisiteServicePeriodtoBecomeFullyVested	P5Y
CY2020	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	508000	USD
CY2019	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	426000	USD
CY2018	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	394000	USD
CY2020	us-gaap	Employee Stock Ownership Plan Esop Compensation Expense EmployeeStockOwnershipPlanESOPCompensationExpense	1400000	USD
CY2019	us-gaap	Employee Stock Ownership Plan Esop Compensation Expense EmployeeStockOwnershipPlanESOPCompensationExpense	1900000	USD
CY2018	us-gaap	Employee Stock Ownership Plan Esop Compensation Expense EmployeeStockOwnershipPlanESOPCompensationExpense	2000000.0	USD
CY2020Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Gain Loss Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear	0	USD
CY2020Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Prior Service Cost Credit Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfPriorServiceCostCreditNextFiscalYear	-19000	USD
CY2020Q4	us-gaap	Defined Benefit Plan Ultimate Health Care Cost Trend Rate1 DefinedBenefitPlanUltimateHealthCareCostTrendRate1	0.0875
CY2020	nfbk	Defined Benefit Plan Ultimate Health Care Cost Trend Rate Reduction DefinedBenefitPlanUltimateHealthCareCostTrendRateReduction	0.0050
CY2020Q4	us-gaap	Defined Benefit Plan Health Care Cost Trend Rate Assumed Next Fiscal Year DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear	0.0475
CY2020	us-gaap	Defined Benefit Plan Benefit Obligation Benefits Paid DefinedBenefitPlanBenefitObligationBenefitsPaid	97000	USD
CY2019	us-gaap	Defined Benefit Plan Benefit Obligation Benefits Paid DefinedBenefitPlanBenefitObligationBenefitsPaid	103000	USD
CY2018	us-gaap	Defined Benefit Plan Benefit Obligation Benefits Paid DefinedBenefitPlanBenefitObligationBenefitsPaid	120000	USD
CY2020Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Next Twelve Months DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths	95000	USD
CY2020Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Two DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo	96000	USD
CY2020Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Three DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree	96000	USD
CY2020Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Four DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour	79000	USD
CY2020Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Five DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive	76000	USD
CY2020Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Five Fiscal Years Thereafter DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter	332000	USD
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0	shares
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0	shares
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0	shares
CY2020	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	1400000	USD
CY2019	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	3200000	USD
CY2018	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	5400000	USD
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	15000	shares
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	3251595	shares
CY2018Q4	nfbk	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageGrantDateFairValue	3.93
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	13.51
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P5Y7M13D
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Options Forfeited Weighted Average Grant Date Fair Value SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue	4.07
CY2019	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice	14.76
CY2019	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	1009402	shares
CY2019	nfbk	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageGrantDateFairValue	3.75
CY2019	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	12.54
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	2227193	shares
CY2019Q4	nfbk	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageGrantDateFairValue	4.01
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	13.93
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P4Y11M15D
CY2020	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	13000	shares
CY2020	nfbk	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageGrantDateFairValue	3.93
CY2020	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	13.38
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	2214193	shares
CY2020Q4	nfbk	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageGrantDateFairValue	4.01
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	13.94
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P3Y11M15D
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber	2197114	shares
CY2020Q4	nfbk	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageGrantDateFairValue	4.00
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice	13.92
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1	P3Y11M12D
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	328962	shares
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	14.31
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	249860	shares
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue	13.99
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	8000	shares
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	14.76
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	71102	shares
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	15.36
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	103581	shares
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	15.81
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	67100	shares
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue	15.18
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	3573	shares
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	15.81
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	104010	shares
CY2020Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	15.91
CY2020Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.08
CY2020Q4	nfbk	Commitments To Extend Credit Allowance For Estimated Losses CommitmentsToExtendCreditAllowanceForEstimatedLosses	808000	USD
CY2019Q4	nfbk	Commitments To Extend Credit Allowance For Estimated Losses CommitmentsToExtendCreditAllowanceForEstimatedLosses	756000	USD
CY2020	nfbk	Agreement Term AgreementTerm	P3Y
CY2020	nfbk	Agreement Term AgreementTerm	P3Y
CY2020Q4	nfbk	Tier One Common Capital Requiredfor Capital Adequacyto Risk Weighted Assets TierOneCommonCapitalRequiredforCapitalAdequacytoRiskWeightedAssets	0.045
CY2020Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.060
CY2020Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.080
CY2020Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	0.040
CY2020Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized To Average Assets TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets	0.050
CY2020Q4	nfbk	Tier One Common Capital Requiredtobe Well Capitalizedto Risk Weighted Assets TierOneCommonCapitalRequiredtobeWellCapitalizedtoRiskWeightedAssets	0.065
CY2020Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	0.080
CY2020Q4	us-gaap	Capital Required To Be Well Capitalized To Risk Weighted Assets CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	0.100
CY2020Q4	nfbk	Tier One Common Capital Requiredfor Capital Adequacyto Risk Weighted Assets TierOneCommonCapitalRequiredforCapitalAdequacytoRiskWeightedAssets	0.045
CY2020Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.06
CY2020Q4	nfbk	Banking Regulation Community Bank Leverage Ratio Well Capitalized Minimum Amount BankingRegulationCommunityBankLeverageRatioWellCapitalizedMinimumAmount	439219000	USD
CY2020Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	0.04
CY2020Q4	nfbk	Tier One Risk Based Capital Requiredfor Capital Adequacyto Risk Weighted Assets Higher Risk Weight TierOneRiskBasedCapitalRequiredforCapitalAdequacytoRiskWeightedAssetsHigherRiskWeight	0.025
CY2016Q1	nfbk	Tier One Common Capitalto Risk Weighted Assets Capital Conservation Buffer TierOneCommonCapitaltoRiskWeightedAssetsCapitalConservationBuffer	0.00625
CY2019Q1	nfbk	Tier One Risk Based Capital Requiredfor Capital Adequacyto Risk Weighted Assets Higher Risk Weight TierOneRiskBasedCapitalRequiredforCapitalAdequacytoRiskWeightedAssetsHigherRiskWeight	0.025
CY2020Q4	nfbk	Banking Regulation Community Bank Leverage Ratio Actual BankingRegulationCommunityBankLeverageRatioActual	698864000	USD
CY2020Q4	nfbk	Banking Regulation Community Bank Leverage Ratio Capital Ratio Actual BankingRegulationCommunityBankLeverageRatioCapitalRatioActual	0.1273
CY2020Q4	nfbk	Banking Regulation Community Bank Leverage Ratio Capital Adequacy Minimum Amount BankingRegulationCommunityBankLeverageRatioCapitalAdequacyMinimumAmount	439219000	USD
CY2020Q4	nfbk	Banking Regulation Community Bank Leverage Ratio Capital Adequacy Minimum BankingRegulationCommunityBankLeverageRatioCapitalAdequacyMinimum	0.0800
CY2020Q4	nfbk	Banking Regulation Community Bank Leverage Ratio Well Capitalized Minimum BankingRegulationCommunityBankLeverageRatioWellCapitalizedMinimum	0.0800
CY2019Q4	nfbk	Tier One Common Equity TierOneCommonEquity	651974000	USD
CY2019Q4	nfbk	Tier One Common Capitalto Risk Weighted Assets TierOneCommonCapitaltoRiskWeightedAssets	0.1635
CY2019Q4	nfbk	Tier One Common Equity Requiredfor Capital Adequacy TierOneCommonEquityRequiredforCapitalAdequacy	179439000	USD
CY2019Q4	nfbk	Tier One Common Capital Requiredfor Capital Adequacyto Risk Weighted Assets TierOneCommonCapitalRequiredforCapitalAdequacytoRiskWeightedAssets	0.0450
CY2019Q4	nfbk	Tier One Common Equity Requiredtobe Well Capitalized TierOneCommonEquityRequiredtobeWellCapitalized	259189000	USD
CY2019Q4	nfbk	Tier One Common Capital Requiredtobe Well Capitalizedto Risk Weighted Assets TierOneCommonCapitalRequiredtobeWellCapitalizedtoRiskWeightedAssets	0.0650
CY2019Q4	us-gaap	Tier One Leverage Capital TierOneLeverageCapital	651974000	USD
CY2019Q4	us-gaap	Tier One Leverage Capital To Average Assets TierOneLeverageCapitalToAverageAssets	0.1337
CY2019Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy TierOneLeverageCapitalRequiredForCapitalAdequacy	195018000	USD
CY2019Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	0.0400
CY2019Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized TierOneLeverageCapitalRequiredToBeWellCapitalized	243772000	USD
CY2019Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized To Average Assets TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets	0.0500
CY2019Q4	us-gaap	Tier One Risk Based Capital TierOneRiskBasedCapital	651974000	USD
CY2019Q4	us-gaap	Tier One Risk Based Capital To Risk Weighted Assets TierOneRiskBasedCapitalToRiskWeightedAssets	0.1635
CY2019Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy TierOneRiskBasedCapitalRequiredForCapitalAdequacy	239251000	USD
CY2019Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.0600
CY2019Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized TierOneRiskBasedCapitalRequiredToBeWellCapitalized	319002000	USD
CY2019Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	0.0800
CY2019Q4	us-gaap	Capital Capital	681467000	USD
CY2019Q4	us-gaap	Capital To Risk Weighted Assets CapitalToRiskWeightedAssets	0.1709
CY2019Q4	us-gaap	Capital Required For Capital Adequacy CapitalRequiredForCapitalAdequacy	319002000	USD
CY2019Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.0800
CY2020	nfbk	Impaired Financing Receivables Charge Off ImpairedFinancingReceivablesChargeOff	3800000	USD
CY2020Q4	us-gaap	Loans Receivable Fair Value Disclosure LoansReceivableFairValueDisclosure	5325000	USD
CY2019Q4	us-gaap	Capital Required To Be Well Capitalized CapitalRequiredToBeWellCapitalized	398752000	USD
CY2019Q4	us-gaap	Capital Required To Be Well Capitalized To Risk Weighted Assets CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	0.1000
CY2019Q4	us-gaap	Loans Receivable Fair Value Disclosure LoansReceivableFairValueDisclosure	4942000	USD
CY2020Q4	nfbk	Principal Amount Outstanding Of Impaired Loans Heldfor Investment And Heldfor Sale PrincipalAmountOutstandingOfImpairedLoansHeldforInvestmentAndHeldforSale	7400000	USD
CY2019Q4	nfbk	Principal Amount Outstanding Of Impaired Loans Heldfor Investment And Heldfor Sale PrincipalAmountOutstandingOfImpairedLoansHeldforInvestmentAndHeldforSale	7000000.0	USD
CY2020Q4	nfbk	Estimated Fair Value Of Impaired Loans Held For Investment EstimatedFairValueOfImpairedLoansHeldForInvestment	5300000	USD
CY2019Q4	nfbk	Estimated Fair Value Of Impaired Loans Held For Investment EstimatedFairValueOfImpairedLoansHeldForInvestment	4900000	USD
CY2020	us-gaap	Asset Impairment Charges AssetImpairmentCharges	69000	USD
CY2019	us-gaap	Asset Impairment Charges AssetImpairmentCharges	116000	USD
CY2019	nfbk	Impaired Financing Receivables Charge Off ImpairedFinancingReceivablesChargeOff	1200000	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents Fair Value Disclosure CashAndCashEquivalentsFairValueDisclosure	87544000	USD
CY2020Q4	us-gaap	Trading Securities Debt TradingSecuritiesDebt	12291000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	1264805000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	7574000	USD
CY2020Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	253000	USD
CY2020Q4	us-gaap	Investment In Federal Home Loan Bank Stock Fair Value Disclosure InvestmentInFederalHomeLoanBankStockFairValueDisclosure	28641000	USD
CY2020Q4	us-gaap	Loans Held For Sale Fair Value Disclosure LoansHeldForSaleFairValueDisclosure	19895000	USD
CY2020Q4	nfbk	Net Loans Held For Investment Fair Value Disclosure NetLoansHeldForInvestmentFairValueDisclosure	3842054000	USD
CY2020Q4	us-gaap	Derivative Assets DerivativeAssets	1498000	USD
CY2020Q4	us-gaap	Deposits Fair Value Disclosure DepositsFairValueDisclosure	4082538000	USD
CY2020Q4	us-gaap	Federal Funds Purchased And Securities Loaned Or Sold Under Agreements To Repurchase Fair Value Disclosure FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure	609900000	USD
CY2020Q4	us-gaap	Advance Payments By Borrowers For Taxes And Insurance AdvancePaymentsByBorrowersForTaxesAndInsurance	19677000	USD
CY2020Q4	us-gaap	Advances Fair Value Disclosure AdvancesFairValueDisclosure	19677000	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents Fair Value Disclosure CashAndCashEquivalentsFairValueDisclosure	147818000	USD
CY2019Q4	us-gaap	Trading Securities Debt TradingSecuritiesDebt	11222000	USD
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	1138352000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	8886000	USD
CY2019Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	250000	USD
CY2019Q4	us-gaap	Investment In Federal Home Loan Bank Stock Fair Value Disclosure InvestmentInFederalHomeLoanBankStockFairValueDisclosure	39575000	USD
CY2019Q4	nfbk	Net Loans Held For Investment Fair Value Disclosure NetLoansHeldForInvestmentFairValueDisclosure	3482804000	USD
CY2019Q4	us-gaap	Derivative Assets DerivativeAssets	79000	USD
CY2019Q4	us-gaap	Deposits Fair Value Disclosure DepositsFairValueDisclosure	3412414000	USD
CY2019Q4	us-gaap	Federal Funds Purchased And Securities Loaned Or Sold Under Agreements To Repurchase Fair Value Disclosure FederalFundsPurchasedAndSecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure	862980000	USD
CY2019Q4	us-gaap	Advances Fair Value Disclosure AdvancesFairValueDisclosure	20045000	USD
CY2019Q4	us-gaap	Equity Securities Without Readily Determinable Fair Value Amount EquitySecuritiesWithoutReadilyDeterminableFairValueAmount	3100000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	36988000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	40235000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	40079000	USD
CY2020	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	48721504	shares
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	46783442	shares
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	46319760	shares
CY2020	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	64459	shares
CY2019	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	380362	shares
CY2018	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	787673	shares
CY2020	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	48785963	shares
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	47163804	shares
CY2018	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	47107433	shares
CY2020	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.76
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.86
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.87
CY2020	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.76
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.85
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.85
CY2020	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	1972136	shares
CY2019	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	546120	shares
CY2018	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	765792	shares
CY2020	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	3967000	USD
CY2020	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	3967000	USD
CY2019	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4881000	USD
CY2018	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4877000	USD
CY2020	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	3774000	USD
CY2020	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	3774000	USD
CY2019	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	7023000	USD
CY2018	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	3705000	USD
CY2020	us-gaap	Debt Securities Available For Sale Gain Loss DebtSecuritiesAvailableForSaleGainLoss	327000	USD
CY2019	us-gaap	Debt Securities Available For Sale Gain Loss DebtSecuritiesAvailableForSaleGainLoss	514000	USD
CY2018	us-gaap	Debt Securities Available For Sale Gain Loss DebtSecuritiesAvailableForSaleGainLoss	178000	USD
CY2020	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	1601000	USD
CY2019	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	1988000	USD
CY2018	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	-879000	USD
CY2020	us-gaap	Gain Loss On Sales Of Loans Net GainLossOnSalesOfLoansNet	665000	USD
CY2019	us-gaap	Gain Loss On Sales Of Loans Net GainLossOnSalesOfLoansNet	0	USD
CY2018	us-gaap	Gain Loss On Sales Of Loans Net GainLossOnSalesOfLoansNet	0	USD
CY2020	us-gaap	Revenue Not From Contract With Customer Other RevenueNotFromContractWithCustomerOther	1138000	USD
CY2019	us-gaap	Revenue Not From Contract With Customer Other RevenueNotFromContractWithCustomerOther	402000	USD
CY2018	us-gaap	Revenue Not From Contract With Customer Other RevenueNotFromContractWithCustomerOther	246000	USD
CY2020	us-gaap	Noninterest Income NoninterestIncome	11472000	USD
CY2019	us-gaap	Noninterest Income NoninterestIncome	14808000	USD
CY2018	us-gaap	Noninterest Income NoninterestIncome	8127000	USD
CY2020Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	36700000	USD
CY2020Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	42700000	USD
CY2019Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	39500000	USD
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	44100000	USD
CY2020	us-gaap	Operating Lease Cost OperatingLeaseCost	6160000	USD
CY2019	us-gaap	Operating Lease Cost OperatingLeaseCost	6119000	USD
CY2020	us-gaap	Variable Lease Cost VariableLeaseCost	3276000	USD
CY2019	us-gaap	Variable Lease Cost VariableLeaseCost	2813000	USD
CY2020	us-gaap	Lease Cost LeaseCost	9436000	USD
CY2019	us-gaap	Lease Cost LeaseCost	8932000	USD
CY2020	us-gaap	Operating Lease Payments OperatingLeasePayments	6490000	USD
CY2019	us-gaap	Operating Lease Payments OperatingLeasePayments	5901000	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	3568000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	1013000	USD
CY2020Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P12Y3M10D
CY2019Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P12Y9M7D
CY2020Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0360
CY2019Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0362
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	6377000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	5550000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	5504000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	5066000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	4711000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	28196000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	55404000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	12670000	USD
CY2020Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	42734000	USD
CY2020	us-gaap	Operating Lease Expense OperatingLeaseExpense	8000000.0	USD
CY2019	us-gaap	Operating Lease Expense OperatingLeaseExpense	6800000	USD
CY2018	us-gaap	Lease And Rental Expense LeaseAndRentalExpense	5700000	USD
CY2020	nfbk	Operating Lease Accelerated Rent Expense OperatingLeaseAcceleratedRentExpense	1800000	USD
CY2019	nfbk	Operating Lease Accelerated Rent Expense OperatingLeaseAcceleratedRentExpense	579000	USD
CY2020Q1	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	42732000	USD
CY2020Q2	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	40911000	USD
CY2020Q3	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	41457000	USD
CY2020Q4	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	43045000	USD
CY2020Q1	us-gaap	Interest Expense InterestExpense	12799000	USD
CY2020Q2	us-gaap	Interest Expense InterestExpense	10681000	USD
CY2020Q3	us-gaap	Interest Expense InterestExpense	8849000	USD
CY2020Q4	us-gaap	Interest Expense InterestExpense	6008000	USD
CY2020Q1	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	29933000	USD
CY2020Q2	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	30230000	USD
CY2020Q3	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	32608000	USD
CY2020Q4	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	37037000	USD
CY2020Q1	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	8183000	USD
CY2020Q2	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	1921000	USD
CY2020Q3	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	165000	USD
CY2020Q4	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	2473000	USD
CY2020Q1	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	21750000	USD
CY2020Q2	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	28309000	USD
CY2020Q3	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	32443000	USD
CY2020Q4	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	34564000	USD
CY2020Q1	us-gaap	Noninterest Income NoninterestIncome	108000	USD
CY2020Q2	us-gaap	Noninterest Income NoninterestIncome	4238000	USD
CY2020Q3	us-gaap	Noninterest Income NoninterestIncome	3022000	USD
CY2020Q4	us-gaap	Noninterest Income NoninterestIncome	4104000	USD
CY2020Q1	us-gaap	Noninterest Expense NoninterestExpense	15682000	USD
CY2020Q2	us-gaap	Noninterest Expense NoninterestExpense	17855000	USD
CY2020Q3	us-gaap	Noninterest Expense NoninterestExpense	23788000	USD
CY2020Q4	us-gaap	Noninterest Expense NoninterestExpense	21188000	USD
CY2020Q1	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	6176000	USD
CY2020Q2	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	14692000	USD
CY2020Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	11677000	USD
CY2020Q4	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	17480000	USD
CY2020Q1	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	1625000	USD
CY2020Q2	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	3899000	USD
CY2020Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	3095000	USD
CY2020Q4	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	4418000	USD
CY2020Q1	us-gaap	Net Income Loss NetIncomeLoss	4551000	USD
CY2020Q2	us-gaap	Net Income Loss NetIncomeLoss	10793000	USD
CY2020Q3	us-gaap	Net Income Loss NetIncomeLoss	8582000	USD
CY2020Q4	us-gaap	Net Income Loss NetIncomeLoss	13062000	USD
CY2020Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.10
CY2020Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.23
CY2020Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.17
CY2020Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.26
CY2020Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.10
CY2020Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.23
CY2020Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.17
CY2020Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.26
CY2019Q1	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	39466000	USD
CY2019Q2	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	40193000	USD
CY2019Q3	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	42847000	USD
CY2019Q4	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	42637000	USD
CY2019Q1	us-gaap	Interest Expense InterestExpense	12136000	USD
CY2019Q2	us-gaap	Interest Expense InterestExpense	13034000	USD
CY2019Q3	us-gaap	Interest Expense InterestExpense	14027000	USD
CY2019Q4	us-gaap	Interest Expense InterestExpense	14161000	USD
CY2019Q1	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	27330000	USD
CY2019Q2	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	27159000	USD
CY2019Q3	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	28820000	USD
CY2019Q4	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	28476000	USD
CY2019Q1	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	59000	USD
CY2019Q2	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	491000	USD
CY2019Q3	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	-1300000	USD
CY2019Q4	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	772000	USD
CY2019Q1	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	27271000	USD
CY2019Q2	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	26668000	USD
CY2019Q3	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	30120000	USD
CY2019Q4	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	27704000	USD
CY2019Q1	us-gaap	Noninterest Income NoninterestIncome	3314000	USD
CY2019Q2	us-gaap	Noninterest Income NoninterestIncome	2566000	USD
CY2019Q3	us-gaap	Noninterest Income NoninterestIncome	4733000	USD
CY2019Q4	us-gaap	Noninterest Income NoninterestIncome	4195000	USD
CY2019Q1	us-gaap	Noninterest Expense NoninterestExpense	19204000	USD
CY2019Q2	us-gaap	Noninterest Expense NoninterestExpense	18750000	USD
CY2019Q3	us-gaap	Noninterest Expense NoninterestExpense	16869000	USD
CY2019Q4	us-gaap	Noninterest Expense NoninterestExpense	18726000	USD
CY2019Q1	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	11381000	USD
CY2019Q2	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	10484000	USD
CY2019Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	17984000	USD
CY2019Q4	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	13173000	USD
CY2019Q1	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	2610000	USD
CY2019Q2	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	2280000	USD
CY2019Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	4845000	USD
CY2019Q4	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	3052000	USD
CY2019Q1	us-gaap	Net Income Loss NetIncomeLoss	8771000	USD
CY2019Q2	us-gaap	Net Income Loss NetIncomeLoss	8204000	USD
CY2019Q3	us-gaap	Net Income Loss NetIncomeLoss	13139000	USD
CY2019Q4	us-gaap	Net Income Loss NetIncomeLoss	10121000	USD
CY2019Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.19
CY2019Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.18
CY2019Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.28
CY2019Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.22
CY2019Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.19
CY2019Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.17
CY2019Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.28
CY2019Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.21

Files In Submission

Name	View Source	Status
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$NFBK
Northfield Bancorp, Inc. Stock $nfbk

2019 Q4 Form 10-K Financial Statement

#000149322521000048 Filed on March 10, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$NFBK Northfield Bancorp, Inc. Stock $nfbk

2019 Q4 Form 10-K Financial Statement

#000149322521000048 Filed on March 10, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$NFBK
Northfield Bancorp, Inc. Stock $nfbk