$NFBK
Northfield Bancorp, Inc. Stock $nfbk

$nfbk Overview Financials Valuation SEC Filings Company Website

2018 Q4 Form 10-K Financial Statement

#000149322520000042 Filed on March 02, 2020

Income Statement

Concept	2018 Q4	2018 Q3	2018 Q2
Revenue	$38.95M	$37.73M	$35.94M
YoY Change		12.53%	10.03%
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	$840.0K	$810.0K	$850.0K
YoY Change	-4.55%	-7.95%	-7.61%
% of Gross Profit
Operating Expenses
YoY Change
Operating Profit
YoY Change
Interest Expense	$10.94M	$9.803M	$8.165M
YoY Change		58.8%	41.98%
% of Operating Profit
Other Income/Expense, Net
YoY Change
Pretax Income	$12.26M	$12.16M	$12.51M
YoY Change	-12.24%	-3.9%	2.36%
Income Tax	$2.314M	$3.081M	$1.893M
% Of Pretax Income	18.87%	25.34%	15.14%
Net Earnings	$9.946M	$9.076M	$10.61M
YoY Change	-678.26%	11.69%	26.18%
Net Earnings / Revenue	25.54%	24.06%	29.53%
Basic Earnings Per Share	$0.21	$0.19	$0.23
Diluted Earnings Per Share	$0.21	$0.19	$0.23
COMMON SHARES
Basic Shares Outstanding	49.54M shares	46.60M shares	46.18M shares
Diluted Shares Outstanding		47.29M shares	47.11M shares

Balance Sheet

Concept	2018 Q4	2018 Q3	2018 Q2
SHORT-TERM ASSETS
Cash & Short-Term Investments
YoY Change
Cash & Equivalents	$77.76M	$58.74M	$58.73M
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	$25.61M	$25.23M	$25.06M
YoY Change	-0.55%	-1.08%	-3.21%
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	$4.408B	$4.286B	$4.188B
YoY Change	10.45%	6.98%	8.51%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$18.00M	$17.00M	$18.00M
YoY Change	21.62%	18.88%	17.65%
Accrued Expenses	$28.60M	$32.50M	$28.90M
YoY Change	-2.05%	14.44%	8.24%
Deferred Revenue
YoY Change
Short-Term Debt	$0.00
YoY Change	-100.0%
Long-Term Debt Due
YoY Change
Total Short-Term Liabilities	$46.60M	$49.50M	$46.90M
YoY Change	5.91%	15.93%	11.67%
LONG-TERM LIABILITIES
Long-Term Debt	$408.9M	$441.2M	$524.3M
YoY Change	136200.0%	-24.41%	4.71%
Other Long-Term Liabilities
YoY Change
Total Long-Term Liabilities	$408.9M	$441.2M	$524.3M
YoY Change	136200.0%	-24.41%	4.71%
TOTAL LIABILITIES
Total Short-Term Liabilities	$46.60M	$49.50M	$46.90M
Total Long-Term Liabilities	$408.9M	$441.2M	$524.3M
Total Liabilities	$3.742B	$3.632B	$3.539B
YoY Change	11.62%	8.04%	9.85%
SHAREHOLDERS EQUITY
Retained Earnings	$302.5M	$297.3M	$292.9M
YoY Change	7.61%	3.74%	3.82%
Common Stock	$609.0K	$609.0K	$609.0K
YoY Change	0.0%	0.0%	0.0%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$152.8M	$154.2M	$154.9M
YoY Change	-6.86%	-5.4%	-5.15%
Treasury Stock Shares	11.30M shares	11.40M shares	11.45M shares
Shareholders Equity	$666.4M	$654.4M	$649.7M
YoY Change
Total Liabilities & Shareholders Equity	$4.408B	$4.286B	$4.188B
YoY Change	10.45%	6.98%	8.51%

Cashflow Statement

Concept	2018 Q4	2018 Q3	2018 Q2
OPERATING ACTIVITIES
Net Income	$9.946M	$9.076M	$10.61M
YoY Change	-678.26%	11.69%	26.18%
Depreciation, Depletion And Amortization	$840.0K	$810.0K	$850.0K
YoY Change	-4.55%	-7.95%	-7.61%
Cash From Operating Activities	$10.67M	$16.08M	$12.44M
YoY Change	16.1%	12.21%	20.78%
INVESTING ACTIVITIES
Capital Expenditures	-$1.140M	-$900.0K	-$530.0K
YoY Change	10.68%	125.0%	0.0%
Acquisitions
YoY Change
Other Investing Activities	-$99.94M	-$100.7M	-$131.9M
YoY Change	156.72%	4.71%	807.98%
Cash From Investing Activities	-$101.1M	-$101.7M	-$132.5M
YoY Change	152.93%	5.22%	779.55%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	109.4M	85.56M	126.2M
YoY Change	-847.47%	-36.73%	3256.12%
NET CHANGE
Cash From Operating Activities	10.67M	16.08M	12.44M
Cash From Investing Activities	-101.1M	-101.7M	-132.5M
Cash From Financing Activities	109.4M	85.56M	126.2M
Net Change In Cash	19.03M	-10.00K	6.170M
YoY Change	-141.91%	-100.02%	-717.0%
FREE CASH FLOW
Cash From Operating Activities	$10.67M	$16.08M	$12.44M
Capital Expenditures	-$1.140M	-$900.0K	-$530.0K
Free Cash Flow	$11.81M	$16.98M	$12.97M
YoY Change	15.56%	15.27%	19.76%

Facts In Submission

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CY2019	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	563000	USD
CY2017	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	5386000	USD
CY2018	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	1065000	USD
CY2017	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	1064000	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
CY2017	us-gaap	Debt Securities Available For Sale Gain Loss DebtSecuritiesAvailableForSaleGainLoss	169000	USD
CY2019	us-gaap	Other Noninterest Expense OtherNoninterestExpense	5988000	USD
CY2019	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	1988000	USD
CY2018	us-gaap	Other Noninterest Expense OtherNoninterestExpense	6857000	USD
CY2018	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	-879000	USD
CY2017	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	1114000	USD
CY2017	us-gaap	Other Noninterest Expense OtherNoninterestExpense	6446000	USD
CY2019	us-gaap	Noninterest Expense NoninterestExpense	73549000	USD
CY2017	us-gaap	Noninterest Income Other Operating Income NoninterestIncomeOtherOperatingIncome	271000	USD
CY2019	us-gaap	Noninterest Income NoninterestIncome	14808000	USD
CY2018	us-gaap	Noninterest Income NoninterestIncome	8127000	USD
CY2017	us-gaap	Noninterest Income NoninterestIncome	11642000	USD
CY2019	us-gaap	Labor And Related Expense LaborAndRelatedExpense	39571000	USD
CY2018	us-gaap	Labor And Related Expense LaborAndRelatedExpense	34802000	USD
CY2017	us-gaap	Labor And Related Expense LaborAndRelatedExpense	38237000	USD
CY2019	us-gaap	Occupancy Net OccupancyNet	13676000	USD
CY2018	us-gaap	Occupancy Net OccupancyNet	12096000	USD
CY2017	us-gaap	Occupancy Net OccupancyNet	11270000	USD
CY2019	us-gaap	Equipment Expense EquipmentExpense	1085000	USD
CY2018	us-gaap	Equipment Expense EquipmentExpense	1004000	USD
CY2017	us-gaap	Equipment Expense EquipmentExpense	1141000	USD
CY2019	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	5679000	USD
CY2018	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	5011000	USD
CY2017	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	4585000	USD
CY2019	us-gaap	Professional Fees ProfessionalFees	3545000	USD
CY2018	us-gaap	Professional Fees ProfessionalFees	3482000	USD
CY2017	us-gaap	Professional Fees ProfessionalFees	2774000	USD
CY2018	us-gaap	Noninterest Expense NoninterestExpense	67043000	USD
CY2017	us-gaap	Noninterest Expense NoninterestExpense	67378000	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
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	51746000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	12787000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	9632000	USD
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	26978000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	40235000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	40079000	USD
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.87
CY2017	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.55
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.85
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.86
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.85
CY2017	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.53
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
CY2017	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	45325445	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
CY2017	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	46875730	shares
CY2019	us-gaap	Net Income Loss NetIncomeLoss	40235000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	40079000	USD
CY2017	us-gaap	Net Income Loss NetIncomeLoss	24768000	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
CY2017	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	-283000	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
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	169000	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
CY2017	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Before Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeTax	-452000	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
CY2017	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-74000	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
CY2017	us-gaap	Other Comprehensive Income Loss Before Tax Portion Attributable To Parent OtherComprehensiveIncomeLossBeforeTaxPortionAttributableToParent	-378000	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
CY2017	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	-113000	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
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	68000	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
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-30000	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
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	54081000	USD
CY2018	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	36383000	USD
CY2017	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	24541000	USD
CY2017	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-227000	USD
CY2019	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	5770000	USD
CY2019	us-gaap	Dividends Common Stock DividendsCommonStock	20198000	USD
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	5576000	USD
CY2016Q4	us-gaap	Stockholders Equity StockholdersEquity	621196000	USD
CY2018	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	2088000	USD
CY2018	us-gaap	Share Based Compensation ShareBasedCompensation	7769000	USD
CY2017	us-gaap	Share Based Compensation ShareBasedCompensation	8686000	USD
CY2018	us-gaap	Dividends Common Stock DividendsCommonStock	18673000	USD
CY2018	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	5000	USD
CY2018Q4	us-gaap	Stockholders Equity StockholdersEquity	666439000	USD
CY2019	us-gaap	Depreciation Nonproduction DepreciationNonproduction	3569000	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	Stock Issued During Period Value Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	0	USD
CY2018	us-gaap	Depreciation Nonproduction DepreciationNonproduction	3020000	USD
CY2017	us-gaap	Net Income Loss NetIncomeLoss	24768000	USD
CY2017	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-227000	USD
CY2017	us-gaap	Amortization Of Esop Award AmortizationOfESOPAward	2489000	USD
CY2017	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	6197000	USD
CY2017	us-gaap	Adjustments To Additional Paid In Capital Tax Effect From Share Based Compensation AdjustmentsToAdditionalPaidInCapitalTaxEffectFromShareBasedCompensation	0	USD
CY2017	us-gaap	Stock Issued During Period Value Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	0	USD
CY2017	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	100000	USD
CY2017	us-gaap	Dividends Common Stock DividendsCommonStock	15646000	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 Restricted Stock Award Forfeitures StockIssuedDuringPeriodValueRestrictedStockAwardForfeitures	0	USD
CY2019	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	15815000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	695853000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	40235000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	40079000	USD
CY2017	us-gaap	Net Income Loss NetIncomeLoss	24768000	USD
CY2019	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	22000	USD
CY2018	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	2615000	USD
CY2017	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	1411000	USD
CY2017	us-gaap	Depreciation Nonproduction DepreciationNonproduction	3229000	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
CY2018	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	-3563000	USD
CY2017	nfbk	Amortization Of Premiums And Deferred Loan Costs AmortizationOfPremiumsAndDeferredLoanCosts	2000000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	265000	USD
CY2018	us-gaap	Increase Decrease In Accrued Interest Receivable Net IncreaseDecreaseInAccruedInterestReceivableNet	2246000	USD
CY2017	us-gaap	Increase Decrease In Accrued Interest Receivable Net IncreaseDecreaseInAccruedInterestReceivableNet	999000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	-2679000	USD
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	326000	USD
CY2017	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	386000	USD
CY2019	nfbk	Operating Lease Right Of Use Asset Amortization OperatingLeaseRightOfUseAssetAmortization	5069000	USD
CY2019	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	7023000	USD
CY2018	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	3705000	USD
CY2017	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	5386000	USD
CY2019	us-gaap	Proceeds From Sale Of Loans Held For Sale ProceedsFromSaleOfLoansHeldForSale	0	USD
CY2018	us-gaap	Proceeds From Sale Of Loans Held For Sale ProceedsFromSaleOfLoansHeldForSale	0	USD
CY2017	us-gaap	Proceeds From Sale Of Loans Held For Sale ProceedsFromSaleOfLoansHeldForSale	494000	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
CY2017	us-gaap	Debt Securities Available For Sale Gain Loss DebtSecuritiesAvailableForSaleGainLoss	169000	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
CY2017	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	1114000	USD
CY2019	us-gaap	Increase Decrease In Trading Securities IncreaseDecreaseInTradingSecurities	266000	USD
CY2018	us-gaap	Increase Decrease In Trading Securities IncreaseDecreaseInTradingSecurities	250000	USD
CY2017	us-gaap	Increase Decrease In Trading Securities IncreaseDecreaseInTradingSecurities	626000	USD
CY2019	us-gaap	Increase Decrease In Accrued Interest Receivable Net IncreaseDecreaseInAccruedInterestReceivableNet	1650000	USD
CY2017	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	3689000	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
CY2017	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	-15193000	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
CY2017	us-gaap	Increase Decrease In Other Accounts Payable And Accrued Liabilities IncreaseDecreaseInOtherAccountsPayableAndAccruedLiabilities	-560000	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
CY2017	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	43624000	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
CY2017	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	110177000	USD
CY2019	us-gaap	Payments To Acquire Loans And Leases Held For Investment PaymentsToAcquireLoansAndLeasesHeldForInvestment	44918000	USD
CY2018	us-gaap	Payments To Acquire Loans And Leases Held For Investment PaymentsToAcquireLoansAndLeasesHeldForInvestment	37593000	USD
CY2017	us-gaap	Payments To Acquire Loans And Leases Held For Investment PaymentsToAcquireLoansAndLeasesHeldForInvestment	64116000	USD
CY2018	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	397312000	USD
CY2019	us-gaap	Proceeds From Life Insurance Policies ProceedsFromLifeInsurancePolicies	5002000	USD
CY2018	us-gaap	Proceeds From Life Insurance Policies ProceedsFromLifeInsurancePolicies	174000	USD
CY2017	us-gaap	Proceeds From Life Insurance Policies ProceedsFromLifeInsurancePolicies	2829000	USD
CY2018	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	32115000	USD
CY2017	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	4975000	USD
CY2019	us-gaap	Proceeds From Sale And Maturity Of Marketable Securities ProceedsFromSaleAndMaturityOfMarketableSecurities	0	USD
CY2018	us-gaap	Proceeds From Sale And Maturity Of Marketable Securities ProceedsFromSaleAndMaturityOfMarketableSecurities	0	USD
CY2017	us-gaap	Proceeds From Sale And Maturity Of Marketable Securities ProceedsFromSaleAndMaturityOfMarketableSecurities	966000	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
CY2017	us-gaap	Payments To Acquire Federal Home Loan Bank Stock PaymentsToAcquireFederalHomeLoanBankStock	18890000	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
CY2017	us-gaap	Proceeds From Sale Of Federal Home Loan Bank Stock ProceedsFromSaleOfFederalHomeLoanBankStock	18967000	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
CY2017	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	137631000	USD
CY2019	us-gaap	Payments To Acquire Marketable Securities PaymentsToAcquireMarketableSecurities	2061000	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
CY2017	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	114416000	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
CY2017	us-gaap	Proceeds From Maturities Prepayments And Calls Of Held To Maturity Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities	200000	USD
CY2019	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	79255000	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
CY2017	nfbk	Proceeds From Sale Of Premises And Equipment And Other Real Estate Owned ProceedsFromSaleOfPremisesAndEquipmentAndOtherRealEstateOwned	0	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
CY2017	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	2065000	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
CY2017	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-190526000	USD
CY2019	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	121721000	USD
CY2018	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	449533000	USD
CY2017	us-gaap	Increase Decrease In Deposits IncreaseDecreaseInDeposits	123392000	USD
CY2019	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	20198000	USD
CY2018	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	18673000	USD
CY2017	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	15646000	USD
CY2017	us-gaap	Repayments Of Long Term Capital Lease Obligations RepaymentsOfLongTermCapitalLeaseObligations	224000	USD
CY2019	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	1206659000	USD
CY2017	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	100000	USD
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	15815000	USD
CY2019	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	5770000	USD
CY2018	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	2088000	USD
CY2018	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	5000	USD
CY2017	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	0	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
CY2017	us-gaap	Increase Decrease In Advance Payments By Borrowers For Taxes And Insurance IncreaseDecreaseInAdvancePaymentsByBorrowersForTaxesAndInsurance	2467000	USD
CY2019	us-gaap	Repayments Of Long Term Capital Lease Obligations RepaymentsOfLongTermCapitalLeaseObligations	44000	USD
CY2018	us-gaap	Repayments Of Long Term Capital Lease Obligations RepaymentsOfLongTermCapitalLeaseObligations	255000	USD
CY2017	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	441570000	USD
CY2019	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	758502000	USD
CY2018	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	459715000	USD
CY2017	us-gaap	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	443003000	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
CY2017	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	108656000	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
CY2017	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-38246000	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
CY2016Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	96085000	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
CY2019	us-gaap	Interest Paid Net InterestPaidNet	51634000	USD
CY2018	us-gaap	Interest Paid Net InterestPaidNet	35822000	USD
CY2017	us-gaap	Interest Paid Net InterestPaidNet	23765000	USD
CY2019	us-gaap	Income Taxes Paid IncomeTaxesPaid	11092000	USD
CY2018	us-gaap	Income Taxes Paid IncomeTaxesPaid	10368000	USD
CY2017	us-gaap	Income Taxes Paid IncomeTaxesPaid	12875000	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
CY2017	us-gaap	Allowance For Loan And Lease Losses Writeoffs Net AllowanceForLoanAndLeaseLossesWriteoffsNet	-154000	USD
CY2019	us-gaap	Transfer Of Portfolio Loans And Leases To Held For Sale1 TransferOfPortfolioLoansAndLeasesToHeldForSale1	0	USD
CY2018	us-gaap	Transfer Of Portfolio Loans And Leases To Held For Sale1 TransferOfPortfolioLoansAndLeasesToHeldForSale1	0	USD
CY2017	us-gaap	Transfer Of Portfolio Loans And Leases To Held For Sale1 TransferOfPortfolioLoansAndLeasesToHeldForSale1	494000	USD
CY2019	nfbk	Operating Lease Right Of Use Asset Initial Recognition Noncash OperatingLeaseRightOfUseAssetInitialRecognitionNoncash	43560000	USD
CY2019	nfbk	Operating Lease Liability Initial Recognition Noncash OperatingLeaseLiabilityInitialRecognitionNoncash	47328000	USD
CY2019	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2019	nfbk	Threshold Of Membership Investment Component Percentage ThresholdOfMembershipInvestmentComponentPercentage	0.00125
CY2019	nfbk	Threshold Of Membership Investment Component ThresholdOfMembershipInvestmentComponent	1000	USD
CY2019	nfbk	Activity Based Investment Component As Percentage Of Outstanding Advances ActivityBasedInvestmentComponentAsPercentageOfOutstandingAdvances	0.045
CY2019Q4	us-gaap	Goodwill Goodwill	38400000	USD
CY2018Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	967000	USD
CY2019	nfbk	Employee Stock Ownership Plan Esop Debt Structure Direct Loan Repayment Period EmployeeStockOwnershipPlanEsopDebtStructureDirectLoanRepaymentPeriod	P30Y
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
CY2017	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	1550285	shares
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
CY2018Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	820801000	USD
CY2018Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	13737000	USD
CY2018Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	808031000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Restricted DebtSecuritiesAvailableForSaleRestricted	730900000	USD
CY2018Q4	us-gaap	Debt Securities Available For Sale Restricted DebtSecuritiesAvailableForSaleRestricted	492400000	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
CY2017	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	5000000.0	USD
CY2017	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	173000	USD
CY2017	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	4000	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
CY2017	us-gaap	Debt Securities Trading Realized Gain Loss DebtSecuritiesTradingRealizedGainLoss	1100000	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
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	2376000	USD
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	302921000	USD
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	11361000	USD
CY2018Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	307354000	USD
CY2018Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	13737000	USD
CY2018Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	610275000	USD
CY2019	us-gaap	Other Than Temporary Impairment Loss Debt Securities Available For Sale Recognized In Earnings OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSaleRecognizedInEarnings	0	USD
CY2019Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	8762000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	5000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	129000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	8886000	USD
CY2018Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	9505000	USD
CY2018Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	0	USD
CY2018Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	256000	USD
CY2018Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	9249000	USD
CY2019	us-gaap	Debt Securities Held To Maturity Sold Amount DebtSecuritiesHeldToMaturitySoldAmount	0	USD
CY2019Q4	us-gaap	Held To Maturity Securities Restricted HeldToMaturitySecuritiesRestricted	7400000	USD
CY2018Q4	us-gaap	Held To Maturity Securities Restricted HeldToMaturitySecuritiesRestricted	6500000	USD
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
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	34000	USD
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue	2133000	USD
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	222000	USD
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue	7116000	USD
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss	256000	USD
CY2018Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue	9249000	USD
CY2019	us-gaap	Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net Heldtomaturity Securities OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNetHeldtomaturitySecurities	0	USD
CY2019Q4	us-gaap	Equity Securities Fv Ni And Without Readily Determinable Fair Value EquitySecuritiesFvNiAndWithoutReadilyDeterminableFairValue	3300000	USD
CY2018Q4	us-gaap	Equity Securities Fv Ni And Without Readily Determinable Fair Value EquitySecuritiesFvNiAndWithoutReadilyDeterminableFairValue	1300000	USD
CY2019Q4	nfbk	Purchased Credit Impaired Loans Held For Investment PurchasedCreditImpairedLoansHeldForInvestment	17365000	USD
CY2018Q4	nfbk	Purchased Credit Impaired Loans Held For Investment PurchasedCreditImpairedLoansHeldForInvestment	20143000	USD
CY2019Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	3437085000	USD
CY2018Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	3245170000	USD
CY2019Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	28707000	USD
CY2018Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	27497000	USD
CY2019Q4	us-gaap	Loans And Leases Receivable Net Reported Amount LoansAndLeasesReceivableNetReportedAmount	3408378000	USD
CY2018Q4	us-gaap	Loans And Leases Receivable Net Reported Amount LoansAndLeasesReceivableNetReportedAmount	3217673000	USD
CY2019Q4	us-gaap	Loans Receivable Held For Sale Amount LoansReceivableHeldForSaleAmount	0	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
CY2018Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	21846000	USD
CY2017Q4	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYield	24502000	USD
CY2019	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Accretion CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion	4142000	USD
CY2018	us-gaap	Certain Loans Acquired In Transfer Not Accounted For As Debt Securities Accretable Yield Accretion CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAccretableYieldAccretion	4176000	USD
CY2019	us-gaap	Certain Loans Acquired In Transfer Accounted For As Debt Securities Accretable Yield Reclassifications From Nonaccretable Difference CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference	-618000	USD
CY2018	us-gaap	Certain Loans Acquired In Transfer Accounted For As Debt Securities Accretable Yield Reclassifications From Nonaccretable Difference CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesAccretableYieldReclassificationsFromNonaccretableDifference	1520000	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
CY2018Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	27497000	USD
CY2017Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	26160000	USD
CY2016Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	24595000	USD
CY2019	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	22000	USD
CY2018	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	2615000	USD
CY2017	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	1411000	USD
CY2019	us-gaap	Allowance For Loan And Lease Loss Recovery Of Bad Debts AllowanceForLoanAndLeaseLossRecoveryOfBadDebts	2175000	USD
CY2018	us-gaap	Allowance For Loan And Lease Loss Recovery Of Bad Debts AllowanceForLoanAndLeaseLossRecoveryOfBadDebts	112000	USD
CY2017	us-gaap	Allowance For Loan And Lease Loss Recovery Of Bad Debts AllowanceForLoanAndLeaseLossRecoveryOfBadDebts	556000	USD
CY2019	us-gaap	Allowance For Loan And Lease Losses Write Offs AllowanceForLoanAndLeaseLossesWriteOffs	987000	USD
CY2018	us-gaap	Allowance For Loan And Lease Losses Write Offs AllowanceForLoanAndLeaseLossesWriteOffs	1390000	USD
CY2017	us-gaap	Allowance For Loan And Lease Losses Write Offs AllowanceForLoanAndLeaseLossesWriteOffs	402000	USD
CY2019Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	28707000	USD
CY2018Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	27497000	USD
CY2017Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	26160000	USD
CY2018Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	27497000	USD
CY2019	us-gaap	Allowance For Loan And Lease Losses Write Offs AllowanceForLoanAndLeaseLossesWriteOffs	987000	USD
CY2019	us-gaap	Allowance For Loan And Lease Loss Recovery Of Bad Debts AllowanceForLoanAndLeaseLossRecoveryOfBadDebts	2175000	USD
CY2019	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	22000	USD
CY2019Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	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	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	3437085000	USD
CY2018	us-gaap	Allowance For Loan And Lease Losses Write Offs AllowanceForLoanAndLeaseLossesWriteOffs	1390000	USD
CY2018	us-gaap	Allowance For Loan And Lease Loss Recovery Of Bad Debts AllowanceForLoanAndLeaseLossRecoveryOfBadDebts	112000	USD
CY2017Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	26160000	USD
CY2018	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	2615000	USD
CY2018Q4	us-gaap	Loans And Leases Receivable Allowance LoansAndLeasesReceivableAllowance	27497000	USD
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses Individually Evaluated For Impairment1 FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1	26000	USD
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses Collectively Evaluated For Impairment FinancingReceivableAllowanceForCreditLossesCollectivelyEvaluatedForImpairment	27471000	USD
CY2018Q4	us-gaap	Loans And Leases Receivable Net Of Deferred Income LoansAndLeasesReceivableNetOfDeferredIncome	3245170000	USD
CY2018Q4	us-gaap	Financing Receivable Individually Evaluated For Impairment FinancingReceivableIndividuallyEvaluatedForImpairment	22329000	USD
CY2018Q4	us-gaap	Financing Receivable Collectively Evaluated For Impairment FinancingReceivableCollectivelyEvaluatedForImpairment	3222841000	USD
CY2019Q4	us-gaap	Loans Receivable Net LoansReceivableNet	2987067000	USD
CY2018Q4	us-gaap	Loans Receivable Net LoansReceivableNet	2678877000	USD
CY2019Q4	nfbk	Investment In Non Accrual Loans InvestmentInNonAccrualLoans	9400000	USD
CY2018Q4	nfbk	Investment In Non Accrual Loans InvestmentInNonAccrualLoans	9200000	USD
CY2019	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2019	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2019Q4	nfbk	Loans Deemed To Be Impaired Non Accrual Amount LoansDeemedToBeImpairedNonAccrualAmount	6800000	USD
CY2018Q4	nfbk	Loans Deemed To Be Impaired Non Accrual Amount LoansDeemedToBeImpairedNonAccrualAmount	5900000	USD
CY2019Q4	nfbk	Principal Balance Threshold For Non Accrual Status PrincipalBalanceThresholdForNonAccrualStatus	2600000	USD
CY2018Q4	nfbk	Principal Balance Threshold For Non Accrual Status PrincipalBalanceThresholdForNonAccrualStatus	3200000	USD
CY2019Q4	nfbk	Loans Held For Sale Non Accrual Amount LoansHeldForSaleNonAccrualAmount	0	USD
CY2019	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2019Q4	us-gaap	Financing Receivable Recorded Investment90 Days Past Due And Still Accruing FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing	518000	USD
CY2018Q4	us-gaap	Financing Receivable Recorded Investment90 Days Past Due And Still Accruing FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing	33000	USD
CY2019	nfbk	Delinquent Status Classification Criteria Days Minimum DelinquentStatusClassificationCriteriaDaysMinimum	P90D
CY2019Q4	us-gaap	Impaired Financing Receivable Recorded Investment ImpairedFinancingReceivableRecordedInvestment	20957000	USD
CY2019Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	23132000	USD
CY2019Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	142000	USD
CY2018Q4	us-gaap	Impaired Financing Receivable Recorded Investment ImpairedFinancingReceivableRecordedInvestment	22329000	USD
CY2018Q4	us-gaap	Impaired Financing Receivable Unpaid Principal Balance ImpairedFinancingReceivableUnpaidPrincipalBalance	27015000	USD
CY2018Q4	us-gaap	Impaired Financing Receivable Related Allowance ImpairedFinancingReceivableRelatedAllowance	26000	USD
CY2019Q4	nfbk	Loans With Carrying Balances Not Written Down LoansWithCarryingBalancesNotWrittenDown	15900000	USD
CY2018Q4	nfbk	Loans With Carrying Balances Not Written Down LoansWithCarryingBalancesNotWrittenDown	16600000	USD
CY2019	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	21641000	USD
CY2019	us-gaap	Impaired Financing Receivable Interest Income Cash Basis Method ImpairedFinancingReceivableInterestIncomeCashBasisMethod	778000	USD
CY2018	us-gaap	Impaired Financing Receivable Average Recorded Investment ImpairedFinancingReceivableAverageRecordedInvestment	21485000	USD
CY2018	us-gaap	Impaired Financing Receivable Interest Income Cash Basis Method ImpairedFinancingReceivableInterestIncomeCashBasisMethod	942000	USD
CY2019Q4	nfbk	Trouble Debt Restructuring Amount TroubleDebtRestructuringAmount	18500000	USD
CY2018Q4	nfbk	Trouble Debt Restructuring Amount TroubleDebtRestructuringAmount	16900000	USD
CY2019	us-gaap	Financing Receivable Modifications Subsequent Default Number Of Contracts1 FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1	2	loan
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
CY2018	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	1	loan
CY2019Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	71343000	USD
CY2018Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	69778000	USD
CY2019Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	45684000	USD
CY2018Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	44173000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	25659000	USD
CY2018Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	25605000	USD
CY2019	us-gaap	Depreciation Depreciation	3600000	USD
CY2019Q4	us-gaap	Weighted Average Rate Domestic Deposit WeightedAverageRateDomesticDeposit	0.0118
CY2018	us-gaap	Depreciation Depreciation	3000000.0	USD
CY2017	us-gaap	Depreciation Depreciation	3200000	USD
CY2019	us-gaap	Gain Loss On Sale Of Property Plant Equipment GainLossOnSaleOfPropertyPlantEquipment	0	USD
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
CY2018Q4	us-gaap	Deposits Negotiable Order Of Withdrawal Now DepositsNegotiableOrderOfWithdrawalNOW	458012000	USD
CY2018Q4	us-gaap	Weighted Average Rate Domestic Deposit Notice Of Withdrawal WeightedAverageRateDomesticDepositNoticeOfWithdrawal	0.0068
CY2019Q4	us-gaap	Noninterest Bearing Deposit Liabilities NoninterestBearingDepositLiabilities	387409000	USD
CY2018Q4	us-gaap	Noninterest Bearing Deposit Liabilities NoninterestBearingDepositLiabilities	395375000	USD
CY2019Q4	nfbk	Deposits Transactions DepositsTransactions	961336000	USD
CY2019Q4	nfbk	Weighted Average Rate Domestic Deposit Transaction WeightedAverageRateDomesticDepositTransaction	0.0052
CY2018Q4	nfbk	Deposits Transactions DepositsTransactions	853387000	USD
CY2018Q4	nfbk	Weighted Average Rate Domestic Deposit Transaction WeightedAverageRateDomesticDepositTransaction	0.0036
CY2019Q4	us-gaap	Deposits Money Market Deposits DepositsMoneyMarketDeposits	651159000	USD
CY2019Q4	us-gaap	Weighted Average Rate Domestic Deposit Money Market WeightedAverageRateDomesticDepositMoneyMarket	0.0118
CY2018Q4	us-gaap	Deposits Money Market Deposits DepositsMoneyMarketDeposits	741939000	USD
CY2018Q4	us-gaap	Weighted Average Rate Domestic Deposit Money Market WeightedAverageRateDomesticDepositMoneyMarket	0.0112
CY2019Q4	us-gaap	Interest Bearing Deposit Liabilities InterestBearingDepositLiabilities	747186000	USD
CY2019Q4	nfbk	Weighted Average Interest Rate Of Time Deposits Interest Bearing Deposit Liabilities WeightedAverageInterestRateOfTimeDepositsInterestBearingDepositLiabilities	0.0102
CY2018Q4	us-gaap	Interest Bearing Deposit Liabilities InterestBearingDepositLiabilities	594290000	USD
CY2018Q4	nfbk	Weighted Average Interest Rate Of Time Deposits Interest Bearing Deposit Liabilities WeightedAverageInterestRateOfTimeDepositsInterestBearingDepositLiabilities	0.0090
CY2019Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	1398345000	USD
CY2019Q4	us-gaap	Weighted Average Rate Domestic Deposit Savings WeightedAverageRateDomesticDepositSavings	0.0109
CY2018Q4	us-gaap	Deposits Savings Deposits DepositsSavingsDeposits	1336229000	USD
CY2018Q4	us-gaap	Weighted Average Rate Domestic Deposit Savings WeightedAverageRateDomesticDepositSavings	0.0102
CY2019Q4	us-gaap	Time Deposits Less Than100000 TimeDepositsLessThan100000	563303000	USD
CY2019Q4	nfbk	Weighted Average Interest Rateof Time Deposits Less Than100000 WeightedAverageInterestRateofTimeDepositsLessThan100000	0.0186
CY2018Q4	us-gaap	Time Deposits Less Than100000 TimeDepositsLessThan100000	599245000	USD
CY2018Q4	nfbk	Weighted Average Interest Rateof Time Deposits Less Than100000 WeightedAverageInterestRateofTimeDepositsLessThan100000	0.0191
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
CY2018Q4	us-gaap	Time Deposits100000 Or More TimeDeposits100000OrMore	497651000	USD
CY2018Q4	us-gaap	Weighted Average Interest Rate Of Time Deposits100000 Or More WeightedAverageInterestRateOfTimeDeposits100000OrMore	0.0201
CY2019Q4	us-gaap	Time Deposits TimeDeposits	1048552000	USD
CY2019Q4	us-gaap	Weighted Average Rate Domestic Deposit Time Deposits WeightedAverageRateDomesticDepositTimeDeposits	0.0192
CY2018Q4	us-gaap	Time Deposits TimeDeposits	1096896000	USD
CY2018Q4	us-gaap	Weighted Average Rate Domestic Deposit Time Deposits WeightedAverageRateDomesticDepositTimeDeposits	0.0196
CY2019Q4	us-gaap	Deposits Deposits	3408233000	USD
CY2018Q4	us-gaap	Weighted Average Rate Domestic Deposit WeightedAverageRateDomesticDeposit	0.0116
CY2018Q4	us-gaap	Deposits Deposits	3286512000	USD
CY2019Q4	us-gaap	Time Deposit Maturities Year One TimeDepositMaturitiesYearOne	908744000	USD
CY2019Q4	us-gaap	Time Deposit Maturities Year Two TimeDepositMaturitiesYearTwo	46856000	USD
CY2019Q4	us-gaap	Time Deposit Maturities Year Three TimeDepositMaturitiesYearThree	49075000	USD
CY2019Q4	us-gaap	Time Deposit Maturities Year Four TimeDepositMaturitiesYearFour	35008000	USD
CY2019Q4	us-gaap	Time Deposit Maturities Year Five TimeDepositMaturitiesYearFive	8869000	USD
CY2019Q4	us-gaap	Time Deposits TimeDeposits	1048552000	USD
CY2019	nfbk	Interest Expense Domestic Deposit Liabilities Transaction InterestExpenseDomesticDepositLiabilitiesTransaction	4623000	USD
CY2018	nfbk	Interest Expense Domestic Deposit Liabilities Transaction InterestExpenseDomesticDepositLiabilitiesTransaction	2175000	USD
CY2017	nfbk	Interest Expense Domestic Deposit Liabilities Transaction InterestExpenseDomesticDepositLiabilitiesTransaction	1429000	USD
CY2019	us-gaap	Interest Expense Domestic Deposit Liabilities Savings InterestExpenseDomesticDepositLiabilitiesSavings	15850000	USD
CY2018	us-gaap	Interest Expense Domestic Deposit Liabilities Savings InterestExpenseDomesticDepositLiabilitiesSavings	8878000	USD
CY2017	us-gaap	Interest Expense Domestic Deposit Liabilities Savings InterestExpenseDomesticDepositLiabilitiesSavings	6804000	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
CY2017	us-gaap	Interest Expense Domestic Deposit Liabilities Certificates Of Deposit InterestExpenseDomesticDepositLiabilitiesCertificatesOfDeposit	8153000	USD
CY2019	us-gaap	Interest Expense Deposits InterestExpenseDeposits	41328000	USD
CY2018	us-gaap	Interest Expense Deposits InterestExpenseDeposits	27741000	USD
CY2017	us-gaap	Interest Expense Deposits InterestExpenseDeposits	16386000	USD
CY2018Q4	nfbk	Repurchase Agreement Included In Overnight Accounts RepurchaseAgreementIncludedInOvernightAccounts	0	USD
CY2019Q4	us-gaap	Federal Home Loan Bank Advances Long Term FederalHomeLoanBankAdvancesLongTerm	776000000	USD
CY2018Q4	us-gaap	Federal Home Loan Bank Advances Long Term FederalHomeLoanBankAdvancesLongTerm	403502000	USD
CY2019Q4	us-gaap	Longterm Debt Percentage Bearing Variable Interest Amount LongtermDebtPercentageBearingVariableInterestAmount	6004000	USD
CY2018Q4	us-gaap	Longterm Debt Percentage Bearing Variable Interest Amount LongtermDebtPercentageBearingVariableInterestAmount	5345000	USD
CY2018Q4	us-gaap	Capital Lease Obligations CapitalLeaseObligations	44000	USD
CY2019Q4	us-gaap	Long Term Debt LongTermDebt	857004000	USD
CY2017	us-gaap	Interest Expense Debt InterestExpenseDebt	7590000	USD
CY2019Q4	nfbk	Repurchase Agreement Included In Overnight Accounts RepurchaseAgreementIncludedInOvernightAccounts	75000000	USD
CY2018Q4	us-gaap	Long Term Debt LongTermDebt	408891000	USD
CY2018Q4	nfbk	Repurchase Agreement Included In Overnight Accounts RepurchaseAgreementIncludedInOvernightAccounts	0	USD
CY2019Q4	nfbk	Additional Funding Federal Home Loan Bank Advances Long Term AdditionalFundingFederalHomeLoanBankAdvancesLongTerm	1430000000	USD
CY2019Q4	nfbk	Unencumbered Securities UnencumberedSecurities	284800000	USD
CY2019Q4	nfbk	Multifamily Loans Held As Collateral By Federal Home Loan Bank MultifamilyLoansHeldAsCollateralByFederalHomeLoanBank	1100000000	USD
CY2019	us-gaap	Interest Expense Debt InterestExpenseDebt	12030000	USD
CY2018	us-gaap	Interest Expense Debt InterestExpenseDebt	8309000	USD
CY2019	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	8543000	USD
CY2018	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	8540000	USD
CY2017	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	10113000	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
CY2017	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	14290000	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
CY2017	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	24403000	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
CY2017	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	1672000	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
CY2017	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	903000	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
CY2017	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	2575000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	12787000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	9632000	USD
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	26978000	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
CY2017	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	18111000	USD
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
CY2017	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.35
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
CY2017	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	1674000	USD
CY2019	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	0	USD
CY2018	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	0	USD
CY2017	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	10453000	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
CY2017	nfbk	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsuranceAmount	1885000	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
CY2017	nfbk	Income Tax Rate Reconciliation Deduction Employee Stock Ownership Plan Fair Market Value Adjustment Amount IncomeTaxRateReconciliationDeductionEmployeeStockOwnershipPlanFairMarketValueAdjustmentAmount	404000	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
CY2017	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	247000	USD
CY2019	nfbk	Income Tax Rate Reconciliation Uncertain Tax Position IncomeTaxRateReconciliationUncertainTaxPosition	0	USD
CY2018	nfbk	Income Tax Rate Reconciliation Uncertain Tax Position IncomeTaxRateReconciliationUncertainTaxPosition	0	USD
CY2017	nfbk	Income Tax Rate Reconciliation Uncertain Tax Position IncomeTaxRateReconciliationUncertainTaxPosition	132000	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
CY2019Q4	nfbk	Deferred Tax Assets Allowance For Credit Losses DeferredTaxAssetsAllowanceForCreditLosses	7985000	USD
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Share Based Compensation Excess Tax Benefit Amount EffectiveIncomeTaxRateReconciliationShareBasedCompensationExcessTaxBenefitAmount	-2309000	USD
CY2019	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-87000	USD
CY2018	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	120000	USD
CY2017	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	151000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	12787000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	9632000	USD
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	26978000	USD
CY2019	nfbk	Tax Cuts And Jobs Act Of2017 Incomplete Accounting Change In Tax Rate Deferred Tax Asset Provisional Income Tax Expense TaxCutsAndJobsActOf2017IncompleteAccountingChangeInTaxRateDeferredTaxAssetProvisionalIncomeTaxExpense	10500000	USD
CY2018Q4	nfbk	Deferred Tax Assets Allowance For Credit Losses DeferredTaxAssetsAllowanceForCreditLosses	7317000	USD
CY2019Q4	nfbk	Deferred Tax Assets Capital Leases DeferredTaxAssetsCapitalLeases	0	USD
CY2018Q4	nfbk	Deferred Tax Assets Capital Leases DeferredTaxAssetsCapitalLeases	13000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits	3498000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits	3426000	USD
CY2019Q4	nfbk	Deferred Tax Assets Accrued Salaries And Benefits And Other DeferredTaxAssetsAccruedSalariesAndBenefitsAndOther	738000	USD
CY2018Q4	nfbk	Deferred Tax Assets Accrued Salaries And Benefits And Other DeferredTaxAssetsAccruedSalariesAndBenefitsAndOther	737000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Postretirement Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits	376000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Postretirement Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPostretirementBenefits	375000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	2164000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	3045000	USD
CY2019Q4	nfbk	Deferred Tax Assets Net Actuarial Loss On Defined Benefit Post Retirement Benefit Plans DeferredTaxAssetsNetActuarialLossOnDefinedBenefitPostRetirementBenefitPlans	-21000	USD
CY2018Q4	nfbk	Deferred Tax Assets Net Actuarial Loss On Defined Benefit Post Retirement Benefit Plans DeferredTaxAssetsNetActuarialLossOnDefinedBenefitPostRetirementBenefitPlans	18000	USD
CY2019Q4	nfbk	Deferred Tax Assets Straight Line Rent Adjustments DeferredTaxAssetsStraightLineRentAdjustments	1277000	USD
CY2018Q4	nfbk	Deferred Tax Assets Straight Line Rent Adjustments DeferredTaxAssetsStraightLineRentAdjustments	1051000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Asset Retirement Obligations DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAssetRetirementObligations	70000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Asset Retirement Obligations DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAssetRetirementObligations	67000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Returns And Allowances DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsReturnsAndAllowances	578000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Returns And Allowances DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsReturnsAndAllowances	602000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	216000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	146000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Compensation DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeCompensation	615000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Employee Compensation DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsEmployeeCompensation	551000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	244000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	261000	USD
CY2019Q4	nfbk	Deferred Tax Assets Depreciation DeferredTaxAssetsDepreciation	2414000	USD
CY2018Q4	nfbk	Deferred Tax Assets Depreciation DeferredTaxAssetsDepreciation	2383000	USD
CY2019Q4	nfbk	Deferred Tax Assets Related To Fair Value Adjustments On Business Acquisitions DeferredTaxAssetsRelatedToFairValueAdjustmentsOnBusinessAcquisitions	3713000	USD
CY2018Q4	nfbk	Deferred Tax Assets Related To Fair Value Adjustments On Business Acquisitions DeferredTaxAssetsRelatedToFairValueAdjustmentsOnBusinessAcquisitions	3934000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	160000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Pensions DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsPensions	154000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Unrealized Losses On Availablefor Sale Securities Gross DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross	0	USD
CY2018Q4	us-gaap	Deferred Tax Assets Unrealized Losses On Availablefor Sale Securities Gross DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross	3575000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	24027000	USD
CY2018Q4	us-gaap	Deferred Tax Liabilities Unrealized Gains On Trading Securities DeferredTaxLiabilitiesUnrealizedGainsOnTradingSecurities	0	USD
CY2019Q4	nfbk	Deferred Tax Liabilities Adjustment Of Investment Securities DeferredTaxLiabilitiesAdjustmentOfInvestmentSecurities	20000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	27655000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Unrealized Gains On Trading Securities DeferredTaxLiabilitiesUnrealizedGainsOnTradingSecurities	1786000	USD
CY2018Q4	nfbk	Deferred Tax Liabilities Adjustment Of Investment Securities DeferredTaxLiabilitiesAdjustmentOfInvestmentSecurities	28000	USD
CY2019Q4	nfbk	Deferred Tax Liabilities Adjustment Of Deposit Liabilities DeferredTaxLiabilitiesAdjustmentOfDepositLiabilities	219000	USD
CY2018Q4	nfbk	Deferred Tax Liabilities Adjustment Of Deposit Liabilities DeferredTaxLiabilitiesAdjustmentOfDepositLiabilities	285000	USD
CY2019Q4	nfbk	Deferred Tax Liability Deferred Loan Fees DeferredTaxLiabilityDeferredLoanFees	2224000	USD
CY2018Q4	nfbk	Deferred Tax Liability Deferred Loan Fees DeferredTaxLiabilityDeferredLoanFees	1984000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	30000	USD
CY2018Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	33000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	4279000	USD
CY2018Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	2330000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	19748000	USD
CY2018Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	25325000	USD
CY2019	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
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	530000	USD
CY2017Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	482000	USD
CY2016Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	459000	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
CY2017	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	109000	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
CY2017	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	132000	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
CY2019	nfbk	Defined Contribution Plan Requisite Service Period DefinedContributionPlanRequisiteServicePeriod	P3M
CY2019	us-gaap	Defined Contribution Plan Employer Matching Contribution Percent Of Match DefinedContributionPlanEmployerMatchingContributionPercentOfMatch	0.25
CY2019	nfbk	Percentage Contribution From Employees First Base Compensation PercentageContributionFromEmployeesFirstBaseCompensation	0.06
CY2019	nfbk	Defined Contribution Plan Vesting Period DefinedContributionPlanVestingPeriod	P3Y
CY2019	nfbk	Defined Contribution Plan Periodof Participationto Trigger Increasein Employee Contribution Percentage DefinedContributionPlanPeriodofParticipationtoTriggerIncreaseinEmployeeContributionPercentage	P3Y
CY2019	nfbk	Percentage Contribution From Employees First Base Compensation PercentageContributionFromEmployeesFirstBaseCompensation	0.06
CY2019	nfbk	Defined Contribution Plan Requisite Service Periodto Become Fully Vested DefinedContributionPlanRequisiteServicePeriodtoBecomeFullyVested	P5Y
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
CY2017	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	387000	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
CY2017	us-gaap	Employee Stock Ownership Plan Esop Compensation Expense EmployeeStockOwnershipPlanESOPCompensationExpense	2200000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Gain Loss Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfGainLossNextFiscalYear	-835	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Prior Service Cost Credit Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfPriorServiceCostCreditNextFiscalYear	-19000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Amortization Of Transition Asset Obligation Next Fiscal Year DefinedBenefitPlanExpectedAmortizationOfTransitionAssetObligationNextFiscalYear	0	USD
CY2019Q4	us-gaap	Defined Benefit Plan Ultimate Health Care Cost Trend Rate1 DefinedBenefitPlanUltimateHealthCareCostTrendRate1	0.0875
CY2019	nfbk	Defined Benefit Plan Ultimate Health Care Cost Trend Rate Reduction DefinedBenefitPlanUltimateHealthCareCostTrendRateReduction	0.0050
CY2019Q4	us-gaap	Defined Benefit Plan Health Care Cost Trend Rate Assumed Next Fiscal Year DefinedBenefitPlanHealthCareCostTrendRateAssumedNextFiscalYear	0.0475
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
CY2017	us-gaap	Defined Benefit Plan Benefit Obligation Benefits Paid DefinedBenefitPlanBenefitObligationBenefitsPaid	112000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Next Twelve Months DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths	108000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Two DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo	108000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Three DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree	107000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Four DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour	88000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Five DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive	85000	USD
CY2019Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Five Fiscal Years Thereafter DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter	359000	USD
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	0	shares
CY2019	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	3200000	USD
CY2018	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	5400000	USD
CY2017	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	6200000	USD
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	4620687	shares
CY2017Q4	nfbk	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageGrantDateFairValue	3.51
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	11.82
CY2017	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P5Y2M1D
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	29378	shares
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested Options Forfeited Weighted Average Grant Date Fair Value SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue	3.36
CY2018	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice	11.51
CY2018	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	1339714	shares
CY2018	nfbk	Share Based Compensation Arrangement By Share Based Payment Award Options Exercises In Period Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageGrantDateFairValue	2.49
CY2018	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	7.75
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	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	15000	shares
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
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber	2046272	shares
CY2019Q4	nfbk	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageGrantDateFairValue	3.99
CY2019Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice	13.83
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1	P4Y10M28D
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Number ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	585895	shares
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Nonvested Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	14.05
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	15000	shares
CY2018	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	16.48
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	266973	shares
CY2018	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	13.86
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeited In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	4960	shares
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Forfeitures Weighted Average Grant Date Fair Value ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue	14.18
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
CY2019	nfbk	Guaranteed Lease Residual Values Period GuaranteedLeaseResidualValuesPeriod	P1Y
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	756000	USD
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	523000	USD
CY2019	nfbk	Agreement Term AgreementTerm	P3Y
CY2019	nfbk	Agreement Term AgreementTerm	P3Y
CY2019Q4	nfbk	Tier One Common Capital Requiredfor Capital Adequacyto Risk Weighted Assets TierOneCommonCapitalRequiredforCapitalAdequacytoRiskWeightedAssets	0.045
CY2019Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.060
CY2019Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.080
CY2019Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	0.040
CY2019Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized To Average Assets TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets	0.050
CY2019Q4	nfbk	Tier One Common Capital Requiredtobe Well Capitalizedto Risk Weighted Assets TierOneCommonCapitalRequiredtobeWellCapitalizedtoRiskWeightedAssets	0.065
CY2019Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	0.080
CY2019Q4	us-gaap	Capital Required To Be Well Capitalized To Risk Weighted Assets CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	0.100
CY2019Q4	nfbk	Tier One Common Capital Requiredfor Capital Adequacyto Risk Weighted Assets TierOneCommonCapitalRequiredforCapitalAdequacytoRiskWeightedAssets	0.045
CY2019Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.06
CY2019Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.08
CY2019Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	0.04
CY2019Q4	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
CY2019Q4	nfbk	Tier One Risk Based Capital Requiredfor Capital Adequacyto Risk Weighted Assets Higher Risk Weight TierOneRiskBasedCapitalRequiredforCapitalAdequacytoRiskWeightedAssetsHigherRiskWeight	0.025
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
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
CY2018Q4	nfbk	Tier One Common Equity TierOneCommonEquity	636141000	USD
CY2018Q4	nfbk	Tier One Common Capitalto Risk Weighted Assets TierOneCommonCapitaltoRiskWeightedAssets	0.1717
CY2018Q4	nfbk	Tier One Common Equity Requiredfor Capital Adequacy TierOneCommonEquityRequiredforCapitalAdequacy	166717000	USD
CY2018Q4	nfbk	Tier One Common Capital Requiredfor Capital Adequacyto Risk Weighted Assets TierOneCommonCapitalRequiredforCapitalAdequacytoRiskWeightedAssets	0.0450
CY2018Q4	nfbk	Tier One Common Equity Requiredtobe Well Capitalized TierOneCommonEquityRequiredtobeWellCapitalized	240814000	USD
CY2018Q4	nfbk	Tier One Common Capital Requiredtobe Well Capitalizedto Risk Weighted Assets TierOneCommonCapitalRequiredtobeWellCapitalizedtoRiskWeightedAssets	0.0650
CY2018Q4	us-gaap	Tier One Leverage Capital TierOneLeverageCapital	636141000	USD
CY2018Q4	us-gaap	Tier One Leverage Capital To Average Assets TierOneLeverageCapitalToAverageAssets	0.1482
CY2018Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy TierOneLeverageCapitalRequiredForCapitalAdequacy	171724000	USD
CY2018Q4	us-gaap	Tier One Leverage Capital Required For Capital Adequacy To Average Assets TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets	0.0400
CY2018Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized TierOneLeverageCapitalRequiredToBeWellCapitalized	214656000	USD
CY2018Q4	us-gaap	Tier One Leverage Capital Required To Be Well Capitalized To Average Assets TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets	0.0500
CY2018Q4	us-gaap	Tier One Risk Based Capital TierOneRiskBasedCapital	636141000	USD
CY2018Q4	us-gaap	Tier One Risk Based Capital To Risk Weighted Assets TierOneRiskBasedCapitalToRiskWeightedAssets	0.1717
CY2018Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy TierOneRiskBasedCapitalRequiredForCapitalAdequacy	222290000	USD
CY2018Q4	us-gaap	Tier One Risk Based Capital Required For Capital Adequacy To Risk Weighted Assets TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.0600
CY2018Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized TierOneRiskBasedCapitalRequiredToBeWellCapitalized	296386000	USD
CY2018Q4	us-gaap	Tier One Risk Based Capital Required To Be Well Capitalized To Risk Weighted Assets TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	0.0800
CY2018Q4	us-gaap	Capital Capital	664190000	USD
CY2018Q4	us-gaap	Capital To Risk Weighted Assets CapitalToRiskWeightedAssets	0.1793
CY2018Q4	us-gaap	Capital Required For Capital Adequacy CapitalRequiredForCapitalAdequacy	296386000	USD
CY2018Q4	us-gaap	Capital Required For Capital Adequacy To Risk Weighted Assets CapitalRequiredForCapitalAdequacyToRiskWeightedAssets	0.0800
CY2018Q4	us-gaap	Capital Required To Be Well Capitalized CapitalRequiredToBeWellCapitalized	370483000	USD
CY2018Q4	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
CY2018Q4	us-gaap	Loans Receivable Fair Value Disclosure LoansReceivableFairValueDisclosure	5697000	USD
CY2019Q4	nfbk	Principal Amount Outstanding Of Impaired Loans Heldfor Investment And Heldfor Sale PrincipalAmountOutstandingOfImpairedLoansHeldforInvestmentAndHeldforSale	7000000.0	USD
CY2018Q4	nfbk	Principal Amount Outstanding Of Impaired Loans Heldfor Investment And Heldfor Sale PrincipalAmountOutstandingOfImpairedLoansHeldforInvestmentAndHeldforSale	10200000	USD
CY2019Q4	nfbk	Estimated Fair Value Of Impaired Loans Held For Investment EstimatedFairValueOfImpairedLoansHeldForInvestment	4900000	USD
CY2018Q4	nfbk	Estimated Fair Value Of Impaired Loans Held For Investment EstimatedFairValueOfImpairedLoansHeldForInvestment	5700000	USD
CY2019	us-gaap	Asset Impairment Charges AssetImpairmentCharges	116000	USD
CY2018	us-gaap	Asset Impairment Charges AssetImpairmentCharges	56000	USD
CY2019	nfbk	Impaired Financing Receivables Charge Off ImpairedFinancingReceivablesChargeOff	1200000	USD
CY2018	nfbk	Impaired Financing Receivables Charge Off ImpairedFinancingReceivablesChargeOff	1300000	USD
CY2019Q4	us-gaap	Equity Securities Without Readily Determinable Fair Value Amount EquitySecuritiesWithoutReadilyDeterminableFairValueAmount	3100000	USD
CY2018Q4	us-gaap	Equity Securities Without Readily Determinable Fair Value Amount EquitySecuritiesWithoutReadilyDeterminableFairValueAmount	1000000.0	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	40235000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	40079000	USD
CY2017	us-gaap	Net Income Loss NetIncomeLoss	24768000	USD
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
CY2017	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	45325445	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
CY2017	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	1550285	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
CY2017	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	46875730	shares
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.86
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.87
CY2017	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.55
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.85
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.85
CY2017	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.53
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
CY2017	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	334927	shares
CY2019Q2	us-gaap	Stock Repurchase Program Authorized Amount1 StockRepurchaseProgramAuthorizedAmount1	37200000	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
CY2017	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	4702000	USD
CY2019	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	7023000	USD
CY2018	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	3705000	USD
CY2017	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	5386000	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
CY2017	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	1114000	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
CY2017	us-gaap	Debt Securities Available For Sale Gain Loss DebtSecuritiesAvailableForSaleGainLoss	169000	USD
CY2019	us-gaap	Noninterest Income Other Operating Income NoninterestIncomeOtherOperatingIncome	402000	USD
CY2018	us-gaap	Noninterest Income Other Operating Income NoninterestIncomeOtherOperatingIncome	246000	USD
CY2017	us-gaap	Noninterest Income Other Operating Income NoninterestIncomeOtherOperatingIncome	271000	USD
CY2019	us-gaap	Noninterest Income NoninterestIncome	14808000	USD
CY2018	us-gaap	Noninterest Income NoninterestIncome	8127000	USD
CY2017	us-gaap	Noninterest Income NoninterestIncome	11642000	USD
CY2019Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	39500000	USD
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	44100000	USD
CY2019	us-gaap	Operating Lease Cost OperatingLeaseCost	6698000	USD
CY2019	us-gaap	Variable Lease Cost VariableLeaseCost	2813000	USD
CY2019	us-gaap	Lease Cost LeaseCost	9511000	USD
CY2019	us-gaap	Operating Lease Payments OperatingLeasePayments	5901000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	1013000	USD
CY2019Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P12Y9M7D
CY2019Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0362
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	6160000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	5730000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	5068000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	4975000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	4629000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	30668000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	57230000	USD
CY2019Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	13161000	USD
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	44069000	USD
CY2019	us-gaap	Operating Lease Expense OperatingLeaseExpense	6800000	USD
CY2018	us-gaap	Lease And Rental Expense LeaseAndRentalExpense	5700000	USD
CY2017	us-gaap	Lease And Rental Expense LeaseAndRentalExpense	5300000	USD
CY2019	nfbk	Operating Lease Accelerated Rent Expense OperatingLeaseAcceleratedRentExpense	579000	USD
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
CY2018Q1	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	34682000	USD
CY2018Q2	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	35935000	USD
CY2018Q3	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	37727000	USD
CY2018Q4	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	38948000	USD
CY2018Q1	us-gaap	Interest Expense InterestExpense	7138000	USD
CY2018Q2	us-gaap	Interest Expense InterestExpense	8165000	USD
CY2018Q3	us-gaap	Interest Expense InterestExpense	9803000	USD
CY2018Q4	us-gaap	Interest Expense InterestExpense	10944000	USD
CY2018Q1	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	27544000	USD
CY2018Q2	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	27770000	USD
CY2018Q3	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	27924000	USD
CY2018Q4	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	28004000	USD
CY2018Q1	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	34000	USD
CY2018Q2	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	670000	USD
CY2018Q3	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	1304000	USD
CY2018Q4	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	607000	USD
CY2018Q1	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	27510000	USD
CY2018Q2	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	27100000	USD
CY2018Q3	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	26620000	USD
CY2018Q4	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	27397000	USD
CY2018Q1	us-gaap	Noninterest Income NoninterestIncome	2405000	USD
CY2018Q2	us-gaap	Noninterest Income NoninterestIncome	2445000	USD
CY2018Q3	us-gaap	Noninterest Income NoninterestIncome	2637000	USD
CY2018Q4	us-gaap	Noninterest Income NoninterestIncome	640000	USD
CY2018Q1	us-gaap	Noninterest Expense NoninterestExpense	17126000	USD
CY2018Q2	us-gaap	Noninterest Expense NoninterestExpense	17040000	USD
CY2018Q3	us-gaap	Noninterest Expense NoninterestExpense	17100000	USD
CY2018Q4	us-gaap	Noninterest Expense NoninterestExpense	15777000	USD
CY2018Q1	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	12789000	USD
CY2018Q2	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	12505000	USD
CY2018Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	12157000	USD
CY2018Q4	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	12260000	USD
CY2018Q1	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	2344000	USD
CY2018Q2	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	1893000	USD
CY2018Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	3081000	USD
CY2018Q4	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	2314000	USD
CY2018Q1	us-gaap	Net Income Loss NetIncomeLoss	10445000	USD
CY2018Q2	us-gaap	Net Income Loss NetIncomeLoss	10612000	USD
CY2018Q3	us-gaap	Net Income Loss NetIncomeLoss	9076000	USD
CY2018Q4	us-gaap	Net Income Loss NetIncomeLoss	9946000	USD
CY2018Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.23
CY2018Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.23
CY2018Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.19
CY2018Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.21
CY2018Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.22
CY2018Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.23
CY2018Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.19
CY2018Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.21

Files In Submission

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$NFBK
Northfield Bancorp, Inc. Stock $nfbk

2018 Q4 Form 10-K Financial Statement

#000149322520000042 Filed on March 02, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$NFBK Northfield Bancorp, Inc. Stock $nfbk

2018 Q4 Form 10-K Financial Statement

#000149322520000042 Filed on March 02, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$NFBK
Northfield Bancorp, Inc. Stock $nfbk