$SIGI
Selective Insurance Group Inc Stock $sigi

$sigi Overview Financials Valuation SEC Filings Company Website

2020 Q4 Form 10-Q Financial Statement

#000023055720000023 Filed on October 29, 2020

Income Statement

Concept	2020 Q4	2020 Q3	2019 Q4
Revenue	$798.4M	$776.6M	$728.9M
YoY Change	9.54%	9.31%	13.36%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin	$6.100M	$3.900M	$2.900M
YoY Change	110.34%	-54.65%	-14.71%
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$15.00M	$142.3M	$12.90M
YoY Change	16.28%	4.19%	30.3%
% of Gross Profit
Operating Expenses	$631.9M	$683.5M	$620.2M
YoY Change	1.89%	8.18%	6.05%
Operating Profit
YoY Change
Interest Expense	-$7.500M	-$7.800M	-$7.400M
YoY Change	1.35%	5.41%	21.31%
% of Operating Profit
Other Income/Expense, Net
YoY Change
Pretax Income	$159.0M	$85.26M	$101.3M
YoY Change	57.01%	19.78%	94.29%
Income Tax	$32.00M	$15.38M	$19.40M
% Of Pretax Income	20.12%	18.04%	19.15%
Net Earnings	$127.1M	$69.88M	$81.86M
YoY Change	55.22%	24.44%	78.89%
Net Earnings / Revenue	15.91%	9.0%	11.23%
Basic Earnings Per Share	$2.12	$1.17	$1.38
Diluted Earnings Per Share	$2.10	$1.16	$1.36
COMMON SHARES
Basic Shares Outstanding	59.83M shares	59.81M shares	59.40M shares
Diluted Shares Outstanding

Balance Sheet

Concept	2020 Q4	2020 Q3	2019 Q4
SHORT-TERM ASSETS
Cash & Short-Term Investments
YoY Change
Cash & Equivalents	$15.23M	$15.90M	$7.975M
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	$77.70M	$78.44M	$77.41M
YoY Change	0.37%	2.64%	18.64%
Goodwill	$7.800M	$7.849M	$7.800M
YoY Change	0.0%	0.0%	-0.62%
Intangibles
YoY Change
Long-Term Investments	$7.506B	$7.278B	$6.689B
YoY Change	12.21%	11.08%	12.21%
Other Assets	$14.80M	$15.10M	$14.50M
YoY Change	2.07%	-0.66%	-79.29%
Total Long-Term Assets
YoY Change
TOTAL ASSETS
Total Short-Term Assets
Total Long-Term Assets
Total Assets	$9.688B	$9.515B	$8.797B
YoY Change	10.13%	9.12%	10.62%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable
YoY Change
Accrued Expenses	$156.5M	$93.10M	$154.3M
YoY Change	1.43%	-28.22%	32.22%
Deferred Revenue
YoY Change
Short-Term Debt	$0.00	$167.0M	$0.00
YoY Change
Long-Term Debt Due
YoY Change
Total Short-Term Liabilities	$170.5M	$260.1M	$157.3M
YoY Change	8.39%	96.45%	33.31%
LONG-TERM LIABILITIES
Long-Term Debt	$550.7M	$550.6M	$550.6M
YoY Change	0.02%	-0.02%	25.28%
Other Long-Term Liabilities	$322.0M	$346.4M	$304.0M
YoY Change	5.92%	26.79%	9.51%
Total Long-Term Liabilities	$872.7M	$897.0M	$854.6M
YoY Change	2.12%	8.87%	19.17%
TOTAL LIABILITIES
Total Short-Term Liabilities	$170.5M	$260.1M	$157.3M
Total Long-Term Liabilities	$872.7M	$897.0M	$854.6M
Total Liabilities	$6.949B	$7.121B	$6.602B
YoY Change	5.25%	8.19%	7.16%
SHAREHOLDERS EQUITY
Retained Earnings	$2.272B	$2.160B	$2.081B
YoY Change	9.18%	7.31%	11.95%
Common Stock	$647.1M	$646.8M	$625.5M
YoY Change	3.45%	4.46%	4.95%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$599.9M	$599.9M	$592.8M
YoY Change	1.19%	1.2%	1.4%
Treasury Stock Shares		44.13M shares	44.02M shares
Shareholders Equity	$2.739B	$2.394B	$2.195B
YoY Change
Total Liabilities & Shareholders Equity	$9.688B	$9.515B	$8.797B
YoY Change	10.13%	9.12%	10.62%

Cashflow Statement

Concept	2020 Q4	2020 Q3	2019 Q4
OPERATING ACTIVITIES
Net Income	$127.1M	$69.88M	$81.86M
YoY Change	55.22%	24.44%	78.89%
Depreciation, Depletion And Amortization	$15.00M	$142.3M	$12.90M
YoY Change	16.28%	4.19%	30.3%
Cash From Operating Activities	$173.1M	$183.5M	$161.3M
YoY Change	7.32%	21.44%	-0.68%
INVESTING ACTIVITIES
Capital Expenditures	-$4.200M	-$5.300M	-$6.600M
YoY Change	-36.36%	-28.38%	34.69%
Acquisitions
YoY Change
Other Investing Activities	-$186.0M	-$70.20M	-$146.0M
YoY Change	27.4%	-45.41%	1.81%
Cash From Investing Activities	-$190.2M	-$75.50M	-$152.6M
YoY Change	24.64%	-44.49%	2.9%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	16.40M	-97.80M	-10.80M
YoY Change	-251.85%	676.19%	8.0%
NET CHANGE
Cash From Operating Activities	173.1M	183.5M	161.3M
Cash From Investing Activities	-190.2M	-75.50M	-152.6M
Cash From Financing Activities	16.40M	-97.80M	-10.80M
Net Change In Cash	-700.0K	10.20M	-2.100M
YoY Change	-66.67%	308.0%	-151.22%
FREE CASH FLOW
Cash From Operating Activities	$173.1M	$183.5M	$161.3M
Capital Expenditures	-$4.200M	-$5.300M	-$6.600M
Free Cash Flow	$177.3M	$188.8M	$167.9M
YoY Change	5.6%	19.12%	0.36%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
	dei	Amendment Flag AmendmentFlag	false
	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2020
	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	Q3
	dei	Entity Central Index Key EntityCentralIndexKey	0000230557
	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
	dei	Document Type DocumentType	10-Q
	dei	Document Quarterly Report DocumentQuarterlyReport	true
	dei	Document Period End Date DocumentPeriodEndDate	2020-09-30
	dei	Document Transition Report DocumentTransitionReport	false
	dei	Entity File Number EntityFileNumber	001-33067
	dei	Entity Registrant Name EntityRegistrantName	SELECTIVE INSURANCE GROUP, INC
	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	NJ
	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	22-2168890
	dei	Entity Address Address Line1 EntityAddressAddressLine1	40 Wantage Avenue
	dei	Entity Address City Or Town EntityAddressCityOrTown	Branchville
	dei	Entity Address State Or Province EntityAddressStateOrProvince	NJ
	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	07890
	dei	City Area Code CityAreaCode	973
	dei	Local Phone Number LocalPhoneNumber	948-3000
	dei	Security12b Title Security12bTitle	Common Stock, par value $2 per share
	dei	Trading Symbol TradingSymbol	SIGI
	dei	Security Exchange Name SecurityExchangeName	NASDAQ
	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
	dei	Entity Small Business EntitySmallBusiness	false
	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
	dei	Entity Shell Company EntityShellCompany	false
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	us-gaap	Deferred Policy Acquisition Cost Amortization Expense DeferredPolicyAcquisitionCostAmortizationExpense	399647000	USD
CY2020Q3	us-gaap	Other Underwriting Expense OtherUnderwritingExpense	89530000	USD
CY2019Q3	us-gaap	Other Underwriting Expense OtherUnderwritingExpense	90234000	USD
	us-gaap	Other Underwriting Expense OtherUnderwritingExpense	269477000	USD
	us-gaap	Other Underwriting Expense OtherUnderwritingExpense	261975000	USD
CY2020Q3	us-gaap	Interest Expense Debt InterestExpenseDebt	7781000	USD
CY2019Q3	us-gaap	Interest Expense Debt InterestExpenseDebt	7397000	USD
	us-gaap	Interest Expense Debt InterestExpenseDebt	23310000	USD
	us-gaap	Interest Expense Debt InterestExpenseDebt	26289000	USD
CY2020Q3	us-gaap	Operating Costs And Expenses OperatingCostsAndExpenses	3905000	USD
CY2019Q3	us-gaap	Operating Costs And Expenses OperatingCostsAndExpenses	6369000	USD
	us-gaap	Operating Costs And Expenses OperatingCostsAndExpenses	19310000	USD
	us-gaap	Operating Costs And Expenses OperatingCostsAndExpenses	28345000	USD
CY2020Q3	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	691309000	USD
CY2019Q3	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	639247000	USD
	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1979895000	USD
	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1882494000	USD
CY2020Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	85257000	USD
CY2019Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	71178000	USD
	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	143947000	USD
	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	235097000	USD
CY2020Q3	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	17412000	USD
CY2019Q3	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	13805000	USD
	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	25948000	USD
	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	44344000	USD
CY2020Q3	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-2030000	USD
CY2019Q3	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	1223000	USD
	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-1295000	USD
	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	989000	USD
CY2020Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	15382000	USD
CY2019Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	15028000	USD
	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	24653000	USD
	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	45333000	USD
CY2020Q3	us-gaap	Net Income Loss NetIncomeLoss	69875000	USD
CY2019Q3	us-gaap	Net Income Loss NetIncomeLoss	56150000	USD
	us-gaap	Net Income Loss NetIncomeLoss	119294000	USD
	us-gaap	Net Income Loss NetIncomeLoss	189764000	USD
CY2020Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.17
CY2019Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.94
	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	1.99
	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.98
	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.16
CY2020Q3	us-gaap	Net Income Loss NetIncomeLoss	69875000	USD
CY2019Q3	us-gaap	Net Income Loss NetIncomeLoss	56150000	USD
	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.20
CY2020Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	1.16
CY2019Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.93
	us-gaap	Net Income Loss NetIncomeLoss	119294000	USD
	us-gaap	Net Income Loss NetIncomeLoss	189764000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	29889000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	27168000	USD
	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	104771000	USD
	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	174483000	USD
CY2020Q3	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncome	7299000	USD
CY2019Q3	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncome	0	USD
	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncome	-14751000	USD
	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncome	0	USD
CY2020Q3	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Netof Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetofTax	0	USD
CY2019Q3	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Netof Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetofTax	2000	USD
	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Netof Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetofTax	5000	USD
	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Netof Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetofTax	26000	USD
CY2020Q3	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Netof Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesNetofTax	-406000	USD
CY2019Q3	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Netof Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesNetofTax	2229000	USD
	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Netof Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesNetofTax	7210000	USD
	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Netof Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesNetofTax	351000	USD
CY2020Q3	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Net DebtSecuritiesAvailableforsaleAllowanceforCreditLossNet	-2254000	USD
CY2019Q3	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Net DebtSecuritiesAvailableforsaleAllowanceforCreditLossNet	0	USD
	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Net DebtSecuritiesAvailableforsaleAllowanceforCreditLossNet	6328000	USD
	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Net DebtSecuritiesAvailableforsaleAllowanceforCreditLossNet	0	USD
CY2020Q3	sigi	Total Unrealized Gains Losseson Investment Securities TotalUnrealizedGainsLossesonInvestmentSecurities	-34528000	USD
CY2019Q3	sigi	Total Unrealized Gains Losseson Investment Securities TotalUnrealizedGainsLossesonInvestmentSecurities	-29395000	USD
	sigi	Total Unrealized Gains Losseson Investment Securities TotalUnrealizedGainsLossesonInvestmentSecurities	-103553000	USD
	sigi	Total Unrealized Gains Losseson Investment Securities TotalUnrealizedGainsLossesonInvestmentSecurities	-174808000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-596000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-525000	USD
	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-1787000	USD
	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-1574000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-596000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-525000	USD
	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-1787000	USD
	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-1574000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	35124000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	29920000	USD
	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	105340000	USD
	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	176382000	USD
CY2020Q3	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	104999000	USD
CY2019Q3	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	86070000	USD
	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	224634000	USD
	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	366146000	USD
CY2020Q3	us-gaap	Stockholders Equity StockholdersEquity	2393613000	USD
CY2019Q3	us-gaap	Stockholders Equity StockholdersEquity	2137376000	USD
CY2020Q3	us-gaap	Stockholders Equity StockholdersEquity	2393613000	USD
CY2019Q3	us-gaap	Stockholders Equity StockholdersEquity	2137376000	USD
CY2020Q3	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	0.23
CY2019Q3	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	0.20
	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	0.69
	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	0.60
CY2020Q2	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	59811742	shares
CY2019Q2	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	59328108	shares
CY2019Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	59461153	shares
CY2018Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	58948554	shares
CY2020Q3	us-gaap	Stock Issued During Period Shares Dividend Reinvestment Plan StockIssuedDuringPeriodSharesDividendReinvestmentPlan	7026	shares
CY2019Q3	us-gaap	Stock Issued During Period Shares Dividend Reinvestment Plan StockIssuedDuringPeriodSharesDividendReinvestmentPlan	4738	shares
	us-gaap	Stock Issued During Period Shares Dividend Reinvestment Plan StockIssuedDuringPeriodSharesDividendReinvestmentPlan	21900	shares
	us-gaap	Stock Issued During Period Shares Dividend Reinvestment Plan StockIssuedDuringPeriodSharesDividendReinvestmentPlan	15650	shares
CY2020Q3	us-gaap	Stock Issued During Period Shares Share Based Compensation StockIssuedDuringPeriodSharesShareBasedCompensation	16936	shares
CY2019Q3	us-gaap	Stock Issued During Period Shares Share Based Compensation StockIssuedDuringPeriodSharesShareBasedCompensation	83979	shares
	us-gaap	Stock Issued During Period Shares Share Based Compensation StockIssuedDuringPeriodSharesShareBasedCompensation	455537	shares
	us-gaap	Stock Issued During Period Shares Share Based Compensation StockIssuedDuringPeriodSharesShareBasedCompensation	557257	shares
CY2020Q3	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	1002	shares
CY2019Q3	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	17256	shares
	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	103888	shares
	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	121892	shares
CY2020Q3	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	59834702	shares
CY2019Q3	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	59399569	shares
CY2020Q3	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	59834702	shares
CY2019Q3	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	59399569	shares
CY2020Q3	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
CY2019Q4	us-gaap	Preferred Stock Shares Outstanding PreferredStockSharesOutstanding	0	shares
CY2019Q4	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2020Q3	us-gaap	Preferred Stock Shares Issued PreferredStockSharesIssued	0	shares
CY2020Q3	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	5000000	shares
CY2019Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	5000000	shares
CY2020Q3	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	0
CY2019Q4	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	0
	us-gaap	Net Income Loss NetIncomeLoss	119294000	USD
	us-gaap	Net Income Loss NetIncomeLoss	189764000	USD
	us-gaap	Depreciation Amortization And Accretion Net DepreciationAmortizationAndAccretionNet	44435000	USD
	us-gaap	Depreciation Amortization And Accretion Net DepreciationAmortizationAndAccretionNet	42346000	USD
	us-gaap	Share Based Compensation ShareBasedCompensation	13935000	USD
	us-gaap	Share Based Compensation ShareBasedCompensation	15857000	USD
	us-gaap	Income Loss From Equity Method Investments Net Of Dividends Or Distributions IncomeLossFromEquityMethodInvestmentsNetOfDividendsOrDistributions	5146000	USD
	us-gaap	Income Loss From Equity Method Investments Net Of Dividends Or Distributions IncomeLossFromEquityMethodInvestmentsNetOfDividendsOrDistributions	8832000	USD
	sigi	Proceedsfromequityinvestmentsinexcessofcurrentyearearnings Proceedsfromequityinvestmentsinexcessofcurrentyearearnings	3136000	USD
	sigi	Proceedsfromequityinvestmentsinexcessofcurrentyearearnings Proceedsfromequityinvestmentsinexcessofcurrentyearearnings	2267000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	-24296000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	15295000	USD
	us-gaap	Gain Loss On Disposition Of Assets1 GainLossOnDispositionOfAssets1	-17000	USD
	us-gaap	Gain Loss On Disposition Of Assets1 GainLossOnDispositionOfAssets1	21000	USD
	sigi	Increase Decrease In Reserves For Losses And Loss Expenses Net Of Reinsurance Recoverables IncreaseDecreaseInReservesForLossesAndLossExpensesNetOfReinsuranceRecoverables	190796000	USD
	sigi	Increase Decrease In Reserves For Losses And Loss Expenses Net Of Reinsurance Recoverables IncreaseDecreaseInReservesForLossesAndLossExpensesNetOfReinsuranceRecoverables	134951000	USD
	sigi	Increase Decrease In Unearned Premiums Net Of Prepaid Reinsurance IncreaseDecreaseInUnearnedPremiumsNetOfPrepaidReinsurance	114672000	USD
	sigi	Increase Decrease In Unearned Premiums Net Of Prepaid Reinsurance IncreaseDecreaseInUnearnedPremiumsNetOfPrepaidReinsurance	122460000	USD
	us-gaap	Increase Decrease In Income Taxes IncreaseDecreaseInIncomeTaxes	-10775000	USD
	us-gaap	Increase Decrease In Income Taxes IncreaseDecreaseInIncomeTaxes	2408000	USD
	us-gaap	Increase Decrease In Premiums Receivable IncreaseDecreaseInPremiumsReceivable	28239000	USD
	us-gaap	Increase Decrease In Premiums Receivable IncreaseDecreaseInPremiumsReceivable	89962000	USD
	us-gaap	Increase Decrease In Deferred Policy Acquisition Costs IncreaseDecreaseInDeferredPolicyAcquisitionCosts	21523000	USD
	us-gaap	Increase Decrease In Deferred Policy Acquisition Costs IncreaseDecreaseInDeferredPolicyAcquisitionCosts	26627000	USD
	us-gaap	Increase Decrease In Interest And Dividends Receivable IncreaseDecreaseInInterestAndDividendsReceivable	1507000	USD
	us-gaap	Increase Decrease In Interest And Dividends Receivable IncreaseDecreaseInInterestAndDividendsReceivable	1460000	USD
	us-gaap	Increase Decrease In Employee Related Liabilities IncreaseDecreaseInEmployeeRelatedLiabilities	-33677000	USD
	us-gaap	Increase Decrease In Employee Related Liabilities IncreaseDecreaseInEmployeeRelatedLiabilities	-16261000	USD
	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	23388000	USD
	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	35810000	USD
	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	-5443000	USD
	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	414000	USD
	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	380883000	USD
	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	316199000	USD
	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	1373226000	USD
	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	1330827000	USD
	sigi	Paymentstoacquirecommercialmortgageloans Paymentstoacquirecommercialmortgageloans	-29800000	USD
	sigi	Paymentstoacquirecommercialmortgageloans Paymentstoacquirecommercialmortgageloans	0	USD
	sigi	Paymentsto Acquire Equity Securities PaymentstoAcquireEquitySecurities	87307000	USD
	sigi	Paymentsto Acquire Equity Securities PaymentstoAcquireEquitySecurities	40233000	USD
	us-gaap	Payments To Acquire Other Investments PaymentsToAcquireOtherInvestments	61051000	USD
	us-gaap	Payments To Acquire Other Investments PaymentsToAcquireOtherInvestments	41248000	USD
	us-gaap	Payments To Acquire Short Term Investments PaymentsToAcquireShortTermInvestments	4475128000	USD
	us-gaap	Payments To Acquire Short Term Investments PaymentsToAcquireShortTermInvestments	4108414000	USD
	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	411263000	USD
	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	461825000	USD
	us-gaap	Proceeds From Sale And Collection Of Mortgage Notes Receivable ProceedsFromSaleAndCollectionOfMortgageNotesReceivable	109000	USD
	us-gaap	Proceeds From Sale And Collection Of Mortgage Notes Receivable ProceedsFromSaleAndCollectionOfMortgageNotesReceivable	0	USD
	us-gaap	Proceeds From Sale Of Short Term Investments ProceedsFromSaleOfShortTermInvestments	4377024000	USD
	us-gaap	Proceeds From Sale Of Short Term Investments ProceedsFromSaleOfShortTermInvestments	4106643000	USD
	us-gaap	Proceeds From Maturities Prepayments And Calls Of Held To Maturity Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities	1646000	USD
	us-gaap	Proceeds From Maturities Prepayments And Calls Of Held To Maturity Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities	10062000	USD
	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	738238000	USD
	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	413220000	USD
	sigi	Proceedsfrom Saleof Equity Securities ProceedsfromSaleofEquitySecurities	1320000	USD
	sigi	Proceedsfrom Saleof Equity Securities ProceedsfromSaleofEquitySecurities	125302000	USD
	us-gaap	Proceeds From Sale Of Other Investments ProceedsFromSaleOfOtherInvestments	3879000	USD
	us-gaap	Proceeds From Sale Of Other Investments ProceedsFromSaleOfOtherInvestments	18016000	USD
	us-gaap	Proceeds From Equity Method Investment Dividends Or Distributions Return Of Capital ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital	12890000	USD
	us-gaap	Proceeds From Equity Method Investment Dividends Or Distributions Return Of Capital ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital	19054000	USD
	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	17858000	USD
	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	24424000	USD
	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	0	USD
	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	35000	USD
	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-498001000	USD
	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-390989000	USD
	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	39972000	USD
	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	34440000	USD
	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	7039000	USD
	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	8071000	USD
	us-gaap	Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions	5478000	USD
	us-gaap	Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions	5599000	USD
	us-gaap	Proceeds From Debt Net Of Issuance Costs ProceedsFromDebtNetOfIssuanceCosts	487000000	USD
	us-gaap	Proceeds From Debt Net Of Issuance Costs ProceedsFromDebtNetOfIssuanceCosts	355757000	USD
	us-gaap	Repayments Of Debt RepaymentsOfDebt	320000000	USD
	us-gaap	Repayments Of Debt RepaymentsOfDebt	250000000	USD
	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	429000	USD
	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	811000	USD
	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	125038000	USD
	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	68034000	USD
	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect	7920000	USD
	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Excluding Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect	-6756000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	7975000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	16919000	USD
CY2020Q3	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	15895000	USD
CY2019Q3	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	10163000	USD
	sigi	Percentof Commercial Mortgage Loans PercentofCommercialMortgageLoans	0.01
	sigi	Interest Paid Operatingand Investing Activities InterestPaidOperatingandInvestingActivities	24449000	USD
	sigi	Interest Paid Operatingand Investing Activities InterestPaidOperatingandInvestingActivities	19261000	USD
	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	34000000	USD
	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	42000000	USD
	us-gaap	Operating Lease Payments OperatingLeasePayments	7077000	USD
	us-gaap	Operating Lease Payments OperatingLeasePayments	6062000	USD
	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	13000	USD
	us-gaap	Finance Lease Interest Payment On Liability FinanceLeaseInterestPaymentOnLiability	12000	USD
	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	429000	USD
	us-gaap	Finance Lease Principal Payments FinanceLeasePrincipalPayments	811000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	119000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Finance Lease Liability RightOfUseAssetObtainedInExchangeForFinanceLeaseLiability	824000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	22104000	USD
	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	13648000	USD
	us-gaap	Noncash Or Part Noncash Acquisition Fixed Assets Acquired1 NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1	9000	USD
	us-gaap	Noncash Or Part Noncash Acquisition Fixed Assets Acquired1 NoncashOrPartNoncashAcquisitionFixedAssetsAcquired1	108000	USD
CY2020Q3	us-gaap	Cash Cash	785000	USD
CY2019Q4	us-gaap	Cash Cash	300000	USD
CY2020Q3	us-gaap	Restricted Cash RestrictedCash	15110000	USD
CY2019Q4	us-gaap	Restricted Cash RestrictedCash	7675000	USD
CY2020Q3	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	15895000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	7975000	USD
CY2020Q3	us-gaap	Available For Sale Securities Amortized Cost AvailableForSaleSecuritiesAmortizedCost	6097973000	USD
CY2020Q3	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss DebtSecuritiesAvailableForSaleAllowanceForCreditLoss	-7180000	USD
CY2020Q3	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	371159000	USD
CY2020Q3	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	24415000	USD
CY2020Q3	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	6437537000	USD
CY2019Q4	us-gaap	Available For Sale Securities Amortized Cost AvailableForSaleSecuritiesAmortizedCost	5879986000	USD
CY2019Q4	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	223372000	USD
CY2019Q4	us-gaap	Available For Sale Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	7738000	USD
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	6095620000	USD
CY2020Q2	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss DebtSecuritiesAvailableForSaleAllowanceForCreditLoss	-10395000	USD
CY2020Q3	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Not Previously Recorded DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded	1025000	USD
CY2020Q3	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Not To Sell Before Recovery Credit Loss Previously Recorded Expense Reversal DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal	-3856000	USD
CY2020Q3	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Securities Sold DebtSecuritiesAvailableForSaleAllowanceForCreditLossSecuritiesSold	-362000	USD
CY2020Q3	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Sell Before Recovery DebtSecuritiesAvailableForSaleAllowanceForCreditLossSellBeforeRecovery	-22000	USD
CY2020Q3	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss DebtSecuritiesAvailableForSaleAllowanceForCreditLoss	-7180000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss DebtSecuritiesAvailableForSaleAllowanceForCreditLoss	0	USD
	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Not Previously Recorded DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded	8100000	USD
	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Not To Sell Before Recovery Credit Loss Previously Recorded Expense Reversal DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotToSellBeforeRecoveryCreditLossPreviouslyRecordedExpenseReversal	0	USD
	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Securities Sold DebtSecuritiesAvailableForSaleAllowanceForCreditLossSecuritiesSold	-830000	USD
	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Sell Before Recovery DebtSecuritiesAvailableForSaleAllowanceForCreditLossSellBeforeRecovery	-90000	USD
CY2020Q3	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss DebtSecuritiesAvailableForSaleAllowanceForCreditLoss	-7180000	USD
CY2020Q3	us-gaap	Available For Sale Securities Debt Maturities Within One Year Fair Value AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue	336142000	USD
CY2020Q3	us-gaap	Held To Maturity Securities Debt Maturities Within One Year Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount	1456000	USD
CY2020Q3	us-gaap	Held To Maturity Securities Debt Maturities Within One Year Fair Value HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue	1490000	USD
CY2020Q3	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	3714414000	USD
CY2020Q3	us-gaap	Held To Maturity Securities Debt Maturities After One Through Five Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount	15131000	USD
CY2020Q3	us-gaap	Held To Maturity Securities Debt Maturities After One Through Five Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	16293000	USD
CY2020Q3	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	1960132000	USD
CY2020Q3	us-gaap	Held To Maturity Securities Debt Maturities After Five Through Ten Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount	2500000	USD
CY2020Q3	us-gaap	Held To Maturity Securities Debt Maturities After Five Through Ten Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	2430000	USD
CY2020Q3	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue	426849000	USD
CY2020Q3	us-gaap	Held To Maturity Securities Debt Maturities After Ten Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount	0	USD
CY2020Q3	us-gaap	Held To Maturity Securities Debt Maturities After Ten Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue	0	USD
CY2020Q3	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	6437537000	USD
CY2020Q3	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	19087000	USD
CY2020Q3	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	20213000	USD
CY2020Q3	us-gaap	Assets Held By Insurance Regulators AssetsHeldByInsuranceRegulators	27800000	USD
CY2020Q3	us-gaap	Security Owned And Pledged As Collateral Fair Value SecurityOwnedAndPledgedAsCollateralFairValue	409900000	USD
CY2020Q3	sigi	Maximumexposuretocreditconcentrationriskofthe Companysstockholdersequityotherthancertain U.S.Governmentagencies MaximumexposuretocreditconcentrationriskoftheCompanysstockholdersequityotherthancertainU.S.governmentagencies	0.10
CY2019Q4	sigi	Maximumexposuretocreditconcentrationriskofthe Companysstockholdersequityotherthancertain U.S.Governmentagencies MaximumexposuretocreditconcentrationriskoftheCompanysstockholdersequityotherthancertainU.S.governmentagencies	0.10
CY2020Q3	us-gaap	Net Investment Income NetInvestmentIncome	68185000	USD
CY2019Q3	us-gaap	Net Investment Income NetInvestmentIncome	55826000	USD
	us-gaap	Net Investment Income NetInvestmentIncome	158596000	USD
	us-gaap	Net Investment Income NetInvestmentIncome	164949000	USD
CY2020Q3	sigi	Creditlossexpenseoninvestmentportfolio Creditlossexpenseoninvestmentportfolio	2854000	USD
CY2020Q3	sigi	Other Impairment Charges OtherImpairmentCharges	-44000	USD
CY2020Q3	sigi	Otti Losses Investments Portion Recognized In Earnings Net OTTILossesInvestmentsPortionRecognizedInEarningsNet	2810000	USD
CY2019Q3	sigi	Otti Losses Investments Portion Recognized In Earnings Net OTTILossesInvestmentsPortionRecognizedInEarningsNet	-2291000	USD
	sigi	Creditlossexpenseoninvestmentportfolio Creditlossexpenseoninvestmentportfolio	-8227000	USD
	sigi	Other Impairment Charges OtherImpairmentCharges	-16259000	USD
	sigi	Otti Losses Investments Portion Recognized In Earnings Net OTTILossesInvestmentsPortionRecognizedInEarningsNet	-24486000	USD
	sigi	Otti Losses Investments Portion Recognized In Earnings Net OTTILossesInvestmentsPortionRecognizedInEarningsNet	-3366000	USD
	sigi	Other Impairment Charges OtherImpairmentCharges	-16300000	USD
	sigi	Creditlossexpenseoninvestmentportfolio Creditlossexpenseoninvestmentportfolio	-8200000	USD
CY2020Q3	sigi	Creditlossexpenseoninvestmentportfolio Creditlossexpenseoninvestmentportfolio	2900000	USD
CY2020Q3	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	573000	USD
CY2019Q3	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	20425000	USD
	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	7288000	USD
	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	26752000	USD
CY2020Q3	sigi	Otti Losses Investments Portion Recognized In Earnings Net OTTILossesInvestmentsPortionRecognizedInEarningsNet	2810000	USD
CY2019Q3	sigi	Otti Losses Investments Portion Recognized In Earnings Net OTTILossesInvestmentsPortionRecognizedInEarningsNet	-2291000	USD
	sigi	Otti Losses Investments Portion Recognized In Earnings Net OTTILossesInvestmentsPortionRecognizedInEarningsNet	-24486000	USD
	sigi	Otti Losses Investments Portion Recognized In Earnings Net OTTILossesInvestmentsPortionRecognizedInEarningsNet	-3366000	USD
CY2020Q3	us-gaap	Realized Investment Gains Losses RealizedInvestmentGainsLosses	3383000	USD
CY2019Q3	us-gaap	Realized Investment Gains Losses RealizedInvestmentGainsLosses	18134000	USD
	us-gaap	Realized Investment Gains Losses RealizedInvestmentGainsLosses	-17198000	USD
	us-gaap	Realized Investment Gains Losses RealizedInvestmentGainsLosses	23386000	USD
CY2020Q3	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	4338000	USD
CY2019Q3	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-20317000	USD
	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-7098000	USD
	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-8091000	USD
CY2020Q3	us-gaap	Gain Loss On Investments GainLossOnInvestments	7721000	USD
CY2019Q3	us-gaap	Gain Loss On Investments GainLossOnInvestments	-2183000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	-24296000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	15295000	USD
CY2020Q3	sigi	Realizedandunrealizedinvestmentchange Realizedandunrealizedinvestmentchange	9900000	USD
CY2019Q3	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-20300000	USD
CY2019Q3	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-20300000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	-24300000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	15300000	USD
CY2020Q3	us-gaap	Unrealized Gain Loss On Investments UnrealizedGainLossOnInvestments	4338000	USD
CY2019Q3	us-gaap	Unrealized Gain Loss On Investments UnrealizedGainLossOnInvestments	1109000	USD
	us-gaap	Unrealized Gain Loss On Investments UnrealizedGainLossOnInvestments	-7101000	USD
	us-gaap	Unrealized Gain Loss On Investments UnrealizedGainLossOnInvestments	1805000	USD
CY2020Q3	sigi	Unrealized Gain Losson Equity Securities Sold UnrealizedGainLossonEquitySecuritiesSold	0	USD
CY2019Q3	sigi	Unrealized Gain Losson Equity Securities Sold UnrealizedGainLossonEquitySecuritiesSold	-21426000	USD
	sigi	Unrealized Gain Losson Equity Securities Sold UnrealizedGainLossonEquitySecuritiesSold	3000	USD
	sigi	Unrealized Gain Losson Equity Securities Sold UnrealizedGainLossonEquitySecuritiesSold	-9896000	USD
CY2020Q3	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	4338000	USD
CY2019Q3	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-20317000	USD
	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-7098000	USD
	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	-8091000	USD
CY2020Q3	us-gaap	Heldtomaturity Securities Sold Security Realized Gain Loss Excluding Other Than Temporary Impairments HeldtomaturitySecuritiesSoldSecurityRealizedGainLossExcludingOtherThanTemporaryImpairments	1000	USD
CY2019Q3	us-gaap	Heldtomaturity Securities Sold Security Realized Gain Loss Excluding Other Than Temporary Impairments HeldtomaturitySecuritiesSoldSecurityRealizedGainLossExcludingOtherThanTemporaryImpairments	0	USD
	us-gaap	Heldtomaturity Securities Sold Security Realized Gain Loss Excluding Other Than Temporary Impairments HeldtomaturitySecuritiesSoldSecurityRealizedGainLossExcludingOtherThanTemporaryImpairments	2000	USD
	us-gaap	Heldtomaturity Securities Sold Security Realized Gain Loss Excluding Other Than Temporary Impairments HeldtomaturitySecuritiesSoldSecurityRealizedGainLossExcludingOtherThanTemporaryImpairments	1000	USD
CY2020Q3	sigi	Commercialmortgageloansrealizedgains Commercialmortgageloansrealizedgains	1000	USD
CY2019Q3	sigi	Commercialmortgageloansrealizedgains Commercialmortgageloansrealizedgains	0	USD
	sigi	Commercialmortgageloansrealizedgains Commercialmortgageloansrealizedgains	2000	USD
	sigi	Commercialmortgageloansrealizedgains Commercialmortgageloansrealizedgains	0	USD
CY2020Q3	sigi	Commercialmortgageloansrealizedlosses Commercialmortgageloansrealizedlosses	0	USD
CY2019Q3	sigi	Commercialmortgageloansrealizedlosses Commercialmortgageloansrealizedlosses	0	USD
	sigi	Commercialmortgageloansrealizedlosses Commercialmortgageloansrealizedlosses	0	USD
	sigi	Commercialmortgageloansrealizedlosses Commercialmortgageloansrealizedlosses	0	USD
CY2020Q3	us-gaap	Equity Securities Fv Ni Realized Gain EquitySecuritiesFvNiRealizedGain	0	USD
CY2019Q3	us-gaap	Equity Securities Fv Ni Realized Gain EquitySecuritiesFvNiRealizedGain	21630000	USD
	us-gaap	Equity Securities Fv Ni Realized Gain EquitySecuritiesFvNiRealizedGain	0	USD
	us-gaap	Equity Securities Fv Ni Realized Gain EquitySecuritiesFvNiRealizedGain	24868000	USD
CY2020Q3	us-gaap	Equity Securities Fv Ni Realized Loss EquitySecuritiesFvNiRealizedLoss	0	USD
CY2019Q3	us-gaap	Equity Securities Fv Ni Realized Loss EquitySecuritiesFvNiRealizedLoss	28000	USD
	us-gaap	Equity Securities Fv Ni Realized Loss EquitySecuritiesFvNiRealizedLoss	3000	USD
	us-gaap	Equity Securities Fv Ni Realized Loss EquitySecuritiesFvNiRealizedLoss	135000	USD
CY2020Q3	sigi	Short Term Investments Realized Gains ShortTermInvestmentsRealizedGains	18000	USD
CY2019Q3	sigi	Short Term Investments Realized Gains ShortTermInvestmentsRealizedGains	2000	USD
	sigi	Short Term Investments Realized Gains ShortTermInvestmentsRealizedGains	355000	USD
	sigi	Short Term Investments Realized Gains ShortTermInvestmentsRealizedGains	18000	USD
CY2020Q3	sigi	Short Term Investments Realized Losses ShortTermInvestmentsRealizedLosses	7000	USD
CY2019Q3	sigi	Short Term Investments Realized Losses ShortTermInvestmentsRealizedLosses	38000	USD
	sigi	Short Term Investments Realized Losses ShortTermInvestmentsRealizedLosses	198000	USD
	sigi	Short Term Investments Realized Losses ShortTermInvestmentsRealizedLosses	39000	USD
CY2020Q3	sigi	Other Investments Realized Gains OtherInvestmentsRealizedGains	0	USD
CY2019Q3	sigi	Other Investments Realized Gains OtherInvestmentsRealizedGains	0	USD
	sigi	Other Investments Realized Gains OtherInvestmentsRealizedGains	0	USD
	sigi	Other Investments Realized Gains OtherInvestmentsRealizedGains	7000	USD
CY2020Q3	sigi	Other Investments Realized Losses OtherInvestmentsRealizedLosses	0	USD
CY2019Q3	sigi	Other Investments Realized Losses OtherInvestmentsRealizedLosses	0	USD
	sigi	Other Investments Realized Losses OtherInvestmentsRealizedLosses	5000	USD
	sigi	Other Investments Realized Losses OtherInvestmentsRealizedLosses	30000	USD
CY2020Q3	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	573000	USD
CY2019Q3	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	20425000	USD
	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	7288000	USD
	us-gaap	Debt And Equity Securities Gain Loss DebtAndEquitySecuritiesGainLoss	26752000	USD
CY2020Q3	us-gaap	Finance Lease Liability FinanceLeaseLiability	424000	USD
CY2019Q4	us-gaap	Finance Lease Liability FinanceLeaseLiability	737000	USD
CY2020Q3	us-gaap	Deferred Finance Costs Net DeferredFinanceCostsNet	3485000	USD
CY2020Q3	us-gaap	Debt Instrument Unamortized Discount DebtInstrumentUnamortizedDiscount	6373000	USD
CY2020Q3	us-gaap	Debt Longterm And Shortterm Combined Amount DebtLongtermAndShorttermCombinedAmount	717566000	USD
CY2019Q4	us-gaap	Debt Longterm And Shortterm Combined Amount DebtLongtermAndShorttermCombinedAmount	550597000	USD
CY2020Q3	us-gaap	Shortterm Debt Fair Value ShorttermDebtFairValue	167055000	USD
CY2019Q4	us-gaap	Shortterm Debt Fair Value ShorttermDebtFairValue	0	USD
CY2020Q3	us-gaap	Long Term Debt Fair Value LongTermDebtFairValue	682253000	USD
CY2019Q4	us-gaap	Long Term Debt Fair Value LongTermDebtFairValue	659272000	USD
CY2020Q3	us-gaap	Finance Lease Liability FinanceLeaseLiability	424000	USD
CY2019Q4	us-gaap	Finance Lease Liability FinanceLeaseLiability	737000	USD
CY2020Q3	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	550566000	USD
CY2019Q4	us-gaap	Long Term Debt And Capital Lease Obligations LongTermDebtAndCapitalLeaseObligations	550597000	USD
CY2020Q3	sigi	Net Asset Value NetAssetValue	46600000	USD
CY2019Q4	sigi	Net Asset Value NetAssetValue	37800000	USD
CY2020Q3	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	20213000	USD
CY2020Q3	sigi	Commercialmortgageloanfairvalue Commercialmortgageloanfairvalue	30595000	USD
CY2020Q3	us-gaap	Shortterm Debt Fair Value ShorttermDebtFairValue	167055000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	21975000	USD
	dei	Document Period End Date DocumentPeriodEndDate	2020-09-30
	dei	Document Period End Date DocumentPeriodEndDate	2020-09-30
CY2020Q3	us-gaap	Reinsurance Recoverables On Unpaid Losses Gross ReinsuranceRecoverablesOnUnpaidLossesGross	613287000	USD
CY2020Q3	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	1831000	USD
CY2020Q3	us-gaap	Reinsurance Recoverables ReinsuranceRecoverables	611456000	USD
CY2020Q3	us-gaap	Reinsurance Recoverable Credit Quality Indicator Date Updated ReinsuranceRecoverableCreditQualityIndicatorDateUpdated	2020-09-30
CY2020Q2	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	2396000	USD
CY2019Q4	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	4400000	USD
CY2020Q3	us-gaap	Reinsurance Recoverable Credit Loss Expense Reversal ReinsuranceRecoverableCreditLossExpenseReversal	-565000	USD
	us-gaap	Reinsurance Recoverable Credit Loss Expense Reversal ReinsuranceRecoverableCreditLossExpenseReversal	334000	USD
CY2020Q3	us-gaap	Reinsurance Loss On Uncollectible Accounts In Period Amount ReinsuranceLossOnUncollectibleAccountsInPeriodAmount	0	USD
	us-gaap	Reinsurance Loss On Uncollectible Accounts In Period Amount ReinsuranceLossOnUncollectibleAccountsInPeriodAmount	0	USD
CY2020Q3	us-gaap	Reinsurance Recoverable Allowance For Credit Loss Recovery ReinsuranceRecoverableAllowanceForCreditLossRecovery	0	USD
	us-gaap	Reinsurance Recoverable Allowance For Credit Loss Recovery ReinsuranceRecoverableAllowanceForCreditLossRecovery	0	USD
CY2020Q3	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	1831000	USD
CY2020Q3	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	1831000	USD
CY2020Q2	sigi	Policyholder Premium Credit PolicyholderPremiumCredit	0.15
CY2020Q3	us-gaap	Loss From Catastrophes LossFromCatastrophes	79500000	USD
CY2019Q3	us-gaap	Loss From Catastrophes LossFromCatastrophes	24200000	USD
	us-gaap	Loss From Catastrophes LossFromCatastrophes	195900000	USD
	us-gaap	Loss From Catastrophes LossFromCatastrophes	74500000	USD
	us-gaap	Schedule Of Liability For Unpaid Claims And Claims Adjustment Expense ScheduleOfLiabilityForUnpaidClaimsAndClaimsAdjustmentExpense	<div style="margin-bottom:5pt;margin-top:8pt"><table style="border-collapse:collapse;display:inline-table;vertical-align:top;width:100.000%"><tr><td style="width:1.0%"/><td style="width:74.046%"/><td style="width:0.1%"/><td style="width:0.1%"/><td style="width:0.530%"/><td style="width:0.1%"/><td style="width:1.0%"/><td style="width:10.595%"/><td style="width:0.1%"/><td style="width:0.1%"/><td style="width:0.530%"/><td style="width:0.1%"/><td style="width:1.0%"/><td style="width:10.599%"/><td style="width:0.1%"/></tr><tr><td colspan="3" style="border-top:1pt solid #000000;padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:0 1pt"/><td colspan="9" style="border-top:1pt solid #000000;padding:2px 1pt;text-align:center;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">Nine Months ended September 30,</span></td></tr><tr><td colspan="3" style="padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">($ in thousands)</span></td><td colspan="3" style="padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:2px 1pt;text-align:center;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">2020</span></td><td colspan="3" style="border-top:1pt solid #000000;padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:2px 1pt;text-align:center;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">2019</span></td></tr><tr><td colspan="3" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Gross reserve for loss and loss expense, at beginning of year</span></td><td colspan="3" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:0 1pt"/><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">$</span></td><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 0;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">4,067,163</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">3,893,868 </span></td><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="padding:2px 1pt;text-align:left;vertical-align:bottom"><div><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Less: reinsurance recoverable on unpaid loss and loss expense, at beginning of year</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:5.2pt;font-weight:400;line-height:100%;position:relative;top:-2.8pt;vertical-align:baseline">1</span></div></td><td colspan="3" style="padding:0 1pt"/><td colspan="2" style="padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">547,066</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="padding:0 1pt"/><td colspan="2" style="padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">537,388 </span></td><td style="padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#ccffcc;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Net reserve for loss and loss expense, at beginning of year</span></td><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">3,520,097</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">3,356,480 </span></td><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Incurred loss and loss expense for claims occurring in the:</span></td><td colspan="3" style="padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%"> </span></td><td colspan="3" style="padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td></tr><tr><td colspan="3" style="background-color:#ccffcc;padding:2px 1pt 2px 6.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Current year</span></td><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">1,295,285</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="background-color:#ccffcc;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">1,200,878 </span></td><td style="background-color:#ccffcc;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="padding:2px 1pt 2px 6.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Prior years</span></td><td colspan="3" style="padding:0 1pt"/><td colspan="2" style="padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">(43,210)</span></td><td style="padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="padding:0 1pt"/><td colspan="2" style="padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(34,640)</span></td><td style="padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#ccffcc;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Total incurred loss and loss expense</span></td><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">1,252,075</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">1,166,238 </span></td><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Paid loss and loss expense for claims occurring in the:</span></td><td colspan="3" style="padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%"> </span></td><td colspan="3" style="padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td></tr><tr><td colspan="3" style="background-color:#ccffcc;padding:2px 1pt 2px 6.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Current year</span></td><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">421,981</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="background-color:#ccffcc;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">384,436 </span></td><td style="background-color:#ccffcc;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="padding:2px 1pt 2px 6.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Prior years</span></td><td colspan="3" style="padding:0 1pt"/><td colspan="2" style="padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">646,974</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="padding:0 1pt"/><td colspan="2" style="padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">631,589 </span></td><td style="padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#ccffcc;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Total paid loss and loss expense</span></td><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">1,068,955</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ccffcc;padding:0 1pt"/><td colspan="2" style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">1,016,025 </span></td><td style="background-color:#ccffcc;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Net reserve for loss and loss expense, at end of period</span></td><td colspan="3" style="padding:0 1pt"/><td colspan="2" style="border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">3,703,217</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="padding:0 1pt"/><td colspan="2" style="border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">3,506,693 </span></td><td style="border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#d0ffd0;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Add: Reinsurance recoverable on unpaid loss and loss expense, at end of period</span></td><td colspan="3" style="background-color:#d0ffd0;padding:0 1pt"/><td colspan="2" style="background-color:#d0ffd0;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">590,059</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="background-color:#d0ffd0;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#d0ffd0;padding:0 1pt"/><td colspan="2" style="background-color:#d0ffd0;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">548,938 </span></td><td style="background-color:#d0ffd0;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Gross reserve for loss and loss expense at end of period</span></td><td colspan="3" style="padding:0 1pt"/><td style="border-bottom:3pt double #000000;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">$</span></td><td style="border-bottom:3pt double #000000;border-top:1pt solid #000000;padding:2px 0;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:700;line-height:100%">4,293,276</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%"> </span></td><td style="border-bottom:3pt double #000000;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="padding:0 1pt"/><td colspan="2" style="border-bottom:3pt double #000000;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">4,055,631 </span></td><td style="border-bottom:3pt double #000000;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr></table></div><div style="margin-top:3pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:5.2pt;font-weight:400;line-height:120%;position:relative;top:-2.8pt;vertical-align:baseline">1</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:120%">Includes an adjustment of $2.9 million related to our adoption of ASU 2016-13. Refer to Note 2. "Adoption of Accounting Pronouncements" for additional information.</span></div>
CY2019Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	4067163000	USD
CY2018Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	3893868000	USD
CY2019Q4	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	547066000	USD
CY2018Q4	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	537388000	USD
CY2019Q4	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	3520097000	USD
CY2018Q4	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	3356480000	USD
	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Current Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense	1295285000	USD
	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Current Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense	1200878000	USD
	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1	1252075000	USD
	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1	1166238000	USD
	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Current Year1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1	421981000	USD
	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Current Year1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1	384436000	USD
	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Prior Years1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1	646974000	USD
	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Prior Years1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1	631589000	USD
	us-gaap	Payments For Losses And Loss Adjustment Expense PaymentsForLossesAndLossAdjustmentExpense	1068955000	USD
	us-gaap	Payments For Losses And Loss Adjustment Expense PaymentsForLossesAndLossAdjustmentExpense	1016025000	USD
CY2020Q3	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	3703217000	USD
CY2019Q3	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	3506693000	USD
CY2020Q3	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	590059000	USD
CY2019Q3	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	548938000	USD
CY2020Q3	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	4293276000	USD
CY2019Q3	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	4055631000	USD
	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Current Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense	1295300000	USD
	us-gaap	Loss From Catastrophes LossFromCatastrophes	195900000	USD
	us-gaap	Loss From Catastrophes LossFromCatastrophes	74500000	USD
	sigi	Loss Reservefor Covid19 LossReserveforCOVID19	10000000.0	USD
	sigi	Loss Reservefor Covid19 LossReserveforCOVID19	10000000.0	USD
	us-gaap	Number Of Operating Segments NumberOfOperatingSegments	4
CY2020Q3	us-gaap	Net Investment Income NetInvestmentIncome	68185000	USD
CY2019Q3	us-gaap	Net Investment Income NetInvestmentIncome	55826000	USD
	us-gaap	Net Investment Income NetInvestmentIncome	158596000	USD
	us-gaap	Net Investment Income NetInvestmentIncome	164949000	USD
CY2020Q3	us-gaap	Gain Loss On Investments GainLossOnInvestments	7721000	USD
CY2019Q3	us-gaap	Gain Loss On Investments GainLossOnInvestments	-2183000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	-24296000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	15295000	USD
CY2020Q3	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	75906000	USD
CY2019Q3	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	53643000	USD
	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	134300000	USD
	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	180244000	USD
CY2020Q3	us-gaap	Revenues Revenues	776566000	USD
CY2019Q3	us-gaap	Revenues Revenues	710425000	USD
	us-gaap	Revenues Revenues	2123842000	USD
	us-gaap	Revenues Revenues	2117591000	USD
CY2020Q3	us-gaap	Net Investment Income NetInvestmentIncome	68185000	USD
CY2019Q3	us-gaap	Net Investment Income NetInvestmentIncome	55826000	USD
	us-gaap	Net Investment Income NetInvestmentIncome	158596000	USD
	us-gaap	Net Investment Income NetInvestmentIncome	164949000	USD
CY2020Q3	us-gaap	Gain Loss On Investments GainLossOnInvestments	7721000	USD
CY2019Q3	us-gaap	Gain Loss On Investments GainLossOnInvestments	-2183000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	-24296000	USD
	us-gaap	Gain Loss On Investments GainLossOnInvestments	15295000	USD
CY2020Q3	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	75906000	USD
CY2019Q3	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	53643000	USD
	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	134300000	USD
	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	180244000	USD
CY2020Q3	sigi	Taxoninvestmentincome Taxoninvestmentincome	14676000	USD
CY2019Q3	sigi	Taxoninvestmentincome Taxoninvestmentincome	10884000	USD
	sigi	Taxoninvestmentincome Taxoninvestmentincome	24338000	USD
	sigi	Taxoninvestmentincome Taxoninvestmentincome	34733000	USD
CY2020Q3	sigi	Totalinvestmentsegmentincomeafterfederalincometax Totalinvestmentsegmentincomeafterfederalincometax	61230000	USD
CY2019Q3	sigi	Totalinvestmentsegmentincomeafterfederalincometax Totalinvestmentsegmentincomeafterfederalincometax	42759000	USD
	sigi	Totalinvestmentsegmentincomeafterfederalincometax Totalinvestmentsegmentincomeafterfederalincometax	109962000	USD
	sigi	Totalinvestmentsegmentincomeafterfederalincometax Totalinvestmentsegmentincomeafterfederalincometax	145511000	USD
CY2020Q3	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	75906000	USD
CY2019Q3	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	53643000	USD
	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	134300000	USD
	sigi	Total Investmentsrevenue TotalInvestmentsrevenue	180244000	USD
CY2020Q3	us-gaap	Interest Expense Debt InterestExpenseDebt	7781000	USD
CY2019Q3	us-gaap	Interest Expense Debt InterestExpenseDebt	7397000	USD
	us-gaap	Interest Expense Debt InterestExpenseDebt	23310000	USD
	us-gaap	Interest Expense Debt InterestExpenseDebt	26289000	USD
CY2020Q3	us-gaap	Other General Expense OtherGeneralExpense	3905000	USD
CY2019Q3	us-gaap	Other General Expense OtherGeneralExpense	6369000	USD
	us-gaap	Other General Expense OtherGeneralExpense	19310000	USD
	us-gaap	Other General Expense OtherGeneralExpense	28345000	USD
CY2020Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	85257000	USD
CY2019Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	71178000	USD
	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	143947000	USD
	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	235097000	USD
CY2020Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	85257000	USD
CY2020Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	15382000	USD
CY2020Q3	us-gaap	Net Income Loss NetIncomeLoss	69875000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	37836000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	7947000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	29889000	USD
CY2020Q3	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income Gross NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncomeGross	9239000	USD
CY2020Q3	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income Tax NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncomeTax	1940000	USD
CY2020Q3	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncome	7299000	USD
CY2020Q3	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Before Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleBeforeTax	1000	USD
CY2020Q3	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleTax	1000	USD
CY2020Q3	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Netof Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetofTax	0	USD
CY2020Q3	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securitiesbefore Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesbeforeTax	-515000	USD
CY2020Q3	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesTax	-109000	USD
CY2020Q3	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Netof Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesNetofTax	-406000	USD
CY2020Q3	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Gross DebtSecuritiesAvailableforsaleAllowanceforCreditLossGross	-2853000	USD
CY2020Q3	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Tax DebtSecuritiesAvailableforsaleAllowanceforCreditLossTax	-599000	USD
CY2020Q3	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Net DebtSecuritiesAvailableforsaleAllowanceforCreditLossNet	-2254000	USD
CY2020Q3	sigi	Total Unrealized Gains Losses On Investment Securities Gross TotalUnrealizedGainsLossesOnInvestmentSecuritiesGross	43706000	USD
CY2020Q3	sigi	Total Unrealized Gains Losses On Investment Securities Tax TotalUnrealizedGainsLossesOnInvestmentSecuritiesTax	9178000	USD
CY2020Q3	sigi	Total Unrealized Gains Losseson Investment Securities TotalUnrealizedGainsLossesonInvestmentSecurities	-34528000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-754000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-158000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-596000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	-754000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	-158000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-596000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	44460000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	9336000	USD
CY2020Q3	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	35124000	USD
CY2020Q3	sigi	Comprehensive Income Loss Before Tax ComprehensiveIncomeLossBeforeTax	129717000	USD
CY2020Q3	sigi	Comprehensive Income Loss Tax ComprehensiveIncomeLossTax	24718000	USD
CY2020Q3	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	104999000	USD
CY2019Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	71178000	USD
CY2019Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	15028000	USD
CY2019Q3	us-gaap	Net Income Loss NetIncomeLoss	56150000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	34392000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	7224000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	27168000	USD
CY2019Q3	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Before Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleBeforeTax	3000	USD
CY2019Q3	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleTax	1000	USD
CY2019Q3	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Netof Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetofTax	2000	USD
CY2019Q3	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securitiesbefore Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesbeforeTax	2821000	USD
CY2019Q3	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesTax	592000	USD
CY2019Q3	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Netof Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesNetofTax	2229000	USD
CY2019Q3	sigi	Total Unrealized Gains Losses On Investment Securities Gross TotalUnrealizedGainsLossesOnInvestmentSecuritiesGross	37210000	USD
CY2019Q3	sigi	Total Unrealized Gains Losses On Investment Securities Tax TotalUnrealizedGainsLossesOnInvestmentSecuritiesTax	7815000	USD
CY2019Q3	sigi	Total Unrealized Gains Losseson Investment Securities TotalUnrealizedGainsLossesonInvestmentSecurities	-29395000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-665000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-140000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-525000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	-665000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	-140000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-525000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	37875000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	7955000	USD
CY2019Q3	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	29920000	USD
CY2019Q3	sigi	Comprehensive Income Loss Before Tax ComprehensiveIncomeLossBeforeTax	109053000	USD
CY2019Q3	sigi	Comprehensive Income Loss Tax ComprehensiveIncomeLossTax	22983000	USD
CY2019Q3	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	86070000	USD
	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	143947000	USD
	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	24653000	USD
	us-gaap	Net Income Loss NetIncomeLoss	119294000	USD
	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	132623000	USD
	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	27852000	USD
	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	104771000	USD
	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income Gross NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncomeGross	-18672000	USD
	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income Tax NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncomeTax	-3921000	USD
	sigi	Non Credit Portionof Other Than Temporary Impairments Recognizedin Other Comprehensive Income NonCreditPortionofOtherThanTemporaryImpairmentsRecognizedinOtherComprehensiveIncome	-14751000	USD
	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Before Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleBeforeTax	7000	USD
	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleTax	2000	USD
	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Netof Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetofTax	5000	USD
	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securitiesbefore Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesbeforeTax	9126000	USD
	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesTax	1916000	USD
	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Netof Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesNetofTax	7210000	USD
	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Gross DebtSecuritiesAvailableforsaleAllowanceforCreditLossGross	8010000	USD
	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Tax DebtSecuritiesAvailableforsaleAllowanceforCreditLossTax	1682000	USD
	sigi	Debt Securities Availableforsale Allowancefor Credit Loss Net DebtSecuritiesAvailableforsaleAllowanceforCreditLossNet	6328000	USD
	sigi	Total Unrealized Gains Losses On Investment Securities Gross TotalUnrealizedGainsLossesOnInvestmentSecuritiesGross	131080000	USD
	sigi	Total Unrealized Gains Losses On Investment Securities Tax TotalUnrealizedGainsLossesOnInvestmentSecuritiesTax	27527000	USD
	sigi	Total Unrealized Gains Losseson Investment Securities TotalUnrealizedGainsLossesonInvestmentSecurities	-103553000	USD
	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-2261000	USD
	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-474000	USD
	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-1787000	USD
	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	-2261000	USD
	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	-474000	USD
	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-1787000	USD
	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	133341000	USD
	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	28001000	USD
	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	105340000	USD
	sigi	Comprehensive Income Loss Before Tax ComprehensiveIncomeLossBeforeTax	277288000	USD
	sigi	Comprehensive Income Loss Tax ComprehensiveIncomeLossTax	52654000	USD
	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	224634000	USD
	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	235097000	USD
	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	45333000	USD
	us-gaap	Net Income Loss NetIncomeLoss	189764000	USD
	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	220864000	USD
	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	46381000	USD
	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	174483000	USD
	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Before Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleBeforeTax	33000	USD
	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleTax	7000	USD
	sigi	Amortization Of Net Unrealized Gains Losses On Held To Maturity Transferred From Available For Sale Netof Tax AmortizationOfNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetofTax	26000	USD
	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securitiesbefore Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesbeforeTax	444000	USD
	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesTax	93000	USD
	sigi	Oci Reclassification Adjustmentfrom Aoc Ifor Writedownof Securities Netof Tax OCIReclassificationAdjustmentfromAOCIforWritedownofSecuritiesNetofTax	351000	USD
	sigi	Total Unrealized Gains Losses On Investment Securities Gross TotalUnrealizedGainsLossesOnInvestmentSecuritiesGross	221275000	USD
	sigi	Total Unrealized Gains Losses On Investment Securities Tax TotalUnrealizedGainsLossesOnInvestmentSecuritiesTax	46467000	USD
	sigi	Total Unrealized Gains Losseson Investment Securities TotalUnrealizedGainsLossesonInvestmentSecurities	-174808000	USD
	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax	-1993000	USD
	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossTax	-419000	USD
	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	-1574000	USD
	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	-1993000	USD
	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	-419000	USD
	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-1574000	USD
	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	223268000	USD
	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	46886000	USD
	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	176382000	USD
	sigi	Comprehensive Income Loss Before Tax ComprehensiveIncomeLossBeforeTax	458365000	USD
	sigi	Comprehensive Income Loss Tax ComprehensiveIncomeLossTax	92219000	USD
	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	366146000	USD
	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-1787000	USD

Files In Submission

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sigi-ex3229302020xq3.htm	Edgar Link	pending

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$SIGI
Selective Insurance Group Inc Stock $sigi

2020 Q4 Form 10-Q Financial Statement

#000023055720000023 Filed on October 29, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$SIGI Selective Insurance Group Inc Stock $sigi

2020 Q4 Form 10-Q Financial Statement

#000023055720000023 Filed on October 29, 2020

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

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$SIGI
Selective Insurance Group Inc Stock $sigi