XML 75 R60.htm IDEA: XBRL DOCUMENT
v3.24.1.u1

Segment Information - Income Before and After Federal Income Tax (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Segment Reporting Information [Line Items] |  |
Net investment income earned | $ 107,849 | $ 91,506
Net realized and unrealized investment gains (losses) | (1,635) | 3,344
Total investments segment income, before federal income tax | 106,214 | 94,850
Tax on investments segment income | 21,866 | 19,156
Total investments segment income, after federal income tax | 84,348 | 75,694
Standard Commercial Lines |  |
Segment Reporting Information [Line Items] |  |
Underwriting income (loss), before federal income tax | 10,381 | 38,921
Underwriting income (loss), after federal income tax | $ 8,201 | $ 30,748
Combined ratio | 98.80% | 94.70%
ROE contribution | 1.20% | 5.10%
Standard Personal Lines |  |
Segment Reporting Information [Line Items] |  |
Underwriting income (loss), before federal income tax | $ (5,335) | $ (13,073)
Underwriting income (loss), after federal income tax | $ (4,215) | $ (10,328)
Combined ratio | 105.10% | 116.00%
ROE contribution | (0.60%) | (1.70%)
E&S Lines |  |
Segment Reporting Information [Line Items] |  |
Underwriting income (loss), before federal income tax | $ 13,985 | $ 13,335
Underwriting income (loss), after federal income tax | $ 11,048 | $ 10,535
Combined ratio | 87.60% | 85.00%
ROE contribution | 1.60% | 1.80%
Investments: |  |
Segment Reporting Information [Line Items] |  |
ROE contribution | 12.30% | 12.20%
Total investments segment income, before federal income tax | $ 106,214 | $ 94,850

X
- Definition The after-tax income divided by average stockholders' equity. + References No definition available. + Details
Name: | sigi_ReturnonEquity
Namespace Prefix: | sigi_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Taxes incurred on investment income + References No definition available. + Details
Name: | sigi_TaxOnInvestmentIncome
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The income earned from investments in securities and other investments including dividends, interest, and returns on other investments, including realized and unrealized gains/losses recognized in income, after-tax. + References No definition available. + Details
Name: | sigi_TotalInvestmentSegmentIncomeAfterFederalIncomeTax
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The income earned from investments in securities and other investments including dividends, interest, and returns on other investments, including realized and unrealized gains/losses recognized in income. + References No definition available. + Details
Name: | sigi_TotalInvestmentsRevenue
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition After-tax amount of net premiums earned and other insurance income less net loss and loss expenses incurred, loss adjustment expenses, policy acquisition costs and other underwriting expenses. + References No definition available. + Details
Name: | sigi_UnderwritingIncomeLossAfterFederalIncomeTaxes
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Net premiums earned and other insurance income less net loss and loss expenses incurred, loss adjustment expenses, policy acquisition costs and other underwriting expenses. + References No definition available. + Details
Name: | sigi_UnderwritingIncomeLossBeforeFederalIncomeTaxes
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Ratio of non-life losses and loss expenses, non-life acquisition expenses and non-life general and administrative expenses, to non-life net premiums earned. + References No definition available. + Details
Name: | us-gaap_CombinedRatio
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of realized and unrealized gain (loss) on investment. + References Reference 1: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-28 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c),9(a)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2 + Details
Name: | us-gaap_GainLossOnInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 946 -SubTopic 830 -Name Accounting Standards Codification -Section 55 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480167/946-830-55-10 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)(d)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(4)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 45 -Paragraph 5 -SubTopic 220 -Topic 946 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483581/946-220-45-5 + Details
Name: | us-gaap_NetInvestmentIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_StandardCommercialLinesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_StandardPersonalLinesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_ESLinesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_InvestmentsSIGIMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |