XML 129 R97.htm IDEA: XBRL DOCUMENT
v3.20.4

Segment Information (Income From Continuing Operations, Before and After Federal Income Tax) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Net investment income | $ 68,511 | $ 68,185 | $ 34,444 | $ 55,967 | $ 57,594 | $ 55,826 | $ 58,505 | $ 50,618 | $ 227,107 | $ 222,543 | $ 195,336
Net realized and unrealized investment (losses) gain | $ 20,079 | $ 7,721 | $ 12,649 | $ (44,666) | $ (873) | $ (2,183) | $ 4,027 | $ 13,451 | (4,217) | 14,422 | (54,923)
Tax on investment income |  |  |  |  |  |  |  |  | 41,609 | 45,301 | 19,560
Total investment income, after federal income tax |  |  |  |  |  |  |  |  | 181,281 | 191,664 | 120,853
Total investment revenues |  |  |  |  |  |  |  |  | 222,890 | 236,965 | 140,413
Standard Commercial Lines [Member] |  |  |  |  |  |  |  |  |  |  |
Underwriting gain (loss), before federal income tax |  |  |  |  |  |  |  |  | 151,731 | 145,990 | 109,104
Underwriting gain (loss), after federal income tax |  |  |  |  |  |  |  |  | $ 119,867 | $ 115,332 | $ 86,192
Combined Ratio |  |  |  |  |  |  |  |  | 92.90% | 92.90% | 94.30%
Return on Equity |  |  |  |  |  |  |  |  | 5.10% | 5.80% | 4.90%
Standard Personal Lines |  |  |  |  |  |  |  |  |  |  |
Underwriting gain (loss), before federal income tax |  |  |  |  |  |  |  |  | $ (15,508) | $ 8,260 | $ 12,764
Underwriting gain (loss), after federal income tax |  |  |  |  |  |  |  |  | $ (12,251) | $ 6,525 | $ 10,084
Combined Ratio |  |  |  |  |  |  |  |  | 105.20% | 97.30% | 95.80%
Return on Equity |  |  |  |  |  |  |  |  | (0.50%) | 0.30% | 0.60%
E&S Lines [Member] |  |  |  |  |  |  |  |  |  |  |
Underwriting gain (loss), before federal income tax |  |  |  |  |  |  |  |  | $ 126 | $ 9,743 | $ (695)
Underwriting gain (loss), after federal income tax |  |  |  |  |  |  |  |  | $ 100 | $ 7,697 | $ (549)
Combined Ratio |  |  |  |  |  |  |  |  | 99.90% | 95.90% | 100.30%
Return on Equity |  |  |  |  |  |  |  |  | 0.00% | 0.40% | 0.00%
Investments SIGI |  |  |  |  |  |  |  |  |  |  |
Return on Equity |  |  |  |  |  |  |  |  | 7.80% | 9.60% | 6.90%

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

X
- Definition Amount of realized and unrealized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27405-111563 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c),9(a)) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 + 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/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)) -URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 + Details
Name: | us-gaap_NetInvestmentIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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: |