XML 55 R40.htm IDEA: XBRL DOCUMENT
v3.21.2

Investments (Net Realized and Unrealized Investment Gains and (Losses)) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Gain (Loss) on Securities [Line Items] |  |  |  |
Gross gains on sales | $ 7,151 | $ 2,975 | $ 12,906 | $ 15,129
Gross losses on sales | (2,505) | (2,402) | (8,787) | (7,841)
Debt and Equity Securities, Realized Gain (Loss) | 4,646 | 573 | 4,119 | 7,288
Net unrealized gains (losses) on equity securities | (3,111) | 4,338 | 15,830 | (7,098)
Losses on securities for which we have the intent to sell | (30) | (44) | (483) | (16,259)
Net realized and unrealized investment gains (losses) | 177 | 7,721 | 15,353 | (24,296)
Available-for-sale Securities [Member] |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |
Net credit loss benefit (expense) on fixed maturities | (1,334) | 2,853 | (4,059) | (8,011)
Held-to-maturity Securities [Member] |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |
Net credit loss benefit (expense) on fixed maturities | 6 | 3 | (54) | 4
Commercial Mortgage Loans [Member] |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |
Net credit loss benefit (expense) on fixed maturities | $ 0 | $ (2) | $ 0 | $ (220)

X
- Definition The credit loss expensed during the period on investment portfolio. + References No definition available. + Details
Name: | sigi_Creditlossexpenseoninvestmentportfolio
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This item represents the gross gain realized on sales of debt and equity investments. + References No definition available. + Details
Name: | sigi_DebtAndEquitySecuritiesRealizedGains
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This item represents the gross losses realized on the sale of debt and equity investments. + References No definition available. + Details
Name: | sigi_DebtAndEquitySecuritiesRealizedLosses
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Losses on investment securities for which we have the intent to sell + References No definition available. + Details
Name: | sigi_LossesOnInvestmentSecuritiesForWhichWeHaveTheIntentToSell
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of realized gain (loss) on investment in debt and equity securities. + References No definition available. + Details
Name: | us-gaap_DebtAndEquitySecuritiesRealizedGainLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + 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(3)(d)) -URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=123583765&loc=SL75117546-209714 + Details
Name: | us-gaap_EquitySecuritiesFvNiUnrealizedGainLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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=123581744&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=123367319&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=123570139&loc=d3e3602-108585 + Details
Name: | us-gaap_GainLossOnInvestments
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_ScheduleOfGainLossOnInvestmentsIncludingMarketableSecuritiesAndInvestmentsHeldAtCostIncomeStatementReportedAmountsSummaryLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_AvailableforsaleSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_HeldtomaturitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=sigi_CommercialMortgageLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |