XML 51 R40.htm IDEA: XBRL DOCUMENT v3.23.1

Investments (Aggregated Income Statement Summarized Financial Information for Partnerhips in our Alternative Investment Portfolio) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Schedule of Equity Method Investments [Line Items]
Net investment income earned	$ 91,506	$ 72,602
Investments accounted for under the equity method [Member]
Schedule of Equity Method Investments [Line Items]
Net investment income	(70,700)	135,500
Realized gains	1,722,300	2,748,000
Net change in unrealized appreciation	1,443,700	5,178,200
Net income	3,095,300	8,061,700
Alternative Investments [Member]
Schedule of Equity Method Investments [Line Items]
Net investment income earned	$ 7,768	$ 19,128

X

- Definition

The amount of net income (loss) reported by an equity method investment of the entity.

+ References

No definition available.

+ Details

Name:	sigi_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLossSIGI
Namespace Prefix:	sigi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

This item represents the disclosure of summarized financial information, specifically the aggregate change in unrealized appreciation (depreciation), for unconsolidated subsidiaries and 50 percent-or-less owned entities accounted for under the equity method of accounting.

+ References

No definition available.

+ Details

Name:	sigi_NetChangeInUnrealizedAppreciationDepreciationOfEquityMethodInvestees
Namespace Prefix:	sigi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

This item represents the disclosure of summarized financial information, specifically aggregate net investment income, for unconsolidated subsidiaries and 50 percent-or-less owned entities accounted for under the equity method accounting.

+ References

No definition available.

+ Details

Name:	sigi_NetInvestmentIncomeOfEquityMethodInvestees
Namespace Prefix:	sigi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

This item represents the disclosure of summarized financial information, specifically aggregate realized gains (losses), for unconsolidated subsidiaries and 50 percent-or-less owned entities accounted for under the equity method of accounting.

+ References

No definition available.

+ Details

Name:	sigi_RealizedGainsLossesOfEquityMethodInvestees
Namespace Prefix:	sigi_
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 https://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

- 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_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_InvestmentTypeAxis=sigi_InvestmentsAccountedForUnderTheEquityMethodMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=srt_PartnershipInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: