XML 93 R65.htm IDEA: XBRL DOCUMENT v2.4.1.9

Investments (Aggregated Income Statement Summarized Financial Information for Partnerhips in our Alternative Investment Portfolio) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Schedule of Equity Method Investments [Line Items]
Net investment income earned	$ 32,108,000us-gaap_NetInvestmentIncome	$ 34,292,000us-gaap_NetInvestmentIncome	$ 36,774,000us-gaap_NetInvestmentIncome	$ 35,534,000us-gaap_NetInvestmentIncome	$ 35,313,000us-gaap_NetInvestmentIncome	$ 32,457,000us-gaap_NetInvestmentIncome	$ 34,003,000us-gaap_NetInvestmentIncome	$ 32,870,000us-gaap_NetInvestmentIncome	$ 138,708,000us-gaap_NetInvestmentIncome	$ 134,643,000us-gaap_NetInvestmentIncome	$ 131,877,000us-gaap_NetInvestmentIncome
Investments Accounted For Under The Equity Method [Member]
Schedule of Equity Method Investments [Line Items]
Net Investment Income												226,000,000sigi_NetInvestmentIncomeOfEquityMethodInvestees / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember	406,000,000sigi_NetInvestmentIncomeOfEquityMethodInvestees / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember	226,000,000sigi_NetInvestmentIncomeOfEquityMethodInvestees / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember
Realized gains												581,000,000sigi_RealizedGainsLossesOfEquityMethodInvestees / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember	913,000,000sigi_RealizedGainsLossesOfEquityMethodInvestees / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember	1,015,000,000sigi_RealizedGainsLossesOfEquityMethodInvestees / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember
Net change in unrealized appreciation (depreciation)												1,098,000,000sigi_NetChangeInUnrealizedAppreciationDepreciationOfEquityMethodInvestees / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember	382,000,000sigi_NetChangeInUnrealizedAppreciationDepreciationOfEquityMethodInvestees / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember	(100,000,000)sigi_NetChangeInUnrealizedAppreciationDepreciationOfEquityMethodInvestees / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember
Net Income												1,905,000,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember	1,701,000,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember	1,141,000,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss / us-gaap_InvestmentTypeAxis = sigi_InvestmentsAccountedForUnderTheEquityMethodMember
Partnership Interest [Member]
Schedule of Equity Method Investments [Line Items]
Net investment income earned									$ 13,600,000us-gaap_NetInvestmentIncome / us-gaap_InvestmentTypeAxis = us-gaap_PartnershipInterestMember	$ 15,200,000us-gaap_NetInvestmentIncome / us-gaap_InvestmentTypeAxis = us-gaap_PartnershipInterestMember	$ 9,000,000us-gaap_NetInvestmentIncome / us-gaap_InvestmentTypeAxis = us-gaap_PartnershipInterestMember

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 of 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

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(g))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33912-111571



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 28

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612



Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph bb

-Article 1



Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 08

-Paragraph g

-Subparagraph 1, 2

-Article 4



Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph w

-Article 1

+ Details

Name:	us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
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/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 16

-Article 12



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.2)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 2

-Article 7

+ Details

Name:	us-gaap_NetInvestmentIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- 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=us-gaap_PartnershipInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: