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v2.4.1.9

Segment Information (Revenue by Segment) (Details) (USD $) In Thousands, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015 | Mar. 31, 2014
Segment Reporting Information [Line Items] |  |
Total net premiums earned | $ 476,123 us-gaap_PremiumsEarnedNetPropertyAndCasualty | $ 456,495 us-gaap_PremiumsEarnedNetPropertyAndCasualty
Investment Income, Net | 26,917 us-gaap_InvestmentIncomeNet | 35,534 us-gaap_InvestmentIncomeNet
Other income | 1,969 us-gaap_OtherIncome | 9,824 us-gaap_OtherIncome
Net realized investment gains | 18,883 us-gaap_RealizedInvestmentGainsLosses | 7,218 us-gaap_RealizedInvestmentGainsLosses
Total investment revenues | 45,800 sigi_TotalInvestmentRevenues | 42,752 sigi_TotalInvestmentRevenues
Total revenues | 523,892 us-gaap_Revenues | 509,071 us-gaap_Revenues
Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Total revenues | 523,892 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_OperatingSegmentsMember | 509,066 us-gaap_Revenues / us-gaap_StatementBusinessSegmentsAxis = us-gaap_OperatingSegmentsMember
Other Income [Member] |  |
Segment Reporting Information [Line Items] |  |
Other income | 0 us-gaap_OtherIncome / us-gaap_StatementBusinessSegmentsAxis = sigi_OtherRevenueMember | 5 us-gaap_OtherIncome / us-gaap_StatementBusinessSegmentsAxis = sigi_OtherRevenueMember
Standard Commercial Lines [Member] | Commercial Automobile [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 86,355 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_CommercialAutomobileMember | 82,216 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_CommercialAutomobileMember
Standard Commercial Lines [Member] | Workers Compensation [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 68,477 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_WorkersCompensationMember | 69,413 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_WorkersCompensationMember
Standard Commercial Lines [Member] | General Liability [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 114,971 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_GeneralLiabilityMember | 108,818 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_GeneralLiabilityMember
Standard Commercial Lines [Member] | Commercial Property [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 64,563 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 60,186 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember
Standard Commercial Lines [Member] | Business Owners' Policies [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 22,699 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_BusinessOwnersPoliciesMember | 20,869 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_BusinessOwnersPoliciesMember
Standard Commercial Lines [Member] | Bonds Segment [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 5,000 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_SuretySegmentMember | 4,756 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_SuretySegmentMember
Standard Commercial Lines [Member] | Other Commercial [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 3,468 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_OtherCommercialMember | 3,183 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_OtherCommercialMember
Standard Commercial Lines [Member] | Miscellaneous Income [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 1,669 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_MiscellaneousIncomeMember | 8,914 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_MiscellaneousIncomeMember
Standard Commercial Lines [Member] | Total Standard Commercial Lines [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 367,202 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_TotalCommercialLinesMember | 358,355 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardCommercialLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_TotalCommercialLinesMember
Standard Personal Lines [Member] | Miscellaneous Income [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 300 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_MiscellaneousIncomeMember | 905 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_MiscellaneousIncomeMember
Standard Personal Lines [Member] | Personal Automobile [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 37,010 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_PersonalAutomobileMember | 38,226 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_PersonalAutomobileMember
Standard Personal Lines [Member] | Homeowners [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 33,721 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_HomeownersMember | 33,298 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_HomeownersMember
Standard Personal Lines [Member] | Other Personal [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 1,748 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_OtherPersonalMember | 3,294 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = sigi_OtherPersonalMember
Standard Personal Lines [Member] | Total Standard Personal Lines [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 72,779 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | 75,723 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_StandardPersonalLinesMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember
Excess And Surplus Operations [Member] | Commercial Automobile [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 1,730 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_ExcessAndSurplusOperationsMember / us-gaap_StatementBusinessSegmentsAxis = sigi_CommercialAutomobileMember | 1,188 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_ExcessAndSurplusOperationsMember / us-gaap_StatementBusinessSegmentsAxis = sigi_CommercialAutomobileMember
Excess And Surplus Operations [Member] | General Liability [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 26,726 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_ExcessAndSurplusOperationsMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_GeneralLiabilityMember | 21,931 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_ExcessAndSurplusOperationsMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_GeneralLiabilityMember
Excess And Surplus Operations [Member] | Commercial Property [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | 9,655 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_ExcessAndSurplusOperationsMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember | 9,117 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_ExcessAndSurplusOperationsMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember
Excess And Surplus Operations [Member] | Total Standard Personal Lines [Member] |  |
Segment Reporting Information [Line Items] |  |
Total net premiums earned | $ 38,111 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_ExcessAndSurplusOperationsMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember | $ 32,236 us-gaap_PremiumsEarnedNetPropertyAndCasualty / sigi_LineOfBusinessBySegmentAxis = sigi_ExcessAndSurplusOperationsMember / us-gaap_StatementBusinessSegmentsAxis = us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember

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