XML 72 R38.htm IDEA: XBRL DOCUMENT v2.4.1.9
Investments (OTTI by Asset Type) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
OTTI Losses Gross $ 2,094us-gaap_ImpairmentOfInvestments $ 963us-gaap_ImpairmentOfInvestments
Other-than-temporary impairments on fixed income securities recognized in other comprehensive income 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterest 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterest
OTTI Losses Recognized in Earnings 2,094us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet 963us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet
Residential Mortgage Backed Securities [Member] | AFS Fixed Income Securities [Member]    
OTTI Losses Gross 1us-gaap_ImpairmentOfInvestments
/ us-gaap_InvestmentTypeAxis
= sigi_AFSFixedIncomeSecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
Other-than-temporary impairments on fixed income securities recognized in other comprehensive income 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterest
/ us-gaap_InvestmentTypeAxis
= sigi_AFSFixedIncomeSecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
OTTI Losses Recognized in Earnings 1us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet
/ us-gaap_InvestmentTypeAxis
= sigi_AFSFixedIncomeSecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
 
AFS Fixed Income Securities [Member]    
OTTI Losses Gross 1,010us-gaap_ImpairmentOfInvestments
/ sigi_ScheduleOfOttiByAssetTypeAxis
= sigi_AFSFixedIncomeSecuritiesMember
 
Other-than-temporary impairments on fixed income securities recognized in other comprehensive income 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterest
/ sigi_ScheduleOfOttiByAssetTypeAxis
= sigi_AFSFixedIncomeSecuritiesMember
 
OTTI Losses Recognized in Earnings 1,010us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet
/ sigi_ScheduleOfOttiByAssetTypeAxis
= sigi_AFSFixedIncomeSecuritiesMember
 
AFS Fixed Income Securities [Member] | Corporate Securities [Member]    
OTTI Losses Gross 1,009us-gaap_ImpairmentOfInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= sigi_AFSFixedIncomeSecuritiesMember
 
Other-than-temporary impairments on fixed income securities recognized in other comprehensive income 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterest
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= sigi_AFSFixedIncomeSecuritiesMember
 
OTTI Losses Recognized in Earnings 1,009us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet
/ us-gaap_InvestmentTypeAxis
= us-gaap_CorporateDebtSecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= sigi_AFSFixedIncomeSecuritiesMember
 
Total AFS Securities [Member] | Equity Securities [Member]    
OTTI Losses Gross 1,084us-gaap_ImpairmentOfInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
963us-gaap_ImpairmentOfInvestments
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
Other-than-temporary impairments on fixed income securities recognized in other comprehensive income 0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterest
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
0us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionInOtherComprehensiveIncomeLossBeforeTaxIncludingPortionAttributableToNoncontrollingInterest
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
OTTI Losses Recognized in Earnings $ 1,084us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember
$ 963us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet
/ us-gaap_InvestmentTypeAxis
= us-gaap_EquitySecuritiesMember
/ sigi_ScheduleOfOttiByAssetTypeAxis
= us-gaap_AvailableforsaleSecuritiesMember