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v2.4.1.9

Consolidation Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Net income | $ 141,827 us-gaap_NetIncomeLoss | $ 106,418 us-gaap_NetIncomeLoss | $ 37,963 us-gaap_NetIncomeLoss
Unrealized holding gains (losses) arising during period | 47,411 us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax | (54,557)us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax | 30,937 us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax
Non-credit portion of other-than-temporary impairments recognized in other comprehensive income | 0 sigi_NonCreditPortionOfOtherThanTemporaryImpairmentsRecognizedInOtherComprehensiveIncome | 50 sigi_NonCreditPortionOfOtherThanTemporaryImpairmentsRecognizedInOtherComprehensiveIncome | 1,660 sigi_NonCreditPortionOfOtherThanTemporaryImpairmentsRecognizedInOtherComprehensiveIncome
Amount reclassified into net income: Held-to-maturity securities | (844)sigi_AmortizationofNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetOfTax | (1,025)sigi_AmortizationofNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetOfTax | (1,581)sigi_AmortizationofNetUnrealizedGainsLossesOnHeldToMaturityTransferredFromAvailableForSaleNetOfTax
Non-credit other-than-temporary impairment | 1,085 sigi_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForNonCreditOtherThanTemporaryImpairedSecuritiesNetOfTax | 9 sigi_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForNonCreditOtherThanTemporaryImpairedSecuritiesNetOfTax | 182 sigi_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForNonCreditOtherThanTemporaryImpairedSecuritiesNetOfTax
Realized gains on available for sale securities | (18,762)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax | (15,301)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax | (6,118)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax
Total unrealized gains (losses) on investment securities | 28,890 sigi_TotalUnrealizedGainsLossesonInvestmentSecurities | (70,824)sigi_TotalUnrealizedGainsLossesonInvestmentSecurities | 25,080 sigi_TotalUnrealizedGainsLossesonInvestmentSecurities
Net actuarial (loss) gain | (35,189)us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax | 38,775 us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax | (17,268)us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax
Amount reclassified into net income: Net actuarial loss | 1,236 us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax | 2,843 us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax | 3,837 us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
Amount reclassified into net income: Prior service cost | 0 us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax | 6 us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax | 97 us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax
Amount reclassified into net income: Curtailment expense | 0 sigi_OtherComprehensiveIncomeLossAmortizationPensionAndOtherPostRetirementBenefitPlansCurtailmentExpenseRecognizedInNetPeriodicBenefitCostNetOfTax | 11 sigi_OtherComprehensiveIncomeLossAmortizationPensionAndOtherPostRetirementBenefitPlansCurtailmentExpenseRecognizedInNetPeriodicBenefitCostNetOfTax | 0 sigi_OtherComprehensiveIncomeLossAmortizationPensionAndOtherPostRetirementBenefitPlansCurtailmentExpenseRecognizedInNetPeriodicBenefitCostNetOfTax
Total defined benefit pension and post-retirement plans | (33,953)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax | 41,635 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax | (13,334)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
Other comprehensive (loss) income | (5,063)us-gaap_OtherComprehensiveIncomeLossNetOfTax | (29,189)us-gaap_OtherComprehensiveIncomeLossNetOfTax | 11,746 us-gaap_OtherComprehensiveIncomeLossNetOfTax
Comprehensive income | $ 136,764 us-gaap_ComprehensiveIncomeNetOfTax | $ 77,229 us-gaap_ComprehensiveIncomeNetOfTax | $ 49,709 us-gaap_ComprehensiveIncomeNetOfTax

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