XML 112 R84.htm IDEA: XBRL DOCUMENT
v3.6.0.2

Reserve for Losses and Loss Expenses Reserve for Losses and Loss Expenses (Reconciliation of Claims Development to Liability) (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Net outstanding liabilities | $ 1,234,797 | $ 1,148,541 | $ 1,157,501 |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 2,944,432 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 611,200 | 551,019 | 571,978 | $ 540,839
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Accumulated Unallocated Claim Adjustment Expense | 136,087 |  |  |
Liability for Claims and Claims Adjustment Expense | 3,691,719 | $ 3,517,728 | $ 3,477,870 | $ 3,349,770
General Liability [Member] | Standard Commercial Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 1,070,929 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 179,997 |  |  |
General Liability [Member] | E&S Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 243,613 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 25,741 |  |  |
Workers Compensation [Member] | Standard Commercial Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 936,766 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 223,327 |  |  |
Commercial Automobile [Member] | Standard Commercial Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 402,281 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 17,373 |  |  |
Business Owners' Policies [Member] | Standard Commercial Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 86,802 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 7,012 |  |  |
Commercial Property [Member] | Standard Commercial Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 42,279 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 13,615 |  |  |
Commercial Property [Member] | E&S Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 13,251 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 468 |  |  |
Other Commercial [Member] | Standard Commercial Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 11,389 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 2,613 |  |  |
Total standard Commercial Lines [Member] | Standard Commercial Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 2,550,446 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 443,937 |  |  |
Total standard Commercial Lines [Member] | E&S Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 256,864 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 26,209 |  |  |
Personal Automobile [Member] | Standard Personal Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 90,416 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 55,223 |  |  |
Homeowners [Member] | Standard Personal Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 38,978 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 3,206 |  |  |
Other Personal [Member] | Standard Personal Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 7,728 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 82,625 |  |  |
Standard Personal Lines [Member] | Standard Personal Lines [Member] |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 137,122 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | $ 141,054 |  |  |

X
- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred and costs incurred in the claim settlement process. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to the ceding insurer but not yet paid and amounts expected for incurred losses and settlement expenses, which have not yet been reported to the ceding insurer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=65670824&loc=d3e14764-158437 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21412-158489 + Details
Name: | us-gaap_ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4B -URI http://asc.fasb.org/extlink&oid=65670685&loc=SL65671311-158438 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4C -URI http://asc.fasb.org/extlink&oid=65670685&loc=SL65671315-158438 + Details
Name: | us-gaap_ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of liability for unallocated claim adjustment expense for short-duration insurance contracts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 4C -URI http://asc.fasb.org/extlink&oid=65670685&loc=SL65671315-158438 + Details
Name: | us-gaap_ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseAccumulatedUnallocatedClaimAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=us-gaap_GeneralLiabilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | sigi_LineOfBusinessBySegmentAxis=sigi_StandardCommercialLinesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | sigi_LineOfBusinessBySegmentAxis=sigi_ESLinesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_WorkersCompensationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_CommercialAutomobileMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_BusinessOwnersPoliciesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_OtherCommercialMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_TotalCommercialLinesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_PersonalAutomobileMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | sigi_LineOfBusinessBySegmentAxis=us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_HomeownersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_OtherPersonalMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |