XML 152 R124.htm IDEA: XBRL DOCUMENT
v3.6.0.2

Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Deferred policy acquisition costs | $ 222,564 | $ 213,159 | $ 185,608
Reserve for loss and loss expenses | 3,691,719 | 3,517,728 | 3,477,870
Unearned premiums | 1,262,819 | 1,169,710 | 1,095,819
Net premiums earned | 2,149,572 | 1,989,909 | 1,852,609
Net investment income | 125,817 | 134,487 | 165,307
Losses and loss expenses incurred | 1,234,797 | 1,148,541 | 1,157,501
Amortization of deferred policy acquisition costs | 450,328 | 399,435 | 364,295
Other operating expenses | 312,515 | 292,904 | 252,670
Net premiums written | 2,237,288 | 2,069,904 | 1,885,280
Policy acquisition costs | 763,758 | 689,820 | 624,470
Other income | (8,881) | (7,456) | (16,945)
Other expenses | 42,989 | 38,371 | 32,696
Total | 762,843 | 692,339 | 616,965
Standard Commercial Lines [Member] |  |  |
Deferred policy acquisition costs | 181,193 | 171,476 | 147,285
Reserve for loss and loss expenses | 3,098,554 | 2,998,749 | 3,000,796
Unearned premiums | 884,976 | 803,648 | 734,697
Net premiums earned | 1,665,483 | 1,529,442 | 1,415,712
Net investment income | 0 | 0 | 0
Losses and loss expenses incurred | 913,506 | 819,573 | 870,018
Amortization of deferred policy acquisition costs | 367,813 | 323,753 | 295,774
Other operating expenses | 237,730 | 221,620 | 188,699
Net premiums written | 1,745,782 | 1,596,965 | 1,441,047
Standard Personal Lines [Member] |  |  |
Deferred policy acquisition costs | 16,664 | 17,258 | 17,495
Reserve for loss and loss expenses | 286,081 | 265,054 | 279,761
Unearned premiums | 282,111 | 276,533 | 285,777
Net premiums earned | 280,607 | 288,134 | 296,747
Net investment income | 0 | 0 | 0
Losses and loss expenses incurred | 177,749 | 200,237 | 197,182
Amortization of deferred policy acquisition costs | 34,105 | 33,638 | 34,851
Other operating expenses | 56,334 | 52,923 | 48,178
Net premiums written | 281,822 | 283,926 | 292,061
Excess And Surplus Operations [Member] |  |  |
Deferred policy acquisition costs | 24,707 | 24,425 | 20,828
Reserve for loss and loss expenses | 307,084 | 253,925 | 197,313
Unearned premiums | 95,732 | 89,529 | 75,345
Net premiums earned | 203,482 | 172,333 | 140,150
Net investment income | 0 | 0 | 0
Losses and loss expenses incurred | 143,542 | 128,731 | 90,301
Amortization of deferred policy acquisition costs | 48,410 | 42,044 | 33,670
Other operating expenses | 18,451 | 18,361 | 15,793
Net premiums written | 209,684 | 189,013 | 152,172
Investments Segment [Member] |  |  |
Deferred policy acquisition costs | 0 | 0 | 0
Reserve for loss and loss expenses | 0 | 0 | 0
Unearned premiums | 0 | 0 | 0
Net premiums earned | 0 | 0 | 0
Net investment income | 125,817 | 134,487 | 165,307
Losses and loss expenses incurred | 0 | 0 | 0
Amortization of deferred policy acquisition costs | 0 | 0 | 0
Other operating expenses | 0 | 0 | 0
Net premiums written | 0 | 0 | 0
Miscellaneous Income [Member] |  |  |
Other income | (8,881) | (7,456) | (16,598)
Other Income [Member] |  |  |
Other income | 0 | 0 | (347)
Miscellaneous Expense [Member] |  |  |
Other expenses | 7,966 | 9,975 | 9,093
Other Expense [Member] |  |  |
Other expenses | $ 35,023 | $ 28,396 | $ 23,603

X
- Definition Amount of deferred and other policy acquisition costs charged to expense in the period, generally in proportion to related revenue earned, estimated gross profits, or over the customer relationship or some other period. + References No definition available. + Details
Name: | sigi_PolicyAcquisitionCosts
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The total amount of amortization of deferred policy acquisition costs recognized and the amount of other operating expense/income incurred. + References No definition available. + Details
Name: | sigi_TotalOfAmortizationOfDeferredPolicyAcqusitionCostAndOperatingExpenses
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The total amount of other operating cost and expense items that are associated with the entity's normal revenue producing operation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.3) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
Name: | us-gaap_OtherCostAndExpenseOperating
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of revenue and income classified as other. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.4) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 + Details
Name: | us-gaap_OtherIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of amortization of deferred policy acquisition costs recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915 + Details
Name: | us-gaap_SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of insurance benefits, claims, losses and settlement expenses incurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915 + Details
Name: | us-gaap_SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Net amount of deferred policy acquisition costs capitalized on contracts remaining in force on the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915 + Details
Name: | us-gaap_SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of reserves for future policy claims payable and loss expenses to be incurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915 + Details
Name: | us-gaap_SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of net investment income earned. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915 + Details
Name: | us-gaap_SupplementaryInsuranceInformationNetInvestmentIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of other operating expense incurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915 + Details
Name: | us-gaap_SupplementaryInsuranceInformationOtherOperatingExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of premium revenue earned. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915 + Details
Name: | us-gaap_SupplementaryInsuranceInformationPremiumRevenue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of actual written premiums, including, as applicable, premiums from reinsurance assumed and net of premiums on reinsurance ceded. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915 + Details
Name: | us-gaap_SupplementaryInsuranceInformationPremiumsWritten
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of premiums not yet earned. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-16) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915 + Details
Name: | us-gaap_SupplementaryInsuranceInformationUnearnedPremiums
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=sigi_StandardCommercialLinesMember
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: |

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

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

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

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

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

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