XML 42 R30.htm IDEA: XBRL DOCUMENT
v3.4.0.3

Investments (Fair Value and Gross Pre-Tax Net Unrealized Unrecognized Loss of Securities By Length of Time) (Details) - USD ($) $ in Thousands | Mar. 31, 2016 | Dec. 31, 2015
--- | --- | ---
AFS Fair Value, Less than 12 months |  | $ 383,502 | $ 1,449,183
AFS Unrealized Losses, Less than 12 months | [1] | (5,104) | (19,953)
AFS Fair Value, 12 months or longer |  | 179,396 | 141,580
AFS Unrealized Losses, 12 months or longer | [1] | (3,012) | (4,900)
AFS Fixed Income Securities [Member] |  |  |
AFS Fair Value, Less than 12 months |  | 377,562 | 1,416,504
AFS Unrealized Losses, Less than 12 months | [1] | (4,779) | (17,915)
AFS Fair Value, 12 months or longer |  | 179,396 | 141,580
AFS Unrealized Losses, 12 months or longer | [1] | (3,012) | (4,900)
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member] |  |  |
AFS Fair Value, Less than 12 months |  | 0 | 16,006
AFS Unrealized Losses, Less than 12 months | [1] | 0 | (87)
AFS Fair Value, 12 months or longer |  | 400 | 396
AFS Unrealized Losses, 12 months or longer | [1] | (1) | (4)
AFS Fixed Income Securities [Member] | Foreign Government [Member] |  |  |
AFS Fair Value, Less than 12 months |  |  | 1,067
AFS Unrealized Losses, Less than 12 months | [1] |  | (2)
AFS Fair Value, 12 months or longer |  |  | 0
AFS Unrealized Losses, 12 months or longer | [1] |  | 0
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member] |  |  |
AFS Fair Value, Less than 12 months |  | 25,867 | 28,617
AFS Unrealized Losses, Less than 12 months | [1] | (123) | (160)
AFS Fair Value, 12 months or longer |  | 820 | 0
AFS Unrealized Losses, 12 months or longer | [1] | (11) | 0
AFS Fixed Income Securities [Member] | Corporate Securities [Member] |  |  |
AFS Fair Value, Less than 12 months |  | 242,392 | 761,479
AFS Unrealized Losses, Less than 12 months | [1] | (4,315) | (12,671)
AFS Fair Value, 12 months or longer |  | 53,418 | 50,382
AFS Unrealized Losses, 12 months or longer | [1] | (2,100) | (2,850)
AFS Fixed Income Securities [Member] | Asset-Backed Securities [Member] |  |  |
AFS Fair Value, Less than 12 months |  | 73,110 | 197,477
AFS Unrealized Losses, Less than 12 months | [1] | (147) | (807)
AFS Fair Value, 12 months or longer |  | 5,900 | 12,022
AFS Unrealized Losses, 12 months or longer | [1] | (20) | (111)
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member] |  |  |
AFS Fair Value, Less than 12 months |  | 24,891 | 146,944
AFS Unrealized Losses, Less than 12 months | [1] | (82) | (2,196)
AFS Fair Value, 12 months or longer |  | 27,310 | 15,385
AFS Unrealized Losses, 12 months or longer | [1] | (127) | (214)
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member] |  |  |
AFS Fair Value, Less than 12 months |  | 11,302 | 264,914
AFS Unrealized Losses, Less than 12 months | [1] | (112) | (1,992)
AFS Fair Value, 12 months or longer |  | 91,548 | 63,395
AFS Unrealized Losses, 12 months or longer | [1] | (753) | (1,721)
Equity Securities [Member] |  |  |
AFS Fair Value, Less than 12 months |  | 5,940 | 32,679
AFS Unrealized Losses, Less than 12 months | [1] | (325) | (2,038)
AFS Fair Value, 12 months or longer |  | 0 | 0
AFS Unrealized Losses, 12 months or longer | [1] | 0 | 0
Common Stock [Member] | Equity Securities [Member] |  |  |
AFS Fair Value, Less than 12 months |  | 5,940 | 31,148
AFS Unrealized Losses, Less than 12 months | [1] | (325) | (1,998)
AFS Fair Value, 12 months or longer |  | 0 | 0
AFS Unrealized Losses, 12 months or longer | [1] | $ 0 | 0
Preferred Stock [Member] | Equity Securities [Member] |  |  |
AFS Fair Value, Less than 12 months |  |  | 1,531
AFS Unrealized Losses, Less than 12 months | [1] |  | (40)
AFS Fair Value, 12 months or longer |  |  | 0
AFS Unrealized Losses, 12 months or longer | [1] |  | $ 0
[1] | Gross unrealized losses include non-OTTI unrealized amounts and OTTI losses recognized in AOCI. In addition, this column includes remaining unrealized gain or loss amounts on securities that were transferred to an HTM designation in the first quarter of 2009 for those securities that are in a net unrealized/unrecognized loss position.

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | sigi_ScheduleOfFairValueAndGrossPreTaxUnrealizedUnrecognizedLossOfSecuritiesByLengthOfTimeAxis=sigi_AFSFixedIncomeSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | sigi_ScheduleOfFairValueAndGrossPreTaxUnrealizedUnrecognizedLossOfSecuritiesByLengthOfTimeAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CommonStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_NonredeemablePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |