XML 88 R60.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Investments (Number of Securities in an Unrealized Unrecognized Loss Position) (Details) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Percentage Decline in Fair Value Percentage of Amortized Cost | 2.00% | 1.00%
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss | $ 200 | $ 100
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | 878,126
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | (4,961)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 35,686
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | (397)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value |  | 913,812
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | (5,358)
AFS Fixed Maturity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 2,142,433 | 869,566
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (36,948) | (4,664)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 275,174 | 35,686
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (8,119) | (397)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 2,417,607 | 905,252
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | (45,067) | (5,061)
Equity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | 8,560
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | (297)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value |  | 8,560
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | (297)
U.S. Government and Government Agencies [Member] | AFS Fixed Maturity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 6,693 | 23,516
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (174) | (233)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 23,163 | 250
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (418) | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 29,856 | 23,766
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | (592) | (233)
Foreign Government [Member] | AFS Fixed Maturity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 12,208 | 1,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (93) | (11)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 1,482 | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (14) | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 13,690 | 1,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | (107) | (11)
Obligations of States and Political Subdivisions [Member] | AFS Fixed Maturity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 196,798 | 107,514
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (2,074) | (422)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 42,821 | 14,139
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (557) | (160)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 239,619 | 121,653
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | (2,631) | (582)
Corporate Securities [Member] | AFS Fixed Maturity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 1,041,952 | 238,326
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (23,649) | (1,744)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 78,953 | 3,228
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (4,316) | (18)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 1,120,905 | 241,554
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | (27,965) | (1,762)
Collateralized Loan Obligations and Other Asset-Backed Securities [Member] | AFS Fixed Maturity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 516,106 | 74,977
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (6,750) | (196)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 16,800 | 1,655
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (193) | (6)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 532,906 | 76,632
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | (6,943) | (202)
Commercial Mortgage Backed Securities [Member] | AFS Fixed Maturity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 229,338 | 154,267
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (2,548) | (773)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 66,294 | 5,214
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (1,200) | (68)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 295,632 | 159,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | (3,748) | (841)
Residential Mortgage Backed Securities [Member] | AFS Fixed Maturity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value | 139,338 | 269,485
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | (1,660) | (1,285)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value | 45,661 | 11,200
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | (1,421) | (145)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value | 184,999 | 280,685
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ (3,081) | (1,430)
Common Stock [Member] | Equity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | 4,727
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | (226)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value |  | 4,727
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | (226)
Nonredeemable Preferred Stock [Member] | Equity Securities [Member] |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value |  | 3,833
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | (71)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value |  | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value |  | 3,833
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | $ (71)

X
- Definition This item represents the percentage decline in fair value of fixed maturity securities compared to amortized cost that have been in a loss position for more than twelve months. This impairment has been determined to be temporary. + References No definition available. + Details
Name: | sigi_PercentageDeclineInFairValuePercentage
Namespace Prefix: | sigi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition This item represents the sum of (i) the excess of amortized cost over fair value for available-for-sale securities that are in a loss position and (ii) the market fluctuations on held-to-maturity securities from the later of (a) the date a security is designated as held-to-maturity; or (b) the date that an other-than-temporary impairment charge is recognized on a held-to-maturity security for securities that are in an unrecognized loss position. + References No definition available. + Details
Name: | sigi_UnrealizedUnrecognizedLoss
Namespace Prefix: | sigi_
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 twelve months or longer. + References No definition available. + 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 in a continuous loss position. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
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 in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
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 No definition available. + 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 No definition available. + 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 No definition available. + 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_AfsFixedMaturitySecuritiesMember
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_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: | us-gaap_FinancialInstrumentAxis=us-gaap_CommonStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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