XML 59 R49.htm IDEA: XBRL DOCUMENT
v3.22.2

Fair Value Measurements (Quantitative Information of Our Financial Assets and Liabilities That Were Disclosed at Fair Value) (Details) - USD ($) $ in Thousands | Jun. 30, 2022 | Dec. 31, 2021
--- | --- | ---
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | $ 31,305 | $ 29,460
Long-term debt, fair value | 507,753 | 651,071
Commercial mortgage loan, fair value | 130,044 | 97,598
Seven Point Twenty Five Percent Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 54,815 | 63,719
Six Point Seventy Percent Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 106,571 | 127,574
Five Point Three Hundred Seventy Five Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 287,115 | 395,652
Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 59,252 | 64,126
Long-term Debt [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 507,753 | 651,071
Obligations of States and Political Subdivisions [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 3,468 | 3,576
Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 27,837 | 25,884
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 0 | 0
Long-term debt, fair value | 0 | 0
Commercial mortgage loan, fair value | 0 | 0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 0 | 0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 0 | 0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Five Point Three Hundred Seventy Five Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 0 | 0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 0 | 0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Obligations of States and Political Subdivisions [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 0 | 0
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 0 | 0
Significant Other Observable Inputs (Level 2) [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 31,305 | 29,460
Long-term debt, fair value | 507,753 | 651,071
Commercial mortgage loan, fair value | 0 | 0
Significant Other Observable Inputs (Level 2) [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 54,815 | 63,719
Significant Other Observable Inputs (Level 2) [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 106,571 | 127,574
Significant Other Observable Inputs (Level 2) [Member] | Five Point Three Hundred Seventy Five Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 287,115 | 395,652
Significant Other Observable Inputs (Level 2) [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 59,252 | 64,126
Significant Other Observable Inputs (Level 2) [Member] | Obligations of States and Political Subdivisions [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 3,468 | 3,576
Significant Other Observable Inputs (Level 2) [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 27,837 | 25,884
Significant Unobservable Inputs (Level 3) [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 0 | 0
Long-term debt, fair value | 0 | 0
Commercial mortgage loan, fair value | 130,044 | 97,598
Significant Unobservable Inputs (Level 3) [Member] | Seven Point Twenty Five Percent Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 0 | 0
Significant Unobservable Inputs (Level 3) [Member] | Six Point Seventy Percent Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 0 | 0
Significant Unobservable Inputs (Level 3) [Member] | Five Point Three Hundred Seventy Five Senior Notes [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 0 | 0
Significant Unobservable Inputs (Level 3) [Member] | Three Point Zero Three Percent Borrowing From Federal Home Loan Bank Due December 16, 2026 [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt, fair value | 0 | 0
Significant Unobservable Inputs (Level 3) [Member] | Obligations of States and Political Subdivisions [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | 0 | 0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Securities [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Fixed income securities, held-to-maturity - fair value | $ 0 | $ 0

X
- Definition Fair value of investment in commercial loan measured at original cost. + References No definition available. + Details
Name: | sigi_Commercialmortgageloanfairvalue
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27232-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123581744&loc=SL120269820-111563 + Details
Name: | us-gaap_HeldToMaturitySecuritiesFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
Name: | us-gaap_LongTermDebtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_SevenPointTwentyFivePercentSeniorNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_SixPointSeventyPercentSeniorNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_FivePointThreeHundredSeventyFiveMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=sigi_ThreePointZeroThreePercentBorrowingFromFederalHomeLoanBankDueDecember162026Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_LongTermDebtMember
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_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |