XML 103 R73.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Investments - Schedule of Investments Pledged as Collateral (Details) $ in Millions | Dec. 31, 2024 USD ($)
--- | ---
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Regulatory Deposits | $ 24.4
Total | 119.3
U.S. government and government agencies |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Regulatory Deposits | 21.4
Total | 21.4
Obligations of states and political subdivisions |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Regulatory Deposits | 3.0
Total | 3.0
RMBS |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Regulatory Deposits | 0.0
Total | 85.3
CMBS |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Regulatory Deposits | 0.0
Total | 9.6
Federal Home Loan Bank of Indianapolis |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | 65.1
Federal Home Loan Bank of Indianapolis | U.S. government and government agencies |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | 0.0
Federal Home Loan Bank of Indianapolis | Obligations of states and political subdivisions |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | 0.0
Federal Home Loan Bank of Indianapolis | RMBS |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | 63.6
Federal Home Loan Bank of Indianapolis | CMBS |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | 1.5
Federal Home Loan Bank of New York |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | 29.8
Federal Home Loan Bank of New York | U.S. government and government agencies |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | 0.0
Federal Home Loan Bank of New York | Obligations of states and political subdivisions |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | 0.0
Federal Home Loan Bank of New York | RMBS |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | 21.7
Federal Home Loan Bank of New York | CMBS |
Financial Instruments Owned and Pledged as Collateral [Line Items] |
Collateral | $ 8.1

X
- Definition Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions. + References No definition available. + Details
Name: | sigi_FairValueOfSecurityOwnedAndPledgedAsCollateral
Namespace Prefix: | sigi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 825 -Name Accounting Standards Codification -Section 50 -Paragraph 1A -Publisher FASB -URI https://asc.fasb.org/1943274/2147477351/944-825-50-1A + Details
Name: | us-gaap_AssetsHeldByInsuranceRegulators
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of the collateral pledged in support of federal home loan bank advances outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 470 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478878/942-470-45-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477734/942-470-50-3 + Details
Name: | us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Namespace Prefix: | us-gaap_
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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-04(11)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479170/946-210-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 860 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481444/860-30-45-1 + Details
Name: | us-gaap_FinancialInstrumentsOwnedAndPledgedAsCollateralLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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

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

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

X
- Details
Name: | srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=srt_FederalHomeLoanBankOfIndianapolisMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=srt_FederalHomeLoanBankOfNewYorkMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |