XML 109 R79.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Reinsurance Allowance for Credit Losses (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items] |  |
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance | $ 1,777 | $ 4,400
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance | 1,600 | 1,777
Current period provision for expected credit losses | (177) | 280
Write-offs charged against the allowance for credit losses | 0 | 0
Recoveries | 0 | 0
Current period provision for expected credit losses | (177) | 280
Write-offs charged against the allowance for credit losses | 0 | 0
Recoveries | 0 | 0
Accounting Standards Update 2016-13 [Member] |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance | 1,777 | 1,497
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance |  | 1,777
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments, Gross [Member] | Accounting Standards Update 2016-13 [Member] | Retained Earnings [Member] |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance | $ 0 | (2,903)
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance |  | $ 0

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_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of the write-down or write-off of a receivable from a reinsurer. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
Name: | us-gaap_ReinsuranceLossOnUncollectibleAccountsInPeriodAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of increase in allowance for credit loss on reinsurance recoverable, from recovery. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
Name: | us-gaap_ReinsuranceRecoverableAllowanceForCreditLossRecovery
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of expense (reversal of expense) for expected credit loss on reinsurance recoverable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 + Details
Name: | us-gaap_ReinsuranceRecoverableCreditLossExpenseReversal
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of allowance for credit loss on reinsurance recoverable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446 + Details
Name: | us-gaap_ReinsuranceRecoverablesAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | srt_CumulativeEffectPeriodOfAdoptionAxis=us-gaap_AccountingStandardsUpdate201613Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | sigi_AllowanceforCreditLossesAxis=sigi_ReinsuranceRecoverableforPaidandUnpaidClaimsandClaimsAdjustmentsGrossMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_RetainedEarningsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |