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v3.23.2

Insider Trading Arrangements | 3 Months Ended
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Jun. 30, 2023
Trading Arrangements [Abstract] |
Non-Rule 10b5-1 Arrangement Adopted | false
Non-Rule 10b5-1 Arrangement Terminated | false
Rule 10b5-1 Arrangement Adopted | false
Rule 10b5-1 Arrangement Terminated | false

X
- Definition ecd_Non-Rule 10b5-1 Arrangement Adopted + References No definition available. + Details
Name: | sigi_Ecd_NonRule10b51ArrangementAdopted
Namespace Prefix: | sigi_
Data Type: | xbrli:booleanItemType
Balance Type: | na
Period Type: | duration

X
- Definition ecd_Non-Rule 10b5-1 Arrangement Terminated + References No definition available. + Details
Name: | sigi_Ecd_NonRule10b51ArrangementTerminated
Namespace Prefix: | sigi_
Data Type: | xbrli:booleanItemType
Balance Type: | na
Period Type: | duration

X
- Definition ecd_Rule 10b5-1 Arrangement Adopted + References No definition available. + Details
Name: | sigi_Ecd_Rule10b51ArrangementAdopted
Namespace Prefix: | sigi_
Data Type: | xbrli:booleanItemType
Balance Type: | na
Period Type: | duration

X
- Definition ecd_Rule 10b5-1 Arrangement Terminated + References No definition available. + Details
Name: | sigi_Ecd_Rule10b51ArrangementTerminated
Namespace Prefix: | sigi_
Data Type: | xbrli:booleanItemType
Balance Type: | na
Period Type: | duration

X
- Definition Trading Arrangements + References No definition available. + Details
Name: | sigi_TradingArrangementsAbstract
Namespace Prefix: | sigi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration