XML 60 R48.htm IDEA: XBRL DOCUMENT v3.19.2

Indebtedness (Short Term Debt Activity) (Details) - Two Point Sixty Four Percent Borrowing from Federal Home Loan Bank Due March 28, 2019 [Member] $ in Millions	Jun. 30, 2019 USD ($)
Short-term Debt [Line Items]
Federal Home Loan Bank Advances	$ 50
Federal Home Loan Bank, Advances, Interest Rate	2.64%

X

- Definition

Amount of Federal Home Loan Bank (FHLBank) advances to member financial institutions.

+ References

No definition available.

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvances
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Interest rate of advances made and reported by Federal Home Loan Bank (FHLBank).

+ References

No definition available.

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvancesInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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_ShortTermDebtLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=sigi_TwoPointSixtyFourPercentBorrowingfromFederalHomeLoanBankDueMarch282019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: