XML 13 R39.htm IDEA: XBRL DOCUMENT v2.4.0.8

Investments (Net Investment Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Net Investment Income [Line Items]
Net investment income earned	$ 36,774	$ 34,003	$ 72,308	$ 66,873
Fixed Income Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	33,781	30,298	64,809	60,387
Equity Securities [Member]
Net Investment Income [Line Items]
Net investment income earned	1,736	1,874	3,185	3,081
Short-Term Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	14	29	33	81
Other Investments [Member]
Net Investment Income [Line Items]
Net investment income earned	3,553	3,869	8,771	7,471
Investment Expenses [Member]
Net Investment Income [Line Items]
Net investment income earned	$ (2,310)	$ (2,067)	$ (4,490)	$ (4,147)

X

- Definition

The income earned from investments in securities and other investments including dividends, interest, and returns on other investments. This item does not include realized gains (losses).

+ References

No definition available.

+ Details

Name:	sigi_NetInvestmentIncomeEarned
Namespace Prefix:	sigi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

Name:	us-gaap_ScheduleOfInvestmentIncomeReportedAmountsByCategoryLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration