XML 146 R88.htm IDEA: XBRL DOCUMENT v2.4.1.9

Segment Information (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014
Segment Reporting [Abstract]
Goodwill balance for our Standard Commercial Lines reporting unit	$ 7,849us-gaap_Goodwill	$ 7,849us-gaap_Goodwill
Percentage of net premiums written related to insurance policies written in New Jersey	23.00%sigi_GeographicConcentrationOfNetPremiumsWrittenPercentage

X

- Definition

This item represents the geographic concentration of net premiusm written, reflected as a percentage of New Jersey net written premiums compared to our total net premiums written.

+ References

No definition available.

+ Details

Name:	sigi_GeographicConcentrationOfNetPremiumsWrittenPercentage
Namespace Prefix:	sigi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

+ Details

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

X

- Details

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