XML 33 R55.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Organization (Narrative) (Details) | Dec. 31, 2011
--- | ---
Organization [Abstract] |
Number Of States Which Excess And Surplus Subsidiary Acquired Operates | 50

X
- Definition The number of states in which our E&S subsidiary is authorized to write business in as of the balance sheet date. + References No definition available. + Details
Name: | sigi_NumberOfStatesWhichExcessAndSurplusSubsidiaryAcquiredOperates
Namespace Prefix: | sigi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | sigi_OrganizationAbstract
Namespace Prefix: | sigi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration