Summary of Business Segment Information (Parenthetical) (Detail) (Insurance Operations, USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Insurance Operations
Segment Reporting Information [Line Items]
Federal excise tax relating to cessions from Insurance Operations to Reinsurance Operations	$ 264	$ 231	$ 746	$ 706

Federal Excise Tax Expense Cessions From Insurance Operations To Reinsurance Operations

No definition available.

Name:	gbli_FederalExciseTaxExpenseCessionsFromInsuranceOperationsToReinsuranceOperations
Namespace Prefix:	gbli_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration