Summary of Business Segment Information (Parenthetical) (Detail) (Insurance Operations, USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Insurance Operations
Segment Reporting Information [Line Items]
Federal excise tax relating to cessions from Insurance Operations to Reinsurance Operations	$ 246	$ 227	$ 482	$ 475

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