Information for United States Insurance Companies & Global Indemnity Reinsurance, Net of Intercompany Eliminations, as Determined in Accordance With SAP and Bermuda (Detail) - Global Indemnity Reinsurance - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statutory Accounting Practices [Line Items]
Statutory capital and surplus, as of end of period	$ 908,433	$ 838,923	$ 713,842
Statutory net income	$ 29,647	$ 32,768	$ 864