Information for Company's United States Insurance Companies, Net of Intercompany Eliminations as Determined in Accordance With Sap (Detail) - U.S. Insurance Companies - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statutory Accounting Practices [Line Items]
Statutory capital and surplus, as of end of period	$ 323,144	$ 318,101	$ 253,362
Statutory net income (loss)	$ 35,618	$ 48,633	$ 36,003