Losses and Loss Adjustment Expenses Incurred and Paid - Schedule of Cumulative Paid Losses and Loss Adjustment Expenses, Net of Reinsurance (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	$ 1,626,199
Total outstanding reserves for unpaid losses and LAE, net of reinsurance	160,310
Accident Year 2007
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	230,860	$ 230,873	$ 230,892	$ 230,891	$ 231,493	$ 228,304	$ 225,978	$ 222,406	$ 210,678	$ 157,162
Accident Year 2008
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	177,154	176,907	176,331	175,700	174,688	172,768	169,373	160,366	$ 122,207
Accident Year 2009
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	142,654	142,441	142,294	141,399	139,436	135,701	127,355	$ 92,372
Accident Year 2010
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	133,896	133,648	132,989	131,878	128,843	120,301	$ 87,319
Accident Year 2011
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	125,383	125,012	123,888	120,790	113,199	$ 82,945
Accident Year 2012
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	139,781	137,968	133,397	123,869	$ 89,159
Accident Year 2013
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	141,444	134,931	124,021	$ 88,726
Accident Year 2014
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	162,702	144,943	$ 98,437
Accident Year 2015
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	208,533	$ 129,216
Accident Year 2016
Claims Development [Line Items]
Cumulative paid losses and loss adjustment expenses, net of reinsurance	$ 163,792