Summarized Activity in Liability for Unpaid Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Claims and Claims Adjustment Expense [Line Items]
Balance at beginning of period	$ 680,047	$ 675,472	$ 779,466
Less:Ceded reinsurance receivables	108,130	123,201	192,491
Net balance at beginning of period	571,917	552,271	586,975
Purchased reserves, gross	2,007	89,489
Less: Purchased reserves ceded	(45)	12,800
Purchase reserves, net of third party reinsurance	2,052	76,689
Incurred losses and loss adjustment expenses related to:
Current year	321,255	310,066	153,994
Prior years	(57,252)	(34,698)	(16,433)
Total incurred losses and loss adjustment expenses	264,003	275,368	137,561
Paid losses and loss adjustment expenses related to:
Current year	177,006	164,058	55,485
Prior years	140,363	168,353	116,780
Total paid losses and loss adjustment expenses	317,369	332,411	172,265
Net balance at end of period	520,603	571,917	552,271
Plus:Ceded reinsurance receivables	130,439	108,130	123,201
Balance at end of period	$ 651,042	$ 680,047	$ 675,472