Summarized Activity in Liability for Unpaid Losses and Loss Adjustment Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Insurance [Abstract]
Balance at beginning of period	$ 608,773	$ 613,670	$ 680,031	$ 634,664
Less: Ceded reinsurance receivables	59,834	91,397	109,342	97,243
Net balance at beginning of period	548,939	522,273	570,689	537,421
Incurred losses and loss adjustment expenses related to:
Current year	80,533	92,469	225,022	222,916
Prior years	(6,950)	(11,976)	(23,043)	(27,490)
Total incurred losses and loss adjustment expenses	73,583	80,493	201,979	195,426
Paid losses and loss adjustment expenses related to:
Current year	47,290	53,121	102,806	103,695
Prior years	20,789	27,312	115,419	106,819
Total paid losses and loss adjustment expenses	68,079	80,433	218,225	210,514
Net balance at end of period	554,443	522,333	554,443	522,333
Plus: Ceded reinsurance receivables	78,844	86,274	78,844	86,274
Balance at end of period	$ 633,287	$ 608,607	$ 633,287	$ 608,607