Liability for Unpaid Losses and Loss Adjustment Expenses - Change in Liability for Unpaid Losses and LAE (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at beginning of period	$ 278,658	$ 147,659	$ 322,465	$ 267,760
Less: Reinsurance recoverable	(113,157)	(26,107)	(119,522)	(123,221)
Net balance at beginning of period	165,501	121,552	202,943	144,539
Incurred related to current year	176,092	208,392	480,782	489,966
Incurred related to prior years	11,489	30,085	17,983	34,904
Total incurred	187,581	238,477	498,765	524,870
Paid related to current year	180,473	172,977	386,302	355,479
Paid related to prior years	42,841	43,661	185,638	170,539
Total paid	223,314	216,638	571,940	526,018
Net balance at end of period	129,768	143,391	129,768	143,391
Plus: Reinsurance recoverable	82,720	59,329	82,720	59,329
Balance at end of period	$ 212,488	$ 202,720	$ 212,488	$ 202,720