Liability for Unpaid Losses and Loss Adjustment Expenses - Change in Liability for Unpaid Losses and LAE (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at beginning of period	$ 315,780	$ 195,978	$ 322,465	$ 267,760
Less: Reinsurance recoverable	(118,671)	(66,158)	(119,522)	(123,221)
Net balance at beginning of period	197,109	129,820	202,943	144,539
Incurred related to current year	159,490	150,867	304,690	281,574
Incurred related to prior years	7,731	478	6,494	4,819
Total incurred	167,221	151,345	311,184	286,393
Paid related to current year	151,348	120,724	205,829	182,502
Paid related to prior years	47,481	38,889	142,797	126,878
Total paid	198,829	159,613	348,626	309,380
Net balance at end of period	165,501	121,552	165,501	121,552
Plus: Reinsurance recoverable	113,157	26,107	113,157	26,107
Balance at end of period	$ 278,658	$ 147,659	$ 278,658	$ 147,659