Loss and Loss Adjustment Expenses - Development Tables of Incurred and Paid Losses and Allocated Loss Adjustment Expenses Net of Reinsurance (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($) Claim	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 2,083,934
Total IBNR Plus Expected Development on Reported Claims	57,308
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	1,593,043
All outstanding liabilities before 2013, net of reinsurance	92,591
Liabilities for loss and loss adjustment expenses, net of reinsurance	583,482
Accident Year 2013 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	204,026	$ 205,421	$ 207,304	$ 209,184	$ 210,588	$ 214,701	$ 220,457	$ 233,656	$ 241,811	$ 241,810
Total IBNR Plus Expected Development on Reported Claims	$ 6,435
Cumulative Number of Claims Reported | Claim	5,768
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 184,500	183,365	182,465	180,614	177,724	172,479	165,994	150,304	119,507	$ 51,396
Claim Frequency	16.56%
Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 210,096	210,811	212,417	218,386	226,933	235,058	249,097	268,846	268,846
Total IBNR Plus Expected Development on Reported Claims	$ 4,510
Cumulative Number of Claims Reported | Claim	5,841
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 193,192	192,169	191,394	186,129	180,683	169,736	153,320	119,820	$ 53,060
Claim Frequency	14.99%
Accident Year 2015 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 207,086	207,929	211,758	220,965	235,471	252,514	262,573	262,573
Total IBNR Plus Expected Development on Reported Claims	$ 4,415
Cumulative Number of Claims Reported | Claim	5,516
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 189,339	188,145	185,657	182,053	170,461	151,818	121,599	$ 54,141
Claim Frequency	14.25%
Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 201,604	202,820	209,214	218,005	241,406	250,491	250,491
Total IBNR Plus Expected Development on Reported Claims	$ 4,452
Cumulative Number of Claims Reported | Claim	5,393
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 174,134	172,133	166,887	156,860	143,016	115,713	$ 52,238
Claim Frequency	14.23%
Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 208,360	211,964	220,096	234,587	244,098	244,094
Total IBNR Plus Expected Development on Reported Claims	$ 4,939
Cumulative Number of Claims Reported | Claim	5,212
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 183,696	175,733	166,448	151,427	122,552	$ 56,951
Claim Frequency	14.68%
Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 208,517	217,369	235,641	250,487	250,487
Total IBNR Plus Expected Development on Reported Claims	$ 5,268
Cumulative Number of Claims Reported | Claim	5,471
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 181,081	172,423	152,328	126,057	$ 62,061
Claim Frequency	15.21%
Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 214,123	227,246	241,344	241,344
Total IBNR Plus Expected Development on Reported Claims	$ 8,550
Cumulative Number of Claims Reported | Claim	5,218
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 168,448	154,391	120,512	$ 58,884
Claim Frequency	15.26%
Accident Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 214,500	220,710	220,710
Total IBNR Plus Expected Development on Reported Claims	$ 17,039
Cumulative Number of Claims Reported | Claim	4,387
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 137,411	109,882	$ 50,113
Claim Frequency	13.94%
Accident Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 222,715	222,715
Total IBNR Plus Expected Development on Reported Claims	$ (5,162)
Cumulative Number of Claims Reported | Claim	4,273
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 130,288	$ 52,292
Claim Frequency	14.92%
Accident Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 192,907
Total IBNR Plus Expected Development on Reported Claims	$ 6,863
Cumulative Number of Claims Reported | Claim	3,886
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 50,954
Claim Frequency	13.77%