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, 2023 USD ($) Claim	Dec. 31, 2022 USD ($)	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 ($)	Dec. 31, 2014 USD ($)
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 2,035,580
Total IBNR Plus Expected Development on Reported Claims	44,927
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	1,583,083
All outstanding liabilities before 2012, net of reinsurance	101,752
Liabilities for loss and loss adjustment expenses, net of reinsurance	554,248
Accident Year 2014 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	209,210	$ 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	$ 4,097
Cumulative Number of Claims Reported | Claim	5,841
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 195,409	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	$ 205,556	207,086	207,929	211,758	220,965	235,471	252,514	262,573	262,573
Total IBNR Plus Expected Development on Reported Claims	$ 4,374
Cumulative Number of Claims Reported | Claim	5,517
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 190,588	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	$ 198,566	201,604	202,820	209,214	218,005	241,406	250,491	250,491
Total IBNR Plus Expected Development on Reported Claims	$ 4,691
Cumulative Number of Claims Reported | Claim	5,394
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 178,572	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	$ 206,293	208,360	211,964	220,096	234,587	244,098	244,094
Total IBNR Plus Expected Development on Reported Claims	$ 5,324
Cumulative Number of Claims Reported | Claim	5,214
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 185,690	183,696	175,733	166,448	151,427	122,552	$ 56,951
Claim Frequency	14.69%
Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 205,001	208,517	217,369	235,641	250,487	250,487
Total IBNR Plus Expected Development on Reported Claims	$ 4,347
Cumulative Number of Claims Reported | Claim	5,477
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 184,797	181,081	172,423	152,328	126,057	$ 62,061
Claim Frequency	15.23%
Accident Year 2019 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 206,109	214,123	227,246	241,344	241,344
Total IBNR Plus Expected Development on Reported Claims	$ 5,672
Cumulative Number of Claims Reported | Claim	5,223
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 176,488	168,448	154,391	120,512	$ 58,884
Claim Frequency	15.28%
Accident Year 2020 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 207,047	214,500	220,710	220,710
Total IBNR Plus Expected Development on Reported Claims	$ 13,909
Cumulative Number of Claims Reported | Claim	4,391
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 153,974	137,411	109,882	$ 50,113
Claim Frequency	13.95%
Accident Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 215,232	222,715	222,715
Total IBNR Plus Expected Development on Reported Claims	$ 2,894
Cumulative Number of Claims Reported | Claim	4,304
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 159,864	130,288	$ 52,292
Claim Frequency	15.02%
Accident Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 192,907	192,907
Total IBNR Plus Expected Development on Reported Claims	$ (12,814)
Cumulative Number of Claims Reported | Claim	4,065
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 110,494	$ 50,954
Claim Frequency	14.40%
Accident Year 2023 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 189,659
Total IBNR Plus Expected Development on Reported Claims	$ 12,433
Cumulative Number of Claims Reported | Claim	3,715
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 47,207
Claim Frequency	13.09%