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, 2025 USD ($) Claim	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 1,973,212
Total IBNR Plus Expected Development on Reported Claims	(18,647)
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	1,566,385
All outstanding liabilities before 2012, net of reinsurance	100,681
Liabilities for loss and loss adjustment expenses, net of reinsurance	507,508
Accident Year 2016 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	195,760	$ 197,359	$ 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	5,395
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 180,382	179,521	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	$ 202,037	203,443	206,293	208,360	211,964	220,096	234,587	244,098	244,094
Total IBNR Plus Expected Development on Reported Claims	$ 4,087
Cumulative Number of Claims Reported | Claim	5,214
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 189,023	186,798	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	$ 201,974	203,456	205,001	208,517	217,369	235,641	250,487	250,487
Total IBNR Plus Expected Development on Reported Claims	$ 3,851
Cumulative Number of Claims Reported | Claim	5,478
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 189,256	187,196	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	$ 203,056	203,072	206,109	214,123	227,246	241,344	241,344
Total IBNR Plus Expected Development on Reported Claims	$ 3,718
Cumulative Number of Claims Reported | Claim	5,225
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 184,463	180,586	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	$ 194,042	200,698	207,047	214,500	220,710	220,710
Total IBNR Plus Expected Development on Reported Claims	$ 7,956
Cumulative Number of Claims Reported | Claim	4,392
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 166,910	162,703	153,974	137,411	109,882	$ 50,113
Claim Frequency	13.96%
Accident Year 2021 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 206,414	211,548	215,232	222,715	222,715
Total IBNR Plus Expected Development on Reported Claims	$ 3,853
Cumulative Number of Claims Reported | Claim	4,325
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 182,265	174,454	159,864	130,288	$ 52,292
Claim Frequency	15.10%
Accident Year 2022 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 185,894	190,117	192,907	192,907
Total IBNR Plus Expected Development on Reported Claims	$ (92)
Cumulative Number of Claims Reported | Claim	4,093
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 151,449	138,000	110,494	$ 50,954
Claim Frequency	14.50%
Accident Year 2023 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 188,080	189,659	189,659
Total IBNR Plus Expected Development on Reported Claims	$ 7,289
Cumulative Number of Claims Reported | Claim	3,945
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 138,084	107,823	$ 47,207
Claim Frequency	13.90%
Accident Year 2024 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 192,153	192,153
Total IBNR Plus Expected Development on Reported Claims	$ (31,986)
Cumulative Number of Claims Reported | Claim	3,792
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 125,418	$ 52,869
Claim Frequency	13.13%
Accident Year 2025 [Member]
Claims Development [Line Items]
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 203,802
Total IBNR Plus Expected Development on Reported Claims	$ (22,014)
Cumulative Number of Claims Reported | Claim	3,887
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 59,135
Claim Frequency	12.94%