Financial Guarantee Insurance Contracts - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Insurance [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered					$ 8,765					$ 8,765	$ 1,397
Reinsurance Payable	$ 53,002				29,666				$ 53,002	29,666
Reinsurance recoveries of losses included in losses and loss expenses									(191,151)	(113,622)	(52,960)
Amortization of intangible assets	8,901	$ 6,423	$ 1,139	$ 1,139	1,139	$ 1,079	$ 966	$ 967	17,602	4,152	2,921
Intangible Assets, Gross (Excluding Goodwill)	371,680				71,108				371,680	71,108
Finite-Lived Intangible Assets, Accumulated Amortization	26,905				9,705				26,905	9,705
Intangible assets, less accumulated amortization	344,775				61,403				344,775	61,403
Allowance for Doubtful Accounts, Premiums and Other Receivables	142				69				142	69	0	$ 0
Premium Receivable, Credit Loss Expense (Reversal)									73	69	0
Premium Receivable, Allowance for Credit Loss, Writeoff									0	0	0
Reinsurance Recoverable, Allowance for Credit Loss	100				100				100	100
Reinsurance Recoverables, Gross	306,290								306,290
Net unsecured reinsurance recoverable	232,310								232,310
Reinsurance Recoverable, Gross, All Other	94,726								94,726
Unsecured Reinsurance Recoverable, All Other	44,329								44,329
Uncollateralized Credit Exposure Supoorted by Unlimited Uncapped Indemnity	35,146				$ 43,688				35,146	43,688
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years									18,231	$ 1,878	$ 0
Financial Guarantee
Insurance [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	36,210								36,210
Financial Guarantee | Assured Guaranty Re Ltd [Member]
Insurance [Line Items]
Reinsurance Recoverables, Gross	20,052								20,052
Net unsecured reinsurance recoverable	16,653								16,653
Property and Casualty, Commercial Insurance | QBE Insurance Corporation
Insurance [Line Items]
Reinsurance Recoverables, Gross	31,502								31,502
Net unsecured reinsurance recoverable	31,502								31,502
Property and Casualty, Commercial Insurance | General Reinsurance Company
Insurance [Line Items]
Reinsurance Recoverables, Gross	135,706								135,706
Net unsecured reinsurance recoverable	$ 117,537								$ 117,537
Maximum [Member] | Furniture and Fixtures [Member]
Insurance [Line Items]
Useful Life - Years	5 years								5 years