Financial Guarantee Insurance Contracts - Estimated Future Amortization Expense for Insurance Intangible Asset (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
Amortization Of Intangible Assets [Line Items]
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
2018	34,847								34,847
2019	34,508								34,508
2020	34,508								34,508
2021	34,504								34,504
2022	34,345								34,345
Thereafter	160,850								160,850
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