Income Taxes - Significant Portions of Deferred Tax Liabilities and Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Deferred Tax Assets, Net of Valuation Allowance	$ 120,738	$ 7,670
Deferred tax assets:
Net operating loss and capital carryforward	349,931	341,886
Deferred Tax Asset, Interest Carryforward	9,138	3,590
Deferred Tax Assets, Investments	0	1,072
Loss reserves	1,102	162
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	3,096	7,650
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation	1,423	1,423
Other	429	1,625
Sub total deferred tax assets	365,119	357,408
Valuation allowance	244,381	349,738
Insurance intangible	71,414
Deferred Tax Liabilities Outside Basis Difference Discontinued Operations	105,630
Unearned premiums and credit fees	9,474	7,531
Investments	3,568	0
Other	787	139
Deferred Tax Liabilities, Gross	190,873	7,670
Deferred Tax Liabilities, Net	70,135	0
Deferred Income Tax Liabilities, Net	70,135	0
Discontinued Operations
Deferred tax assets:
Deferred Income Tax Liabilities, Net	20,382	19,138
Discontinued Operations, Held-for-Sale or Disposed of by Sale | Ambac Assurance Corporation
Deferred tax assets:
Other liabilities, net	$ 105,772	$ 131,294