Income Taxes - Significant Portions of Deferred Tax Liabilities and Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Schedule of Deferred Income Tax Assets and Liabilities [Line Items]
Deferred Tax Assets, Net of Valuation Allowance	$ 6,583	$ 15,108
Deferred tax assets:
Net operating loss and capital carryforward	356,575	349,931
OutsidDeferred Tax Assets Outside Basis Difference Discontinued Operationse basis difference		17,044
Deferred Tax Asset, Interest Carryforward	1,714	9,138
Deferred Tax Assets, Investments	4,322	0
Loss reserves	1,400	1,102
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	256,665	3,096
Deferred Tax Assets, Debentures	12,813	0
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation	189	1,423
Deferred Tax Assets, Variable Interest Entities	1,721	0
Other	1,262	429
Sub total deferred tax assets	636,661	382,163
Valuation allowance	630,078	367,055
Insurance intangible	69,929	71,414
Unearned premiums and credit fees	1,871	9,474
Investments	0	3,568
Other	0	787
Deferred Tax Liabilities, Gross	71,800	85,243
Deferred Tax Liabilities, Net	65,217	70,135
Deferred Income Tax Liabilities, Net	65,217	$ 70,135
Discontinued Operations
Deferred tax assets:
Deferred Income Tax Liabilities, Net	20,382
Discontinued Operations, Held-for-Sale or Disposed of by Sale | Ambac Assurance Corporation
Deferred tax assets:
Other liabilities, net	$ 105,772