Business and Basis of Presentation Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2025	Dec. 31, 2023
Derivative [Line Items]
Stockholders' Equity Attributable to Noncontrolling Interest	$ 173,827			$ 197,755
Preferred Stock, Shares Issued	0			0
Redeemable Noncontrolling Interest, Equity, Carrying Amount	$ 185,417	$ 17,079		$ 140,860		$ 17,079
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	258	703
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(708)	(650)
Redeemable Noncontrolling Interest, Equity, Redemption Value	185,417
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	(1,654)	(701)
Noncontrolling Interest, Change in Redemption Value	(907)	53	$ 45
Temporary Equity, Accretion to Redemption Value, Adjustment	907	(53)
Disposal Group, Including Discontinued Operation, Assets	6,392,004	7,454,216			$ 6,267,200
Disposal Group, Including Discontinued Operation, Liabilities	6,003,908				5,887,685
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(30,247)	24,140
Discontinued Operations, Held-for-Sale or Disposed of by Sale | Ambac Assurance Corporation [Member]
Derivative [Line Items]
Disposal Group, Including Discontinued Operation, Consideration, Fair Value, Net	409,759			399,727
Disposal Group, Including Discontinued Operation, Estimated Closing Costs	(7,535)			(7,235)
Disposal Group, Including Discontinued Operation, Consideration, Fair Value, Net, After Allowance For Closing Costs	402,224				$ 392,492
Disposal Group, Including Discontinued Operation, Net Assets Held-For Sale	986,866			962,637
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	(14,496)			(570,145)
Disposal Group, Including Discontinued Operation, Investment	2,286,236			2,226,505
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents	14,394			8,322
Disposal Group, Including Discontinued Operation, Premiums Receivable, Net	218,049			217,096
Disposal Group, Including Discontinued Operation, Reinsurance Recoverable For Paid And Unpaid Claims And Claims Adjustments	25,918			25,274
Disposal Group, Including Discontinued Operation, Prepaid Reinsurance Premiums	76,681			79,074
Disposal Group, Including Discontinued Operation, Subrogation Recoverable	113,636			113,962
Disposal Group, Including Discontinued Operation, Intangible Assets	209,677			213,457
Disposal Group, Including Discontinued Operation, Other Assets	42,632			49,396
Disposal Group, Including Discontinued Operation, Variable Interest Entity Assets	3,989,423			3,904,259
Disposal Group, Including Discontinued Operation, Valuation Allowance On Assets Held-For-Sale	(584,642)			(570,145)
Disposal Group, Including Discontinued Operation, Assets	6,392,004			6,267,200
Disposal Group, Including Discontinued Operation, Unearned Premiums	229,035			228,177
Disposal Group, Including Discontinued Operation, Liability for Claims and Claims Adjustment Expense	601,411			577,167
Disposal Group, Including Discontinued Operation, Reinsurance Payable	55,571			56,404
Disposal Group, Including Discontinued Operation, Liabilities, Long-Term Debt And Accrued Interest	1,062,616			1,046,658
Disposal Group, Including Discontinued Operation, Other Liabilities	100,988			105,772
Disposal Group, Including Discontinued Operation, Variable Interest Entity Liabilities	3,954,287			3,873,507
Disposal Group, Including Discontinued Operation, Liabilities	6,003,908			5,887,685
Disposal Group, Including Discontinued Operation, Revenue	26,797	53,058
Disposal Group, Including Discontinued Operation, Restricted Cash	60,593			$ 57,754
Disposal Group, Including Discontinued Operation, Reclassification From AOCI At Closing	$ (132,778)
Retained Earnings [Member]
Derivative [Line Items]
Noncontrolling Interest, Change in Redemption Value		$ 47