Insurance Contracts Financial Guarantee Insurance Contracts - Components of Loss and Loss Expense Reserves and Subrogation Recoverable (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered		$ 56,190
Policyholder Benefits and Claims Incurred, Ceded	$ 45,601	45,778
Liability for Claims and Claims Adjustment Expense	487,261		$ 459,990
Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables	$ 487,261	$ 373,105	$ 459,990	$ 349,062

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

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