Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments Held by Successor Ambac, by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Mar. 31, 2025
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 289,712	$ 266,292
Fixed maturity securities, at fair value		263,179
Amortized Cost, Due in one year or less		135,653
Amortized Cost, Due after one year through five years		58,649
Amortized Cost, Due after five years through ten years		57,785
Amortized Cost, Due after ten years		977
Amortized Cost, Total		253,064
Estimated Fair Value, Due in one year or less		135,297
Estimated Fair Value, Due after one year through five years		57,690
Estimated Fair Value, Due after five years through ten years		55,980
Estimated Fair Value, Due after ten years		977
Estimated Fair Value due, Total		249,944
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	162,124	164,688
Fixed maturity securities, at fair value	157,020	161,569
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	2,475	3,447
Fixed maturity securities, at fair value	2,446	3,445
Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost		2,067
Fixed maturity securities, at fair value		2,049
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	3,131	2,941
Fixed maturity securities, at fair value	3,142	2,954
Fixed Income Securities [Member] | Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	5,049	4,773
Fixed maturity securities, at fair value	$ 5,061	$ 4,787