ASU 2018 - 12 Transition (Transition Adjustment Stockholders' Equity) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Liability for Future Policy Benefit, before Reinsurance [Abstract]
Deferred acquisition costs and related asset balances	$ 121,224	$ 128,463	$ 131,430
Tax effect	223,216	285,623		$ 106,857	$ 42,319
Stockholders' Equity Attributable to Parent	7,172,445	6,504,191		4,919,091	$ 4,846,436
Accumulated Other Comprehensive Income (Loss) [Member]
Liability for Future Policy Benefit, before Reinsurance [Abstract]
Tax effect	$ 223,216	$ 285,623	$ 1,906	106,857
Cumulative Effect, Period of Adoption, Adjustment [Member]
Liability for Future Policy Benefit, before Reinsurance [Abstract]
Tax effect				64,538
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings [Member]
Liability for Future Policy Benefit, before Reinsurance [Abstract]
Liability For Future Policy Benefits				(4,326)
Market risk benefits				(3,791)
Stockholders' Equity Attributable to Parent				(8,117)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Liability for Future Policy Benefit, before Reinsurance [Abstract]
Liability For Future Policy Benefits				(123,132)
Deferred acquisition costs and related asset balances				41,438
Tax effect				17,156
Stockholders' Equity Attributable to Parent				$ (64,538)