ASU 2018 - 12 Transition (Effects of Adoption of ASU 2018-12 Balance Sheet) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Statements Adjusted [Abstract]
Deferred policy acquisition costs, net	$ 121,224	$ 128,463		$ 89,749	$ 131,187
Assets	19,058,758	18,100,734	$ 17,327,183	14,651,606	14,693,044
Policy benefits and losses, claims and loss expenses payable	849,113	880,202		909,701	1,040,951
Deferred Income Tax Liabilities, Net	1,447,125	1,329,489		1,199,280	1,182,123
Total liabilities	11,886,313	11,596,543		9,732,515	9,846,608
Accumulated other comprehensive loss	223,216	285,623		106,857	42,319
Retained earnings	7,600,090	7,003,148		5,025,568	5,017,451
Stockholders' Equity Attributable to Parent	7,172,445	6,504,191		4,919,091	4,846,436
Liabilities and Equity	$ 19,058,758	18,100,734		$ 14,651,606	$ 14,693,044
Previously Reported
Statements Adjusted [Abstract]
Deferred policy acquisition costs, net		152,377
Assets		18,124,648	$ 17,299,581
Policy benefits and losses, claims and loss expenses payable		875,034
Deferred Income Tax Liabilities, Net		1,334,427
Total liabilities		11,596,313
Accumulated other comprehensive loss		267,046
Retained earnings		7,008,715
Stockholders' Equity Attributable to Parent		6,528,335
Liabilities and Equity		18,124,648
Effect of adoption
Statements Adjusted [Abstract]
Deferred policy acquisition costs, net		23,914
Assets		23,914
Policy benefits and losses, claims and loss expenses payable		5,168
Deferred Income Tax Liabilities, Net		4,938
Total liabilities		230
Accumulated other comprehensive loss		18,577
Retained earnings		5,567
Stockholders' Equity Attributable to Parent		24,144
Liabilities and Equity		$ 23,914