Provision for Taxes (Significant Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2021	Mar. 31, 2020
Deferred tax assets:
Net operating loss and credit carry forwards	$ 36,978	$ 33,778
Accrued expenses	117,481	112,971
Policy benefits and losses, claims and loss expenses payable, net	33,736	36,374
Unrealized losses	32,856	48,179
Operating leases, assets	11,521	12,058
Total deferred tax assets	232,572	243,360
Deferred tax liabilities:
Property, plant and equipment	1,655,074	1,545,628
Operating leases, liabilities	11,214	12,175
Deferred policy acquisition costs	10,709	12,038
Other	2,700	3,008
Total deferred tax liabilities	1,679,697	1,572,849
Net deferred tax liability	$ 1,447,125	$ 1,329,489	$ 1,199,280	$ 1,182,123