Provision for Taxes (Significant components of deferred tax assets and liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Mar. 31, 2020
Deferred tax assets:
Net operating loss and credit carry forwards	$ 30,432	$ 25,973
Accrued expenses	109,740	105,171
Policy benefits and losses, claims and loss expenses payable, net	26,799	20,189
Operating leases, assets	19,370	22,353
Total deferred tax assets	186,341	173,686
Deferred tax liabilities:
Property, plant and equipment	1,280,703	1,198,198
Operating leases, liabilities	19,370	22,353
Deferred policy acquisition costs	13,696	12,795
Unrealized gains	48,667	29,873
Other	2,394	4,010
Total deferred tax liabilities	1,364,830	1,267,229
Net deferred tax liability	$ 1,178,489	$ 1,093,543