Provision for Taxes (Significant components of deferred tax assets and liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Deferred tax assets:
Net operating loss and credit carry forwards	$ 3,136	$ 1,948
Accrued expenses	104,309	168,331
Policy benefits and losses, claims and loss expenses payable, net	11,148	21,287
Total deferred tax assets	118,593	191,566
Deferred tax liabilities:
Property, plant and equipment	741,607	986,334
Deferred policy acquisition costs	12,995	20,901
Unrealized gains	18,863	19,140
Other	3,236	200
Total deferred tax liabilities	776,701	1,026,575
Net deferred tax liability	$ 658,108	$ 835,009