Provision for Taxes (Significant components of deferred tax assets and liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Mar. 31, 2016
Deferred tax assets:
Net operating loss and credit carry forwards	$ 1,948	$ 1,462
Accrued expenses	168,331	185,088
Policy benefits and losses, claims and loss expenses payable, net	21,287	21,911
Unrealized losses
Total deferred tax assets	191,566	208,461
Deferred tax liabilities:
Property, plant and equipment	986,334	831,914
Deferred policy acquisition costs	20,901	20,557
Unrealized gains	19,140	9,593
Other	200	9
Total deferred tax liabilities	1,026,575	862,073
Net deferred tax liability	$ 835,009	$ 653,612