Provision for Taxes (Significant components of deferred tax assets and liabilities) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018
Deferred tax assets:
Net operating loss and credit carry forwards	$ 90,061	$ 3,136
Accrued expenses	105,727	104,309
Policy benefits and losses, claims and loss expenses payable, net	16,515	11,148
Total deferred tax assets	212,303	118,593
Deferred tax liabilities:
Property, plant and equipment	940,433	741,607
Deferred policy acquisition costs	14,191	12,995
Unrealized gains	4,223	18,863
Other	4,426	3,236
Total deferred tax liabilities	963,273	776,701
Net deferred tax liability	$ 750,970	$ 658,108