Comprehensive (Loss) Income (Schedule of Reclassifications of Recognized Transactions out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss)	$ (2,962)	$ 121	$ 7,233	$ (658)
Net income	(251,086)	107,175	108,657	27,731
Unrealized holding gains (losses) on available-for-sale securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss)	0	(1,433)	0	(1,522)
Net income	(214)	(1,433)	(630)	(1,522)
Amortization of actuarial loss | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (loss)	$ (214)	$ 0	$ (630)	$ 0