CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 170,587	$ (113,363)
Available-for-sale securities:
Unrealized holding losses, net of tax effect	(844)	(1,325)
Reclassification of realized transactions, net of tax effect	0	82
Defined benefit plans:
Actuarial losses related to defined benefit pension plans, net of tax benefit of $926 and $3,003, respectively	(4,114)	(6,805)
Reclassification of realized transactions, net of tax effect	203	0
Change in net foreign currency translation adjustment	0	(3,023)
Other comprehensive income (loss), net of tax effect	(4,755)	(11,071)
Comprehensive income (loss)	$ 165,832	$ (124,434)