Basic and Diluted Net Income (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income (loss) (1)	$ 37,141	$ 12,819	$ 72,361	$ 233,258
Weighted-average shares outstanding:
Basic (in shares)	57,799	49,819	57,570	48,607
Assumed conversion of employee stock grants (in shares)	1,398	2,284	1,549	2,489
Assumed conversion of warrants (in shares)	0	6,306	0	7,040
Diluted (in shares)	59,197	58,409	59,119	58,136
Net income (loss) per basic share (in usd per share)	$ 0.64	$ 0.26	$ 1.26	$ 4.80
Net income (loss) per diluted share (in usd per share)	$ 0.63	$ 0.22	$ 1.22	$ 4.01
Common stock equivalents that could potentially dilute net income per basic share in the future, but were not included in the computation of diluted earnings per share because the impact would have been antidilutive
Common stock equivalents (in shares)	0	121	0	97