Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 349,233	$ 301,568	$ 676,849	$ 575,514
Operating costs and expenses:
Cost of sales (1)	235,668	216,664	468,463	416,493
Selling, general and administrative expenses	52,258	42,417	100,800	78,048
Research and development (1)	10,995	9,536	21,683	18,783
Restructuring charges	0	1,393	(96)	3,006
(Gain) loss on write down and disposal of long-lived assets	312	(39)	823	(20)
Total operating costs and expenses (1)	299,233	269,971	591,673	516,310
Operating income (loss) (1)	50,000	31,597	85,176	59,204
Non-operating (income) expense:
Interest income	(375)	(95)	(753)	(161)
Interest expense	7,287	7,365	14,323	18,325
Acquisition (gain) loss	0	(1,285)	0	(136,873)
Other (income) expense, net	4,011	10,153	(7,360)	16,292
Income (loss) before income taxes and equity income (loss) from equity method investments (1)	39,077	15,459	78,966	161,621
Income tax expense (benefit) (1)	2,000	2,864	6,600	4,004
Income (loss) before equity income (loss) from equity method investments (1)	37,077	12,595	72,366	157,617
Equity income (loss) from equity method investments	64	224	(5)	75,641
Net income (loss) (1)	$ 37,141	$ 12,819	$ 72,361	$ 233,258
Net income (loss) per basic share:
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
Weighted-average shares outstanding:
Basic (in shares)	57,799	49,819	57,570	48,607
Diluted (in shares)	59,197	58,409	59,119	58,136