Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Revenues [Abstract]
Net sales (1)	$ 327,616	$ 273,946
Operating costs and expenses:
Cost of sales (1) (2)	232,795	199,829
Selling, general and administrative expenses (2)	48,542	35,631
Research and development (1)	10,688	9,247
Restructuring charges	(96)	1,613
(Gain) loss on write down and disposal of long-lived assets	511	19
Total operating costs and expenses (1)	292,440	246,339
Operating income (loss) (1)	35,176	27,607
Non-operating (income) expense:
Interest income	(378)	(66)
Interest expense	7,036	10,960
Acquisition (gain) loss	0	(135,588)
Other (income) expense, net	(11,371)	6,139
Income (loss) before income taxes and equity income (loss) from equity method investments (1)	39,889	146,162
Income tax expense (benefit) (1)	4,600	1,140
Income (loss) before equity income (loss) from equity method investments (1)	35,289	145,022
Equity income (loss) from equity method investments	(69)	75,417
Net income (loss) (1)	$ 35,220	$ 220,439
Net income (loss) per basic share:
Net income (loss) per basic share (in usd per share)	$ 0.61	$ 4.65
Net income (loss) per diluted share (in usd per share)	$ 0.60	$ 3.82
Weighted-average shares outstanding:
Basic (in shares)	57,339	47,381
Diluted (in shares)	59,038	57,731