Basis of Financial Statement Presentation - ASC 606 Adjustment Statement of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	$ 327,397		$ 349,233		$ 672,639	$ 676,849
Operating costs and expenses:
Cost of sales	213,727		235,668		437,341	468,463
Research and development	12,274		10,995		24,449	21,683
Operating Income (Loss)	49,090		50,000		107,490	85,176
Income tax expense	1,700		2,000		18,500	6,600
Net income (loss)	$ (15,260)	[1]	$ 37,141	[1]	$ 25,080	$ 72,361
Net income (loss) per basic share (in usd per share)	$ (0.26)		$ 0.64		$ 0.43	$ 1.26
Earnings Per Share, Diluted	$ (0.26)		$ 0.63		$ 0.42	$ 1.22

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