Basis of Financial Statement Presentation - ASC 606 Adjustment Statement of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales	[1]	$ 350,175	$ 306,576	$ 1,027,024	$ 882,090
Operating costs and expenses:
Cost of sales	[1]	226,425	214,288	694,888	630,781
Research and development		11,357	9,907	33,040	28,690
Operating Income (Loss)	[1]	61,616	32,002	146,792	91,206
Income tax expense	[1]	2,600	2,037	9,200	6,041
Net income (loss)	[1],[2]	$ 40,806	$ 18,589	$ 113,167	$ 251,847
Net income (loss) per basic share (in usd per share)		$ 0.70	$ 0.33	$ 1.96	$ 4.91
Earnings Per Share, Diluted		$ 0.69	$ 0.32	$ 1.91	$ 4.31
As Previously Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales			$ 306,408		$ 881,879
Operating costs and expenses:
Cost of sales			213,947		629,905
Research and development			10,005		29,057
Operating Income (Loss)			32,077		91,504
Income tax expense			2,060		6,090
Net income (loss)			18,641		252,096
ASC 606 Adjustments | ASC 606 Adjustments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net sales			168		211
Operating costs and expenses:
Cost of sales			341		876
Research and development			(98)		(367)
Operating Income (Loss)			(75)		(298)
Income tax expense			(23)		(49)
Net income (loss)			$ (52)		$ (249)

[1] Three and nine months ended December 31, 2017 adjusted due to the adoption of ASC 606.

[2] Three and nine months ended December 31, 2017 adjusted due to the adoption of ASC 606.