CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Net sales	$ 222,241	$ 220,602	$ 440,538	$ 446,532
Costs and expenses:
Cost of goods sold	165,414	153,184	322,858	311,145
Selling, general and administrative	27,522	35,256	63,110	72,517
Gain on disposal	(33,921)		(33,599)
Design and development	14,040	12,981	27,284	26,842
Operating income	49,186	19,181	60,885	36,028
Interest expense, net	1,001	1,170	2,004	2,524
Equity in earnings of investee	(548)	(665)	(912)	(1,186)
Other income, net	(97)	(264)	(529)	(863)
Income before income taxes	48,830	18,940	60,322	35,553
Provision for income taxes	9,066	3,820	10,901	7,053
Net income	$ 39,764	$ 15,120	$ 49,421	$ 28,500
Earnings per share:
Basic (in dollars per share)	$ 1.43	$ 0.53	$ 1.75	$ 1.01
Diluted (in dollars per share)	$ 1.41	$ 0.52	$ 1.72	$ 0.99
Weighted-average shares outstanding:
Basic (in shares)	27,887,157	28,449,303	28,208,229	28,349,362
Diluted (in shares)	28,293,547	28,977,747	28,715,725	28,907,357