CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Net sales	$ 201,424	$ 157,489	$ 405,252	$ 318,056
Cost of sales	120,878	97,290	244,356	197,349
Gross margin	80,546	60,199	160,896	120,707
Selling, general and administrative expenses	39,567	34,369	73,731	64,229
Research and development expenses	7,141	7,074	14,102	13,622
Restructuring charges	1,079	0	1,805	0
Gain on sale of long-lived asset	0	0	(942)	0
Operating income	32,759	18,756	72,200	42,856
Equity income in unconsolidated joint ventures	966	708	1,976	1,321
Other income (expense), net	(185)	191	530	(356)
Interest expense, net	(1,947)	(1,115)	(3,195)	(2,236)
Income before income tax expense	31,593	18,540	71,511	41,585
Income tax expense	10,697	13,163	23,583	21,280
Net income	$ 20,896	$ 5,377	$ 47,928	$ 20,305
Basic earnings per share (in dollars per share)	$ 1.15	$ 0.30	$ 2.65	$ 1.13
Diluted earnings per share (in dollars per share)	$ 1.13	$ 0.29	$ 2.60	$ 1.11
Shares used in computing:
Basic earnings per share (shares)	18,140	18,007	18,098	17,986
Diluted earnings per share (shares)	18,547	18,253	18,460	18,234