CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net sales	$ 214,675	$ 201,424	$ 429,286	$ 405,252
Cost of sales	138,003	120,878	276,007	244,356
Gross margin	76,672	80,546	153,279	160,896
Selling, general and administrative expenses	42,540	40,012	83,137	74,580
Research and development expenses	8,750	7,141	16,884	14,102
Restructuring and impairment charges	541	1,079	963	1,805
Gain (Loss) on Disposition of Assets	383	0
Other operating (income) expense, net		0	(3,974)	(942)
Operating income	25,224	32,314	56,269	71,351
Equity income in unconsolidated joint ventures	1,804	966	2,811	1,976
Other income (expense), net	(34)	260	32	1,379
Interest expense, net	(1,292)	(1,947)	(2,503)	(3,195)
Income before income tax expense	25,702	31,593	56,609	71,511
Income tax expense	8,373	10,697	13,144	23,583
Net income	$ 17,329	$ 20,896	$ 43,465	$ 47,928
Basic earnings per share (in dollars per share)	$ 0.94	$ 1.15	$ 2.37	$ 2.65
Diluted earnings per share (in dollars per share)	$ 0.93	$ 1.13	$ 2.33	$ 2.60
Shares used in computing:
Basic earnings per share (shares)	18,389	18,140	18,338	18,098
Diluted earnings per share (shares)	18,660	18,547	18,635	18,460