CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ 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	$ 242,852	$ 214,675	$ 482,650	$ 429,286
Cost of sales	157,024	138,003	311,428	276,007
Gross margin	85,828	76,672	171,222	153,279
Selling, general and administrative expenses	43,649	42,540	86,901	83,137
Research and development expenses	7,843	8,750	15,452	16,884
Restructuring and impairment charges	1,083	541	1,905	963
Other operating (income) expense, net	40	(383)	951	(3,974)
Operating income	33,213	25,224	66,013	56,269
Equity income in unconsolidated joint ventures	1,742	1,804	2,579	2,811
Other income (expense), net	(1,401)	(34)	3	32
Interest expense, net	(2,038)	(1,292)	(3,976)	(2,503)
Income before income tax expense	31,516	25,702	64,619	56,609
Income tax expense	7,223	8,373	11,927	13,144
Net income	$ 24,293	$ 17,329	$ 52,692	$ 43,465
Basic earnings per share (in dollars per share)	$ 1.31	$ 0.94	$ 2.84	$ 2.37
Diluted earnings per share (in dollars per share)	$ 1.30	$ 0.93	$ 2.82	$ 2.33
Shares used in computing:
Basic earnings per share (in shares)	18,568	18,389	18,562	18,338
Diluted earnings per share (in shares)	18,730	18,660	18,711	18,635