CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Net sales	$ 221,842	$ 226,863	$ 704,492	$ 656,149
Cost of sales	142,975	147,733	454,403	423,741
Gross margin	78,867	79,130	250,089	232,408
Selling, general and administrative expenses	40,448	39,943	127,349	123,080
Research and development expenses	7,830	7,630	23,282	24,514
Restructuring and impairment charges	580	1,052	2,485	2,015
Other operating (income) expense, net	124	863	1,075	(3,111)
Operating income	29,885	29,642	95,898	85,910
Equity income in unconsolidated joint ventures	1,498	1,642	4,077	4,453
Other income (expense), net	(918)	(680)	(915)	(647)
Interest expense, net	(1,747)	(2,000)	(5,723)	(4,503)
Income before income tax expense	28,718	28,604	93,337	85,213
Income tax expense	5,331	8,870	17,258	22,014
Net income	$ 23,387	$ 19,734	$ 76,079	$ 63,199
Basic earnings per share (in dollars per share)	$ 1.26	$ 1.07	$ 4.10	$ 3.44
Diluted earnings per share (in dollars per share)	$ 1.25	$ 1.06	$ 4.07	$ 3.39
Shares used in computing:
Basic earnings per share (in shares)	18,581	18,403	18,569	18,360
Diluted earnings per share (in shares)	18,724	18,678	18,715	18,649