CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales	$ 226,863	$ 206,783	$ 656,149	$ 612,035
Cost of sales	147,733	124,595	423,741	368,951
Gross margin	79,130	82,188	232,408	243,084
Selling, general and administrative expenses	39,943	39,010	123,080	113,590
Research and development expenses	7,630	7,411	24,514	21,512
Restructuring and impairment charges	1,052	962	2,015	2,767
Other operating (income) expense, net	863	(4,387)	(3,111)	(5,329)
Operating income	29,642	39,192	85,910	110,544
Equity income in unconsolidated joint ventures	1,642	1,384	4,453	3,359
Other income (expense), net	(680)	1,991	(647)	3,370
Interest expense, net	(2,000)	(1,639)	(4,503)	(4,834)
Income before income tax expense	28,604	40,928	85,213	112,439
Income tax expense	8,870	15,396	22,014	38,979
Net income	$ 19,734	$ 25,532	$ 63,199	$ 73,460
Basic earnings per share (in dollars per share)	$ 1.07	$ 1.40	$ 3.44	$ 4.05
Diluted earnings per share (in dollars per share)	$ 1.06	$ 1.37	$ 3.39	$ 3.97
Shares used in computing:
Basic earnings per share (shares)	18,403	18,181	18,360	18,126
Diluted earnings per share (shares)	18,678	18,588	18,649	18,503