CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Net sales	$ 879,091	$ 821,043	$ 656,314
Cost of sales	568,308	502,468	406,829
Gross margin	310,783	318,575	249,485
Selling, general and administrative expenses	164,046	161,651	139,272
Research and development expenses	33,075	29,547	28,582
Restructuring and impairment charges	4,038	3,567	734
Other operating (income) expense, net	(3,087)	(5,329)	0
Operating income	112,711	129,139	80,897
Equity income in unconsolidated joint ventures	5,501	4,898	4,146
Other income (expense), net	(994)	5,019	1,167
Interest expense, net	(6,629)	(6,131)	(3,930)
Income before income tax expense	110,589	132,925	82,280
Income tax expense	22,938	52,466	33,997
Net income	$ 87,651	$ 80,459	$ 48,283
Earnings per share:
Basic earnings per share (in dollars per share)	$ 4.77	$ 4.43	$ 2.68
Diluted earnings per share (in dollars per share)	$ 4.70	$ 4.34	$ 2.65
Shares used in computing:
Basic earnings per share (in shares)	18,374	18,154	17,991
Diluted earnings per share (in shares)	18,659	18,547	18,223