CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net sales	$ 821,043	$ 656,314	$ 641,443
Cost of sales	502,468	406,829	406,081
Gross margin	318,575	249,485	235,362
Selling, general and administrative expenses	160,011	136,317	131,463
Research and development expenses	29,547	28,582	27,644
Restructuring and asset impairment charges	3,567	734	0
Gain on sale of long-lived assets	(5,329)	0	0
Operating income	130,779	83,852	76,255
Equity income in unconsolidated joint ventures	4,898	4,146	2,890
Other income (expense), net	3,379	(1,788)	(8,492)
Interest expense, net	(6,131)	(3,930)	(4,480)
Income before income tax expense	132,925	82,280	66,173
Income tax expense	52,466	33,997	19,853
Net income	$ 80,459	$ 48,283	$ 46,320
Earnings per share:
Basic earnings per share (in dollars per share)	$ 4.43	$ 2.68	$ 2.52
Diluted earnings per share (in dollars per share)	$ 4.34	$ 2.65	$ 2.48
Shares used in computing:
Basic earnings per share (in shares)	18,154	17,991	18,371
Diluted earnings per share (in shares)	18,547	18,223	18,680