CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Net sales	$ 898,260	$ 879,091	$ 821,043
Cost of sales	583,968	568,308	502,468
Gross margin	314,292	310,783	318,575
Selling, general and administrative expenses	168,682	164,046	161,651
Research and development expenses	31,685	33,075	29,547
Restructuring and impairment charges	2,485	4,038	3,567
Other operating (income) expense, net	959	(3,087)	(5,329)
Operating income	110,481	112,711	129,139
Equity income in unconsolidated joint ventures	5,319	5,501	4,898
Pension settlement charges	(53,213)	0	0
Other income (expense), net	(592)	(994)	5,019
Interest expense, net	(6,869)	(6,629)	(6,131)
Income before income tax expense	55,126	110,589	132,925
Income tax expense	7,807	22,938	52,466
Net income	$ 47,319	$ 87,651	$ 80,459
Earnings per share:
Basic earnings per share (in dollars per share)	$ 2.55	$ 4.77	$ 4.43
Diluted earnings per share (in dollars per share)	$ 2.53	$ 4.70	$ 4.34
Shares used in computing:
Basic earnings per share (in shares)	18,573	18,374	18,154
Diluted earnings per share (in shares)	18,713	18,659	18,547