CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Net sales	$ 802,583	$ 898,260	$ 879,091
Cost of sales	510,763	583,968	568,308
Gross margin	291,820	314,292	310,783
Selling, general and administrative expenses	182,283	168,682	164,046
Research and development expenses	29,320	31,685	33,075
Restructuring and impairment charges	12,987	2,485	4,038
Other operating (income) expense, net	(104)	959	(3,087)
Operating income	67,334	110,481	112,711
Equity income in unconsolidated joint ventures	4,877	5,319	5,501
Pension settlement charges	(55)	(53,213)	0
Other income (expense), net	3,513	(592)	(994)
Interest expense, net	(7,135)	(6,869)	(6,629)
Income before income tax expense	68,534	55,126	110,589
Income tax expense	18,544	7,807	22,938
Net income	$ 49,990	$ 47,319	$ 87,651
Basic earnings per share (in dollars per share)	$ 2.68	$ 2.55	$ 4.77
Diluted earnings per share (in dollars per share)	$ 2.67	$ 2.53	$ 4.70
Shares used in computing:
Basic earnings per share (in shares)	18,681	18,573	18,374
Diluted earnings per share (in shares)	18,706	18,713	18,659