CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Net sales	$ 201,944	$ 221,842	$ 591,911	$ 704,492
Cost of sales	126,426	142,975	380,794	454,403
Gross margin	75,518	78,867	211,117	250,089
Selling, general and administrative expenses	50,230	40,448	132,254	127,349
Research and development expenses	7,085	7,830	22,185	23,282
Restructuring and impairment charges	9,413	580	9,413	2,485
Other operating (income) expense, net	(4)	124	(96)	1,075
Operating income	8,794	29,885	47,361	95,898
Equity income in unconsolidated joint ventures	937	1,498	3,177	4,077
Pension settlement charges	0	0	(55)	0
Other income (expense), net	1,446	(918)	1,294	(915)
Interest expense, net	(3,553)	(1,747)	(6,539)	(5,723)
Income before income tax expense	7,624	28,718	45,238	93,337
Income tax expense	618	5,331	10,453	17,258
Net income	$ 7,006	$ 23,387	$ 34,785	$ 76,079
Basic earnings per share (in dollars per share)	$ 0.37	$ 1.26	$ 1.86	$ 4.10
Diluted earnings per share (in dollars per share)	$ 0.37	$ 1.25	$ 1.86	$ 4.07
Shares used in computing:
Basic earnings per share (in shares)	18,688	18,581	18,678	18,569
Diluted earnings per share (in shares)	18,713	18,724	18,695	18,715