Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Net sales	$ 465,771	$ 492,412
Cost of sales	346,041	382,439
Gross profit	119,730	109,973
Research and development costs	23,611	26,925
Selling, general and administrative expenses	78,704	77,416
Impairment of goodwill	0	8,891
Restructuring charges	601	2,593
Gain on sale of property	(1,853)	(4,257)
Income (loss) from operations	18,667	(1,595)
Interest expense	(4,746)	(5,448)
Other expense, net	(1,785)	(259)
Earnings (loss) before (benefit) provision for income taxes	12,136	(7,302)
(Benefit) provision for income taxes	(659)	1,441
Net earnings (loss) available to common shareholders	12,795	(8,743)
Common Class A [Member]
Net earnings (loss) available to common shareholders	$ 2,089	$ (1,531)
Net earnings (loss) per common share:
Common shares - basic and diluted (in dollars per share)	$ 0.97	$ (0.71)
Weighted-average shares outstanding:
Common shares - basic and diluted (in shares)	2,145	2,167
Common Class B [Member]
Net earnings (loss) available to common shareholders	$ 10,706	$ (7,212)
Net earnings (loss) per common share:
Common shares - basic and diluted (in dollars per share)	$ 1.05	$ (0.71)
Weighted-average shares outstanding:
Common shares - basic and diluted (in shares)	10,185	10,117