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
Revenue	$ 124,492	$ 124,479	$ 349,642	$ 377,284
Cost of sales	90,958	95,859	259,227	291,184
Gross profit	33,534	28,620	90,415	86,100
Research and development costs	5,713	6,162	17,889	20,198
Selling, general and administrative expenses	18,891	18,510	59,013	56,950
Impairment of goodwill	0	8,891	0	8,891
Restructuring charges	111	281	283	1,651
Gain on sale of property	0	0	0	(4,257)
Income (loss) from operations	8,819	(5,224)	13,230	2,667
Interest expense	(1,242)	(1,305)	(3,843)	(4,126)
Other (expense) income, net	(1,185)	629	(1,576)	117
Earnings (loss) before (benefit from) provision for income taxes	6,392	(5,900)	7,811	(1,342)
(Benefit from) provision for income taxes	(1,083)	590	(1,433)	1,049
Net earnings (loss) available to common stockholders	7,475	(6,490)	9,244	(2,391)
Common Class A [Member]
Net earnings (loss) available to common stockholders	$ 1,233	$ (1,112)	$ 1,512	$ (442)
Net earnings (loss) per common share:
Common shares - basic and diluted (in dollars per share)	$ 0.57	$ (0.51)	$ 0.70	$ (0.20)
Weighted-average number of shares outstanding:
Common shares - basic and diluted (in shares)	2,145	2,173	2,145	2,174
Common Class B [Member]
Net earnings (loss) available to common stockholders	$ 6,242	$ (5,378)	$ 7,732	$ (1,949)
Net earnings (loss) per common share:
Common shares - basic and diluted (in dollars per share)	$ 0.61	$ (0.53)	$ 0.76	$ (0.19)
Weighted-average number of shares outstanding:
Common shares - basic and diluted (in shares)	10,223	10,139	10,176	10,113