Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenue	$ 146,966	$ 124,492	$ 396,351	$ 349,642
Cost of sales	110,992	91,183	301,234	259,286
Gross profit	35,974	33,309	95,117	90,356
Research and development costs	5,918	5,713	16,301	17,889
Selling, general and administrative expenses	21,188	19,368	64,757	59,140
Restructuring charges	398	111	675	283
Gain on sale of property	(403)	0	(6,578)	0
Income from operations	8,873	8,117	19,962	13,044
Interest expense	(1,491)	(1,242)	(3,014)	(3,843)
Other (expense) income, net	(201)	(483)	458	(1,390)
Earnings before provision for (benefit from) income taxes	7,181	6,392	17,406	7,811
Provision for (benefit from) income taxes	1,447	(1,083)	593	(1,433)
Net earnings available to common stockholders	5,734	7,475	16,813	9,244
Common Class A [Member]
Net earnings available to common stockholders	$ 940	$ 1,233	$ 2,761	$ 1,512
Net earnings per common share:
Common shares - basic and diluted (in dollars per share)	$ 0.44	$ 0.57	$ 1.29	$ 0.70
Weighted-average number of shares outstanding:
Common shares - basic and diluted (in shares)	2,145	2,145	2,145	2,145
Common Class B [Member]
Net earnings available to common stockholders	$ 4,794	$ 6,242	$ 14,052	$ 7,732
Net earnings per common share:
Common shares - basic and diluted (in dollars per share)	$ 0.47	$ 0.61	$ 1.37	$ 0.76
Weighted-average number of shares outstanding:
Common shares - basic and diluted (in shares)	10,269	10,223	10,237	10,176