Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue	$ 138,741	$ 121,172	$ 249,385	$ 225,149
Cost of sales	104,537	89,882	190,241	168,104
Gross profit	34,204	31,290	59,144	57,045
Research and development costs	5,464	6,116	10,384	12,175
Selling, general and administrative expenses	21,828	19,079	43,569	39,772
Restructuring charges	277	44	277	172
Gain on sale of property	0	0	(6,175)	0
Income from operations	6,635	6,051	11,089	4,926
Interest expense	(721)	(1,250)	(1,523)	(2,601)
Other income (expense), net	113	1,195	660	(905)
Earnings before (benefit from) provision for income taxes	6,027	5,996	10,226	1,420
(Benefit from) provision for income taxes	(1,853)	423	(854)	(349)
Net earnings available to common stockholders	7,880	5,573	11,080	1,769
Common Class A [Member]
Net earnings available to common stockholders	$ 1,299	$ 923	$ 1,822	$ 274
Net earnings per common share:
Common shares - basic and diluted (in dollars per share)	$ 0.61	$ 0.43	$ 0.85	$ 0.13
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	$ 6,581	$ 4,650	$ 9,258	$ 1,495
Net earnings per common share:
Common shares - basic and diluted (in dollars per share)	$ 0.64	$ 0.46	$ 0.91	$ 0.15
Weighted-average number of shares outstanding:
Common shares - basic and diluted (in shares)	10,237	10,178	10,220	10,151