Business Segments - Summary of company's operations (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	$ 13,504		$ 14,067		$ 28,952	$ 26,070
Cost of goods sold, inclusive of depreciation	(10,484)		(10,798)		(21,220)	(20,728)
Gross margin (loss)	3,020		3,269		7,732	5,342
Selling, general and administrative	(1,748)		(2,375)		(4,016)	(4,302)
Interest	(50)		(30)		(92)	(57)
Total costs and expenses	(1,798)		(2,405)		(4,108)	(4,359)
Income/(loss) before income tax provision	1,222		864		3,624	983
Income tax provision (benefits)	257		150		761	171
Net income/(loss)	965	$ 1,898	714	$ 98	2,863	812
Capital expenditures					593	1,140
Operating Segments
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	13,504		14,067		28,952	26,070
Cost of goods sold, inclusive of depreciation	(10,485)		(10,798)		(21,221)	(20,728)
Gross margin (loss)	$ 3,019		$ 3,269		$ 7,731	$ 5,342
Gross margin %	22.40%		23.20%		26.70%	20.50%
Selling, general and administrative	$ (1,748)		$ (2,375)		$ (4,016)	$ (4,302)
Interest	(49)		(30)		(91)	(57)
Total costs and expenses	(12,282)		(13,203)		(25,328)	(25,087)
Income/(loss) before income tax provision	1,222		864		3,624	983
Income tax provision (benefits)	257		150		761	171
Net income/(loss)	965		714		2,863	812
Capital expenditures	180		711		593	1,353
Operating Segments | ATG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	11,230		12,151		25,044	22,746
Cost of goods sold, inclusive of depreciation	(8,494)		(8,555)		(17,860)	(17,022)
Gross margin (loss)	$ 2,736		$ 3,596		$ 7,184	$ 5,724
Gross margin %	24.40%		29.60%		28.70%	25.20%
Selling, general and administrative	$ (1,402)		$ (1,739)		$ (3,145)	$ (3,019)
Interest	(46)		(22)		(84)	(41)
Total costs and expenses	(9,942)		(10,316)		(21,089)	(20,082)
Income/(loss) before income tax provision	1,288		1,835		3,955	2,664
Income tax provision (benefits)	270		318		830	463
Net income/(loss)	1,018		1,517		3,125	2,201
Capital expenditures	128		562		541	1,161
Operating Segments | CPG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	2,274		1,916		3,908	3,324
Cost of goods sold, inclusive of depreciation	(1,991)		(2,243)		(3,361)	(3,706)
Gross margin (loss)	$ 283		$ (327)		$ 547	$ (382)
Gross margin %	12.40%		(17.10%)		14.00%	(11.50%)
Selling, general and administrative	$ (346)		$ (636)		$ (871)	$ (1,283)
Interest	(3)		(8)		(7)	(16)
Total costs and expenses	(2,340)		(2,887)		(4,239)	(5,005)
Income/(loss) before income tax provision	(66)		(971)		(331)	(1,681)
Income tax provision (benefits)	(13)		(168)		(69)	(292)
Net income/(loss)	(53)		(803)		(262)	(1,389)
Capital expenditures	$ 52		$ 149		$ 52	$ 192