Business Segments - Summary of company's operations (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	$ 10,297			$ 12,362			$ 39,249	$ 38,432
Cost of goods sold, inclusive of depreciation	(10,462)			(8,827)			(31,682)	(29,555)
Gross margin	(165)			3,535			7,567	8,877
Selling, general and administrative	(2,096)			(2,134)			(6,112)	(6,436)
Interest	(42)			(31)			(134)	(88)
Total costs and expenses	(2,138)			(2,165)			(6,246)	(6,524)
Income before income tax provision	(2,303)			1,370			1,321	2,353
Income tax provision (benefit)	(521)			238			240	409
Net income (loss)	(1,782)	$ 965	$ 1,898	1,132	$ 714	$ 98	1,081	1,944
Capital expenditures							708	1,660
Operating Segments
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	10,297			12,362			39,249	38,432
Cost of goods sold, inclusive of depreciation	(10,462)			(8,827)			(31,682)	(29,555)
Gross margin	$ (165)			$ 3,535			$ 7,567	$ 8,877
Gross margin %	(1.60%)			28.60%			19.30%	23.10%
Selling, general and administrative	$ (2,096)			$ (2,134)			$ (6,112)	$ (6,436)
Interest	(42)			(31)			(134)	(88)
Total costs and expenses	(12,600)			(10,992)			(37,928)	(36,079)
Income before income tax provision	(2,303)			1,370			1,321	2,353
Income tax provision (benefit)	(521)			238			240	409
Net income (loss)	(1,782)			1,132			1,081	1,944
Capital expenditures	115			307			708	1,660
Operating Segments | ATG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	8,184			11,180			33,228	33,926
Cost of goods sold, inclusive of depreciation	(8,636)			(7,378)			(26,495)	(24,400)
Gross margin	$ (452)			$ 3,802			$ 6,733	$ 9,526
Gross margin %	(5.50%)			34.00%			20.30%	28.10%
Selling, general and administrative	$ (1,712)			$ (1,539)			$ (4,857)	$ (4,558)
Interest	(40)			(25)			(125)	(66)
Total costs and expenses	(10,388)			(8,942)			(31,477)	(29,024)
Income before income tax provision	(2,204)			2,238			1,751	4,902
Income tax provision (benefit)	(512)			389			318	852
Net income (loss)	(1,692)			1,849			1,433	4,050
Capital expenditures	99			288			640	1,449
Operating Segments | CPG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	2,113			1,182			6,021	4,506
Cost of goods sold, inclusive of depreciation	(1,826)			(1,449)			(5,187)	(5,155)
Gross margin	$ 287			$ (267)			$ 834	$ (649)
Gross margin %	13.60%			(22.60%)			13.90%	(14.40%)
Selling, general and administrative	$ (384)			$ (595)			$ (1,255)	$ (1,878)
Interest	(2)			(6)			(9)	(22)
Total costs and expenses	(2,212)			(2,050)			(6,451)	(7,055)
Income before income tax provision	(99)			(868)			(430)	(2,549)
Income tax provision (benefit)	(9)			(151)			(78)	(443)
Net income (loss)	(90)			(717)			(352)	(2,106)
Capital expenditures	$ 16			$ 19			$ 68	$ 211