Business Segments - Summary of company's operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	$ 12,003	$ 10,559
Cost of goods sold, inclusive of depreciation	(9,930)	(8,510)
Gross margin (loss)	2,073	2,049
Selling, general and administrative	(1,927)	(1,627)
Interest	(27)	(25)
Total costs and expenses	(1,954)	(1,652)
Income/(loss) before income tax provision	119	397
Income tax provision (benefit)	21	66
Net income/(loss)	98	331
Capital expenditures	642	511
Operating Segments
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	12,003	10,559
Cost of goods sold, inclusive of depreciation	(9,930)	(8,510)
Gross margin (loss)	$ 2,073	$ 2,049
Gross margin %	17.30%	19.40%
Selling, general and administrative	$ (1,927)	$ (1,627)
Interest	(27)	(25)
Total costs and expenses	(11,884)	(10,162)
Income/(loss) before income tax provision	119	397
Income tax provision (benefit)	21	66
Net income/(loss)	98	331
Capital expenditures	642	511
Operating Segments | ATG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	10,595	9,115
Cost of goods sold, inclusive of depreciation	(8,467)	(7,084)
Gross margin (loss)	$ 2,128	$ 2,031
Gross margin %	20.10%	22.30%
Selling, general and administrative	$ (1,280)	$ (1,228)
Interest	(19)	(17)
Total costs and expenses	(9,766)	(8,329)
Income/(loss) before income tax provision	829	786
Income tax provision (benefit)	145	130
Net income/(loss)	684	656
Capital expenditures	599	405
Operating Segments | CPG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	1,408	1,444
Cost of goods sold, inclusive of depreciation	(1,463)	(1,426)
Gross margin (loss)	$ (55)	$ 18
Gross margin %	(3.90%)	1.20%
Selling, general and administrative	$ (647)	$ (399)
Interest	(8)	(8)
Total costs and expenses	(2,118)	(1,833)
Income/(loss) before income tax provision	(710)	(389)
Income tax provision (benefit)	(124)	(64)
Net income/(loss)	(586)	(325)
Capital expenditures	$ 43	$ 106