Business Segments - Summary of company's operations (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	$ 14,067		$ 11,946		$ 26,070	$ 22,505
Cost of goods sold, inclusive of depreciation	(10,798)		(9,022)		(20,728)	(17,531)
Gross margin (loss)	3,269		2,924		5,342	4,974
Selling, general and administrative	(2,375)		(2,013)		(4,302)	(3,641)
Interest	(30)		(27)		(57)	(52)
Total costs and expenses	(2,405)		(2,040)		(4,359)	(3,693)
Income/(loss) before income tax provision	864		884		983	1,281
Income tax provision (benefit)	150		177		171	243
Net income/(loss)	714	$ 98	707	$ 331	812	1,038
Capital expenditures					1,140	984
Operating Segments
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	14,067		11,946		26,070	22,505
Cost of goods sold, inclusive of depreciation	(10,798)		(9,022)		(20,728)	(17,531)
Gross margin (loss)	$ 3,269		$ 2,924		$ 5,342	$ 4,974
Gross margin %	23.20%		24.50%		20.50%	22.10%
Selling, general and administrative	$ (2,375)		$ (2,013)		$ (4,302)	$ (3,641)
Interest	(30)		(27)		(57)	(52)
Total costs and expenses	(13,203)		(11,062)		(25,087)	(21,224)
Income/(loss) before income tax provision	864		884		983	1,281
Income tax provision (benefit)	150		177		171	243
Net income/(loss)	714		707		812	1,038
Capital expenditures	711		473		1,353	984
Operating Segments | ATG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	12,151		10,274		22,746	19,389
Cost of goods sold, inclusive of depreciation	(8,555)		(7,552)		(17,022)	(14,635)
Gross margin (loss)	$ 3,596		$ 2,722		$ 5,724	$ 4,754
Gross margin %	29.60%		26.50%		25.20%	24.50%
Selling, general and administrative	$ (1,739)		$ (1,426)		$ (3,019)	$ (2,655)
Interest	(22)		(18)		(41)	(35)
Total costs and expenses	(10,316)		(8,996)		(20,082)	(17,325)
Income/(loss) before income tax provision	1,835		1,278		2,664	2,064
Income tax provision (benefit)	318		262		463	392
Net income/(loss)	1,517		1,016		2,201	1,672
Capital expenditures	562		440		1,161	845
Operating Segments | CPG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	1,916		1,672		3,324	3,116
Cost of goods sold, inclusive of depreciation	(2,243)		(1,470)		(3,706)	(2,896)
Gross margin (loss)	$ (327)		$ 202		$ (382)	$ 220
Gross margin %	(17.10%)		12.10%		(11.50%)	7.10%
Selling, general and administrative	$ (636)		$ (587)		$ (1,283)	$ (986)
Interest	(8)		(9)		(16)	(17)
Total costs and expenses	(2,887)		(2,066)		(5,005)	(3,899)
Income/(loss) before income tax provision	(971)		(394)		(1,681)	(783)
Income tax provision (benefit)	(168)		(85)		(292)	(149)
Net income/(loss)	(803)		(309)		(1,389)	(634)
Capital expenditures	$ 149		$ 33		$ 192	$ 139