Business Segments - Summary of company's operations (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	$ 12,362			$ 12,768			$ 38,432	$ 35,273
Cost of goods sold, inclusive of depreciation	(8,827)			(8,828)			(29,555)	(26,359)
Gross margin	3,535			3,940			8,877	8,914
Selling, general and administrative	(2,134)			(2,074)			(6,436)	(5,715)
Interest expense	(31)			(28)			(88)	(80)
Total costs and expenses	(2,165)			(2,102)			(6,524)	(5,795)
Income before income tax provision	1,370			1,838			2,353	3,119
Income tax provision	(238)			(381)			(409)	(624)
Net Income	1,132	$ 714	$ 98	1,457	$ 707	$ 331	1,944	2,495
Capital expenditures							1,660	1,452
Operating Segments
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	12,362			12,768			38,432	35,273
Cost of goods sold, inclusive of depreciation	(8,827)			(8,828)			(29,555)	(26,359)
Gross margin	$ 3,535			$ 3,940			$ 8,877	$ 8,914
Gross margin %	28.60%			30.90%			23.10%	25.30%
Selling, general and administrative	$ (2,134)			$ (2,074)			$ (6,436)	$ (5,715)
Interest expense	(31)			(28)			(88)	(80)
Total costs and expenses	(10,992)			(10,930)			(36,079)	(32,154)
Income before income tax provision	1,370			1,838			2,353	3,119
Income tax provision	(238)			(381)			(409)	(624)
Net Income	1,132			1,457			1,944	2,495
Capital expenditures	307			468			1,660	1,452
Operating Segments | ATG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	11,180			10,639			33,926	30,028
Cost of goods sold, inclusive of depreciation	(7,378)			(6,965)			(24,400)	(21,600)
Gross margin	$ 3,802			$ 3,674			$ 9,526	$ 8,428
Gross margin %	34.00%			34.50%			28.10%	28.10%
Selling, general and administrative	$ (1,539)			$ (1,476)			$ (4,558)	$ (4,131)
Interest expense	(25)			(20)			(66)	(55)
Total costs and expenses	(8,942)			(8,461)			(29,024)	(25,786)
Income before income tax provision	2,238			2,178			4,902	4,242
Income tax provision	(389)			(457)			(852)	(849)
Net Income	1,849			1,721			4,050	3,393
Capital expenditures	288			432			1,449	1,277
Operating Segments | CPG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	1,182			2,129			4,506	5,245
Cost of goods sold, inclusive of depreciation	(1,449)			(1,863)			(5,155)	(4,759)
Gross margin	$ (267)			$ 266			$ (649)	$ 486
Gross margin %	(22.60%)			12.50%			(14.40%)	9.30%
Selling, general and administrative	$ (595)			$ (598)			$ (1,878)	$ (1,584)
Interest expense	(6)			(8)			(22)	(25)
Total costs and expenses	(2,050)			(2,469)			(7,055)	(6,368)
Income before income tax provision	(868)			(340)			(2,549)	(1,123)
Income tax provision	151			76			443	225
Net Income	(717)			(264)			(2,106)	(898)
Capital expenditures	$ 19			$ 36			$ 211	$ 175