Business Segments - Summary of company's operations (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	$ 9,060,000	$ 15,448,000
Cost of goods sold, inclusive of depreciation	(8,067,000)	(10,736,000)
Gross margin (loss)	993,000	4,712,000
Selling, general and administrative	(1,973,000)	(2,268,000)
Interest	(61,000)	(42,000)
Total operating costs and expenses	980,000	(2,444,000)
Operating (loss)/income	1,669,000	(42,000)
Other income: employee retention credit (ERC)	1,730,000
Interest expense	61,000	42,000
Income (loss) before income tax provision	689,000	2,402,000
Income tax provision (benefit)	148,000	504,000
Net income/(loss)	541,000	1,898,000
Total Assets	51,671,000		$ 50,328,000
Capital expenditures	14,000	413,000
Operating Segments
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	9,060,000	15,448,000
Cost of goods sold, inclusive of depreciation	(8,067,000)	(10,736,000)
Gross margin (loss)	$ 993,000	$ 4,712,000
Gross margin %	11.00%	30.50%
Selling, general and administrative	$ (1,973,000)	$ (2,268,000)
Interest	(61,000)	(42,000)
Total operating costs and expenses	10,040,000	13,004,000
Operating (loss)/income	980,000	(2,444,000)
Other income: employee retention credit (ERC)	1,730,000
Interest expense	61,000	42,000
Total other income / (expense)	1,669,000	(42,000)
Income (loss) before income tax provision	689,000	2,402,000
Income tax provision (benefit)	148,000	504,000
Net income/(loss)	541,000	1,898,000
Total Assets	51,671,000		50,328,000
Capital expenditures	14,000	413,000
Operating Segments | ATG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	7,223,000	13,814,000
Cost of goods sold, inclusive of depreciation	(6,210,000)	(9,366,000)
Gross margin (loss)	$ 1,013,000	$ 4,448,000
Gross margin %	14.00%	32.20%
Selling, general and administrative	$ (1,585,000)	$ (1,743,000)
Interest	(60,000)	(38,000)
Total operating costs and expenses	7,795,000	11,109,000
Operating (loss)/income	572,000	(2,705,000)
Other income: employee retention credit (ERC)	1,413,000
Interest expense	60,000	38,000
Total other income / (expense)	1,353,000	(38,000)
Income (loss) before income tax provision	781,000	2,667,000
Income tax provision (benefit)	168,000	560,000
Net income/(loss)	613,000	2,107,000
Total Assets	42,360,000		40,826,000
Capital expenditures	10,000	413,000
Operating Segments | CPG
Segment Reporting Information [Line Items]
Revenues from unaffiliated customers	1,837,000	1,634,000
Cost of goods sold, inclusive of depreciation	(1,857,000)	(1,370,000)
Gross margin (loss)	$ (20,000)	$ 264,000
Gross margin %	(1.10%)	16.20%
Selling, general and administrative	$ (388,000)	$ (525,000)
Interest	(1,000)	(4,000)
Total operating costs and expenses	2,245,000	1,895,000
Operating (loss)/income	408,000	261,000
Other income: employee retention credit (ERC)	317,000
Interest expense	1,000	4,000
Total other income / (expense)	316,000	(4,000)
Income (loss) before income tax provision	(92,000)	(265,000)
Income tax provision (benefit)	(20,000)	(56,000)
Net income/(loss)	(72,000)	$ (209,000)
Total Assets	9,311,000		$ 9,502,000
Capital expenditures	$ 4,000