CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND RETAINED EARNINGS - USD ($) shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND RETAINED EARNINGS
Net sales	$ 40,978,000	$ 38,627,000	$ 121,151,000	$ 112,617,000
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Costs and expenses:
Cost of sales (exclusive of depreciation, depletion and amortization)	$ 34,745,000	$ 31,426,000	$ 101,185,000	$ 91,232,000
Depreciation, depletion and amortization	682,000	617,000	2,065,000	1,932,000
Selling and administrative	7,006,000	5,361,000	18,656,000	17,210,000
Charges related to write off of deferred development			6,840,000
Gain on disposition of property and equipment	(3,000)	(95,000)	(892,000)	(119,000)
Total costs and expenses	42,430,000	37,309,000	127,854,000	110,255,000
Operating (loss) income	(1,452,000)	1,318,000	(6,703,000)	2,362,000
Interest income	14,000	18,000	59,000	50,000
Interest expense	(140,000)	(98,000)	(415,000)	(272,000)
Other (expense) income, net	(70,000)	28,000	(29,000)	44,000
(Loss) income before income taxes	(1,648,000)	1,266,000	(7,088,000)	2,184,000
(Benefit) provision for income taxes	(412,000)	431,000	1,772,000	(743,000)
Net (loss) income	(1,236,000)	835,000	(5,316,000)	1,441,000
Retained earnings, beginning of period	62,907,000	65,775,000	66,987,000	65,169,000
Retained earnings, end of period	$ 61,671,000	$ 66,610,000	$ 61,671,000	$ 66,610,000
Basic and diluted (loss) income per share (in dollar per share)	$ (0.73)	$ 0.50	$ (3.13)	$ 0.86
Average shares outstanding (in shares)	1,698	1,682	1,697	1,679