CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND RETAINED EARNINGS - USD ($) shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND RETAINED EARNINGS
Net sales	$ 43,300,000	$ 39,887,000	$ 80,173,000	$ 73,990,000
Costs and expenses:
Cost of sales (exclusive of depreciation, depletion and amortization)	35,095,000	31,734,000	66,440,000	59,806,000
Depreciation, depletion and amortization	707,000	677,000	1,383,000	1,315,000
Selling and administrative	5,539,000	5,845,000	11,650,000	11,849,000
Net reduction to write off of deferred development	(94,000)
Charges related to cessation of mining an aggregates deposit			6,840,000
Gain on disposition of property and equipment	(889,000)	(24,000)	(889,000)	(24,000)
Total costs and expenses	40,358,000	38,232,000	85,424,000	72,946,000
Operating (loss) income	2,942,000	1,655,000	(5,251,000)	1,044,000
Interest income	21,000	14,000	45,000	32,000
Interest expense	(167,000)	(108,000)	(275,000)	(174,000)
Other income (expense), net	22,000	(4,000)	41,000	16,000
(Loss) income before income taxes	2,818,000	1,557,000	(5,440,000)	918,000
Provision for income taxes	(705,000)	(529,000)	1,360,000	(312,000)
Net (loss) income	2,113,000	1,028,000	(4,080,000)	606,000
Retained earnings, beginning of period	60,794,000	64,747,000	66,987,000	65,169,000
Retained earnings, end of period	$ 62,907,000	$ 65,775,000	$ 62,907,000	$ 65,775,000
Basic and diluted (loss) income per share (in dollar per share)	$ 1.24	$ 0.61	$ (2.40)	$ 0.36
Average shares outstanding (in shares)	1,698	1,682	1,697	1,678