Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 26, 2020	Jun. 28, 2019
Cash flows from operating activities:
Net income	$ 3,575,000	$ 32,446,000
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation, depletion, and amortization	23,522,000	22,607,000
Amortization of deferred financing costs in interest expense	364,000	472,000
Stock-based compensation expense (non-cash)	3,966,000	3,541,000
Deferred income tax expense (benefit)	(234,000)	4,578,000
Net pension curtailments and settlements	94,000	3,296,000
Held for sale impairment charges	10,766,000	0
Changes in assets and liabilities:
Decrease (increase) in accounts receivable	5,331,000	(11,778,000)
Decrease (increase) in inventory	(20,585,000)	1,306,000
Decrease (increase) in prepaid and other current assets	(7,264,000)	(588,000)
Increase (decrease) in accounts payable and accrued expenses	(7,634,000)	(18,813,000)
Increase (decrease) in unearned revenue	(257,000)	(88,000)
Increase (decrease) in interest and taxes payable	1,058,000	(1,130,000)
Increase (decrease) in unearned income due to customer prepayments	26,713,000	0
Domestic pension plan contributions	0	(3,000,000)
Other-net	(2,982,000)	(2,803,000)
Net cash provided by operating activities	36,433,000	30,046,000
Cash flows from investing activities:
Payments for purchase of property, plant, and equipment	(32,034,000)	(13,833,000)
Payments for mine development	0	1,591,000
Proceeds from sale of property, plant, and equipment	33,000	15,000
Net cash used in investing activities	(32,001,000)	(15,409,000)
Cash flows from financing activities:
Short-term debt under revolving credit agreement	150,000,000	0
Repayment of long-term debt	(428,000)	(397,000)
Principal payments under finance lease obligations	626,000	599,000
Cash dividends paid	(4,582,000)	(4,368,000)
Repurchase of common stock	(6,766,000)	(199,000)
Payments of withholding taxes for stock-based compensation awards	(2,025,000)	(4,763,000)
Net cash provided by (used in) financing activities	135,573,000	(10,326,000)
Effects of exchange rate changes	56,000	(100,000)
Net change in cash and cash equivalents	140,061,000	4,211,000
Cash and cash equivalents at beginning of period	125,007,000	70,645,000
Cash and cash equivalents at end of period	$ 265,068,000	$ 74,856,000