CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
OPERATING ACTIVITIES:
Net income	$ 15,454	$ 15,565
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	13,011	12,711
Amortization of deferred financing costs	23	11
Deferred income taxes	1,119	(1,243)
Loss on disposition of property, plant and equipment	466	78
Stock-based compensation	1,144	1,073
Changes in operating assets and liabilities:
Trade receivables, net	(1,900)	(1,461)
Inventories, net	358	(448)
Prepaid expenses and other current assets	670	(325)
Other assets	118	2
Accounts payable and accrued expenses	1,566	(1,963)
Other liabilities	(191)	(42)
Net cash provided by operating activities	31,838	23,958
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(31,687)	(14,504)
Proceeds from sale of property, plant and equipment	460	459
Net cash used in investing activities	(31,227)	(14,045)
FINANCING ACTIVITIES:
Cash dividends paid	(2,267)	(2,259)
Proceeds from exercise of stock options	73	72
Purchase of treasury shares	(251)	(193)
Net cash used in financing activities	(2,445)	(2,380)
Net (decrease) increase in cash and cash equivalents	(1,834)	7,533
Cash and cash equivalents at beginning of period	85,000	74,712
Cash and cash equivalents at end of period	$ 83,166	$ 82,245