CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
OPERATING ACTIVITIES:
Net income	$ 10,900	$ 9,898
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	8,572	8,393
Amortization of deferred financing costs	15	7
Deferred income taxes	1,157	(852)
Loss on disposition of property, plant and equipment	345	28
Stock-based compensation	713	655
Changes in operating assets and liabilities:
Trade receivables, net	(4,450)	(2,106)
Inventories, net	1,289	737
Prepaid expenses and other current assets	438	(70)
Other assets	93	(2)
Accounts payable and accrued expenses	(697)	(267)
Other liabilities	(145)	227
Net cash provided by operating activities	18,230	16,648
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(19,378)	(8,585)
Proceeds from sale of property, plant and equipment	183	443
Net cash used in investing activities	(19,195)	(8,142)
FINANCING ACTIVITIES:
Cash dividends paid	(1,511)	(1,506)
Proceeds from exercise of stock options	73	72
Purchase of treasury shares	(251)	(193)
Net cash used in financing activities	(1,689)	(1,627)
Net (decrease) increase in cash and cash equivalents	(2,654)	6,879
Cash and cash equivalents at beginning of period	85,000	74,712
Cash and cash equivalents at end of period	$ 82,346	$ 81,591