CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
OPERATING ACTIVITIES:
Net income	$ 4,262	$ 4,620
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	4,230	4,290
Amortization of deferred financing costs	8	4
Deferred income taxes	471	(565)
Loss on disposition of property, plant and equipment	211	50
Stock-based compensation	316	289
Changes in operating assets and liabilities:
Trade receivables, net	(2,601)	(3,244)
Inventories, net	947	616
Prepaid expenses and other current assets	417	43
Other assets	20	1
Accounts payable and accrued expenses	(1,705)	84
Other liabilities	(56)	(49)
Net cash provided by operating activities	6,520	6,139
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(7,620)	(4,208)
Proceeds from sale of property, plant and equipment	108
Net cash used in investing activities	(7,512)	(4,208)
FINANCING ACTIVITIES:
Cash dividends paid	(755)	(753)
Proceeds from exercise of stock options	73
Purchase of treasury shares	(61)	(77)
Net cash used in financing activities	(743)	(830)
Net (decrease) increase in cash and cash equivalents	(1,735)	1,101
Cash and cash equivalents at beginning of period	85,000	74,712
Cash and cash equivalents at end of period	$ 83,265	$ 75,813