CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
OPERATING ACTIVITIES:
Net income	$ 9,898	$ 7,753
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	8,393	7,984
Amortization of deferred financing costs	7	6
Deferred income taxes	(852)	96
Loss on disposition of property, plant and equipment	28	31
Stock-based compensation	655	485
Changes in operating assets and liabilities:
Trade receivables, net	(2,106)	(1,516)
Inventories, net	737	1,238
Prepaid expenses and other current assets	(70)	549
Other assets	(2)	3
Accounts payable and accrued expenses	(267)	(1,612)
Other liabilities	227	(100)
Net cash provided by operating activities	16,648	14,917
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(8,585)	(7,900)
Proceeds from sale of property, plant and equipment	443	70
Net cash used in investing activities	(8,142)	(7,830)
FINANCING ACTIVITIES:
Cash dividends paid	(1,506)	(1,391)
Proceeds from exercise of stock options	72	154
Purchase of treasury shares	(193)	(2,818)
Net cash used in financing activities	(1,627)	(4,055)
Net increase in cash and cash equivalents	6,879	3,032
Cash and cash equivalents at beginning of period	74,712
Cash and cash equivalents at end of period	$ 81,591	$ 62,958