CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
OPERATING ACTIVITIES:
Net income	$ 4,620	$ 4,066
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	4,290	3,992
Amortization of deferred financing costs	4	4
Deferred income taxes	(565)	58
Loss on disposition of property, plant and equipment	50	47
Stock-based compensation	289	223
Changes in operating assets and liabilities:
Trade receivables, net	(3,244)	(948)
Inventories, net	616	956
Prepaid expenses and other current assets	43	350
Other assets	1	1
Accounts payable and accrued expenses	84	(815)
Other liabilities	(49)	(52)
Net cash provided by operating activities	6,139	7,882
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(4,208)	(3,935)
Proceeds from sale of property, plant and equipment		28
Net cash used in investing activities	(4,208)	(3,907)
FINANCING ACTIVITIES:
Cash dividends paid	(753)	(696)
Proceeds from exercise of stock options		154
Purchase of treasury shares	(77)	(2,733)
Net cash used in financing activities	(830)	(3,275)
Net increase in cash and cash equivalents	1,101	700
Cash and cash equivalents at beginning of period	74,712
Cash and cash equivalents at end of period	$ 75,813	$ 60,626