CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
OPERATING ACTIVITIES:
Net income	$ 15,565	$ 13,834
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	12,711	12,032
Amortization of deferred financing costs	11	11
Deferred income taxes	(1,243)	311
Loss on disposition of property, plant and equipment	78	107
Stock-based compensation	1,073	778
Changes in operating assets and liabilities:
Trade receivables, net	(1,461)	(3,496)
Inventories, net	(448)	2,015
Prepaid expenses and other current assets	(325)	700
Other assets	2	5
Accounts payable and accrued expenses	(1,963)	(341)
Other liabilities	(42)	(86)
Net cash provided by operating activities	23,958	25,870
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(14,504)	(12,230)
Proceeds from sale of property, plant and equipment	459	126
Net cash used in investing activities	(14,045)	(12,104)
FINANCING ACTIVITIES:
Cash dividends paid	(2,259)	(2,087)
Proceeds from exercise of stock options	72	153
Purchase of treasury shares	(193)	(2,818)
Net cash used in financing activities	(2,380)	(4,752)
Net increase in cash and cash equivalents	7,533	9,014
Cash and cash equivalents at beginning of period	74,712	59,926
Cash and cash equivalents at end of period	$ 82,245	$ 68,940