Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING ACTIVITIES:
Net income	$ 17,754	$ 12,886	$ 19,367
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	16,141	16,033	14,903
Amortization of deferred financing costs	14	29	34
Deferred income taxes	648	(227)	1,059
Loss on disposition of property, plant and equipment	622	39	78
Stock-based compensation	1,036	1,199	1,102
Changes in operating assets and liabilities:
Trade receivables, net	(892)	1,555	(3,347)
Inventories, net	2,295	(1,292)	252
Prepaid expenses and other current assets	308	698	(882)
Other assets	4	(47)	16
Accounts payable and accrued expenses	532	198	(952)
Other liabilities	(615)	1,423	344
Net cash provided by operating activities	37,847	32,494	31,974
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(17,664)	(11,459)	(11,672)
Acquisition of assets of a business	(50)	(50)	(3,705)
Proceeds from sale of property, plant and equipment	208	449	316
Net cash used in investing activities	(17,506)	(11,060)	(15,061)
FINANCING ACTIVITIES:
Repayments of term loans		(16,667)	(5,000)
Cash dividends paid	(2,782)	(2,798)	(2,790)
Proceeds from exercise of stock options	155	28
Purchase of treasury shares	(2,928)	(403)	(266)
Net cash used in financing activities	(5,555)	(19,840)	(8,056)
Net increase in cash and cash equivalents	14,786	1,594	8,857
Cash and cash equivalents at beginning of period	59,926	58,332	49,475
Cash and cash equivalents at end of period	$ 74,712	$ 59,926	$ 58,332