CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
OPERATING ACTIVITIES:
Net income	$ 15,636	$ 12,171
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	11,091	11,008
Amortization of deferred financing costs	34	34
Deferred income taxes	165	1,297
Gain on sale of property, plant and equipment	54	53
Stock-based compensation	822	684
Changes in operating assets and liabilities:
Trade receivables, net	(5,590)	(3,215)
Inventories	829	577
Prepaid expenses and other current assets	213	(80)
Other assets	1	3
Accounts payable and accrued expenses	(267)	1,515
Other liabilities	298	120
Net cash provided by operating activities	23,286	24,167
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(8,725)	(6,690)
Proceeds from sale of property, plant and equipment	246	78
Net cash used in investing activities	(8,479)	(6,612)
FINANCING ACTIVITIES:
Repayments of term loans	(3,750)	(3,750)
Cash dividends paid	(2,092)
Purchase of treasury shares	(168)	(212)
Proceeds from exercise of stock options		21
Net cash used in financing activities	(6,010)	(3,941)
Net increase in cash and cash equivalents	8,797	13,614
Cash and cash equivalents at beginning of period	49,475	29,787
Cash and cash equivalents at end of period	$ 58,272	$ 43,401