Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
OPERATING ACTIVITIES:
Net income	$ 19,367	$ 14,800	$ 16,423
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	14,903	14,498	15,044
Amortization of deferred financing costs	34us-gaap_AmortizationOfFinancingCosts	46us-gaap_AmortizationOfFinancingCosts	46us-gaap_AmortizationOfFinancingCosts
Deferred income taxes	1,059	1,793	2,131
Gain on sale of property, plant and equipment	78	86	145
Stock-based compensation	1,102us-gaap_ShareBasedCompensation	934us-gaap_ShareBasedCompensation	1,082us-gaap_ShareBasedCompensation
Changes in operating assets and liabilities:
Trade receivables, net	(3,347)	455	1,043
Inventories, net	252us-gaap_IncreaseDecreaseInInventories	439us-gaap_IncreaseDecreaseInInventories	(3,363)us-gaap_IncreaseDecreaseInInventories
Prepaid expenses and other current assets	(882)	(249)	392
Other assets	16	4	4
Accounts payable and accrued expenses	(952)	637	(1,086)
Other liabilities	344	89	(174)
Net cash provided by operating activities	31,974	33,532	31,687
INVESTING ACTIVITIES:
Purchase of property, plant and equipment	(11,672)	(8,921)	(8,292)
Acquisition of assets of a business	(3,705)
Proceeds from sale of property, plant and equipment	316	255	42
Net cash used in investing activities	(15,061)	(8,666)	(8,250)
FINANCING ACTIVITIES:
Repayments of term loans	(5,000)us-gaap_RepaymentsOfLongTermDebt	(5,000)us-gaap_RepaymentsOfLongTermDebt	(6,250)us-gaap_RepaymentsOfLongTermDebt
Cash dividends paid	(2,790)us-gaap_PaymentsOfDividendsCommonStock
Proceeds from exercise of stock options		34	75
Purchase of treasury shares	(266)	(212)	(40,847)
Net cash used in financing activities	(8,056)	(5,178)	(47,022)
Net increase in cash and cash equivalents	8,857	19,688	(23,585)
Cash and cash equivalents at beginning of period	49,475	29,787	53,372
Cash and cash equivalents at end of period	$ 58,332	$ 49,475	$ 29,787

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