Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 58,332	$ 49,475
Trade receivables, net	17,444	14,097
Inventories, net	13,436	13,688
Prepaid expenses and other current assets	2,550	1,584
Total current assets	91,762	78,844
Property, plant and equipment:
Mineral reserves and land	20,030	18,272
Proved natural gas properties, successful-efforts method	18,384	18,359
Buildings and building and leasehold improvements	5,466	4,052
Machinery and equipment	214,194	206,303
Furniture and fixtures	887	919
Automotive equipment	3,501	1,809
Property, plant and equipment	262,462	249,714
Less accumulated depreciation and depletion	(153,949)	(141,227)
Property, plant and equipment, net	108,513	108,487
Other assets, net	145	195
Total assets	200,420	187,526
Current liabilities:
Current installments of debt	16,667	5,000
Accounts payable	5,166	5,812
Accrued expenses	3,132	3,536
Total current liabilities	24,965	14,348
Debt, excluding current installments		16,667
Deferred tax liabilities, net	19,259	17,799
Other liabilities	1,505	1,907
Total liabilities	45,729	50,721
Commitments and contingencies
Stockholders' equity:
Preferred stock, $5.00 par value; authorized 500,000 shares; none issued or outstanding
Common stock, $0.10 par value; authorized 15,000,000 shares; 6,523,788 and 6,499,403 shares issued at December 31, 2014 and 2013, respectively	652	650
Additional paid-in capital	20,418	19,319
Accumulated other comprehensive loss	(1,024)	(1,498)
Retained earnings	184,710	168,133
Less treasury stock at cost, 928,469 and 924,271 shares at December 31, 2014 and 2013, respectively	(50,065)	(49,799)
Total stockholders' equity	154,691	136,805
Total liabilities and stockholders' equity	$ 200,420	$ 187,526