Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current assets:
Cash and cash equivalents	$ 29,787	$ 53,372
Trade receivables, net	14,552	15,595
Inventories	14,127	10,764
Prepaid expenses and other current assets	1,493	1,722
Total current assets	59,959	81,453
Property, plant and equipment:
Mineral reserves and land	18,085	17,001
Proved natural gas properties, successful-efforts method	18,301	18,220
Buildings and building and leasehold improvements	3,845	3,477
Machinery and equipment	199,994	195,443
Furniture and fixtures	831	909
Automotive equipment	1,619	1,690
Property, plant and equipment, at cost	242,675	236,740
Less accumulated depreciation and depletion	(128,633)	(115,422)
Property, plant and equipment, net	114,042	121,318
Other assets, net	245	302
Total assets	174,246	203,073
Current liabilities:
Current installments of debt	5,000	6,250
Accounts payable	4,171	5,392
Accrued expenses	4,169	4,376
Total current liabilities	13,340	16,018
Debt, excluding current installments	21,667	26,667
Deferred tax liabilities, net	15,654	13,012
Other liabilities	3,230	4,363
Total liabilities	53,891	60,060
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; 6,477,716 and 6,450,718 shares issued at December 31, 2012 and 2011, respectively	648	645
Additional paid-in capital	18,353	17,199
Accumulated other comprehensive loss	(2,392)	(3,001)
Retained earnings	153,333	136,910
Less treasury stock at cost, 919,708 and 215,279 shares at December 31, 2012 and 2011, respectively	(49,587)	(8,740)
Total stockholders' equity	120,355	143,013
Total liabilities and stockholders' equity	$ 174,246	$ 203,073