CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 48,487	$ 49,475
Trade receivables, net	18,832	14,097
Inventories	11,992	13,688
Prepaid expenses and other current assets	1,855	1,584
Total current assets	81,166	78,844
Property, plant and equipment	251,542	249,714
Less accumulated depreciation and depletion	(144,044)	(141,227)
Property, plant and equipment, net	107,498	108,487
Other assets, net	183	195
Total assets	188,847	187,526
Current liabilities:
Current installments of debt	5,000	5,000
Accounts payable	3,458	5,812
Accrued expenses	4,397	3,536
Total current liabilities	12,855	14,348
Debt, excluding current installments	15,417	16,667
Deferred tax liabilities, net	17,967	17,799
Other liabilities	1,708	1,907
Total liabilities	47,947	50,721
Stockholders' equity:
Common stock	650	650
Additional paid-in capital	19,552	19,319
Accumulated other comprehensive loss	(1,352)	(1,498)
Retained earnings	171,928	168,133
Less treasury stock, at cost	(49,878)	(49,799)
Total stockholders' equity	140,900	136,805
Total liabilities and stockholders' equity	$ 188,847	$ 187,526