CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 36,873	$ 29,787
Trade receivables, net	17,724	14,552
Inventories	14,177	14,127
Prepaid expenses and other current assets	1,864	1,493
Total current assets	70,638	59,959
Property, plant and equipment	246,444	242,675
Less accumulated depreciation and depletion	(135,436)	(128,633)
Property, plant and equipment, net	111,008	114,042
Other assets, net	220	245
Total assets	181,866	174,246
Current liabilities:
Current installments of debt	6,250	5,000
Accounts payable	5,711	4,171
Accrued expenses	3,158	4,169
Total current liabilities	15,119	13,340
Debt, excluding current installments	19,167	21,667
Deferred tax liabilities, net	16,572	15,654
Other liabilities	2,615	3,230
Total liabilities	53,473	53,891
Stockholders' equity:
Common stock	649	648
Additional paid-in capital	18,820	18,353
Accumulated other comprehensive loss	(1,992)	(2,392)
Retained earnings	160,715	153,333
Less treasury stock, at cost	(49,799)	(49,587)
Total stockholders' equity	128,393	120,355
Total liabilities and stockholders' equity	$ 181,866	$ 174,246