CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 43,401	$ 29,787
Trade receivables, net	17,767	14,552
Inventories	13,550	14,127
Prepaid expenses and other current assets	1,573	1,493
Total current assets	76,291	59,959
Property, plant and equipment	247,771	242,675
Less accumulated depreciation and depletion	(138,253)	(128,633)
Property, plant and equipment, net	109,518	114,042
Other assets, net	208	245
Total assets	186,017	174,246
Current liabilities:
Current installments of debt	5,000	5,000
Accounts payable	6,029	4,171
Accrued expenses	3,892	4,169
Total current liabilities	14,921	13,340
Debt, excluding current installments	17,917	21,667
Deferred tax liabilities, net	17,180	15,654
Other liabilities	2,438	3,230
Total liabilities	52,456	53,891
Stockholders' equity:
Common stock	649	648
Additional paid-in capital	19,057	18,353
Accumulated other comprehensive loss	(1,850)	(2,392)
Retained earnings	165,504	153,333
Less treasury stock, at cost	(49,799)	(49,587)
Total stockholders' equity	133,561	120,355
Total liabilities and stockholders' equity	$ 186,017	$ 174,246