CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 33,488	$ 29,787
Trade receivables, net	16,776	14,552
Inventories	13,689	14,127
Prepaid expenses and other current assets	1,824	1,493
Total current assets	65,777	59,959
Property, plant and equipment, at cost	243,953	242,675
Less accumulated depreciation and depletion	(132,060)	(128,633)
Property, plant and equipment, net	111,893	114,042
Other assets, net	233	245
Total assets	177,903	174,246
Current liabilities:
Current installments of debt	6,250	5,000
Accounts payable	4,928	4,171
Accrued expenses	4,070	4,169
Total current liabilities	15,248	13,340
Debt, excluding current installments	20,417	21,667
Deferred tax liabilities, net	16,011	15,654
Other liabilities	2,909	3,230
Total liabilities	54,585	53,891
Stockholders' equity:
Common stock	649	648
Additional paid-in capital	18,583	18,353
Accumulated other comprehensive loss	(2,205)	(2,392)
Retained earnings	156,090	153,333
Less treasury stock, at cost	(49,799)	(49,587)
Total stockholders' equity	123,318	120,355
Total liabilities and stockholders' equity	$ 177,903	$ 174,246