CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 56,015	$ 49,475
Trade receivables, net	17,737	14,097
Inventories	11,539	13,688
Prepaid expenses and other current assets	1,138	1,584
Total current assets	86,429	78,844
Property, plant and equipment	253,423	249,714
Less accumulated depreciation and depletion	(147,003)	(141,227)
Property, plant and equipment, net	106,420	108,487
Other assets, net	171	195
Total assets	193,020	187,526
Current liabilities:
Current installments of debt	5,000	5,000
Accounts payable	4,499	5,812
Accrued expenses	3,306	3,536
Total current liabilities	12,805	14,348
Debt, excluding current installments	14,167	16,667
Deferred tax liabilities, net	18,126	17,799
Other liabilities	1,660	1,907
Total liabilities	46,758	50,721
Stockholders' equity:
Common stock	650	650
Additional paid-in capital	19,843	19,319
Accumulated other comprehensive loss	(1,213)	(1,498)
Retained earnings	176,949	168,133
Less treasury stock, at cost	(49,967)	(49,799)
Total stockholders' equity	146,262	136,805
Total liabilities and stockholders' equity	$ 193,020	$ 187,526