CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 54,519	$ 58,332
Trade receivables, net	19,214	17,444
Inventories	14,121	13,436
Prepaid expenses and other current assets	927	2,550
Total current assets	88,781	91,762
Property, plant and equipment	268,505	262,462
Less accumulated depreciation and depletion	(163,941)	(153,949)
Property, plant and equipment, net	104,564	108,513
Other assets, net	138	145
Total assets	193,483	200,420
Current liabilities:
Current installments of debt		16,667
Accounts payable	4,075	5,166
Accrued expenses	3,771	3,132
Total current liabilities	7,846	24,965
Deferred tax liabilities, net	19,491	19,259
Other liabilities	1,151	1,505
Total liabilities	28,488	45,729
Stockholders' equity:
Common stock	654	652
Additional paid-in capital	21,353	20,418
Accumulated other comprehensive loss		(1,024)
Retained earnings	193,211	184,710
Less treasury stock, at cost	(50,223)	(50,065)
Total stockholders' equity	164,995	154,691
Total liabilities and stockholders' equity	$ 193,483	$ 200,420