CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 60,626	$ 59,926
Trade receivables, net	16,837	15,889
Inventories, net	13,772	14,728
Prepaid expenses and other current assets	1,068	1,418
Total current assets	92,303	91,961
Property, plant and equipment	274,427	271,686
Less accumulated depreciation and depletion	(171,071)	(167,308)
Property, plant and equipment, net	103,356	104,378
Other assets, net	155	160
Total assets	195,814	196,499
Current liabilities:
Accounts payable	4,199	6,022
Accrued expenses	2,819	2,720
Total current liabilities	7,018	8,742
Deferred tax liabilities, net	19,242	19,184
Other liabilities	1,914	1,946
Total liabilities	28,174	29,872
Stockholders' equity:
Common stock	655	655
Additional paid-in capital	22,018	21,642
Retained earnings	198,168	194,798
Less treasury stock, at cost	(53,201)	(50,468)
Total stockholders' equity	167,640	166,627
Total liabilities and stockholders' equity	$ 195,814	$ 196,499