CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 83,166	$ 85,000
Trade receivables, net	18,373	16,473
Inventories, net	12,903	13,546
Prepaid expenses and other current assets	2,326	2,996
Total current assets	116,768	118,015
Property, plant and equipment	330,196	300,236
Less accumulated depreciation and depletion	(201,522)	(190,518)
Property, plant and equipment, net	128,674	109,718
Other assets, net	573	713
Total assets	246,015	228,446
Current liabilities:
Accounts payable	8,848	6,263
Accrued expenses	2,997	3,096
Total current liabilities	11,845	9,359
Deferred tax liabilities, net	13,468	12,374
Other liabilities	1,409	1,461
Total liabilities	26,722	23,194
Stockholders' equity:
Common stock	660	659
Additional paid-in capital	25,523	24,307
Accumulated other comprehensive (loss) income	(27)	86
Retained earnings	247,093	233,905
Less treasury stock, at cost	(53,956)	(53,705)
Total stockholders' equity	219,293	205,252
Total liabilities and stockholders' equity	$ 246,015	$ 228,446