CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 80,731	$ 67,218
Trade receivables, net	23,180	19,602
Inventories, net	13,237	12,846
Prepaid expenses and other current assets	1,660	1,692
Total current assets	118,808	101,358
Property, plant and equipment	366,446	348,472
Less accumulated depreciation and depletion	(215,413)	(205,708)
Property, plant and equipment, net	151,033	142,764
Operating lease right-of-use assets	3,535
Other assets, net	457	549
Total assets	273,833	244,671
Current liabilities:
Accounts payable	6,521	4,570
Current portion of operating lease liabilities	1,351
Accrued expenses	3,438	3,393
Total current liabilities	11,310	7,963
Deferred tax liabilities, net	16,354	12,365
Operating lease liabilities, excluding current portion	2,144
Other liabilities	1,356	1,376
Total liabilities	31,164	21,704
Stockholders' equity:
Common stock	662	661
Additional paid-in capital	27,045	25,867
Accumulated other comprehensive loss	(39)	(13)
Retained earnings	269,358	250,568
Less treasury stock, at cost	(54,357)	(54,116)
Total stockholders' equity	242,669	222,967
Total liabilities and stockholders' equity	$ 273,833	$ 244,671