CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 156,198	$ 133,384
Trade receivables, net	40,735	33,592
Inventories, net	22,350	19,579
Prepaid expenses and other current assets	2,824	3,435
Total current assets	222,107	189,990
Property, plant and equipment	454,550	441,597
Less accumulated depreciation and depletion	(280,019)	(269,627)
Property, plant and equipment, net	174,531	171,970
Operating lease right-of-use assets	5,254	5,372
Other assets, net	480	440
Total assets	402,372	367,772
Current liabilities:
Accounts payable	7,511	7,725
Current portion of operating lease liabilities	1,457	1,411
Accrued expenses	5,596	6,401
Total current liabilities	14,564	15,537
Deferred tax liabilities, net	25,129	25,582
Operating lease liabilities, excluding current portion	4,015	4,129
Other liabilities	1,413	1,436
Total liabilities	45,121	46,684
Stockholders' equity:
Common stock	672	671
Additional paid-in capital	36,248	34,528
Retained earnings	377,044	342,504
Less treasury stock, at cost	(56,713)	(56,615)
Total stockholders' equity	357,251	321,088
Total liabilities and stockholders' equity	$ 402,372	$ 367,772