CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 176,305	$ 133,384
Trade receivables, net	44,061	33,592
Inventories, net	23,778	19,579
Prepaid expenses and other current assets	2,250	3,435
Total current assets	246,394	189,990
Property, plant and equipment	456,530	441,597
Less accumulated depreciation and depletion	(284,469)	(269,627)
Property, plant and equipment, net	172,061	171,970
Operating lease right-of-use assets	5,010	5,372
Other assets, net	590	440
Total assets	424,055	367,772
Current liabilities:
Accounts payable	8,070	7,725
Current portion of operating lease liabilities	1,494	1,411
Accrued expenses	6,438	6,401
Total current liabilities	16,002	15,537
Deferred tax liabilities, net	25,263	25,582
Operating lease liabilities, excluding current portion	3,740	4,129
Other liabilities	1,418	1,436
Total liabilities	46,423	46,684
Stockholders' equity:
Common stock	672	671
Additional paid-in capital	37,035	34,528
Retained earnings	396,638	342,504
Less treasury stock, at cost	(56,713)	(56,615)
Total stockholders' equity	377,632	321,088
Total liabilities and stockholders' equity	$ 424,055	$ 367,772