CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 206,995	$ 187,964
Trade receivables, net	42,155	38,052
Inventories	25,724	24,313
Prepaid expenses and other current assets	4,001	4,640
Total current assets	278,875	254,969
Property, plant and equipment	474,280	469,598
Less accumulated depreciation and depletion	(294,604)	(289,803)
Property, plant and equipment, net	179,676	179,795
Operating lease right-of-use assets	4,897	5,273
Other assets, net	548	565
Total assets	463,996	440,602
Current liabilities:
Accounts payable	6,980	7,404
Current portion of operating lease liabilities	1,520	1,582
Accrued expenses	10,746	8,505
Total current liabilities	19,246	17,491
Deferred tax liabilities, net	24,421	24,659
Operating lease liabilities, excluding current portion	3,601	3,919
Other liabilities	1,412	1,429
Total liabilities	48,680	47,498
Stockholders' equity:
Common stock	674	674
Additional paid-in capital	39,191	37,820
Retained earnings	433,512	412,499
Less treasury stock, at cost	(58,061)	(57,889)
Total stockholders' equity	415,316	393,104
Total liabilities and stockholders' equity	$ 463,996	$ 440,602