CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 222,501	$ 187,964
Trade receivables, net	46,284	38,052
Inventories	27,300	24,313
Prepaid expenses and other current assets	3,466	4,640
Total current assets	299,551	254,969
Property, plant and equipment	477,341	469,598
Less accumulated depreciation and depletion	(299,493)	(289,803)
Property, plant and equipment, net	177,848	179,795
Operating lease right-of-use assets	4,629	5,273
Other assets, net	2,127	565
Total assets	484,155	440,602
Current liabilities:
Accounts payable	7,186	7,404
Current portion of operating lease liabilities	1,506	1,582
Accrued expenses	5,377	8,505
Total current liabilities	14,069	17,491
Deferred tax liabilities, net	24,258	24,659
Operating lease liabilities, excluding current portion	3,343	3,919
Other liabilities	1,396	1,429
Total liabilities	43,066	47,498
Stockholders' equity:
Common stock, $0.10 par value; 45,000,000 shares authorized; 28,594,207 and 28,522,780 shares outstanding at June 30, 2024 and December 31, 2023, respectively	2,963	2,955
Additional paid-in capital	38,049	35,539
Retained earnings	458,138	412,499
Less treasury stock, at cost	(58,061)	(57,889)
Total stockholders' equity	441,089	393,104
Total liabilities and stockholders' equity	$ 484,155	$ 440,602