Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 278,031	$ 187,964
Trade receivables, net	43,982	38,052
Inventories	27,686	24,313
Prepaid expenses and other current assets	5,083	4,640
Total current assets	354,782	254,969
Property, plant and equipment:
Mineral reserves and land	60,952	59,307
Proved natural gas properties, successful-efforts method	15,934	15,934
Buildings and building and leasehold improvements	13,246	10,732
Machinery and equipment	393,312	374,000
Furniture and fixtures	1,409	1,312
Automotive equipment	8,393	8,313
Property, plant and equipment	493,246	469,598
Less accumulated depreciation and depletion	(310,355)	(289,803)
Property, plant and equipment, net	182,891	179,795
Operating lease right-of-use assets	4,855	5,273
Other assets, net	635	565
Total assets	543,163	440,602
Current liabilities:
Accounts payable	8,819	7,404
Current portion of operating lease liabilities	1,602	1,582
Accrued expenses	6,541	8,505
Total current liabilities	16,962	17,491
Deferred tax liabilities, net	23,659	24,659
Operating lease liabilities, excluding current portion	3,437	3,919
Other liabilities	1,364	1,429
Total liabilities	45,422	47,498
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock, $5.00 par value; authorized 500,000 shares; none issued or outstanding
Common stock, $0.10 par value; 45,000,000 and 30,000,000 shares authorized at December 31, 2024 and 2023, respectively; 29,671,768 and 29,549,431 shares issued at December 31, 2024 and 2023, respectively	2,968	2,955
Additional paid-in capital	40,549	35,539
Retained earnings	515,622	412,499
Less treasury stock; 1,051,931 and 1,026,651 shares at December 31, 2024 and 2023, respectively, at cost	(61,398)	(57,889)
Total stockholders' equity	497,741	393,104
Total liabilities and stockholders' equity	$ 543,163	$ 440,602