CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 125,991	$ 98,500
Restricted cash	2,532	2,532
Short-term investments	139,238	207,434
Accounts receivable	54,108	40,749
Allowance for doubtful accounts	(366)	(364)
Accounts receivable, net	53,742	40,385
Inventories:
Finished goods	19,643	26,329
Raw materials	2,320	1,799
Total inventories	21,963	28,128
Supplies, prepaid items and other:
Prepaid insurance	10,768	14,846
Precious metals	11,560	12,094
Supplies	30,682	30,486
Other	2,767	2,337
Total supplies, prepaid items and other	55,777	59,763
Total current assets	399,243	436,742
Property, plant and equipment, net	832,192	835,298
Other assets:
Operating lease assets	27,235	24,852
Intangible and other assets, net	1,449	1,292
Total other assets	28,684	26,144
Total assets	1,260,119	1,298,184
Current liabilities:
Accounts payable	56,064	68,323
Short-term financing	9,018	13,398
Accrued and other liabilities	38,820	30,961
Current portion of long-term debt	5,742	5,847
Total current liabilities	109,644	118,529
Long-term debt, net	543,835	575,874
Noncurrent operating lease liabilities	18,260	16,074
Other noncurrent accrued and other liabilities	523	523
Deferred income taxes	69,672	68,853
Commitments and contingencies (Note 5)
Stockholders' equity:
Common stock, $.10 par value; 150 million shares authorized, 91.2 million shares issued	9,117	9,117
Capital in excess of par value	501,097	501,026
Retained earnings	232,638	227,015
Total stockholders' equity	742,852	737,158
Less treasury stock, at cost:
Common stock, 18.9 million shares (18.1 million shares at December 31, 2023)	224,667	218,827
Total stockholders' equity	518,185	518,331
Total liabilities and stockholders' equity	$ 1,260,119	$ 1,298,184