Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net sales		$ 807,473	$ 691,873	$ 673,266
Cost of sales and other direct production costs		417,879	382,663	447,985
Depreciation, depletion and amortization:	[1]	171,793	148,110	191,451
Total cost of sales		589,672	530,773	639,436
Gross profit		217,801	161,100	33,830
Other operating expenses:
General and administrative		34,570	35,561	35,832
Exploration and pre-development		47,901	18,295	19,069
Provision for closed operations and environmental matters		14,571	3,929	4,690
Ramp-up and suspension costs		23,012	24,911	12,051
Loss on disposition of properties, plants, equipment and mineral interests		87	572	4,643
Other operating expense		14,240	10,854	4,223
Total other operating expenses		134,381	94,122	80,508
Income (loss) from operations	[1]	83,420	66,978	(46,678)
Other expense:
Fair value adjustments, net		(35,792)	(11,806)	(5,437)
Foreign exchange loss, net		417	(4,605)	(8,236)
Other net expense		(574)	(2,256)	(4,429)
Interest expense, net		(41,945)	(49,569)	(48,447)
Total other expense:		(77,894)	(68,236)	(66,549)
Income (loss) before income taxes		5,526	(1,258)	(113,227)
Income and mining tax benefit (provision)		29,569	(8,199)	18,318
Net income (loss)		35,095	(9,457)	(94,909)
Preferred stock dividends		(552)	(552)	(552)
Income (loss) applicable to common stockholders		34,543	(10,009)	(95,461)
Comprehensive income (loss):
Net income (loss)		35,095	(9,457)	(94,909)
Unrealized gain (loss) and amortization of prior service on pension plans		16,740	(3,559)	(3,277)
Unrealized (loss) gain on derivative contracts designated as hedge transactions		(12,307)	7,980	8,436
Total change in accumulated other comprehensive income (loss), net		4,433	4,421	5,159
Comprehensive income (loss)		$ 39,528	$ (5,036)	$ (89,750)
Basic income (loss) per common share after preferred dividends (in dollars per share)		$ 0.06	$ (0.02)	$ (0.19)
Diluted income (loss) per common share after preferred dividends (in dollars per share)		$ 0.06	$ (0.02)	$ (0.19)
Weighted average number of common shares outstanding – basic (in shares)		536,192	527,329	490,449
Weighted average number of common shares outstanding – diluted (in shares)		542,176	527,329	490,449

[1] Amounts reported as of and for the years ended December 31, 2020 and 2019 have been revised. See Note 3 for more information.