Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Sales of products	$ 193,560	$ 199,703	$ 622,395	$ 502,983
Cost of sales and other direct production costs	112,542	103,025	318,917	280,303
Depreciation, depletion and amortization	45,790	37,990	138,918	112,492
Total cost of sales	158,332	141,015	457,835	392,795
Gross profit	35,228	58,688	164,560	110,188
Other operating expenses:
General and administrative	8,874	11,713	27,985	27,631
Exploration	13,675	3,407	27,993	7,899
Pre-development	3,433	759	7,046	1,857
Other operating expense	3,344	3,499	10,626	5,864
Provision for closed operations and environmental matters	7,564	1,254	12,297	2,807
Ramp-up and suspension costs	6,910	1,541	17,014	24,109
Foundation grant	0	0	0	1,970
Total other operating expense	43,800	22,173	102,961	72,137
(Loss) income from operations	(8,572)	36,515	61,599	38,051
Other income (expense):
Gain (loss) on derivative contracts	12,148	(6,666)	(4,692)	(12,775)
Gain on exchange of investments	0	0	1,158	0
Unrealized (loss) gain on investments	(2,861)	3,979	(7,117)	9,410
Foreign exchange gain (loss)	3,995	(2,196)	24	1,235
Other income (expense)	247	(392)	(192)	(2,141)
Interest expense	(10,469)	(10,779)	(31,484)	(38,919)
Total other income (expense)	3,060	(16,054)	(42,303)	(43,190)
(Loss) income before income and mining taxes	(5,512)	20,461	19,296	(5,139)
Income and mining tax benefit (provision)	4,533	(5,181)	3,924	(7,423)
Net (loss) income	(979)	15,280	23,220	(12,562)
Preferred stock dividends	(138)	(138)	(414)	(414)
(Loss) income applicable to common shareholders	(1,117)	15,142	22,806	(12,976)
Comprehensive (loss) income:
Net income (loss)	(979)	15,280	23,220	(12,562)
Change in fair value of derivative contracts designated as hedge transactions	(6,267)	6,150	(2,815)	(2,801)
Comprehensive (loss) income	$ (7,246)	$ 21,430	$ 20,405	$ (15,363)
Basic (loss) income per common share after preferred dividends (in cents) (in dollars per share)	$ (0.002)	$ 0.029	$ 0.043	$ (0.025)
Diluted (loss) income per common share after preferred dividends (in cents) (in dollars per share)	$ (0.002)	$ 0.028	$ 0.042	$ (0.025)
Weighted average number of common shares outstanding - basic (in shares)	536,966	529,838	535,542	526,098
Weighted average number of common shares outstanding - diluted (in shares)	536,966	535,788	541,769	526,098
Cash dividends declared per common share (in cents) (in dollars per share)	$ 0.01125	$ 0.0025	$ 0.03125	$ 0.00750