Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Sales of products	$ 217,983	$ 166,355	$ 428,835	$ 303,280
Cost of sales and other direct production costs	110,320	92,853	207,029	178,740
Depreciation, depletion and amortization	48,403	39,423	97,734	79,089
Total cost of sales	158,723	132,276	304,763	257,829
Gross profit	59,260	34,079	124,072	45,451
Other operating expenses:
General and administrative	11,104	6,979	19,111	15,918
Exploration	8,367	1,962	14,318	4,492
Pre-development	2,874	563	3,613	1,098
Other operating expense	3,643	1,445	7,282	2,365
Provision for closed operations and environmental matters	1,024	1,037	4,733	1,553
Ramp-up and suspension costs	5,786	9,572	10,104	22,568
Foundation grant	0	1,970	0	1,970
Total other operating expenses	32,798	23,528	59,161	49,964
Income (loss) from operations	26,462	10,551	64,911	(4,513)
Other income (expense):
Gain on exchange of investments	0	0	1,158	0
Unrealized (loss) gain on investments	(750)	6,409	(4,256)	5,431
Loss on derivative contracts	(17,313)	(14,002)	(16,840)	(6,109)
Net foreign exchange (loss) gain	(1,907)	(3,205)	(3,971)	3,431
Other expense	(278)	(1,326)	(439)	(1,749)
Interest expense	(10,271)	(11,829)	(21,015)	(28,140)
Total other expense	(30,519)	(23,953)	(45,363)	(27,136)
(Loss) income before income and mining taxes	(4,057)	(13,402)	19,548	(31,649)
Income and mining tax benefit (provision)	4,842	(626)	208	436
Net income (loss)	785	(14,028)	19,756	(31,213)
Preferred stock dividends	(138)	(138)	(276)	(276)
Income (loss) applicable to common shareholders	647	(14,166)	19,480	(31,489)
Comprehensive income (loss):
Net income (loss)	785	(14,028)	19,756	(31,213)
Change in fair value of derivative contracts designated as hedge transactions	1,620	10,384	3,452	(8,951)
Comprehensive income (loss)	$ 2,405	$ (3,644)	$ 23,208	$ (40,164)
Basic income (loss) per common share after preferred dividends (in cents) (in dollars per share)	$ 0.001	$ (0.027)	$ 0.036	$ (0.06)
Diluted income (loss) per common share after preferred dividends (in cents) (in dollars per share)	$ 0.001	$ (0.027)	$ 0.036	$ (0.06)
Weighted average number of common shares outstanding - basic (in shares)	535,531	525,243	534,819	524,218
Weighted average number of common shares outstanding - diluted (in shares)	542,262	525,243	541,468	524,218
Cash dividends declared per common share (in cents) (in dollars per share)	$ 1.125	$ 0.250	$ 2.000	$ 0.500