Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Sales of products	$ 199,703	$ 161,532	$ 502,983	$ 448,321
Cost of sales and other direct production costs	105,977	95,878	284,717	311,202
Depreciation, depletion and amortization	40,238	50,774	119,327	139,038
Total cost of sales	146,215	146,652	404,044	450,240
Gross profit (loss)	53,488	14,880	98,939	(1,919)
Other operating expenses:
General and administrative	11,713	7,978	27,631	26,855
Exploration	3,407	4,808	7,899	13,556
Pre-development	759	881	1,857	2,535
Research and development	0	53	0	614
Other operating expense	3,497	437	5,851	1,681
(Gain) loss on disposition of properties, plants, equipment and mineral interests	(14)	24	559	4,666
Provision for closed operations and reclamation	1,254	1,907	2,807	3,529
Ramp-up and suspension costs	1,541	3,722	24,109	8,766
Foundation grant	0	0	1,970	0
Acquisition costs	2	183	13	593
Total other operating expense	22,159	19,993	72,696	62,795
Income (loss) from operations	31,329	(5,113)	26,243	(64,714)
Other income (expense):
Loss on derivative contracts	(6,666)	(4,718)	(12,775)	(2,719)
Gain on disposition of investments	0	927	0	927
Unrealized gain (loss) on investments	3,979	(126)	9,410	(1,159)
Foreign exchange (loss) gain	(2,196)	773	1,235	(6,741)
Other expense	(406)	(1,096)	(1,582)	(3,407)
Interest expense	(10,779)	(11,777)	(38,919)	(33,777)
Total other expense	(16,068)	(16,017)	(42,631)	(46,876)
Income (loss) before income taxes	15,261	(21,130)	(16,388)	(111,590)
Income tax (provision) benefit	(1,633)	1,614	(1,197)	20,009
Net income (loss)	13,628	(19,516)	(17,585)	(91,581)
Preferred stock dividends	(138)	(138)	(414)	(414)
Income (loss) applicable to common shareholders	13,490	(19,654)	(17,999)	(91,995)
Comprehensive income (loss):
Net income (loss)	13,628	(19,516)	(17,585)	(91,581)
Change in fair value of derivative contracts designated as hedge transactions	6,150	(3,288)	(2,801)	4,511
Comprehensive income (loss)	$ 19,778	$ (22,804)	$ (20,386)	$ (87,070)
Basic income (loss) per common share after preferred dividends (in dollars per share)	$ 0.03	$ (0.04)	$ (0.03)	$ (0.19)
Diluted income (loss) per common share after preferred dividends (in dollars per share)	$ 0.03	$ (0.04)	$ (0.03)	$ (0.19)
Weighted average number of common shares outstanding - basic (in shares)	529,838	489,971	526,098	486,298
Weighted average number of common shares outstanding - diluted (in shares)	535,788	489,971	526,098	486,298
Cash dividends declared per common share (in dollars per share)	$ 0.0025	$ 0.0025	$ 0.0075	$ 0.0075