Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Sales of products	$ 179,393	$ 104,941	$ 481,712	$ 328,230
Cost of sales and other direct production costs	94,061	79,273	251,335	220,805
Depreciation, depletion and amortization	26,647	28,229	82,419	80,649
	120,708	107,502	333,754	301,454
Gross profit (loss)	58,685	(2,561)	147,958	26,776
Other operating expenses:
General and administrative	11,155	9,461	31,728	26,477
Exploration	3,859	5,540	10,171	14,748
Pre-development	550	1,696	1,475	3,834
Other operating expense	954	743	2,216	2,137
Provision for closed operations and reclamation	2,162	1,181	4,779	10,983
Business Combination, Acquisition Related Costs	1,765	15	2,167	2,162
	20,445	18,636	52,536	60,341
Income (loss) from operations	38,240	(21,197)	95,422	(33,565)
Other income (expense):
Gain on derivative contracts	7	3,347		8,252
Unrealized gain (loss) on investments	49	(100)	488	(3,226)
Foreign exchange gain (loss)	2,375	9,077	(7,713)	19,518
Interest and other income	145	100	346	173
Interest expense, net of amount capitalized	(5,574)	(6,617)	(16,655)	(19,350)
	(2,998)	5,807	(23,534)	5,367
Income (loss) before income taxes	35,242	(15,390)	71,888	(28,198)
Income tax (provision) benefit	(9,453)	5,500	(22,603)	4,193
Net income (loss)	25,789	(9,890)	49,285	(24,005)
Preferred stock dividends	(138)	(138)	(414)	(414)
Income (loss) applicable to common shareholders	25,651	(10,028)	48,871	(24,419)
Comprehensive income (loss):
Net income (loss)	25,789	(9,890)	49,285	(24,005)
Reclassification of loss on disposition or impairment of marketable securities included in net income (loss)			1,000	2,993
Change in fair value of derivative contracts designated as hedge transactions	(1,602)		(1,556)
Unrealized holding gains (losses) on investments	987	(391)	2,245	(2,603)
Comprehensive income (loss)	$ 25,174	$ (10,281)	$ 50,974	$ (23,615)
Basic income (loss) per common share after preferred dividends (in dollars per share)	$ 0.07	$ (0.03)	$ 0.13	$ (0.07)
Diluted income (loss) per common share after preferred dividends (in dollars per share)	$ 0.07	$ (0.03)	$ 0.13	$ (0.07)
Weighted average number of common shares outstanding - basic (in shares)	387,578	377,508	383,458	372,555
Weighted average number of common shares outstanding - diluted (in shares)	389,918	377,508	386,318	372,555
Cash dividends declared per common share (in dollars per share)	$ 0.0025	$ 0.0025	$ 0.0075	$ 0.0075