Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Sales of products	$ 171,302	$ 104,197	$ 302,319	$ 223,289
Cost of sales and other direct production costs	82,953	67,567	157,273	141,532
Depreciation, depletion and amortization	29,897	27,166	55,772	52,420
	112,850	94,733	213,045	193,952
Gross profit	58,452	9,464	89,274	29,337
Other operating expenses:
General and administrative	10,359	8,296	20,573	17,016
Exploration	3,362	4,592	6,312	9,208
Pre-development	521	1,618	925	2,138
Other operating expense	622	766	1,262	1,394
Provision for closed operations and environmental matters	1,576	9,335	2,617	9,802
Acquisition costs	402	2,147	402	2,147
	16,842	26,754	32,091	41,705
Income (loss) from operations	41,610	(17,290)	57,183	(12,368)
Other income (expense):
Loss on disposition of investments		(166)		(166)
Unrealized gain (loss) on investments	1,150	(117)	439	(2,960)
(Loss) gain on derivative contracts	(6)	(887)	(6)	4,905
Net foreign exchange (loss) gain	(1,885)	(1,833)	(10,088)	10,441
Interest and other income	113	35	201	73
Interest expense, net of amount capitalized	(5,370)	(6,541)	(11,081)	(12,733)
	(5,998)	(9,509)	(20,535)	(440)
Income (loss) before income taxes	35,612	(26,799)	36,648	(12,808)
Income tax (provision) benefit	(11,496)	132	(13,150)	(1,307)
Net income (loss)	24,116	(26,667)	23,498	(14,115)
Preferred stock dividends	(138)	(138)	(276)	(276)
Income (loss) applicable to common shareholders	23,978	(26,805)	23,222	(14,391)
Comprehensive income (loss):
Net income (loss)	24,116	(26,667)	23,498	(14,115)
Change in fair value of derivative contracts designated as hedge transactions	46		46
Reclassification of loss on disposition or impairment of marketable securities included in net income (loss)		166	1,000	2,993
Unrealized holding (losses) gains on investments	1,193	(1,321)	1,258	(2,212)
Comprehensive income (loss)	$ 25,355	$ (27,822)	$ 25,802	$ (13,334)
Basic income (loss) per common share after preferred dividends (in dollars per share)	$ 0.06	$ (0.07)	$ 0.06	$ (0.04)
Diluted income (loss) per common share after preferred dividends (in dollars per share)	$ 0.06	$ (0.07)	$ 0.06	$ (0.04)
Weighted average number of common shares outstanding - basic (in shares)	383,790	371,295	381,389	370,042
Weighted average number of common shares outstanding - diluted (in shares)	387,512	371,295	384,685	370,042
Cash dividends declared per common share (in dollars per share)	$ 0.0025	$ 0.0025	$ 0.005	$ 0.005