Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Sales of products	$ 117,502	$ 85,330	$ 243,289	$ 161,780
Cost of sales and other direct production costs	71,039	60,008	148,780	96,833
Depreciation, depletion and amortization	27,735	20,211	53,538	34,218
	98,774	80,219	202,318	131,051
Gross profit	18,728	5,111	40,971	30,729
Other operating expenses:
General and administrative	8,159	7,482	16,100	14,421
Exploration	3,140	6,221	7,290	12,714
Pre-development	437	4,512	856	9,303
Other operating expense	693	205	1,411	1,229
Provision for closed operations and environmental matters	1,267	1,845	2,371	3,639
Lucky Friday suspension-related income		(2,840)		(1,342)
Aurizon acquisition costs		20,308		25,600
	13,696	37,733	28,028	65,564
Income (loss) from operations	5,032	(32,622)	12,943	(34,835)
Other income (expense):
Gain on sale of investments		197		197
Unrealized gain (loss) on investments	(608)		80
Gain (loss) on derivative contracts	(11,601)	6,541	(2,149)	28,080
Net foreign exchange gain (loss)	(5,382)	(144)	(1,248)	389
Interest and other income	97	829	176	183
Interest expense, net of amount capitalized	(6,962)	(6,454)	(13,802)	(7,158)
	(24,456)	969	(16,943)	21,691
Loss before income taxes	(19,424)	(31,653)	(4,000)	(13,144)
Income tax benefit (provision)	5,025	6,795	1,242	(620)
Net loss	(14,399)	(24,858)	(2,758)	(13,764)
Preferred stock dividends	(138)	(138)	(276)	(276)
Loss applicable to common shareholders	(14,537)	(24,996)	(3,034)	(14,040)
Net loss	(14,399)	(24,858)	(2,758)	(13,764)
Unrealized loss and amortization of prior service on pension plans	(1,192)		(1,192)
Reclassification of net gain on sale of marketable securities included in net income		(197)		(197)
Unrealized holding (losses) gains on investments	(996)	(1,747)	354	(4,578)
Comprehensive income (loss)	$ (16,587)	$ (26,802)	$ (3,596)	$ (18,539)
Basic loss per common share after preferred dividends (in Dollars per share)	$ (0.04)	$ (0.08)	$ (0.01)	$ (0.05)
Diluted loss per common share after preferred dividends (in Dollars per share)	$ (0.04)	$ (0.08)	$ (0.01)	$ (0.05)
Weighted average number of common shares outstanding - basic (in Shares)	344,216	303,566	343,437	294,317
Weighted average number of common shares outstanding - diluted (in Shares)	344,216	303,566	343,437	294,317
Cash dividends declared per common share (in Dollars per share)	$ 0.0025	$ 0.0025	$ 0.0050	$ 0.0050