Consolidated Statements of Operations and Comprehensive Income (Loss) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Sales of products	$ 500,781	$ 382,589	$ 321,143
Cost of sales and other direct production costs	304,446	235,316	134,105
Depreciation, depletion and amortization	111,134	81,127	43,522
Total cost of sales	415,580	316,443	177,627
Gross profit	85,201	66,146	143,516
Other operating expenses:
General and administrative	31,538	28,925	21,253
Exploration	17,698	23,502	31,822
Pre-development	1,969	14,148	17,916
Provision for closed operations and environmental matters	10,098	5,403	4,652
Other operating expense	2,295	1,641	4,423
(Gain) loss on disposition of property, plants, equipment and mineral interests	(25)	(75)	275
Lucky Friday suspension-related (income) costs		(1,401)	25,309
Aurizon acquisition costs		26,397
Total other operating expense	63,573	98,540	105,650
Income (loss) from operations	21,628	(32,394)	37,866
Other income (expense):
Gain (loss) on derivative contracts	9,134	17,979	(10,457)
Net gain on sale of investments		197
Unrealized loss on investments	(3,224)	(2,639)	(1,171)
Net foreign exchange gain (loss)	11,535	2,959	(63)
Interest and other income	286	662	85
Interest expense	(26,775)	(21,689)	(2,427)
Total other income (expense):	(9,044)	(2,531)	(14,033)
Income (loss) before income taxes	12,584	(34,925)	23,833
Income tax benefit (provision)	5,240	9,795	(8,879)
Net income (loss)	17,824	(25,130)	14,954
Unrealized gain (loss) and amortization of prior service on pension plans	(6,875)	2,230	(1,644)
Unrealized holding gains (losses) on investments	(1,282)	(7,249)	53
Reclassification of impairment of investments included in net income (loss)	2,425	2,638	1,171
Total change in accumulated other comprehensive income (loss), net	(5,732)	(2,381)	(420)
Preferred stock dividends	(552)	(552)	(552)
Income (loss) applicable to common stockholders	17,272	(25,682)	14,402
Net income (loss)	17,824	(25,130)	14,954
Unrealized gain (loss) and amortization of prior service on pension plans	(6,875)	2,230	(1,644)
Unrealized holding gains (losses) on investments	(1,282)	(7,249)	53
Reclassification of impairment of investments included in net income (loss)	2,425	2,638	1,171
Total change in accumulated other comprehensive income (loss), net	(5,732)	(2,381)	(420)
Comprehensive income (loss)	$ 12,092	$ (27,511)	$ 14,534
Basic income (loss) per common share after preferred dividends (in Dollars per share)	$ 0.05	$ (0.08)	$ 0.05
Diluted income (loss) per common share after preferred dividends (in Dollars per share)	$ 0.05	$ (0.08)	$ 0.05
Weighted average number of common shares outstanding – basic (in Shares)	353,442	318,679	285,375
Weighted average number of common shares outstanding – diluted (in Shares)	357,435	318,679	297,566