Condensed Consolidated Statements of Operations and Comprehensive (Loss) Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Sales of products	$ 134,279	$ 171,302	$ 276,823	$ 302,319
Cost of sales and other direct production costs	77,503	82,953	156,179	157,273
Depreciation, depletion and amortization	25,569	29,897	54,521	55,772
Total cost of sales	103,072	112,850	210,700	213,045
Gross profit	31,207	58,452	66,123	89,274
Other operating expenses:
General and administrative	10,309	10,359	19,515	20,573
Exploration	5,853	3,362	10,367	6,312
Pre-development	1,052	521	2,304	925
Research and development	312		995
Other operating expense	697	1,024	1,387	1,664
Provision for closed operations and environmental matters	985	1,576	2,104	2,617
Lucky Friday suspension-related costs	8,024		9,605
Total other operating expenses	27,232	16,842	46,277	32,091
Income (loss) from operations	3,975	41,610	19,846	57,183
Other income (expense):
Loss on disposition of investments			(117)	439
Unrealized (loss) gain on investments	(276)	1,150	51	439
Gain (loss) on derivative contracts	2,487	(6)	(5,322)	(6)
Net foreign exchange (loss) gain	(3,883)	(1,885)	(6,145)	(10,088)
Interest and other income	319	113	644	201
Interest expense, net of amount capitalized	(10,543)	(5,370)	(19,065)	(11,081)
Total other income (expense)	(11,896)	(5,998)	(30,004)	(20,535)
(Loss) income before income taxes	(7,921)	35,612	(10,158)	36,648
Income tax (provision) benefit	(16,095)	(11,496)	12,976	(13,150)
Net income (loss)	(24,016)	24,116	2,818	23,498
Preferred stock dividends	(138)	(138)	(276)	(276)
(Loss) income applicable to common shareholders	(24,154)	23,978	2,542	23,222
Comprehensive (loss) income:
Net income (loss)	(24,016)	24,116	2,818	23,498
Unrealized loss and amortization of prior service on pension plans	(16)		16
Change in fair value of derivative contracts designated as hedge transactions	2,047	46	5,308	46
Reclassification of loss on disposition or impairment of marketable securities included in net (loss) income			167	1,000
Unrealized holding (losses) gains on investments	847	1,193	591	1,258
Comprehensive (loss) income	$ (21,138)	$ 25,355	$ 8,900	$ 25,802
Basic (loss) income per common share after preferred dividends (in dollars per share)	$ (0.06)	$ 0.06	$ 0.01	$ 0.06
Diluted (loss) income per common share after preferred dividends (in dollars per share)	$ (0.06)	$ 0.06	$ 0.01	$ 0.06
Weighted average number of common shares outstanding - basic (in shares)	396,178	383,790	395,774	381,389
Weighted average number of common shares outstanding - diluted (in shares)	396,178	387,512	399,236	384,685
Cash dividends declared per common share (in dollars per share)	$ 0.0025	$ 0.0025	$ 0.005	$ 0.005