Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Sales of products	$ 577,775	$ 645,957	$ 443,567
Cost of sales and other direct production costs	304,727	338,325	292,378
Depreciation, depletion and amortization	116,062	116,126	112,678
Total cost of sales	420,789	454,451	405,056
Gross profit	156,986	191,506	38,511
Other operating expenses:
General and administrative	35,611	45,040	34,201
Exploration	23,510	14,720	17,745
Pre-development	5,448	3,137	4,213
Research and development	3,276	243
Provision for closed operations and environmental matters	6,701	5,721	12,220
Other operating expense	2,513	3,153	3,177
(Gain) loss on disposition of properties, plants, equipment and mineral interests	(6,042)	(147)	404
Lucky Friday suspension-related costs	21,301
Acquisition costs	25	2,695	2,162
Total other operating expense	92,343	74,562	74,122
Income (loss) from operations	64,643	116,944	(35,611)
Other income (expense):
(Loss) gain on derivative contracts	(21,250)	4,423	8,252
Loss on disposition of investments	(166)		(44)
Unrealized loss on investments	(251)	(177)	(3,333)
Net foreign exchange (loss) gain	(10,300)	(2,926)	24,551
Interest and other income	1,692	507	916
Interest expense, net of amount capitalized	(38,012)	(21,796)	(25,389)
Total other (expense) income:	(68,283)	(19,969)	4,953
(Loss) income before income taxes	(3,640)	96,975	(30,658)
Income tax provision	(19,879)	(27,428)	(56,310)
Net income (loss)	(23,519)	69,547	(86,968)
Series B Preferred Stock dividends declared	(552)	(552)	(552)
(Loss) income applicable to common stockholders	(24,071)	68,995	(87,520)
Comprehensive (loss) income:
Net Income (Loss)	(23,519)	69,547	(86,968)
Unrealized gain (loss) and amortization of prior service on pension plans	(1,326)	676	(850)
Change in fair value of derivative contracts designated as hedge transactions	10,290	(5,260)
Unrealized holding gains (losses) on investments	2,098	1,613	(2,743)
Reclassification of disposition or impairment of investments included in net (loss) income	167	1,000	2,993
Total change in accumulated other comprehensive income (loss), net	11,229	(1,971)	(600)
Comprehensive income (loss)	$ (12,290)	$ 67,576	$ (87,568)
Basic (loss) income per common share after preferred dividends (in dollars per share)	$ (0.06)	$ 0.18	$ (0.23)
Diluted (loss) income per common share after preferred dividends (in dollars per share)	$ (0.06)	$ 0.18	$ (0.23)
Weighted average number of common shares outstanding – basic (in shares)	397,394	386,416	373,954
Weighted average number of common shares outstanding – diluted (in shares)	397,394	389,322	373,954