Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Sales of products	$ 139,709	$ 142,544
Cost of sales and other direct production costs	72,869	78,676
Depreciation, depletion and amortization	28,054	28,952
Total cost of sales	100,923	107,628
Gross profit	38,786	34,916
Other operating expenses:
General and administrative	7,735	9,206
Exploration	7,360	4,514
Pre-development	1,005	1,252
Research and development	1,436	683
Other operating expense	515	663
Lucky Friday suspension-related costs	5,017	1,581
Acquisition costs	2,507	27
Provision for closed operations and environmental matters	1,262	1,119
Total other operating expense	26,837	19,045
Income from operations	11,949	15,871
Other income (expense):
Loss on disposal of investments		(167)
Unrealized gain on investments	310	327
Gain (loss) on derivative contracts	4,007	(7,809)
Net foreign exchange gain (loss )	2,592	(2,262)
Other (expense) income	(56)	325
Interest expense, net of amounts capitalized	(9,794)	(8,522)
Total other expense	(2,941)	(18,108)
Income (loss) before income taxes	9,008	(2,237)
Income tax (provision) benefit	(768)	29,071
Net income (loss)	8,240	26,834
Preferred stock dividends	(138)	(138)
Income applicable to common stockholders	8,102	26,696
Comprehensive income:
Net income	8,240	26,834
Reclassification of disposal and impairment of investments included in net income		167
Unrealized holding losses on investments	(31)	(256)
Unrealized gain and amortization of prior service on pension plans		32
Change in fair value of derivative contracts designated as hedge transactions	(2,073)	3,261
Comprehensive income	$ 6,136	$ 30,038
Basic income per common share after preferred dividends (in dollars per share)	$ 0.02	$ 0.07
Diluted income per common share after preferred dividends (in dollars per share)	$ 0.02	$ 0.07
Weighted average number of common shares outstanding - basic (in shares)	399,322	395,370
Weighted average number of common shares outstanding - diluted (in shares)	401,923	398,149