Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Sales of products	$ 645,957	$ 443,567	$ 500,781
Cost of sales and other direct production costs	338,983	293,567	304,446
Depreciation, depletion and amortization	115,468	111,489	111,134
Total cost of sales	454,451	405,056	304,446
Gross profit	191,506	38,511	85,201
Other operating expenses:
General and administrative	45,040	34,201	31,538
Exploration	14,720	17,745	17,698
Pre-development	3,137	4,213	1,969
Research and development	243
Provision for closed operations and environmental matters	5,721	12,220	10,098
Other operating expense	3,153	3,177	2,295
(Gain) loss on disposition of properties, plants, equipment and mineral interests	(147)	404	(25)
Acquisition costs	2,695	2,162
Total other operating expense	74,562	74,122	63,573
Income (loss) from operations	116,944	(35,611)	21,628
Other income (expense):
Gain on derivative contracts	4,423	8,252	9,134
Net (loss) on sale of investments		(44)
Unrealized loss on investments	(177)	(3,333)	(3,224)
Net foreign exchange (loss) gain	(2,926)	24,551	11,535
Interest and other income	507	916	286
Interest expense, net of amount capitalized	(21,796)	(25,389)	(26,775)
Total other (expense) income:	(19,969)	4,953	(9,044)
Income (loss) before income taxes	96,975	(30,658)	12,584
Income tax (provision) benefit	(27,428)	(56,310)	5,240
Net income (loss)	69,547	(86,968)	17,824
Preferred stock dividends	(552)	(552)	(552)
Income (loss) applicable to common stockholders	68,995	(87,520)	17,272
Comprehensive income (loss):
Net income (loss)	69,547	(86,968)	17,824
Unrealized gain (loss) and amortization of prior service on pension plans	676	(850)	(6,875)
Change in fair value of derivative contracts designated as hedge transactions	(5,260)
Unrealized holding gains (losses) on investments	1,613	(2,743)	(1,282)
Reclassification of impairment of investments included in net income (loss)	1,000	2,993	2,425
Total change in accumulated other comprehensive income (loss), net	(1,971)	(600)	(5,732)
Comprehensive income (loss)	$ 67,576	$ (87,568)	$ 12,092
Basic income (loss) per common share after preferred dividends (in dollars per share)	$ 0.18	$ (0.23)	$ 0.05
Diluted income (loss) per common share after preferred dividends (in dollars per share)	$ 0.18	$ (0.23)	$ 0.05
Weighted average number of common shares outstanding – basic (in shares)	386,416	373,954	353,442
Weighted average number of common shares outstanding – diluted (in shares)	389,322	373,954	357,435