Condensed Consolidated Statements of Operations and Comprehensive Income (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Sales of products	$ 119,092	$ 125,787
Cost of sales and other direct production costs	73,965	77,741
Depreciation, depletion and amortization	25,254	25,803
	99,219	103,544
Gross profit	19,873	22,243
Other operating expenses:
General and administrative	8,720	7,941
Exploration	4,615	4,150
Pre-development	521	419
Other operating expense	628	718
Provision for closed operations and environmental matters	467	1,104
	14,951	14,332
Income from operations	4,922	7,911
Other income (expense):
Unrealized (loss) gain on investments	(2,843)	688
Gain on derivative contracts	5,792	9,452
Net foreign exchange gain	12,274	4,134
Interest and other income	38	79
Interest expense, net of amounts capitalized	(6,192)	(6,840)
	9,069	7,513
Income before income taxes	13,991	15,424
Income tax provision	(1,439)	(3,783)
Net income	12,552	11,641
Reclassification of impairment of investments included in net income	2,827
Unrealized holding gains (losses) on investments	(891)	1,350
Preferred stock dividends	(138)	(138)
Income applicable to common stockholders	12,414	11,503
Net income	12,552	11,641
Reclassification of impairment of investments included in net income	2,827
Unrealized holding gains (losses) on investments	(891)	1,350
Comprehensive income	$ 14,488	$ 12,991
Basic income per common share after preferred dividends (in Dollars per share)	$ 0.03	$ 0.03
Diluted income per common share after preferred dividends (in Dollars per share)	$ 0.03	$ 0.03
Weighted average number of common shares outstanding - basic (in Shares)	368,789	342,666
Weighted average number of common shares outstanding - diluted (in Shares)	369,691	350,018