Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement of Other Comprehensive Income [Abstract]
Sales of metal	$ 171,797	$ 204,564
Production costs applicable to sales	(88,784)	(92,554)
Depreciation, depletion and amortization	(50,436)	(52,592)
Gross profit	32,577	59,418
COSTS AND EXPENSES
Administrative and general	10,227	7,596
Exploration	6,841	6,567
Loss on impairment	119	0
Pre-development, care, maintenance and other	4,485	1,068
Total cost and expenses	21,672	15,231
OPERATING INCOME	10,905	44,187
OTHER INCOME AND EXPENSE
Fair value adjustments, net	17,796	(23,113)
Interest income and other	3,821	5,007
Interest expense, net of capitalized interest	(9,732)	(6,670)
Total other income and expense	11,885	(24,776)
Income before income taxes	22,790	19,411
Income tax provision	(10,520)	(15,436)
Net income	$ 12,270	$ 3,975
Basic income per share:
Net income	$ 0.14	$ 0.04
Diluted income per share:
Net income	$ 0.14	$ 0.04
Weighted average number of shares of common stock
Basic	89,948	89,591
Diluted	90,036	89,821