Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Sales of metal	$ 895,492	$ 1,021,200	$ 515,457
Production costs applicable to sales	(456,757)	(419,956)	(257,636)
Depreciation, depletion and amortization	(218,857)	(224,500)	(141,619)
Gross profit	219,878	376,744	116,202
COSTS AND EXPENSES
Administrative and general	32,977	31,379	24,176
Exploration	26,270	19,128	14,249
Loss on impairment	5,825	0	0
Pre-development, care, maintenance and other	1,261	19,441	2,877
Total cost and expenses	66,333	69,948	41,302
OPERATING INCOME	153,545	306,796	74,900
OTHER INCOME AND EXPENSE
Loss on debt extinguishments	(1,036)	(5,526)	(20,300)
Fair value adjustments, net	(23,487)	(52,050)	(117,094)
Interest income and other	14,436	(6,610)	771
Interest expense, net of capitalized interest	(26,169)	(34,774)	(30,942)
Total other income and expense	(36,256)	(98,960)	(167,565)
Income before income taxes	117,289	207,836	(92,665)
Income tax provision	(68,612)	(114,337)	9,481
NET INCOME	48,677	93,499	(91,308)
Income (Loss) from Continuing Operations Attributable to Parent	48,677	93,499	(83,184)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	0	0	(6,029)
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	$ 0	$ 0	$ (2,095)
Basic income per share:
Net income	$ 0.54	$ 1.05	$ (1.05)
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.54	$ 1.05	$ (0.95)
Income (Loss) from Discontinued Operations, Net of Tax, Per Basic Share	$ 0	$ 0	$ (0.10)
Diluted income per share:
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.54	$ 1.04	$ (0.95)
Income (Loss) from Discontinued Operations, Net of Tax, Per Diluted Share	$ 0.00	$ 0.00	$ (0.10)
Net income	$ 0.54	$ 1.04	$ (1.05)
Weighted average number of shares of common stock
Basic	89,437	89,383	87,185
Diluted	89,603	89,725	87,185