Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Statement of Other Comprehensive Income [Abstract]
Sales of metal	$ 254,406	$ 231,090	$ 458,970	$ 430,714
Production costs applicable to sales	(131,823)	(77,102)	(224,377)	(169,576)
Depreciation, depletion and amortization	(61,024)	(57,641)	(113,616)	(107,682)
Gross profit	61,559	96,347	120,977	153,456
COSTS AND EXPENSES
Administrative and general	8,594	1,827	16,190	14,058
Exploration	6,305	4,077	12,872	6,839
Loss on impairment	4,813	0	4,813	0
Pre-development, care, maintenance and other	273	11,104	1,341	14,678
Total cost and expenses	19,985	17,008	35,216	35,575
OPERATING INCOME	41,574	79,339	85,761	117,881
OTHER INCOME AND EXPENSE
Loss on debt extinguishments	0	(389)	0	(856)
Fair value adjustments, net	16,039	(12,432)	(7,074)	(17,700)
Interest income and other	(3,221)	2,763	1,786	4,664
Interest expense, net of capitalized interest	(7,557)	(9,268)	(14,227)	(18,573)
Total other income and expense	5,261	(19,326)	(19,515)	(32,465)
Income before income taxes	46,835	60,013	66,246	85,416
Income tax provision	(23,862)	(21,402)	(39,298)	(34,341)
NET INCOME	$ 22,973	$ 38,611	$ 26,948	$ 51,075
Basic income per share:
Net income	$ 0.26	$ 0.43	$ 0.30	$ 0.57
Diluted income per share:
Net income	$ 0.26	$ 0.43	$ 0.30	$ 0.57
Weighted average number of shares of common stock
Basic	89,631	89,310	89,611	89,299
Diluted	89,733	89,712	89,777	89,683