Condensed Consolidated Statements of Comprehensive Income (Loss) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Revenue	$ 152,956		$ 159,633
COSTS AND EXPENSES
Costs applicable to sales	115,062	[1]	106,896	[1]
Amortization	33,090		40,459
General and administrative	8,834		13,896
Exploration	4,266		4,217
Pre-development, reclamation, and other	6,763		6,984
Total costs and expenses	168,015		172,452
OTHER INCOME (EXPENSE), NET
Fair value adjustments, net	(4,884)		(11,436)
Impairment of equity securities	(1,514)		(2,588)
Interest and other income, net	(997)		(1,983)
Interest expense, net of capitalized interest	(10,765)		(13,054)
Total other income and expense	(18,160)		(29,061)
Income before income and mining taxes	(33,219)		(41,880)
Income and mining tax benefit (expense)	(68)		4,689
NET INCOME (LOSS)	(33,287)		(37,191)
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on equity securities, net of tax of $578 and $(234) for the three months ended March 31, 2015 and 2014, respectively	(915)		371
Reclassification adjustments for impairment of equity securities, net of tax of $(586) and $(1,001) for the three months ended March 31, 2015 and 2014, respectively	928		1,587
Other comprehensive income (loss)	13		1,958
COMPREHENSIVE INCOME (LOSS)	$ (33,274)		$ (35,233)
NET INCOME (LOSS) PER SHARE
Basic	$ (0.32)		$ (0.36)
Diluted	$ (0.32)		$ (0.36)

[1] Excludes amortization.