Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Revenue		$ 148,387	$ 152,956
COSTS AND EXPENSES
Costs applicable to sales	[1]	101,555	115,062
Amortization		27,964	33,090
General and administrative		8,276	8,834
Exploration		1,731	4,266
Write-downs		4,446	0
Pre-development, reclamation, and other		4,204	6,763
Total costs and expenses		148,176	168,015
OTHER INCOME (EXPENSE), NET
Fair value adjustments, net		(8,695)	(4,884)
Interest expense, net of capitalized interest		(11,120)	(10,765)
Other, net		1,314	(2,511)
Total other income (expense), net		(18,501)	(18,160)
Income (loss) before income and mining taxes		(18,290)	(33,219)
Income and mining tax benefit (expense)		(2,106)	(68)
NET INCOME (LOSS)		(20,396)	(33,287)
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on equity securities, net of tax of $(1,011) and $578 for the three months ended March 31, 2016 and 2015, respectively		1,043	(915)
Reclassification adjustments for impairment of equity securities, net of tax of $(586) for the three months ended March 31, 2015		0	928
Reclassification adjustments for realized loss on sale of equity securities		588	0
Other comprehensive income (loss)		1,631	13
COMPREHENSIVE INCOME (LOSS)		$ (18,765)	$ (33,274)
NET INCOME (LOSS) PER SHARE
Basic (in dollars per share)		$ (0.14)	$ (0.32)
Diluted (in dollars per share)		$ (0.14)	$ (0.32)

[1] Excludes amortization.