Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Revenue		$ 162,552	$ 170,938	$ 481,770	$ 495,133
COSTS AND EXPENSES
Costs applicable to sales	[1]	120,237	125,910	354,397	351,492
Amortization		35,497	41,985	107,560	123,834
General and administrative		6,694	8,515	23,979	31,809
Exploration		2,112	6,587	9,957	15,957
Pre-development, reclamation, and other		4,938	4,244	13,968	20,019
Total costs and expenses		169,478	187,241	509,861	543,111
OTHER INCOME (EXPENSE), NET
Fair value adjustments, net		5,786	16,105	3,657	(3,611)
Other, net		(8,893)	(1,303)	(14,257)	(6,927)
Interest expense, net of capitalized interest		(12,446)	(11,616)	(33,945)	(36,980)
Total other income (expense), net		(15,553)	3,186	(44,545)	(47,518)
Income (loss) before income and mining taxes		(22,479)	(13,117)	(72,636)	(95,496)
Income and mining tax benefit (expense)		8,260	16,583	8,451	18,650
NET INCOME (LOSS)		(14,219)	3,466	(64,185)	(76,846)
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on equity securities, net of tax of $686 and $939 for the three and nine months ended September 30, 2014, respectively		(931)	(1,086)	(3,744)	(1,487)
Reclassification adjustments for impairment of equity securities, net of tax of $(423) and $(1,768) for the three and nine months ended September 30, 2014, respectively		483	669	2,028	2,828
Reclassification adjustments for realized loss on sale of equity securities, net of tax of $(140) and $(150) for the three and nine months ended September 30, 2014, respectively		0	221	904	238
Other comprehensive income (loss)		(448)	(196)	(812)	1,579
COMPREHENSIVE INCOME (LOSS)		$ (14,667)	$ 3,270	$ (64,997)	$ (75,267)
NET INCOME (LOSS) PER SHARE
Basic		$ (0.11)	$ 0.03	$ (0.52)	$ (0.75)
Diluted		$ (0.11)	$ 0.03	$ (0.52)	$ (0.75)

[1] Excludes amortization.