Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Revenue		$ 646,086	$ 635,742	$ 745,994
COSTS AND EXPENSES
Costs applicable to sales	[1]	479,654	477,945	463,663
Amortization		143,751	162,436	229,564
General and administrative		32,834	40,845	55,343
Exploration		11,647	21,740	22,360
Litigation settlement		0	0	32,046
Write-downs		313,337	1,472,721	772,993
Pre-development, reclamation, and other		17,793	26,037	15,184
Total costs and expenses		999,016	2,201,724	1,591,153
OTHER INCOME (EXPENSE), NET
Fair value adjustments, net		5,202	3,618	82,768
Interest expense, net of capitalized interest		(45,703)	(47,546)	(41,303)
Other, net		(15)	(5,218)	(4,985)
Total other income (expense), net		(40,516)	(49,146)	36,480
Income (loss) before income and mining taxes		(393,446)	(1,615,128)	(808,679)
Income and mining tax benefit (expense)		26,263	428,254	158,116
NET INCOME (LOSS)		(367,183)	(1,186,874)	(650,563)
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on equity securities, net of tax of $1,446 and $5,362 for the years ended December 31, 2014 and 2013, respectively		(4,154)	(2,290)	(8,489)
Reclassification adjustments for impairment of equity securities, net of tax of $(2,552) and $(7,087) for the years ended December 31, 2014 and 2013, respectively		2,346	4,042	11,221
Reclassification adjustments for realized loss on sale of equity securities, net of tax of $(219) and $(53) for the years ended December 31, 2014 and 2013 respectively		894	346	83
Other comprehensive income (loss)		(914)	2,098	2,815
COMPREHENSIVE INCOME (LOSS)		$ (368,097)	$ (1,184,776)	$ (647,748)
NET INCOME (LOSS) PER SHARE
Basic (in dollars per share)		$ (2.83)	$ (11.59)	$ (6.65)
Diluted (in dollars per share)		$ (2.83)	$ (11.59)	$ (6.65)

[1] Excludes amortization.