Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Revenues		$ 665,777	$ 646,086	$ 635,742
COSTS AND EXPENSES
Costs applicable to sales	[1]	409,541	479,654	477,945
Amortization		123,161	143,751	162,436
General and administrative		29,376	32,834	40,845
Exploration		12,930	11,647	21,740
Write-downs		4,446	313,337	1,472,721
Pre-development, reclamation, and other		17,219	17,793	26,037
Total costs and expenses		596,673	999,016	2,201,724
OTHER INCOME (EXPENSE), NET
Gains (Losses) on Extinguishment of Debt		(21,365)	15,916	0
Fair value adjustments, net		(11,581)	5,202	3,618
Interest expense, net of capitalized interest		(36,920)	(45,703)	(47,546)
Other, net		1,875	(15,931)	(5,218)
Total other income (expense), net		(67,991)	(40,516)	(49,146)
Income (loss) before income and mining taxes		1,113	(393,446)	(1,615,128)
Income and mining tax benefit (expense)		54,239	26,263	428,254
NET INCOME (LOSS)		55,352	(367,183)	(1,186,874)
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on equity securities, net of tax of $(767) and $1,446 for the years ended December 31, 2016, and 2014, respectively		3,222	(4,154)	(2,290)
Reclassification adjustments for impairment of equity securities, net of tax of $(2,552) for the year ended December 31, 2014		703	2,346	4,042
Reclassification adjustments for realized (gain) loss on sale of equity securities, net of tax of $(219) for the year ended December 31, 2014		(2,691)	894	346
Other comprehensive income (loss)		1,234	(914)	2,098
COMPREHENSIVE INCOME (LOSS)		$ 56,586	$ (368,097)	$ (1,184,776)
NET INCOME (LOSS) PER SHARE
Basic (in dollars per share)		$ 0.35	$ (2.83)	$ (11.59)
Diluted (in dollars per share)		$ 0.34	$ (2.83)	$ (11.59)

[1] Excludes amortization.