Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015		Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Revenue	$ 166,263	$ 164,562	$ 319,219		$ 324,195
COSTS AND EXPENSES
Costs applicable to sales	119,097	118,687	234,160	[1]	225,583	[1]
Amortization	38,974	41,422	72,064		81,849
General and administrative	8,451	9,398	17,286		23,294
Exploration	3,579	5,153	7,845		9,370
Pre-development, reclamation, and other	2,267	8,760	9,030		15,775
Total costs and expenses	172,368	183,420	340,385		355,871
OTHER INCOME (EXPENSE), NET
Fair value adjustments, net	2,754	(8,282)	(2,130)		(19,717)
Impairment of equity securities	(31)	(934)	(1,545)		(3,522)
Interest and other income, net	(2,821)	(116)	(3,817)		(2,100)
Interest expense, net of capitalized interest	(10,734)	(12,310)	(21,499)		(25,365)
Total other income and expense	(10,832)	(21,642)	(28,991)		(50,704)
Income before income and mining taxes	(16,937)	(40,500)	(50,157)		(82,380)
Income and mining tax benefit (expense)	260	(2,621)	192		2,068
NET INCOME (LOSS)	(16,677)	(43,121)	(49,965)		(80,312)
OTHER COMPREHENSIVE INCOME (LOSS), Net of Tax:
Unrealized gain (loss) on equity securities, net of tax of $7 for the three months ended June 30, 2015 and $487 and $253 for the three and six months ended June 30, 2014, respectively	(1,312)	(773)	(2,813)		(401)
Reclassification adjustments for impairment of equity securities, net of tax of $(362) and $(1,363) for the three and six months ended June 30, 2014, respectively	31	572	1,545		2,159
Reclassification adjustments for realized loss on sale of equity securities, net of tax of $(10) for the three and six months ended June 30, 2014, respectively	904	17	904		17
Other comprehensive income (loss)	(377)	(184)	(364)		1,775
COMPREHENSIVE INCOME (LOSS)	$ (17,054)	$ (43,305)	$ (50,329)		$ (78,537)
NET INCOME (LOSS) PER SHARE
Basic	$ (0.12)	$ (0.42)	$ (0.42)		$ (0.78)
Diluted	$ (0.12)	$ (0.42)	$ (0.42)		$ (0.78)

[1] Excludes amortization.