Asset Impairment (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Impaired Long-Lived Assets Held and Used [Line Items]
Estimated reclamation costs	$ 1,100
Impairment charge	$ 0			$ 0	$ 46,772	$ 0
Marathon Property [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment charge		$ 46,800	$ 500
Estimated fair value		$ 8,600