ASSET RETIREMENT OBLIGATIONS, CONTRACTUAL THIRD-PARTY RECLAMATION RECEIVABLES, AND RECLAMATION DEPOSITS - Amortized Cost, Gross Unrealized Holding Gains and Losses and Fair Value of Available for Sale Securities (Details) (Reclamation Deposits, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Reclamation Deposits
Schedule of Available-for-sale Securities [Line Items]
Cost basis	$ 33,118
Gross unrealized holding gains	964
Gross unrealized holding losses	(595)
Fair value	$ 33,487