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 $ in Thousands	Sep. 30, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Cost basis	$ 31,141
Gross unrealized holding gains	573
Gross unrealized holding losses	(833)
Fair value	$ 30,881