ASSET RETIREMENT OBLIGATIONS, CONTRACTUAL THIRD-PARTY RECLAMATION RECEIVABLES, AND RECLAMATION DEPOSITS Maturities of Available for Sale Maturities (Details) - Reclamation Deposits $ in Thousands	Sep. 30, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Due within one year, Amortized Cost Basis	$ 0
Due in five years or less, Amortized Cost Basis	16,804
Due after five years to ten years, Amortized Cost Basis	5,424
Due in more than ten years, Amortized Cost Basis	8,913
Cost basis	31,141
Due within one year, Fair Value	0
Due in five years or less, Fair Value	16,601
Due after five years to ten years, Fair Value	5,262
Due in more than ten years, Fair Value	9,018
Available-for-sale Securities, Fair Value	$ 30,881