ASSET RETIREMENT OBLIGATIONS, CONTRACTUAL THIRD-PARTY RECLAMATION RECEIVABLES, AND RECLAMATION DEPOSITS Maturities of Available for Sale Maturities (Details) (Reclamation Deposits, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Reclamation Deposits
Schedule of Available-for-sale Securities [Line Items]
Due within one year, Amortized Cost Basis	$ 226
Due in five years or less, Amortized Cost Basis	17,820
Due after five years to ten years, Amortized Cost Basis	6,622
Due in more than ten years, Amortized Cost Basis	8,450
Available-for-sale Securities, Amortized Cost Basis	33,118
Due within one year, Fair Value	240
Due in five years or less, Fair Value	18,030
Due after five years to ten years, Fair Value	6,514
Due in more than ten years, Fair Value	8,703
Available-for-sale Securities, Fair Value	$ 33,487