COMMITMENTS AND CONTINGENCIES - Operating Leases (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) installment $ / item	Dec. 31, 2016 USD ($)
Operating leases
Estimated advance royalty due in 2016, which is accrued	$ 5,200	$ 5,200
Mt. Hope Project
Operating leases
Payment of royalty installment	$ 500
Molybdenum price (in dollars per pound) | $ / item	8.40
Eureka Moly LLC | Mt. Hope Project
Operating leases
Lease Term	30 years
Lease period for written notice of termination	30 days
Maximum period for receipt of notice of default	90 days
Maximum period for receipt of notice of default in non-payment obligation	10 days
Royalty advance percentage required by long-term lease	3.00%
Cumulative amount paid for Construction Royalty Fee	$ 24,600
Estimated advance royalty due in 2016, which is accrued	4,200
Annual advance royalty payment	500
Accrued annual advance royalty	$ 1,500
Number of installments | installment	3
Molybdenum price (in dollars per pound) | $ / item	12
Period of commercial production	5 years
Eureka Moly LLC | Mt. Hope Project | Minimum
Operating leases
Period of commercial production	20 months
Eureka Moly LLC | Mt. Hope Project | Maximum
Operating leases
Period of commercial production	24 months