VARIABLE INTEREST ENTITIES - Cavalier Minerals (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Oct. 06, 2015	Dec. 31, 2014	Nov. 10, 2014
All Dale I | Cavalier Minerals
Variable Interest Entities
Noncontrolling ownership interest (as a percent)	71.70%
All Dale I | Funding Commitments | Cavalier Minerals
Variable Interest Entities
Funding commitment					$ 49,000
All Dale II | Cavalier Minerals
Variable Interest Entities
Noncontrolling ownership interest (as a percent)	72.80%
All Dale II | Funding Commitments | Cavalier Minerals
Variable Interest Entities
Funding commitment			$ 100,000
Cavalier Minerals | Funding Commitments | Alliance Minerals
Variable Interest Entities
Funding commitment	$ 6,923	$ 80,502		$ 36,480
Cavalier Minerals | Funding Commitments | Bluegrass Minerals
Variable Interest Entities
Funding commitment	$ 288	$ 3,354		$ 1,520
Cavalier Minerals | Initial Funding Commitment | Bluegrass Minerals
Variable Interest Entities
Funding commitment					2,000
Cavalier Minerals | Initial Funding Commitment | Variable Interest Entity, Primary Beneficiary | Alliance Minerals
Variable Interest Entities
Funding commitment					$ 48,000
Cavalier Minerals | Additional Funding Commitment | Bluegrass Minerals
Variable Interest Entities
Funding commitment			4,000
Cavalier Minerals | Additional Funding Commitment | Variable Interest Entity, Primary Beneficiary | Alliance Minerals
Variable Interest Entities
Funding commitment			$ 96,000