VARIABLE INTEREST ENTITIES - Cavalier Minerals (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Oct. 06, 2015	Sep. 30, 2015	Nov. 11, 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	$ 17,834		$ 878
Cavalier Minerals | Funding Commitments | Bluegrass Minerals
Variable Interest Entities
Funding commitment	$ 743		$ 37
Cavalier Minerals | Initial Funding Commitment | Alliance Minerals
Variable Interest Entities
Funding commitment				48,000
Cavalier Minerals | Initial Funding Commitment | Bluegrass Minerals
Variable Interest Entities
Funding commitment				$ 2,000
Cavalier Minerals | Additional Funding Commitment | Alliance Minerals
Variable Interest Entities
Funding commitment		96,000
Cavalier Minerals | Additional Funding Commitment | Bluegrass Minerals
Variable Interest Entities
Funding commitment		$ 4,000