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RELATED-PARTY TRANSACTIONS - Cavalier Minerals (Details) - Cavalier Minerals - AllDale Minerals - USD ($)
$ in Millions
12 Months Ended
Nov. 10, 2014
Dec. 31, 2015
Dec. 31, 2014
Related Party Transaction      
Contributions to investee to date   $ 65.9 $ 11.6
Contribution to equity investee $ 7.4 $ 54.3