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EQUITY INVESTMENT (Details) - AllDale Minerals - Cavalier Minerals - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Nov. 10, 2014
Jun. 30, 2016
Jun. 30, 2016
Dec. 31, 2015
Equity Investments        
Contribution to equity investee $ 7.4 $ 13.0 $ 33.2  
Contributions to investee to date   $ 99.1 $ 99.1 $ 65.9