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Goodwill and Other Intangible Assets Changes in Carrying Amount of Goodwill (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
Goodwill [Roll Forward]  
December 31, 2017 $ 0
March 31, 2018 796,359
Midstream Acquisition [Member]  
Goodwill [Roll Forward]  
Acquisitions $ 796,359