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Partners' Capital and Distributions (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Millions
Mar. 24, 2017
Jun. 30, 2017
Dec. 31, 2016
Partners Capital And Distributions [Line Items]      
Limited Partners' Capital Account, Units Outstanding   122,579,218 117,979,218
Common units, issued   122,579,218 117,979,218
Limited Partner | Common Class A [Member]      
Partners Capital And Distributions [Line Items]      
Limited Partners' Capital Account, Units Outstanding   122,539,221  
Limited Partner | Class B [Member]      
Partners Capital And Distributions [Line Items]      
Limited Partners' Capital Account, Units Outstanding   39,997  
Common Class A [Member]      
Partners Capital And Distributions [Line Items]      
Common units, issued 4,600,000    
Common units issued to underwriters 600,000    
Public sale of units net of offering costs $ 140.5    
Sale of Stock, Price Per Share $ 30.65