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Partnership Operations, Organization and Basis of Presentation (Details)
9 Months Ended 12 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Duncan Merger [Member]
Common units [Member]
Partnership Operations, Organization and Basis of Presentation [Abstract]    
Number of reportable segments 5  
Limited partners ownership interest (in hundredths) 100.00%  
Mergers [Line Items]    
Common unit exchange ratio in connection with merger   1.01
Common units issued in connection with merger (in units)   24,277,310