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Related Party Transactions - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Related Party Transaction Due From To Related Party [Line Items]          
Revenue from contracts with affiliated entities $ 14.2 $ 1.8 $ 25.1 $ 2.8  
Fees from contracts with affiliated entities 0.5   0.8 0.1  
Distributions payable to the owners         0.5
Maximum
         
Related Party Transaction Due From To Related Party [Line Items]          
Fees from contracts with affiliated entities   $ 0.1