Net Income Per Limited Partner Unit (Schedule of Net Income Per Limited Partner Unit) (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
3 Months Ended 8 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2015
Sep. 30, 2016
Schedule Of Earnings Per Unit [Line Items]        
Partners' Capital Account, Distributions $ 20.0 $ 17.4 $ 43.5 $ 58.8
Undistributed Earnings, Basic (17.1) 4.6 8.1 [1] (10.5)
Net Income (Loss) Allocated to Limited Partners $ 2.9 $ 22.0 $ 51.6 $ 48.3
Weighted Average Number of Shares Outstanding, Basic and Diluted 100.6 100.6 100.6 100.6
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax $ 0.03 $ 0.22 $ 0.51 $ 0.46
Incentive Distribution Rights [Member]        
Schedule Of Earnings Per Unit [Line Items]        
Incentive Distribution, Distribution $ 0.1 $ 0.0 $ 0.0 $ 0.1
Undistributed Earnings, Basic (0.1) 0.0 0.0 [1] 2.2
Net Income (Loss) Allocated to Limited Partners 0.0 0.0 0.0 2.3
Subordinated Units        
Schedule Of Earnings Per Unit [Line Items]        
Distribution Made to Limited Partner, Cash Distributions Declared 9.3 8.1 20.3 27.4
Undistributed Earnings, Basic (9.3) 2.1 3.4 [1] (7.3)
Net Income (Loss) Allocated to Limited Partners $ 0.0 $ 10.2 $ 23.7 $ 20.1
Weighted Average Number of Shares Outstanding, Basic and Diluted 46.8 46.8 46.8 46.8
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax $ 0.00 $ 0.22 $ 0.51 $ 0.43
Common Units        
Schedule Of Earnings Per Unit [Line Items]        
Distribution Made to Limited Partner, Cash Distributions Declared $ 10.6 $ 9.3 $ 23.2 $ 31.3
Undistributed Earnings, Basic (7.7) 2.5 4.7 [1] (5.4)
Net Income (Loss) Allocated to Limited Partners $ 2.9 $ 11.8 $ 27.9 $ 25.9
Weighted Average Number of Shares Outstanding, Basic and Diluted 53.8 53.8 53.8 53.8
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax $ 0.05 $ 0.22 $ 0.52 $ 0.48
[1] Net income attributable to partners and in excess of distribution is for the period subsequent to the IPO.