Annual report pursuant to Section 13 and 15(d)

Sale of Common Units (Details)

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Sale of Common Units (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Feb. 10, 2017
Sep. 30, 2016
Dec. 31, 2017
Sale Of Common Units      
Maximum aggregate offering price of common limited partners units under an equity distribution agreement   $ 250.0  
Units issued and sold (in shares)     777,262
Net proceeds from issue and sale of common units     $ 25.5
Compensation payable     0.6
Other offering costs     0.4
Remaining capacity to issue additional common units under an equity distribution agreement     $ 157.3
Common Unitholders Public      
Sale Of Common Units      
Sale of units to public (in shares) 6,900,000    
Net proceeds from sale of units $ 223.0