Equity - Public Offering (Details) - USD ($) $ / shares in Units, $ in Millions					3 Months Ended		6 Months Ended
		Jun. 09, 2016	May 23, 2016	Mar. 29, 2016	Jun. 30, 2017	Mar. 31, 2016	Jun. 30, 2017		Jun. 30, 2016	[3]
Class of Stock [Line Items]
Units issued in connection with public offering (in units)							96,863
Net proceeds from public offering	[1]						$ 3.0
Consideration for units issued in connection with private placement							$ 0.1	[2]	$ 9.8
Aggregate percentage of general partner interest							2.00%
Shell Treasury Center West Inc | Five Year Revolver
Class of Stock [Line Items]
Debt instrument term				5 years		5 years	5 years
Shell Treasury Center West Inc | Five Year Revolver | May 2016 Acquisition
Class of Stock [Line Items]
Debt instrument term			5 years
Shell Treasury Center West Inc | 364 Day Revolver
Class of Stock [Line Items]
Debt instrument term				364 days		364 days	364 days
Common Units | May 2016 Acquisition
Class of Stock [Line Items]
Units issued in connection with public offering (in units)			10,500,000
Net proceeds from public offering			$ 345.8
Common Units | General Public
Class of Stock [Line Items]
Units issued in connection with public offering (in units)			1,575,000	12,650,000			94,925
Net proceeds from public offering		$ 51.8		$ 395.1
Gross proceeds from public offering		$ 52.4		$ 401.6
Common units per share (in units per share)		$ 33.25		$ 31.75	$ 31.51	$ 34.00	$ 31.51
Underwriter fees		$ 0.5		$ 6.3
Placement fees		$ 0.1		$ 0.2	$ 0.1	$ 0.1
Common Units | General Public | May 2016 Acquisition
Class of Stock [Line Items]
Units issued in connection with public offering (in units)			10,500,000
Net proceeds from public offering			$ 345.8
Gross proceeds from public offering			$ 349.1
Common units per share (in units per share)			$ 33.25
Underwriter fees			$ 2.9
Placement fees			$ 0.4
General Partner
Class of Stock [Line Items]
Units issued in connection with public offering (in units)		32,143		258,163			1,938
Consideration for units issued in connection with private placement		$ 1.1		$ 8.2	$ 0.1	$ 0.5
Aggregate percentage of general partner interest		2.00%		2.00%	2.00%	2.00%	2.00%
General Partner | May 2016 Acquisition
Class of Stock [Line Items]
Units issued in connection with public offering (in units)			214,285
Consideration for units issued in connection with private placement			$ 7.1
Aggregate percentage of general partner interest			2.00%

[1] Prior period financial information has been retrospectively adjusted for the acquisition of the Shell Delta, Na Kika and Refinery Gas Pipeline Operations.

[2] The 2017 financial information reflects adjustments for the acquisition of the Shell Delta, Na Kika and Refinery Gas Pipeline Operations from January 1, 2017 through May 9, 2017.

[3] Prior period financial information has been retrospectively adjusted for the acquisition of the Shell Delta, Na Kika and Refinery Gas Pipeline Operations.