Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions									3 Months Ended													12 Months Ended
	Feb. 06, 2018	Jan. 25, 2018	Sep. 15, 2017	Jun. 09, 2016	May 23, 2016	Mar. 29, 2016	Nov. 17, 2015	May 18, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Subsequent Event [Line Items]
Distributions per Limited Partner unit (in dollars per share)									$ 0.3330	$ 0.31800	$ 0.30410	$ 0.29100	$ 0.277000	$ 0.26375	$ 0.25000	$ 0.23500	$ 0.2200	$ 0.2050	$ 0.1900	$ 0.1750	$ 0.1042	$ 1.2461	$ 1.0258	[1]	$ 0.79	[1]
Units issued in connection with public offering (in units)																						5,275,510	25,229,591
Contributions from general partner																						$ 5.8	$ 9.8	[2]	$ 6.1	[2]
Aggregate percentage of interest																						2.00%
Units issued in connection with private placement (in units)																						5,402,985	765,307
Number of days within combined tax filing submission																						15 days
Common Units
Subsequent Event [Line Items]
Gross proceeds from public offering							$ 299.4
Underwriter fees							$ 2.6
Placement fees								$ 2.6		$ 0.4
Units issued in connection with public offering (in units)							9,200,000
Contributions from general partner								$ 6.1
Units issued in connection with private placement (in units)								7,692,308		5,200,000
Gross proceed issuance of private placement offering								$ 300.0		$ 140.2
General Partner
Subsequent Event [Line Items]
Units issued in connection with public offering (in units)			105,510	32,143		258,163	187,755															105,510	504,591
Contributions from general partner				$ 1.1		$ 8.2				$ 2.9	$ 0.1					$ 0.5
Units issued in connection with private placement (in units)								156,986		106,122	1,938					15,307						108,060	15,307
Shell Pipeline Company L P | Common Units
Subsequent Event [Line Items]
Units issued in connection with public offering (in units)																						0	0
Units issued in connection with private placement (in units)																						0	0
Shell Pipeline Company L P | General Partner
Subsequent Event [Line Items]
Aggregate percentage of interest																						2.00%
Subsequent Event
Subsequent Event [Line Items]
Distributions per Limited Partner unit (in dollars per share)		$ 0.333
May 2016 Acquisition
Subsequent Event [Line Items]
Contributions from general partner					$ 7.1
May 2016 Acquisition | Common Units
Subsequent Event [Line Items]
Units issued in connection with public offering (in units)					10,500,000
May 2016 Acquisition | General Partner
Subsequent Event [Line Items]
Units issued in connection with public offering (in units)					214,285
May 2016 Acquisition | Shell Pipeline Company L P | General Partner
Subsequent Event [Line Items]
Aggregate percentage of interest																						2.00%
IPO | Subsequent Event | Common Units
Subsequent Event [Line Items]
Sale of common units (in units)	25,000,000
Net proceeds from public offering	$ 673.5
Gross proceeds from public offering	$ 680.0
Sale of Stock, Price Per Share	$ 27.20
Underwriter fees	$ 6.0
Placement fees	$ 0.5
Units issued in connection with public offering (in units)	3,750,000
IPO | Subsequent Event | General Partner
Subsequent Event [Line Items]
Units issued in connection with public offering (in units)	510,204
Contributions from general partner	$ 13.9
Private Placement | Subsequent Event | Common Units
Subsequent Event [Line Items]
Sale of Stock, Price Per Share	$ 27.20
Units issued in connection with private placement (in units)	11,029,412
Gross proceed issuance of private placement offering	$ 300.0
Private Placement | Subsequent Event | General Partner
Subsequent Event [Line Items]
Contributions from general partner	$ 6.1
Units issued in connection with private placement (in units)	225,091

[1] The financial information presented has been retrospectively adjusted for acquisitions of businesses under common control.

[2] The financial information presented has been retrospectively adjusted for acquisitions of businesses under common control.