(Deficit) Equity - At-the-Market Program (Details) - USD ($)					1 Months Ended	3 Months Ended			12 Months Ended
	Jun. 09, 2016	May 23, 2016	Mar. 29, 2016	Mar. 02, 2016	Nov. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Issuance of common units, maximum (in units)				$ 300,000,000.0
Units issued in connection with private placement (in units)										5,402,985
Consideration for units issued in connection with private placement									$ 20,000,000.0	$ 5,800,000	$ 9,800,000
Aggregate percentage of interest										200.00%
May 2016 Acquisition
Class of Stock [Line Items]
Consideration for units issued in connection with private placement		$ 7,100,000
Common Units
Class of Stock [Line Items]
Units issued in connection with private placement (in units)					1,000,000,000.00	5,200,000
Net proceeds from private equity placement						$ 139,800,000
Gross proceed issuance of private placement offering						$ 140,200,000
Common units per share (in units per share)						$ 26.96
Placement fees (less than)						$ 400,000
General Partner
Class of Stock [Line Items]
Units issued in connection with private placement (in units)						106,122	1,938	15,307		108,060
Consideration for units issued in connection with private placement	$ 1,100,000		$ 8,200,000			$ 2,900,000		$ 500,000
General Public | Common Units
Class of Stock [Line Items]
Units issued in connection with private placement (in units)							94,925	750,000		5,294,925
Gross proceed issuance of private placement offering							$ 3,000,000.0	$ 25,500,000
Common units per share (in units per share)	$ 33.25	$ 33.25	$ 31.75				$ 31.51	$ 34.00
Placement fees (less than)	$ 100,000	$ 400,000	$ 200,000				$ 100,000
Net proceeds from public offerings							$ 2,900,000	$ 25,400,000
Shell Pipeline Company L P | Common Units
Class of Stock [Line Items]
Units issued in connection with private placement (in units)										0
Shell Pipeline Company L P | General Partner | May 2016 Acquisition
Class of Stock [Line Items]
Aggregate percentage of interest									2.00%