Related Party Debt - Additional Information (Details) - USD ($)													3 Months Ended			9 Months Ended
	Sep. 15, 2017	May 10, 2017	Mar. 07, 2017	Mar. 01, 2017	Sep. 27, 2016	May 23, 2016	Mar. 29, 2016	Nov. 11, 2015	Jun. 29, 2015	May 12, 2015	Nov. 03, 2014	Aug. 06, 2014	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2017		Sep. 30, 2016
Line Of Credit Facility [Line Items]
Interest and fee expenses													$ 9,100,000	$ 2,000,000		$ 19,800,000		$ 5,000,000
Repayments of debt																265,000,000	[1]	$ 410,000,000	[2]
Level 2
Line Of Credit Facility [Line Items]
Long-term debt, carrying value													1,001,900,000			1,001,900,000
Long-term debt, fair value													$ 1,017,700,000			$ 1,017,700,000
Revolving Credit Facility | Zydeco Pipeline Company LLC (“Zydeco”)
Line Of Credit Facility [Line Items]
Weighted average interest rate																2.80%
Revolving Credit Facility | STCW | Zydeco Pipeline Company LLC (“Zydeco”)
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity												$ 30,000,000.0
Line of credit facility, expiration period												6 months
Shell Treasury Center West Inc | Five Year Revolver, variable rate, due October 31, 2019
Line Of Credit Facility [Line Items]
Debt instrument term	5 years						5 years						5 years		5 years	5 years
Shell Treasury Center West Inc | Five Year Fixed Facility, fixed rate, due March 1, 2022
Line Of Credit Facility [Line Items]
Debt instrument term																5 years
Shell Treasury Center West Inc | 364-Day Revolver, variable rate, due March 1, 2017
Line Of Credit Facility [Line Items]
Debt instrument term							364 days								364 days	364 days
Repayments of debt							$ 137,400,000
Shell Treasury Center West Inc | Revolving Credit Facility | Zydeco Pipeline Company LLC (“Zydeco”)
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity													$ 30,000,000			$ 30,000,000
Shell Treasury Center West Inc | Revolving Credit Facility | Five Year Revolver, variable rate, due October 31, 2019
Line Of Credit Facility [Line Items]
Debt instrument term					5 years		5 years			5 years	5 years					5 years
Repayments of debt	$ 265,000,000						$ 272,600,000
Line of credit facility maximum borrowing capacity											$ 300,000,000.0		760,000,000.0			$ 760,000,000.0
Shell Treasury Center West Inc | Revolving Credit Facility | 364-Day Revolver, variable rate, due March 1, 2017
Line Of Credit Facility [Line Items]
Debt instrument term								364 days	364 days							364 days
Line of credit facility maximum borrowing capacity								$ 180,000,000.0
Shell Treasury Center West Inc | Revolving Credit Facility | 364-Day Revolver, variable rate, due March 1, 2017 | STCW
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity									$ 100,000,000.0
Shell Treasury Center West Inc | Revolving Credit Facility | Amended And Restated Revolver
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity					$ 760,000,000.0					$ 400,000,000.0
Issuance fee paid					$ 600,000
Weighted average interest rate																2.40%
Shell Treasury Center West Inc | Fixed Facility | Five Year Fixed Facility, fixed rate, due March 1, 2022
Line Of Credit Facility [Line Items]
Debt instrument term				5 years												5 years
Line of credit facility maximum borrowing capacity													$ 600,000,000.0			$ 600,000,000.0
Issuance fee paid			$ 700,000
Fixed interest rate				3.23%
Shell Treasury Center West Inc | Fixed Facility | Five Year Fixed Facility, fixed rate, due March 1, 2022 | STCW
Line Of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity				$ 600,000,000.0
May 2017 Acquisition
Line Of Credit Facility [Line Items]
Consideration, cash on hand		$ 50,000,000
May 2017 Acquisition | Shell Treasury Center West Inc | Five Year Revolver, variable rate, due October 31, 2019
Line Of Credit Facility [Line Items]
Debt instrument term		5 years
May 2017 Acquisition | Shell Treasury Center West Inc | Five Year Fixed Facility, fixed rate, due March 1, 2022
Line Of Credit Facility [Line Items]
Debt instrument term		5 years
May 2017 Acquisition | Shell Treasury Center West Inc | Revolving Credit Facility | Five Year Revolver, variable rate, due October 31, 2019
Line Of Credit Facility [Line Items]
Debt instrument term		5 years				5 years
Consideration, funded with borrowings		$ 73,100,000
May 2017 Acquisition | Shell Treasury Center West Inc | Fixed Facility | Five Year Fixed Facility, fixed rate, due March 1, 2022
Line Of Credit Facility [Line Items]
Debt instrument term																5 years
Consideration, funded with borrowings		$ 506,900,000
May 2016 Acquisition
Line Of Credit Facility [Line Items]
Consideration, cash on hand						$ 50,400,000
May 2016 Acquisition | Shell Treasury Center West Inc | Five Year Revolver, variable rate, due October 31, 2019
Line Of Credit Facility [Line Items]
Debt instrument term						5 years
May 2016 Acquisition | Shell Treasury Center West Inc | Revolving Credit Facility | Five Year Revolver, variable rate, due October 31, 2019
Line Of Credit Facility [Line Items]
Consideration, funded with borrowings						$ 296,700,000

[1] The financial information for the nine months ended September 30, 2017 reflects adjustments for the acquisition of the Shell Delta,Na Kika and Refinery Gas Pipeline Operations from January 1, 2017 through May 9, 2017.

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