Related Party Debt - Additional Information (Details) - USD ($)								1 Months Ended	12 Months Ended
	Dec. 01, 2017	Sep. 15, 2017	May 10, 2017	Mar. 01, 2017	May 23, 2016	Mar. 29, 2016	Aug. 06, 2014	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015		Sep. 27, 2016	Nov. 11, 2015	Jun. 29, 2015	May 12, 2015	Nov. 03, 2014
Line Of Credit Facility [Line Items]
Interest and fee expenses associated with borrowings									$ 29,400,000	$ 8,600,000		$ 4,000,000
Interest paid									25,000,000	7,000,000		2,700,000
Repayments of credit facilities									533,100,000	410,000,000	[1]	$ 0	[1]
Total Capacity								$ 2,390,000,000	$ 2,390,000,000	970,000,000
May 2017 Acquisition
Line Of Credit Facility [Line Items]
Consideration, cash on hand			$ 50,000,000
May 2016 Acquisition
Line Of Credit Facility [Line Items]
Consideration, cash on hand					$ 50,400,000
Five Year Revolver | STCW
Line Of Credit Facility [Line Items]
Total Capacity																		$ 300,000,000
Five Year Fixed Facility
Line Of Credit Facility [Line Items]
Debt instrument term									5 years
Borrowings under credit facilities	$ 93,100,000
Total Capacity								600,000,000	$ 600,000,000	0
Five Year Fixed Facility | STCW
Line Of Credit Facility [Line Items]
Payments of issuance fee				$ 700,000
Total Capacity				$ 600,000,000
Five Year Revolver due December 2022
Line Of Credit Facility [Line Items]
Borrowings under credit facilities	1,000,000,000
Payments of issuance fee	1,700,000
Total Capacity								1,000,000,000	$ 1,000,000,000	0
Five Year Revolver due October 2019
Line Of Credit Facility [Line Items]
Interest paid	700,000
Repayments of credit facilities		$ 265,000,000						268,100,000
Unused capacity commitment fee percentage									0.19%
Total Capacity								760,000,000	$ 760,000,000	760,000,000
Five Year Revolver due October 2019 | May 2017 Acquisition
Line Of Credit Facility [Line Items]
Consideration, funded with borrowings			73,100,000
Amended and Restated Revolver 1 | STCW
Line Of Credit Facility [Line Items]
Increase in maximum borrowing capacity																	$ 400,000,000
Credit facility issuance fee																	$ 200,000
364 Day Revolver
Line Of Credit Facility [Line Items]
Total Capacity								0	$ 0	$ 180,000,000
364 Day Revolver | STCW
Line Of Credit Facility [Line Items]
Total Capacity															$ 180,000,000	$ 100,000,000
Credit facility issuance fee															$ 100,000	$ 100,000
Revolving Credit Facility | Zydeco Pipeline Company LLC (“Zydeco”)
Line Of Credit Facility [Line Items]
Unused capacity commitment fee percentage									0.23%
Interest rate									3.10%
Revolving Credit Facility | STCW | Zydeco Pipeline Company LLC (“Zydeco”)
Line Of Credit Facility [Line Items]
Total Capacity							$ 30,000,000
Line of credit facility, expiration period							6 months
Five Year Fixed Facility
Line Of Credit Facility [Line Items]
Debt instrument term									5 years
Five Year Fixed Facility | Line of Credit | May 2017 Acquisition
Line Of Credit Facility [Line Items]
Consideration, funded with borrowings			506,900,000
Five Year Fixed Facility | Line of Credit | Shell Treasury Center West Inc
Line Of Credit Facility [Line Items]
Fixed interest rate				3.23%
Five Year Fixed Facility | Line of Credit | Shell Treasury Center West Inc | May 2017 Acquisition
Line Of Credit Facility [Line Items]
Consideration, funded with borrowings			$ 506,900,000
Five Year Revolver due December 2022
Line Of Credit Facility [Line Items]
Debt instrument term									5 years
Interest rate									2.50%
Five Year Revolver due December 2022 | Shell Treasury Center West Inc
Line Of Credit Facility [Line Items]
Debt instrument term									5 years
Five Year Revolver due December 2022 | Five Year Fixed Facility | December 2017 Acquisition
Line Of Credit Facility [Line Items]
Consideration, funded with borrowings	$ 825,000,000
Five Year Revolver due October 2019
Line Of Credit Facility [Line Items]
Debt instrument term									5 years
Five Year Revolver due October 2019 | Affiliated Entity | Shell Treasury Center West Inc | May 2016 Acquisition
Line Of Credit Facility [Line Items]
Consideration, funded with borrowings					$ 296,700,000
Five Year Revolver due October 2019 | Shell Treasury Center West Inc
Line Of Credit Facility [Line Items]
Debt instrument term									5 years
Total Capacity														$ 760,000,000.0
Credit facility issuance fee														$ 600,000
Interest rate									2.50%
Five Year Revolver due October 2019 | Revolving Credit Facility | Shell Treasury Center West Inc
Line Of Credit Facility [Line Items]
Repayments of credit facilities						$ 272,600,000
364 Day Revolver
Line Of Credit Facility [Line Items]
Debt instrument term									364 days
364 Day Revolver | Shell Treasury Center West Inc
Line Of Credit Facility [Line Items]
Debt instrument term						364 days			364 days
Repayments of credit facilities						$ 137,400,000
Fair Value, Inputs, Level 2
Line Of Credit Facility [Line Items]
Carrying amount of total debt								1,846,900,000	$ 1,846,900,000
Estimated fair value of total debt								$ 1,858,400,000	$ 1,858,400,000

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