Percentage of voting equity interests acquired at the acquisition date in the business combination.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8813-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_EquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_AmberjackPipelineCompanyLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_AmberjackPipelineCompanyLLCSeriesAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_AmberjackPipelineCompanyLLCSeriesBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_MarsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_BengalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_PermianBasinMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_LOCAPLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_PoseidonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_ProteusMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_EndymionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=shlx_MarsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=shlx_LOCAPLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=shlx_CrestwoodPermianBasinLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Equity Method Investments - Schedule of Equity Investments in Affiliates (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 01, 2017	Oct. 17, 2017	Oct. 03, 2016
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 822,900,000	$ 362,600,000
Amberjack Pipeline Company LLC ("Amberjack")
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)		0.00%
Equity method investments	$ 457,500,000	$ 0
Amberjack Pipeline Company LLC - Series A
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)	75.00%
Amberjack Pipeline Company LLC - Series B
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)	50.00%
Mars Oil Pipeline Company LLC (“Mars”)
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)	71.50%	71.50%
Equity method investments	$ 168,900,000	$ 187,400,000
Bengal Pipeline Company LLC (“Bengal”)
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)	50.00%	50.00%
Equity method investments	$ 81,500,000	$ 79,700,000
Permian Basin
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)	50.00%	50.00%
Equity method investments	$ 72,200,000	$ 49,400,000
LOCAP
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)	41.48%	41.48%
Equity method investments	$ 8,200,000	$ 6,900,000
Poseidon Oil Pipeline Company LLC (“Poseidon”)
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)	36.00%	36.00%
Equity method investments	$ 0	$ 2,300,000
Proteus
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)	10.00%	10.00%
Equity method investments	$ 16,300,000	$ 17,400,000
Endymion Oil Pipeline Company, LLC (“Endymion”)
Schedule of Equity Method Investments [Line Items]
Ownership interest (in percentage)	10.00%	10.00%
Equity method investments	$ 18,300,000	$ 19,500,000
Mars Oil Pipeline Company LLC (“Mars”)
Schedule of Equity Method Investments [Line Items]
Voting interest acquired			22.90%		20.00%
LOCAP
Schedule of Equity Method Investments [Line Items]
Voting interest acquired			41.48%
Permian Basin
Schedule of Equity Method Investments [Line Items]
Voting interest acquired				50.00%