Cost method investment, ownership percentage.

No definition available.

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- Definition

Organization and business operations.

+ References

No definition available.

+ Details

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- Definition

Ownership percentage

+ References

No definition available.

+ Details

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Balance Type:	na
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- 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

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- Definition

Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of limited partner units outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

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

- Definition

The number of units or percentage investment held in the subsidiary by the limited liability company or limited partnership.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611443-123010

+ Details

Name:	us-gaap_SubsidiaryOfLimitedLiabilityCompanyOrLimitedPartnershipOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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- Details

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- Details

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- Details

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- Details

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Name:	dei_LegalEntityAxis=smlp_GrandRiverGatheringLLCMember
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- Details

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- Details

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ORGANIZATION, BUSINESS OPERATIONS AND PRESENTATION AND CONSOLIDATION - Narrative (Details) - shares	1 Months Ended	6 Months Ended
	Feb. 29, 2016	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2016
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)		73,355,775	73,085,996
Summit Midstream Niobrara, LLC \| Summit Midstream Partners, LP
Organization And Business Operations [Line Items]
Cost method ownership interest			1.00%
SMP Holdings \| Contributed Entities
Organization And Business Operations [Line Items]
Percent of issued and outstanding membership interest	100.00%
SMP Holdings \| OGC
Organization And Business Operations [Line Items]
Percentage of ownership interest	40.00%
Subsidiary of Summit Investments
Organization And Business Operations [Line Items]
Ownership interest				1.00%
Grand River Gathering, LLC
Organization And Business Operations [Line Items]
Percentage of ownership interest			100.00%
Common units \| SMP Holdings
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)		25,854,581
Common units \| Energy Capital Partners
Organization And Business Operations [Line Items]
Common limited partner capital (in shares)		5,915,827
General Partner
Organization And Business Operations [Line Items]
General partner interest		2.00%
General Partner \| Summit Investments \| Summit Midstream Partners, LP
Organization And Business Operations [Line Items]
General partner interest		2.00%