CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 370		$ 1,430	$ 2,911	$ 7,428
Accounts receivable	85,458		72,301
Other current assets	4,360		4,327
Due from affiliate			0
Total current assets	90,188		78,058
Property, plant and equipment, net	1,911,630	$ 1,828,252	1,795,129
Intangible assets, net	281,207		301,345
Goodwill	16,211		16,211
Investment in equity method investees	660,254		690,485
Other noncurrent assets	18,566		13,565
Investment in subsidiaries			0
Total assets	2,978,056		2,894,793
Liabilities and Partners' Capital
Trade accounts payable	22,569		16,375
Accrued expenses	18,347		12,499
Due to affiliate	13		1,088
Deferred revenue	11,152	10,088	4,000
Ad valorem taxes payable	8,223		8,329
Accrued interest	15,285		12,310
Accrued environmental remediation	2,702		3,130
Other current liabilities	10,388		11,258
Total current liabilities	88,679		68,989
Long-term debt	1,175,313		1,051,192
Deferred Purchase Price Obligation	416,718		362,959
Noncurrent deferred revenue	39,624	$ 35,528	12,707
Noncurrent accrued environmental remediation	1,182		2,214
Other noncurrent liabilities	5,525		7,063
Total liabilities	1,727,041		1,505,124
Total partners' capital	1,251,015		1,389,669	1,161,308	1,169,673
Total liabilities and partners' capital	2,978,056		2,894,793
Consolidating adjustments
Assets
Cash and cash equivalents	0		0	0	0
Accounts receivable			0
Other current assets			0
Due from affiliate	(581,988)		(515,097)
Total current assets	(581,988)		(515,097)
Property, plant and equipment, net			0
Intangible assets, net			0
Goodwill			0
Investment in equity method investees			0
Other noncurrent assets			0
Investment in subsidiaries	(5,514,884)		(5,344,164)
Total assets	(6,096,872)		(5,859,261)
Liabilities and Partners' Capital
Trade accounts payable			0
Accrued expenses			0
Due to affiliate	(581,988)		(515,097)
Deferred revenue			0
Ad valorem taxes payable			0
Accrued interest			0
Accrued environmental remediation			0
Other current liabilities			0
Total current liabilities	(581,988)		(515,097)
Long-term debt			0
Deferred Purchase Price Obligation			0
Noncurrent deferred revenue			0
Noncurrent accrued environmental remediation			0
Other noncurrent liabilities			0
Total liabilities	(581,988)		(515,097)
Total partners' capital	(5,514,884)		(5,344,164)
Total liabilities and partners' capital	(6,096,872)		(5,859,261)
Summit Midstream Partners, LP | Reportable Legal Entities
Assets
Cash and cash equivalents	29		126	492	698
Accounts receivable	22		22
Other current assets	843		1,188
Due from affiliate			0
Total current assets	894		1,336
Property, plant and equipment, net	5,134		4,206
Intangible assets, net			0
Goodwill			0
Investment in equity method investees			0
Other noncurrent assets	3,320		2,547
Investment in subsidiaries	2,082,686		2,019,700
Total assets	2,092,034		2,027,789
Liabilities and Partners' Capital
Trade accounts payable	219		209
Accrued expenses	725		928
Due to affiliate	413,900		263,935
Deferred revenue			0
Ad valorem taxes payable	14		0
Accrued interest			0
Accrued environmental remediation			0
Other current liabilities	5,386		6,395
Total current liabilities	420,244		271,467
Long-term debt			0
Deferred Purchase Price Obligation	416,718		362,959
Noncurrent deferred revenue			0
Noncurrent accrued environmental remediation			0
Other noncurrent liabilities	4,057		3,694
Total liabilities	841,019		638,120
Total partners' capital	1,251,015		1,389,669
Total liabilities and partners' capital	2,092,034		2,027,789
Co-Issuers | Reportable Legal Entities
Assets
Cash and cash equivalents	3		75	51	51
Accounts receivable			0
Other current assets			0
Due from affiliate			0
Total current assets	3		75
Property, plant and equipment, net			0
Intangible assets, net			0
Goodwill			0
Investment in equity method investees			0
Other noncurrent assets	9,184		10,913
Investment in subsidiaries	3,432,198		3,324,464
Total assets	3,441,385		3,335,452
Liabilities and Partners' Capital
Trade accounts payable			0
Accrued expenses			0
Due to affiliate	168,101		252,250
Deferred revenue			0
Ad valorem taxes payable			0
Accrued interest	15,285		12,310
Accrued environmental remediation			0
Other current liabilities			0
Total current liabilities	183,386		264,560
Long-term debt	1,175,313		1,051,192
Deferred Purchase Price Obligation			0
Noncurrent deferred revenue			0
Noncurrent accrued environmental remediation			0
Other noncurrent liabilities			0
Total liabilities	1,358,699		1,315,752
Total partners' capital	2,082,686		2,019,700
Total liabilities and partners' capital	3,441,385		3,335,452
Guarantor Subsidiaries | Reportable Legal Entities
Assets
Cash and cash equivalents	330		1,138	1,543	5,768
Accounts receivable	74,766		65,842
Other current assets	2,922		2,697
Due from affiliate	513,867		493,067
Total current assets	591,885		562,744
Property, plant and equipment, net	1,563,950		1,442,333
Intangible assets, net	255,317		278,958
Goodwill	16,211		16,211
Investment in equity method investees			0
Other noncurrent assets	6,062		105
Investment in subsidiaries			0
Total assets	2,433,425		2,300,351
Liabilities and Partners' Capital
Trade accounts payable	18,523		11,283
Accrued expenses	16,051		10,592
Due to affiliate			0
Deferred revenue	10,716		4,000
Ad valorem taxes payable	7,802		7,809
Accrued interest			0
Accrued environmental remediation			0
Other current liabilities	4,488		4,385
Total current liabilities	57,580		38,069
Long-term debt			0
Deferred Purchase Price Obligation			0
Noncurrent deferred revenue	37,802		12,707
Noncurrent accrued environmental remediation			0
Other noncurrent liabilities	1,437		3,293
Total liabilities	96,819		54,069
Total partners' capital	2,336,606		2,246,282
Total liabilities and partners' capital	2,433,425		2,300,351
Non-Guarantor Subsidiaries | Reportable Legal Entities
Assets
Cash and cash equivalents	8		91	$ 825	$ 911
Accounts receivable	10,670		6,437
Other current assets	595		442
Due from affiliate	68,121		22,030
Total current assets	79,394		29,000
Property, plant and equipment, net	342,546		348,590
Intangible assets, net	25,890		22,387
Goodwill			0
Investment in equity method investees	660,254		690,485
Other noncurrent assets			0
Investment in subsidiaries			0
Total assets	1,108,084		1,090,462
Liabilities and Partners' Capital
Trade accounts payable	3,827		4,883
Accrued expenses	1,571		979
Due to affiliate			0
Deferred revenue	436		0
Ad valorem taxes payable	407		520
Accrued interest			0
Accrued environmental remediation	2,702		3,130
Other current liabilities	514		478
Total current liabilities	9,457		9,990
Long-term debt			0
Deferred Purchase Price Obligation			0
Noncurrent deferred revenue	1,822		0
Noncurrent accrued environmental remediation	1,182		2,214
Other noncurrent liabilities	31		76
Total liabilities	12,492		12,280
Total partners' capital	1,095,592		1,078,182
Total liabilities and partners' capital	$ 1,108,084		$ 1,090,462