SUMMARY OF SIGNIFCANT ACCOUNTING POLICIES - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	7 Months Ended	12 Months Ended
Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Midstream services revenue - affiliate	$ 0	$ 76,750	$ 15,142
Gas gathering
Disaggregation of Revenue [Line Items]
Midstream services revenue - affiliate	0	7,656	820
Gas processing
Disaggregation of Revenue [Line Items]
Midstream services revenue - affiliate	0	53,108	11,037
Transmission
Disaggregation of Revenue [Line Items]
Midstream services revenue - affiliate	0	15,848	3,285
NGL transmission
Disaggregation of Revenue [Line Items]
Midstream services revenue - affiliate	$ 0	$ 138	$ 0

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration