The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Goodwill	$ 680,996	$ 681,100
Amortization expense for intangible assets	11,900	11,900	$ 11,900
Gross intangible assets and accumulated amortization [Abstract]
Gross intangible assets	414,345	411,650
Accumulated amortization	(137,508)	(125,608)
Net intangible assets	276,837	286,042
Future amortization expense for next five years [Abstract]
Future amortization expense, year one	11,900
Future amortization expense, year two	11,900
Future amortization expense, year three	11,900
Future amortization expense, year four	11,900
Future amortization expense, year five	$ 11,900
Natural Gas Gathering And Processing and Natural Gas Liquids [Member] \| Minimum [Member]
Segment Reporting Information [Line Items]
Finite-Lived Intangible Asset, Useful Life	15 years
Natural Gas Gathering And Processing and Natural Gas Liquids [Member] \| Maximum [Member]
Segment Reporting Information [Line Items]
Finite-Lived Intangible Asset, Useful Life	40 years
Natural Gas Gathering and Processing
Segment Reporting Information [Line Items]
Goodwill	$ 153,404	153,404
Natural Gas Liquids
Segment Reporting Information [Line Items]
Goodwill	371,217	371,217
Natural Gas Pipelines
Segment Reporting Information [Line Items]
Goodwill	$ 156,375	$ 156,479