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GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Segment Reporting Information [Line Items]      
Goodwill $ 681,100 $ 681,100  
Amortization expense for intangible assets 11,900 11,900 $ 11,900
Gross intangible assets and accumulated amortization [Abstract]      
Gross intangible assets 411,650 426,068  
Accumulated amortization (125,608) (113,708)  
Net intangible assets 286,042 312,360  
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 20 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 $ 156,479 $ 156,479