Property, Plant and Equipment - Historical Cost Table (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 11,852,158	$ 11,258,773	[1]
Less accumulated depreciation	3,058,512	2,848,420	[1]
Net property, plant and equipment	8,793,646	8,410,353	[1]
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	8,863	5,298
Gathering Systems – Pipelines [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 4,938,224	4,764,099
Estimated useful life	30 years
Gathering Systems – Compressors [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 1,839,353	1,712,939
Estimated useful life	15 years
Processing Complexes And Treating Facilities [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 2,952,268	2,844,337
Estimated useful life	25 years
Transportation Pipeline And Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 172,807	172,558
Transportation Pipeline And Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	6 years
Transportation Pipeline And Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	45 years
Produced Water Disposal Systems [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 697,949	629,946
Estimated useful life	20 years
Assets Under Construction [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 660,397	604,265
Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 582,297	$ 525,331
Other [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Other [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years

[1] Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.