Description of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended			12 Months Ended
	Feb. 28, 2019	Sep. 30, 2019	Sep. 30, 2018		Sep. 30, 2019	Sep. 30, 2018		Dec. 31, 2018
Acquisitions					$ 92,546
Common units outstanding		453,032,050			453,032,050			218,937,797
Conversion ratio per unit	1.525
Revenues and other		$ 666,027	$ 587,900	[1]	$ 2,022,964	$ 1,607,032	[1]
Impairments		3,107	27,902	[1]	4,294	155,286	[1]	$ 230,600
Kitty Draw and Third Creek Gathering Systems [Member]
Impairments			6,800			134,000
Anadarko Midstream Assets [Member]
Conversion ratio per unit	1.4056
Revenues and other			89,714			200,064
Affiliates [Member]
Revenues and other		398,753	350,291	[1]	1,162,374	925,011	[1]
Affiliates [Member] | Product Sales [Member]
Revenues and other		$ 38,658	71,487	[1]	130,167	188,488	[1]
Affiliates [Member] | Product Sales [Member] | Kitty Draw and Third Creek Gathering Systems [Member]
Revenues and other			0		$ 6,100	(10,900)
WES Operating [Member]
Ownership interest by noncontrolling interest owner		2.00%			2.00%
Chipeta [Member]
Ownership interest by noncontrolling interest owner		25.00%			25.00%
WES Operating [Member]
Units issued					308,723
General partner units owned		0			0			2,583,068
Conversion of units					0
Revenues and other		$ 666,027	587,900	[1]	$ 2,022,964	1,607,032	[1]
Impairments		3,107	27,902	[1]	$ 4,294	155,286	[1]
WES Operating [Member] | Anadarko Midstream Assets [Member]
Units issued					45,760,201
Revenues and other			89,714			200,064
WES Operating [Member] | Anadarko [Member] | Anadarko Midstream Assets [Member]
Cash payment for acquisition	$ 1,814,000
Acquisitions	$ 193,900
WES Operating [Member] | Affiliates [Member]
Revenues and other		398,753	350,291	[1]	$ 1,162,374	925,011	[1]
WES Operating [Member] | Affiliates [Member] | Product Sales [Member]
Revenues and other		$ 38,658	$ 71,487	[1]	$ 130,167	$ 188,488	[1]
WES Operating [Member] | Common Units [Member]
Conversion of units	105,624,704				14,681,388
Common units outstanding	152,609,285
WES Operating [Member] | Common Units [Member] | Anadarko Midstream Assets [Member]
Units issued	45,760,201				45,760,201
WES Operating [Member] | Class C Units [Member]
Units issued					308,723
Class C units, common units issued upon conversion	1
Conversion of units					(14,681,388)
Common units outstanding	14,681,388
Anadarko [Member] | WES Operating [Member] | Common Units [Member]
Common units outstanding		6,400,000			6,400,000
Anadarko [Member] | WES Operating [Member] | Common Units [Member] | Anadarko Midstream Assets [Member]
Common units outstanding	6,375,284
WES [Member] | Common Units [Member]
Conversion of units	178,692,081
Common units outstanding	452,990,862							218,937,797
WES [Member] | Common Units [Member] | Anadarko Midstream Assets [Member]
Conversion of units	55,360,984
WES [Member] | WES Operating [Member]
Ownership interest					98.00%
General partner units owned	2,583,068
WES [Member] | WES Operating [Member] | Common Units [Member]
Common units outstanding	50,132,046

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