Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
		Nov. 30, 2014	Mar. 31, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Jan. 01, 2018	May 31, 2008
Acquisitions					$ 162,615,000
Common units outstanding					218,937,797	218,933,141
Revenues and other					$ 1,990,276,000	$ 2,248,356,000	$ 1,804,270,000
Cost of product	[1]				431,921,000	908,693,000	494,194,000
Note receivable - Anadarko					260,000,000	260,000,000
Impairments					228,338,000	178,374,000	15,535,000
Imbalance receivables					8,864,000	1,640,000
Imbalance payables					9,500,000	2,900,000
Loss on divestiture and other, net	[2]				(1,312,000)	(132,388,000)	14,641,000
Proceeds from property insurance claims					0	22,977,000	17,465,000
Cumulative effect of accounting change	[3]				$ (44,379,000)
Accounting Standards Update 2014-09 [Member]
Cumulative effect of accounting change									$ (44,379,000)
Accounting Standards Update 2016-02 [Member] | Subsequent Event [Member]
Right-of-use assets								$ 10,000,000
Lease liabilities								$ 10,000,000
Western Gas Equity Partners Long-Term Incentive Plan [Member]
Units authorized under LTIP					3,000,000
Units available under LTIP					2,937,197
Affiliates [Member]
Revenues and other	[4]				$ 1,067,860,000	1,365,318,000	1,228,232,000
Cost of product	[4]				193,663,000	86,010,000	80,455,000
Service Revenues - Fee Based [Member]
Revenues and other					1,609,245,000
Service Revenues - Fee Based [Member] | Affiliates [Member]
Revenues and other					793,594,000	656,795,000	750,087,000
Product Sales [Member]
Revenues and other					293,992,000
Product Sales [Member] | Affiliates [Member]
Revenues and other					$ 272,018,000	$ 692,447,000	478,145,000
Prior Period Adjustment [Member]
Cost of product				$ 56,400,000
Prior Period Adjustment [Member] | Service Revenues - Fee Based [Member]
Revenues and other				42,600,000
Prior Period Adjustment [Member] | Product Sales [Member]
Revenues and other				$ 13,800,000
Chipeta [Member]
Ownership interest by noncontrolling interest owner					25.00%
Western Gas Equity Partners, LP [Member] | Western Gas Partners, LP [Member]
General partner units owned					2,583,068
Western Gas Equity Partners, LP [Member] | Common Units [Member] | Western Gas Partners, LP [Member]
Common units outstanding					50,132,046
Western Gas Equity Partners, LP [Member] | General Partner [Member] | Western Gas Partners, LP [Member]
Percentage ownership interest					100.00%
Western Gas Partners, LP [Member]
WES units issued					1,128,782	885,760
Conversion of units						0
Western Gas Partners, LP [Member] | Western Gas Partners Long-Term Incentive Plan [Member]
Units authorized under LTIP					2,250,000
Units available under LTIP					2,241,980
Western Gas Partners, LP [Member] | Kitty Draw and Third Creek Gathering Systems [Member]
Impairments					$ 134,000,000
Western Gas Partners, LP [Member] | Delaware Basin Midstream Complex [Member]
Loss on divestiture and other, net						$ 5,700,000
Proceeds from insurance claims, total						52,900,000	33,800,000
Proceeds from business interruption insurance claims						29,882,000	16,270,000
Proceeds from property insurance claims						$ 22,977,000	$ 17,465,000
Western Gas Partners, LP [Member] | Affiliates [Member]
Note receivable - Anadarko					$ 260,000,000					$ 260,000,000
Western Gas Partners, LP [Member] | Other Subsidiaries of Anadarko [Member]
WES common units issued					2,011,380
Western Gas Partners, LP [Member] | Product Sales [Member] | Affiliates [Member] | Kitty Draw and Third Creek Gathering Systems [Member]
Revenues and other					$ (10,900,000)
Western Gas Partners, LP [Member] | Class C Units [Member]
WES units issued					1,128,782	885,760
Class C units, common units issued upon conversion					1
Western Gas Partners, LP [Member] | Class C Units [Member] | Other Subsidiaries of Anadarko [Member]
WES units issued		10,913,853
Western Gas Partners, LP [Member] | Common Units [Member]
Conversion of units						21,922,831
Scenario, Forecast [Member] | Anadarko [Member] | Common Units [Member] | Western Gas Partners, LP [Member]
Common units outstanding			6,375,284
Scenario, Forecast [Member] | Western Gas Equity Partners, LP [Member] | Western Gas Partners, LP [Member]
General partner units owned			2,583,068
Scenario, Forecast [Member] | Western Gas Equity Partners, LP [Member] | Common Units [Member]
Conversion of units			55,360,984
Scenario, Forecast [Member] | Western Gas Partners, LP [Member] | Anadarko [Member] | Anadarko Midstream Assets [Member]
Cash payment for acquisition			$ 1,814,000,000
Acquisitions			$ 193,900,000
Scenario, Forecast [Member] | Western Gas Partners, LP [Member] | Class C Units [Member]
Class C units, common units issued upon conversion			1
Scenario, Forecast [Member] | Western Gas Partners, LP [Member] | Common Units [Member]
Conversion of units			105,624,704
Scenario, Forecast [Member] | Western Gas Partners, LP [Member] | Common Units [Member] | Anadarko [Member] | Anadarko Midstream Assets [Member]
WES units issued			45,760,201

[1] Cost of product includes product purchases from affiliates (as defined in Note 1) of $193.7 million, $86.0 million and $80.5 million for the years ended December 31, 2018, 2017 and 2016, respectively. Operation and maintenance includes charges from affiliates of $98.8 million, $72.5 million and $72.3 million for the years ended December 31, 2018, 2017 and 2016, respectively. General and administrative includes charges from affiliates of $46.2 million, $39.9 million and $38.9 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 6.

[2] Includes losses related to an incident at the DBM complex for the year ended December 31, 2017. See Note 1.

[3] See Note 1.

[4] Represents amounts earned or incurred on and subsequent to the date of the acquisition of WES assets, as well as amounts earned or incurred by Anadarko on a historical basis related to WES assets prior to the acquisition of such assets by WES.