Western Midstream Partners (WES) 10-K16 Feb 182017 FY Annual reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2017	Feb. 12, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Trading Symbol	WGP
Entity Registrant Name	Western Gas Equity Partners, LP
Entity Central Index Key	1,423,902
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 1.7
Entity Common Units Outstanding		218,933,141

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues and Other
Total revenues and other		$ 2,248,356	$ 1,804,270	$ 1,752,072
Equity income, net – affiliates	[1]	85,194	78,717	71,251
Operating expenses
Cost of product	[2]	908,693	494,194	528,369
Operation and maintenance	[2]	315,994	308,010	331,972
General and administrative	[2]	50,668	49,248	44,428
Property and other taxes		46,818	40,161	33,327
Depreciation and amortization		290,874	272,933	272,611
Impairments		178,374	15,535	515,458
Total operating expenses		1,791,421	1,180,081	1,726,165
Gain (loss) on divestiture and other, net	[3],[4]	132,388	(14,641)	57,024
Proceeds from business interruption insurance claims		29,882	16,270	0
Operating income (loss)		704,399	704,535	154,182
Interest income – affiliates	[5]	16,900	16,900	16,900
Interest expense	[6]	(144,615)	(116,628)	(113,874)
Other income (expense), net		1,384	545	(578)
Income (loss) before income taxes		578,068	605,352	56,630
Income tax (benefit) expense		4,866	8,372	45,532
Net income (loss)		573,202	596,980	11,098
Net income (loss) attributable to noncontrolling interests		196,595	251,208	(154,409)
Net income (loss) attributable to Western Gas Equity Partners, LP		376,607	345,772	165,507
Limited partners' interest in net income (loss):
Pre-acquisition net (income) loss allocated to Anadarko		0	(11,326)	(79,386)
Limited partners' interest in net income (loss)	[7]	376,607	334,446	86,121
Affiliates [Member]
Revenues and Other
Gathering, processing, transportation and disposal		656,795	750,087	772,361
Natural gas and natural gas liquids sales		692,447	478,145	447,106
Other		16,076	0	1,172
Total revenues and other	[1]	1,365,318	1,228,232	1,220,639
Operating expenses
Cost of product	[1]	86,010	80,455	167,354
Operation and maintenance	[8]	72,489	72,330	77,061
General and administrative	[9]	39,940	38,873	34,703
Total operating expenses		198,439	191,658	279,118
Interest expense	[10]	(71)	7,747	(14,400)
Third Parties [Member]
Revenues and Other
Gathering, processing, transportation and disposal		581,154	477,762	356,477
Natural gas and natural gas liquids sales		297,486	94,168	170,843
Other		4,398	4,108	4,113
Total revenues and other		883,038	576,038	531,433
Operating expenses
Interest expense		$ (144,544)	$ (124,375)	$ (99,474)
Limited Partner [Member]
Limited partners' interest in net income (loss):
Net income (loss) per common unit - basic and diluted		$ 1.72	$ 1.53	$ 0.39
Weighted-average common units outstanding - basic and diluted		218,931	218,922	218,913

[1]	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, recognized under gathering, treating or processing agreements, and purchase and sale agreements.
[2]	Cost of product includes product purchases from Anadarko (as defined in Note 1) of $86.0 million, $80.5 million and $167.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. Operation and maintenance includes charges from Anadarko of $72.5 million, $72.3 million and $77.1 million for the years ended December 31, 2017, 2016 and 2015, respectively. General and administrative includes charges from Anadarko of $39.9 million, $38.9 million and $34.7 million for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 5.
[3]	Includes losses related to an incident at the DBM complex for the years ended December 31, 2017 and 2015. See Note 1.
[4]	Includes losses related to an incident at the DBM complex for the years ended December 31, 2017 and 2015. See Note 1.
[5]	Represents interest income recognized on the note receivable from Anadarko.
[6]	Includes affiliate (as defined in Note 1) amounts of $(0.1) million, $7.7 million and $(14.4) million for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 2 and Note 12.
[7]	Represents net income (loss) earned on and subsequent to the date of acquisition of WES assets (as defined in Note 1). See Note 4.
[8]	Represents expenses incurred on and subsequent to the date of the acquisition of WES assets, as well as expenses incurred by Anadarko on a historical basis related to WES assets prior to the acquisition of such assets by WES.
[9]	Represents general and administrative expense incurred on and subsequent to the date of the acquisition of WES assets, as well as a management services fee for reimbursement of expenses incurred by Anadarko for periods prior to the acquisition of WES assets by WES. These amounts include equity-based compensation expense allocated to WES and WGP by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plans within this Note 5) and amounts charged by Anadarko under the WGP and WES omnibus agreements.
[10]	Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 2 and Note 12) and for the year ended December 31, 2015, includes interest expense recognized on the WGP WCF (see Note 12).

Consolidated Statements of Ope3

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cost of product	[1]	$ 908,693	$ 494,194	$ 528,369
Operation and maintenance	[1]	315,994	308,010	331,972
General and administrative	[1]	50,668	49,248	44,428
Interest expense	[2]	(144,615)	(116,628)	(113,874)
Affiliates [Member]
Cost of product	[3]	86,010	80,455	167,354
Operation and maintenance	[4]	72,489	72,330	77,061
General and administrative	[5]	39,940	38,873	34,703
Interest expense	[6]	$ (71)	$ 7,747	$ (14,400)

[1]	Cost of product includes product purchases from Anadarko (as defined in Note 1) of $86.0 million, $80.5 million and $167.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. Operation and maintenance includes charges from Anadarko of $72.5 million, $72.3 million and $77.1 million for the years ended December 31, 2017, 2016 and 2015, respectively. General and administrative includes charges from Anadarko of $39.9 million, $38.9 million and $34.7 million for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 5.
[2]	Includes affiliate (as defined in Note 1) amounts of $(0.1) million, $7.7 million and $(14.4) million for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 2 and Note 12.
[3]	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, recognized under gathering, treating or processing agreements, and purchase and sale agreements.
[4]	Represents expenses incurred on and subsequent to the date of the acquisition of WES assets, as well as expenses incurred by Anadarko on a historical basis related to WES assets prior to the acquisition of such assets by WES.
[5]	Represents general and administrative expense incurred on and subsequent to the date of the acquisition of WES assets, as well as a management services fee for reimbursement of expenses incurred by Anadarko for periods prior to the acquisition of WES assets by WES. These amounts include equity-based compensation expense allocated to WES and WGP by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plans within this Note 5) and amounts charged by Anadarko under the WGP and WES omnibus agreements.
[6]	Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 2 and Note 12) and for the year ended December 31, 2015, includes interest expense recognized on the WGP WCF (see Note 12).

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents		$ 79,588	$ 359,072
Accounts receivable, net	[1]	160,239	223,021
Other current assets		15,383	13,498
Total current assets		255,210	595,591
Note receivable - Anadarko		260,000	260,000
Property, plant and equipment
Cost		7,871,102	6,861,942
Less accumulated depreciation		2,140,211	1,812,010
Net property, plant and equipment		5,730,891	5,049,932
Goodwill		416,160	417,610
Other intangible assets		775,269	803,698
Equity investments		566,211	594,208
Other assets		12,570	15,058
Total assets		8,016,311	7,736,097
Current liabilities
Accounts and imbalance payables	[2]	349,801	247,076
Accrued ad valorem taxes		26,633	23,121
Accrued liabilities	[3]	47,992	45,190
Total current liabilities		424,426	315,387
Long-term debt		3,492,712	3,119,461
Deferred income taxes		7,409	6,402
Asset retirement obligations and other		146,885	142,641
Deferred purchase price obligation - Anadarko	[4]	0	41,440
Total long-term liabilities		3,647,006	3,309,944
Total liabilities		4,071,432	3,625,331
Equity and partners' capital
Common units (218,933,141 and 218,928,570 units issued and outstanding at December 31, 2017 and 2016, respectively)		1,061,125	1,048,143
Total partners' capital		1,061,125	1,048,143
Noncontrolling interests		2,883,754	3,062,623
Total equity and partners' capital		3,944,879	4,110,766
Total liabilities, equity and partners' capital		$ 8,016,311	$ 7,736,097

[1]	Accounts receivable, net includes amounts receivable from affiliates (as defined in Note 1) of $36.1 million and $76.4 million as of December 31, 2017 and 2016, respectively. Accounts receivable, net as of December 31, 2016, also includes an insurance claim receivable related to an incident at the DBM complex. See Note 1.
[2]	Accounts and imbalance payables includes affiliate amounts of $0.3 million and zero as of December 31, 2017 and 2016, respectively.
[3]	Accrued liabilities includes affiliate amounts of $0.2 million and zero as of December 31, 2017 and 2016, respectively.
[4]	See Note 2.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Common units issued		218,933,141	218,928,570
Common units outstanding		218,933,141	218,928,570
Accounts receivable, net	[1]	$ 160,239	$ 223,021
Accounts and imbalance payables	[2]	349,801	247,076
Accrued liabilities	[3]	47,992	45,190
Affiliates [Member]
Accounts receivable, net		36,100	76,400
Accounts and imbalance payables		300	0
Accrued liabilities		$ 200	$ 0

[1]	Accounts receivable, net includes amounts receivable from affiliates (as defined in Note 1) of $36.1 million and $76.4 million as of December 31, 2017 and 2016, respectively. Accounts receivable, net as of December 31, 2016, also includes an insurance claim receivable related to an incident at the DBM complex. See Note 1.
[2]	Accounts and imbalance payables includes affiliate amounts of $0.3 million and zero as of December 31, 2017 and 2016, respectively.
[3]	Accrued liabilities includes affiliate amounts of $0.2 million and zero as of December 31, 2017 and 2016, respectively.

Consolidated Statements of Equi

Consolidated Statements of Equity and Partners' Capital - USD ($) $ in Thousands		Total		Western Gas Partners, LP [Member]	Chipeta [Member]	Net Investment by Anadarko [Member]	Common Units [Member]	Noncontrolling Interests [Member]	Noncontrolling Interests [Member]Western Gas Partners, LP [Member]	Noncontrolling Interests [Member]Chipeta [Member]
Balance at Dec. 31, 2014		$ 4,567,946				$ 556,596	$ 1,260,195	$ 2,751,155
Net income (loss)		11,098				79,386	86,121	(154,409)
Above-market component of swap agreements with Anadarko	[1]	18,449					18,449
WES equity transactions, net	[2]	57,353					(19,687)	77,040
Distributions to noncontrolling interest owners				$ (233,178)	$ (12,187)				$ (233,178)	$ (12,187)
Distributions to WGP unitholders		(306,477)					(306,477)
Acquisitions from affiliates		(174,276)				(197,562)	23,286
Contributions of equity-based compensation to WES by Anadarko		3,471					3,471
Net pre-acquisition contributions from (distributions to) Anadarko		(49,801)				(49,801)
Net contributions from (distributions to) Anadarko of other assets		(4,632)	[3]				(4,632)
Other		488				135	116	237
Elimination of net deferred tax liabilities		41,844				41,844
Balance at Dec. 31, 2015		3,920,098				430,598	1,060,842	2,428,658
Net income (loss)		596,980				11,326	334,446	251,208
Above-market component of swap agreements with Anadarko	[1]	45,820					45,820
WES equity transactions, net	[2]	0					(4,180)	4,180
Distributions to noncontrolling interest owners				(294,841)	(13,784)				(294,841)	(13,784)
Distributions to WGP unitholders		(374,082)					(374,082)
Acquisitions from affiliates		(712,500)				(553,833)	(158,667)
Revision to Deferred purchase price obligation – Anadarko	[4]	139,487					139,487
Contributions of equity-based compensation to WES by Anadarko		4,170					4,170
Net pre-acquisition contributions from (distributions to) Anadarko		(23,491)				(23,491)
Net contributions from (distributions to) Anadarko of other assets		(581)	[3]				(581)
Other		1,153					888	265
Elimination of net deferred tax liabilities		135,400				135,400
WES issuance of Series A Preferred units, net of offering expenses		686,937						686,937
Balance at Dec. 31, 2016		4,110,766				0	1,048,143	3,062,623
Net income (loss)		573,202				0	376,607	196,595
Above-market component of swap agreements with Anadarko	[1]	58,551					58,551
WES equity transactions, net	[2]	(183)					6,615	(6,798)
Distributions to noncontrolling interest owners				$ (355,623)	$ (13,569)				$ (355,623)	$ (13,569)
Distributions to WGP unitholders		(441,967)					(441,967)
Acquisitions from affiliates		0				(1,263)	1,263
Revision to Deferred purchase price obligation – Anadarko	[4]	4,165					4,165
Contributions of equity-based compensation to WES by Anadarko		4,587					4,587
Net pre-acquisition contributions from (distributions to) Anadarko		1,263				1,263
Net contributions from (distributions to) Anadarko of other assets		3,189	[3]				3,189
Other		498					(28)	526
Balance at Dec. 31, 2017		$ 3,944,879				$ 0	$ 1,061,125	$ 2,883,754

[1]	See Note 5.
[2]	Includes the impact of WES’s (as defined in Note 1) equity offerings as described in Note 4. The $6.6 million, $(4.2) million and $(19.7) million increase (decrease) to partners’ capital, together with net income (loss) attributable to Western Gas Equity Partners, LP, totaled $383.2 million, $341.6 million and $145.8 million for the years ended December 31, 2017, 2016 and 2015, respectively.
[3]	Includes $(1.4) million related to pipe and equipment purchases and $(1.8) million related to other assets for the year ended December 31, 2017. See Note 5.
[4]	See Note 2.

Consolidated Statements of Equ7

Consolidated Statements of Equity and Partners' Capital (Parenthetical) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
WES equity transactions, net	[1]	$ (183)	$ 0	$ 57,353
Combined change in Partners' Capital from WES equity transactions, net and net income (loss) attributable to Western Gas Equity Partners, LP		383,200	341,600	145,800
Common Units [Member]
WES equity transactions, net	[1]	$ 6,615	$ (4,180)	$ (19,687)

[1]	Includes the impact of WES’s (as defined in Note 1) equity offerings as described in Note 4. The $6.6 million, $(4.2) million and $(19.7) million increase (decrease) to partners’ capital, together with net income (loss) attributable to Western Gas Equity Partners, LP, totaled $383.2 million, $341.6 million and $145.8 million for the years ended December 31, 2017, 2016 and 2015, respectively.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Cash flows from operating activities
Net income (loss)		$ 573,202		$ 596,980		$ 11,098
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization		290,874		272,933		272,611
Impairments		178,374		15,535		515,458
Non-cash equity-based compensation expense		5,169		4,986		4,445
Deferred income taxes		2,458		2,555		11,346
Accretion and amortization of long-term obligations, net		4,932		(3,262)		17,698
Equity income, net – affiliates	[1]	(85,194)		(78,717)		(71,251)
Distributions from equity investment earnings – affiliates		87,380		82,185		82,054
(Gain) loss on divestiture and other, net	[2],[3]	(132,388)		14,641		(57,024)
Lower of cost or market inventory adjustments		145		168		443
Changes in assets and liabilities:
(Increase) decrease in accounts receivable, net		(16,195)		(48,998)		(4,428)
Increase (decrease) in accounts and imbalance payables and accrued liabilities, net		(6,919)		58,365		1,006
Change in other items, net		(4,426)		(4,295)		(647)
Net cash provided by operating activities		897,412		913,076		782,809
Cash flows from investing activities
Capital expenditures		(675,025)		(479,993)		(637,964)
Investments in equity affiliates		(384)		(27)		(11,442)
Distributions from equity investments in excess of cumulative earnings – affiliates		23,085	[4]	21,238	[4]	16,244
Proceeds from property insurance claims		22,977		17,465		0
Net cash used in investing activities		(763,604)		(1,105,534)		(500,277)
Cash flows from financing activities
Borrowings, net of debt issuance costs		369,989		1,323,198		889,606
Repayments of debt		0		(900,000)		(611,150)
Increase (decrease) in outstanding checks		5,593		2,079		(2,666)
Distributions to WGP unitholders	[5]	(441,967)		(374,082)		(306,477)
Net contributions from (distributions to) Anadarko		1,263		(23,491)		(49,801)
Above-market component of swap agreements with Anadarko	[5]	58,551		45,820		18,449
Net cash provided by (used in) financing activities		(413,292)		451,836		(250,051)
Net increase (decrease) in cash and cash equivalents		(279,484)		259,378		32,481
Cash and cash equivalents at beginning of period		359,072		99,694		67,213
Cash and cash equivalents at end of period		79,588		359,072		99,694
Supplemental disclosures
Accretion expense and revisions to the Deferred purchase price obligation – Anadarko	[6]	(4,094)		(147,234)		174,276
Net distributions to (contributions from) Anadarko of other assets	[7]	(3,189)		581		4,632
Interest paid, net of capitalized interest		138,871		107,657		94,720
Taxes paid (reimbursements received)		1,194		838		(138)
Accrued capital expenditures		204,309		79,253		61,454
Fair value of properties and equipment from non-cash third party transactions	[6]	551,453		0		0
Chipeta [Member]
Cash flows from financing activities
Distributions to Chipeta noncontrolling interest owner		(13,569)		(13,784)		(12,187)
Western Gas Partners, LP [Member]
Cash flows from financing activities
Proceeds from the issuance of WES common units, net of offering expenses		(183)		0		57,353
Distributions to noncontrolling interest owners of WES		(355,623)		(294,841)		(233,178)
Western Gas Partners, LP [Member] \| Series A Preferred Units [Member]
Cash flows from financing activities
Proceeds from the issuance of WES Series A Preferred units, net of offering expenses		0		686,937		0
Affiliates [Member]
Cash flows from investing activities
Contributions in aid of construction costs from affiliates		1,387		6,135		461
Acquisitions		(3,910)		(716,465)		(10,903)
Proceeds from the sale of assets		0		623		925
Cash flows from financing activities
Settlement of the Deferred purchase price obligation - Anadarko	[6]	(37,346)		0		0
Distributions to WGP unitholders	[8]	(360,523)		(315,505)		(269,029)
Affiliates [Member] \| Western Gas Partners, LP [Member]
Cash flows from financing activities
Distributions to WGP unitholders	[9]	(7,100)		(5,614)		(2,235)
Third Parties [Member]
Cash flows from investing activities
Acquisitions		(155,298)		0		(3,514)
Proceeds from the sale of assets		$ 23,564		$ 45,490		$ 145,916

[1]	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, recognized under gathering, treating or processing agreements, and purchase and sale agreements.
[2]	Includes losses related to an incident at the DBM complex for the years ended December 31, 2017 and 2015. See Note 1.
[3]	Includes losses related to an incident at the DBM complex for the years ended December 31, 2017 and 2015. See Note 1.
[4]	Distributions in excess of cumulative earnings, classified as investing cash flows in the consolidated statements of cash flows, are calculated on an individual investment basis.
[5]	See Note 5.
[6]	See Note 2.
[7]	Includes $(1.4) million related to pipe and equipment purchases and $(1.8) million related to other assets for the year ended December 31, 2017. See Note 5.
[8]	Represents distributions paid under WGP’s partnership agreement (see Note 3 and Note 4).
[9]	Represents distributions paid to other subsidiaries of Anadarko under WES’s partnership agreement (see Note 3 and Note 4).

Consolidated Statements of Cas9

Consolidated Statements of Cash Flows (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Net distributions to (contributions from) Anadarko of other assets	$ (3,189)	[1]
Equipment [Member]
Net distributions to (contributions from) Anadarko of other assets	(1,400)
Other [Member]
Net distributions to (contributions from) Anadarko of other assets	$ (1,800)

[1]	Includes $(1.4) million related to pipe and equipment purchases and $(1.8) million related to other assets for the year ended December 31, 2017. See Note 5.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	General. Western Gas Equity Partners, LP is a Delaware master limited partnership (“MLP”) formed in September 2012 to own three types of partnership interests in Western Gas Partners, LP. Western Gas Equity Partners, LP was formed by converting WGR Holdings, LLC into a limited partnership and changing its name. Western Gas Partners, LP (together with its subsidiaries, “WES”) is a Delaware MLP formed by Anadarko Petroleum Corporation in 2007 to acquire, own, develop and operate midstream assets. For purposes of these consolidated financial statements, “WGP” refers to Western Gas Equity Partners, LP in its individual capacity or to Western Gas Equity Partners, LP and its subsidiaries, including Western Gas Holdings, LLC and WES, as the context requires. “WES GP” refers to Western Gas Holdings, LLC, individually as the general partner of WES, and excludes WES. WGP’s general partner, Western Gas Equity Holdings, LLC (“WGP GP”), is a wholly owned subsidiary of Anadarko Petroleum Corporation. WES GP owns all of the general partner interest in WES, which constitutes substantially all of its business, which primarily is to manage the affairs and operations of WES. Refer to Note 4 for a discussion of WGP’s holdings of WES equity. “Anadarko” refers to Anadarko Petroleum Corporation and its subsidiaries, excluding WGP and WGP GP, and “affiliates” refers to subsidiaries of Anadarko, excluding WGP, but including equity interests in Fort Union Gas Gathering, LLC (“Fort Union”), White Cliffs Pipeline, LLC (“White Cliffs”), Rendezvous Gas Services, LLC (“Rendezvous”), Enterprise EF78 LLC (the “Mont Belvieu JV”), Texas Express Pipeline LLC (“TEP”), Texas Express Gathering LLC (“TEG”) and Front Range Pipeline LLC (“FRP”). The interests in TEP, TEG and FRP are referred to collectively as the “TEFR Interests.” “MGR assets” refers to the Red Desert complex and the Granger straddle plant. WES is engaged in the business of gathering, compressing, treating, processing and transporting natural gas; gathering, stabilizing and transporting condensate, natural gas liquids (“NGLs”) and crude oil; and gathering and disposing of produced water. In addition, in its capacity as a processor of natural gas, WES also buys and sells natural gas, NGLs or condensate under certain of its contracts. WES provides these midstream services for Anadarko, as well as for third-party producers and customers. As of December 31, 2017 , WES’s assets and investments consisted of the following: Owned and Operated Operated Interests Non-Operated Interests Equity Interests Gathering systems (1) 12 3 3 2 Treating facilities 19 3 — 3 Natural gas processing plants/trains 20 4 — 2 NGL pipelines 2 — — 3 Natural gas pipelines 5 — — — Oil pipelines — 1 — 1 (1) Includes the DBM water systems. These assets and investments are located in the Rocky Mountains (Colorado, Utah and Wyoming), North-central Pennsylvania, Texas and New Mexico. WES commenced operation of two produced water disposal systems in West Texas in the second quarter of 2017 and Train VI at the DBM complex in the fourth quarter of 2017. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Basis of presentation. The following table outlines WES’s ownership interests and the accounting method of consolidation used in WES’s consolidated financial statements: Percentage Interest Equity investments (1) Fort Union 14.81 % White Cliffs 10 % Rendezvous 22 % Mont Belvieu JV 25 % TEP 20 % TEG 20 % FRP 33.33 % Proportionate consolidation (2) Marcellus Interest systems 33.75 % Newcastle system 50 % Springfield system 50.1 % Full consolidation Chipeta (3) 75 % DBJV system (4) 100 % (1) Investments in non-controlled entities over which WES exercises significant influence are accounted for under the equity method. “Equity investment throughput” refers to WES’s share of average throughput for these investments. (2) WGP proportionately consolidates WES’s associated share of the assets, liabilities, revenues and expenses attributable to these assets. (3) The 25% interest in Chipeta Processing LLC (“Chipeta”) held by a third-party member is reflected within noncontrolling interests in the consolidated financial statements, in addition to the noncontrolling interests noted below. (4) WES acquired an additional 50% interest in the DBJV system (the “Additional DBJV System Interest”) from a third party on March 17, 2017. See Note 2 . The consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). The consolidated financial statements include the accounts of WGP and entities in which it holds a controlling financial interest, including WES and WES GP. All significant intercompany transactions have been eliminated. The consolidated financial results of WES are included in WGP’s consolidated financial statements due to WGP’s 100% ownership interest in WES GP and WES GP’s control of WES. Throughout these notes to consolidated financial statements, and to the extent material, any differences between the consolidated financial results of WGP and WES are discussed separately. WGP has no independent operations or material assets other than its partnership interests in WES. WGP’s consolidated financial statements differ from those of WES primarily as a result of (i) the presentation of noncontrolling interest ownership (attributable to the limited partner interests in WES held by the public, other subsidiaries of Anadarko and private investors, see Note 4 ), (ii) the elimination of WES GP’s investment in WES with WES GP’s underlying capital account, (iii) the general and administrative expenses incurred by WGP, which are separate from, and in addition to, those incurred by WES, (iv) the inclusion of the impact of WGP equity balances and WGP distributions, and (v) WGP’s senior secured revolving credit facility (“WGP RCF”). See Note 12 . 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Variable interest entity. WES is a variable interest entity (“VIE”) because the partners in WES with equity at risk lack the power, through voting or similar rights, to direct the activities that most significantly impact WES’s economic performance. A reporting entity that concludes it has a variable interest in a VIE must evaluate whether it has a controlling financial interest in the VIE, such that it is the VIE’s primary beneficiary and should consolidate. WGP is the primary beneficiary of WES and therefore should consolidate because (i) WGP has the power to direct the activities of WES that most significantly affect its economic performance and (ii) WGP has the right to receive benefits or the obligation to absorb losses that could be potentially significant to WES. As noted above, WGP has no independent operations or material assets other than its partnership interests in WES. The assets of WES cannot be used by WGP for general partnership purposes. WES’s long-term debt is recourse to WES GP, which is wholly owned by WGP. In turn, WES GP is indemnified by wholly owned subsidiaries of Anadarko for any claims made against WES GP under the indentures governing WES’s outstanding notes or borrowings under WES’s senior unsecured revolving credit facility (“WES RCF”). WES’s sources of liquidity include cash and cash equivalents, cash flows generated from operations, interest income on its $260.0 million note receivable from Anadarko, available borrowing capacity under the WES RCF, and issuances of additional equity or debt securities. As further discussed in Note 2 , WGP purchased WES common units in connection with WES’s financing of an acquisition from Anadarko in March 2016. Noncontrolling interests. WGP’s noncontrolling interests in the consolidated financial statements consist of the following for all periods presented: (i) the 25% interest in Chipeta held by a third-party member, (ii) the publicly held limited partner interests in WES, (iii) the 2,011,380 WES common units issued by WES to other subsidiaries of Anadarko as part of the consideration paid for the acquisitions of the Non-Operated Marcellus Interest, the TEFR Interests and Springfield, and (iv) the WES Class C units issued by WES to a subsidiary of Anadarko as part of the funding for the acquisition of Delaware Basin Midstream, LLC (“DBM”). The WES Series A Preferred units issued to private investors as part of the funding of the Springfield acquisition were also noncontrolling interests in the consolidated financial statements until converted into WES common units in 2017. See Note 2 and Note 4 . When WES issues equity, the carrying amount of the noncontrolling interest reported by WGP is adjusted to reflect the noncontrolling ownership interest in WES. The resulting impact of such noncontrolling interest adjustment on WGP’s interest in WES is reflected as an adjustment to WGP’s partners’ capital. Presentation of WES assets. The term “WES assets” includes both the assets indirectly owned and the interests accounted for under the equity method by WGP through its partnership interests in WES as of December 31, 2017 (see Note 9 ). Because WGP owns the entire interest in and controls WES GP, and WGP GP is controlled by Anadarko, each of WES’s acquisitions of WES assets from Anadarko has been considered a transfer of net assets between entities under common control. As such, WES assets acquired from Anadarko were initially recorded at Anadarko’s historic carrying value, which did not correlate to the total acquisition price paid by WES. Further, after an acquisition of WES assets from Anadarko, WES and WGP (by virtue of its consolidation of WES) may be required to recast their financial statements to include the activities of such WES assets from the date of common control. For those periods requiring recast, the consolidated financial statements for periods prior to the acquisition of WES assets from Anadarko are prepared from Anadarko’s historical cost-basis accounts and may not necessarily be indicative of the actual results of operations that would have occurred if WES had owned the WES assets during the periods reported. Net income (loss) attributable to the WES assets acquired from Anadarko for periods prior to WES’s acquisition of the WES assets is not allocated to the limited partners. Use of estimates. In preparing financial statements in accordance with GAAP, management makes informed judgments and estimates that affect the reported amounts of assets, liabilities, revenues and expenses. Management evaluates its estimates and related assumptions regularly, using historical experience and other methods considered reasonable. Changes in facts and circumstances or additional information may result in revised estimates and actual results may differ from these estimates. Effects on the business, financial condition and results of operations resulting from revisions to estimates are recognized when the facts that give rise to the revisions become known. The information furnished herein reflects all normal recurring adjustments which are, in the opinion of management, necessary for a fair presentation of the consolidated financial statements, and certain prior-period amounts have been reclassified to conform to the current-year presentation. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Fair value. The fair-value-measurement standard defines fair value as the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The standard characterizes inputs used in determining fair value according to a hierarchy that prioritizes those inputs based upon the degree to which they are observable. The three input levels of the fair value hierarchy are as follows: Level 1 – Inputs represent unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 – Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly (for example, quoted market prices for similar assets or liabilities in active markets or quoted market prices for identical assets or liabilities in markets not considered to be active, inputs other than quoted prices that are observable for the asset or liability, or market-corroborated inputs). Level 3 – Inputs that are not observable from objective sources, such as management’s internally developed assumptions used in pricing an asset or liability (for example, an estimate of future cash flows used in management’s internally developed present value of future cash flows model that underlies the fair value measurement). In determining fair value, management uses observable market data when available, or models that incorporate observable market data. When a fair value measurement is required and there is not a market-observable price for the asset or liability or a market-observable price for a similar asset or liability, the cost, income, or multiples approach is used, depending on the quality of information available to support management’s assumptions. The cost approach is based on management’s best estimate of the current asset replacement cost. The income approach uses management’s best assumptions regarding expectations of projected cash flows, and discounts the expected cash flows using a commensurate risk adjusted discount rate. Such evaluations involve a significant amount of judgment, since the results are based on expected future events or conditions, such as sales prices, estimates of future throughput, capital and operating costs and the timing thereof, economic and regulatory climates and other factors. A multiples approach uses management’s best assumptions regarding expectations of projected earnings before interest, taxes, depreciation, and amortization (“EBITDA”) and the multiple of that EBITDA that a buyer would pay to acquire an asset. Management’s estimates of future net cash flows and EBITDA are inherently imprecise because they reflect management’s expectation of future conditions that are often outside of management’s control. However, the assumptions used reflect a market participant’s view of long-term prices, costs and other factors, and are consistent with assumptions used in WES’s business plans and investment decisions. In arriving at fair-value estimates, management uses relevant observable inputs available for the valuation technique employed. If a fair value measurement reflects inputs at multiple levels within the hierarchy, the fair value measurement is characterized based on the lowest level of input that is significant to the fair value measurement. Nonfinancial assets and liabilities initially measured at fair value include certain assets and liabilities acquired in a third-party business combination, assets and liabilities exchanged in non-monetary transactions, goodwill and other intangibles, initial recognition of asset retirement obligations, and initial recognition of environmental obligations assumed in a third-party acquisition. Impairment analyses for long-lived assets, goodwill and other intangibles, and the initial recognition of asset retirement obligations and environmental obligations use Level 3 inputs. The fair value of debt reflects any premium or discount for the difference between the stated interest rate and the quarter-end market interest rate, and is based on quoted market prices for identical instruments, if available, or based on valuations of similar debt instruments. See Note 12 . The carrying amounts of cash and cash equivalents, accounts receivable and accounts payable reported on the consolidated balance sheets approximate fair value due to the short-term nature of these items. Cash equivalents. All highly liquid investments with a maturity of three months or less when purchased are considered to be cash equivalents. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Bad-debt reserve. Revenues are primarily from Anadarko, for which no credit limit is maintained. Exposure to bad debts is analyzed on a customer-by-customer basis for its third-party accounts receivable and WES may establish credit limits for significant third-party customers. As of December 31, 2017 and 2016 , bad-debt reserve was immaterial. Imbalances. The consolidated balance sheets include imbalance receivables and payables resulting from differences in volumes received into WES’s systems and volumes delivered by WES to customers. Volumes owed to or by WES that are subject to monthly cash settlement are valued according to the terms of the contract as of the balance sheet dates and reflect market index prices. Other volumes owed to or by WES are valued at the weighted-average cost as of the balance sheet dates and are settled in-kind. As of December 31, 2017 , imbalance receivables and payables were $1.6 million and $2.9 million , respectively. As of December 31, 2016 , imbalance receivables and payables were $3.5 million and $3.0 million , respectively. Net changes in imbalance payables and receivables are reported in Cost of product in the consolidated statements of operations. Inventory. The cost of NGLs inventories is determined by the weighted-average cost method on a location-by-location basis. Inventory is stated at the lower of weighted-average cost or market value and is reported in Other current assets on the consolidated balance sheets. See Note 10 . Property, plant and equipment. Property, plant and equipment are generally stated at the lower of historical cost less accumulated depreciation or fair value, if impaired. Because acquisitions of assets from Anadarko are transfers of net assets between entities under common control, the assets acquired from Anadarko are initially recorded at Anadarko’s historic carrying value. The difference between the carrying value of net assets acquired from Anadarko and the consideration paid is recorded as an adjustment to partners’ capital. Assets acquired in a business combination or non-monetary exchange with a third party are initially recorded at fair value. All construction-related direct labor and material costs are capitalized. The cost of renewals and betterments that extend the useful life of property, plant and equipment is also capitalized. The cost of repairs, replacements and major maintenance projects that do not extend the useful life or increase the expected output of property, plant and equipment is expensed as incurred. Depreciation is computed using the straight-line method based on estimated useful lives and salvage values of assets. However, subsequent events could cause a change in estimates, thereby impacting future depreciation amounts. Uncertainties that may impact these estimates include, but are not limited to, changes in laws and regulations relating to environmental matters, including air and water quality, restoration and abandonment requirements, economic conditions, and supply and demand in the area. Management evaluates the ability to recover the carrying amount of its long-lived assets to determine whether its long-lived assets have been impaired. Impairments exist when the carrying amount of an asset exceeds estimates of the undiscounted cash flows expected to result from the use and eventual disposition of the asset. When alternative courses of action to recover the carrying amount of a long-lived asset are under consideration, estimates of future undiscounted cash flows take into account possible outcomes and probabilities of their occurrence. If the carrying amount of the long-lived asset is not recoverable based on the estimated future undiscounted cash flows, the impairment loss is measured as the excess of the asset’s carrying amount over its estimated fair value, such that the asset’s carrying amount is adjusted to its estimated fair value with an offsetting charge to impairment expense. Refer to Note 7 for a description of impairments recorded during the years ended December 31, 2017 , 2016 and 2015 . 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Insurance recoveries. Involuntary conversions result from the loss of an asset because of some unforeseen event (e.g., destruction due to fire). Some of these events are insurable and result in property damage insurance recovery. Amounts that are received from insurance carriers are net of any deductibles related to the covered event. A receivable is recorded from insurance to the extent a loss is recognized from an involuntary conversion event and the likelihood of recovering such loss is deemed probable. To the extent that any insurance claim receivables are later judged not probable of recovery (e.g., due to new information), such amounts are expensed. A gain on involuntary conversion is recognized when the amount received from insurance exceeds the net book value of the retired asset(s). In addition, gains related to insurance recoveries are not recognized until all contingencies related to such proceeds have been resolved; that is, a cash payment is received from the insurance carrier or there is a binding settlement agreement with the carrier that clearly states that a payment will be made. To the extent that an asset is rebuilt, the associated expenditures are capitalized, as appropriate, on the consolidated balance sheets and presented as Capital expenditures in the consolidated statements of cash flows. With respect to business interruption insurance claims, income is recognized only when cash proceeds are received from insurers, which are presented in the consolidated statements of operations as a component of Operating income (loss). On December 3, 2015, there was an initial fire and secondary explosion at the processing facility within the DBM complex. The majority of the damage from the incident was to the liquid handling facilities and the amine treating units at the inlet of the complex. Train II sustained the most damage of the processing trains and returned to service in December 2016. Train III experienced minimal damage and returned to full service in May 2016. For the year ended December 31, 2015, $20.3 million of losses were recorded in Gain (loss) on divestiture and other, net in the consolidated statements of operations, related to this involuntary conversion event based on the difference between the net book value of the affected assets and the insurance claim receivable. During the year ended December 31, 2017 , a $5.7 million loss was recorded in Gain (loss) on divestiture and other, net in the consolidated statements of operations, related to a change in WES’s estimate of the amount that would be recovered under the property insurance claim based on further discussions with insurers. During the second quarter of 2017, WES reached a settlement with insurers and final proceeds were received. During the years ended December 31, 2017 and 2016, WES received $52.9 million and $33.8 million , respectively, in cash proceeds from insurers, including $29.9 million and $16.3 million , respectively, in proceeds from business interruption insurance claims and $23.0 million and $17.5 million , respectively, in proceeds from property insurance claims. As of December 31, 2017 and 2016 , the consolidated balance sheets included receivables of zero and $30.0 million , respectively, for the property insurance claim related to the incident at the DBM complex. Capitalized interest. Interest is capitalized as part of the historical cost of constructing assets for significant projects that are in progress. Capitalized interest is determined by multiplying WES’s weighted-average borrowing cost on debt by the average amount of qualifying costs incurred. Once the construction of an asset subject to interest capitalization is completed and the asset is placed in service, the associated capitalized interest is expensed through depreciation or impairment, together with other capitalized costs related to that asset. Goodwill. Goodwill is recorded when the purchase price of a business acquired exceeds the fair market value of the tangible and separately measurable intangible net assets. In addition, goodwill represents the allocated portion of Anadarko’s midstream goodwill attributed to the WES assets WGP, through its consolidation of WES, has acquired from Anadarko. Refer to Note 8 for a discussion of goodwill. Goodwill is evaluated for impairment annually, as of October 1, or more often as facts and circumstances warrant. WES has allocated goodwill on its two reporting units: (i) gathering and processing and (ii) transportation. An initial qualitative assessment is performed prior to proceeding to the comparison of the fair value of each reporting unit to which goodwill has been assigned, to the carrying amount of net assets, including goodwill, of each reporting unit. If management concludes, based on qualitative factors, that it is more likely than not that the fair value of the reporting unit exceeds its carrying amount, then goodwill is not impaired, and estimating the fair value of the reporting unit is not necessary. If the carrying amount of the reporting unit exceeds its fair value, goodwill is written down to its implied fair value through a charge to operating expense. The carrying value of goodwill after such an impairment would represent a Level 3 fair value measurement. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Other intangible assets. WES assesses intangible assets, as described in Note 8 , for impairment together with related underlying long-lived assets whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. See Property, plant and equipment within this Note 1 for further discussion of management’s process to evaluate potential impairment of long-lived assets. Asset retirement obligations. A liability based on the estimated costs of retiring tangible long-lived assets is recognized as an asset retirement obligation in the period incurred. The liability is recognized at fair value, measured using discounted expected future cash outflows for the asset retirement obligation when the obligation originates, which generally is when an asset is acquired or constructed. The carrying amount of the associated asset is increased commensurate with the liability recognized. Over time, the discounted liability is adjusted to its expected settlement value through accretion expense, which is reported within Depreciation and amortization in the consolidated statements of operations. Subsequent to the initial recognition, the liability is also adjusted for any changes in the expected value of the retirement obligation (with a corresponding adjustment to property, plant and equipment) until the obligation is settled. Revisions in estimated asset retirement obligations may result from changes in estimated inflation rates, discount rates, asset retirement costs and the estimated timing of settling asset retirement obligations. See Note 11 . Environmental expenditures. WES expenses environmental obligations related to conditions caused by past operations that do not generate current or future revenues. Environmental obligations related to operations that generate current or future revenues are expensed or capitalized, as appropriate. Liabilities are recorded when the necessity for environmental remediation or other potential environmental liabilities becomes probable and the costs can be reasonably estimated. Accruals for estimated losses from environmental remediation obligations are recognized no later than at the time of the completion of the remediation feasibility study. These accruals are adjusted as additional information becomes available or as circumstances change. Costs of future expenditures for environmental-remediation obligations are not discounted to their present value. See Note 13 . Segments. Because WGP reflects its ownership interest in WES on a consolidated basis, and has no independent operations or material assets outside those of WES, WGP’s segment analysis and presentation is the same as that of WES. WES’s operations are organized into a single operating segment, the assets of which gather, compress, treat, process and transport natural gas; gather, stabilize and transport condensate, NGLs and crude oil; and gather and dispose of produced water in the United States. Revenues and cost of product. The revenue recognition policies described in this section reflect WGP’s revenue recognition through December 31, 2017. WGP adopted Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) (“Topic 606”), effective January 1, 2018. See Accounting standards adopted in 2018 below for further discussion. Under its fee-based gathering, treating, processing and disposal arrangements, WES is paid a fixed fee based on the volume and/or thermal content of natural gas or produced water and recognizes revenues for its services in the month such services are performed. Producers’ wells or production facilities are connected to WES’s gathering systems for delivery of natural gas to WES’s processing or treating plants, where the natural gas is processed to extract NGLs and condensate or treated in order to satisfy pipeline specifications. In some areas, where no processing is required, the producers’ gas is gathered and delivered to pipelines for market delivery. Under cost-of-service gathering agreements, fees are earned for gathering and compression services based on rates calculated in a cost-of-service model and reviewed periodically over the life of the agreements. Under percent-of-proceeds contracts, revenue is recognized when the natural gas, NGLs or condensate is sold. The percentage of the product sale ultimately paid to the producer is recorded as a related cost of product expense. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) In certain circumstances, WES purchases natural gas volumes at the wellhead or production facility for gathering and processing. As a result, WES has volumes of NGLs and condensate to sell and volumes of residue to sell, to use for system fuel or to satisfy keep-whole obligations. In addition, depending upon specific contract terms, condensate and NGLs recovered during gathering and processing are either returned to the producer or retained and sold. Under keep-whole contracts, when condensate or NGLs are retained and sold, producers are kept whole for the condensate or NGL volumes through the receipt of a thermally equivalent volume of residue. The keep-whole contract conveys an economic benefit to WES when the combined value of the individual NGLs is greater in the form of liquids than as a component of the natural gas stream; however, WES is adversely impacted when the value of the NGLs is lower than the value of the natural gas stream including the liquids. WES has commodity price swap agreements with Anadarko to mitigate exposure to a majority of the commodity price risk inherent in its percent-of-proceeds and keep-whole contracts. See Note 5 . Revenue is recognized from the sale of condensate and NGLs upon transfer of title, and related purchases are recorded as cost of product. WES earns transportation revenues through firm contracts that obligate each of its customers to pay a monthly reservation or demand charge regardless of the pipeline capacity used by that customer. An additional commodity usage fee is charged to the customer based on the actual volume of natural gas transported. Transportation revenues are also generated from interruptible contracts pursuant to which a fee is charged to the customer based on volumes transported through the pipeline. Revenues for transportation of natural gas and NGLs are recognized over the period of firm transportation contracts or, in the case of usage fees and interruptible contracts, when the volumes are received into the pipeline. From time to time, certain revenues may be subject to refund pending the outcome of rate matters before the Federal Energy Regulatory Commission, and refund reserve liabilities are established where appropriate. Revenues attributable to the fixed-fee component of gathering and processing contracts as well as demand charges and commodity usage fees on transportation contracts are reported as revenues from gathering, processing, transportation and disposal in the consolidated statements of operations. Proceeds from the sale of residue, NGLs and condensate are reported as revenues from natural gas and natural gas liquids sales in the consolidated statements of operations. Equity-based compensation. Concurrently with WGP’s initial public offering (“IPO”), WGP GP adopted the Western Gas Equity Partners, LP 20

Acquisitions and Divestitures

Acquisitions and Divestitures	12 Months Ended
Acquisitions and Divestitures	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Acquisitions and Divestitures	2. ACQUISITIONS AND DIVESTITURES The following table presents the acquisitions completed by WES during 2017 , 2016 and 2015, and identifies the funding sources for such acquisitions: thousands except unit and percent amounts Acquisition Date Percentage Borrowings Cash On Hand WES Common Units Issued WES Series A Preferred Units Issued DBJV system (1) 03/02/2015 50 % $ — $ — — — Springfield system (2) 03/14/2016 50.1 % 247,500 — 2,089,602 14,030,611 DBJV system (3) 03/17/2017 50 % — 155,000 — — (1) WES acquired Delaware Basin JV Gathering LLC (“DBJV”) from Anadarko. At the time of acquisition, DBJV owned a 50% interest in a gathering system and related facilities (the “DBJV system”) located in the Delaware Basin in Loving, Ward, Winkler and Reeves Counties, Texas. At the acquisition date, WES estimated the future payment would be $282.8 million , the estimated net present value of which was $174.3 million . For further information, see DBJV acquisition—deferred purchase price obligation - Anadarko below. (2) WES acquired Springfield Pipeline LLC (“Springfield”) from Anadarko for $750.0 million , consisting of $712.5 million in cash and the issuance of 1,253,761 of WES common units. Springfield owns a 50.1% interest in an oil gathering system and a gas gathering system. The Springfield oil and gas gathering systems (collectively, the “Springfield system”) are located in Dimmit, La Salle, Maverick and Webb Counties in South Texas. WES financed the cash portion of the acquisition through: (i) borrowings of $247.5 million on the WES RCF, (ii) the issuance of 835,841 of WES common units to WGP and (iii) the issuance of WES Series A Preferred units to private investors. See Note 4 for further information regarding WES’s Series A Preferred units. WGP financed the purchase of the WES common units by borrowing $25.0 million under the WGP RCF. See Note 12 . (3) WES acquired the Additional DBJV System Interest from a third party. See Property exchange below. Property exchange. On March 17, 2017, WES acquired the Additional DBJV System Interest from a third party in exchange for (a) WES’s 33.75% non-operated interest in two natural gas gathering systems located in northern Pennsylvania (the “Non-Operated Marcellus Interest”), commonly referred to as the Liberty and Rome systems, and (b) $155.0 million of cash consideration (collectively, the “Property Exchange”). WES previously held a 50% interest in, and operated, the DBJV system. The Property Exchange is reflected as a nonmonetary transaction whereby the acquired Additional DBJV System Interest is recorded at the fair value of the divested Non-Operated Marcellus Interest plus the $155.0 million of cash consideration. The Property Exchange resulted in a net gain of $125.7 million recorded as Gain (loss) on divestiture and other, net in the consolidated statements of operations. Results of operations attributable to the Property Exchange were included in the consolidated statements of operations beginning on the acquisition date in the first quarter of 2017. 2. ACQUISITIONS AND DIVESTITURES (CONTINUED) DBJV acquisition - Deferred purchase price obligation - Anadarko. Prior to WES’s agreement with Anadarko to settle its deferred purchase price obligation early, the consideration that would have been paid by WES for the March 2015 acquisition of DBJV from Anadarko consisted of a cash payment to Anadarko due on March 31, 2020. The cash payment would have been equal to (a) eight multiplied by the average of WES’s share of Net Earnings (as defined below) of DBJV for the calendar years 2018 and 2019, less (b) WES’s share of all capital expenditures incurred for DBJV between March 1, 2015, and February 29, 2020. Net Earnings was defined as all revenues less cost of product, operating expenses and property taxes, in each case attributable to DBJV on an accrual basis. In May 2017, WES reached an agreement with Anadarko to settle this obligation with a cash payment to Anadarko of $37.3 million , which was equal to the estimated net present value of the obligation at March 31, 2017. The following table summarizes the financial statement impact of the Deferred purchase price obligation - Anadarko: Deferred purchase price obligation - Anadarko Estimated future payment obligation (1) Balance at December 31, 2015 $ 188,674 $ 282,807 Accretion revision (2) (7,747 ) Revision to Deferred purchase price obligation – Anadarko (3) (139,487 ) Balance at December 31, 2016 41,440 56,455 Accretion expense (4) 71 Revision to Deferred purchase price obligation – Anadarko (3) (4,165 ) Settlement of the Deferred purchase price obligation – Anadarko (37,346 ) Balance at December 31, 2017 $ — $ — (1) Calculated using Level 3 inputs. (2) Financing-related accretion revisions were recorded in Interest expense in the consolidated statements of operations. (3) Recorded as revisions within Common units in the consolidated balance sheets and consolidated statements of equity and partners’ capital. (4) Accretion expense was recorded as a charge to Interest expense in the consolidated statements of operations. Helper and Clawson systems divestiture. During the second quarter of 2017, the Helper and Clawson systems, located in Utah, were sold to a third party, resulting in a net gain on sale of $16.3 million recorded as Gain (loss) on divestiture and other, net in the consolidated statements of operations. Hugoton system divestiture. During the fourth quarter of 2016, the Hugoton system, located in Southwest Kansas and Oklahoma, was sold to a third party, resulting in a net loss on sale of $12.0 million recorded as Gain (loss) on divestiture and other, net in the consolidated statements of operations. WES allocated $1.6 million in goodwill to this divestiture. Dew and Pinnacle systems divestiture. During the third quarter of 2015, the Dew and Pinnacle systems in East Texas were sold to a third party, resulting in a net gain on sale of $77.3 million recorded as Gain (loss) on divestiture and other, net in the consolidated statements of operations. WES allocated $5.1 million in goodwill to this divestiture.

Partnership Distributions

Partnership Distributions	12 Months Ended
Partnership Distributions	Dec. 31, 2017
Distributions Made to Members or Limited Partners [Abstract]
Partnership Distributions	3. PARTNERSHIP DISTRIBUTIONS WGP partnership distributions. WGP’s partnership agreement requires WGP to distribute all of its available cash (as defined in its partnership agreement) to WGP unitholders of record on the applicable record date within 55 days of the end of each quarter. The Board of Directors declared the following cash distributions to WGP unitholders for the periods presented: thousands except per-unit amounts Quarters Ended Total Quarterly Distribution per Unit Total Quarterly Cash Distribution Date of Distribution 2015 March 31 $ 0.34250 $ 74,977 May 2015 June 30 0.36375 79,630 August 2015 September 30 0.38125 83,461 November 2015 December 31 0.40375 88,389 February 2016 2016 March 31 $ 0.42375 $ 92,767 May 2016 June 30 0.43375 94,958 August 2016 September 30 0.44750 97,968 November 2016 December 31 0.46250 101,254 February 2017 2017 March 31 $ 0.49125 $ 107,549 May 2017 June 30 0.52750 115,487 August 2017 September 30 0.53750 117,677 November 2017 December 31 (1) 0.54875 120,140 February 2018 (1) The Board of Directors declared a cash distribution to WGP unitholders for the fourth quarter of 2017 of $0.54875 per unit, or $120.1 million in aggregate. The cash distribution is payable on February 22, 2018 , to WGP unitholders of record at the close of business on February 1, 2018 . 3. PARTNERSHIP DISTRIBUTIONS (CONTINUED) WES partnership distributions. WES’s partnership agreement requires WES to distribute all of its available cash (as defined in WES’s partnership agreement) to WES unitholders of record on the applicable record date within 45 days of the end of each quarter. The Board of Directors of WES GP declared the following cash distributions to WES’s common and general partner unitholders for the periods presented: thousands except per-unit amounts Quarters Ended Total Quarterly Total Quarterly Date of 2015 March 31 $ 0.725 $ 133,203 May 2015 June 30 0.750 139,736 August 2015 September 30 0.775 146,160 November 2015 December 31 0.800 152,588 February 2016 2016 March 31 $ 0.815 $ 158,905 May 2016 June 30 0.830 162,827 August 2016 September 30 0.845 166,742 November 2016 December 31 0.860 170,657 February 2017 2017 March 31 $ 0.875 $ 188,753 May 2017 June 30 0.890 207,491 August 2017 September 30 0.905 212,038 November 2017 December 31 (1) 0.920 216,586 February 2018 (1) The Board of Directors of WES GP declared a cash distribution to WES unitholders for the fourth quarter of 2017 of $0.920 per unit, or $216.6 million in aggregate, including incentive distributions, but excluding distributions on WES Class C units (see WES Class C unit distributions below). The cash distribution was paid on February 13, 2018 , to WES unitholders of record at the close of business on February 1, 2018 . WES’s available cash. The amount of available cash (as defined in WES’s partnership agreement) generally is all cash on hand at the end of the quarter, plus, at the discretion of WES GP, working capital borrowings made subsequent to the end of such quarter, less the amount of cash reserves established by WES GP to provide for the proper conduct of WES’s business, including reserves to fund future capital expenditures; to comply with applicable laws, debt instruments or other agreements; or to provide funds for distributions to WES unitholders and to WES GP for any one or more of the next four quarters. Working capital borrowings generally include borrowings made under a credit facility or similar financing arrangement. Working capital borrowings may only be those that, at the time of such borrowings, were intended to be repaid within 12 months. In all cases, working capital borrowings are used solely for working capital purposes or to fund distributions to partners. WES Class C unit distributions. WES’s Class C units receive quarterly distributions at a rate equivalent to WES’s common units. The distributions are paid in the form of additional Class C units (“PIK Class C units”) until the scheduled conversion date on March 1, 2020 (unless earlier converted), and the Class C units are disregarded with respect to WES’s distributions of WES’s available cash until they are converted into WES common units. The number of additional PIK Class C units to be issued in connection with a distribution payable on the Class C units is determined by dividing the corresponding distribution attributable to the Class C units by the volume-weighted-average price of WES’s common units for the ten days immediately preceding the payment date for the WES common unit distribution, less a 6% discount. WES records the PIK Class C unit distributions at fair value at the time of issuance. This Level 2 fair value measurement uses WES’s unit price as a significant input in the determination of the fair value. See Note 4 for further discussion of the WES Class C units. 3. PARTNERSHIP DISTRIBUTIONS (CONTINUED) WES Series A Preferred unit distributions. As further described in Note 4 , WES issued Series A Preferred units representing limited partner interests in WES to private investors in 2016. The Series A Preferred unitholders received quarterly distributions in cash equal to $0.68 per Series A Preferred unit, subject to certain adjustments. The following table summarizes the Series A Preferred unitholders’ cash distributions for the periods presented: thousands except per-unit amounts Quarters Ended Total Quarterly Distribution per Unit Total Quarterly Cash Distribution Date of Distribution 2016 March 31 (1) $ 0.68 $ 1,887 May 2016 June 30 (2) 0.68 14,082 August 2016 September 30 0.68 14,907 November 2016 December 31 0.68 14,908 February 2017 2017 March 31 $ 0.68 $ 7,453 May 2017 (1) Quarterly per unit distribution prorated for the 18 -day period during which 14,030,611 WES Series A Preferred units were outstanding during the first quarter of 2016. (2) Full quarterly per unit distribution on 14,030,611 WES Series A Preferred units and quarterly per unit distribution prorated for the 77 -day period during which 7,892,220 WES Series A Preferred units were outstanding during the second quarter of 2016. On March 1, 2017, 50% of the outstanding WES Series A Preferred units converted into WES common units on a one -for-one basis, and on May 2, 2017, all remaining WES Series A Preferred units converted into WES common units on a one -for-one basis. Such converted WES common units were entitled to distributions made to WES common unitholders with respect to the quarter during which the applicable conversion occurred and did not include a prorated WES Series A Preferred unit distribution. WES’s general partner interest and incentive distribution rights. As of December 31, 2017 , WES GP was entitled to 1.5% of all quarterly distributions that WES makes prior to its liquidation and, as the holder of the incentive distribution rights (“IDRs”), was entitled to incentive distributions at the maximum distribution sharing percentage of 48.0% for all periods presented, after the minimum quarterly distribution and the target distribution levels had been achieved. The maximum distribution sharing percentage of 49.5% does not include any distributions that WES GP may receive on common units that it may acquire.

Equity and Partners' Capital

Equity and Partners' Capital	12 Months Ended
Equity and Partners' Capital	Dec. 31, 2017
Partners' Capital Notes [Abstract]
Equity and Partners' Capital	4. EQUITY AND PARTNERS’ CAPITAL Holdings of WGP equity. WGP’s common units are listed on the New York Stock Exchange under the symbol “WGP.” As of December 31, 2017 , Anadarko held 178,587,365 of WGP’s common units, representing an 81.6% limited partner interest in WGP, and, through its ownership of WGP GP, Anadarko indirectly held the entire non-economic general partner interest in WGP. The public held 40,345,776 WGP common units, representing an 18.4% limited partner interest in WGP. In June 2016, Anadarko sold 12,500,000 of its WGP common units to the public through an underwritten offering. WGP did not receive any proceeds from, or incur any expense in, the public offering. In June 2015, Anadarko sold 2,300,000 of its WGP common units to the public through an underwritten offering, including 300,000 common units pursuant to the full exercise of the underwriters’ over-allotment option. WGP did not receive any proceeds from, or incur any expense in, the public offering. Tangible equity units. In June 2015, Anadarko completed the public issuance of 9,200,000 7.50% tangible equity units (“TEUs”), including 1,200,000 TEUs pursuant to the full exercise of the underwriters’ over-allotment option, at a price to the public of $50.00 per TEU. Each TEU that Anadarko issued consists of (1) a prepaid equity purchase contract for WGP common units owned by Anadarko (subject to Anadarko’s right to elect to deliver shares of its common stock in lieu of such WGP common units) and (2) a senior amortizing note due June 7, 2018 . WGP did not receive any proceeds from, or incur any expense in, the public offering. Net income (loss) per common unit. For WGP, basic net income (loss) per common unit is calculated by dividing the limited partners’ interest in net income (loss) by the weighted-average number of common units outstanding during the period. Dilutive net income (loss) per common unit is calculated by dividing the limited partners’ interest in net income (loss) adjusted for distributions on the WES Series A Preferred units and a reallocation of the limited partners’ interest in net income (loss) assuming, prior to the actual conversion, conversion of the WES Series A Preferred units into WES common units, by the weighted-average number of WGP common units outstanding during the period. As of May 2, 2017, all WES Series A Preferred units were converted into WES common units on a one-for-one basis. The impact of the Series A Preferred units assuming, prior to the actual conversion, conversion to WES common units would be anti-dilutive for all periods presented. Net income (loss) per common unit is calculated assuming that cash distributions are equal to the net income attributable to WGP. Net income (loss) attributable to the WES assets (as defined in Note 1 ) acquired from Anadarko for periods prior to WES’s acquisition of the WES assets is not allocated to the limited partners when calculating net income (loss) per common unit. Net income equal to the amount of available cash (as defined by WGP’s partnership agreement) is allocated to WGP common unitholders consistent with actual cash distributions. Holdings of WES equity. As of December 31, 2017 , WGP held 50,132,046 WES common units, representing a 29.8% limited partner interest in WES, and, through its ownership of WES GP, WGP indirectly held 2,583,068 general partner units, representing a 1.5% general partner interest in WES, and 100% of WES’s IDRs. As of December 31, 2017 , (i) other subsidiaries of Anadarko collectively held 2,011,380 WES common units and 13,243,883 Class C units, representing an aggregate 9.1% limited partner interest in WES and (ii) the public held 100,458,679 WES common units, representing a 59.6% limited partner interest in WES, which are all reflected as noncontrolling interests within the consolidated financial statements of WGP (see Note 1 and Note 2 ). 4. EQUITY AND PARTNERS’ CAPITAL (CONTINUED) WES equity offerings. Pursuant to WES’s registration statement filed with the SEC in August 2014 authorizing the issuance of up to an aggregate of $500.0 million of WES common units in a continuous offering program, during the year ended December 31, 2015, WES issued 873,525 common units, at an average price of $66.61 , generating proceeds to WES of $57.4 million (net of $0.8 million for the underwriting discount and other offering expenses). Net proceeds were used for general partnership purposes, including funding capital expenditures. Gross proceeds generated during the three months and year ended December 31, 2015, were zero and $58.2 million , respectively. Commissions paid during the three months and year ended December 31, 2015, were zero and $0.6 million , respectively. During the years ended December 31, 2016 and 2017, WES issued no common units under the registration statement filed in August 2014. In July 2017, WES filed a registration statement with the SEC for the issuance of up to an aggregate of $500.0 million of WES common units pursuant to a new continuous offering program that has not yet been initiated. WES Class C units. In November 2014, WES issued 10,913,853 Class C units to APC Midstream Holdings, LLC (“AMH”), pursuant to a Unit Purchase Agreement with Anadarko and AMH. The Class C units were issued to partially fund WES’s acquisition of DBM. When issued, the WES Class C units were scheduled to convert into WES common units on a one -for-one basis on December 31, 2017. In February 2017, Anadarko elected to extend the conversion date of the WES Class C units to March 1, 2020. WES can elect to convert the Class C units earlier or Anadarko can extend the conversion date again. WES Series A Preferred units. In connection with the closing of the Springfield acquisition on March 14, 2016, WES issued 14,030,611 Series A Preferred units to private investors for a cash purchase price of $32.00 per unit, generating proceeds of $440.0 million (net of fees and expenses, but including a 2.0% transaction fee paid to the private investors). In April 2016, WES issued an additional 7,892,220 Series A Preferred units pursuant to the full exercise of an option granted in connection with the Series A units issuance in March 2016, generating net proceeds of $246.9 million . Pursuant to an agreement between WES and the holders of the WES Series A Preferred units, 50% of the WES Series A Preferred units converted into WES common units on a one -for-one basis on March 1, 2017, and all remaining Series A Preferred units converted into WES common units on a one -for-one basis on May 2, 2017. WES has an effective registration statement with the SEC relating to the public resale of the WES common units issued upon conversion of the WES Series A Preferred units. WES interests . The following table summarizes WES’s common, Class C, Series A Preferred and general partner units issued during the years ended December 31, 2017 and 2016: WES Common Units WES Class C Units WES Series A Preferred Units WES General Partner Units Total Balance at December 31, 2015 128,576,965 11,411,862 — 2,583,068 142,571,895 PIK Class C units — 946,261 — — 946,261 Springfield acquisition 2,089,602 — 14,030,611 — 16,120,213 April 2016 Series A units issuance — — 7,892,220 — 7,892,220 Long-Term Incentive Plan award vestings 5,403 — — — 5,403 Balance at December 31, 2016 130,671,970 12,358,123 21,922,831 2,583,068 167,535,992 PIK Class C units — 885,760 — — 885,760 Conversion of Series A Preferred units 21,922,831 — (21,922,831 ) — — Long-Term Incentive Plan award vestings 7,304 — — — 7,304 Balance at December 31, 2017 152,602,105 13,243,883 — 2,583,068 168,429,056

Transactions with Affiliates

Transactions with Affiliates	12 Months Ended
Transactions with Affiliates	Dec. 31, 2017
Related Party Fees and Other Arrangements, Limited Liability Company (LLC) or Limited Partnership (LP) [Abstract]
Transactions with Affiliates	5. TRANSACTIONS WITH AFFILIATES Affiliate transactions. Revenues from affiliates include amounts earned by WES from services provided to Anadarko as well as from the sale of residue and NGLs to Anadarko. In addition, WES purchases natural gas from an affiliate of Anadarko pursuant to gas purchase agreements. Operation and maintenance expense includes amounts accrued for or paid to affiliates for the operation of WES assets, whether in providing services to affiliates or to third parties, including field labor, measurement and analysis, and other disbursements. A portion of general and administrative expenses is paid by Anadarko, which results in affiliate transactions pursuant to the reimbursement provisions of the omnibus agreements of WES and WGP. Affiliate expenses do not bear a direct relationship to affiliate revenues, and third-party expenses do not bear a direct relationship to third-party revenues. See Note 2 for further information related to contributions of assets to WES by Anadarko. Cash management. Anadarko operates a cash management system whereby excess cash from most of its subsidiaries’ separate bank accounts is generally swept to centralized accounts. Prior to the acquisition of WES assets, third-party sales and purchases related to such assets were received or paid in cash by Anadarko within its centralized cash management system. The outstanding affiliate balances were entirely settled through an adjustment to net investment by Anadarko in connection with the acquisition of WES assets. Subsequent to the acquisition of WES assets from Anadarko, transactions related to such assets are cash-settled directly with third parties and with Anadarko affiliates. Chipeta cash settles its transactions directly with third parties and Anadarko, as well as with the other subsidiaries of WES. Note receivable - Anadarko. Concurrently with the closing of WES’s May 2008 initial public offering, WES loaned $260.0 million to Anadarko in exchange for a 30-year note bearing interest at a fixed annual rate of 6.50% , payable quarterly. The fair value of the note receivable from Anadarko was $325.2 million and $313.3 million at December 31, 2017 and 2016 , respectively. The fair value of the note reflects consideration of credit risk and any premium or discount for the differential between the stated interest rate and quarter-end market interest rate, based on quoted market prices of similar debt instruments. Accordingly, the fair value of the note receivable from Anadarko is measured using Level 2 inputs. WGP working capital facility. On November 1, 2012, WGP entered into a $30.0 million working capital facility (the “WGP WCF”) with Anadarko as the lender. The WGP WCF matured on November 1, 2017 . See Note 12 . Commodity price swap agreements. WES has commodity price swap agreements with Anadarko to mitigate exposure to a majority of the commodity price risk inherent in its percent-of-proceeds and keep-whole contracts. Notional volumes for each of the commodity price swap agreements are not specifically defined. Instead, the commodity price swap agreements apply to the actual volume of natural gas, condensate and NGLs purchased and sold. The commodity price swap agreements do not satisfy the definition of a derivative financial instrument and, therefore, are not required to be measured at fair value. 5. TRANSACTIONS WITH AFFILIATES (CONTINUED) The following table summarizes gains and losses upon settlement of WES’s commodity price swap agreements recognized in the consolidated statements of operations: Year Ended December 31, thousands 2017 2016 2015 Gains (losses) on commodity price swap agreements related to sales: (1) Natural gas sales $ 19,924 $ 11,116 $ 45,978 Natural gas liquids sales (21,722 ) 59,918 145,258 Total (1,798 ) 71,034 191,236 Gains (losses) on commodity price swap agreements related to purchases (2) 2,446 (42,577 ) (124,944 ) Net gains (losses) on commodity price swap agreements $ 648 $ 28,457 $ 66,292 (1) Reported in affiliate Natural gas and natural gas liquids sales in the consolidated statements of operations in the period in which the related sale is recorded. (2) Reported in Cost of product in the consolidated statements of operations in the period in which the related purchase is recorded. Swap agreements - DJ Basin complex, Hugoton system and MGR assets. On June 25, 2015, WES extended its commodity price swap agreements with Anadarko for the DJ Basin complex from July 1, 2015, through December 31, 2015, and for the Hugoton system from October 1, 2015, through December 31, 2015. On December 8, 2015, the commodity price swap agreements with Anadarko for the DJ Basin complex and Hugoton system were extended from January 1, 2016, through December 31, 2016. On December 1, 2016, the commodity price swap agreements with Anadarko for the DJ Basin complex and the MGR assets were extended from January 1, 2017 through December 31, 2017. On December 20, 2017 , the commodity price swap agreements with Anadarko for the DJ Basin complex and the MGR assets were extended from January 1, 2018 through December 31, 2018. Revenues or costs attributable to volumes settled during the respective extension period, at the applicable market price in the tables below, are recognized in the consolidated statements of operations. WES also records a capital contribution from Anadarko in its consolidated statements of equity and partners’ capital for an amount equal to (i) the amount by which the swap price recognized as revenue exceeds the applicable market price in the tables below, minus (ii) the amount by which the swap price recognized as cost of product exceeds the market price in the tables below. For the years ended December 31, 2017 , 2016 and 2015 , the capital contributions from Anadarko were $58.6 million , $45.8 million and $18.4 million , respectively. The tables below summarize the swap prices for the extension periods compared to the forward market prices as of the various agreement dates. DJ Basin Complex per barrel except natural gas 2015 - 2018 Swap Prices 2015 Market Prices (1) 2016 Market Prices (1) 2017 Market Prices (1) 2018 Market Prices (1) Ethane $ 18.41 $ 1.96 $ 0.60 $ 5.09 $ 5.41 Propane 47.08 13.10 10.98 18.85 28.72 Isobutane 62.09 19.75 17.23 26.83 32.92 Normal butane 54.62 18.99 16.86 26.20 32.71 Natural gasoline 72.88 52.59 26.15 41.84 48.04 Condensate 76.47 52.59 34.65 45.40 49.36 Natural gas (per MMBtu) 5.96 2.75 2.11 3.05 2.21 5. TRANSACTIONS WITH AFFILIATES (CONTINUED) Hugoton System (2) per barrel except natural gas 2015 - 2016 Swap Prices 2015 Market Prices (1) 2016 Market Prices (1) Condensate $ 78.61 $ 32.56 $ 18.81 Natural gas (per MMBtu) 5.50 2.74 2.12 MGR Assets per barrel except natural gas 2015 Swap Prices 2016 - 2018 Swap Prices 2017 Market Prices (1) 2018 Market Prices (1) Ethane $ 23.41 $ 23.11 $ 4.08 $ 2.52 Propane 52.99 52.90 19.24 25.83 Isobutane 74.02 73.89 25.79 30.03 Normal butane 65.04 64.93 25.16 29.82 Natural gasoline 81.82 81.68 45.01 47.25 Condensate 81.82 81.68 53.55 56.76 Natural gas (per MMBtu) 4.66 4.87 3.05 2.21 (1) Represents the New York Mercantile Exchange forward strip price as of June 25, 2015, December 8, 2015, December 1, 2016, and December 20, 2017 , for the 2015 Market Prices, 2016 Market Prices, 2017 Market Prices, and 2018 Market Prices, respectively, adjusted for product specification, location, basis and, in the case of NGLs, transportation and fractionation costs. (2) The Hugoton system was sold in October 2016. See Note 2 . Gathering and processing agreements. WES has significant gathering and processing arrangements with affiliates of Anadarko on a majority of its systems. WES’s natural gas gathering, treating and transportation throughput (excluding equity investment throughput) attributable to production owned or controlled by Anadarko was 34% , 37% and 53% for the years ended December 31, 2017 , 2016 and 2015 , respectively. WES’s natural gas processing throughput (excluding equity investment throughput) attributable to production owned or controlled by Anadarko was 41% , 54% and 51% for the years ended December 31, 2017 , 2016 and 2015 , respectively. WES’s crude oil, NGL and produced water gathering, treating, transportation and disposal throughput (excluding equity investment throughput) attributable to production owned or controlled by Anadarko was 56% , 65% , and 100% for the years ended December 31, 2017 , 2016 and 2015 , respectively. Prior to January 1, 2016, Springfield’s contracts were with a subsidiary of Anadarko who contracted with third parties. Effective January 1, 2016, Springfield’s contracts are with both a subsidiary of Anadarko and third parties directly. Commodity purchase and sale agreements. WES sells a significant amount of its natural gas, condensate and NGLs to Anadarko Energy Services Company (“AESC”), Anadarko’s marketing affiliate. In addition, WES purchases natural gas, condensate and NGLs from AESC pursuant to purchase agreements. WES’s purchase and sale agreements with AESC are generally one-year contracts, subject to annual renewal. Acquisitions from Anadarko. On March 14, 2016, WES acquired Springfield from Anadarko, and on March 2, 2015, WES acquired DBJV from Anadarko. (see Note 2 ). Omnibus agreements. Pursuant to the omnibus agreements discussed below, Anadarko performs centralized corporate functions for WGP and WES such as legal; accounting; treasury; cash management; investor relations; insurance administration and claims processing; risk management; health, safety and environmental; information technology; human resources; credit; payroll; internal audit; tax; marketing; and midstream administration. Anadarko, in accordance with WES’s partnership agreement and the omnibus agreement between Anadarko and WES GP that governs certain reimbursement and indemnification matters (the “WES omnibus agreement”), determines, in its reasonable discretion, amounts to be reimbursed by WES in exchange for services provided under the WES omnibus agreement. See Summary of affiliate transactions below. 5. TRANSACTIONS WITH AFFILIATES (CONTINUED) WGP omnibus agreement. In connection with WGP’s IPO in December 2012, WGP entered into an omnibus agreement with WGP GP and Anadarko that governs the following: (i) WGP’s obligation to reimburse Anadarko for expenses incurred or payments made on WGP’s behalf in conjunction with Anadarko’s provision of general and administrative services to WGP, including public company expenses and general and administrative expenses; (ii) WGP’s obligation to pay Anadarko, in quarterly installments, an administrative services fee of $250,000 per year (subject to an annual increase as described in the agreement); and (iii) WGP’s obligation to reimburse Anadarko for all insurance coverage expenses it incurs or payments it makes on WGP’s behalf. The following table summarizes the amounts WGP reimbursed to Anadarko, separate from, and in addition to, those reimbursed by WES: Year Ended December 31, thousands 2017 2016 2015 General and administrative expenses $ 263 $ 258 $ 256 Public company expenses 1,821 2,449 1,997 Total reimbursement $ 2,084 $ 2,707 $ 2,253 WES omnibus agreement. In connection with WES’s IPO in 2008, WES entered into the WES omnibus agreement with Anadarko and WES GP, which governs its relationship regarding certain reimbursement and indemnification matters. The following table summarizes the amounts WES reimbursed to Anadarko: Year Ended December 31, thousands 2017 2016 2015 General and administrative expenses $ 31,733 $ 29,360 $ 22,896 Public company expenses 9,379 8,410 8,950 Total reimbursement $ 41,112 $ 37,770 $ 31,846 Services and secondment agreement. Pursuant to the services and secondment agreement, specified employees of Anadarko are seconded to provide operating, routine maintenance and other services with respect to the assets owned and operated by WES under the direction, supervision and control of WES GP. Pursuant to the services and secondment agreement, WES reimburses Anadarko for services provided by the seconded employees. The initial term of the services and secondment agreement extends through May 2018 and the term will automatically extend for additional twelve-month periods unless either party provides 180 days written notice of termination before the applicable twelve-month period expires. The consolidated financial statements include costs allocated by Anadarko for expenses incurred under the services and secondment agreement for periods including and subsequent to WES’s acquisition of the WES assets. WGP tax sharing agreement. Prior to WGP’s conversion from WGR Holdings, LLC to a limited partnership in September 2012, WGP was a single-member limited liability company, required to reflect its income tax expense liability on a separate-return basis. Upon the completion of WGP’s IPO in December 2012, WGP became a partnership for U.S. federal and state income tax purposes and is therefore not subject to U.S. federal and state income taxes, except for Texas margin tax on the portion of WGP’s income apportionable to Texas. See Note 6 . In connection with WGP’s IPO in December 2012, WGP entered into a tax sharing agreement with Anadarko, pursuant to which WGP reimburses Anadarko for its estimated share of taxes from all forms of taxation, excluding taxes imposed by the United States. Taxes for which WGP reimburses Anadarko include state taxes attributable to WGP’s income which are directly borne by Anadarko on WGP’s behalf as a result of WGP’s results being included in a combined or consolidated tax return filed by Anadarko with respect to periods including and subsequent to the closing date of the IPO. Anadarko may use its tax attributes to cause its combined or consolidated group, of which WGP may be a member for this purpose, to owe no tax. Nevertheless, WGP will be required to reimburse Anadarko for the estimated share of taxes that WGP would have owed had the attributes not been available or used for WGP’s benefit, regardless of whether Anadarko pays taxes for the period. 5. TRANSACTIONS WITH AFFILIATES (CONTINUED) WES tax sharing agreement. Concurrently with WES’s IPO in 2008, WES entered into a tax sharing agreement, pursuant to which WES reimburses Anadarko for its estimated share of taxes from all forms of taxation, excluding taxes imposed by the United States. Taxes for which WES reimburses Anadarko include state taxes attributable to WES’s income, which are directly borne by Anadarko through its filing of a combined or consolidated tax return with respect to periods beginning on and subsequent to the acquisition of the WES assets from Anadarko. Anadarko may use its own tax attributes to reduce or eliminate the tax liability of its combined or consolidated group, which may include WES as a member. However, under this circumstance, WES nevertheless is required to reimburse Anadarko for its allocable share of taxes that would have been owed had tax attributes not been available to Anadarko. WES long-term debt and WES RCF indemnification agreements. WES’s long-term debt is recourse to WES GP. In turn, WES GP has been indemnified by wholly owned subsidiaries of Anadarko for any claims made against WES GP under WES’s long-term debt or the WES RCF. See Note 12 . Allocation of costs. For periods prior to WES’s acquisition of the WES assets, the consolidated financial statements include costs allocated by Anadarko in the form of a management services fee, which approximated the general and administrative costs incurred by Anadarko attributable to the WES assets. This management services fee was allocated to WES based on its proportionate share of Anadarko’s assets and revenues or other contractual arrangements. Management believes these allocation methodologies are reasonable. The employees supporting WES’s operations are employees of Anadarko. Anadarko allocates costs to WES for its share of personnel costs, including costs associated with equity-based compensation plans, non-contributory defined pension and postretirement plans and defined contribution savings plans pursuant to the WES omnibus agreement and services and secondment agreement. In general, WES’s reimbursement to Anadarko under the WES omnibus agreement or services and secondment agreement is either (i) on an actual basis for direct expenses Anadarko and WES GP incur on behalf of WES, or (ii) based on an allocation of salaries and related employee benefits between WES, WES GP and Anadarko based on estimates of time spent on each entity’s business and affairs. Most general and administrative expenses charged to WES by Anadarko are attributed to WES on an actual basis, and do not include any mark-up or subsidy component. With respect to allocated costs, management believes the allocation method employed by Anadarko is reasonable. Although it is not practicable to determine what the amount of these direct and allocated costs would be if WES were to directly obtain these services, management believes that aggregate costs charged to WES by Anadarko are reasonable. WGP LTIP and Anadarko Incentive Plans. WGP GP awards phantom units under the WGP LTIP to its independent directors and executive officers. The phantom units awarded to the independent directors vest one year from the grant date, while awards granted to executive officers are subject to graded vesting over a three -year service period. The following table summarizes WGP LTIP award activity for WGP GP independent directors and executive officers for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Weighted-Average Grant-Date Fair Value Units Weighted-Average Grant-Date Fair Value Units Weighted-Average Grant-Date Fair Value Units Phantom units outstanding at beginning of year $ 39.78 5,658 $ 47.20 12,537 $ 43.10 22,236 Vested 39.78 (5,658 ) 47.20 (12,537 ) 44.44 (13,317 ) Granted 43.39 5,763 39.78 5,658 62.21 3,618 Phantom units outstanding at end of year 43.39 5,763 39.78 5,658 47.20 12,537 5. TRANSACTIONS WITH AFFILIATES (CONTINUED) WGP LTIP and Anadarko Incentive Plans Compensation Expense. Compensation expense under the WGP LTIP is recognized over the vesting period and was $0.2 million for each of the years ended December 31, 2017 , 2016 and 2015 . As of December 31, 2017 , there was $0.1 million of unrecognized compensation expense attributable to the outstanding independent director awards under the WGP LTIP, which will be realized by WGP and is expected to be recognized in 0.4 years. For the years ended December 31, 2017 , 2016 and 2015 , general and administrative expenses included $4.6 million , $5.2 million and $3.9 million , respectively, of equity-based compensation expense, allocated to WES by Anadarko, for awards granted to the executive officers of WES GP and other employees under the WGP LTIP and the Anadarko Incentive Plans. Of these amounts, $4.6 million , $4.2 million and $3.6 million for the years ended December 31, 2017 , 2016 and 2015 , respectively, are reflected as contributions to partners’ capital in the consolidated statements of equity and partners’ capital. As of December 31, 2017 , $13.2 million of estimated unrecognized compensation expense attributable to the Anadarko Incentive Plans will be allocated to WES over a weighted-average period of 2.5 years. WES LTIP. WES GP awards phantom units under the WES LTIP primarily to its independent directors, but also from time to time to its executive officers and Anadarko employees performing services for WES. The phantom units awarded to the independent directors vest one year from the grant date, while all other awards are subject to graded vesting over a three -year service period. The following table summarizes WES LTIP award activity for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Weighted-Average Grant-Date Fair Value Units Weighted-Average Grant-Date Fair Value Units Weighted-Average Grant-Date Fair Value Units Phantom units outstanding at beginning of year $ 49.30 7,304 $ 68.78 5,477 $ 60.74 9,522 Vested 49.30 (7,304 ) 68.78 (5,477 ) 60.69 (9,257 ) Granted 55.73 7,180 49.30 7,304 69.10 5,212 Phantom units outstanding at end of year 55.73 7,180 49.30 7,304 68.78 5,477 WES LTIP Compensation Expense. Compensation expense is recognized over the vesting period and was $0.4 million for each of the years ended December 31, 2017 and 2016 , and $0.5 million for the year ended December 31, 2015 . As of December 31, 2017 , there was $0.2 million of unrecognized compensation expense attributable to the outstanding awards under the WES LTIP, all of which will be realized by WES, and which is expected to be recognized over a weighted-average period of 0.4 years. Equipment purchases and sales. The following table summarizes WES’s purchases from and sales to Anadarko of pipe and equipment: Year Ended December 31, 2017 2016 2015 2017 2016 2015 thousands Purchases Sales Cash consideration $ 3,910 $ 3,965 $ 10,903 $ — $ 623 $ 925 Net carrying value (5,283 ) (3,366 ) (6,318 ) — (605 ) (972 ) Partners’ capital adjustment $ (1,373 ) $ 599 $ 4,585 $ — $ 18 $ (47 ) 5. TRANSACTIONS WITH AFFILIATES (CONTINUED) Contributions in aid of construction costs from affiliates. On certain of WES’s capital projects, Anadarko is obligated to reimburse WES for all or a portion of project capital expenditures. The majority of such arrangements are associated with projects related to pipeline construction activities and production well tie-ins. The cash receipts resulting from such reimbursements are presented as “Contributions in aid of construction costs from affiliates” within the investing section of the consolidated statements of cash flows. See Accounting standards adopted in 2018 in Note 1 for a discussion of the expected impact the adoption of Topic 606 will have on future aid in construction costs. Summary of affiliate transactions. The following table summarizes material affiliate transactions. See Note 2 for discussion of affiliate acquisitions and related funding. Year ended December 31, thousands 2017 2016 2015 Revenues and other (1) $ 1,365,318 $ 1,228,232 $ 1,220,639 Equity income, net – affiliates (1) 85,194 78,717 71,251 Cost of product (1) 86,010 80,455 167,354 Operation and maintenance (2) 72,489 72,330 77,061 General and administrative (3) 39,940 38,873 34,703 Operating expenses 198,439 191,658 279,118 Interest income (4) 16,900 16,900 16,900 Interest expense (5) 71 (7,747 ) 14,400 Settlement of the Deferred purchase price obligation – Anadarko (6) (37,346 ) — — Distributions to WGP unitholders (7) 360,523 315,505 269,029 Distributions to WES unitholders (8) 7,100 5,614 2,235 Above-market component of swap agreements with Anadarko 58,551 45,820 18,449 (1) 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, recognized under gathering, treating or processing agreements, and purchase and sale agreements. (2) Represents expenses incurred on and subsequent to the date of the acquisition of WES assets, as well as expenses incurred by Anadarko on a historical basis related to WES assets prior to the acquisition of such assets by WES. (3) Represents general and administrative expense incurred on and subsequent to the date of the acquisition of WES assets, as well as a management services fee for reimbursement of expenses incurred by Anadarko for periods prior to the acquisition of WES assets by WES. These amounts include equity-based compensation expense allocated to WES and WGP by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plans within this Note 5 ) and amounts charged by Anadarko under the WGP and WES omnibus agreements. (4) Represents interest income recognized on the note receivable from Anadarko. (5) Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 2 and Note 12 ) and for the year ended December 31, 2015, includes interest expense recognized on the WGP WCF (see Note 12 ). (6) Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 2 ). (7) Represents distributions paid under WGP’s partnership agreement (see Note 3 and Note 4 ). (8) Represents distributions paid to other subsidiaries of Anadarko under WES’s partnership agreement (see Note 3 and Note 4 ). Concentration of credit risk. Anadarko was the only customer from whom revenues exceeded 10% of consolidated revenues for all periods presented in the consolidated statements of operations.

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	6. INCOME TAXES The components of income tax expense (benefit) are as follows: Year Ended December 31, thousands 2017 2016 2015 Current income tax expense (benefit) Federal income tax expense (benefit) $ — $ 4,477 $ 32,422 State income tax expense (benefit) 2,408 1,340 1,764 Total current income tax expense (benefit) 2,408 5,817 34,186 Deferred income tax expense (benefit) Federal income tax expense (benefit) — 1,622 10,251 State income tax expense (benefit) 2,458 933 1,095 Total deferred income tax expense (benefit) 2,458 2,555 11,346 Total income tax expense (benefit) $ 4,866 $ 8,372 $ 45,532 Total income taxes differed from the amounts computed by applying the statutory income tax rate to income (loss) before income taxes. The sources of these differences are as follows: Year Ended December 31, thousands except percentages 2017 2016 2015 Income (loss) before income taxes $ 578,068 $ 605,352 $ 56,630 Statutory tax rate — % — % — % Tax computed at statutory rate $ — $ — $ — Adjustments resulting from: Federal taxes on income attributable to Anadarko’s investment in WES — 6,162 42,823 State taxes on income attributable to Anadarko’s investment in WES (net of federal benefit) — 117 298 Texas margin tax expense (benefit) (1) 4,866 2,093 2,411 Income tax expense (benefit) $ 4,866 $ 8,372 $ 45,532 Effective tax rate 1 % 1 % 80 % (1) Includes a reduction of $2.2 million in deferred state income taxes for the year ended December 31, 2015. Texas House Bill 32, signed into law in June 2015, reduced the Texas margin tax rates by 0.25% . The law became effective January 1, 2016. WGP is required to include the impact of the law change on its deferred state income taxes in the period enacted. The tax effects of temporary differences that give rise to significant portions of deferred tax assets (liabilities) are as follows: December 31, thousands 2017 2016 Depreciable property $ (7,676 ) $ (4,976 ) Credit carryforwards 448 498 Other intangible assets (189 ) (1,928 ) Other 8 4 Net long-term deferred income tax liabilities $ (7,409 ) $ (6,402 ) Credit carryforwards, which are available for use on future income tax returns, consist of $0.4 million of state income tax credits that expire in 2026.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
Property, Plant and Equipment	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	7. PROPERTY, PLANT AND EQUIPMENT A summary of the historical cost of property, plant and equipment is as follows: December 31, thousands Estimated Useful Life 2017 2016 Land n/a $ 4,450 $ 4,012 Gathering systems and processing complexes 3 to 47 years 7,114,701 6,462,053 Pipelines and equipment 15 to 45 years 137,644 139,646 Assets under construction n/a 577,914 226,626 Other 3 to 40 years 36,393 29,605 Total property, plant and equipment 7,871,102 6,861,942 Accumulated depreciation 2,140,211 1,812,010 Net property, plant and equipment $ 5,730,891 $ 5,049,932 The cost of property classified as “Assets under construction” is excluded from capitalized costs being depreciated. These amounts represent property that is not yet suitable to be placed into productive service as of the respective balance sheet date. Impairments. During 2017, WES recognized impairments of $178.4 million , including an impairment of $158.8 million at the Granger complex, which was impaired to its estimated fair value of $48.5 million using the income approach and Level 3 fair value inputs, due to a reduced throughput fee as a result of a producer’s bankruptcy. The remaining $19.6 million of impairments was primarily related to (i) an $8.2 million impairment due to the cancellation of a plant project at the Hilight system, (ii) a $3.7 million impairment at the Granger straddle plant, which was impaired to its estimated salvage value of $0.6 million using the income approach and Level 3 fair value inputs, (iii) a $3.1 million impairment of the Fort Union equity investment (see Note 9 ), (iv) a $2.0 million impairment of an idle facility in northeast Wyoming, which was impaired to its estimated salvage value of $0.4 million using the market approach and Level 3 fair value inputs, and (v) the cancellation of a pipeline project in West Texas. During 2016, WES recognized impairments of $15.5 million , including an impairment of $6.1 million at the Newcastle system, which was impaired to its estimated fair value of $3.1 million using the income approach and Level 3 fair value inputs, due to a reduction in estimated future cash flows caused by the low commodity price environment. Also during 2016, WES recognized impairments of $9.4 million , primarily related to the cancellation of projects at the DJ Basin complex and Springfield and DBJV systems, and the abandonment of compressors at the MIGC system. During 2015, WES recognized impairments of $515.5 million , primarily due to impairments of $280.2 million at the Red Desert complex and $220.9 million at the Hilight system. Using the income approach and Level 3 fair value inputs, the Red Desert complex was impaired to its estimated salvage value of $6.3 million and the Hilight system was impaired to its estimated fair value of $28.8 million . These impairments were triggered by a reduction in estimated future cash flows caused by the low commodity price environment and resulting reduced producer drilling activity and related throughput. Also during 2015, WES recognized impairments of $14.4 million , primarily due to (i) the abandonment of compressors at the MIGC system and (ii) the cancellation of projects at the Non-Operated Marcellus Interest systems and the Brasada, Red Desert and DJ Basin complexes.

Goodwill and Intangibles

Goodwill and Intangibles	12 Months Ended
Goodwill and Intangibles	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangibles	8. GOODWILL AND INTANGIBLES Goodwill. Goodwill is recorded when the purchase price of a business acquired exceeds the fair market value of the tangible and separately measurable intangible net assets. In addition, goodwill represents the allocated portion of Anadarko’s midstream goodwill attributed to the WES assets WGP, through its consolidation of WES, has acquired from Anadarko. The carrying value of Anadarko’s midstream goodwill represents the excess of the purchase price paid to a third-party entity over the estimated fair value of the identifiable assets acquired and liabilities assumed by Anadarko. Accordingly, WES’s allocated goodwill balance does not represent, and in some cases is significantly different from, the difference between the consideration WES paid for its acquisitions from Anadarko and the fair value of such net assets on their respective acquisition dates. Goodwill is evaluated for impairment annually (see Note 1 ). Estimating the fair value of the reporting units was not necessary based on the qualitative evaluation as of October 1, 2017 , and no goodwill impairment has been recognized in these consolidated financial statements. Qualitative factors were also assessed in the fourth quarter of 2017 to review any changes in circumstances subsequent to the annual test, including changes in commodity prices. This assessment also indicated no impairment. Other intangible assets. The intangible asset balance on the consolidated balance sheets includes the fair value, net of amortization, of (i) contracts assumed by WES in connection with the Platte Valley acquisition in February 2011, which are being amortized on a straight-line basis over 50 years , (ii) interconnect agreements at Chipeta entered into in November 2012, which are being amortized on a straight-line basis over 10 years , and (iii) contracts assumed by WES in connection with the DBM acquisition in November 2014, which are being amortized on a straight-line basis over 30 years . WES assesses intangible assets for impairment together with related underlying long-lived assets whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. See Property, plant and equipment in Note 1 for further discussion of management’s process to evaluate potential impairment of long-lived assets. No intangible asset impairment has been recognized in these consolidated financial statements. The following table presents the gross carrying amount and accumulated amortization of other intangible assets: December 31, thousands 2017 2016 Gross carrying amount $ 868,035 $ 868,035 Accumulated amortization (92,766 ) (64,337 ) Other intangible assets $ 775,269 $ 803,698 Amortization expense for intangible assets was $28.4 million for each of the years ended December 31, 2017 and 2016 , and $28.2 million for the year ended December 31, 2015 . An estimated $28.4 million of intangible asset amortization will be recorded for each of the next five years.

Equity Investments

Equity Investments	12 Months Ended
Equity Investments	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Equity Investments	9. EQUITY INVESTMENTS The following table presents the activity in WES’s equity investments for the years ended December 31, 2017 and 2016: Equity Investments thousands Fort (1) White (2) Rendezvous (3) Mont (4) TEG (5) TEP (6) FRP (7) Total Balance at December 31, 2015 $ 17,122 $ 50,439 $ 50,913 $ 117,089 $ 16,283 $ 194,803 $ 172,238 $ 618,887 Investment earnings (loss), net of amortization 608 13,858 1,931 26,204 708 16,683 18,725 78,717 Contributions — 441 — — 166 (580 ) — 27 Distributions (1,543 ) (13,277 ) (3,873 ) (26,243 ) (730 ) (16,934 ) (19,585 ) (82,185 ) Distributions in excess of cumulative earnings (8) (3,354 ) (4,142 ) (2,232 ) (4,245 ) (581 ) (4,778 ) (1,906 ) (21,238 ) Balance at December 31, 2016 $ 12,833 $ 47,319 $ 46,739 $ 112,805 $ 15,846 $ 189,194 $ 169,472 $ 594,208 Investment earnings (loss), net of amortization 3,821 12,547 1,144 29,444 3,350 17,387 17,501 85,194 Impairment expense (9) (3,110 ) — — — — — — (3,110 ) Contributions — 277 — — — 107 — 384 Distributions (4,217 ) (11,965 ) (3,085 ) (29,482 ) (3,317 ) (17,639 ) (17,675 ) (87,380 ) Distributions in excess of cumulative earnings (8) (2,297 ) (3,233 ) (2,270 ) (2,468 ) — (10,074 ) (2,743 ) (23,085 ) Balance at December 31, 2017 $ 7,030 $ 44,945 $ 42,528 $ 110,299 $ 15,879 $ 178,975 $ 166,555 $ 566,211 (1) WES has a 14.81% interest in Fort Union, a joint venture that owns a gathering pipeline and treating facilities in the Powder River Basin. Anadarko is the construction manager and physical operator of the Fort Union facilities. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the owners’ firm gathering agreements, require 65% or unanimous approval of the owners. (2) WES has a 10% interest in White Cliffs, a limited liability company that owns a crude oil pipeline that originates in Platteville, Colorado and terminates in Cushing, Oklahoma. The third-party majority owner is the manager of the White Cliffs operations. Certain business decisions, including, but not limited to, approval of annual budgets and decisions with respect to significant expenditures, contractual commitments, acquisitions, material financings, dispositions of assets or admitting new members, require more than 75% approval of the members. (3) WES has a 22% interest in Rendezvous, a limited liability company that operates gas gathering facilities in Southwestern Wyoming. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the members’ gas servicing agreements, require unanimous approval of the members. (4) WES has a 25% interest in the Mont Belvieu JV, an entity formed to design, construct, and own two fractionation trains located in Mont Belvieu, Texas. A third party is the operator of the Mont Belvieu JV fractionation trains. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require 50% or unanimous approval of the owners. (5) WES has a 20% interest in TEG, which owns two NGL gathering systems that link natural gas processing plants to TEP. Midcoast Energy Partners, L.P., a wholly-owned subsidiary of Enbridge, Inc., is the operator of the two gathering systems. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the delegation, creation, appointment, or removal of officer positions require more than 50% approval of the members. (6) WES has a 20% interest in TEP, which owns an NGL pipeline that originates in Skellytown, Texas and extends to Mont Belvieu, Texas. Enterprise Products Operating LLC (“Enterprise”) is the operator of TEP. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require more than 50% approval of the members. (7) WES has a 33.33% interest in FRP, which owns an NGL pipeline that extends from Weld County, Colorado to Skellytown, Texas. Enterprise is the operator of FRP. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require more than 50% approval of the members. (8) Distributions in excess of cumulative earnings, classified as investing cash flows in the consolidated statements of cash flows, are calculated on an individual investment basis. (9) Recorded in Impairments in the consolidated statements of operations. 9. EQUITY INVESTMENTS (CONTINUED) The investment balance in Fort Union at December 31, 2017, is $3.1 million less than WES’s underlying equity in Fort Union’s net assets due to an impairment loss recognized by WES in the second quarter of 2017 for its investment in Fort Union. This investment was impaired to its estimated fair value of $8.5 million , using the income approach and Level 3 fair value inputs. The investment balance in Rendezvous at December 31, 2017 , includes $36.2 million for the purchase price allocated to the investment in Rendezvous in excess of the historic cost basis of Western Gas Resources, Inc. (“WGRI”), the entity that previously owned the interest in Rendezvous, which Anadarko acquired in August 2006. This excess balance is attributable to the difference between the fair value and book value of such gathering and treating facilities (at the time WGRI was acquired by Anadarko) and is being amortized over the remaining estimated useful life of those facilities. The investment balance in White Cliffs at December 31, 2017 , is $6.9 million less than WES’s underlying equity in White Cliffs’ net assets, primarily due to WES recording the acquisition of its initial 0.4% interest in White Cliffs at Anadarko’s historic carrying value. This difference is being amortized to Equity income, net – affiliates over the remaining estimated useful life of the White Cliffs pipeline. An impairment loss was recognized by the operator of Fort Union during both the years ended December 31, 2016 and 2015. WES’s 14.81% share of the impairment loss was $3.0 million and $9.5 million for the years ended December 31, 2016 and 2015, respectively, recorded in Equity income, net – affiliates in the consolidated statements of operations. Management evaluates its equity investments for impairment whenever events or changes in circumstances indicate that the carrying value of such investments may have experienced a decline in value that is other than temporary. When evidence of loss in value has occurred, management compares the estimated fair value of the investment to the carrying value of the investment to determine whether the investment has been impaired. Management assesses the fair value of equity investments using commonly accepted techniques, and may use more than one method, including, but not limited to, recent third-party comparable sales and discounted cash flow models. If the estimated fair value is less than the carrying value, the excess of the carrying value over the estimated fair value is recognized as an impairment loss. The following tables present the summarized combined financial information for WES’s equity investments (amounts represent 100% of investee financial information): Year Ended December 31, thousands 2017 2016 2015 Consolidated Statements of Income Revenues $ 703,424 $ 687,554 $ 667,554 Operating income 435,735 428,454 359,899 Net income 434,749 427,511 359,443 December 31, thousands 2017 2016 Consolidated Balance Sheets Current assets $ 137,957 $ 118,472 Property, plant and equipment, net 2,512,214 2,626,466 Other assets 36,373 39,802 Total assets $ 2,686,544 $ 2,784,740 Current liabilities 80,490 63,468 Non-current liabilities 7,447 6,662 Equity 2,598,607 2,714,610 Total liabilities and equity $ 2,686,544 $ 2,784,740

Components of Working Capital

Components of Working Capital	12 Months Ended
Components of Working Capital	Dec. 31, 2017
Components Of Working Capital [Abstract]
Components of Working Capital	10. COMPONENTS OF WORKING CAPITAL A summary of accounts receivable, net is as follows: December 31, thousands 2017 2016 Trade receivables, net $ 160,194 $ 192,606 Other receivables, net 45 30,415 Total accounts receivable, net $ 160,239 $ 223,021 A summary of other current assets is as follows: December 31, thousands 2017 2016 Natural gas liquids inventory $ 10,788 $ 7,126 Imbalance receivables 1,640 3,483 Prepaid insurance 2,955 2,889 Total other current assets $ 15,383 $ 13,498 A summary of accrued liabilities is as follows: December 31, thousands 2017 2016 Accrued interest expense $ 40,646 $ 39,834 Short-term asset retirement obligations 2,304 3,114 Short-term remediation and reclamation obligations 833 630 Income taxes payable 2,495 1,006 Other 1,714 606 Total accrued liabilities $ 47,992 $ 45,190

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
Asset Retirement Obligations	Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	11. ASSET RETIREMENT OBLIGATIONS The following table provides a summary of changes in asset retirement obligations: Year Ended December 31, thousands 2017 2016 Carrying amount of asset retirement obligations at beginning of year $ 142,407 $ 130,631 Liabilities incurred 16,153 5,515 Liabilities settled (10,468 ) (10,650 ) Accretion expense 6,956 6,794 Revisions in estimated liabilities (9,350 ) 10,117 Carrying amount of asset retirement obligations at end of year $ 145,698 $ 142,407 The liabilities incurred for the year ended December 31, 2017 , represented additions in asset retirement obligations primarily due to (i) capital expansions at the DJ Basin and DBM complexes and the DBJV system, (ii) the Property Exchange in March 2017 and (iii) the start-up of the DBM water systems in 2017. Revisions in estimated liabilities for the year ended December 31, 2017 , were related to (i) changes in expected settlement costs and timing primarily at the Hilight system and the DJ Basin and DBM complexes, and (ii) changes in property lives primarily at the Granger, DJ Basin and DBM complexes and the Hilight and DBJV systems. The liabilities incurred for the year ended December 31, 2016 , represented additions in asset retirement obligations primarily due to capital expansions at the DJ Basin and DBM complexes and the DBJV system. Revisions in estimated liabilities for the year ended December 31, 2016 , were related to (i) changes in expected settlement costs and timing primarily at the MGR assets, Granger complex and the Hilight and Springfield systems, and (ii) changes in property lives primarily at the DJ Basin and DBM complexes and the Hilight, Springfield and Haley systems.

Debt and Interest Expense

Debt and Interest Expense	12 Months Ended
Debt and Interest Expense	Dec. 31, 2017
Debt Instruments [Abstract]
Debt and Interest Expense	12. DEBT AND INTEREST EXPENSE At December 31, 2017 , WGP’s debt consisted of borrowings under the WGP RCF and WES’s 5.375% Senior Notes due 2021 (the “2021 Notes”), 4.000% Senior Notes due 2022 (the “2022 Notes”), 2.600% Senior Notes due 2018 (the “2018 Notes”), 5.450% Senior Notes due 2044 (the “2044 Notes”), 3.950% Senior Notes due 2025 (the “2025 Notes”), 4.650% Senior Notes due 2026 (the “2026 Notes”) and borrowings on the WES RCF. The following table presents WES and WGP’s outstanding debt as of December 31, 2017 and 2016: December 31, 2017 December 31, 2016 thousands Principal Carrying Value Fair Value (1) Principal Carrying Value Fair Value (1) WGP RCF $ 28,000 $ 28,000 $ 28,000 $ 28,000 $ 28,000 $ 28,000 2021 Notes 500,000 495,815 530,647 500,000 494,734 536,252 2022 Notes 670,000 668,849 684,043 670,000 668,634 681,723 2018 Notes 350,000 349,684 350,631 350,000 349,188 351,531 2044 Notes 600,000 593,234 637,827 600,000 593,132 615,753 2025 Notes 500,000 491,885 500,885 500,000 490,971 492,499 2026 Notes 500,000 495,245 520,144 500,000 494,802 518,441 WES RCF 370,000 370,000 370,000 — — — Total long-term debt $ 3,518,000 $ 3,492,712 $ 3,622,177 $ 3,148,000 $ 3,119,461 $ 3,224,199 (1) Fair value is measured using the market approach and Level 2 inputs. 12. DEBT AND INTEREST EXPENSE (CONTINUED) Debt activity. The following table presents WES and WGP’s debt activity for the years ended December 31, 2017 and 2016: thousands Carrying Value Balance at December 31, 2015 $ 2,690,651 WES RCF borrowings 600,000 Issuance of 2026 Notes 500,000 Issuance of 2044 Notes 200,000 Repayments of WES RCF borrowings (900,000 ) WGP RCF borrowings 28,000 Other 810 Balance at December 31, 2016 $ 3,119,461 WES RCF borrowings 370,000 Other 3,251 Balance at December 31, 2017 $ 3,492,712 WGP RCF. In March 2016, WGP entered into a $250.0 million WGP RCF, which matures in March 2019. The WGP RCF may be used to buy WES common units and for general partnership purposes. The WGP RCF contains an accordion feature whereby WGP can increase the commitments under the WGP RCF up to an aggregate of $500.0 million , subject to receiving increased or new commitments from lenders and the satisfaction of certain other conditions precedent. In 2016, WGP borrowed $28.0 million under the WGP RCF to fund the purchase of 835,841 WES common units (see Note 2 ) and to pay fees and expenses associated with entering into the WGP RCF. Pursuant to a collateral agreement with the WGP RCF lenders, WGP’s obligations under the WGP RCF are secured by a first priority lien on all of WGP’s assets (not including the consolidated assets of WES), as well as all present and after acquired equity interests owned by WGP in WES GP and WES. Borrowings under the WGP RCF bear interest, at WGP’s option, at either (a) a base rate equal to the greatest of (i) the Prime Rate, (ii) the Federal Funds Effective Rate plus 0.50% and (iii) London Interbank Offered Rate (“LIBOR”) plus 1.00% , in each case plus applicable margins ranging from 1.00% to 1.75% based upon WGP’s consolidated leverage ratio or (b) LIBOR (with a floor of 0% ), plus applicable margins ranging from 2.00% to 2.75% based upon WGP’s consolidated leverage ratio. The unused portion of the WGP RCF is subject to a quarterly commitment fee ranging from 0.30% to 0.50% per annum on the daily unused amount of the WGP RCF based upon WGP’s consolidated leverage ratio. The commitment fee rate on the WGP RCF was 0.30% at December 31, 2017 and 2016. As of December 31, 2017 , WGP had $28.0 million of outstanding borrowings ( $222.0 million of available borrowing capacity) and was in compliance with all covenants under the WGP RCF. As of December 31, 2017 and 2016, the interest rate on the outstanding WGP RCF borrowings was 3.57% and 2.77% , respectively. In February 2018, WGP voluntarily reduced the aggregate commitments of the lenders under the WGP RCF to $35.0 million . WGP WCF. The WGP WCF matured on November 1, 2017. WES Senior Notes. The 2018 Notes, which are due in August 2018, were classified as long-term debt on the consolidated balance sheet at December 31, 2017 , as WES has the ability and intent to refinance these obligations using long-term debt. In October 2016, WES issued an additional $200.0 million in aggregate principal amount of 2044 Notes at a price to the public of 102.776% of the face amount plus accrued interest from October 1, 2016 to the settlement date. These notes were offered as additional notes under the indenture governing the 2044 Notes issued in March 2014 and are treated as a single class of securities with the 2044 Notes under such indenture. Including the effects of (i) the issuance premium for the October 2016 offering of the 2044 Notes, (ii) the issuance discount for the March 2014 offering of the 2044 Notes and (iii) the underwriting discounts, the effective interest rate of the 2044 Notes is 5.530% . Proceeds (net of underwriting discount of $1.8 million and debt issuance costs and excluding accrued interest from October 1, 2016 to the settlement date) were used to repay amounts then outstanding under the WES RCF and for general partnership purposes, including capital expenditures. 12. DEBT AND INTEREST EXPENSE (CONTINUED) The 2026 Notes issued in July 2016 were offered at a price to the public of 99.796% of the face amount. Including the effects of the issuance and underwriting discounts, the effective interest rate of the 2026 Notes is 4.787% . Interest is paid semi-annually on January 1 and July 1 of each year. Proceeds (net of underwriting discount of $3.1 million , original issue discount and debt issuance costs) were used to repay a portion of the amount outstanding under the WES RCF. At December 31, 2017 , WES was in compliance with all covenants under the indentures governing its outstanding notes. WES RCF. The $1.2 billion WES RCF, which is expandable to a maximum of $1.5 billion , bears interest at LIBOR, plus applicable margins ranging from 0.975% to 1.45% , or an alternate base rate equal to the greatest of (a) the Prime Rate, (b) the Federal Funds Effective Rate plus 0.50% , or (c) LIBOR plus 1.00% , in each case plus applicable margins currently ranging from zero to 0.45% , based upon WES’s senior unsecured debt rating. In December 2016, the WES RCF was amended to extend the maturity date from February 2019 to February 2020. WES is required to pay a quarterly facility fee currently ranging from 0.15% to 0.30% of the commitment amount (whether used or unused), based upon its senior unsecured debt rating. The facility fee rate was 0.20% at December 31, 2017 and 2016 . As of December 31, 2017 , WES had $370.0 million of outstanding WES RCF borrowings and $4.6 million in outstanding letters of credit (resulting in $825.4 million available borrowing capacity), and was in compliance with all covenants under the WES RCF. As of December 31, 2017 and 2016 , the interest rate on the outstanding WES RCF borrowings was 2.87% and 2.07% , respectively. In February 2018, the WES RCF was amended to extend the maturity date from February 2020 to February 2023 and expand borrowing capacity to $1.5 billion . All of WES’s notes and obligations under the WES RCF are recourse to WES GP. WES GP is indemnified by wholly owned subsidiaries of Anadarko against any claims made against WES GP for WES’s long-term debt and/or borrowings under the WES RCF. Interest expense. The following table summarizes the amounts included in interest expense: Year Ended December 31, thousands 2017 2016 2015 Third parties Long-term debt $ (143,400 ) $ (122,428 ) $ (102,058 ) Amortization of debt issuance costs and commitment fees (7,970 ) (7,509 ) (5,734 ) Capitalized interest 6,826 5,562 8,318 Total interest expense – third parties (144,544 ) (124,375 ) (99,474 ) Affiliates WGP WCF — — (2 ) Deferred purchase price obligation – Anadarko (1) (71 ) 7,747 (14,398 ) Total interest expense – affiliates (71 ) 7,747 (14,400 ) Interest expense $ (144,615 ) $ (116,628 ) $ (113,874 ) (1) See Note 2 for a discussion of the Deferred purchase price obligation - Anadarko.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. COMMITMENTS AND CONTINGENCIES Environmental obligations. WGP, through its partnership interest in WES, is subject to various environmental-remediation obligations arising from federal, state and local regulations regarding air and water quality, hazardous and solid waste disposal and other environmental matters. As of December 31, 2017 and 2016 , the consolidated balance sheets included $1.8 million and $2.2 million , respectively, of liabilities for remediation and reclamation obligations. The current portion of these amounts is included in Accrued liabilities and the long-term portion of these amounts is included in Asset retirement obligations and other. The recorded obligations do not include any anticipated insurance recoveries. The majority of payments related to these obligations are expected to be made over the next five years. Management regularly monitors the remediation and reclamation process and the liabilities recorded and believes its environmental obligations are adequate to fund remedial actions to comply with present laws and regulations, and that the ultimate liability for these matters, if any, will not differ materially from recorded amounts nor materially affect the overall results of operations, cash flows or financial condition of WGP. There can be no assurance, however, that current regulatory requirements will not change, or past non-compliance with environmental issues will not be discovered. See Note 10 and Note 11 . Litigation and legal proceedings. In February 2017, DBJV, at the time a 50 / 50 joint venture between a third party and WES, initiated an arbitration against SWEPI LP (“SWEPI”) for breach of a 2007 gas gathering agreement between it and DBJV (the “GGA”). Specifically, DBJV seeks to collect approximately $190.0 million in gathering fees under the GGA for the period January 1, 2016 to July 1, 2017. SWEPI disputes DBJV’s calculation of the cost of service based rate and filed a counterclaim for alleged unpaid revenue associated with its condensate and for alleged overpayment of fees under the GGA for the years 2013 through 2016. Before the arbitration, SWEPI claimed that it is owed approximately $18.0 million in connection with these counterclaims. The final arbitration hearing will begin April 30, 2018, and WES expects to receive a decision by the end of the third quarter in 2018. Under the terms of the Property Exchange, WES’s former joint venture partner in DBJV will owe 50% of any amounts to be paid, and have a right to 50% of any amounts received, by WES as a result of this arbitration proceeding. Pursuant to an agreement between the parties, if the arbitrators determine that DBJV is owed an amount of money by SWEPI for underpaid gathering fees, that amount will be paid out over five years as a supplemental gathering fee under the currently effective gas gathering agreement between the parties. Any other amounts owed by either party will be paid in cash within ninety days of the conclusion of the arbitration. WES intends to vigorously prosecute its claims and vigorously defend the counterclaims asserted by SWEPI. Management does not believe the outcome of this proceeding will have a materially unfavorable effect on the financial condition, results of operation or cash flows of WGP. In addition, from time to time, WGP, through its partnership interests in WES, is involved in legal, tax, regulatory and other proceedings in various forums regarding performance, contracts and other matters that arise in the ordinary course of business. Management is not aware of any such proceeding the final disposition of which could have a material adverse effect on the financial condition, results of operations or cash flows of WGP. Other commitments. WES has short-term payment obligations, or commitments, related to its capital spending programs, as well as those of its unconsolidated affiliates, the majority of which is expected to be paid in the next twelve months. These commitments relate primarily to expansion projects at the DBJV system and the DJ Basin and DBM complexes. 13. COMMITMENTS AND CONTINGENCIES (CONTINUED) Lease commitments. Anadarko, on WES’s behalf, has entered into lease arrangements for corporate offices, shared field offices, a warehouse and equipment supporting WES’s operations, for which Anadarko charges WES rent. The leases for the corporate off ices and shared field offices extend throug h 2028 and 2033, r espectively , and the lease for the warehouse expired in February 2017. Rent expense charged to WES associated with these lease arrangements was $42.5 million , $35.9 million and $34.1 million for the years ended December 31, 2017 , 2016 and 2015, respectively. Operating leases. The amounts in the table below represent existing contractual operating lease obligations as of December 31, 2017 , that may be assigned or otherwise charged to WES pursuant to the reimbursement provisions of the omnibus agreement: thousands Operating Leases 2018 $ 8,402 2019 7,506 2020 1,615 2021 460 2022 467 Thereafter 2,021 Total $ 20,471

Summary of Significant Accoun23

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2017
Accounting Policies [Abstract]
Consolidation policy	Basis of presentation. The following table outlines WES’s ownership interests and the accounting method of consolidation used in WES’s consolidated financial statements: Percentage Interest Equity investments (1) Fort Union 14.81 % White Cliffs 10 % Rendezvous 22 % Mont Belvieu JV 25 % TEP 20 % TEG 20 % FRP 33.33 % Proportionate consolidation (2) Marcellus Interest systems 33.75 % Newcastle system 50 % Springfield system 50.1 % Full consolidation Chipeta (3) 75 % DBJV system (4) 100 % (1) Investments in non-controlled entities over which WES exercises significant influence are accounted for under the equity method. “Equity investment throughput” refers to WES’s share of average throughput for these investments. (2) WGP proportionately consolidates WES’s associated share of the assets, liabilities, revenues and expenses attributable to these assets. (3) The 25% interest in Chipeta Processing LLC (“Chipeta”) held by a third-party member is reflected within noncontrolling interests in the consolidated financial statements, in addition to the noncontrolling interests noted below. (4) WES acquired an additional 50% interest in the DBJV system (the “Additional DBJV System Interest”) from a third party on March 17, 2017. See Note 2 . The consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). The consolidated financial statements include the accounts of WGP and entities in which it holds a controlling financial interest, including WES and WES GP. All significant intercompany transactions have been eliminated. The consolidated financial results of WES are included in WGP’s consolidated financial statements due to WGP’s 100% ownership interest in WES GP and WES GP’s control of WES. Throughout these notes to consolidated financial statements, and to the extent material, any differences between the consolidated financial results of WGP and WES are discussed separately. WGP has no independent operations or material assets other than its partnership interests in WES. WGP’s consolidated financial statements differ from those of WES primarily as a result of (i) the presentation of noncontrolling interest ownership (attributable to the limited partner interests in WES held by the public, other subsidiaries of Anadarko and private investors, see Note 4 ), (ii) the elimination of WES GP’s investment in WES with WES GP’s underlying capital account, (iii) the general and administrative expenses incurred by WGP, which are separate from, and in addition to, those incurred by WES, (iv) the inclusion of the impact of WGP equity balances and WGP distributions, and (v) WGP’s senior secured revolving credit facility (“WGP RCF”). See Note 12 . Noncontrolling interests. WGP’s noncontrolling interests in the consolidated financial statements consist of the following for all periods presented: (i) the 25% interest in Chipeta held by a third-party member, (ii) the publicly held limited partner interests in WES, (iii) the 2,011,380 WES common units issued by WES to other subsidiaries of Anadarko as part of the consideration paid for the acquisitions of the Non-Operated Marcellus Interest, the TEFR Interests and Springfield, and (iv) the WES Class C units issued by WES to a subsidiary of Anadarko as part of the funding for the acquisition of Delaware Basin Midstream, LLC (“DBM”). The WES Series A Preferred units issued to private investors as part of the funding of the Springfield acquisition were also noncontrolling interests in the consolidated financial statements until converted into WES common units in 2017. See Note 2 and Note 4 . When WES issues equity, the carrying amount of the noncontrolling interest reported by WGP is adjusted to reflect the noncontrolling ownership interest in WES. The resulting impact of such noncontrolling interest adjustment on WGP’s interest in WES is reflected as an adjustment to WGP’s partners’ capital.
Variable interest entity policy	Variable interest entity. WES is a variable interest entity (“VIE”) because the partners in WES with equity at risk lack the power, through voting or similar rights, to direct the activities that most significantly impact WES’s economic performance. A reporting entity that concludes it has a variable interest in a VIE must evaluate whether it has a controlling financial interest in the VIE, such that it is the VIE’s primary beneficiary and should consolidate. WGP is the primary beneficiary of WES and therefore should consolidate because (i) WGP has the power to direct the activities of WES that most significantly affect its economic performance and (ii) WGP has the right to receive benefits or the obligation to absorb losses that could be potentially significant to WES. As noted above, WGP has no independent operations or material assets other than its partnership interests in WES. The assets of WES cannot be used by WGP for general partnership purposes. WES’s long-term debt is recourse to WES GP, which is wholly owned by WGP. In turn, WES GP is indemnified by wholly owned subsidiaries of Anadarko for any claims made against WES GP under the indentures governing WES’s outstanding notes or borrowings under WES’s senior unsecured revolving credit facility (“WES RCF”). WES’s sources of liquidity include cash and cash equivalents, cash flows generated from operations, interest income on its $260.0 million note receivable from Anadarko, available borrowing capacity under the WES RCF, and issuances of additional equity or debt securities. As further discussed in Note 2 , WGP purchased WES common units in connection with WES’s financing of an acquisition from Anadarko in March 2016.
Business combinations policy	Presentation of WES assets. The term “WES assets” includes both the assets indirectly owned and the interests accounted for under the equity method by WGP through its partnership interests in WES as of December 31, 2017 (see Note 9 ). Because WGP owns the entire interest in and controls WES GP, and WGP GP is controlled by Anadarko, each of WES’s acquisitions of WES assets from Anadarko has been considered a transfer of net assets between entities under common control. As such, WES assets acquired from Anadarko were initially recorded at Anadarko’s historic carrying value, which did not correlate to the total acquisition price paid by WES. Further, after an acquisition of WES assets from Anadarko, WES and WGP (by virtue of its consolidation of WES) may be required to recast their financial statements to include the activities of such WES assets from the date of common control. For those periods requiring recast, the consolidated financial statements for periods prior to the acquisition of WES assets from Anadarko are prepared from Anadarko’s historical cost-basis accounts and may not necessarily be indicative of the actual results of operations that would have occurred if WES had owned the WES assets during the periods reported. Net income (loss) attributable to the WES assets acquired from Anadarko for periods prior to WES’s acquisition of the WES assets is not allocated to the limited partners.
Use of estimates policy	Use of estimates. In preparing financial statements in accordance with GAAP, management makes informed judgments and estimates that affect the reported amounts of assets, liabilities, revenues and expenses. Management evaluates its estimates and related assumptions regularly, using historical experience and other methods considered reasonable. Changes in facts and circumstances or additional information may result in revised estimates and actual results may differ from these estimates. Effects on the business, financial condition and results of operations resulting from revisions to estimates are recognized when the facts that give rise to the revisions become known. The information furnished herein reflects all normal recurring adjustments which are, in the opinion of management, necessary for a fair presentation of the consolidated financial statements, and certain prior-period amounts have been reclassified to conform to the current-year presentation.
Fair value policy	Fair value. The fair-value-measurement standard defines fair value as the price that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The standard characterizes inputs used in determining fair value according to a hierarchy that prioritizes those inputs based upon the degree to which they are observable. The three input levels of the fair value hierarchy are as follows: Level 1 – Inputs represent unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 – Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly (for example, quoted market prices for similar assets or liabilities in active markets or quoted market prices for identical assets or liabilities in markets not considered to be active, inputs other than quoted prices that are observable for the asset or liability, or market-corroborated inputs). Level 3 – Inputs that are not observable from objective sources, such as management’s internally developed assumptions used in pricing an asset or liability (for example, an estimate of future cash flows used in management’s internally developed present value of future cash flows model that underlies the fair value measurement). In determining fair value, management uses observable market data when available, or models that incorporate observable market data. When a fair value measurement is required and there is not a market-observable price for the asset or liability or a market-observable price for a similar asset or liability, the cost, income, or multiples approach is used, depending on the quality of information available to support management’s assumptions. The cost approach is based on management’s best estimate of the current asset replacement cost. The income approach uses management’s best assumptions regarding expectations of projected cash flows, and discounts the expected cash flows using a commensurate risk adjusted discount rate. Such evaluations involve a significant amount of judgment, since the results are based on expected future events or conditions, such as sales prices, estimates of future throughput, capital and operating costs and the timing thereof, economic and regulatory climates and other factors. A multiples approach uses management’s best assumptions regarding expectations of projected earnings before interest, taxes, depreciation, and amortization (“EBITDA”) and the multiple of that EBITDA that a buyer would pay to acquire an asset. Management’s estimates of future net cash flows and EBITDA are inherently imprecise because they reflect management’s expectation of future conditions that are often outside of management’s control. However, the assumptions used reflect a market participant’s view of long-term prices, costs and other factors, and are consistent with assumptions used in WES’s business plans and investment decisions. In arriving at fair-value estimates, management uses relevant observable inputs available for the valuation technique employed. If a fair value measurement reflects inputs at multiple levels within the hierarchy, the fair value measurement is characterized based on the lowest level of input that is significant to the fair value measurement. Nonfinancial assets and liabilities initially measured at fair value include certain assets and liabilities acquired in a third-party business combination, assets and liabilities exchanged in non-monetary transactions, goodwill and other intangibles, initial recognition of asset retirement obligations, and initial recognition of environmental obligations assumed in a third-party acquisition. Impairment analyses for long-lived assets, goodwill and other intangibles, and the initial recognition of asset retirement obligations and environmental obligations use Level 3 inputs. The fair value of debt reflects any premium or discount for the difference between the stated interest rate and the quarter-end market interest rate, and is based on quoted market prices for identical instruments, if available, or based on valuations of similar debt instruments. See Note 12 . The carrying amounts of cash and cash equivalents, accounts receivable and accounts payable reported on the consolidated balance sheets approximate fair value due to the short-term nature of these items.
Cash equivalents policy	Cash equivalents. All highly liquid investments with a maturity of three months or less when purchased are considered to be cash equivalents.
Bad-debt reserve policy	Bad-debt reserve. Revenues are primarily from Anadarko, for which no credit limit is maintained. Exposure to bad debts is analyzed on a customer-by-customer basis for its third-party accounts receivable and WES may establish credit limits for significant third-party customers. As of December 31, 2017 and 2016 , bad-debt reserve was immaterial.
Imbalances policy	Imbalances. The consolidated balance sheets include imbalance receivables and payables resulting from differences in volumes received into WES’s systems and volumes delivered by WES to customers. Volumes owed to or by WES that are subject to monthly cash settlement are valued according to the terms of the contract as of the balance sheet dates and reflect market index prices. Other volumes owed to or by WES are valued at the weighted-average cost as of the balance sheet dates and are settled in-kind. As of December 31, 2017 , imbalance receivables and payables were $1.6 million and $2.9 million , respectively. As of December 31, 2016 , imbalance receivables and payables were $3.5 million and $3.0 million , respectively. Net changes in imbalance payables and receivables are reported in Cost of product in the consolidated statements of operations.
Inventory policy	Inventory. The cost of NGLs inventories is determined by the weighted-average cost method on a location-by-location basis. Inventory is stated at the lower of weighted-average cost or market value and is reported in Other current assets on the consolidated balance sheets. See Note 10 .
Property, plant and equipment policy	Property, plant and equipment. Property, plant and equipment are generally stated at the lower of historical cost less accumulated depreciation or fair value, if impaired. Because acquisitions of assets from Anadarko are transfers of net assets between entities under common control, the assets acquired from Anadarko are initially recorded at Anadarko’s historic carrying value. The difference between the carrying value of net assets acquired from Anadarko and the consideration paid is recorded as an adjustment to partners’ capital. Assets acquired in a business combination or non-monetary exchange with a third party are initially recorded at fair value. All construction-related direct labor and material costs are capitalized. The cost of renewals and betterments that extend the useful life of property, plant and equipment is also capitalized. The cost of repairs, replacements and major maintenance projects that do not extend the useful life or increase the expected output of property, plant and equipment is expensed as incurred. Depreciation is computed using the straight-line method based on estimated useful lives and salvage values of assets. However, subsequent events could cause a change in estimates, thereby impacting future depreciation amounts. Uncertainties that may impact these estimates include, but are not limited to, changes in laws and regulations relating to environmental matters, including air and water quality, restoration and abandonment requirements, economic conditions, and supply and demand in the area. Management evaluates the ability to recover the carrying amount of its long-lived assets to determine whether its long-lived assets have been impaired. Impairments exist when the carrying amount of an asset exceeds estimates of the undiscounted cash flows expected to result from the use and eventual disposition of the asset. When alternative courses of action to recover the carrying amount of a long-lived asset are under consideration, estimates of future undiscounted cash flows take into account possible outcomes and probabilities of their occurrence. If the carrying amount of the long-lived asset is not recoverable based on the estimated future undiscounted cash flows, the impairment loss is measured as the excess of the asset’s carrying amount over its estimated fair value, such that the asset’s carrying amount is adjusted to its estimated fair value with an offsetting charge to impairment expense. Refer to Note 7 for a description of impairments recorded during the years ended December 31, 2017 , 2016 and 2015 . 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Insurance recoveries. Involuntary conversions result from the loss of an asset because of some unforeseen event (e.g., destruction due to fire). Some of these events are insurable and result in property damage insurance recovery. Amounts that are received from insurance carriers are net of any deductibles related to the covered event. A receivable is recorded from insurance to the extent a loss is recognized from an involuntary conversion event and the likelihood of recovering such loss is deemed probable. To the extent that any insurance claim receivables are later judged not probable of recovery (e.g., due to new information), such amounts are expensed. A gain on involuntary conversion is recognized when the amount received from insurance exceeds the net book value of the retired asset(s). In addition, gains related to insurance recoveries are not recognized until all contingencies related to such proceeds have been resolved; that is, a cash payment is received from the insurance carrier or there is a binding settlement agreement with the carrier that clearly states that a payment will be made. To the extent that an asset is rebuilt, the associated expenditures are capitalized, as appropriate, on the consolidated balance sheets and presented as Capital expenditures in the consolidated statements of cash flows. With respect to business interruption insurance claims, income is recognized only when cash proceeds are received from insurers, which are presented in the consolidated statements of operations as a component of Operating income (loss). On December 3, 2015, there was an initial fire and secondary explosion at the processing facility within the DBM complex. The majority of the damage from the incident was to the liquid handling facilities and the amine treating units at the inlet of the complex. Train II sustained the most damage of the processing trains and returned to service in December 2016. Train III experienced minimal damage and returned to full service in May 2016. For the year ended December 31, 2015, $20.3 million of losses were recorded in Gain (loss) on divestiture and other, net in the consolidated statements of operations, related to this involuntary conversion event based on the difference between the net book value of the affected assets and the insurance claim receivable. During the year ended December 31, 2017 , a $5.7 million loss was recorded in Gain (loss) on divestiture and other, net in the consolidated statements of operations, related to a change in WES’s estimate of the amount that would be recovered under the property insurance claim based on further discussions with insurers. During the second quarter of 2017, WES reached a settlement with insurers and final proceeds were received. During the years ended December 31, 2017 and 2016, WES received $52.9 million and $33.8 million , respectively, in cash proceeds from insurers, including $29.9 million and $16.3 million , respectively, in proceeds from business interruption insurance claims and $23.0 million and $17.5 million , respectively, in proceeds from property insurance claims. As of December 31, 2017 and 2016 , the consolidated balance sheets included receivables of zero and $30.0 million , respectively, for the property insurance claim related to the incident at the DBM complex.
Capitalized interest policy	Capitalized interest. Interest is capitalized as part of the historical cost of constructing assets for significant projects that are in progress. Capitalized interest is determined by multiplying WES’s weighted-average borrowing cost on debt by the average amount of qualifying costs incurred. Once the construction of an asset subject to interest capitalization is completed and the asset is placed in service, the associated capitalized interest is expensed through depreciation or impairment, together with other capitalized costs related to that asset.
Goodwill policy	Goodwill. Goodwill is recorded when the purchase price of a business acquired exceeds the fair market value of the tangible and separately measurable intangible net assets. In addition, goodwill represents the allocated portion of Anadarko’s midstream goodwill attributed to the WES assets WGP, through its consolidation of WES, has acquired from Anadarko. Refer to Note 8 for a discussion of goodwill. Goodwill is evaluated for impairment annually, as of October 1, or more often as facts and circumstances warrant. WES has allocated goodwill on its two reporting units: (i) gathering and processing and (ii) transportation. An initial qualitative assessment is performed prior to proceeding to the comparison of the fair value of each reporting unit to which goodwill has been assigned, to the carrying amount of net assets, including goodwill, of each reporting unit. If management concludes, based on qualitative factors, that it is more likely than not that the fair value of the reporting unit exceeds its carrying amount, then goodwill is not impaired, and estimating the fair value of the reporting unit is not necessary. If the carrying amount of the reporting unit exceeds its fair value, goodwill is written down to its implied fair value through a charge to operating expense. The carrying value of goodwill after such an impairment would represent a Level 3 fair value measurement.
Other intangible assets policy	Other intangible assets. WES assesses intangible assets, as described in Note 8 , for impairment together with related underlying long-lived assets whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. See Property, plant and equipment within this Note 1 for further discussion of management’s process to evaluate potential impairment of long-lived assets.
Asset retirement obligations and environmental expenditures policy	Asset retirement obligations. A liability based on the estimated costs of retiring tangible long-lived assets is recognized as an asset retirement obligation in the period incurred. The liability is recognized at fair value, measured using discounted expected future cash outflows for the asset retirement obligation when the obligation originates, which generally is when an asset is acquired or constructed. The carrying amount of the associated asset is increased commensurate with the liability recognized. Over time, the discounted liability is adjusted to its expected settlement value through accretion expense, which is reported within Depreciation and amortization in the consolidated statements of operations. Subsequent to the initial recognition, the liability is also adjusted for any changes in the expected value of the retirement obligation (with a corresponding adjustment to property, plant and equipment) until the obligation is settled. Revisions in estimated asset retirement obligations may result from changes in estimated inflation rates, discount rates, asset retirement costs and the estimated timing of settling asset retirement obligations. See Note 11 . Environmental expenditures. WES expenses environmental obligations related to conditions caused by past operations that do not generate current or future revenues. Environmental obligations related to operations that generate current or future revenues are expensed or capitalized, as appropriate. Liabilities are recorded when the necessity for environmental remediation or other potential environmental liabilities becomes probable and the costs can be reasonably estimated. Accruals for estimated losses from environmental remediation obligations are recognized no later than at the time of the completion of the remediation feasibility study. These accruals are adjusted as additional information becomes available or as circumstances change. Costs of future expenditures for environmental-remediation obligations are not discounted to their present value. See Note 13 .
Segments policy	Segments. Because WGP reflects its ownership interest in WES on a consolidated basis, and has no independent operations or material assets outside those of WES, WGP’s segment analysis and presentation is the same as that of WES. WES’s operations are organized into a single operating segment, the assets of which gather, compress, treat, process and transport natural gas; gather, stabilize and transport condensate, NGLs and crude oil; and gather and dispose of produced water in the United States.
Revenues and cost of product policy	Revenues and cost of product. The revenue recognition policies described in this section reflect WGP’s revenue recognition through December 31, 2017. WGP adopted Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) (“Topic 606”), effective January 1, 2018. See Accounting standards adopted in 2018 below for further discussion. Under its fee-based gathering, treating, processing and disposal arrangements, WES is paid a fixed fee based on the volume and/or thermal content of natural gas or produced water and recognizes revenues for its services in the month such services are performed. Producers’ wells or production facilities are connected to WES’s gathering systems for delivery of natural gas to WES’s processing or treating plants, where the natural gas is processed to extract NGLs and condensate or treated in order to satisfy pipeline specifications. In some areas, where no processing is required, the producers’ gas is gathered and delivered to pipelines for market delivery. Under cost-of-service gathering agreements, fees are earned for gathering and compression services based on rates calculated in a cost-of-service model and reviewed periodically over the life of the agreements. Under percent-of-proceeds contracts, revenue is recognized when the natural gas, NGLs or condensate is sold. The percentage of the product sale ultimately paid to the producer is recorded as a related cost of product expense. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) In certain circumstances, WES purchases natural gas volumes at the wellhead or production facility for gathering and processing. As a result, WES has volumes of NGLs and condensate to sell and volumes of residue to sell, to use for system fuel or to satisfy keep-whole obligations. In addition, depending upon specific contract terms, condensate and NGLs recovered during gathering and processing are either returned to the producer or retained and sold. Under keep-whole contracts, when condensate or NGLs are retained and sold, producers are kept whole for the condensate or NGL volumes through the receipt of a thermally equivalent volume of residue. The keep-whole contract conveys an economic benefit to WES when the combined value of the individual NGLs is greater in the form of liquids than as a component of the natural gas stream; however, WES is adversely impacted when the value of the NGLs is lower than the value of the natural gas stream including the liquids. WES has commodity price swap agreements with Anadarko to mitigate exposure to a majority of the commodity price risk inherent in its percent-of-proceeds and keep-whole contracts. See Note 5 . Revenue is recognized from the sale of condensate and NGLs upon transfer of title, and related purchases are recorded as cost of product. WES earns transportation revenues through firm contracts that obligate each of its customers to pay a monthly reservation or demand charge regardless of the pipeline capacity used by that customer. An additional commodity usage fee is charged to the customer based on the actual volume of natural gas transported. Transportation revenues are also generated from interruptible contracts pursuant to which a fee is charged to the customer based on volumes transported through the pipeline. Revenues for transportation of natural gas and NGLs are recognized over the period of firm transportation contracts or, in the case of usage fees and interruptible contracts, when the volumes are received into the pipeline. From time to time, certain revenues may be subject to refund pending the outcome of rate matters before the Federal Energy Regulatory Commission, and refund reserve liabilities are established where appropriate. Revenues attributable to the fixed-fee component of gathering and processing contracts as well as demand charges and commodity usage fees on transportation contracts are reported as revenues from gathering, processing, transportation and disposal in the consolidated statements of operations. Proceeds from the sale of residue, NGLs and condensate are reported as revenues from natural gas and natural gas liquids sales in the consolidated statements of operations.
Equity-based compensation policy	Equity-based compensation. Concurrently with WGP’s initial public offering (“IPO”), WGP GP adopted the Western Gas Equity Partners, LP 2012 Long-Term Incentive Plan (the “WGP LTIP”). The WGP LTIP permits the issuance of up to 3,000,000 WGP common units, of which 2,944,325 units remained available for future issuance as of December 31, 2017 . Upon vesting of each phantom unit, the holder will receive common units of WGP or, at the discretion of WGP GP’s Board of Directors (the “Board of Directors”), cash in an amount equal to the market value of common units of WGP on the vesting date. Equity-based compensation expense attributable to grants made under the WGP LTIP impacts cash flows from operating activities only to the extent cash payments are made to a participant in lieu of issuance of WGP common units to the participant. Stock-based compensation expense attributable to awards granted under the WGP LTIP is amortized over the vesting periods applicable to the awards. Prior to October 17, 2017, phantom unit awards were granted under the Western Gas Partners, LP 2008 Long-Term Incentive Plan (the “WES 2008 LTIP”). On October 17, 2017, however, WES’s common and Class C unitholders approved the Western Gas Partners, LP 2017 Long-Term Incentive Plan (the “WES 2017 LTIP”), which replaced the WES 2008 LTIP. As used in this section, the term “WES LTIP” refers to the WES 2008 LTIP with respect to awards granted prior to October 17, 2017, and to the WES 2017 LTIP with respect to awards granted after October 17, 2017. The WES 2017 LTIP permits the issuance of up to 2,250,000 units, all of which remain available for future issuance as of December 31, 2017 . Upon vesting of each phantom unit awarded under the WES LTIP, the holder will receive common units of WES or, at the discretion of WES GP’s Board of Directors, cash in an amount equal to the market value of common units of WES on the vesting date. Equity-based compensation expense attributable to grants made under the WES LTIP impacts cash flows from operating activities only to the extent cash payments are made to a participant in lieu of issuance of common units to the participant. Stock-based compensation expense attributable to awards granted under the WES LTIP is amortized over the vesting periods applicable to the awards. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Additionally, general and administrative expenses include equity-based compensation costs allocated by Anadarko for grants made pursuant to the Anadarko Petroleum Corporation 2008 and 2012 Omnibus Incentive Compensation Plans (Anadarko’s plans are referred to collectively as the “Anadarko Incentive Plans”) for all periods presented. Grants made under equity-based compensation plans result in equity-based compensation expense, which is determined by reference to the fair value of equity compensation. For equity-based awards ultimately settled through the issuance of units or stock, the fair value is measured as of the date of the relevant equity grant. Equity-based compensation granted under the Anadarko Incentive Plans does not impact cash flows from operating activities since the offset to compensation expense is recorded as a contribution to partners’ capital in the consolidated financial statements at the time of contribution, when the expense is realized.
Income taxes policy	WGP income taxes. Prior to its September 2012 conversion from a limited liability company to a limited partnership, WGP was WGR Holdings, LLC, a single-member Delaware limited liability company treated as a division of Anadarko and disregarded for U.S. federal income tax purposes. As such, WGR Holdings, LLC was included in Anadarko’s consolidated income tax return for federal and state income tax purposes. In addition to WES’s historic Texas margin tax expense and liabilities, the accompanying consolidated financial statements of WGP include income tax expense and liabilities incurred by WGR Holdings, LLC, computed on a separate-return basis. Deferred federal and state income taxes included in the accompanying consolidated financial statements are attributable to temporary differences between the financial statement carrying amount and tax basis of WGP’s investment in WES. WGP’s accounting policy is to “look through” its investment in WES for purposes of calculating deferred income tax asset and liability balances attributable to WGP’s interests in WES. The application of such accounting policy resulted in no deferred income taxes being recognized for the book and tax basis difference in goodwill, which is non-deductible for tax purposes for all periods presented. WGP had no material uncertain tax positions at December 31, 2017 or 2016 . WES income taxes. WES generally is not subject to federal income tax or state income tax other than Texas margin tax on the portion of its income that is apportionable to Texas. Deferred state income taxes are recorded on temporary differences between the financial statement carrying amounts of assets and liabilities and their respective tax bases. WES routinely assesses the realizability of its deferred tax assets. If WES concludes that it is more likely than not that some of the deferred tax assets will not be realized, the tax asset is reduced by a valuation allowance. Federal and state current and deferred income tax expense was recorded on WES assets prior to WES’s acquisition of these assets from Anadarko. For periods beginning on and subsequent to WES’s acquisition of the WES assets, WES makes payments to Anadarko pursuant to the tax sharing agreement entered into between Anadarko and WES for its estimated share of taxes from all forms of taxation, excluding taxes imposed by the United States, that are included in any combined or consolidated returns filed by Anadarko. The aggregate difference in the basis of WES’s assets for financial and tax reporting purposes cannot be readily determined as WES does not have access to information about each partner’s tax attributes in WES. The accounting standards for uncertain tax positions defines the criteria an individual tax position must satisfy for any part of the benefit of that position to be recognized in the financial statements. WES had no material uncertain tax positions at December 31, 2017 or 2016 . With respect to assets acquired from Anadarko, WES recorded Anadarko’s historic deferred income taxes for the periods prior to WES’s ownership of the assets. For periods subsequent to WES’s acquisition, WES is not subject to tax except for the Texas margin tax and, accordingly, does not record deferred federal income taxes related to the assets acquired from Anadarko.
Net income (loss) per common unit policy	Net income (loss) per common unit. For WGP, basic net income (loss) per common unit is calculated by dividing the limited partners’ interest in net income (loss) by the weighted-average number of common units outstanding during the period. Dilutive net income (loss) per common unit is calculated by dividing the limited partners’ interest in net income (loss) adjusted for distributions on the WES Series A Preferred units and a reallocation of the limited partners’ interest in net income (loss) assuming, prior to the actual conversion, conversion of the WES Series A Preferred units into WES common units, by the weighted-average number of WGP common units outstanding during the period. As of May 2, 2017, all WES Series A Preferred units were converted into WES common units on a one-for-one basis. The impact of the Series A Preferred units assuming, prior to the actual conversion, conversion to WES common units would be anti-dilutive for all periods presented. Net income (loss) per common unit is calculated assuming that cash distributions are equal to the net income attributable to WGP. Net income (loss) attributable to the WES assets (as defined in Note 1 ) acquired from Anadarko for periods prior to WES’s acquisition of the WES assets is not allocated to the limited partners when calculating net income (loss) per common unit. Net income equal to the amount of available cash (as defined by WGP’s partnership agreement) is allocated to WGP common unitholders consistent with actual cash distributions.
New accounting standards policy	Accounting standards adopted in 2017. ASU 2017-04, Intangibles—Goodwill and Other (Topic 350) eliminates Step 2 from the goodwill impairment test in an effort to simplify the subsequent measurement of goodwill. WGP adopted this ASU using a prospective approach on January 1, 2017. This ASU will only be applicable to the extent that WGP determines its goodwill is impaired. ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business assists in determining whether a transaction should be accounted for as an acquisition or disposal of assets or a business. This ASU provides a screen that when substantially all of the fair value of the gross assets acquired, or disposed of, are concentrated in a single identifiable asset, or a group of similar identifiable assets, the assets will not be considered a business. If the screen is not met, the assets must include an input and a substantive process that together significantly contribute to the ability to create an output to be considered a business. WGP’s adoption of this ASU on January 1, 2017, using a prospective approach, could have a material impact on future consolidated financial statements as goodwill will not be allocated to divestitures or recorded on acquisitions that are not considered businesses. ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs and eliminates the exception for an intra-entity transfer of an asset other than inventory. WGP adopted this ASU on January 1, 2017, using a modified retrospective approach, with no impact to its consolidated financial statements. Accounting standards adopted in 2018. ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash requires an entity to explain the changes in the total of cash, cash equivalents, restricted cash, and restricted cash equivalents on the statement of cash flows and to provide a reconciliation of the totals in that statement to the related captions in the balance sheet when the cash, cash equivalents, restricted cash, and restricted cash equivalents are presented in more than one line item on the balance sheet. WGP adopted this ASU using a retrospective approach on January 1, 2018. Adoption will not have a material impact on the consolidated financial statements. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) ASU 2014-09, Revenue from Contracts with Customers (Topic 606) supersedes current revenue recognition requirements and industry-specific guidance, and requires an entity to recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration the entity expects to be entitled to in exchange for those goods or services. WGP adopted this new standard beginning January 1, 2018, using the modified retrospective method applied to contracts that were not completed as of January 1, 2018. The cumulative effect adjustment that will be recognized in the opening balance of equity and partners’ capital will not be material. WGP implemented new business processes, procedures, controls and system changes to gather, categorize and analyze the necessary data for the accounting changes and expanded disclosure under Topic 606. Beginning in 2018, additional quantitative and qualitative disclosures will be required, including (i) expanded descriptions of the nature, amount, timing, and uncertainty of revenue and cash flows from contracts with customers, (ii) details of customer contract assets and liabilities, (iii) revenue from customers on a disaggregated basis, and (iv) comparative information presented under both Topic 605, Revenue Recognition (“Topic 605”) and Topic 606. While WGP does not expect 2018 net income to be materially impacted by revenue recognition timing changes as a result of applying Topic 606, there will be significant changes to the presentation of revenues and related expenses recognized beginning January 1, 2018. The impacts of adopting Topic 606 include the following: Transactions that will affect net income in 2018: • Fee-based gathering / processing. Under Topic 605, fee revenue was recognized based on the rate in effect for the month of service, even when certain fees were charged on an upfront or limited-term basis. In addition, certain contingent fees were charged and recognized only when the customer did not meet the specified delivery minimums for the completed performance period. Under Topic 606, WES will recognize revenue associated with upfront or limited-term fees over the expected period of benefit. In addition, the contingent fees will be estimated and recognized as the services are performed for the customer’s delivered volumes. Differences between revenue recognized and amounts billed to customers will be recognized as contract assets or contract liabilities as appropriate. This will result in a change in the timing of revenue and changes to net income as a result of the consideration provisions. The magnitude of this change is dependent on WES’s future customer volumes subject to the impacted contracts. • Cost of service rate adjustments. WES receives fee revenue from contracts that require periodic rate redeterminations based upon its costs of service. Under Topic 605, revenue was recognized based on the amounts billed to customers each period. WES’s management is continuing to evaluate the proper accounting for these cost of service-based rate changes under Topic 606. The final conclusion about the accounting for these rate redeterminations could impact the cumulative effect adjustment that will be recorded effective January 1, 2018. • Aid in construction. Under certain midstream service contracts, WES receives reimbursement for capital costs necessary to provide services to the customer (i.e., connection costs, etc.). These reimbursements historically have been reflected as a reduction to property, plant and equipment upon receipt (and a reduction to capital expenditures). Beginning in 2018, reimbursement of capital costs received from customers will be reflected as a contract liability (deferred revenue) upon receipt. The contract liability will be amortized to revenue over the expected period of benefit. The magnitude of this change to net income and to WES’s capital expenditures is dependent on the amount of aid in construction reimbursements received from customers. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Transactions with a presentation change beginning in 2018, but no effect on net income: • Percentage of proceeds - gathering / processing. Under Topic 605, WES recognized cost of product expense when the product was purchased from a producer to whom WES provided midstream services and recognized revenue when the product was sold to a third party. Under Topic 606, in some instances where all or a percentage of the proceeds from the sale must be returned to the producer, the net margin from the purchase and sale transactions will be presented net within revenue because WES is acting as the producer’s agent in the sale. While reported product sales revenue and expense will be materially reduced, these presentation changes will not impact net income. The magnitude of this change is dependent on WES’s future customer volumes subject to the impacted contracts and commodity prices for those volumes. • Noncash consideration - keep-whole and percentage of product agreements. WES receives noncash consideration in the form of gas and/or NGL products in exchange for services under certain midstream contracts. Under Topic 605, WES recognized revenue only upon the sale of the related products. Under Topic 606, WES will recognize revenue for the products received as noncash consideration in exchange for the services provided to the customer, with the keep-whole noncash consideration value based on the net value of the NGLs over the replacement residue gas. WES will also recognize both revenue and cost of product expense upon sale of the related products to a different customer. Reported revenue and expense are not expected to be materially impacted by this change, and there will be no impact to net income. The magnitude of this change is dependent on WES’s future customer volumes subject to the impacted contracts and commodity prices for those volumes. • Wellhead purchase / sale incorporated into gathering / processing. Under Topic 605, the gas purchase cost was recognized as cost of product expense and any specified gathering or processing fees charged to the producer were recognized as revenue. Under Topic 606, the fees charged to the contract counterparty are recognized as adjustments to the purchase cost instead of revenue when such fees relate to services performed after control of the product transfers to WES. While there is no impact to net income, it will result in decreased revenue and cost of product expense. The magnitude of this change is dependent on WES’s future customer volumes subject to the impacted contracts. New accounting standards issued but not yet adopted. ASU 2016-02, Leases (Topic 842) requires lessees to recognize a lease liability and a right-of-use (“ROU”) asset for all leases, including operating leases, with a term greater than 12 months on the balance sheet. This ASU modifies the definition of a lease and outlines the recognition, measurement, presentation, and disclosure of leasing arrangements by both lessees and lessors. Certain practical expedients will be used to implement the new standard and WGP will not reassess contracts that commenced prior to adoption. WGP will make a policy election not to recognize ROU assets or lease liabilities for leases with a term of 12 months or less. WGP is reviewing contracts for WES’s portfolio of leased assets to assess the impact of adopting the new standard, which is expected to primarily affect other assets and other long-term liabilities. WGP is also evaluating its systems, processes, and internal controls to facilitate compliance with this new standard. WGP will complete its evaluation in 2018 and adopt this new standard on January 1, 2019, using a modified retrospective approach for all comparative periods presented.
Equity investments policy	Management evaluates its equity investments for impairment whenever events or changes in circumstances indicate that the carrying value of such investments may have experienced a decline in value that is other than temporary. When evidence of loss in value has occurred, management compares the estimated fair value of the investment to the carrying value of the investment to determine whether the investment has been impaired. Management assesses the fair value of equity investments using commonly accepted techniques, and may use more than one method, including, but not limited to, recent third-party comparable sales and discounted cash flow models. If the estimated fair value is less than the carrying value, the excess of the carrying value over the estimated fair value is recognized as an impairment loss.

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Tables)	12 Months Ended
Summary of Significant Accounting Policies (Tables)	Dec. 31, 2017
Accounting Policies [Abstract]
Assets and Investments Table	As of December 31, 2017 , WES’s assets and investments consisted of the following: Owned and Operated Operated Interests Non-Operated Interests Equity Interests Gathering systems (1) 12 3 3 2 Treating facilities 19 3 — 3 Natural gas processing plants/trains 20 4 — 2 NGL pipelines 2 — — 3 Natural gas pipelines 5 — — — Oil pipelines — 1 — 1
Ownership Interests and Method of Consolidation Table	The following table outlines WES’s ownership interests and the accounting method of consolidation used in WES’s consolidated financial statements: Percentage Interest Equity investments (1) Fort Union 14.81 % White Cliffs 10 % Rendezvous 22 % Mont Belvieu JV 25 % TEP 20 % TEG 20 % FRP 33.33 % Proportionate consolidation (2) Marcellus Interest systems 33.75 % Newcastle system 50 % Springfield system 50.1 % Full consolidation Chipeta (3) 75 % DBJV system (4) 100 % (1) Investments in non-controlled entities over which WES exercises significant influence are accounted for under the equity method. “Equity investment throughput” refers to WES’s share of average throughput for these investments. (2) WGP proportionately consolidates WES’s associated share of the assets, liabilities, revenues and expenses attributable to these assets. (3) The 25% interest in Chipeta Processing LLC (“Chipeta”) held by a third-party member is reflected within noncontrolling interests in the consolidated financial statements, in addition to the noncontrolling interests noted below. (4) WES acquired an additional 50% interest in the DBJV system (the “Additional DBJV System Interest”) from a third party on March 17, 2017. See Note 2 .

Acquisitions and Divestitures (

Acquisitions and Divestitures (Tables)	12 Months Ended
Acquisitions and Divestitures (Tables)	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Acquisitions Table	The following table presents the acquisitions completed by WES during 2017 , 2016 and 2015, and identifies the funding sources for such acquisitions: thousands except unit and percent amounts Acquisition Date Percentage Borrowings Cash On Hand WES Common Units Issued WES Series A Preferred Units Issued DBJV system (1) 03/02/2015 50 % $ — $ — — — Springfield system (2) 03/14/2016 50.1 % 247,500 — 2,089,602 14,030,611 DBJV system (3) 03/17/2017 50 % — 155,000 — — (1) WES acquired Delaware Basin JV Gathering LLC (“DBJV”) from Anadarko. At the time of acquisition, DBJV owned a 50% interest in a gathering system and related facilities (the “DBJV system”) located in the Delaware Basin in Loving, Ward, Winkler and Reeves Counties, Texas. At the acquisition date, WES estimated the future payment would be $282.8 million , the estimated net present value of which was $174.3 million . For further information, see DBJV acquisition—deferred purchase price obligation - Anadarko below. (2) WES acquired Springfield Pipeline LLC (“Springfield”) from Anadarko for $750.0 million , consisting of $712.5 million in cash and the issuance of 1,253,761 of WES common units. Springfield owns a 50.1% interest in an oil gathering system and a gas gathering system. The Springfield oil and gas gathering systems (collectively, the “Springfield system”) are located in Dimmit, La Salle, Maverick and Webb Counties in South Texas. WES financed the cash portion of the acquisition through: (i) borrowings of $247.5 million on the WES RCF, (ii) the issuance of 835,841 of WES common units to WGP and (iii) the issuance of WES Series A Preferred units to private investors. See Note 4 for further information regarding WES’s Series A Preferred units. WGP financed the purchase of the WES common units by borrowing $25.0 million under the WGP RCF. See Note 12 . (3) WES acquired the Additional DBJV System Interest from a third party. See Property exchange below.
Impact of Deferred Purchase Price Obligation - Anadarko Table	The following table summarizes the financial statement impact of the Deferred purchase price obligation - Anadarko: Deferred purchase price obligation - Anadarko Estimated future payment obligation (1) Balance at December 31, 2015 $ 188,674 $ 282,807 Accretion revision (2) (7,747 ) Revision to Deferred purchase price obligation – Anadarko (3) (139,487 ) Balance at December 31, 2016 41,440 56,455 Accretion expense (4) 71 Revision to Deferred purchase price obligation – Anadarko (3) (4,165 ) Settlement of the Deferred purchase price obligation – Anadarko (37,346 ) Balance at December 31, 2017 $ — $ — (1) Calculated using Level 3 inputs. (2) Financing-related accretion revisions were recorded in Interest expense in the consolidated statements of operations. (3) Recorded as revisions within Common units in the consolidated balance sheets and consolidated statements of equity and partners’ capital. (4) Accretion expense was recorded as a charge to Interest expense in the consolidated statements of operations.

Partnership Distributions (Tabl

Partnership Distributions (Tables)	12 Months Ended
Partnership Distributions (Tables)	Dec. 31, 2017
Distribution Made to Limited Partner [Line Items]
Cash Distributions Tables	The Board of Directors declared the following cash distributions to WGP unitholders for the periods presented: thousands except per-unit amounts Quarters Ended Total Quarterly Distribution per Unit Total Quarterly Cash Distribution Date of Distribution 2015 March 31 $ 0.34250 $ 74,977 May 2015 June 30 0.36375 79,630 August 2015 September 30 0.38125 83,461 November 2015 December 31 0.40375 88,389 February 2016 2016 March 31 $ 0.42375 $ 92,767 May 2016 June 30 0.43375 94,958 August 2016 September 30 0.44750 97,968 November 2016 December 31 0.46250 101,254 February 2017 2017 March 31 $ 0.49125 $ 107,549 May 2017 June 30 0.52750 115,487 August 2017 September 30 0.53750 117,677 November 2017 December 31 (1) 0.54875 120,140 February 2018 (1) The Board of Directors declared a cash distribution to WGP unitholders for the fourth quarter of 2017 of $0.54875 per unit, or $120.1 million in aggregate. The cash distribution is payable on February 22, 2018 , to WGP unitholders of record at the close of business on February 1, 2018 .
Western Gas Partners, LP [Member]
Distribution Made to Limited Partner [Line Items]
Cash Distributions Tables	The Board of Directors of WES GP declared the following cash distributions to WES’s common and general partner unitholders for the periods presented: thousands except per-unit amounts Quarters Ended Total Quarterly Total Quarterly Date of 2015 March 31 $ 0.725 $ 133,203 May 2015 June 30 0.750 139,736 August 2015 September 30 0.775 146,160 November 2015 December 31 0.800 152,588 February 2016 2016 March 31 $ 0.815 $ 158,905 May 2016 June 30 0.830 162,827 August 2016 September 30 0.845 166,742 November 2016 December 31 0.860 170,657 February 2017 2017 March 31 $ 0.875 $ 188,753 May 2017 June 30 0.890 207,491 August 2017 September 30 0.905 212,038 November 2017 December 31 (1) 0.920 216,586 February 2018 (1) The Board of Directors of WES GP declared a cash distribution to WES unitholders for the fourth quarter of 2017 of $0.920 per unit, or $216.6 million in aggregate, including incentive distributions, but excluding distributions on WES Class C units (see WES Class C unit distributions below). The cash distribution was paid on February 13, 2018 , to WES unitholders of record at the close of business on February 1, 2018 .
Western Gas Partners, LP [Member] \| Series A Preferred Units [Member]
Distribution Made to Limited Partner [Line Items]
Cash Distributions Tables	The following table summarizes the Series A Preferred unitholders’ cash distributions for the periods presented: thousands except per-unit amounts Quarters Ended Total Quarterly Distribution per Unit Total Quarterly Cash Distribution Date of Distribution 2016 March 31 (1) $ 0.68 $ 1,887 May 2016 June 30 (2) 0.68 14,082 August 2016 September 30 0.68 14,907 November 2016 December 31 0.68 14,908 February 2017 2017 March 31 $ 0.68 $ 7,453 May 2017 (1) Quarterly per unit distribution prorated for the 18 -day period during which 14,030,611 WES Series A Preferred units were outstanding during the first quarter of 2016. (2) Full quarterly per unit distribution on 14,030,611 WES Series A Preferred units and quarterly per unit distribution prorated for the 77 -day period during which 7,892,220 WES Series A Preferred units were outstanding during the second quarter of 2016.

Equity and Partners' Capital (T

Equity and Partners' Capital (Tables)	12 Months Ended
Equity and Partners' Capital (Tables)	Dec. 31, 2017
Partners' Capital Notes [Abstract]
Partnership Interests Table	The following table summarizes WES’s common, Class C, Series A Preferred and general partner units issued during the years ended December 31, 2017 and 2016: WES Common Units WES Class C Units WES Series A Preferred Units WES General Partner Units Total Balance at December 31, 2015 128,576,965 11,411,862 — 2,583,068 142,571,895 PIK Class C units — 946,261 — — 946,261 Springfield acquisition 2,089,602 — 14,030,611 — 16,120,213 April 2016 Series A units issuance — — 7,892,220 — 7,892,220 Long-Term Incentive Plan award vestings 5,403 — — — 5,403 Balance at December 31, 2016 130,671,970 12,358,123 21,922,831 2,583,068 167,535,992 PIK Class C units — 885,760 — — 885,760 Conversion of Series A Preferred units 21,922,831 — (21,922,831 ) — — Long-Term Incentive Plan award vestings 7,304 — — — 7,304 Balance at December 31, 2017 152,602,105 13,243,883 — 2,583,068 168,429,056

Transactions with Affiliates (T

Transactions with Affiliates (Tables)	12 Months Ended
Transactions with Affiliates (Tables)	Dec. 31, 2017
Related Party Transaction [Line Items]
Gains (Losses) on Commodity Price Swap Agreements Table	The following table summarizes gains and losses upon settlement of WES’s commodity price swap agreements recognized in the consolidated statements of operations: Year Ended December 31, thousands 2017 2016 2015 Gains (losses) on commodity price swap agreements related to sales: (1) Natural gas sales $ 19,924 $ 11,116 $ 45,978 Natural gas liquids sales (21,722 ) 59,918 145,258 Total (1,798 ) 71,034 191,236 Gains (losses) on commodity price swap agreements related to purchases (2) 2,446 (42,577 ) (124,944 ) Net gains (losses) on commodity price swap agreements $ 648 $ 28,457 $ 66,292 (1) Reported in affiliate Natural gas and natural gas liquids sales in the consolidated statements of operations in the period in which the related sale is recorded. (2) Reported in Cost of product in the consolidated statements of operations in the period in which the related purchase is recorded.
Commodity Price Swap Agreements Tables	The tables below summarize the swap prices for the extension periods compared to the forward market prices as of the various agreement dates. DJ Basin Complex per barrel except natural gas 2015 - 2018 Swap Prices 2015 Market Prices (1) 2016 Market Prices (1) 2017 Market Prices (1) 2018 Market Prices (1) Ethane $ 18.41 $ 1.96 $ 0.60 $ 5.09 $ 5.41 Propane 47.08 13.10 10.98 18.85 28.72 Isobutane 62.09 19.75 17.23 26.83 32.92 Normal butane 54.62 18.99 16.86 26.20 32.71 Natural gasoline 72.88 52.59 26.15 41.84 48.04 Condensate 76.47 52.59 34.65 45.40 49.36 Natural gas (per MMBtu) 5.96 2.75 2.11 3.05 2.21 5. TRANSACTIONS WITH AFFILIATES (CONTINUED) Hugoton System (2) per barrel except natural gas 2015 - 2016 Swap Prices 2015 Market Prices (1) 2016 Market Prices (1) Condensate $ 78.61 $ 32.56 $ 18.81 Natural gas (per MMBtu) 5.50 2.74 2.12 MGR Assets per barrel except natural gas 2015 Swap Prices 2016 - 2018 Swap Prices 2017 Market Prices (1) 2018 Market Prices (1) Ethane $ 23.41 $ 23.11 $ 4.08 $ 2.52 Propane 52.99 52.90 19.24 25.83 Isobutane 74.02 73.89 25.79 30.03 Normal butane 65.04 64.93 25.16 29.82 Natural gasoline 81.82 81.68 45.01 47.25 Condensate 81.82 81.68 53.55 56.76 Natural gas (per MMBtu) 4.66 4.87 3.05 2.21 (1) Represents the New York Mercantile Exchange forward strip price as of June 25, 2015, December 8, 2015, December 1, 2016, and December 20, 2017 , for the 2015 Market Prices, 2016 Market Prices, 2017 Market Prices, and 2018 Market Prices, respectively, adjusted for product specification, location, basis and, in the case of NGLs, transportation and fractionation costs. (2) The Hugoton system was sold in October 2016. See Note 2 .
Related Party Transactions Tables	The following table summarizes WES’s purchases from and sales to Anadarko of pipe and equipment: Year Ended December 31, 2017 2016 2015 2017 2016 2015 thousands Purchases Sales Cash consideration $ 3,910 $ 3,965 $ 10,903 $ — $ 623 $ 925 Net carrying value (5,283 ) (3,366 ) (6,318 ) — (605 ) (972 ) Partners’ capital adjustment $ (1,373 ) $ 599 $ 4,585 $ — $ 18 $ (47 ) The following table summarizes material affiliate transactions. See Note 2 for discussion of affiliate acquisitions and related funding. Year ended December 31, thousands 2017 2016 2015 Revenues and other (1) $ 1,365,318 $ 1,228,232 $ 1,220,639 Equity income, net – affiliates (1) 85,194 78,717 71,251 Cost of product (1) 86,010 80,455 167,354 Operation and maintenance (2) 72,489 72,330 77,061 General and administrative (3) 39,940 38,873 34,703 Operating expenses 198,439 191,658 279,118 Interest income (4) 16,900 16,900 16,900 Interest expense (5) 71 (7,747 ) 14,400 Settlement of the Deferred purchase price obligation – Anadarko (6) (37,346 ) — — Distributions to WGP unitholders (7) 360,523 315,505 269,029 Distributions to WES unitholders (8) 7,100 5,614 2,235 Above-market component of swap agreements with Anadarko 58,551 45,820 18,449 (1) 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, recognized under gathering, treating or processing agreements, and purchase and sale agreements. (2) Represents expenses incurred on and subsequent to the date of the acquisition of WES assets, as well as expenses incurred by Anadarko on a historical basis related to WES assets prior to the acquisition of such assets by WES. (3) Represents general and administrative expense incurred on and subsequent to the date of the acquisition of WES assets, as well as a management services fee for reimbursement of expenses incurred by Anadarko for periods prior to the acquisition of WES assets by WES. These amounts include equity-based compensation expense allocated to WES and WGP by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plans within this Note 5 ) and amounts charged by Anadarko under the WGP and WES omnibus agreements. (4) Represents interest income recognized on the note receivable from Anadarko. (5) Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 2 and Note 12 ) and for the year ended December 31, 2015, includes interest expense recognized on the WGP WCF (see Note 12 ). (6) Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 2 ). (7) Represents distributions paid under WGP’s partnership agreement (see Note 3 and Note 4 ). (8) Represents distributions paid to other subsidiaries of Anadarko under WES’s partnership agreement (see Note 3 and Note 4 ). The following table summarizes the amounts WGP reimbursed to Anadarko, separate from, and in addition to, those reimbursed by WES: Year Ended December 31, thousands 2017 2016 2015 General and administrative expenses $ 263 $ 258 $ 256 Public company expenses 1,821 2,449 1,997 Total reimbursement $ 2,084 $ 2,707 $ 2,253
LTIP Award Activity Tables	The following table summarizes WGP LTIP award activity for WGP GP independent directors and executive officers for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Weighted-Average Grant-Date Fair Value Units Weighted-Average Grant-Date Fair Value Units Weighted-Average Grant-Date Fair Value Units Phantom units outstanding at beginning of year $ 39.78 5,658 $ 47.20 12,537 $ 43.10 22,236 Vested 39.78 (5,658 ) 47.20 (12,537 ) 44.44 (13,317 ) Granted 43.39 5,763 39.78 5,658 62.21 3,618 Phantom units outstanding at end of year 43.39 5,763 39.78 5,658 47.20 12,537
Western Gas Partners, LP [Member]
Related Party Transaction [Line Items]
Related Party Transactions Tables	The following table summarizes the amounts WES reimbursed to Anadarko: Year Ended December 31, thousands 2017 2016 2015 General and administrative expenses $ 31,733 $ 29,360 $ 22,896 Public company expenses 9,379 8,410 8,950 Total reimbursement $ 41,112 $ 37,770 $ 31,846
LTIP Award Activity Tables	The following table summarizes WES LTIP award activity for the years ended December 31, 2017 , 2016 and 2015 : 2017 2016 2015 Weighted-Average Grant-Date Fair Value Units Weighted-Average Grant-Date Fair Value Units Weighted-Average Grant-Date Fair Value Units Phantom units outstanding at beginning of year $ 49.30 7,304 $ 68.78 5,477 $ 60.74 9,522 Vested 49.30 (7,304 ) 68.78 (5,477 ) 60.69 (9,257 ) Granted 55.73 7,180 49.30 7,304 69.10 5,212 Phantom units outstanding at end of year 55.73 7,180 49.30 7,304 68.78 5,477

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Components of Income Tax Expense (Benefit) Table	The components of income tax expense (benefit) are as follows: Year Ended December 31, thousands 2017 2016 2015 Current income tax expense (benefit) Federal income tax expense (benefit) $ — $ 4,477 $ 32,422 State income tax expense (benefit) 2,408 1,340 1,764 Total current income tax expense (benefit) 2,408 5,817 34,186 Deferred income tax expense (benefit) Federal income tax expense (benefit) — 1,622 10,251 State income tax expense (benefit) 2,458 933 1,095 Total deferred income tax expense (benefit) 2,458 2,555 11,346 Total income tax expense (benefit) $ 4,866 $ 8,372 $ 45,532
Tax Rate Reconciliation Table	Total income taxes differed from the amounts computed by applying the statutory income tax rate to income (loss) before income taxes. The sources of these differences are as follows: Year Ended December 31, thousands except percentages 2017 2016 2015 Income (loss) before income taxes $ 578,068 $ 605,352 $ 56,630 Statutory tax rate — % — % — % Tax computed at statutory rate $ — $ — $ — Adjustments resulting from: Federal taxes on income attributable to Anadarko’s investment in WES — 6,162 42,823 State taxes on income attributable to Anadarko’s investment in WES (net of federal benefit) — 117 298 Texas margin tax expense (benefit) (1) 4,866 2,093 2,411 Income tax expense (benefit) $ 4,866 $ 8,372 $ 45,532 Effective tax rate 1 % 1 % 80 % (1) Includes a reduction of $2.2 million in deferred state income taxes for the year ended December 31, 2015. Texas House Bill 32, signed into law in June 2015, reduced the Texas margin tax rates by 0.25% . The law became effective January 1, 2016. WGP is required to include the impact of the law change on its deferred state income taxes in the period enacted.
Income Tax Temporary Differences Table	The tax effects of temporary differences that give rise to significant portions of deferred tax assets (liabilities) are as follows: December 31, thousands 2017 2016 Depreciable property $ (7,676 ) $ (4,976 ) Credit carryforwards 448 498 Other intangible assets (189 ) (1,928 ) Other 8 4 Net long-term deferred income tax liabilities $ (7,409 ) $ (6,402 )

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
Property, Plant and Equipment (Tables)	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment Table	A summary of the historical cost of property, plant and equipment is as follows: December 31, thousands Estimated Useful Life 2017 2016 Land n/a $ 4,450 $ 4,012 Gathering systems and processing complexes 3 to 47 years 7,114,701 6,462,053 Pipelines and equipment 15 to 45 years 137,644 139,646 Assets under construction n/a 577,914 226,626 Other 3 to 40 years 36,393 29,605 Total property, plant and equipment 7,871,102 6,861,942 Accumulated depreciation 2,140,211 1,812,010 Net property, plant and equipment $ 5,730,891 $ 5,049,932

Goodwill and Intangibles (Table

Goodwill and Intangibles (Tables)	12 Months Ended
Goodwill and Intangibles (Tables)	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Other Intangible Assets Table	The following table presents the gross carrying amount and accumulated amortization of other intangible assets: December 31, thousands 2017 2016 Gross carrying amount $ 868,035 $ 868,035 Accumulated amortization (92,766 ) (64,337 ) Other intangible assets $ 775,269 $ 803,698

Equity Investments (Tables)

Equity Investments (Tables)	12 Months Ended
Equity Investments (Tables)	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Equity Investments Table	The following table presents the activity in WES’s equity investments for the years ended December 31, 2017 and 2016: Equity Investments thousands Fort (1) White (2) Rendezvous (3) Mont (4) TEG (5) TEP (6) FRP (7) Total Balance at December 31, 2015 $ 17,122 $ 50,439 $ 50,913 $ 117,089 $ 16,283 $ 194,803 $ 172,238 $ 618,887 Investment earnings (loss), net of amortization 608 13,858 1,931 26,204 708 16,683 18,725 78,717 Contributions — 441 — — 166 (580 ) — 27 Distributions (1,543 ) (13,277 ) (3,873 ) (26,243 ) (730 ) (16,934 ) (19,585 ) (82,185 ) Distributions in excess of cumulative earnings (8) (3,354 ) (4,142 ) (2,232 ) (4,245 ) (581 ) (4,778 ) (1,906 ) (21,238 ) Balance at December 31, 2016 $ 12,833 $ 47,319 $ 46,739 $ 112,805 $ 15,846 $ 189,194 $ 169,472 $ 594,208 Investment earnings (loss), net of amortization 3,821 12,547 1,144 29,444 3,350 17,387 17,501 85,194 Impairment expense (9) (3,110 ) — — — — — — (3,110 ) Contributions — 277 — — — 107 — 384 Distributions (4,217 ) (11,965 ) (3,085 ) (29,482 ) (3,317 ) (17,639 ) (17,675 ) (87,380 ) Distributions in excess of cumulative earnings (8) (2,297 ) (3,233 ) (2,270 ) (2,468 ) — (10,074 ) (2,743 ) (23,085 ) Balance at December 31, 2017 $ 7,030 $ 44,945 $ 42,528 $ 110,299 $ 15,879 $ 178,975 $ 166,555 $ 566,211 (1) WES has a 14.81% interest in Fort Union, a joint venture that owns a gathering pipeline and treating facilities in the Powder River Basin. Anadarko is the construction manager and physical operator of the Fort Union facilities. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the owners’ firm gathering agreements, require 65% or unanimous approval of the owners. (2) WES has a 10% interest in White Cliffs, a limited liability company that owns a crude oil pipeline that originates in Platteville, Colorado and terminates in Cushing, Oklahoma. The third-party majority owner is the manager of the White Cliffs operations. Certain business decisions, including, but not limited to, approval of annual budgets and decisions with respect to significant expenditures, contractual commitments, acquisitions, material financings, dispositions of assets or admitting new members, require more than 75% approval of the members. (3) WES has a 22% interest in Rendezvous, a limited liability company that operates gas gathering facilities in Southwestern Wyoming. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the members’ gas servicing agreements, require unanimous approval of the members. (4) WES has a 25% interest in the Mont Belvieu JV, an entity formed to design, construct, and own two fractionation trains located in Mont Belvieu, Texas. A third party is the operator of the Mont Belvieu JV fractionation trains. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require 50% or unanimous approval of the owners. (5) WES has a 20% interest in TEG, which owns two NGL gathering systems that link natural gas processing plants to TEP. Midcoast Energy Partners, L.P., a wholly-owned subsidiary of Enbridge, Inc., is the operator of the two gathering systems. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the delegation, creation, appointment, or removal of officer positions require more than 50% approval of the members. (6) WES has a 20% interest in TEP, which owns an NGL pipeline that originates in Skellytown, Texas and extends to Mont Belvieu, Texas. Enterprise Products Operating LLC (“Enterprise”) is the operator of TEP. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require more than 50% approval of the members. (7) WES has a 33.33% interest in FRP, which owns an NGL pipeline that extends from Weld County, Colorado to Skellytown, Texas. Enterprise is the operator of FRP. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require more than 50% approval of the members. (8) Distributions in excess of cumulative earnings, classified as investing cash flows in the consolidated statements of cash flows, are calculated on an individual investment basis. (9) Recorded in Impairments in the consolidated statements of operations.
Summarized Equity Investments Financial Information Presented at 100 Percent Tables	The following tables present the summarized combined financial information for WES’s equity investments (amounts represent 100% of investee financial information): Year Ended December 31, thousands 2017 2016 2015 Consolidated Statements of Income Revenues $ 703,424 $ 687,554 $ 667,554 Operating income 435,735 428,454 359,899 Net income 434,749 427,511 359,443 December 31, thousands 2017 2016 Consolidated Balance Sheets Current assets $ 137,957 $ 118,472 Property, plant and equipment, net 2,512,214 2,626,466 Other assets 36,373 39,802 Total assets $ 2,686,544 $ 2,784,740 Current liabilities 80,490 63,468 Non-current liabilities 7,447 6,662 Equity 2,598,607 2,714,610 Total liabilities and equity $ 2,686,544 $ 2,784,740

Components of Working Capital (

Components of Working Capital (Tables)	12 Months Ended
Components of Working Capital (Tables)	Dec. 31, 2017
Components Of Working Capital [Abstract]
Accounts Receivable, Net Table	A summary of accounts receivable, net is as follows: December 31, thousands 2017 2016 Trade receivables, net $ 160,194 $ 192,606 Other receivables, net 45 30,415 Total accounts receivable, net $ 160,239 $ 223,021
Other Current Assets Table	A summary of other current assets is as follows: December 31, thousands 2017 2016 Natural gas liquids inventory $ 10,788 $ 7,126 Imbalance receivables 1,640 3,483 Prepaid insurance 2,955 2,889 Total other current assets $ 15,383 $ 13,498
Accrued Liabilities Table	A summary of accrued liabilities is as follows: December 31, thousands 2017 2016 Accrued interest expense $ 40,646 $ 39,834 Short-term asset retirement obligations 2,304 3,114 Short-term remediation and reclamation obligations 833 630 Income taxes payable 2,495 1,006 Other 1,714 606 Total accrued liabilities $ 47,992 $ 45,190

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
Asset Retirement Obligations (Tables)	Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations Table	The following table provides a summary of changes in asset retirement obligations: Year Ended December 31, thousands 2017 2016 Carrying amount of asset retirement obligations at beginning of year $ 142,407 $ 130,631 Liabilities incurred 16,153 5,515 Liabilities settled (10,468 ) (10,650 ) Accretion expense 6,956 6,794 Revisions in estimated liabilities (9,350 ) 10,117 Carrying amount of asset retirement obligations at end of year $ 145,698 $ 142,407

Debt and Interest Expense (Tabl

Debt and Interest Expense (Tables)	12 Months Ended
Debt and Interest Expense (Tables)	Dec. 31, 2017
Debt Instruments [Abstract]
Debt Outstanding and Debt Activity Tables	The following table presents WES and WGP’s outstanding debt as of December 31, 2017 and 2016: December 31, 2017 December 31, 2016 thousands Principal Carrying Value Fair Value (1) Principal Carrying Value Fair Value (1) WGP RCF $ 28,000 $ 28,000 $ 28,000 $ 28,000 $ 28,000 $ 28,000 2021 Notes 500,000 495,815 530,647 500,000 494,734 536,252 2022 Notes 670,000 668,849 684,043 670,000 668,634 681,723 2018 Notes 350,000 349,684 350,631 350,000 349,188 351,531 2044 Notes 600,000 593,234 637,827 600,000 593,132 615,753 2025 Notes 500,000 491,885 500,885 500,000 490,971 492,499 2026 Notes 500,000 495,245 520,144 500,000 494,802 518,441 WES RCF 370,000 370,000 370,000 — — — Total long-term debt $ 3,518,000 $ 3,492,712 $ 3,622,177 $ 3,148,000 $ 3,119,461 $ 3,224,199 (1) Fair value is measured using the market approach and Level 2 inputs. 12. DEBT AND INTEREST EXPENSE (CONTINUED) Debt activity. The following table presents WES and WGP’s debt activity for the years ended December 31, 2017 and 2016: thousands Carrying Value Balance at December 31, 2015 $ 2,690,651 WES RCF borrowings 600,000 Issuance of 2026 Notes 500,000 Issuance of 2044 Notes 200,000 Repayments of WES RCF borrowings (900,000 ) WGP RCF borrowings 28,000 Other 810 Balance at December 31, 2016 $ 3,119,461 WES RCF borrowings 370,000 Other 3,251 Balance at December 31, 2017 $ 3,492,712
Interest Expense Table	The following table summarizes the amounts included in interest expense: Year Ended December 31, thousands 2017 2016 2015 Third parties Long-term debt $ (143,400 ) $ (122,428 ) $ (102,058 ) Amortization of debt issuance costs and commitment fees (7,970 ) (7,509 ) (5,734 ) Capitalized interest 6,826 5,562 8,318 Total interest expense – third parties (144,544 ) (124,375 ) (99,474 ) Affiliates WGP WCF — — (2 ) Deferred purchase price obligation – Anadarko (1) (71 ) 7,747 (14,398 ) Total interest expense – affiliates (71 ) 7,747 (14,400 ) Interest expense $ (144,615 ) $ (116,628 ) $ (113,874 ) (1) See Note 2 for a discussion of the Deferred purchase price obligation - Anadarko.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
Commitments and Contingencies (Tables)	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Operating Lease Obligations Table	The amounts in the table below represent existing contractual operating lease obligations as of December 31, 2017 , that may be assigned or otherwise charged to WES pursuant to the reimbursement provisions of the omnibus agreement: thousands Operating Leases 2018 $ 8,402 2019 7,506 2020 1,615 2021 460 2022 467 Thereafter 2,021 Total $ 20,471

Summary of Significant Accoun37

Summary of Significant Accounting Policies - Assets and Investments Table (Details) - Western Gas Partners, LP [Member]	Dec. 31, 2017unit
Owned and Operated [Member] \| Gathering Systems [Member]
Assets [Line Items]
Assets, number of units	12	[1]
Owned and Operated [Member] \| Treating Facilities [Member]
Assets [Line Items]
Assets, number of units	19
Owned and Operated [Member] \| Natural Gas Processing Plants/Trains [Member]
Assets [Line Items]
Assets, number of units	20
Owned and Operated [Member] \| Natural Gas Liquids Pipelines [Member]
Assets [Line Items]
Assets, number of units	2
Owned and Operated [Member] \| Natural Gas Pipelines [Member]
Assets [Line Items]
Assets, number of units	5
Operated Interests [Member] \| Gathering Systems [Member]
Assets [Line Items]
Assets, number of units	3	[1]
Operated Interests [Member] \| Treating Facilities [Member]
Assets [Line Items]
Assets, number of units	3
Operated Interests [Member] \| Natural Gas Processing Plants/Trains [Member]
Assets [Line Items]
Assets, number of units	4
Operated Interests [Member] \| Oil Pipelines [Member]
Assets [Line Items]
Assets, number of units	1
Non-Operated Interests [Member] \| Gathering Systems [Member]
Assets [Line Items]
Assets, number of units	3	[1]
Equity Interests [Member] \| Gathering Systems [Member]
Assets [Line Items]
Assets, number of units	2	[1]
Equity Interests [Member] \| Treating Facilities [Member]
Assets [Line Items]
Assets, number of units	3
Equity Interests [Member] \| Natural Gas Processing Plants/Trains [Member]
Assets [Line Items]
Assets, number of units	2
Equity Interests [Member] \| Natural Gas Liquids Pipelines [Member]
Assets [Line Items]
Assets, number of units	3
Equity Interests [Member] \| Oil Pipelines [Member]
Assets [Line Items]
Assets, number of units	1

[1]	Includes the DBM water systems.

Summary of Significant Accoun38

Summary of Significant Accounting Policies - Ownership Interests and Method of Consolidation Table (Details)		Mar. 17, 2017	Dec. 31, 2017
Chipeta [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest by noncontrolling interest owner			25.00%
Western Gas Partners, LP [Member] \| DBJV System [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership percentage acquired	[1]	50.00%
Western Gas Partners, LP [Member] \| Equity Investments [Member] \| Fort Union [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[2]		14.81%
Western Gas Partners, LP [Member] \| Equity Investments [Member] \| White Cliffs [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[2]		10.00%
Western Gas Partners, LP [Member] \| Equity Investments [Member] \| Rendezvous [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[2]		22.00%
Western Gas Partners, LP [Member] \| Equity Investments [Member] \| Mont Belvieu JV [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[2]		25.00%
Western Gas Partners, LP [Member] \| Equity Investments [Member] \| Texas Express Pipeline LLC [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[2]		20.00%
Western Gas Partners, LP [Member] \| Equity Investments [Member] \| Texas Express Gathering LLC [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[2]		20.00%
Western Gas Partners, LP [Member] \| Equity Investments [Member] \| Front Range Pipeline LLC [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[2]		33.33%
Western Gas Partners, LP [Member] \| Proportionate Consolidation [Member] \| Marcellus Interest Systems [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[3]		33.75%
Western Gas Partners, LP [Member] \| Proportionate Consolidation [Member] \| Newcastle System [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[3]		50.00%
Western Gas Partners, LP [Member] \| Proportionate Consolidation [Member] \| Springfield System [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[3]		50.10%
Western Gas Partners, LP [Member] \| Full Consolidation [Member] \| Chipeta [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[4]		75.00%
Western Gas Partners, LP [Member] \| Full Consolidation [Member] \| DBJV System [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	[5]		100.00%

[1]	WES acquired the Additional DBJV System Interest from a third party. See Property exchange below.
[2]	Investments in non-controlled entities over which WES exercises significant influence are accounted for under the equity method. “Equity investment throughput” refers to WES’s share of average throughput for these investments.
[3]	WGP proportionately consolidates WES’s associated share of the assets, liabilities, revenues and expenses attributable to these assets.
[4]	The 25% interest in Chipeta Processing LLC (“Chipeta”) held by a third-party member is reflected within noncontrolling interests in the consolidated financial statements, in addition to the noncontrolling interests noted below.
[5]	WES acquired an additional 50% interest in the DBJV system (the “Additional DBJV System Interest”) from a third party on March 17, 2017. See Note 2.

Summary of Significant Accoun39

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 31, 2008
Note receivable - Anadarko		$ 260,000,000	$ 260,000,000
Imbalance receivables		1,640,000	3,483,000
Imbalance payables		2,900,000	3,000,000
Loss on divestiture and other, net	[1],[2]	(132,388,000)	14,641,000	$ (57,024,000)
Proceeds from property insurance claims		$ 22,977,000	17,465,000	0
Western Gas Equity Partners Long Term Incentive Plan [Member]
Units authorized under LTIP		3,000,000
Units available under LTIP		2,944,325
Chipeta [Member]
Ownership interest by noncontrolling interest owner		25.00%
Western Gas Equity Partners, LP [Member] \| Western Gas Partners, LP [Member] \| General Partner [Member]
Percentage ownership interest		100.00%
Western Gas Partners, LP [Member] \| Western Gas Partners Long Term Incentive Plan [Member]
Units authorized under LTIP		2,250,000
Units available under LTIP		2,250,000
Western Gas Partners, LP [Member] \| Delaware Basin Midstream Complex [Member]
Loss on divestiture and other, net		$ 5,700,000		$ 20,300,000
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
Property insurance claim receivable		0	$ 30,000,000
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

[1]	Includes losses related to an incident at the DBM complex for the years ended December 31, 2017 and 2015. See Note 1.
[2]	Includes losses related to an incident at the DBM complex for the years ended December 31, 2017 and 2015. See Note 1.

Acquisitions and Divestitures -

Acquisitions and Divestitures - Acquisitions Table (Details) - USD ($) $ in Thousands

Mar. 17, 2017

Mar. 14, 2016

Mar. 02, 2015

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Business Acquisition [Line Items]

Deferred purchase price obligation - Anadarko, present value

[1]

$ 0

$ 41,440

Affiliates [Member]

Business Acquisition [Line Items]

Cash on hand

$ 3,910

716,465

$ 10,903

Revolving Credit Facility [Member] | WGP RCF [Member]

Business Acquisition [Line Items]

Borrowings - revolving credit facility

$ 25,000

$ 28,000

Western Gas Partners, LP [Member]

Business Acquisition [Line Items]

WES units issued

885,760

946,261

Western Gas Partners, LP [Member] | Revolving Credit Facility [Member] | WES RCF [Member]

Business Acquisition [Line Items]

Borrowings - revolving credit facility

$ 370,000

$ 600,000

Western Gas Partners, LP [Member] | Delaware Basin JV Gathering LLC [Member]

Business Acquisition [Line Items]

Ownership percentage acquired

50.00%

[2]

50.00%

[3]

Cash on hand

[2]

$ 155,000

Western Gas Partners, LP [Member] | Delaware Basin JV Gathering LLC [Member] | Deferred Purchase Price Obligation - Anadarko [Member] | Affiliates [Member]

Business Acquisition [Line Items]

Deferred purchase price obligation - Anadarko, future value

$ 282,800

[4]

56,455

[4]

282,807

[4]

Deferred purchase price obligation - Anadarko, present value

$ 174,300

$ 0

$ 41,440

$ 188,674

Western Gas Partners, LP [Member] | Springfield [Member]

Business Acquisition [Line Items]

Ownership percentage acquired

[5]

50.10%

Acquisition price

$ 750,000

Cash payment for acquisition

$ 712,500

Western Gas Partners, LP [Member] | Springfield [Member] | Common Units [Member]

Business Acquisition [Line Items]

WES units issued

[5]

2,089,602

Western Gas Partners, LP [Member] | Springfield [Member] | Common Units [Member] | Anadarko [Member]

Business Acquisition [Line Items]

WES units issued

1,253,761

Western Gas Partners, LP [Member] | Springfield [Member] | Common Units [Member] | Western Gas Equity Partners, LP [Member]

Business Acquisition [Line Items]

WES units issued

835,841

Western Gas Partners, LP [Member] | Springfield [Member] | Series A Preferred Units [Member]

Business Acquisition [Line Items]

WES units issued

[5]

14,030,611

Western Gas Partners, LP [Member] | Springfield [Member] | Revolving Credit Facility [Member] | WES RCF [Member]

Business Acquisition [Line Items]

Borrowings - revolving credit facility

[5]

$ 247,500

[1]

See Note 2.

[2]

WES acquired the Additional DBJV System Interest from a third party. See Property exchange below.

[3]

WES acquired Delaware Basin JV Gathering LLC (“DBJV”) from Anadarko. At the time of acquisition, DBJV owned a 50% interest in a gathering system and related facilities (the “DBJV system”) located in the Delaware Basin in Loving, Ward, Winkler and Reeves Counties, Texas. At the acquisition date, WES estimated the future payment would be $282.8 million, the estimated net present value of which was $174.3 million. For further information, see DBJV acquisition—deferred purchase price obligation - Anadarko below.

[4]

Calculated using Level 3 inputs.

[5]

WES acquired Springfield Pipeline LLC (“Springfield”) from Anadarko for $750.0 million, consisting of $712.5 million in cash and the issuance of 1,253,761 of WES common units. Springfield owns a 50.1% interest in an oil gathering system and a gas gathering system. The Springfield oil and gas gathering systems (collectively, the “Springfield system”) are located in Dimmit, La Salle, Maverick and Webb Counties in South Texas. WES financed the cash portion of the acquisition through: (i) borrowings of $247.5 million on the WES RCF, (ii) the issuance of 835,841 of WES common units to WGP and (iii) the issuance of WES Series A Preferred units to private investors. See Note 4 for further information regarding WES’s Series A Preferred units. WGP financed the purchase of the WES common units by borrowing $25.0 million under the WGP RCF. See Note 12.

Acquisitions and Divestitures41

Acquisitions and Divestitures - Impact of Deferred Purchase Price Obligation - Anadarko Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015		Mar. 02, 2015
Property, Plant and Equipment [Line Items]
Deferred purchase price obligation - Anadarko, present value	[1]	$ 0		$ 41,440
Affiliates [Member]
Property, Plant and Equipment [Line Items]
Settlement of the Deferred purchase price obligation - Anadarko	[2]	(37,346)		0		$ 0
Affiliates [Member] \| Deferred Purchase Price Obligation - Anadarko [Member]
Property, Plant and Equipment [Line Items]
Accretion revision/expense	[3]	71		(7,747)		14,398
Settlement of the Deferred purchase price obligation - Anadarko	[4]	(37,346)		0		0
Western Gas Partners, LP [Member] \| Affiliates [Member] \| Delaware Basin JV Gathering LLC [Member] \| Deferred Purchase Price Obligation - Anadarko [Member]
Property, Plant and Equipment [Line Items]
Deferred purchase price obligation - Anadarko, present value		0		41,440		188,674		$ 174,300
Accretion revision/expense		71	[5]	(7,747)	[6]
Revision to Deferred purchase price obligation – Anadarko	[7]	(4,165)		(139,487)
Settlement of the Deferred purchase price obligation - Anadarko		(37,346)
Deferred purchase price obligation - Anadarko, future value		$ 0	[8]	$ 56,455	[8]	$ 282,807	[8]	$ 282,800

[1]	See Note 2.
[2]	See Note 2.
[3]	See Note 2 for a discussion of the Deferred purchase price obligation - Anadarko.
[4]	Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 2).
[5]	Accretion expense was recorded as a charge to Interest expense in the consolidated statements of operations.
[6]	Financing-related accretion revisions were recorded in Interest expense in the consolidated statements of operations.
[7]	Recorded as revisions within Common units in the consolidated balance sheets and consolidated statements of equity and partners’ capital.
[8]	Calculated using Level 3 inputs.

Acquisitions and Divestitures42

Acquisitions and Divestitures - Additional Information (Details) - USD ($) $ in Thousands		Mar. 17, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Affiliates [Member]
Property, Plant and Equipment [Line Items]
Cash payment			$ 3,910	$ 716,465	$ 10,903
Settlement of the Deferred purchase price obligation - Anadarko	[1]		37,346	0	0
Deferred Purchase Price Obligation - Anadarko [Member] \| Affiliates [Member]
Property, Plant and Equipment [Line Items]
Settlement of the Deferred purchase price obligation - Anadarko	[2]		37,346	0	0
Western Gas Partners, LP [Member] \| Helper and Clawson Systems [Member]
Property, Plant and Equipment [Line Items]
Gain (loss) on sale of assets			16,300
Western Gas Partners, LP [Member] \| Hugoton System [Member]
Property, Plant and Equipment [Line Items]
Gain (loss) on sale of assets				(12,000)
Goodwill allocated to divestiture				$ 1,600
Western Gas Partners, LP [Member] \| Dew and Pinnacle Systems [Member]
Property, Plant and Equipment [Line Items]
Gain (loss) on sale of assets					77,300
Goodwill allocated to divestiture					$ 5,100
Western Gas Partners, LP [Member] \| Delaware Basin JV Gathering LLC [Member]
Property, Plant and Equipment [Line Items]
Percentage ownership interest		50.00%
Cash payment	[3]	$ 155,000
Net gain from property exchange			125,700
Western Gas Partners, LP [Member] \| Delaware Basin JV Gathering LLC [Member] \| Deferred Purchase Price Obligation - Anadarko [Member] \| Affiliates [Member]
Property, Plant and Equipment [Line Items]
Settlement of the Deferred purchase price obligation - Anadarko			$ 37,346
Western Gas Partners, LP [Member] \| Non-Operated Marcellus Interest [Member]
Property, Plant and Equipment [Line Items]
Percentage ownership interest		33.75%

[1]	See Note 2.
[2]	Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 2).
[3]	WES acquired the Additional DBJV System Interest from a third party. See Property exchange below.

Partnership Distributions - Cas

Partnership Distributions - Cash Distributions Tables (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015
Distribution Made to Limited Partner [Line Items]
Total quarterly distribution per unit	$ 0.54875	[1]	$ 0.53750	$ 0.52750	$ 0.49125	$ 0.46250	$ 0.44750	$ 0.43375	$ 0.42375	$ 0.40375	$ 0.38125	$ 0.36375	$ 0.34250
Total quarterly cash distribution	$ 120,140	[1]	$ 117,677	$ 115,487	$ 107,549	$ 101,254	$ 97,968	$ 94,958	$ 92,767	$ 88,389	$ 83,461	$ 79,630	$ 74,977
Western Gas Partners, LP [Member]
Distribution Made to Limited Partner [Line Items]
Total quarterly distribution per unit	$ 0.920	[2]	$ 0.905	$ 0.890	$ 0.875	$ 0.860	$ 0.845	$ 0.830	$ 0.815	$ 0.800	$ 0.775	$ 0.750	$ 0.725
Total quarterly cash distribution	$ 216,586	[2]	$ 212,038	$ 207,491	$ 188,753	$ 170,657	$ 166,742	$ 162,827	$ 158,905	$ 152,588	$ 146,160	$ 139,736	$ 133,203

[1]	The Board of Directors declared a cash distribution to WGP unitholders for the fourth quarter of 2017 of $0.54875 per unit, or $120.1 million in aggregate. The cash distribution is payable on February 22, 2018, to WGP unitholders of record at the close of business on February 1, 2018.
[2]	The Board of Directors of WES GP declared a cash distribution to WES unitholders for the fourth quarter of 2017 of $0.920 per unit, or $216.6 million in aggregate, including incentive distributions, but excluding distributions on WES Class C units (see WES Class C unit distributions below). The cash distribution was paid on February 13, 2018, to WES unitholders of record at the close of business on February 1, 2018.

Partnership Distributions - Ser

Partnership Distributions - Series A Preferred Unit Distributions Table (Details) - Western Gas Partners, LP [Member] - USD ($) $ / shares in Units, $ in Thousands	Mar. 14, 2016	Apr. 30, 2016	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016
Distribution Made to Limited Partner [Line Items]
Units issued										885,760	946,261
Private Investor [Member] \| Over-Allotment Option [Member]
Distribution Made to Limited Partner [Line Items]
Units issued											7,892,220
Series A Preferred Units [Member]
Distribution Made to Limited Partner [Line Items]
Series A Preferred units quarterly distribution per unit			$ 0.68	$ 0.68	$ 0.68	$ 0.68	[1]	$ 0.68	[2]
Series A Preferred units quarterly cash distribution			$ 7,453	$ 14,908	$ 14,907	$ 14,082	[1]	$ 1,887	[2]
Number of days in prorated period						77 days		18 days
Series A Preferred Units [Member] \| Private Investor [Member]
Distribution Made to Limited Partner [Line Items]
Units issued	14,030,611							14,030,611
Series A Preferred Units [Member] \| Private Investor [Member] \| Over-Allotment Option [Member]
Distribution Made to Limited Partner [Line Items]
Units issued		7,892,220				7,892,220					7,892,220

[1]	Full quarterly per unit distribution on 14,030,611 WES Series A Preferred units and quarterly per unit distribution prorated for the 77-day period during which 7,892,220 WES Series A Preferred units were outstanding during the second quarter of 2016.
[2]	Quarterly per unit distribution prorated for the 18-day period during which 14,030,611 WES Series A Preferred units were outstanding during the first quarter of 2016.

Partnership Distributions - Add

Partnership Distributions - Additional Information (Details) - $ / shares	May 02, 2017	Mar. 01, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	[1]	Mar. 31, 2016	[2]	Dec. 31, 2017
Distribution Made to Limited Partner [Line Items]
Partnership agreement day requirement of distribution of available cash										55 days
Western Gas Partners, LP [Member]
Distribution Made to Limited Partner [Line Items]
Partnership agreement day requirement of distribution of available cash										45 days
Incentive distributions percentage										48.00%
Western Gas Partners, LP [Member] \| Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Distribution sharing percentage										1.50%
Western Gas Partners, LP [Member] \| Maximum [Member]
Distribution Made to Limited Partner [Line Items]
Distribution sharing percentage										49.50%
Western Gas Partners, LP [Member] \| Class C Units [Member]
Distribution Made to Limited Partner [Line Items]
Discount rate percentage										6.00%
Western Gas Partners, LP [Member] \| Series A Preferred Units [Member]
Distribution Made to Limited Partner [Line Items]
Series A Preferred units quarterly distribution per unit			$ 0.68	$ 0.68	$ 0.68	$ 0.68		$ 0.68
Western Gas Partners, LP [Member] \| Series A Preferred Units [Member] \| Series A Preferred Units March 2017 Conversion [Member]
Distribution Made to Limited Partner [Line Items]
Series A Preferred units, percentage converted		50.00%
Series A Preferred units, common units issued upon conversion		1
Western Gas Partners, LP [Member] \| Series A Preferred Units [Member] \| Series A Preferred Units May 2017 Conversion [Member]
Distribution Made to Limited Partner [Line Items]
Series A Preferred units, percentage converted	50.00%
Series A Preferred units, common units issued upon conversion	1

[1]	Full quarterly per unit distribution on 14,030,611 WES Series A Preferred units and quarterly per unit distribution prorated for the 77-day period during which 7,892,220 WES Series A Preferred units were outstanding during the second quarter of 2016.
[2]	Quarterly per unit distribution prorated for the 18-day period during which 14,030,611 WES Series A Preferred units were outstanding during the first quarter of 2016.

Equity and Partners' Capital -

Equity and Partners' Capital - Partnership Interests Table (Details) - Western Gas Partners, LP [Member] - shares		Mar. 14, 2016	Apr. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Capital Unit [Line Items]
Balance					142,571,895	167,535,992	142,571,895
Units issued						885,760	946,261
Long-Term Incentive Plan award vestings						7,304	5,403
Conversion of Series A Preferred units						0
Balance						168,429,056	167,535,992
Common Units [Member]
Capital Unit [Line Items]
Balance					128,576,965	130,671,970	128,576,965
Long-Term Incentive Plan award vestings						7,304	5,403
Conversion of Series A Preferred units						21,922,831
Balance						152,602,105	130,671,970
Class C Units [Member]
Capital Unit [Line Items]
Balance					11,411,862	12,358,123	11,411,862
Units issued						885,760	946,261
Balance						13,243,883	12,358,123
Series A Preferred Units [Member]
Capital Unit [Line Items]
Balance					0	21,922,831	0
Conversion of Series A Preferred units						(21,922,831)
Balance						0	21,922,831
General Partner [Member]
Capital Unit [Line Items]
Balance					2,583,068	2,583,068	2,583,068
Balance						2,583,068	2,583,068
Private Investor [Member] \| Series A Preferred Units [Member]
Capital Unit [Line Items]
Units issued		14,030,611			14,030,611
Private Investor [Member] \| Over-Allotment Option [Member]
Capital Unit [Line Items]
Units issued							7,892,220
Private Investor [Member] \| Over-Allotment Option [Member] \| Series A Preferred Units [Member]
Capital Unit [Line Items]
Units issued			7,892,220	7,892,220			7,892,220
Springfield [Member]
Capital Unit [Line Items]
WES units issued, acquisition							16,120,213
Springfield [Member] \| Common Units [Member]
Capital Unit [Line Items]
Units issued	[1]	2,089,602
WES units issued, acquisition							2,089,602
Springfield [Member] \| Series A Preferred Units [Member]
Capital Unit [Line Items]
Units issued	[1]	14,030,611
WES units issued, acquisition							14,030,611

[1]	WES acquired Springfield Pipeline LLC (“Springfield”) from Anadarko for $750.0 million, consisting of $712.5 million in cash and the issuance of 1,253,761 of WES common units. Springfield owns a 50.1% interest in an oil gathering system and a gas gathering system. The Springfield oil and gas gathering systems (collectively, the “Springfield system”) are located in Dimmit, La Salle, Maverick and Webb Counties in South Texas. WES financed the cash portion of the acquisition through: (i) borrowings of $247.5 million on the WES RCF, (ii) the issuance of 835,841 of WES common units to WGP and (iii) the issuance of WES Series A Preferred units to private investors. See Note 4 for further information regarding WES’s Series A Preferred units. WGP financed the purchase of the WES common units by borrowing $25.0 million under the WGP RCF. See Note 12.

Equity and Partners' Capital 47

Equity and Partners' Capital - Additional Information (Details) $ / shares in Units, $ in Thousands

May 02, 2017shares

Mar. 01, 2017shares

Mar. 14, 2016USD ($)$ / sharesshares

Jun. 30, 2016shares

Apr. 30, 2016USD ($)shares

Jun. 30, 2015$ / unitshares

Nov. 30, 2014shares

Jun. 30, 2016shares

Mar. 31, 2016shares

Dec. 31, 2015USD ($)

Dec. 31, 2017USD ($)shares

Dec. 31, 2016USD ($)shares

Dec. 31, 2015USD ($)$ / sharesshares

Jul. 31, 2017USD ($)

Aug. 31, 2014USD ($)

Schedule of Investments [Line Items]

Limited partner units owned

218,933,141

218,928,570

Common Units [Member] | Anadarko [Member]

Schedule of Investments [Line Items]

Common units issued

12,500,000

2,300,000

Common Units [Member] | Anadarko [Member] | Over-Allotment Option [Member]

Schedule of Investments [Line Items]

Common units issued

300,000

7.50% Tangible Equity Units [Member] | Anadarko [Member]

Schedule of Investments [Line Items]

Tangible equity units issued

9,200,000

Tangible equity unit rate

7.50%

Stated amount per tangible equity unit | $ / unit

Debt instrument, maturity date

Jun. 7,
2018

7.50% Tangible Equity Units [Member] | Anadarko [Member] | Over-Allotment Option [Member]

Schedule of Investments [Line Items]

Tangible equity units issued

1,200,000

Public [Member] | Western Gas Equity Partners, LP [Member]

Schedule of Investments [Line Items]

Limited partner units owned

40,345,776

Ownership interest

18.40%

Public [Member] | Western Gas Partners, LP [Member] | Common Units [Member]

Schedule of Investments [Line Items]

Limited partner units owned

100,458,679

Ownership interest

59.60%

Anadarko [Member] | Western Gas Equity Partners, LP [Member]

Schedule of Investments [Line Items]

Limited partner units owned

178,587,365

Ownership interest

81.60%

Western Gas Equity Partners, LP [Member] | Western Gas Partners, LP [Member]

Schedule of Investments [Line Items]

General partner units owned

2,583,068

General partner's interest

1.50%

Western Gas Equity Partners, LP [Member] | Western Gas Partners, LP [Member] | Common Units [Member]

Schedule of Investments [Line Items]

Limited partner units owned

50,132,046

Ownership interest

29.80%

Western Gas Equity Partners, LP [Member] | Western Gas Partners, LP [Member] | Incentive Distribution Rights [Member]

Schedule of Investments [Line Items]

General partner's interest

100.00%

Western Gas Partners, LP [Member]

Schedule of Investments [Line Items]

Units issued

885,760

946,261

Western Gas Partners, LP [Member] | August 2014 COP [Member]

Schedule of Investments [Line Items]

Maximum aggregate principal of common units | $

$ 500,000

Average price per unit | $ / shares

$ 66.61

Net proceeds to WES | $

$ 57,400

Underwriting discount and other offering expenses | $

$ 800

800

Gross proceeds | $

58,200

Commissions paid | $

$ 0

$ 600

Western Gas Partners, LP [Member] | July 2017 COP [Member]

Schedule of Investments [Line Items]

Maximum aggregate principal of common units | $

$ 500,000

Western Gas Partners, LP [Member] | Private Investor [Member] | Over-Allotment Option [Member]

Schedule of Investments [Line Items]

Units issued

7,892,220

Western Gas Partners, LP [Member] | Common Units [Member] | August 2014 COP [Member]

Schedule of Investments [Line Items]

Common units issued

873,525

Western Gas Partners, LP [Member] | Class C Units [Member]

Schedule of Investments [Line Items]

Units issued

885,760

946,261

Class C units, common units issued upon conversion

Western Gas Partners, LP [Member] | Class C Units [Member] | Other Subsidiaries Of Anadarko [Member]

Schedule of Investments [Line Items]

Units issued

10,913,853

Western Gas Partners, LP [Member] | Series A Preferred Units [Member]

Schedule of Investments [Line Items]

Series A Preferred units, proceeds from issuance | $

$ 0

$ 686,937

$ 0

Western Gas Partners, LP [Member] | Series A Preferred Units [Member] | Series A Preferred Units March 2017 Conversion [Member]

Schedule of Investments [Line Items]

Series A Preferred units, percentage converted

50.00%

Series A Preferred units, common units issued upon conversion

Western Gas Partners, LP [Member] | Series A Preferred Units [Member] | Series A Preferred Units May 2017 Conversion [Member]

Schedule of Investments [Line Items]

Series A Preferred units, percentage converted

50.00%

Series A Preferred units, common units issued upon conversion

Western Gas Partners, LP [Member] | Series A Preferred Units [Member] | Private Investor [Member]

Schedule of Investments [Line Items]

Units issued

14,030,611

Series A Preferred units, price per unit | $ / shares

$ 32

Series A Preferred units, transaction fee percentage

2.00%

Series A Preferred units, proceeds from issuance | $

$ 440,000

Western Gas Partners, LP [Member] | Series A Preferred Units [Member] | Private Investor [Member] | Over-Allotment Option [Member]

Schedule of Investments [Line Items]

Units issued

7,892,220

Series A Preferred units, proceeds from issuance | $

$ 246,900

Other Subsidiaries Of Anadarko [Member] | Western Gas Partners, LP [Member] | Common Units [Member]

Schedule of Investments [Line Items]

Limited partner units owned

2,011,380

Other Subsidiaries Of Anadarko [Member] | Western Gas Partners, LP [Member] | Class C Units [Member]

Schedule of Investments [Line Items]

Limited partner units owned

13,243,883

Other Subsidiaries Of Anadarko [Member] | Western Gas Partners, LP [Member] | Common and Class C Units [Member]

Schedule of Investments [Line Items]

Ownership interest

9.10%

Transactions with Affiliates -

Transactions with Affiliates - Gains (Losses) on Commodity Price Swap Agreements Table (Details) - Affiliates [Member] - Western Gas Partners, LP [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements		$ 648	$ 28,457	$ 66,292
Sales [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[1]	(1,798)	71,034	191,236
Sales [Member] \| Natural Gas [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[1]	19,924	11,116	45,978
Sales [Member] \| Natural Gas Liquids [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[1]	(21,722)	59,918	145,258
Purchases [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[2]	$ 2,446	$ (42,577)	$ (124,944)

[1]	Reported in affiliate Natural gas and natural gas liquids sales in the consolidated statements of operations in the period in which the related sale is recorded.
[2]	Reported in Cost of product in the consolidated statements of operations in the period in which the related purchase is recorded.

Transactions with Affiliates 49

Transactions with Affiliates - Commodity Price Swap Agreements Tables (Details) - Western Gas Partners, LP [Member]		Dec. 31, 2017$ / bbl$ / MMBTU	Dec. 20, 2017$ / bbl$ / MMBTU	Dec. 31, 2016$ / bbl$ / MMBTU	Dec. 01, 2016$ / bbl$ / MMBTU	Dec. 31, 2015$ / bbl$ / MMBTU	Dec. 08, 2015$ / bbl$ / MMBTU	Jun. 25, 2015$ / bbl$ / MMBTU
DJ Basin Complex [Member] \| Years 2015 - 2018 [Member] \| Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		18.41
DJ Basin Complex [Member] \| Years 2015 - 2018 [Member] \| Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		47.08
DJ Basin Complex [Member] \| Years 2015 - 2018 [Member] \| Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		62.09
DJ Basin Complex [Member] \| Years 2015 - 2018 [Member] \| Normal butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		54.62
DJ Basin Complex [Member] \| Years 2015 - 2018 [Member] \| Natural gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		72.88
DJ Basin Complex [Member] \| Years 2015 - 2018 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		76.47
DJ Basin Complex [Member] \| Years 2015 - 2018 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price \| $ / MMBTU		5.96
DJ Basin Complex [Member] \| Year 2015 [Member] \| Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]							1.96
DJ Basin Complex [Member] \| Year 2015 [Member] \| Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]							13.10
DJ Basin Complex [Member] \| Year 2015 [Member] \| Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]							19.75
DJ Basin Complex [Member] \| Year 2015 [Member] \| Normal butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]							18.99
DJ Basin Complex [Member] \| Year 2015 [Member] \| Natural gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]							52.59
DJ Basin Complex [Member] \| Year 2015 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]							52.59
DJ Basin Complex [Member] \| Year 2015 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price \| $ / MMBTU	[1]							2.75
DJ Basin Complex [Member] \| Year 2016 [Member] \| Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]						0.60
DJ Basin Complex [Member] \| Year 2016 [Member] \| Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]						10.98
DJ Basin Complex [Member] \| Year 2016 [Member] \| Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]						17.23
DJ Basin Complex [Member] \| Year 2016 [Member] \| Normal butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]						16.86
DJ Basin Complex [Member] \| Year 2016 [Member] \| Natural gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]						26.15
DJ Basin Complex [Member] \| Year 2016 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]						34.65
DJ Basin Complex [Member] \| Year 2016 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price \| $ / MMBTU	[1]						2.11
DJ Basin Complex [Member] \| Year 2017 [Member] \| Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				5.09
DJ Basin Complex [Member] \| Year 2017 [Member] \| Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				18.85
DJ Basin Complex [Member] \| Year 2017 [Member] \| Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				26.83
DJ Basin Complex [Member] \| Year 2017 [Member] \| Normal butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				26.20
DJ Basin Complex [Member] \| Year 2017 [Member] \| Natural gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				41.84
DJ Basin Complex [Member] \| Year 2017 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				45.40
DJ Basin Complex [Member] \| Year 2017 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price \| $ / MMBTU	[1]				3.05
DJ Basin Complex [Member] \| Year 2018 [Member] \| Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		5.41
DJ Basin Complex [Member] \| Year 2018 [Member] \| Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		28.72
DJ Basin Complex [Member] \| Year 2018 [Member] \| Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		32.92
DJ Basin Complex [Member] \| Year 2018 [Member] \| Normal butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		32.71
DJ Basin Complex [Member] \| Year 2018 [Member] \| Natural gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		48.04
DJ Basin Complex [Member] \| Year 2018 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		49.36
DJ Basin Complex [Member] \| Year 2018 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price \| $ / MMBTU	[1]		2.21
Hugoton System [Member] \| Years 2015 - 2016 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price	[2]			78.61
Hugoton System [Member] \| Years 2015 - 2016 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price \| $ / MMBTU	[2]			5.50
Hugoton System [Member] \| Year 2015 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1],[2]							32.56
Hugoton System [Member] \| Year 2015 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price \| $ / MMBTU	[1],[2]							2.74
Hugoton System [Member] \| Year 2016 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1],[2]						18.81
Hugoton System [Member] \| Year 2016 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price \| $ / MMBTU	[1],[2]						2.12
MGR Assets [Member] \| Year 2015 [Member] \| Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price						23.41
MGR Assets [Member] \| Year 2015 [Member] \| Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price						52.99
MGR Assets [Member] \| Year 2015 [Member] \| Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price						74.02
MGR Assets [Member] \| Year 2015 [Member] \| Normal butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price						65.04
MGR Assets [Member] \| Year 2015 [Member] \| Natural gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price						81.82
MGR Assets [Member] \| Year 2015 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price						81.82
MGR Assets [Member] \| Year 2015 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price \| $ / MMBTU						4.66
MGR Assets [Member] \| Years 2016 - 2018 [Member] \| Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		23.11
MGR Assets [Member] \| Years 2016 - 2018 [Member] \| Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		52.90
MGR Assets [Member] \| Years 2016 - 2018 [Member] \| Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		73.89
MGR Assets [Member] \| Years 2016 - 2018 [Member] \| Normal butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		64.93
MGR Assets [Member] \| Years 2016 - 2018 [Member] \| Natural gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		81.68
MGR Assets [Member] \| Years 2016 - 2018 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		81.68
MGR Assets [Member] \| Years 2016 - 2018 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price \| $ / MMBTU		4.87
MGR Assets [Member] \| Year 2017 [Member] \| Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				4.08
MGR Assets [Member] \| Year 2017 [Member] \| Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				19.24
MGR Assets [Member] \| Year 2017 [Member] \| Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				25.79
MGR Assets [Member] \| Year 2017 [Member] \| Normal butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				25.16
MGR Assets [Member] \| Year 2017 [Member] \| Natural gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				45.01
MGR Assets [Member] \| Year 2017 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]				53.55
MGR Assets [Member] \| Year 2017 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price \| $ / MMBTU	[1]				3.05
MGR Assets [Member] \| Year 2018 [Member] \| Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		2.52
MGR Assets [Member] \| Year 2018 [Member] \| Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		25.83
MGR Assets [Member] \| Year 2018 [Member] \| Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		30.03
MGR Assets [Member] \| Year 2018 [Member] \| Normal butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		29.82
MGR Assets [Member] \| Year 2018 [Member] \| Natural gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		47.25
MGR Assets [Member] \| Year 2018 [Member] \| Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price	[1]		56.76
MGR Assets [Member] \| Year 2018 [Member] \| Natural gas (per MMBtu) [Member]
Commodity Price Risk Swap [Line Items]
Commodity market price \| $ / MMBTU	[1]		2.21

[1]	Represents the New York Mercantile Exchange forward strip price as of June 25, 2015, December 8, 2015, December 1, 2016, and December 20, 2017, for the 2015 Market Prices, 2016 Market Prices, 2017 Market Prices, and 2018 Market Prices, respectively, adjusted for product specification, location, basis and, in the case of NGLs, transportation and fractionation costs.
[2]	The Hugoton system was sold in October 2016. See Note 2.

Transactions with Affiliates 50

Transactions with Affiliates - Omnibus Agreement Tables (Details) - Omnibus Agreement [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Allocated costs from Anadarko	$ 2,084	$ 2,707	$ 2,253
Western Gas Partners, LP [Member]
Related Party Transaction [Line Items]
Allocated costs from Anadarko	41,112	37,770	31,846
General and Administrative Expenses [Member]
Related Party Transaction [Line Items]
Allocated costs from Anadarko	263	258	256
General and Administrative Expenses [Member] \| Western Gas Partners, LP [Member]
Related Party Transaction [Line Items]
Allocated costs from Anadarko	31,733	29,360	22,896
Public Company Expenses [Member]
Related Party Transaction [Line Items]
Allocated costs from Anadarko	1,821	2,449	1,997
Public Company Expenses [Member] \| Western Gas Partners, LP [Member]
Related Party Transaction [Line Items]
Allocated costs from Anadarko	$ 9,379	$ 8,410	$ 8,950

Transactions with Affiliates 51

Transactions with Affiliates - LTIP Award Activity Tables (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Value per unit of phantom units outstanding at beginning of year	$ 39.78	$ 47.20	$ 43.10
Value per unit of phantom units vested during the period	39.78	47.20	44.44
Value per unit of phantom units granted during the period	43.39	39.78	62.21
Value per unit of phantom units outstanding at end of year	$ 43.39	$ 39.78	$ 47.20
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Phantom units outstanding at beginning of year	5,658	12,537	22,236
Phantom units vested	(5,658)	(12,537)	(13,317)
Phantom units granted	5,763	5,658	3,618
Phantom units outstanding at end of year	5,763	5,658	12,537
Western Gas Partners, LP [Member]
Related Party Transaction [Line Items]
Value per unit of phantom units outstanding at beginning of year	$ 49.30	$ 68.78	$ 60.74
Value per unit of phantom units vested during the period	49.30	68.78	60.69
Value per unit of phantom units granted during the period	55.73	49.30	69.10
Value per unit of phantom units outstanding at end of year	$ 55.73	$ 49.30	$ 68.78
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Phantom units outstanding at beginning of year	7,304	5,477	9,522
Phantom units vested	(7,304)	(5,477)	(9,257)
Phantom units granted	7,180	7,304	5,212
Phantom units outstanding at end of year	7,180	7,304	5,477

Transactions with Affiliates 52

Transactions with Affiliates - Equipment Purchases and Sales Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Partners’ capital adjustment	[1]	$ (3,189)	$ 581	$ 4,632
Western Gas Partners, LP [Member] \| Affiliates [Member] \| Purchases [Member]
Related Party Transaction [Line Items]
Cash consideration - purchases		3,910	3,965	10,903
Net carrying value		(5,283)	(3,366)	(6,318)
Partners’ capital adjustment		(1,373)	599	4,585
Western Gas Partners, LP [Member] \| Affiliates [Member] \| Sales [Member]
Related Party Transaction [Line Items]
Cash consideration - sales		0	623	925
Net carrying value		0	(605)	(972)
Partners’ capital adjustment		$ 0	$ (18)	$ 47

[1]	Includes $(1.4) million related to pipe and equipment purchases and $(1.8) million related to other assets for the year ended December 31, 2017. See Note 5.

Transactions with Affiliates 53

Transactions with Affiliates - Summary of Affiliate Transactions Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Revenues and other		$ 2,248,356	$ 1,804,270	$ 1,752,072
Equity income, net – affiliates	[1]	85,194	78,717	71,251
Cost of product	[2]	908,693	494,194	528,369
Operation and maintenance	[2]	315,994	308,010	331,972
General and administrative	[2]	50,668	49,248	44,428
Operating expenses		1,791,421	1,180,081	1,726,165
Interest income	[3]	16,900	16,900	16,900
Interest expense	[4]	144,615	116,628	113,874
Distributions to unitholders	[5]	441,967	374,082	306,477
Above-market component of swap agreements with Anadarko	[5]	58,551	45,820	18,449
Affiliates [Member]
Related Party Transaction [Line Items]
Revenues and other	[1]	1,365,318	1,228,232	1,220,639
Cost of product	[1]	86,010	80,455	167,354
Operation and maintenance	[6]	72,489	72,330	77,061
General and administrative	[7]	39,940	38,873	34,703
Operating expenses		198,439	191,658	279,118
Interest expense	[8]	71	(7,747)	14,400
Settlement of the Deferred purchase price obligation - Anadarko	[9]	(37,346)	0	0
Distributions to unitholders	[10]	360,523	315,505	269,029
Affiliates [Member] \| Western Gas Partners, LP [Member]
Related Party Transaction [Line Items]
Distributions to unitholders	[11]	7,100	5,614	2,235
Affiliates [Member] \| Deferred Purchase Price Obligation - Anadarko [Member]
Related Party Transaction [Line Items]
Settlement of the Deferred purchase price obligation - Anadarko	[12]	$ (37,346)	$ 0	$ 0

[1]	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, recognized under gathering, treating or processing agreements, and purchase and sale agreements.
[2]	Cost of product includes product purchases from Anadarko (as defined in Note 1) of $86.0 million, $80.5 million and $167.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. Operation and maintenance includes charges from Anadarko of $72.5 million, $72.3 million and $77.1 million for the years ended December 31, 2017, 2016 and 2015, respectively. General and administrative includes charges from Anadarko of $39.9 million, $38.9 million and $34.7 million for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 5.
[3]	Represents interest income recognized on the note receivable from Anadarko.
[4]	Includes affiliate (as defined in Note 1) amounts of $(0.1) million, $7.7 million and $(14.4) million for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 2 and Note 12.
[5]	See Note 5.
[6]	Represents expenses incurred on and subsequent to the date of the acquisition of WES assets, as well as expenses incurred by Anadarko on a historical basis related to WES assets prior to the acquisition of such assets by WES.
[7]	Represents general and administrative expense incurred on and subsequent to the date of the acquisition of WES assets, as well as a management services fee for reimbursement of expenses incurred by Anadarko for periods prior to the acquisition of WES assets by WES. These amounts include equity-based compensation expense allocated to WES and WGP by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plans within this Note 5) and amounts charged by Anadarko under the WGP and WES omnibus agreements.
[8]	Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 2 and Note 12) and for the year ended December 31, 2015, includes interest expense recognized on the WGP WCF (see Note 12).
[9]	See Note 2.
[10]	Represents distributions paid under WGP’s partnership agreement (see Note 3 and Note 4).
[11]	Represents distributions paid to other subsidiaries of Anadarko under WES’s partnership agreement (see Note 3 and Note 4).
[12]	Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 2).

Transactions with Affiliates 54

Transactions with Affiliates - Additional Information (Details) - USD ($)		Nov. 01, 2012	May 31, 2008	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Note receivable - Anadarko				$ 260,000,000	$ 260,000,000
Above-market component of swap agreements with Anadarko	[1]			58,551,000	45,820,000	$ 18,449,000
Administrative services fee	[2]			50,668,000	49,248,000	44,428,000
Contributions of equity-based compensation to WES by Anadarko				$ 4,587,000	4,170,000	3,471,000
Western Gas Equity Partners Long Term Incentive Plan [Member]
Related Party Transaction [Line Items]
Units vesting period				3 years
Equity-based compensation expense				$ 200,000	200,000	200,000
Unvested equity-based compensation expense				$ 100,000
Weighted-average term of unvested awards				5 months
Omnibus Agreement [Member]
Related Party Transaction [Line Items]
Administrative services fee				$ 250,000
Affiliates [Member]
Related Party Transaction [Line Items]
Administrative services fee	[3]			$ 39,940,000	38,873,000	34,703,000
Affiliates [Member] \| Working Capital Facility [Member]
Related Party Transaction [Line Items]
Facility, maximum borrowing capacity		$ 30,000,000
Facility, expiration date		Nov. 1, 2017
Independent Director [Member] \| Western Gas Equity Partners Long Term Incentive Plan [Member]
Related Party Transaction [Line Items]
Units vesting period				1 year
Western Gas Partners, LP [Member] \| Western Gas Equity Partners Long Term Incentive Plan [Member] \| Anadarko Incentive Plan [Member]
Related Party Transaction [Line Items]
Equity-based compensation expense				$ 4,600,000	5,200,000	3,900,000
Unvested equity-based compensation expense				$ 13,200,000
Weighted-average term of unvested awards				2 years 6 months
Contributions of equity-based compensation to WES by Anadarko				$ 4,600,000	4,200,000	3,600,000
Western Gas Partners, LP [Member] \| Western Gas Partners Long Term Incentive Plan [Member]
Related Party Transaction [Line Items]
Units vesting period				3 years
Equity-based compensation expense				$ 400,000	$ 400,000	$ 500,000
Unvested equity-based compensation expense				$ 200,000
Weighted-average term of unvested awards				5 months
Western Gas Partners, LP [Member] \| Natural Gas [Member] \| Gathering, Treating and Transportation [Member]
Related Party Transaction [Line Items]
Affiliate throughput percent				34.00%	37.00%	53.00%
Western Gas Partners, LP [Member] \| Natural Gas [Member] \| Processing [Member]
Related Party Transaction [Line Items]
Affiliate throughput percent				41.00%	54.00%	51.00%
Western Gas Partners, LP [Member] \| Crude, NGL and Produced Water [Member] \| Gathering, Treating and Transportation [Member]
Related Party Transaction [Line Items]
Affiliate throughput percent				56.00%	65.00%	100.00%
Western Gas Partners, LP [Member] \| Affiliates [Member]
Related Party Transaction [Line Items]
Note receivable - Anadarko			$ 260,000,000	$ 260,000,000
Note receivable, due date			May 14, 2038
Fixed annual rate for note receivable bearing interest			6.50%
Western Gas Partners, LP [Member] \| Affiliates [Member] \| Level 2 Inputs [Member] \| Market Approach Valuation Technique [Member]
Related Party Transaction [Line Items]
Fair value of the note receivable				$ 325,200,000	$ 313,300,000
Western Gas Partners, LP [Member] \| Independent Director [Member] \| Western Gas Partners Long Term Incentive Plan [Member]
Related Party Transaction [Line Items]
Units vesting period				1 year

[1]	See Note 5.
[2]	Cost of product includes product purchases from Anadarko (as defined in Note 1) of $86.0 million, $80.5 million and $167.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. Operation and maintenance includes charges from Anadarko of $72.5 million, $72.3 million and $77.1 million for the years ended December 31, 2017, 2016 and 2015, respectively. General and administrative includes charges from Anadarko of $39.9 million, $38.9 million and $34.7 million for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 5.
[3]	Represents general and administrative expense incurred on and subsequent to the date of the acquisition of WES assets, as well as a management services fee for reimbursement of expenses incurred by Anadarko for periods prior to the acquisition of WES assets by WES. These amounts include equity-based compensation expense allocated to WES and WGP by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plans within this Note 5) and amounts charged by Anadarko under the WGP and WES omnibus agreements.

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Benefit) Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax expense (benefit)
Federal income tax expense (benefit)	$ 0	$ 4,477	$ 32,422
State income tax expense (benefit)	2,408	1,340	1,764
Total current income tax expense (benefit)	2,408	5,817	34,186
Deferred income tax expense (benefit)
Federal income tax expense (benefit)	0	1,622	10,251
State income tax expense (benefit)	2,458	933	1,095
Total deferred income tax expense (benefit)	2,458	2,555	11,346
Total income tax expense (benefit)	$ 4,866	$ 8,372	$ 45,532

Income Taxes - Tax Rate Reconci

Income Taxes - Tax Rate Reconciliation Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Income (loss) before income taxes		$ 578,068	$ 605,352	$ 56,630
Statutory tax rate		0.00%	0.00%	0.00%
Adjustments resulting from:
Federal taxes on income		$ 0	$ 0	$ 0
State taxes on income (net of federal benefit) and Texas margin tax expense (benefit)	[1]	4,866	2,093	2,411
Income tax expense (benefit)		$ 4,866	$ 8,372	$ 45,532
Effective tax rate		1.00%	1.00%	80.00%
Change in deferred state income taxes				$ 2,200
Change in Texas margin tax rates				0.25%
Western Gas Partners, LP [Member]
Adjustments resulting from:
Federal taxes on income		$ 0	$ 6,162	$ 42,823
State taxes on income (net of federal benefit) and Texas margin tax expense (benefit)		$ 0	$ 117	$ 298

[1]	Includes a reduction of $2.2 million in deferred state income taxes for the year ended December 31, 2015. Texas House Bill 32, signed into law in June 2015, reduced the Texas margin tax rates by 0.25%. The law became effective January 1, 2016. WGP is required to include the impact of the law change on its deferred state income taxes in the period enacted.

Income Taxes - Income Tax Tempo

Income Taxes - Income Tax Temporary Differences Table (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Depreciable property	$ (7,676)	$ (4,976)
Credit carryforwards	448	498
Other intangible assets	(189)	(1,928)
Other	8	4
Net long-term deferred income tax liabilities	$ (7,409)	$ (6,402)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Credit carryforwards	$ 448	$ 498
Tax credit carryforward, expiration date	Dec. 31, 2026

Property, Plant and Equipment -

Property, Plant and Equipment - Historical Cost Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 7,871,102	$ 6,861,942
Accumulated depreciation	2,140,211	1,812,010
Net property, plant and equipment	5,730,891	5,049,932
Western Gas Partners, LP [Member] \| Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	4,450	4,012
Western Gas Partners, LP [Member] \| Gathering Systems and Processing Complexes [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 7,114,701	6,462,053
Western Gas Partners, LP [Member] \| Gathering Systems and Processing Complexes [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Western Gas Partners, LP [Member] \| Gathering Systems and Processing Complexes [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	47 years
Western Gas Partners, LP [Member] \| Pipelines and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 137,644	139,646
Western Gas Partners, LP [Member] \| Pipelines and Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Western Gas Partners, LP [Member] \| Pipelines and Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	45 years
Western Gas Partners, LP [Member] \| Assets Under Construction [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 577,914	226,626
Western Gas Partners, LP [Member] \| Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 36,393	$ 29,605
Western Gas Partners, LP [Member] \| Other [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Western Gas Partners, LP [Member] \| Other [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years

Property, Plant and Equipment60

Property, Plant and Equipment - Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Impairments		$ 178,374		$ 15,535	$ 515,458
Equity investment impairment loss	[1]	3,110
Western Gas Partners, LP [Member] \| Fort Union [Member]
Property, Plant and Equipment [Line Items]
Equity investment impairment loss		3,110	[1],[2]	3,000	9,500
Western Gas Partners, LP [Member] \| Granger Complex [Member]
Property, Plant and Equipment [Line Items]
Impairments		158,800
Western Gas Partners, LP [Member] \| Granger Complex [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Level 3 Inputs [Member] \| Income Approach Valuation Technique [Member]
Property, Plant and Equipment [Line Items]
Estimated fair value		48,500
Western Gas Partners, LP [Member] \| Equipment [Member]
Property, Plant and Equipment [Line Items]
Impairments		19,600		9,400	14,400
Western Gas Partners, LP [Member] \| Granger Straddle Plant [Member]
Property, Plant and Equipment [Line Items]
Impairments		3,700
Western Gas Partners, LP [Member] \| Granger Straddle Plant [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Level 3 Inputs [Member] \| Income Approach Valuation Technique [Member]
Property, Plant and Equipment [Line Items]
Estimated salvage value		600
Western Gas Partners, LP [Member] \| Northeast Wyoming Facility [Member]
Property, Plant and Equipment [Line Items]
Impairments		2,000
Western Gas Partners, LP [Member] \| Northeast Wyoming Facility [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Level 3 Inputs [Member] \| Market Approach Valuation Technique [Member]
Property, Plant and Equipment [Line Items]
Estimated salvage value		400
Western Gas Partners, LP [Member] \| Newcastle System [Member]
Property, Plant and Equipment [Line Items]
Impairments				6,100
Western Gas Partners, LP [Member] \| Newcastle System [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Level 3 Inputs [Member] \| Income Approach Valuation Technique [Member]
Property, Plant and Equipment [Line Items]
Estimated fair value				$ 3,100
Western Gas Partners, LP [Member] \| Red Desert Complex [Member]
Property, Plant and Equipment [Line Items]
Impairments					280,200
Western Gas Partners, LP [Member] \| Red Desert Complex [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Level 3 Inputs [Member] \| Income Approach Valuation Technique [Member]
Property, Plant and Equipment [Line Items]
Estimated salvage value					6,300
Western Gas Partners, LP [Member] \| Hilight System [Member]
Property, Plant and Equipment [Line Items]
Impairments		$ 8,200			220,900
Western Gas Partners, LP [Member] \| Hilight System [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Level 3 Inputs [Member] \| Income Approach Valuation Technique [Member]
Property, Plant and Equipment [Line Items]
Estimated fair value					$ 28,800

[1]	Recorded in Impairments in the consolidated statements of operations.
[2]	WES has a 14.81% interest in Fort Union, a joint venture that owns a gathering pipeline and treating facilities in the Powder River Basin. Anadarko is the construction manager and physical operator of the Fort Union facilities. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the owners’ firm gathering agreements, require 65% or unanimous approval of the owners.

Goodwill and Intangibles - Othe

Goodwill and Intangibles - Other Intangible Assets Table (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Gross carrying amount	$ 868,035	$ 868,035
Accumulated amortization	(92,766)	(64,337)
Other intangible assets	$ 775,269	$ 803,698

Goodwill and Intangibles - Addi

Goodwill and Intangibles - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0
Impairment of intangible assets (excluding goodwill)	0
Amortization expense for intangible assets	28,400,000	$ 28,400,000	$ 28,200,000
Estimated amortization expense for intangible assets in 2018	28,400,000
Estimated amortization expense for intangible assets in 2019	28,400,000
Estimated amortization expense for intangible assets in 2020	28,400,000
Estimated amortization expense for intangible assets in 2021	28,400,000
Estimated amortization expense for intangible assets in 2022	$ 28,400,000
Western Gas Partners, LP [Member] \| Platte Valley [Member]
Finite-Lived Intangible Assets [Line Items]
Straight-line basis of amortization	50 years
Western Gas Partners, LP [Member] \| Chipeta [Member]
Finite-Lived Intangible Assets [Line Items]
Straight-line basis of amortization	10 years
Western Gas Partners, LP [Member] \| Delaware Basin Midstream LLC [Member]
Finite-Lived Intangible Assets [Line Items]
Straight-line basis of amortization	30 years

Equity Investments - Equity Inv

Equity Investments - Equity Investments Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Balance		$ 594,208		$ 618,887
Investment earnings (loss), net of amortization	[1]	85,194		78,717		$ 71,251
Impairment expense	[2]	(3,110)
Contributions		384		27		11,442
Distributions		(87,380)		(82,185)		(82,054)
Distributions in excess of cumulative earnings		(23,085)	[3]	(21,238)	[3]	(16,244)
Balance		566,211		594,208		618,887
Western Gas Partners, LP [Member] \| Fort Union [Member]
Schedule of Equity Method Investments [Line Items]
Balance	[4]	12,833		17,122
Investment earnings (loss), net of amortization	[4]	3,821		608
Impairment expense		(3,110)	[2],[4]	(3,000)		(9,500)
Contributions	[4]	0		0
Distributions	[4]	(4,217)		(1,543)
Distributions in excess of cumulative earnings	[3],[4]	(2,297)		(3,354)
Balance	[4]	$ 7,030		12,833		17,122
Equity investment ownership percentage		14.81%
Approval percentage		65.00%
Western Gas Partners, LP [Member] \| White Cliffs [Member]
Schedule of Equity Method Investments [Line Items]
Balance	[5]	$ 47,319		50,439
Investment earnings (loss), net of amortization	[5]	12,547		13,858
Impairment expense	[2],[5]	0
Contributions	[5]	277		441
Distributions	[5]	(11,965)		(13,277)
Distributions in excess of cumulative earnings	[3],[5]	(3,233)		(4,142)
Balance	[5]	$ 44,945		47,319		50,439
Equity investment ownership percentage		10.00%
Approval percentage		75.00%
Western Gas Partners, LP [Member] \| Rendezvous [Member]
Schedule of Equity Method Investments [Line Items]
Balance	[6]	$ 46,739		50,913
Investment earnings (loss), net of amortization	[6]	1,144		1,931
Impairment expense	[2],[6]	0
Contributions	[6]	0		0
Distributions	[6]	(3,085)		(3,873)
Distributions in excess of cumulative earnings	[3],[6]	(2,270)		(2,232)
Balance	[6]	$ 42,528		46,739		50,913
Equity investment ownership percentage		22.00%
Approval percentage		100.00%
Western Gas Partners, LP [Member] \| Mont Belvieu JV [Member]
Schedule of Equity Method Investments [Line Items]
Balance	[7]	$ 112,805		117,089
Investment earnings (loss), net of amortization	[7]	29,444		26,204
Impairment expense	[2],[7]	0
Contributions	[7]	0		0
Distributions	[7]	(29,482)		(26,243)
Distributions in excess of cumulative earnings	[3],[7]	(2,468)		(4,245)
Balance	[7]	$ 110,299		112,805		117,089
Equity investment ownership percentage		25.00%
Approval percentage		50.00%
Western Gas Partners, LP [Member] \| Mont Belvieu JV [Member] \| Fractionation Train [Member]
Schedule of Equity Method Investments [Line Items]
Assets, number of units		2
Western Gas Partners, LP [Member] \| Texas Express Gathering LLC [Member]
Schedule of Equity Method Investments [Line Items]
Balance	[8]	$ 15,846		16,283
Investment earnings (loss), net of amortization	[8]	3,350		708
Impairment expense	[2],[8]	0
Contributions	[8]	0		166
Distributions	[8]	(3,317)		(730)
Distributions in excess of cumulative earnings	[3],[8]	0		(581)
Balance	[8]	$ 15,879		15,846		16,283
Equity investment ownership percentage		20.00%
Approval percentage		50.00%
Western Gas Partners, LP [Member] \| Texas Express Gathering LLC [Member] \| Natural Gas Liquids Gathering System [Member]
Schedule of Equity Method Investments [Line Items]
Assets, number of units		2
Western Gas Partners, LP [Member] \| Texas Express Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Balance	[9]	$ 189,194		194,803
Investment earnings (loss), net of amortization	[9]	17,387		16,683
Impairment expense	[2],[9]	0
Contributions	[9]	107		(580)
Distributions	[9]	(17,639)		(16,934)
Distributions in excess of cumulative earnings	[3],[9]	(10,074)		(4,778)
Balance	[9]	$ 178,975		189,194		194,803
Equity investment ownership percentage		20.00%
Approval percentage		50.00%
Western Gas Partners, LP [Member] \| Front Range Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Balance	[10]	$ 169,472		172,238
Investment earnings (loss), net of amortization	[10]	17,501		18,725
Impairment expense	[2],[10]	0
Contributions	[10]	0		0
Distributions	[10]	(17,675)		(19,585)
Distributions in excess of cumulative earnings	[3],[10]	(2,743)		(1,906)
Balance	[10]	$ 166,555		$ 169,472		$ 172,238
Equity investment ownership percentage		33.33%
Approval percentage		50.00%

[1]	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, recognized under gathering, treating or processing agreements, and purchase and sale agreements.
[2]	Recorded in Impairments in the consolidated statements of operations.
[3]	Distributions in excess of cumulative earnings, classified as investing cash flows in the consolidated statements of cash flows, are calculated on an individual investment basis.
[4]	WES has a 14.81% interest in Fort Union, a joint venture that owns a gathering pipeline and treating facilities in the Powder River Basin. Anadarko is the construction manager and physical operator of the Fort Union facilities. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the owners’ firm gathering agreements, require 65% or unanimous approval of the owners.
[5]	WES has a 10% interest in White Cliffs, a limited liability company that owns a crude oil pipeline that originates in Platteville, Colorado and terminates in Cushing, Oklahoma. The third-party majority owner is the manager of the White Cliffs operations. Certain business decisions, including, but not limited to, approval of annual budgets and decisions with respect to significant expenditures, contractual commitments, acquisitions, material financings, dispositions of assets or admitting new members, require more than 75% approval of the members.
[6]	WES has a 22% interest in Rendezvous, a limited liability company that operates gas gathering facilities in Southwestern Wyoming. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the members’ gas servicing agreements, require unanimous approval of the members.
[7]	WES has a 25% interest in the Mont Belvieu JV, an entity formed to design, construct, and own two fractionation trains located in Mont Belvieu, Texas. A third party is the operator of the Mont Belvieu JV fractionation trains. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require 50% or unanimous approval of the owners.
[8]	WES has a 20% interest in TEG, which owns two NGL gathering systems that link natural gas processing plants to TEP. Midcoast Energy Partners, L.P., a wholly-owned subsidiary of Enbridge, Inc., is the operator of the two gathering systems. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the delegation, creation, appointment, or removal of officer positions require more than 50% approval of the members.
[9]	WES has a 20% interest in TEP, which owns an NGL pipeline that originates in Skellytown, Texas and extends to Mont Belvieu, Texas. Enterprise Products Operating LLC (“Enterprise”) is the operator of TEP. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require more than 50% approval of the members.
[10]	WES has a 33.33% interest in FRP, which owns an NGL pipeline that extends from Weld County, Colorado to Skellytown, Texas. Enterprise is the operator of FRP. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require more than 50% approval of the members.

Equity Investments - Summarized

Equity Investments - Summarized Combined Financial Data For Equity Investments - Income Statement Table (Details) - Western Gas Partners, LP [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Revenues	$ 703,424	$ 687,554	$ 667,554
Operating income	435,735	428,454	359,899
Net income	$ 434,749	$ 427,511	$ 359,443

Equity Investments - Summariz65

Equity Investments - Summarized Combined Financial Data For Equity Investments - Balance Sheet Table (Details) - Western Gas Partners, LP [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Current assets	$ 137,957	$ 118,472
Property, plant and equipment, net	2,512,214	2,626,466
Other assets	36,373	39,802
Total assets	2,686,544	2,784,740
Current liabilities	80,490	63,468
Non-current liabilities	7,447	6,662
Equity	2,598,607	2,714,610
Total liabilities and equity	$ 2,686,544	$ 2,784,740

Equity Investments - Additional

Equity Investments - Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Equity investment impairment loss	[1]	$ 3,110
Western Gas Partners, LP [Member] \| Fort Union [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value		$ (3,100)
Equity investment ownership percentage		14.81%
Equity investment impairment loss		$ 3,110	[1],[2]	$ 3,000	$ 9,500
Western Gas Partners, LP [Member] \| Fort Union [Member] \| Fair Value, Measurements, Nonrecurring [Member] \| Level 3 Inputs [Member] \| Income Approach Valuation Technique [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment fair value		8,500
Western Gas Partners, LP [Member] \| Rendezvous [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value		$ 36,200
Equity investment ownership percentage		22.00%
Equity investment impairment loss	[1],[3]	$ 0
Western Gas Partners, LP [Member] \| White Cliffs [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value		$ (6,900)
Equity investment ownership percentage		10.00%
Equity investment impairment loss	[1],[4]	$ 0
Western Gas Partners, LP [Member] \| White Cliffs [Member] \| Affiliates [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment ownership percentage		0.40%

[1]	Recorded in Impairments in the consolidated statements of operations.
[2]	WES has a 14.81% interest in Fort Union, a joint venture that owns a gathering pipeline and treating facilities in the Powder River Basin. Anadarko is the construction manager and physical operator of the Fort Union facilities. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the owners’ firm gathering agreements, require 65% or unanimous approval of the owners.
[3]	WES has a 22% interest in Rendezvous, a limited liability company that operates gas gathering facilities in Southwestern Wyoming. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the members’ gas servicing agreements, require unanimous approval of the members.
[4]	WES has a 10% interest in White Cliffs, a limited liability company that owns a crude oil pipeline that originates in Platteville, Colorado and terminates in Cushing, Oklahoma. The third-party majority owner is the manager of the White Cliffs operations. Certain business decisions, including, but not limited to, approval of annual budgets and decisions with respect to significant expenditures, contractual commitments, acquisitions, material financings, dispositions of assets or admitting new members, require more than 75% approval of the members.

Components of Working Capital -

Components of Working Capital - Accounts Receivable, Net Table (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Trade receivables, net		$ 160,194	$ 192,606
Other receivables, net		45	30,415
Total accounts receivable, net	[1]	$ 160,239	$ 223,021

[1]	Accounts receivable, net includes amounts receivable from affiliates (as defined in Note 1) of $36.1 million and $76.4 million as of December 31, 2017 and 2016, respectively. Accounts receivable, net as of December 31, 2016, also includes an insurance claim receivable related to an incident at the DBM complex. See Note 1.

Components of Working Capital68

Components of Working Capital - Other Current Assets Table (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other Current Assets [Line Items]
Natural gas liquids inventory	$ 10,788	$ 7,126
Imbalance receivables	1,640	3,483
Prepaid insurance	2,955	2,889
Total other current assets	$ 15,383	$ 13,498

Components of Working Capital69

Components of Working Capital - Accrued Liabilities Table (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Components Of Working Capital [Abstract]
Accrued interest expense		$ 40,646	$ 39,834
Short-term asset retirement obligations		2,304	3,114
Short-term remediation and reclamation obligations		833	630
Income taxes payable		2,495	1,006
Other accrued liabilities		1,714	606
Total accrued liabilities	[1]	$ 47,992	$ 45,190

[1]	Accrued liabilities includes affiliate amounts of $0.2 million and zero as of December 31, 2017 and 2016, respectively.

Asset Retirement Obligations -

Asset Retirement Obligations - Asset Retirement Obligations Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Carrying amount of asset retirement obligations at beginning of year	$ 142,407	$ 130,631
Liabilities incurred	16,153	5,515
Liabilities settled	(10,468)	(10,650)
Accretion expense	6,956	6,794
Revisions in estimated liabilities	(9,350)	10,117
Carrying amount of asset retirement obligations at end of year	$ 145,698	$ 142,407

Debt and Interest Expense - Deb

Debt and Interest Expense - Debt Outstanding Table (Details) - USD ($)		Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2016
Debt Instrument [Line Items]
Total long-term debt principal		$ 3,518,000,000	$ 3,148,000,000
Carrying value		3,492,712,000	3,119,461,000
Market Approach Valuation Technique [Member] \| Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[1]	3,622,177,000	3,224,199,000
WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Principal		28,000,000	28,000,000
Carrying value		28,000,000	28,000,000
WGP RCF [Member] \| Revolving Credit Facility [Member] \| Market Approach Valuation Technique [Member] \| Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[1]	28,000,000	28,000,000
Western Gas Partners, LP [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Principal		370,000,000	0
Carrying value		370,000,000	0
Western Gas Partners, LP [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member] \| Market Approach Valuation Technique [Member] \| Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[1]	370,000,000	0
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 5.375% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Principal		500,000,000	500,000,000
Carrying value		495,815,000	494,734,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 5.375% Senior Notes due 2021 [Member] \| Market Approach Valuation Technique [Member] \| Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[1]	530,647,000	536,252,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 4.000% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Principal		670,000,000	670,000,000
Carrying value		668,849,000	668,634,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 4.000% Senior Notes due 2022 [Member] \| Market Approach Valuation Technique [Member] \| Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[1]	684,043,000	681,723,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 2.600% Senior Notes due 2018 [Member]
Debt Instrument [Line Items]
Principal		350,000,000	350,000,000
Carrying value		349,684,000	349,188,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 2.600% Senior Notes due 2018 [Member] \| Market Approach Valuation Technique [Member] \| Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[1]	350,631,000	351,531,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 5.450% Senior Notes due 2044 [Member]
Debt Instrument [Line Items]
Principal		600,000,000	600,000,000	$ 200,000,000
Carrying value		593,234,000	593,132,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 5.450% Senior Notes due 2044 [Member] \| Market Approach Valuation Technique [Member] \| Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[1]	637,827,000	615,753,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 3.950% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Principal		500,000,000	500,000,000
Carrying value		491,885,000	490,971,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 3.950% Senior Notes due 2025 [Member] \| Market Approach Valuation Technique [Member] \| Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[1]	500,885,000	492,499,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 4.650% Senior Notes due 2026 [Member]
Debt Instrument [Line Items]
Principal		500,000,000	500,000,000
Carrying value		495,245,000	494,802,000
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 4.650% Senior Notes due 2026 [Member] \| Market Approach Valuation Technique [Member] \| Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[1]	$ 520,144,000	$ 518,441,000

[1]	Fair value is measured using the market approach and Level 2 inputs.

Debt and Interest Expense - D72

Debt and Interest Expense - Debt Activity Table (Details) - USD ($) $ in Thousands	Mar. 14, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Beginning balance		$ 3,119,461	$ 2,690,651
Other		3,251	810
Ending balance		3,492,712	3,119,461
Revolving Credit Facility [Member] \| WGP RCF [Member]
Debt Instrument [Line Items]
RCF borrowings	$ 25,000		28,000
Western Gas Partners, LP [Member] \| Revolving Credit Facility [Member] \| WES RCF [Member]
Debt Instrument [Line Items]
RCF borrowings		$ 370,000	600,000
Repayments of RCF borrowings			(900,000)
Senior Notes [Member] \| Western Gas Partners, LP [Member] \| 4.650% Senior Notes due 2026 [Member]
Debt Instrument [Line Items]
Issuance of senior notes			500,000
Senior Notes [Member] \| Western Gas Partners, LP [Member] \| 5.450% Senior Notes due 2044 [Member]
Debt Instrument [Line Items]
Issuance of senior notes			$ 200,000

Debt and Interest Expense - Int

Debt and Interest Expense - Interest Expense Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Interest expense	[1]	$ (144,615)	$ (116,628)	$ (113,874)
Third Parties [Member]
Debt Instrument [Line Items]
Long-term debt		(143,400)	(122,428)	(102,058)
Amortization of debt issuance costs and commitment fees		(7,970)	(7,509)	(5,734)
Capitalized interest		6,826	5,562	8,318
Interest expense		(144,544)	(124,375)	(99,474)
Affiliates [Member]
Debt Instrument [Line Items]
Interest expense	[2]	(71)	7,747	(14,400)
Affiliates [Member] \| Deferred Purchase Price Obligation - Anadarko [Member]
Debt Instrument [Line Items]
Interest expense, affiliate	[3]	71	(7,747)	14,398
Working Capital Facility [Member] \| Affiliates [Member]
Debt Instrument [Line Items]
Interest expense, affiliate		$ 0	$ 0	$ 2

[1]	Includes affiliate (as defined in Note 1) amounts of $(0.1) million, $7.7 million and $(14.4) million for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 2 and Note 12.
[2]	Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 2 and Note 12) and for the year ended December 31, 2015, includes interest expense recognized on the WGP WCF (see Note 12).
[3]	See Note 2 for a discussion of the Deferred purchase price obligation - Anadarko.

Debt and Interest Expense - Add

Debt and Interest Expense - Additional Information (Details) - USD ($)		Feb. 16, 2018	Oct. 31, 2016	Mar. 14, 2016	Jul. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Facility, maximum borrowing capacity								$ 250,000,000
Facility, expandable maximum borrowing capacity								$ 500,000,000
Borrowings - revolving credit facility				$ 25,000,000			$ 28,000,000
Facility, fee rate						0.30%	0.30%
Facility, outstanding borrowings						$ 28,000,000
Facility, available borrowing capacity						$ 222,000,000
Facility, interest rate at period end						3.57%	2.77%
Principal						$ 28,000,000	$ 28,000,000
Facility, expiration date						Mar. 14, 2019
WGP RCF [Member] \| Revolving Credit Facility [Member] \| Subsequent Event [Member]
Debt Instrument [Line Items]
Facility, maximum borrowing capacity		$ 35,000,000
Percentage Above Federal Funds Effective Rate [Member] \| Alternate Base Rate [Member] \| WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						0.50%
London Interbank Offered Rate (LIBOR) [Member] \| WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, variable rate floor						0.00%
London Interbank Offered Rate (LIBOR) [Member] \| Alternate Base Rate [Member] \| WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						1.00%
Minimum [Member] \| WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Facility, fee rate						0.30%
Minimum [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						2.00%
Minimum [Member] \| Base Rate [Member] \| WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						1.00%
Maximum [Member] \| WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Facility, fee rate						0.50%
Maximum [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						2.75%
Maximum [Member] \| Base Rate [Member] \| WGP RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						1.75%
Western Gas Partners, LP [Member]
Debt Instrument [Line Items]
Units issued						885,760	946,261
Western Gas Partners, LP [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Facility, maximum borrowing capacity						$ 1,200,000,000
Facility, expandable maximum borrowing capacity						1,500,000,000
Borrowings - revolving credit facility						$ 370,000,000	$ 600,000,000
Facility, fee rate						0.20%	0.20%
Facility, outstanding borrowings						$ 370,000,000
Facility, available borrowing capacity						$ 825,400,000
Facility, interest rate at period end						2.87%	2.07%
Principal						$ 370,000,000	$ 0
Facility, expiration date						Feb. 26, 2020
Outstanding letters of credit						$ 4,600,000
Western Gas Partners, LP [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member] \| Subsequent Event [Member]
Debt Instrument [Line Items]
Facility, maximum borrowing capacity		$ 1,500,000,000
Facility, expiration date		Feb. 15, 2023
Western Gas Partners, LP [Member] \| Percentage Above Federal Funds Effective Rate [Member] \| Alternate Base Rate [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						0.50%
Western Gas Partners, LP [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| Alternate Base Rate [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						1.00%
Western Gas Partners, LP [Member] \| Minimum [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Facility, fee rate						0.15%
Western Gas Partners, LP [Member] \| Minimum [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						0.975%
Western Gas Partners, LP [Member] \| Minimum [Member] \| Base Rate [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						0.00%
Western Gas Partners, LP [Member] \| Maximum [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Facility, fee rate						0.30%
Western Gas Partners, LP [Member] \| Maximum [Member] \| London Interbank Offered Rate (LIBOR) [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						1.45%
Western Gas Partners, LP [Member] \| Maximum [Member] \| Base Rate [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Applicable margin added						0.45%
Western Gas Partners, LP [Member] \| Springfield [Member] \| WES RCF [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowings - revolving credit facility	[1]			$ 247,500,000
Western Gas Partners, LP [Member] \| Common Units [Member] \| Springfield [Member]
Debt Instrument [Line Items]
Units issued	[1]			2,089,602
Western Gas Partners, LP [Member] \| Common Units [Member] \| Springfield [Member] \| Western Gas Equity Partners, LP [Member]
Debt Instrument [Line Items]
Units issued				835,841
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 5.375% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Fixed interest rate						5.375%
Principal						$ 500,000,000	500,000,000
Debt instrument, maturity date						Jun. 1, 2021
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 4.000% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Fixed interest rate						4.00%
Principal						$ 670,000,000	670,000,000
Debt instrument, maturity date						Jul. 1, 2022
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 2.600% Senior Notes due 2018 [Member]
Debt Instrument [Line Items]
Fixed interest rate						2.60%
Principal						$ 350,000,000	350,000,000
Debt instrument, maturity date						Aug. 15, 2018
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 5.450% Senior Notes due 2044 [Member]
Debt Instrument [Line Items]
Fixed interest rate						5.45%
Principal			$ 200,000,000			$ 600,000,000	600,000,000
Offering percent			102.776%
Effective interest rate			5.53%
Underwriting discount			$ 1,800,000
Debt instrument, maturity date						Apr. 1, 2044
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 3.950% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Fixed interest rate						3.95%
Principal						$ 500,000,000	500,000,000
Debt instrument, maturity date						Jun. 1, 2025
Western Gas Partners, LP [Member] \| Senior Notes [Member] \| 4.650% Senior Notes due 2026 [Member]
Debt Instrument [Line Items]
Fixed interest rate						4.65%
Principal						$ 500,000,000	$ 500,000,000
Offering percent					99.796%
Effective interest rate					4.787%
Underwriting discount					$ 3,100,000
Debt instrument, maturity date						Jul. 1, 2026

[1]	WES acquired Springfield Pipeline LLC (“Springfield”) from Anadarko for $750.0 million, consisting of $712.5 million in cash and the issuance of 1,253,761 of WES common units. Springfield owns a 50.1% interest in an oil gathering system and a gas gathering system. The Springfield oil and gas gathering systems (collectively, the “Springfield system”) are located in Dimmit, La Salle, Maverick and Webb Counties in South Texas. WES financed the cash portion of the acquisition through: (i) borrowings of $247.5 million on the WES RCF, (ii) the issuance of 835,841 of WES common units to WGP and (iii) the issuance of WES Series A Preferred units to private investors. See Note 4 for further information regarding WES’s Series A Preferred units. WGP financed the purchase of the WES common units by borrowing $25.0 million under the WGP RCF. See Note 12.

Commitments and Contingencies -

Commitments and Contingencies - Operating Lease Obligations Table (Details) - Western Gas Partners, LP [Member] $ in Thousands	Dec. 31, 2017USD ($)
Loss Contingencies [Line Items]
2,018	$ 8,402
2,019	7,506
2,020	1,615
2,021	460
2,022	467
Thereafter	2,021
Total	$ 20,471

Commitments and Contingencies76

Commitments and Contingencies - Additional Information (Details) - Western Gas Partners, LP [Member] - USD ($) $ in Millions	Mar. 17, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Liability for remediation and reclamation obligations		$ 1.8	$ 2.2
Rent expense associated with office, warehouse and equipment leases		42.5	$ 35.9	$ 34.1
DBJV Arbitration [Member] \| Pending Litigation [Member]
Loss Contingencies [Line Items]
Gathering Fees Sought In Arbitration		190
Fees Sought In Counterclaim		$ 18
Percentage recovery from a third party		50.00%
Percentage due to third party		50.00%
Delaware Basin JV Gathering LLC [Member] \| DBJV Arbitration [Member]
Loss Contingencies [Line Items]
Percentage ownership interest	50.00%
Percentage third-party ownership interest	50.00%