Western Midstream Partners 8-K 17 May 19 2018 FY Other Events Financial data

Document and Entity Information

Document and Entity Information	12 Months Ended
	Dec. 31, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	Western Midstream Operating, LP
Entity Central Index Key	0001414475
Document Type	8-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Entity Emerging Growth Company	false

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues and Other
Revenues and other	[1]	$ 2,299,658	$ 2,429,614	$ 1,941,330
Equity income, net – affiliates	[1],[2]	195,469	115,141	101,692
Operating expenses
Cost of product	[1],[3]	415,505	953,792	517,371
Operation and maintenance	[1],[3]	480,861	345,617	332,405
General and administrative	[1],[3]	63,166	51,077	48,701
Property and other taxes	[1]	51,848	53,147	45,638
Depreciation and amortization	[1]	389,164	318,771	295,959
Impairments	[1]	230,584	180,051	17,822
Total operating expenses	[1]	1,631,128	1,902,455	1,257,896
Gain (loss) on divestiture and other, net	[1],[4]	1,312	132,388	(14,641)
Proceeds from business interruption insurance claims	[1]	0	29,882	16,270
Operating income (loss)	[1]	865,311	804,570	786,755
Interest income - affiliates	[1],[5]	16,900	16,900	16,900
Interest expense	[1],[6]	(181,796)	(140,291)	(107,565)
Other income (expense), net	[1]	(4,955)	1,299	479
Income (loss) before income taxes	[1]	695,460	682,478	696,569
Income tax expense (benefit)	[1]	58,934	(59,923)	32,969
Net income (loss)	[1]	636,526	742,401	663,600
Net income attributable to noncontrolling interest	[1]	8,609	10,735	10,963
Net income (loss) attributable to Western Gas Partners, LP	[1]	627,917	731,666	652,637
Limited partners' interest in net income (loss):
Pre-acquisition net (income) loss allocated to Anadarko	[1]	(182,142)	(164,183)	(72,632)
General partner interest in net (income) loss	[1],[7]	(346,538)	(303,835)	(236,561)
Series A Preferred Units [Member]
Limited partners' interest in net income (loss):
Limited partners’ interest in net income (loss)	[1],[7],[8]	0	(42,373)	(76,893)
Common and Class C Units [Member]
Limited partners' interest in net income (loss):
Limited partners’ interest in net income (loss)	[1],[7]	(99,237)	(221,275)	(266,551)
Common Units [Member]
Limited partners' interest in net income (loss):
Limited partners’ interest in net income (loss)	[8]	$ (84,334)	$ (192,066)	$ (226,611)
Net income (loss) per common unit – basic and diluted	[1],[7],[9]	$ 0.55	$ 1.30	$ 1.74
Service Revenues - Fee Based [Member]
Revenues and Other
Revenues and other		$ 1,905,728
Service Revenues - Product Based [Member]
Revenues and Other
Revenues and other		88,785
Product Sales [Member]
Revenues and Other
Revenues and other		303,020
Affiliates [Member]
Revenues and Other
Revenues and other	[1],[2]	1,353,711	$ 1,539,105	$ 1,358,918
Operating expenses
Cost of product	[2]	168,535	74,560	75,983
Operation and maintenance	[10]	115,948	82,249	82,133
General and administrative	[11]	48,819	42,411	41,176
Total operating expenses		333,302	199,220	199,292
Interest expense	[12],[13]	(6,746)	(224)	7,747
Affiliates [Member] | Service Revenues - Fee Based [Member]
Revenues and Other
Revenues and other	[1]	1,070,066	769,305	853,837
Affiliates [Member] | Service Revenues - Product Based [Member]
Revenues and Other
Revenues and other	[1]	3,339	0	0
Affiliates [Member] | Product Sales [Member]
Revenues and Other
Revenues and other	[1]	280,306	753,724	505,081
Affiliates [Member] | Other [Member]
Revenues and Other
Revenues and other	[1]	0	16,076	0
Third Parties [Member]
Revenues and Other
Revenues and other	[1]	945,947	890,509	582,412
Operating expenses
Interest expense		(175,050)	(140,067)	(115,312)
Third Parties [Member] | Service Revenues - Fee Based [Member]
Revenues and Other
Revenues and other	[1]	835,662	588,571	484,093
Third Parties [Member] | Service Revenues - Product Based [Member]
Revenues and Other
Revenues and other	[1]	85,446	0	0
Third Parties [Member] | Product Sales [Member]
Revenues and Other
Revenues and other	[1]	22,714	297,486	94,168
Third Parties [Member] | Other [Member]
Revenues and Other
Revenues and other	[1]	$ 2,125	$ 4,452	$ 4,151
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Represents amounts earned or incurred on and subsequent to the date of the acquisition of Partnership assets, as well as amounts earned or incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.
[3]	Cost of product includes product purchases from affiliates (as defined in Note 1) of $168.5 million, $74.6 million and $76.0 million for the years ended December 31, 2018, 2017 and 2016, respectively. Operation and maintenance includes charges from affiliates of $115.9 million, $82.2 million and $82.1 million for the years ended December 31, 2018, 2017 and 2016, respectively. General and administrative includes charges from affiliates of $48.8 million, $42.4 million and $41.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 6.
[4]	Includes losses related to an incident at the DBM complex for the year ended December 31, 2017. See Note 1.
[5]	Represents interest income recognized on the note receivable from Anadarko.
[6]	Includes affiliate (as defined in Note 1) amounts of $(6.7) million, $(0.2) million and $7.7 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 3 and Note 13.
[7]	See Note 5 for the calculation of net income (loss) per common unit.
[8]	Adjusted to reflect amortization of the beneficial conversion features.
[9]	The impact of Class C units would be anti-dilutive for all periods presented and the conversion of Series A Preferred units would be anti-dilutive for the years ended December 31, 2017 and 2016. On March 1, 2017, 50% of the outstanding Series A Preferred units converted into common units on a one-for-one basis, and on May 2, 2017, all remaining Series A Preferred units converted into common units on a one-for-one basis.
[10]	Represents expenses incurred on and subsequent to the date of the acquisition of Partnership assets, as well as expenses incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.
[11]	Represents general and administrative expense incurred on and subsequent to the date of the acquisition of Partnership assets, as well as a management services fee for expenses incurred by Anadarko for periods prior to the acquisition of the Partnership assets by the Partnership. These amounts include equity-based compensation expense allocated to the Partnership by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plan within this Note 6) and amounts charged by Anadarko under the omnibus agreement.
[12]	Includes amounts related to the APCWH Note Payable (see Note 13 and Note 15).
[13]	Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 3 and Note 13).

Consolidated Statements of Op_2

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cost of product	[1],[2]	$ 415,505	$ 953,792	$ 517,371
Operation and maintenance	[1],[2]	480,861	345,617	332,405
General and administrative	[1],[2]	63,166	51,077	48,701
Interest expense	[2],[3]	(181,796)	(140,291)	(107,565)
Affiliates [Member]
Cost of product	[4]	168,535	74,560	75,983
Operation and maintenance	[5]	115,948	82,249	82,133
General and administrative	[6]	48,819	42,411	41,176
Interest expense	[7],[8]	$ (6,746)	$ (224)	$ 7,747
[1]	Cost of product includes product purchases from affiliates (as defined in Note 1) of $168.5 million, $74.6 million and $76.0 million for the years ended December 31, 2018, 2017 and 2016, respectively. Operation and maintenance includes charges from affiliates of $115.9 million, $82.2 million and $82.1 million for the years ended December 31, 2018, 2017 and 2016, respectively. General and administrative includes charges from affiliates of $48.8 million, $42.4 million and $41.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 6.
[2]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[3]	Includes affiliate (as defined in Note 1) amounts of $(6.7) million, $(0.2) million and $7.7 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 3 and Note 13.
[4]	Represents amounts earned or incurred on and subsequent to the date of the acquisition of Partnership assets, as well as amounts earned or incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.
[5]	Represents expenses incurred on and subsequent to the date of the acquisition of Partnership assets, as well as expenses incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.
[6]	Represents general and administrative expense incurred on and subsequent to the date of the acquisition of Partnership assets, as well as a management services fee for expenses incurred by Anadarko for periods prior to the acquisition of the Partnership assets by the Partnership. These amounts include equity-based compensation expense allocated to the Partnership by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plan within this Note 6) and amounts charged by Anadarko under the omnibus agreement.
[7]	Includes amounts related to the APCWH Note Payable (see Note 13 and Note 15).
[8]	Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 3 and Note 13).

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	[1]	$ 90,448	$ 78,814
Accounts receivable, net	[1],[2]	221,373	160,910
Other current assets	[1],[3]	26,181	15,409
Total current assets	[1]	338,002	255,133
Note receivable - Anadarko	[1]	260,000	260,000
Property, plant and equipment
Cost	[1]	11,258,773	8,979,618
Less accumulated depreciation	[1]	2,848,420	2,213,718
Net property, plant and equipment	[1]	8,410,353	6,765,900
Goodwill	[1]	445,800	445,800
Other intangible assets	[1]	841,408	872,187
Equity investments	[1]	1,092,088	817,352
Other assets	[1],[4]	67,194	11,757
Total assets	[1]	11,454,845	9,428,129
Current liabilities
Accounts and imbalance payables	[1]	443,343	466,838
Accrued ad valorem taxes	[1]	36,986	33,136
Accrued liabilities	[1],[5]	127,874	47,899
Total current liabilities	[1]	608,203	547,873
Long-term liabilities
Long-term debt	[1]	4,787,381	3,464,712
APCWH Note Payable	[1],[6]	427,493	98,966
Deferred income taxes	[1]	280,017	139,635
Asset retirement obligations	[1]	300,024	152,267
Other liabilities	[1],[7]	132,130	3,494
Total long-term liabilities	[1]	5,927,045	3,859,074
Total liabilities	[1]	6,535,248	4,406,947
Equity and partners' capital
General partner units (2,583,068 units issued and outstanding at December 31, 2018 and 2017)	[1]	206,862	179,232
Net investment by Anadarko	[1]	1,388,018	1,050,171
Total partners' capital	[1]	4,861,830	4,959,453
Noncontrolling interest	[1]	57,767	61,729
Total equity and partners' capital	[1]	4,919,597	5,021,182
Total liabilities, equity and partners' capital	[1]	11,454,845	9,428,129
Common Units [Member]
Equity and partners' capital
Common units and Class C units	[1]	2,475,540	2,950,010
Class C Units [Member]
Equity and partners' capital
Common units and Class C units	[1],[8]	$ 791,410	$ 780,040
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Accounts receivable, net includes amounts receivable from affiliates (as defined in Note 1) of $72.8 million and $36.3 million as of December 31, 2018 and 2017, respectively.
[3]	Other current assets includes affiliate amounts of $3.7 million and zero as of December 31, 2018 and 2017, respectively.
[4]	Other assets includes affiliate amounts of $42.2 million and zero as of December 31, 2018 and 2017, respectively.
[5]	Accrued liabilities includes affiliate amounts of $2.2 million and $0.2 million as of December 31, 2018 and 2017, respectively.
[6]	See Note 6 and Note 15.
[7]	Other liabilities includes affiliate amounts of $47.8 million and $0.7 million as of December 31, 2018 and 2017, respectively.
[8]	All outstanding Class C units will convert into the Partnership’s common units on a one-for-one basis immediately prior to the closing of the Merger (as defined in Note 15), if consummated. If the Merger is not consummated, the conversion will occur on March 1, 2020, unless the Partnership elects to convert such units earlier or Anadarko extends the conversion date. See Note 5 and Note 15.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
General partner units issued		2,583,068	2,583,068
General partner units outstanding		2,583,068	2,583,068
Accounts receivable, net	[1],[2]	$ 221,373	$ 160,910
Other current assets	[2],[3]	26,181	15,409
Other assets	[2],[4]	67,194	11,757
Accrued liabilities	[2],[5]	127,874	47,899
Other liabilities	[2],[6]	132,130	3,494
Affiliates [Member]
Accounts receivable, net		72,800	36,300
Other current assets		3,700	0
Other assets		42,200	0
Accrued liabilities		2,200	200
Other liabilities		$ 47,800	$ 700
Common Units [Member]
Units issued		152,609,285	152,602,105
Units outstanding		152,609,285	152,602,105
Class C Units [Member]
Units issued		14,372,665	13,243,883
Units outstanding		14,372,665	13,243,883
Class C units, common units issued upon conversion		1
[1]	Accounts receivable, net includes amounts receivable from affiliates (as defined in Note 1) of $72.8 million and $36.3 million as of December 31, 2018 and 2017, respectively.
[2]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[3]	Other current assets includes affiliate amounts of $3.7 million and zero as of December 31, 2018 and 2017, respectively.
[4]	Other assets includes affiliate amounts of $42.2 million and zero as of December 31, 2018 and 2017, respectively.
[5]	Accrued liabilities includes affiliate amounts of $2.2 million and $0.2 million as of December 31, 2018 and 2017, respectively.
[6]	Other liabilities includes affiliate amounts of $47.8 million and $0.7 million as of December 31, 2018 and 2017, respectively.

Consolidated Statements of Equi

Consolidated Statements of Equity and Partners' Capital - USD ($) $ in Thousands		Total		Net Investment by Anadarko [Member]	Common Units [Member]	Class C Units [Member]	Series A Preferred Units [Member]	General Partner Units [Member]	Noncontrolling Interest [Member]
Balance at Dec. 31, 2015	[1]	$ 4,643,386		$ 1,155,956	$ 2,588,991	$ 710,891	$ 0	$ 120,164	$ 67,384
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income (loss)	[1]	663,600		72,632	269,018	28,642	45,784	236,561	10,963
Above-market component of swap agreements with Anadarko	[1],[2]	45,820			45,820
Issuance of common units, net of offering expenses	[1]	25,000			25,000
Issuance of Series A Preferred units, net of offering expenses	[1]	686,937					686,937
Beneficial conversion feature of Series A Preferred units	[1]	0			93,409		(93,409)
Amortization of beneficial conversion feature of Class C units and Series A Preferred units	[1]	0			(42,407)	11,298	31,109
Distributions to noncontrolling interest owner	[1]	(13,784)							(13,784)
Distributions to unitholders	[1]	(671,938)			(428,231)		(30,876)	(212,831)
Acquisitions from affiliates	[1]	(712,500)		(553,833)	(158,667)
Revision to Deferred purchase price obligation – Anadarko	[1],[3]	139,487			139,487
Contributions of equity-based compensation from Anadarko	[1]	4,214			4,131			83
Net pre-acquisition contributions from (distributions to) Anadarko	[1]	(42,224)		(42,224)
Net contributions from (distributions to) Anadarko of other assets	[1]	(451)	[4]	130	(572)			(9)
Elimination of net deferred tax liabilities	[1]	129,229		129,229
Other	[1]	893			893
Balance at Dec. 31, 2016	[1]	4,897,669		761,890	2,536,872	750,831	639,545	143,968	64,563
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income (loss)	[1]	742,401		164,183	231,405	24,790	7,453	303,835	10,735
Above-market component of swap agreements with Anadarko	[1],[2]	58,551			58,551
Conversion of Series A Preferred units into common units	[1],[5]	0			686,936		(686,936)
Amortization of beneficial conversion feature of Class C units and Series A Preferred units	[1]	0			(66,718)	4,419	62,299
Distributions to noncontrolling interest owner	[1]	(13,569)							(13,569)
Distributions to unitholders	[1]	(801,300)			(510,228)		(22,361)	(268,711)
Acquisitions from affiliates	[1]	0		(1,263)	1,263
Revision to Deferred purchase price obligation – Anadarko	[1],[3]	4,165			4,165
Contributions of equity-based compensation from Anadarko	[1]	4,563			4,473			90
Net pre-acquisition contributions from (distributions to) Anadarko	[1]	126,866		126,866
Net contributions from (distributions to) Anadarko of other assets	[1]	3,189	[4]		3,139			50
Elimination of net deferred tax liabilities	[1]	(1,505)		(1,505)
Other	[1]	152			152
Balance at Dec. 31, 2017	[1]	5,021,182		1,050,171	2,950,010	780,040	0	179,232	61,729
Increase (Decrease) in Partners' Capital [Roll Forward]
Net income (loss)	[1]	636,526		182,142	87,581	11,656	0	346,538	8,609
Above-market component of swap agreements with Anadarko	[1],[2]	51,618			51,618
Amortization of beneficial conversion feature of Class C units and Series A Preferred units	[1]	0			(3,247)	3,247
Distributions to noncontrolling interest owner	[1]	(13,529)							(13,529)
Distributions to unitholders	[1]	(893,649)			(575,323)			(318,326)
Contributions of equity-based compensation from Anadarko	[1]	5,727			5,613			114
Net pre-acquisition contributions from (distributions to) Anadarko	[1]	97,755		97,755
Net contributions from (distributions to) Anadarko of other assets	[1]	58,835	[4]	58,835
Elimination of net deferred tax liabilities	[1]	(1,514)		(1,514)
Other	[1]	396			396
Balance at Dec. 31, 2018	[1]	4,919,597		1,388,018	2,475,540	791,410	$ 0	206,862	57,767
Increase (Decrease) in Partners' Capital [Roll Forward]
Cumulative effect of accounting change	[1],[6]	$ (43,750)		$ 629	$ (41,108)	$ (3,533)		$ (696)	$ 958
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	See Note 6.
[3]	See Note 3.
[4]	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 6.
[5]	See Note 5.
[6]	See Note 1.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Cash flows from operating activities
Net income (loss)	[1]	$ 636,526		$ 742,401		$ 663,600
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	[1]	389,164		318,771		295,959
Impairments	[1]	230,584		180,051		17,822
Non-cash equity-based compensation expense	[1]	6,153		4,922		4,735
Deferred income taxes	[1]	139,048		(53,138)		51,192
Accretion and amortization of long-term obligations, net	[1]	5,142		4,254		(3,789)
Equity income, net – affiliates	[1],[2]	(195,469)		(115,141)		(101,692)
Distributions from equity investment earnings – affiliates	[1]	187,392		117,093		104,948
(Gain) loss on divestiture and other, net	[1],[3]	(1,312)		(132,388)		14,641
(Gain) loss on interest-rate swaps	[1]	7,972		0		0
Lower of cost or market inventory adjustments	[1]	752		145		168
Changes in assets and liabilities:
(Increase) decrease in accounts receivable, net	[1]	(60,460)		(16,177)		(48,441)
Increase (decrease) in accounts and imbalance payables and accrued liabilities, net	[1]	44,424		(947)		60,696
Change in other items, net	[1]	(37,802)		(3,048)		819
Net cash provided by operating activities	[1]	1,352,114		1,046,798		1,060,658
Cash flows from investing activities
Capital expenditures	[1]	(1,948,595)		(1,028,319)		(554,121)
Investments in equity affiliates	[1]	(133,629)	[4]	(2,884)		(58,726)
Distributions from equity investments in excess of cumulative earnings – affiliates	[1]	29,585	[5]	31,659	[5]	29,725
Proceeds from property insurance claims	[1]	0		22,977		17,465
Net cash used in investing activities	[1]	(2,210,813)		(1,133,324)		(1,229,874)
Cash flows from financing activities
Borrowings, net of debt issuance costs	[1],[6]	2,671,344		468,803		1,297,218
Repayments of debt	[1]	(1,040,000)		0		(900,000)
Increase (decrease) in outstanding checks	[1]	(3,206)		5,593		2,079
Proceeds from the issuance of common units, net of offering expenses	[1]	0		(183)		25,000
Distributions to unitholders	[1],[7]	(893,649)		(801,300)		(671,938)
Distributions to noncontrolling interest owner	[1]	(13,529)		(13,569)		(13,784)
Net contributions from (distributions to) Anadarko	[1]	97,755		126,866		(42,224)
Above-market component of swap agreements with Anadarko	[1],[7]	51,618		58,551		45,820
Net cash provided by (used in) financing activities	[1]	870,333		(192,585)		429,108
Net increase (decrease) in cash and cash equivalents	[1]	11,634		(279,111)		259,892
Cash and cash equivalents at beginning of period	[1]	78,814		357,925		98,033
Cash and cash equivalents at end of period	[1]	90,448		78,814		357,925
Supplemental disclosures
Accretion expense and revisions to the Deferred purchase price obligation – Anadarko	[1],[8]	0		(4,094)		(147,234)
Net distributions to (contributions from) Anadarko of other assets	[1],[9]	(58,835)		(3,189)		451
Interest paid, net of capitalized interest	[1]	139,482		135,079		98,241
Taxes paid (reimbursements received)	[1]	2,408		1,194		838
Accrued capital expenditures	[1]	274,632		312,720		87,586
Fair value of properties and equipment from non-cash third party transactions	[1],[8]	0		551,453		0
Series A Preferred Units [Member]
Cash flows from financing activities
Proceeds from the issuance of Series A Preferred units, net of offering expenses	[1]	0		0		686,937
Affiliates [Member]
Cash flows from investing activities
Contributions in aid of construction costs from affiliates	[1]	0		1,387		6,135
Acquisitions	[1]	(254)		(3,910)		(716,465)
Proceeds from the sale of assets	[1]	0		0		623
Cash flows from financing activities
Settlement of the Deferred purchase price obligation - Anadarko	[1],[8]	0		(37,346)		0
Proceeds from the issuance of common units, net of offering expenses	[10]	0		0		25,000
Distributions to unitholders	[11]	(514,906)		(452,777)		(382,711)
Third Parties [Member]
Cash flows from investing activities
Acquisitions	[1]	(161,858)		(177,798)		0
Proceeds from the sale of assets	[1]	$ 3,938		$ 23,564		$ 45,490
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Represents amounts earned or incurred on and subsequent to the date of the acquisition of Partnership assets, as well as amounts earned or incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.
[3]	Includes losses related to an incident at the DBM complex for the year ended December 31, 2017. See Note 1.
[4]	Includes capitalized interest of $1.4 million related to the construction of the Cactus II pipeline.
[5]	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.
[6]	For the years ended December 31, 2018 and 2017, includes $321.8 million and $98.8 million of borrowings, respectively, under the APCWH Note Payable.
[7]	See Note 6.
[8]	See Note 3.
[9]	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 6.
[10]	Represents proceeds from the issuance of 835,841 common units to WGP as partial funding for the acquisition of Springfield (see Note 3).
[11]	Represents distributions paid under the partnership agreement (see Note 4 and Note 5).

Consolidated Statements of Ca_2

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],[2]
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)
Affiliates [Member]
APCWH Note Payable borrowings	$ 98,813	[3]
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	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 6.
[3]	Includes amounts related to the APCWH Note Payable (see Note 13 and Note 15).

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES General. Western Gas Partners, LP is a growth-oriented Delaware master limited partnership (“MLP”) formed by Anadarko Petroleum Corporation in 2007 to acquire, own, develop and operate midstream assets. For purposes of these consolidated financial statements, the “Partnership” refers to Western Gas Partners, LP and its subsidiaries. The Partnership’s general partner, Western Gas Holdings, LLC (the “general partner”), is owned by Western Gas Equity Partners, LP (“WGP”), a Delaware MLP formed by Anadarko Petroleum Corporation in September 2012 to own the Partnership’s general partner, as well as a significant limited partner interest in the Partnership. WGP has no independent operations or material assets other than owning the partnership interests in the Partnership (see Holdings of Partnership equity in Note 5 ). Western Gas Equity Holdings, LLC is WGP’s general partner and is a wholly owned subsidiary of Anadarko Petroleum Corporation. “Anadarko” refers to Anadarko Petroleum Corporation and its subsidiaries, excluding the Partnership and the general partner, and “affiliates” refers to subsidiaries of Anadarko, excluding the Partnership, 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”), Front Range Pipeline LLC (“FRP”), Whitethorn Pipeline Company LLC (“Whitethorn LLC”), Cactus II Pipeline LLC (“Cactus II”), Saddlehorn Pipeline Company, LLC (“Saddlehorn”), Panola Pipeline Company, LLC (“Panola”), Mi Vida JV LLC (“Mi Vida”) and Ranch Westex JV LLC (“Ranch Westex”). See Note 3 . 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. The “West Texas complex” refers to the Delaware Basin Midstream, LLC (“DBM”) complex and DBJV and Haley systems, all of which were combined into a single complex effective January 1, 2018. The Partnership 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, the Partnership also buys and sells natural gas, NGLs and condensate on behalf of itself and as agent for its customers under certain of its contracts. The Partnership provides these midstream services for Anadarko, as well as for third-party customers. As of December 31, 2018 , the Partnership’s assets and investments, including AMA (as defined in Note 3 ), consisted of the following: Owned and Operated Operated Interests Non-Operated Interests Equity Interests Gathering systems (1) 17 2 3 2 Treating facilities 34 3 — 3 Natural gas processing plants/trains 23 3 — 5 NGLs pipelines 2 — — 4 Natural gas pipelines 5 — — — Oil pipelines 3 1 — 3 (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. Mentone Train I, a processing train that is part of the West Texas complex, and an additional water system at the DBM water systems commenced operation in the fourth quarter of 2018. Mentone Train II, a second processing train that is part of the West Texas complex, is expected to commence operation in the first quarter of 2019. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Basis of presentation. The following table outlines the Partnership’s ownership interests and the accounting method of consolidation used in the Partnership’s consolidated financial statements for entities not wholly owned: Percentage Interest Equity investments (1) Fort Union 14.81 % White Cliffs 10.00 % Rendezvous 22.00 % Mont Belvieu JV 25.00 % TEP 20.00 % TEG 20.00 % FRP 33.33 % Whitethorn 20.00 % Cactus II 15.00 % Saddlehorn 20.00 % Panola 15.00 % Mi Vida 50.00 % Ranch Westex 50.00 % Proportionate consolidation (2) Marcellus Interest systems 33.75 % Springfield system 50.10 % Full consolidation Chipeta (3) 75.00 % (1) Investments in non-controlled entities over which the Partnership exercises significant influence are accounted for under the equity method. “Equity investment throughput” refers to the Partnership’s share of average throughput for these investments. (2) The Partnership proportionately consolidates its 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 interest in the consolidated financial statements. 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 the Partnership and entities in which it holds a controlling financial interest. All significant intercompany transactions have been eliminated. Adjustments to previously issued financial statements. The Partnership’s consolidated statements of operations for the year ended December 31, 2018, include adjustments to revenue and cost of product expense of the following amounts: (i) $42.6 million increase in Service revenues - fee based, (ii) $13.8 million increase in Product sales and (iii) $56.4 million increase in Cost of product; all of which relate to the nine months ended September 30, 2018. During the third quarter of 2018, management determined that under ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (“Topic 606”) adopted on January 1, 2018, the Partnership’s marketing affiliate was acting as the Partnership’s agent in certain product sales transactions on behalf of the Partnership and in performing marketing services on behalf of the Partnership’s customers. The adjustments have no impact to Operating income (loss), Net income (loss), the balance sheets, cash flows or any non-GAAP metric the Partnership uses to evaluate its operations (see How We Evaluate Our Operations under Part II, Item 7 of Exhibit 99.1 to this Current Report on Form 8-K) and are not considered material to the Partnership’s results of operations for the year ended December 31, 2018. The Partnership will revise its previously reported unaudited financial statements for the 2018 interim periods to reflect the adjustments in future filings. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Presentation of Partnership assets. The term “Partnership assets” includes both the assets owned and the interests accounted for under the equity method by the Partnership, including AMA (as defined in Note 3 ), as of December 31, 2018 (see Note 10 ). Because Anadarko controls the Partnership through its control of WGP, which owns the Partnership’s entire general partner interest, each acquisition of Partnership assets from Anadarko has been considered a transfer of net assets between entities under common control. As such, the Partnership assets acquired from Anadarko were initially recorded at Anadarko’s historic carrying value, which did not correlate to the total acquisition price paid by the Partnership. Further, after an acquisition of assets from Anadarko, the Partnership is required to recast its financial statements to include the activities of such Partnership assets from the date of common control. For those periods requiring recast, the consolidated financial statements for periods prior to the Partnership’s acquisition of the Partnership assets from Anadarko, including AMA, 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 the Partnership had owned the Partnership assets during the periods reported. Net income (loss) attributable to the Partnership assets acquired from Anadarko for periods prior to the Partnership’s acquisition of the Partnership 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 included 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. Shutdown of gathering systems. In May 2018, after assessing a number of factors, with safety and protection of the environment as the primary focus, the Partnership decided to take the Kitty Draw gathering system in Wyoming (part of the Hilight system) and the Third Creek gathering system in Colorado (part of the DJ Basin complex) permanently out of service. Results for the year ended December 31, 2018 , reflect (i) an accrual of $10.9 million in anticipated costs associated with the shutdown of the systems, recorded as a reduction in affiliate Product sales in the consolidated statements of operations and (ii) impairment expense of $134.0 million associated with reducing the net book value of the gathering systems and increasing the asset retirement obligation. 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). 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) 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 the Partnership’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 13 . 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. Allowance for uncollectible accounts. 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 the Partnership may establish credit limits for significant third-party customers. The allowance for uncollectible accounts was immaterial at December 31, 2018 and 2017 . Imbalances. The consolidated balance sheets include imbalance receivables and payables resulting from differences in volumes received into the Partnership’s systems and volumes delivered by the Partnership to customers. Volumes owed to or by the Partnership 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 the Partnership are valued at the Partnership’s weighted-average cost as of the balance sheet dates and are settled in-kind. As of December 31, 2018 , imbalance receivables and payables were $9.0 million and $9.6 million , respectively. As of December 31, 2017 , imbalance receivables and payables were $2.1 million and $3.1 million , respectively. Net changes in imbalance receivables and payables 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 net realizable value and is reported in Other current assets on the consolidated balance sheets. See Note 11 . 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) 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 8 for a description of impairments recorded during the years ended December 31, 2018 , 2017 and 2016 . 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). In December 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. 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 the Partnership’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, the Partnership reached a settlement with insurers and final proceeds were received. During the years ended December 31, 2017 and 2016, the Partnership 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. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) 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 the Partnership’s weighted-average borrowing cost on debt by the average amount of qualifying costs incurred during the period. 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 Partnership assets acquired from Anadarko. The Partnership has allocated goodwill on its two reporting units: (i) gathering and processing and (ii) transportation. Goodwill is evaluated for impairment annually, as of October 1, or more often as facts and circumstances warrant. An initial qualitative assessment is performed to determine the likelihood of whether or not goodwill is impaired. 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 further testing is not necessary. If a quantitative assessment must be performed and the carrying amount of the reporting unit exceeds its fair value, goodwill is written down to its implied fair value through a charge to impairment expense. The carrying value of goodwill after such an impairment would represent a Level 3 fair value measurement. See Note 9 . Other intangible assets. The Partnership assesses intangible assets, as described in Note 9 , 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 12 . Environmental expenditures. The Partnership 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 14 . Segments. The Partnership’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. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Revenue and cost of product. Upon adoption of the new revenue recognition standard on January 1, 2018 (discussed in Recently adopted accounting standards ), the Partnership changed its accounting policy for revenue recognition as described below. The Partnership provides gathering, processing, treating, transportation and disposal services pursuant to a variety of contracts. Under these arrangements, the Partnership receives fees and/or retains a percentage of products or a percentage of the proceeds from the sale of the customer’s products. These revenues are included in Service revenues and Product sales in the consolidated statements of operations. Payment is generally received from the customer in the month following the service or delivery of the product. Contracts with customers generally have initial terms ranging from 5 to 10 years. Service revenues – fee based is recognized for fee-based contracts in the month of service based on the volumes delivered by the customer. Producers’ wells or production facilities are connected to the Partnership’s gathering systems for gathering, processing, treating, transportation and disposal of natural gas, NGLs, condensate, crude oil and produced water, as applicable. Revenues are valued based on the rate in effect for the month of service when the fee is either the same rate per unit over the contract term or when the fee escalates and the escalation factor approximates inflation. Deficiency fees charged to customers that do not meet their minimum delivery requirements are recognized as services are performed based on an estimate of the fees that will be billed upon completion of the performance period. Because of its significant upfront capital investment, the Partnership may charge additional service fees to customers for only a portion of the contract term (i.e., for the first year of a contract or until reaching a volume threshold), and these fees are recognized as revenue over the expected period of customer benefit, which is generally the life of the related properties. The Partnership also recognizes revenue and cost of product expense from marketing services performed on behalf of its customers by Anadarko. The Partnership also receives Service revenues – fee based from contracts that have minimum volume commitment demand fees and fees that require periodic rate redeterminations based upon the related facility cost of service. These fees include fixed and variable consideration that are recognized on a consistent per-unit rate over the term of the contract. Annual adjustments are made to the cost of service rates charged to customers, and a cumulative catch-up revenue adjustment related to services already provided to the minimum volumes under the contract may be recorded in future periods, with revenues for the remaining term of the contract recognized on a consistent per-unit rate. Service revenues – product based includes service revenues from percent-of-proceeds gathering and processing contracts that are recognized net of the cost of product for purchases from the Partnership’s customers since it is acting as the agent in the product sale. Keep-whole and percent-of-product agreements result in Service revenues – product based being recognized when the natural gas and/or NGLs are received from the customer as noncash consideration for the services provided. Noncash consideration for these services is valued at the time the services are provided. Revenue from product sales is also recognized, along with the cost of product expense related to the sale, when the product received as noncash consideration is sold to either Anadarko or a third party. When the product is sold to Anadarko, Anadarko is acting as the Partnership’s agent in the product sale, with the Partnership recognizing revenue and related cost of product expense associated with these marketing activities based on the Anadarko sales price to the third party. The Partnership also purchases natural gas volumes from producers at the wellhead or from a production facility, typically at an index price, and charges the producer fees associated with the downstream gathering and processing services. When the fees relate to services performed after control of the product has transferred to the Partnership, the fees are treated as a reduction of the purchase cost. If the fees relate to services performed before control of the product has transferred to the Partnership, the fees are treated as Service revenues – fee based. Product sales revenue is recognized, along with cost of product expense related to the sale, when the purchased product is sold to either Anadarko or a third party. The Partnership receives aid in construction reimbursements for certain capital costs necessary to provide services to customers (i.e., connection costs, etc.) under certain service contracts. Aid in construction reimbursements are reflected as a contract liability upon receipt and amortized to Service revenues – fee based over the expected period of customer benefit, which is generally the life of the related properties. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Equity-based compensation. 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, the Partnership’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, of which 2,241,980 units remained available for future issuance as of December 31, 2018 . Upon vesting of each phantom unit, the holder will receive common units of the Partnership or, at the discretion of the Board of Directors of its general partner (the “Board of Directors”), cash in an amount equal to the market value of common units of the Partnership 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. Equity-based compensation expense attributable to grants mad

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	2. REVENUE FROM CONTRACTS WITH CUSTOMERS The following table summarizes the Partnership’s revenue from contracts with customers: thousands Year Ended Revenue from customers Service revenues – fee based $ 1,905,728 Service revenues – product based 88,785 Product sales 310,895 Total revenue from customers 2,305,408 Revenue from other than customers Net gains (losses) on commodity price swap agreements (7,875 ) Other 2,125 Total revenues and other $ 2,299,658 2. REVENUE FROM CONTRACTS WITH CUSTOMERS (CONTINUED) Contract balances. Receivables from customers, which are included in Accounts receivable, net on the consolidated balance sheets were $214.3 million and $244.9 million as of December 31, 2018 and 2017 , respectively. Contract assets primarily relate to accrued deficiency fees the Partnership expects to charge customers once the related performance periods are completed and revenue accrued but not yet billed under cost of service contracts with fixed and variable fees. The following table summarizes the current period activity related to contract assets from contracts with customers: thousands Balance at December 31, 2017 $ — Cumulative effect of adopting Topic 606 5,950 Amounts transferred to Accounts receivable, net from contract assets recognized in the adoption effect (4,952 ) Additional estimated revenues recognized 30,519 Cumulative catch up adjustment for change in estimated consideration due to cost of service rate updates 16,104 Balance at December 31, 2018 $ 47,621 Contract assets at December 31, 2018 Other current assets $ 5,399 Other assets 42,222 Total contract assets from contracts with customers $ 47,621 Contract liabilities primarily relate to (i) fees that are charged to customers for only a portion of the contract term and must be recognized as revenues over the expected period of customer benefit, (ii) fixed and variable fees under cost of service contracts that are received from customers for which revenue recognition is deferred and (iii) aid in construction payments received from customers that must be recognized over the expected period of customer benefit. The following table summarizes the current period activity related to contract liabilities from contracts with customers: thousands Balance at December 31, 2017 $ — Cumulative effect of adopting Topic 606 120,309 Cash received or receivable, excluding revenues recognized during the period 55,786 Assets received from customer 12,933 Revenues recognized during the period that were included in the adoption effect (1) (21,556 ) Cumulative catch up adjustment for change in estimated consideration due to cost of service rate updates (21,848 ) Balance at December 31, 2018 $ 145,624 Contract liabilities at December 31, 2018 Accrued liabilities $ 16,235 Other liabilities 129,389 Total contract liabilities from contracts with customers $ 145,624 (1) Includes $(7.5) million from a performance obligation satisfied in a previous period related to the arbitration against SWEPI LP (see Note 14 ). 2. REVENUE FROM CONTRACTS WITH CUSTOMERS (CONTINUED) Transaction price allocated to remaining performance obligations. Revenues expected to be recognized from certain performance obligations that are unsatisfied (or partially unsatisfied) as of December 31, 2018 , are reflected in the following table. The Partnership applies the optional exemptions in Topic 606 and does not disclose consideration for remaining performance obligations with an original expected duration of one year or less or for variable consideration related to unsatisfied (or partially unsatisfied) performance obligations. Therefore, the following table represents only a portion of expected future revenues from existing contracts as most future revenues from customers are dependent on future variable customer volumes and, in some cases, variable commodity prices for those volumes. thousands 2019 $ 674,609 2020 847,045 2021 894,706 2022 947,310 2023 913,099 Thereafter 4,565,428 Total $ 8,842,197

Acquisitions and Divestitures

Acquisitions and Divestitures	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Acquisitions and Divestitures	3. ACQUISITIONS AND DIVESTITURES AMA acquisition. In February 2019, the Partnership acquired the following assets from Anadarko (see Note 15 ), which are collectively referred to as the Anadarko Midstream Assets (“AMA”): • Wattenberg processing plant. The Wattenberg processing plant consists of a cryogenic train (with capacity of 190 million cubic feet per day (“MMcf/d”)) and a refrigeration train (with capacity of 100 MMcf/d) located in Adams County, Colorado, now part of the DJ Basin complex. • Wamsutter pipeline. The Wamsutter pipeline is a crude oil gathering pipeline located in Sweetwater County, Wyoming and delivers crude oil into Andeavor’s Wamsutter Pipeline System. • DJ Basin oil system. The DJ Basin oil system consists of (i) a crude oil gathering system, (ii) a centralized oil stabilization facility (“COSF”), which commenced operation in 2015, and (iii) a 12 -mile crude oil pipeline, located in Weld County, Colorado. The COSF consists of Trains I through VI with total capacity of 155 thousand barrels per day (“MBbls/d”) and two storage tanks with total capacity of 500,000 barrels. Train VI, with capacity of 30 MBbls/d, commenced operation in 2018. The pipeline connects the COSF to Tampa Rail. • DBM oil system. The DBM oil system consists of (i) a crude oil gathering system, (ii) three central production facilities (“CPFs”), which include ten processing trains with total capacity of 75 MBbls/d, (iii) three storage tanks with total capacity of 30,000 barrels, (iv) a 14 -mile crude oil pipeline, and (v) two regional oil treating facilities (“ROTFs”), which include four trains with total capacity of 120 MBbls/d, located in Reeves and Loving Counties, Texas. The ROTFs commenced operation in 2018. The pipeline transports crude oil from the DBM oil system and one third-party CPF into Plains All American Pipeline. • APC water systems. The APC water systems consist of one produced-water disposal system (with capacity of 30 MBbls/d), which commenced operation in 2017. Four additional produced-water disposal systems commenced operation in 2018, increasing the total capacity to 565 MBbls/d. The APC water systems are located in Reeves, Loving, Winkler and Ward Counties, Texas, which are now part of the DBM water systems. 3. ACQUISITIONS AND DIVESTITURES (CONTINUED) • A 20% interest in Saddlehorn. Saddlehorn owns (i) a 600 -mile crude oil and condensate pipeline (excluding pipeline capacity leased by Saddlehorn) that originates in Laramie County, Wyoming and terminates in Cushing, Oklahoma, and (ii) four storage tanks with total capacity of 300,000 barrels. The Saddlehorn interest is accounted for under the equity method. The pipeline commenced operation in 2016 and is operated by a third party. • A 15% interest in Panola. Panola owns a 248 -mile NGLs pipeline that originates in Panola County, Texas and terminates in Mont Belvieu, Texas. The Panola interest is accounted for under the equity method and is operated by a third party. • A 50% interest in Mi Vida. Mi Vida owns a cryogenic gas processing plant (with capacity of 200 MMcf/d) located in Ward County, Texas. The interest in Mi Vida is accounted for under the equity method. The processing plant commenced operation in 2015 and is operated by a third party. • A 50% interest in Ranch Westex. Ranch Westex owns a processing plant consisting of a cryogenic train (with capacity of 100 MMcf/d) and a refrigeration train (with capacity of 25 MMcf/d), located in Ward County, Texas. In 2017, an additional interest in Ranch Westex was purchased from a third party for a net investment of $22.5 million , increasing the ownership from 33% to 50% . The interest in Ranch Westex is accounted for under the equity method and the processing plant is operated by a third party. Because the acquisition of AMA was a transfer of net assets between entities under common control, the Partn ership’s historical financial statements previously filed with the SEC have been recast in this Form 8-K to include the results attributable to AMA as if the Partnership owned AMA for all periods presented. The consolidated financial statements for periods prior to the Partnership’s acquisition of AMA have been 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 the Partnership had owned AMA during the periods reported. The following table presents the impact of AMA on Revenues and other, Equity income, net – affiliates and Net income (loss) as presented in the Partnership’s historical consolidated statements of operations: Year Ended December 31, 2018 thousands Partnership Historical AMA Eliminations Combined Revenues and other $ 1,990,276 $ 343,499 $ (34,117 ) $ 2,299,658 Equity income, net – affiliates 153,024 42,445 — 195,469 Net income (loss) 454,384 182,142 — 636,526 Year Ended December 31, 2017 thousands Partnership Historical AMA Eliminations Combined Revenues and other $ 2,248,356 $ 192,853 $ (11,595 ) $ 2,429,614 Equity income, net – affiliates 85,194 29,947 — 115,141 Net income (loss) 578,218 164,183 — 742,401 3. ACQUISITIONS AND DIVESTITURES (CONTINUED) Year Ended December 31, 2016 thousands Partnership Historical AMA Eliminations Combined Revenues and other $ 1,804,270 $ 138,269 $ (1,209 ) $ 1,941,330 Equity income, net – affiliates 78,717 22,975 — 101,692 Net income (loss) 602,294 61,306 — 663,600 Red Bluff Express acquisition. In January 2019, the Partnership acquired a 30% interest in Red Bluff Express Pipeline, LLC (“Red Bluff Express”), which owns a natural gas pipeline operated by a third party (the “Red Bluff Express pipeline”) connecting Reeves County and Loving County, Texas to the WAHA hub in Pecos County, Texas. The Partnership acquired its 30% interest from a third party via an initial net investment of $92.5 million , which represented its share of costs incurred up to the date of acquisition. The initial investment was funded with cash on hand and the interest in Red Bluff Express will be accounted for under the equity method. Whitethorn LLC acquisition. In June 2018, the Partnership acquired a 20% interest in Whitethorn LLC, which owns a crude oil and condensate pipeline that originates in Midland, Texas and terminates in Sealy, Texas (the “Midland-to-Sealy pipeline”) and related storage facilities (collectively referred to as “Whitethorn”). A third party operates Whitethorn and oversees the related commercial activities. In connection with its investment in Whitethorn, the Partnership will share proportionally in the commercial activities. The Partnership acquired its 20% interest via a $150.6 million net investment, which was funded with cash on hand and is accounted for under the equity method. See Note 10 . Cactus II acquisition. In June 2018, the Partnership acquired a 15% interest in Cactus II, which will own a crude oil pipeline operated by a third party (the “Cactus II pipeline”) connecting West Texas to the Corpus Christi area. The Cactus II pipeline is under construction and is expected to become operational in late 2019. The Partnership acquired its 15% interest from a third party via an initial net investment of $12.1 million , which represented its share of costs incurred up to the date of acquisition. The initial investment was funded with cash on hand and the interest in Cactus II is accounted for under the equity method. See Note 10 . Property exchange. In March 2017, the Partnership acquired an additional 50% interest in the Delaware Basin JV Gathering LLC (“DBJV”) system (the “Additional DBJV System Interest”) from a third party in exchange for (a) the Partnership’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”). The Partnership previously held a 50% interest in, and operated, the DBJV system. The Property Exchange was reflected as a nonmonetary transaction whereby the acquired Additional DBJV System Interest was 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. 3. ACQUISITIONS AND DIVESTITURES (CONTINUED) DBJV acquisition - Deferred purchase price obligation - Anadarko. Prior to the Partnership’s agreement with Anadarko to settle its deferred purchase price obligation early, the consideration that would have been paid by the Partnership for the March 2015 acquisition of DBJV from Anadarko consisted of a cash payment to Anadarko due on March 31, 2020. In May 2017, the Partnership 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. Springfield acquisition. In March 2016, the Partnership 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 the Partnership’s 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. The Partnership financed the cash portion of the acquisition through: (i) borrowings of $247.5 million on the Partnership’s senior unsecured revolving credit facility originally entered into in February 2014, (ii) the issuance of 835,841 of the Partnership’s common units to WGP and (iii) the issuance of Series A Preferred units to private investors. See Note 5 for further information regarding the Series A Preferred units. Newcastle system divestiture. In December 2018, the Newcastle system, located in Northeast Wyoming, was sold to a third party for $3.2 million , resulting in a net gain on sale of $0.6 million recorded as Gain (loss) on divestiture and other, net in the consolidated statements of operations. The Partnership previously held a 50% interest in, and operated, the Newcastle system. Helper and Clawson systems divestiture. In June 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. In October 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. The Partnership allocated $1.6 million in goodwill to this divestiture.

Partnership Distributions

Partnership Distributions	12 Months Ended
	Dec. 31, 2018
Distributions Made to Members or Limited Partners [Abstract]
Partnership Distributions	4. PARTNERSHIP DISTRIBUTIONS The partnership agreement requires the Partnership to distribute all of its available cash (as defined in the partnership agreement) to unitholders of record on the applicable record date within 45 days of the end of each quarter. The Board of Directors declared the following cash distributions to the Partnership’s common and general partner unitholders 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 $ 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 0.920 216,586 February 2018 2018 March 31 $ 0.935 $ 221,133 May 2018 June 30 0.950 225,691 August 2018 September 30 0.965 230,239 November 2018 December 31 (1) 0.980 234,787 February 2019 (1) The Board of Directors declared a cash distribution to the Partnership’s unitholders for the fourth quarter of 2018 of $0.980 per unit, or $234.8 million in aggregate, including incentive distributions, but excluding distributions on Class C units (see Class C unit distributions below). The cash distribution was paid on February 13, 2019 , to unitholders of record at the close of business on February 1, 2019 . Available cash. The amount of available cash (as defined in the partnership agreement) generally is all cash on hand at the end of the quarter, plus, at the discretion of the general partner, working capital borrowings made subsequent to the end of such quarter, less the amount of cash reserves established by the Partnership’s general partner to provide for the proper conduct of the Partnership’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 its unitholders and to its general partner 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. 4. PARTNERSHIP DISTRIBUTIONS (CONTINUED) Class C unit distributions. The Class C units receive quarterly distribut ions at a rate equivalent to the Partnership’s common units. The distributions are paid in the form of additional Class C units (“PIK Class C units”) until the earlier of (i) the consummation of the Merger (see Note 15 ) or (ii) March 1, 2020, unless the Partnership elects to convert such units earlier or Anadarko extends the conversion date, and the Class C units are disregarded with respect to distributions of the Partnership’s available cash until such event. 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 the Partnership’s common units for the ten days immediately pr eceding the payment date for the common unit distribution, less a 6% discount. The Partnership records the PIK Class C unit distributions at fair value at the time of issuance. This Level 2 fair value measurement uses the Partnership’s unit price as a significant input in the determination of the fair value. See Note 5 for further discussion of the Class C units. Series A Preferred unit distributions. As further described in Note 5 , the Partnership issued Series A Preferred units representing limited partner interests in the Partnership 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. On March 1, 2017, 50% of the outstanding Series A Preferred units converted into common units on a one -for-one basis, and on May 2, 2017, all remaining Series A Preferred units converted into common units on a one -for-one basis. Such converted common units were entitled to distributions made to common unitholders with respect to the quarter during which the applicable conversion occurred and did not include a prorated Series A Preferred unit distribution. 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 Series A Preferred units were outstanding during the first quarter of 2016. (2) Full quarterly per unit distribution on 14,030,611 Series A Preferred units and quarterly per unit distribution prorated for the 77 -day period during which 7,892,220 Series A Preferred units were outstanding during the second quarter of 2016. General partner interest and incentive distribution rights. As of December 31, 2018 , the general partner was entitled to 1.5% of all quarterly distributions that the Partnership 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 the general partner may receive on common units that it may acquire.

Equity and Partners' Capital

Equity and Partners' Capital	12 Months Ended
	Dec. 31, 2018
Partners' Capital Notes [Abstract]
Equity and Partners' Capital	5. EQUITY AND PARTNERS’ CAPITAL Equity offerings. In July 2017, the Partnership filed a registration statement with the SEC for the issuance of up to an aggregate of $500.0 million of common units pursuant to a new continuous offering program that has not yet been initiated (the “$500.0 million COP”). Upon the consummation of the Merger (see Note 15 ), the Partnership will terminate the registration statement relating to the $500.0 million COP and, therefore, common units will no longer be available for issuance thereunder. Class C units. In November 2014, the Partnership 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 the acquisition of DBM. When issued, the Class C units were scheduled to convert into common units on a one -for-one basis on December 31, 2017, and in February 2017, Anadarko elected to extend the conversion date of the Class C units to March 1, 2020. All outstanding Class C units will convert into the Partnership’s common units on a one-for-one basis immediately prior to the closing of the Merger, if consummated. If the Merger is not consummated, the conversion will occur on March 1, 2020, unless the Partnership elects to convert such units earlier or Anadarko extends the conversion date (see Note 15 ). The Class C units were issued at a discount to the then-current market price of the common units into which they are convertible. This discount, totaling $34.8 million , represents a beneficial conversion feature, and at issuance, was reflected as an increase in common unitholders’ capital and a decrease in Class C unitholder capital to reflect the fair value of the Class C units at issuance. The beneficial conversion feature is considered a non-cash distribution that is recognized from the date of issuance through the date of conversion, resulting in an increase in Class C unitholder capital and a decrease in common unitholders’ capital as amortized. The beneficial conversion feature is amortized assuming the extended conversion date of March 1, 2020, using the effective yield method. The impact of the beneficial conversion feature amortization is included in the calculation of earnings per unit. Series A Preferred units. In 2016, the Partnership issued 21,922,831 Series A Preferred units to private investors, generating proceeds of $686.9 million (net of fees and expenses, but including a 2.0% transaction fee paid to the private investors). The Series A Preferred units were issued at a discount to the then-current market price of the common units into which they were convertible. This discount, totaling $93.4 million , represented a beneficial conversion feature, and at issuance, was reflected as an increase in common unitholders’ capital and a decrease in Series A Preferred unitholders’ capital to reflect the fair value of the Series A Preferred units on the date of issuance. The beneficial conversion feature was considered a non-cash distribution that was recognized from the date of issuance through the date of conversion, resulting in an increase in Series A Preferred unitholders’ capital and a decrease in common unitholders’ capital as amortized. The beneficial conversion feature was amortized using the effective yield method. The impact of the beneficial conversion feature amortization is also included in the calculation of earnings per unit. For the year ended December 31, 2017 , the amortization for the beneficial conversion feature of the Series A Preferred units was $62.3 million . Pursuant to an agreement between the Partnership and the holders of the Series A Preferred units, 50% of the Series A Preferred units converted into common units on a one -for-one basis on March 1, 2017, and all remaining Series A Preferred units converted into common units on a one -for-one basis on May 2, 2017. 5. EQUITY AND PARTNERS’ CAPITAL (CONTINUED) Partnership interests. As of December 31, 2018, the Partnership’s common units were listed on the New York Stock Exchange under the symbol “WES.” The following table summarizes the Partnership’s units issued during the years ended December 31, 2018 and 2017: Common Units Class C Units Series A Preferred Units General Partner Units Total 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 PIK Class C units — 1,128,782 — — 1,128,782 Long-Term Incentive Plan award vestings 7,180 — — — 7,180 Balance at December 31, 2018 152,609,285 14,372,665 — 2,583,068 169,565,018 Holdings of Partnership equity. As of December 31, 2018 , WGP held 50,132,046 common units, representing a 29.6% limited partner interest in the Partnership, and, through its ownership of the general partner, WGP indirectly held 2,583,068 general partner units, representing a 1.5% general partner interest in the Partnership, and 100% of the IDRs. As of December 31, 2018 , (i) other subsidiaries of Anadarko collectively held 2,011,380 common units and 14,372,665 Class C units, representing an aggregate 9.7% limited partner interest in the Partnership and (ii) the public held 100,465,859 common units, representing the remaining 59.2% limited partner interest in the Partnership. Net income (loss) per common unit. Net income (loss) attributable to the Partnership assets acquired from Anadarko for periods prior to the Partnership’s acquisition of the Partnership assets is not allocated to the unitholders for purposes of calculating net income (loss) per common unit. Net income (loss) attributable to Western Gas Partners, LP earned on and subsequent to the date of acquisition of the Partnership assets is allocated as follows: General partner. The general partner’s allocation is equal to cash distributions plus its portion of undistributed earnings or losses. Specifically, net income equal to the amount of available cash (as defined by the partnership agreement) is allocated to the general partner consistent with actual cash distributions and capital account allocations, including incentive distributions. Undistributed earnings (net income in excess of distributions) or undistributed losses (available cash in excess of net income) are then allocated to the general partner in accordance with its weighted-average ownership percentage during each period. Series A Preferred unitholders. The Series A Preferred units were not considered a participating security as they only had distribution rights up to the specified per-unit quarterly distribution and had no rights to the Partnership’s undistributed earnings and losses. As such, the Series A Preferred unitholders’ allocation was equal to their cash distribution plus the amortization of the Series A Preferred units beneficial conversion feature (see Series A Preferred units above). 5. EQUITY AND PARTNERS’ CAPITAL (CONTINUED) Common and Class C unitholders. The Class C units are considered a participating security because they participate in distributions with common units according to a predetermined formula (see Note 4 ). The common and Class C unitholders’ allocation is equal to their cash distributions plus their respective allocations of undistributed earnings or losses. Specifically, net income equal to the amount of available cash (as defined by the partnership agreement) is allocated to the common and Class C unitholders consistent with actual cash distributions and capital account allocations. Undistributed earnings or undistributed losses are then allocated to the common and Class C unitholders in accordance with their respective weighted-average ownership percentages during each period. The common unitholder allocation also includes the impact of the amortization of the Series A Preferred units and Class C units beneficial conversion features. The Class C unitholder allocation is similarly impacted by the amortization of the Class C units beneficial conversion feature (see Class C units above). Calculation of net income (loss) per unit. Basic net income (loss) per common unit is calculated by dividing the net income (loss) attributable to common unitholders by the weighted-average number of common units outstanding during the period. The common units issued in connection with acquisitions and equity offerings are included on a weighted-average basis for periods they were outstanding. Diluted net income (loss) per common unit is calculated by dividing the sum of (i) the net income (loss) attributable to common units adjusted for distributions on the Series A Preferred units and a reallocation of the common and Class C limited partners’ interest in net income (loss) assuming, prior to the actual conversion, conversion of the Series A Preferred units into common units, and (ii) the net income (loss) attributable to the Class C units as a participating security, by the sum of the weighted-average number of common units outstanding plus the dilutive effect of (i) the weighted-average number of outstanding Class C units and (ii) the weighted-average number of common units outstanding assuming, prior to the actual conversion, conversion of the Series A Preferred units. The following table illustrates the Partnership’s calculation of net income (loss) per common unit: Year Ended December 31, thousands except per-unit amounts 2018 2017 2016 Net income (loss) attributable to Western Gas Partners, LP $ 627,917 $ 731,666 $ 652,637 Pre-acquisition net (income) loss allocated to Anadarko (182,142 ) (164,183 ) (72,632 ) Series A Preferred units interest in net (income) loss (1) — (42,373 ) (76,893 ) General partner interest in net (income) loss (346,538 ) (303,835 ) (236,561 ) Common and Class C limited partners’ interest in net income (loss) $ 99,237 $ 221,275 $ 266,551 Net income (loss) allocable to common units (1) $ 84,334 $ 192,066 $ 226,611 Net income (loss) allocable to Class C units (1) 14,903 29,209 39,940 Common and Class C limited partners’ interest in net income (loss) $ 99,237 $ 221,275 $ 266,551 Net income (loss) per unit Common units – basic and diluted (2) $ 0.55 $ 1.30 $ 1.74 Weighted-average units outstanding Common units – basic and diluted 152,606 147,194 130,253 Excluded due to anti-dilutive effect: Class C units (2) 13,795 12,776 11,945 Series A Preferred units assuming conversion to common units (2) — 5,406 16,860 (1) Adjusted to reflect amortization of the beneficial conversion features. (2) The impact of Class C units would be anti-dilutive for all periods presented and the conversion of Series A Preferred units would be anti-dilutive for the years ended December 31, 2017 and 2016. On March 1, 2017, 50% of the outstanding Series A Preferred units converted into common units on a one -for-one basis, and on May 2, 2017, all remaining Series A Preferred units converted into common units on a one -for-one basis.

Transactions with Affiliates

Transactions with Affiliates	12 Months Ended
	Dec. 31, 2018
Related Party Fees and Other Arrangements, Limited Liability Company (LLC) or Limited Partnership (LP) [Abstract]
Transactions with Affiliates	6. TRANSACTIONS WITH AFFILIATES Affiliate transactions. Revenues from affiliates include amounts earned by the Partnership from services provided to Anadarko as well as from the sale of natural gas, condensate and NGLs to Anadarko. Anadarko sells such natural gas, condensate and NGLs as an agent on behalf of either the Partnership or the Partnership’s customers. When such sales are on the Partnership’s customers’ behalf, the Partnership recognizes associated service revenues and cost of product expense. When such sales are on the Partnership’s behalf, the Partnership recognizes product sales revenues based on the Anadarko sales price to the third party and cost of product expense associated with these sales activities. In addition, the Partnership purchases natural gas, condensate and NGLs 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 the Partnership assets, whether in providing services to affiliates or to third parties, including field labor, measurement and analysis, and other disbursements. A portion of the Partnership’s general and administrative expenses is paid by Anadarko, which results in affiliate transactions pursuant to the reimbursement provisions of the Partnership’s omnibus agreement. 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. Merger transactions. As discussed in more detail in Note 15 , the Partnership has entered into the Merger Agreement with WGP, Anadarko and certain of their affiliates. 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 Partnership’s acquisition of the Partnership 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 the Partnership assets. Subsequent to the acquisition of Partnership 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 the Partnership. Note receivable - Anadarko. Concurrently with the closing of the Partnership’s May 2008 initial public offering, the Partnership 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 $279.6 million and $325.2 million at December 31, 2018 and 2017 , 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. APCWH Note Payable. In June 2017, APC Water Holdings 1, LLC (“APCWH”) entered into an eight-year note payable agreement with Anadarko. See Note 13 and Note 15 . Commodity price swap agreements. The Partnership had commodity price swap agreements with Anadarko to mitigate exposure to the commodity price risk inherent in its percent-of-proceeds, percent-of-product and keep-whole contracts. Notional volumes for each of the commodity price swap agreements were not specifically defined. Instead, the commodity price swap agreements applied to the actual volume of natural gas, condensate and NGLs purchased and sold. The commodity price swap agreements did not satisfy the definition of a derivative financial instrument and, therefore, were not required to be measured at fair value. The Partnership’s net gains (losses) on commodity price swap agreements were $(7.9) million , $0.6 million and $28.5 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, and are reported in the consolidated statements of operations as affiliate Product sales in 2018 and as affiliate Product sales and Cost of product in 2017 and 2016 (see Note 1 ). These commodity price swap agreements expired without renewal on December 31, 2018. 6. TRANSACTIONS WITH AFFILIATES (CONTINUED) Swap agreements - DJ Basin complex, Hugoton system and MGR assets. 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 sold and purchased during 2016, 2017 and 2018 for the DJ Basin complex, MGR assets and Hugoton system are recognized in the consolidated statements of operations at the applicable market price in the tables below. The Partnership 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 for product sales exceeds the applicable market price in the tables below, minus (ii) the amount by which the swap price for product purchases exceeds the applicable market price in the tables below. For the years ended December 31, 2018, 2017 and 2016, the capital contributions from Anadarko were $51.6 million , $58.6 million and $45.8 million , respectively. The tables below summarize the swap prices compared to the forward market prices: DJ Basin Complex per barrel except natural gas 2016 - 2018 Swap Prices 2016 Market Prices (1) 2017 Market Prices (1) 2018 Market Prices (1) Ethane $ 18.41 $ 0.60 $ 5.09 $ 5.41 Propane 47.08 10.98 18.85 28.72 Isobutane 62.09 17.23 26.83 32.92 Normal butane 54.62 16.86 26.20 32.71 Natural gasoline 72.88 26.15 41.84 48.04 Condensate 76.47 34.65 45.40 49.36 Natural gas (per MMBtu) 5.96 2.11 3.05 2.21 Hugoton System (2) per barrel except natural gas 2016 Swap Prices 2016 Market Prices (1) Condensate $ 78.61 $ 18.81 Natural gas (per MMBtu) 5.50 2.12 MGR Assets per barrel except natural gas 2016 - 2018 Swap Prices 2017 Market Prices (1) 2018 Market Prices (1) Ethane $ 23.11 $ 4.08 $ 2.52 Propane 52.90 19.24 25.83 Isobutane 73.89 25.79 30.03 Normal butane 64.93 25.16 29.82 Natural gasoline 81.68 45.01 47.25 Condensate 81.68 53.55 56.76 Natural gas (per MMBtu) 4.87 3.05 2.21 (1) Represents the New York Mercantile Exchange forward strip price as of December 8, 2015, December 1, 2016, and December 20, 2017, for the 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 3 . 6. TRANSACTIONS WITH AFFILIATES (CONTINUED) Gathering and processing agreements. The Partnership has significant gathering and processing arrangements with affiliates of Anadarko on a majority of its systems. The combination of the DBM complex and DBJV and Haley systems, effective January 1, 2018, into a single complex now referred to as the “West Texas complex” resulted in natural gas throughput previously reported as “Gathering, treating and transportation” now being reported as “Processing.” The Partnership’s natural gas gathering, treating and transportation throughput (excluding equity investment throughput) attributable to production owned or controlled by Anadarko was 7% , 34% and 37% for the years ended December 31, 2018 , 2017 and 2016 , respectively. The Partnership’s natural gas processing throughput (excluding equity investment throughput) attributable to production owned or controlled by Anadarko was 40% , 41% and 53% for the years ended December 31, 2018 , 2017 and 2016 , respectively. The Partnership’s crude oil, NGLs and produced water gathering, treating, transportation and disposal throughput (excluding equity investment throughput) attributable to production owned or controlled by Anadarko was 85% , 81% and 86% for the years ended December 31, 2018 , 2017 and 2016 , respectively. Commodity purchase and sale agreements. The Partnership sells a significant amount of its natural gas, condensate and NGLs to Anadarko Energy Services Company (“AESC”), Anadarko’s marketing affiliate that acts as an agent in the sale to a third party. In addition, the Partnership purchases natural gas, condensate and NGLs from AESC pursuant to purchase agreements. The Partnership’s purchase and sale agreements with AESC are generally one-year contracts, subject to annual renewal. Acquisitions from Anadarko. On March 14, 2016, the Partnership acquired Springfield from Anadarko (see Note 3 ). Omnibus agreement. Pursuant to the omnibus agreement, Anadarko performs centralized corporate functions for the Partnership, 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 the partnership and omnibus agreements, determines, in its reasonable discretion, amounts to be reimbursed by the Partnership in exchange for services provided under the omnibus agreement. See Summary of affiliate transactions below. The following table summarizes the amounts the Partnership reimbursed to Anadarko: Year Ended December 31, thousands 2018 2017 2016 General and administrative expenses $ 35,077 $ 31,733 $ 29,360 Public company expenses 15,409 9,379 8,410 Total reimbursement $ 50,486 $ 41,112 $ 37,770 Services and secondment agreement. Pursuant to the services and secondment agreement, specified employees of Anadarko are seconded to the general partner to provide operating, routine maintenance and other services with respect to the assets owned and operated by the Partnership under the direction, supervision and control of the general partner. Pursuant to the services and secondment agreement, the Partnership reimburses Anadarko for services provided by the seconded employees. The initial term of the services and secondment agreement expired in May 2018, but was extended for a twelve-month period and will continue to 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 the Partnership’s acquisition of the Partnership assets. 6. TRANSACTIONS WITH AFFILIATES (CONTINUED) Tax sharing agreement. Pursuant to a tax sharing agreement, the Partnership reimburses Anadarko for its estimated share of taxes from all forms of taxation, excluding taxes imposed by the United States. Taxes for which the Partnership reimburses Anadarko include state taxes attributable to the Partnership’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 Partnership 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 the Partnership as a member. However, under this circumstance, the Partnership 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. Allocation of costs. For periods prior to the Partnership’s acquisition of the Partnership assets, the consolidated financial statements include costs allocated by Anadarko in the form of a management services fee. This management services fee was allocated to the Partnership based on its proportionate share of Anadarko’s revenues and expenses or other contractual arrangements. Management believes these allocation methodologies are reasonable. The employees supporting the Partnership’s operations are employees of Anadarko. Anadarko allocates costs to the Partnership for its share of personnel costs, including costs associated with equity-based compensation plans, non-contributory defined benefit pension and postretirement plans and defined contribution savings plans pursuant to the omnibus agreement and services and secondment agreement. In general, the Partnership’s reimbursement to Anadarko under the omnibus agreement or services and secondment agreement is either (i) on an actual basis for direct expenses Anadarko and the general partner incur on behalf of the Partnership, or (ii) based on an allocation of salaries and related employee benefits between the Partnership, the general partner and Anadarko based on estimates of time spent on each entity’s business and affairs. Most general and administrative expenses charged to the Partnership by Anadarko are attributed to the Partnership 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 the Partnership were to directly obtain these services, management believes that aggregate costs charged to the Partnership by Anadarko are reasonable. WES LTIP. The general partner 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 the Partnership. 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. Compensation expense is recognized over the vesting period and was $0.4 million for each of the years ended December 31, 2018 , 2017 and 2016 . As of December 31, 2018 , there was $0.1 million of unrecognized compensation expense attributable to the outstanding awards under the WES LTIP, all of which will be realized by the Partnership, and which is expected to be recognized over a weighted-average period of 0.4 years. The following table summarizes WES LTIP award activity for the years ended December 31, 2018 , 2017 and 2016 : 2018 2017 2016 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 $ 55.73 7,180 $ 49.30 7,304 $ 68.78 5,477 Vested 55.73 (7,180 ) 49.30 (7,304 ) 68.78 (5,477 ) Granted 49.88 8,020 55.73 7,180 49.30 7,304 Phantom units outstanding at end of year 49.88 8,020 55.73 7,180 49.30 7,304 6. TRANSACTIONS WITH AFFILIATES (CONTINUED) WGP LTIP and Anadarko Incentive Plan. General and administrative expenses included $6.6 million , $4.6 million and $5.2 million for the years ended December 31, 2018 , 2017 and 2016 , respectively, of equity-based compensation expense, allocated to the Partnership by Anadarko, for awards granted to the executive officers of the general partner and other employees under the WGP LTIP and Anadarko Incentive Plan. Of these amounts, $5.7 million , $4.6 million and $4.2 million are reflected as contributions to partners’ capital in the Partnership’s consolidated statements of equity and partners’ capital for the years ended December 31, 2018 , 2017 and 2016 , respectively. As of December 31, 2018 , the Partnership estimated that $12.5 million of estimated unrecognized compensation expense attributable to the Anadarko Incentive Plan will be allocated to the Partnership over a weighted-average period of 2.0 years. Affiliate asset contributions and distributions. The following table summarizes Anadarko’s contributions and distributions of other assets to the Partnership: Year Ended December 31, 2018 2017 2016 2018 2017 2016 thousands Purchases Sales Cash consideration $ (254 ) $ (3,910 ) $ (3,965 ) $ — $ — $ 623 Net carrying value 59,089 5,283 3,496 — — (605 ) Partners’ capital adjustment $ 58,835 $ 1,373 $ (469 ) $ — $ — $ 18 Contributions in aid of construction costs from affiliates. On certain of the Partnership’s capital projects, Anadarko is obligated to reimburse the Partnership 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. For periods prior to January 1, 2018, the cash receipts resulting from such reimbursements were presented as “Contributions in aid of construction costs from affiliates” within the investing section of the consolidated statements of cash flows. As discussed in Recently adopted accounting standards in Note 1 , upon adoption of Topic 606, affiliate reimbursements of capital costs are reflected as contract liabilities upon receipt, amortized to Service revenues – fee based over the expected period of customer benefit, and presented within the operating section of the consolidated statements of cash flows. 6. TRANSACTIONS WITH AFFILIATES (CONTINUED) Summary of affiliate transactions. The following table summarizes material affiliate transactions: Year ended December 31, thousands 2018 2017 2016 Revenues and other (1) $ 1,353,711 $ 1,539,105 $ 1,358,918 Equity income, net – affiliates (1) 195,469 115,141 101,692 Cost of product (1) 168,535 74,560 75,983 Operation and maintenance (2) 115,948 82,249 82,133 General and administrative (3) 48,819 42,411 41,176 Operating expenses 333,302 199,220 199,292 Interest income (4) 16,900 16,900 16,900 Interest expense (5) (6) 6,746 224 (7,747 ) APCWH Note Payable borrowings (6) 321,780 98,813 — Settlement of the Deferred purchase price obligation – Anadarko (7) — (37,346 ) — Proceeds from the issuance of common units, net of offering expenses (8) — — 25,000 Distributions to unitholders (9) 514,906 452,777 382,711 Above-market component of swap agreements with Anadarko 51,618 58,551 45,820 (1) Represents amounts earned or incurred on and subsequent to the date of the acquisition of Partnership assets, as well as amounts earned or incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets. (2) Represents expenses incurred on and subsequent to the date of the acquisition of Partnership assets, as well as expenses incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets. (3) Represents general and administrative expense incurred on and subsequent to the date of the acquisition of Partnership assets, as well as a management services fee for expenses incurred by Anadarko for periods prior to the acquisition of the Partnership assets by the Partnership. These amounts include equity-based compensation expense allocated to the Partnership by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plan within this Note 6 ) and amounts charged by Anadarko under the omnibus agreement. (4) Represents interest income recognized on the note receivable from Anadarko. (5) Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 3 and Note 13 ). (6) Includes amounts related to the APCWH Note Payable (see Note 13 and Note 15 ). (7) Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 3 ). (8) Represents proceeds from the issuance of 835,841 common units to WGP as partial funding for the acquisition of Springfield (see Note 3 ). (9) Represents distributions paid under the partnership agreement (see Note 4 and Note 5 ). Concentration of credit risk. Anadarko was the only customer from whom revenues exceeded 10% of the Partnership’s consolidated revenues for all periods presented in the consolidated statements of operations.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	7. INCOME TAXES The Partnership is not a taxable entity for U.S. federal income tax purposes. For all periods presented, income attributable to AMA was subject to federal and state income tax. Following the adoption of the U.S. Tax Cuts and Jobs Act signed into law on December 22, 2017, AMA recognized a one-time deferred tax benefit of $87.3 million due to the remeasurement of its U.S. deferred tax assets and liabilities based on the reduction of the corporate tax rate from 35% to 21% . During 2018, the accounting for the income tax effects related to the adoption of the Tax Reform Legislation was completed before the end of the measurement period. No additional adjustments to the provisional amount recorded in 2017 were recognized. The federal tax benefit is included in the Deferred income taxes balance as presented on the consolidated balance sheet. The components of the Partnership’s income tax expense (benefit) are as follows: Year Ended December 31, thousands 2018 2017 2016 Current income tax expense (benefit) Federal income tax expense (benefit) $ (79,264 ) $ (9,207 ) $ (19,480 ) State income tax expense (benefit) (850 ) 2,422 1,257 Total current income tax expense (benefit) (80,114 ) (6,785 ) (18,223 ) Deferred income tax expense (benefit) Federal income tax expense (benefit) 133,044 (55,835 ) 49,855 State income tax expense (benefit) 6,004 2,697 1,337 Total deferred income tax expense (benefit) 139,048 (53,138 ) 51,192 Total income tax expense (benefit) $ 58,934 $ (59,923 ) $ 32,969 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 2018 2017 2016 Income (loss) before income taxes $ 695,460 $ 682,478 $ 696,569 Statutory tax rate — % — % — % Tax computed at statutory rate $ — $ — $ — Adjustments resulting from: U.S. federal tax reform — (87,306 ) — Federal taxes on income attributable to Partnership assets pre-acquisition 54,243 22,353 30,550 State taxes on income attributable to Partnership assets pre-acquisition (net of federal benefit) 1,745 164 326 Texas margin tax expense (benefit) 2,946 4,866 2,093 Income tax expense (benefit) $ 58,934 $ (59,923 ) $ 32,969 Effective tax rate 8 % (9 )% 5 % 7. INCOME TAXES (CONTINUED) The tax effects of temporary differences that give rise to significant portions of deferred tax assets (liabilities) are as follows: December 31, thousands 2018 2017 Depreciable property $ (280,377 ) $ (139,902 ) Credit carryforwards 497 448 Other intangible assets (299 ) (189 ) Other 162 8 Net long-term deferred income tax liabilities $ (280,017 ) $ (139,635 ) Credit carryforwards, which are available for use on future income tax returns, consist of $0.5 million of state income tax credits that expire in 2026.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	8. PROPERTY, PLANT AND EQUIPMENT A summary of the historical cost of property, plant and equipment is as follows: December 31, thousands Estimated Useful Life 2018 2017 Land n/a $ 5,298 $ 5,096 Gathering systems and processing complexes 3 to 49 years 10,441,574 7,851,458 Pipelines and equipment 6 to 45 years 172,497 137,644 Assets under construction n/a 604,265 954,719 Other 3 to 40 years 35,139 30,701 Total property, plant and equipment 11,258,773 8,979,618 Less accumulated depreciation 2,848,420 2,213,718 Net property, plant and equipment $ 8,410,353 $ 6,765,900 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 the year ended December 31, 2018 , the Partnership recognized impairments of $230.6 million , including impairments of $125.9 million at the Third Creek gathering system and $8.1 million at the Kitty Draw gathering system. These assets were impaired to their estimated salvage values of $1.8 million and zero , respectively, using the market approach and Level 3 fair value inputs, due to the shutdown of the systems. See Note 1 for further information. Also during 2018, the Partnership recognized impairments of $38.7 million and $34.6 million at the Hilight and MIGC systems, respectively. These assets were impaired to their estimated fair values of $4.9 million and $15.2 million , respectively, using the income approach and Level 3 fair value inputs, due to a reduction in estimated future cash flows. The remaining $23.3 million of impairments was primarily related to (i) a $10.9 million impairment at the GNB NGL pipeline, which was impaired to its estimated fair value of $10.0 million using the income approach and Level 3 fair value inputs, and (ii) a $5.6 million impairment related to an idle facility at the Chipeta complex, which was impaired to its estimated salvage value of $1.5 million using the market approach and Level 3 fair value inputs. During the year ended December 31, 2017, the Partnership recognized impairments of $180.1 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 $21.3 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, (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 the year ended December 31, 2016, the Partnership recognized impairments of $17.8 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, the Partnership recognized impairments of $11.7 million , primarily related to the cancellation of projects at the DJ Basin complex and at the Springfield, DBJV and DBM oil systems and the abandonment of compressors at the MIGC system.

Goodwill and Intangibles

Goodwill and Intangibles	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangibles	9. 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 Partnership assets 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, the Partnership’s allocated goodwill balance does not represent, and in some cases is significantly different from, the difference between the consideration the Partnership 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 ). The Partnership’s annual qualitative goodwill impairment assessment as of October 1, 2018 , indicated no impairment. Qualitative factors were also assessed in the fourth quarter of 2018 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 in connection with the Platte Valley and Wattenberg processing plant acquisitions in 2011, which are being amortized on a straight-line basis over 38 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 the Partnership in connection with the DBM acquisition in November 2014, which are being amortized on a straight-line basis over 30 years . The Partnership 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 2018 2017 Gross carrying amount $ 979,863 $ 979,863 Accumulated amortization (138,455 ) (107,676 ) Other intangible assets $ 841,408 $ 872,187 Amortization expense for intangible assets was $30.8 million for the year ended December 31, 2018 , and $30.7 million for each of the years ended December 31, 2017 and 2016 . Intangible asset amortization recorded in each of the next five years is estimated to be $32.0 million for the years ended December 31, 2019 to December 31, 2022 , and $31.7 million for the year ended December 31, 2023 .

Equity Investments

Equity Investments	12 Months Ended
	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity Investments	10. EQUITY INVESTMENTS The following tables present the activity in the Partnership’s equity investments for the years ended December 31, 2018 and 2017: thousands Balance at December 31, 2016 Impairment expense (1) Acquisitions Equity income, net Contributions Distributions Distributions in excess of cumulative earnings (2) Balance at December 31, 2017 Fort Union $ 12,833 $ (3,110 ) $ — $ 3,821 $ — $ (4,217 ) $ (2,297 ) $ 7,030 White Cliffs 47,319 — — 12,547 277 (11,965 ) (3,233 ) 44,945 Rendezvous 46,739 — — 1,144 — (3,085 ) (2,270 ) 42,528 Mont Belvieu JV 112,805 — — 29,444 — (29,482 ) (2,468 ) 110,299 TEG 15,846 — — 3,350 — (3,317 ) — 15,879 TEP 189,194 — — 17,387 107 (17,639 ) (10,074 ) 178,975 FRP 169,472 — — 17,501 — (17,675 ) (2,743 ) 166,555 Saddlehorn 107,420 — — 10,001 2,454 (10,127 ) (521 ) 109,227 Panola 24,546 — — 2,230 46 (2,470 ) (727 ) 23,625 Mi Vida 67,738 — — 10,029 — (9,161 ) (3,618 ) 64,988 Ranch Westex 34,777 — 22,500 7,687 — (7,955 ) (3,708 ) 53,301 Total $ 828,689 $ (3,110 ) $ 22,500 $ 115,141 $ 2,884 $ (117,093 ) $ (31,659 ) $ 817,352 thousands Balance at December 31, 2017 Acquisitions Equity income, net Contributions (3) Distributions Distributions in excess of cumulative earnings (2) Balance at December 31, 2018 Fort Union $ 7,030 $ — $ (1,433 ) $ — $ (194 ) $ (3,144 ) $ 2,259 White Cliffs 44,945 — 11,841 1,278 (11,259 ) (3,785 ) 43,020 Rendezvous 42,528 — 767 — (2,709 ) (2,745 ) 37,841 Mont Belvieu JV 110,299 — 29,200 — (29,239 ) (5,311 ) 104,949 TEG 15,879 — 4,290 3,720 (4,368 ) (163 ) 19,358 TEP 178,975 — 37,963 11,980 (33,552 ) (2,168 ) 193,198 FRP 166,555 — 23,308 14,980 (23,481 ) (4,926 ) 176,436 Saddlehorn 109,227 — 15,833 294 (16,017 ) (830 ) 108,507 Panola 23,625 — 2,200 — (2,200 ) (856 ) 22,769 Mi Vida 64,988 — 13,734 — (14,000 ) (91 ) 64,631 Ranch Westex 53,301 — 10,678 — (10,876 ) (2,201 ) 50,902 Whitethorn — 150,563 47,088 7,069 (39,497 ) (3,365 ) 161,858 Cactus II — 12,052 — 94,308 — — 106,360 Total $ 817,352 $ 162,615 $ 195,469 $ 133,629 $ (187,392 ) $ (29,585 ) $ 1,092,088 (1) Recorded in Impairments in the consolidated statements of operations. (2) 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. (3) Includes capitalized interest of $1.4 million related to the construction of the Cactus II pipeline. 10. EQUITY INVESTMENTS (CONTINUED) The investment balance in Fort Union at December 31, 2018 , is $3.1 million less than the Partnership’s underlying equity in Fort Union’s net assets due to an impairment loss recognized by the Partnership in 2017 for its investment in Fort Union. The investment balance in Rendezvous at December 31, 2018 , includes $34.3 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 to Equity income, net – affiliates over the remaining estimated useful life of those facilities. The investment balance in White Cliffs at December 31, 2018 , is $6.4 million less than the Partnership’s underlying equity in White Cliffs’ net assets, primarily due to the Partnership 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. The investment balance in Whitethorn at December 31, 2018 , is $39.1 million less than the Partnership’s underlying equity in Whitethorn’s net assets, primarily due to terms of the acquisition agreement which provided the Partnership a share of pre-acquisition operating cash flow. This difference is being amortized to Equity income, net – affiliates over the remaining estimated useful life of Whitethorn. An impairment loss was recognized by the operator of Fort Union during the year ended December 31, 2016. The Partnership’s 14.81% share of the impairment loss was $3.0 million for the year ended December 31, 2016, 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 the Partnership’s equity investments (amounts represent 100% of investee financial information): Year Ended December 31, thousands 2018 2017 2016 Revenues $ 1,300,921 $ 877,020 $ 806,671 Operating income 876,910 542,390 503,239 Net income 874,587 540,538 502,260 December 31, thousands 2018 2017 Current assets $ 297,143 $ 214,473 Property, plant and equipment, net 4,251,020 3,366,754 Other assets 81,769 84,522 Total assets $ 4,629,932 $ 3,665,749 Current liabilities 101,729 112,143 Non-current liabilities 42,431 45,413 Equity 4,485,772 3,508,193 Total liabilities and equity $ 4,629,932 $ 3,665,749

Components of Working Capital

Components of Working Capital	12 Months Ended
	Dec. 31, 2018
Components Of Working Capital [Abstract]
Components of Working Capital	11. COMPONENTS OF WORKING CAPITAL A summary of accounts receivable, net is as follows: December 31, thousands 2018 2017 Trade receivables, net $ 221,328 $ 160,700 Other receivables, net 45 210 Total accounts receivable, net $ 221,373 $ 160,910 A summary of other current assets is as follows: December 31, thousands 2018 2017 NGLs inventory $ 6,466 $ 10,958 Imbalance receivables 9,035 2,063 Prepaid insurance 1,972 2,388 Contract assets 5,399 — Other 3,309 — Total other current assets $ 26,181 $ 15,409 A summary of accrued liabilities is as follows: December 31, thousands 2018 2017 Accrued interest expense $ 70,959 $ 40,632 Short-term asset retirement obligations 25,938 2,304 Short-term remediation and reclamation obligations 863 833 Income taxes payable 384 2,495 Contract liabilities 16,235 — Other 13,495 1,635 Total accrued liabilities $ 127,874 $ 47,899

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2018
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations	12. ASSET RETIREMENT OBLIGATIONS The following table provides a summary of changes in asset retirement obligations: Year Ended December 31, thousands 2018 2017 Carrying amount of asset retirement obligations at beginning of year $ 154,571 $ 150,082 Liabilities incurred 34,558 17,932 Liabilities settled (12,432 ) (10,468 ) Accretion expense 7,909 7,339 Revisions in estimated liabilities 141,356 (10,314 ) Carrying amount of asset retirement obligations at end of year $ 325,962 $ 154,571 The liabilities incurred for the year ended December 31, 2018 , represented additions in asset retirement obligations primarily due to capital expansions at the West Texas and DJ Basin complexes, the DBM water systems and the DBM oil system. Revisions in estimated liabilities for the year ended December 31, 2018 , primarily included (i) $71.8 million related to changes in expected settlement costs and timing, primarily at the DJ Basin and West Texas complexes and the MGR assets, and (ii) $43.4 million related to th e shutdown of the Third Creek gathering system during the second quarter of 2018. See Note 1 for further information. 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.

Debt and Interest Expense

Debt and Interest Expense	12 Months Ended
	Dec. 31, 2018
Debt Instruments [Abstract]
Debt and Interest Expense	13. DEBT AND INTEREST EXPENSE The following table presents the Partnership’s outstanding debt: December 31, 2018 December 31, 2017 thousands Principal Carrying Value Fair Value (1) Principal Carrying Value Fair Value (1) 2.600% Senior Notes due 2018 $ — $ — $ — $ 350,000 $ 349,684 $ 350,631 5.375% Senior Notes due 2021 500,000 496,959 515,990 500,000 495,815 530,647 4.000% Senior Notes due 2022 670,000 669,078 662,109 670,000 668,849 684,043 3.950% Senior Notes due 2025 500,000 492,837 466,135 500,000 491,885 500,885 4.650% Senior Notes due 2026 500,000 495,710 483,994 500,000 495,245 520,144 4.500% Senior Notes due 2028 400,000 394,631 377,475 — — — 4.750% Senior Notes due 2028 400,000 395,841 384,370 — — — 5.450% Senior Notes due 2044 600,000 593,349 522,386 600,000 593,234 637,827 5.300% Senior Notes due 2048 700,000 686,648 605,327 — — — 5.500% Senior Notes due 2048 350,000 342,328 311,536 — — — RCF 220,000 220,000 220,000 370,000 370,000 370,000 APCWH Note Payable 427,493 427,493 427,493 98,966 98,966 98,966 Total long-term debt $ 5,267,493 $ 5,214,874 $ 4,976,815 $ 3,588,966 $ 3,563,678 $ 3,693,143 (1) Fair value is measured using the market approach and Level 2 inputs. Debt activity. The following table presents the debt activity of the Partnership for the years ended December 31, 2018 and 2017: thousands Carrying Value Balance at December 31, 2016 $ 3,091,461 RCF borrowings 370,000 APCWH Note Payable borrowings 98,813 Other 3,404 Balance at December 31, 2017 $ 3,563,678 RCF borrowings 540,000 APCWH Note Payable borrowings 321,780 Issuance of 4.500% Senior Notes due 2028 400,000 Issuance of 5.300% Senior Notes due 2048 700,000 Issuance of 4.750% Senior Notes due 2028 400,000 Issuance of 5.500% Senior Notes due 2048 350,000 Repayment of 2.600% Senior Notes due 2018 (350,000 ) Repayments of RCF borrowings (690,000 ) Other (20,584 ) Balance at December 31, 2018 $ 5,214,874 13. DEBT AND INTEREST EXPENSE (CONTINUED) Senior Notes. In August 2018, the 4.750% Senior Notes due 2028 and 5.500% Senior Notes due 2048 were offered to the public at prices of 99.818% and 98.912% , respectively, of the face amount. Including the effects of the issuance and underwriting discounts, the effective interest rates of the senior notes are 4.885% and 5.652% , respectively. Interest is paid on each such series semi-annually on February 15 and August 15 of each year, beginning February 15, 2019. The net proceeds were used to repay the maturing 2.600% Senior Notes due August 2018, repay amounts outstanding under the senior unsecured revolving credit facility (“RCF”) and for general partnership purposes, including to fund capital expenditures. In March 2018, the 4.500% Senior Notes due 2028 and 5.300% Senior Notes due 2048 were offered to the public at prices of 99.435% and 99.169% , respectively, of the face amount. Including the effects of the issuance and underwriting discounts, the effective interest rates of the senior notes are 4.682% and 5.431% , respectively. Interest is paid on each such series semi-annually on March 1 and September 1 of each year, beginning September 1, 2018. The net proceeds were used to repay amounts outstanding under the RCF and for general partnership purposes, including to fund capital expenditures. At December 31, 2018 , the Partnership was in compliance with all covenants under the indentures governing its outstanding notes. Revolving credit facility. In February 2018, the Partnership entered into the five-year $1.5 billion RCF by amending and restating the $1.2 billion credit facility that was originally entered into in February 2014. The RCF is expandable to a maximum of $2.0 billion , matures in February 2023, with options to extend maturity by up to two additional one year increments, and bears interest at the London Interbank Offered Rate (“LIBOR”), plus applicable margins ranging from 1.00% to 1.50% , 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 0.50% , based upon the Partnership’s senior unsecured debt rating. The Partnership is required to pay a quarterly facility fee ranging from 0.125% to 0.250% of the commitment amount (whether used or unused), also based upon its senior unsecured debt rating. As of December 31, 2018 , the Partnership had $220.0 million in outstanding borrowings and $4.6 million in outstanding letters of credit, resulting in $1.3 billion available borrowing capacity under the RCF. As of December 31, 2018 and 2017 , the interest rate on any outstanding RCF borrowings was 3.74% and 2.87% , respectively. The facility fee rate was 0.20% at December 31, 2018 and 2017 . At December 31, 2018 , the Partnership was in compliance with all covenants under the RCF. In December 2018, the Partnership entered into an amendment to the RCF for (i) subject to the consummation of the Merger (see Note 15 ), an increase to the size of the RCF to $2.0 billion , while leaving the $0.5 billion accordion feature of the RCF unexercised, and (ii) effective on February 15, 2019, the exercise of one of the Partnership’s one-year extension options to extend the maturity date of the RCF to February 2024. All notes and obligations under the RCF are recourse to the Partnership’s general partner. The Partnership’s general partner is indemnified by wholly owned subsidiaries of Anadarko against any claims made against the general partner for the Partnership’s long-term debt and/or borrowings under the RCF. 364-day Facility. In December 2018, the Partnership entered into a $2.0 billion 364-day senior unsecured credit agreement (the “364-day Facility”), the proceeds of which will be used to fund substantially all of the cash portion of the consideration under the Merger Agreement and the payment of related transaction costs (see Note 15 ). The 364-day Facility will mature on the day prior to the one-year anniversary of the completion of the Merger, and will bear interest at LIBOR, plus applicable margins ranging from 1.000% to 1.625% , 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 as defined in the 364-day Facility and plus applicable margins currently ranging from zero to 0.625% , based upon the Partnership’s senior unsecured debt rating. The Partnership is also required to pay a ticking fee of 0.175% on the commitment amount beginning 90 days after the effective date of the credit agreement through the date of funding under the 364-day Facility. Funding of the 364-day Facility is conditioned upon the consummation of the Merger and net cash proceeds received from future asset sales and debt or equity offerings by the Partnership must be used to repay amounts outstanding under the facility. See Note 15 . 13. DEBT AND INTEREST EXPENSE (CONTINUED) APCWH Note Payable. In June 2017, in connection with funding the construction of the APC water systems, which were acquired as part of the AMA acquisition, APCWH entered into an eight-year note payable agreement with Anadarko (the “APCWH Note Payable”). This note payable has a maximum borrowing limit of $500 million , and accrues interest, which is payable upon maturity, at the applicable mid-term federal rate based on a quarterly compounding basis as determined by the U.S. Secretary of the Treasury. As of December 31, 2018, the Partnership had $427.5 million in outstanding borrowings under the APCWH Note Payable. As of December 31, 2018 and 2017, the interest rate on outstanding borrowings was 3.04% and 2.09% , respectively. At December 31, 2018, the Partnership was in compliance with all covenants under this agreement. Interest-rate swaps. In December 2018, the Partnership entered into interest-rate swap agreements to manage interest rate risk associated with anticipated 2019 debt issuances. Pursuant to these swap agreements, the Partnership exchanged a floating interest rate indexed to the three-month LIBOR for a fixed interest rate. Depending on market conditions, liability management actions or other factors, the Partnership may settle or amend certain or all of the currently outstanding interest-rate swaps. The following interest-rate swaps were outstanding as of December 31, 2018 : Notional Principal Amount Reference Period Mandatory Termination Date Fixed Interest Rate $250.0 million December 2019 - 2024 December 2019 2.730% $250.0 million December 2019 - 2029 December 2019 2.856% $250.0 million December 2019 - 2049 December 2019 2.905% The Partnership does not apply hedge accounting and, therefore, gains and losses associated with the interest-rate swaps are recognized currently in earnings. For the year ended December 31, 2018 , the Partnership recognized a non-cash loss of $8.0 million , which is included in Other income (expense), net in the consolidated statements of operations. Valuation of the interest-rate swaps is based on similar transactions observable in active markets and industry standard models that primarily rely on market-observable inputs. Inputs used to estimate fair value in industry standard models are categorized as Level 2 inputs, because substantially all assumptions and inputs are observable in active markets throughout the full term of the instruments. Inputs used to estimate the fair value include market price curves, contract terms and prices, and credit risk adjustments. The fair value of the interest-rate swaps as of December 31, 2018 , was an $8.0 million liability, which is reported in Accrued liabilities on the consolidated balance sheets. Credit risk considerations. Over-the-counter traded swaps expose the Partnership to counterparty credit risk. The Partnership monitors the creditworthiness of its counterparties, establishes credit limits according to the Partnership’s credit policies and guidelines, and assesses the impact on the fair value of its counterparties’ creditworthiness. The Partnership has the ability to require cash collateral or letters of credit to mitigate its credit risk exposure. The Partnership’s interest-rate swaps are subject to individually negotiated credit provisions that may require collateral of cash or letters of credit depending on the derivative’s portfolio valuation versus negotiated credit thresholds. These credit thresholds generally require full or partial collateralization of the Partnership’s obligations depending on certain credit risk related provisions. Specifically, the Partnership may be required to post collateral with respect to its interest-rate swaps if its credit ratings decline below current levels, the liability associated with the swaps increases substantially or certain credit event of default provisions occur. For example, based on the derivative positions as of December 31, 2018, if the Partnership’s credit ratings from both Standard and Poor’s and Moody’s Investors Service were below the investment grade thresholds of BBB- and Baa3, respectively, the Partnership would be required to post collateral of up to approximately $2.7 million . The aggregate fair value of interest-rate swaps with credit risk related contingent features for which a net liability position existed was $5.7 million at December 31, 2018. 13. DEBT AND INTEREST EXPENSE (CONTINUED) Interest expense. The following table summarizes the amounts included in interest expense: Year Ended December 31, thousands 2018 2017 2016 Third parties Long-term debt $ (199,322 ) $ (142,525 ) $ (121,832 ) Amortization of debt issuance costs and commitment fees (8,207 ) (6,616 ) (6,398 ) Capitalized interest 32,479 9,074 12,918 Total interest expense – third parties (175,050 ) (140,067 ) (115,312 ) Affiliates Deferred purchase price obligation – Anadarko (1) — (71 ) 7,747 APCWH Note Payable (6,746 ) (153 ) — Total interest expense – affiliates (6,746 ) (224 ) 7,747 Interest expense $ (181,796 ) $ (140,291 ) $ (107,565 ) (1) See Note 3 for a discussion of the Deferred purchase price obligation - Anadarko.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	14. COMMITMENTS AND CONTINGENCIES Environmental obligations. The Partnership 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, 2018 and 2017 , the consolidated balance sheets included $1.7 million and $1.8 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 Other liabilities. 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 Partnership’s overall results of operations, cash flows or financial condition. 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 11 and Note 12 . Litigation and legal proceedings. In February 2017, DBJV, at the time a 50 / 50 joint venture between a third party and the Partnership, initiated an arbitration against SWEPI LP (“SWEPI”) for breach of a 2007 gas gathering agreement between it and DBJV (the “GGA”). Specifically, DBJV sought to collect certain gathering fees under the GGA for the period January 1, 2016 to July 1, 2017. SWEPI disputed DBJV’s calculation of the cost of service based rate and filed a counterclaim alleging overpayment of fees under the GGA for the years 2013 through 2015. As part of the adoption of Topic 606 (see Note 1 ), during the first quarter of 2018, the Partnership recorded a $7.5 million contract liability and reduced total equity and partners’ capital related to the counterclaim for the years 2013 through 2015 under the GGA revenue contract. The arbitration hearing concluded on June 27, 2018. On September 14, 2018, the panel issued a binding non-appealable decision awarding no damages to either DBJV or SWEPI. As such, during the third quarter of 2018, the previously recorded contract liability was reversed, resulting in a $7.5 million increase to Service revenues - fee based in the consolidated statements of operations. In addition, from time to time, the Partnership 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 for which the final disposition could have a material adverse effect on the Partnership’s financial condition, results of operations or cash flows. 14. COMMITMENTS AND CONTINGENCIES (CONTINUED) Other commitments. The Partnership 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 construction and expansion projects at the DBM oil and DBM water systems and the West Texas and DJ Basin complexes. Lease commitments. Anadarko, on behalf of the Partnership, has entered into lease arrangements for corporate offices, shared field offices, a warehouse and equipment supporting the Partnership’s operations, for which Anadarko charges the Partnership rent. The leases for the corporate offices and shared field offices extend through 2028 and 2033, respectively, and the lease for the warehouse expired in February 2017. Rent expense charged to the Partnership associated with these lease arrangements was $56.5 million , $45.5 million and $37.8 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Operating leases. The amounts in the table below represent existing contractual operating lease obligations as of December 31, 2018 , that may be assigned or otherwise charged to the Partnership pursuant to the reimbursement provisions of the omnibus agreement: thousands Operating Leases 2019 $ 8,711 2020 2,236 2021 460 2022 467 2023 473 Thereafter 1,547 Total $ 13,894 See Accounting standards adopted in 2019 in Note 1 for a discussion of the expected impact the adoption of ASU 2016-02, Leases (Topic 842) will have on the consolidated financial statements.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	15. SUBSEQUENT EVENTS On November 7, 2018, WGP, the Partnership, Anadarko and certain of their affiliates entered into a Contribution Agreement and Agreement and Plan of Merger (the “Merger Agreement”), pursuant to which, among other things, Clarity Merger Sub, LLC, a wholly owned subsidiary of WGP, merged with and into the Partnership, with the Partnership continuing as the surviving entity and a subsidiary of WGP (the “Merger”). On February 28, 2019, immediately following the Merger, the common units of the Partnership ceased to trade on the NYSE under the symbol “WES.” The common units of WGP began to trade on the NYSE under the symbol “WES.” Pursuant to the Merger Agreement, the following transactions, among others, occurred immediately prior to the Merger becoming effective in the order as follows: (1) Anadarko E&P Onshore LLC and WGR Asset Holding Company LLC (“WGRAH”) (the “Contributing Parties”) contributed to the Partnership all of their interests in each of Anadarko Wattenberg Oil Complex LLC, Anadarko DJ Oil Pipeline LLC, Anadarko DJ Gas Processing LLC, Wamsutter Pipeline LLC, DBM Oil Services, LLC, Anadarko Pecos Midstream LLC, Anadarko Mi Vida LLC and APCWH to WGR Operating, LP, Kerr-McGee Gathering LLC and DBM (each wholly owned by the Partnership) in exchange for aggregate consideration of $1.814 billion in cash from the Partnership, minus the outstanding amount payable on the APCWH Note Payable assumed by the Partnership in connection with the transaction, and 45,760,201 of the Partnership’s common units; (2) AMH sold to the Partnership its interests in Saddlehorn and Panola in exchange for aggregate consideration of $193.9 million in cash; (3) the Partnership contributed cash in an amount equal to the outstanding balance of the APCWH Note Payable immediately prior to the effective time to APCWH, and APCWH paid such cash to Anadarko in satisfaction of the APCWH Note Payable; (4) Class C units converted into the Partnership’s common units on a one -for-one basis; and (5) the Partnership and its general partner caused the conversion of the IDRs and the 2,583,068 general partner units held by the general partner into a non-economic general partner interest in the Partnership and 105,624,704 of the Partnership’s common units. The 45,760,201 of the common units issued to the Contributing Parties, less 6,375,284 common units retained by WGRAH, converted into the right to receive an aggregate of 55,360,984 WGP common units upon the consummation of the Merger. See Note 13 for additional information.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Consolidation policy	Basis of presentation. The following table outlines the Partnership’s ownership interests and the accounting method of consolidation used in the Partnership’s consolidated financial statements for entities not wholly owned: Percentage Interest Equity investments (1) Fort Union 14.81 % White Cliffs 10.00 % Rendezvous 22.00 % Mont Belvieu JV 25.00 % TEP 20.00 % TEG 20.00 % FRP 33.33 % Whitethorn 20.00 % Cactus II 15.00 % Saddlehorn 20.00 % Panola 15.00 % Mi Vida 50.00 % Ranch Westex 50.00 % Proportionate consolidation (2) Marcellus Interest systems 33.75 % Springfield system 50.10 % Full consolidation Chipeta (3) 75.00 % (1) Investments in non-controlled entities over which the Partnership exercises significant influence are accounted for under the equity method. “Equity investment throughput” refers to the Partnership’s share of average throughput for these investments. (2) The Partnership proportionately consolidates its 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 interest in the consolidated financial statements. 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 the Partnership and entities in which it holds a controlling financial interest. All significant intercompany transactions have been eliminated.
Business combinations policy	Presentation of Partnership assets. The term “Partnership assets” includes both the assets owned and the interests accounted for under the equity method by the Partnership, including AMA (as defined in Note 3 ), as of December 31, 2018 (see Note 10 ). Because Anadarko controls the Partnership through its control of WGP, which owns the Partnership’s entire general partner interest, each acquisition of Partnership assets from Anadarko has been considered a transfer of net assets between entities under common control. As such, the Partnership assets acquired from Anadarko were initially recorded at Anadarko’s historic carrying value, which did not correlate to the total acquisition price paid by the Partnership. Further, after an acquisition of assets from Anadarko, the Partnership is required to recast its financial statements to include the activities of such Partnership assets from the date of common control. For those periods requiring recast, the consolidated financial statements for periods prior to the Partnership’s acquisition of the Partnership assets from Anadarko, including AMA, 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 the Partnership had owned the Partnership assets during the periods reported. Net income (loss) attributable to the Partnership assets acquired from Anadarko for periods prior to the Partnership’s acquisition of the Partnership 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 included 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). 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) 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 the Partnership’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 13 . 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.
Allowance for uncollectible accounts policy	Allowance for uncollectible accounts. 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 the Partnership may establish credit limits for significant third-party customers. The allowance for uncollectible accounts was immaterial at December 31, 2018 and 2017 .
Imbalances policy	Imbalances. The consolidated balance sheets include imbalance receivables and payables resulting from differences in volumes received into the Partnership’s systems and volumes delivered by the Partnership to customers. Volumes owed to or by the Partnership 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 the Partnership are valued at the Partnership’s weighted-average cost as of the balance sheet dates and are settled in-kind. As of December 31, 2018 , imbalance receivables and payables were $9.0 million and $9.6 million , respectively. As of December 31, 2017 , imbalance receivables and payables were $2.1 million and $3.1 million , respectively. Net changes in imbalance receivables and payables 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 net realizable value and is reported in Other current assets on the consolidated balance sheets. See Note 11 .
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 8 for a description of impairments recorded during the years ended December 31, 2018 , 2017 and 2016 . 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). In December 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. 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 the Partnership’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, the Partnership reached a settlement with insurers and final proceeds were received. During the years ended December 31, 2017 and 2016, the Partnership 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.
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 the Partnership’s weighted-average borrowing cost on debt by the average amount of qualifying costs incurred during the period. 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 Partnership assets acquired from Anadarko. The Partnership has allocated goodwill on its two reporting units: (i) gathering and processing and (ii) transportation. Goodwill is evaluated for impairment annually, as of October 1, or more often as facts and circumstances warrant. An initial qualitative assessment is performed to determine the likelihood of whether or not goodwill is impaired. 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 further testing is not necessary. If a quantitative assessment must be performed and the carrying amount of the reporting unit exceeds its fair value, goodwill is written down to its implied fair value through a charge to impairment expense. The carrying value of goodwill after such an impairment would represent a Level 3 fair value measurement. See Note 9 .
Other intangible assets policy	Other intangible assets. The Partnership assesses intangible assets, as described in Note 9 , 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 12 . Environmental expenditures. The Partnership 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 14 .
Segments policy	Segments. The Partnership’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.
Revenue and cost of product policy	Revenue and cost of product. Upon adoption of the new revenue recognition standard on January 1, 2018 (discussed in Recently adopted accounting standards ), the Partnership changed its accounting policy for revenue recognition as described below. The Partnership provides gathering, processing, treating, transportation and disposal services pursuant to a variety of contracts. Under these arrangements, the Partnership receives fees and/or retains a percentage of products or a percentage of the proceeds from the sale of the customer’s products. These revenues are included in Service revenues and Product sales in the consolidated statements of operations. Payment is generally received from the customer in the month following the service or delivery of the product. Contracts with customers generally have initial terms ranging from 5 to 10 years. Service revenues – fee based is recognized for fee-based contracts in the month of service based on the volumes delivered by the customer. Producers’ wells or production facilities are connected to the Partnership’s gathering systems for gathering, processing, treating, transportation and disposal of natural gas, NGLs, condensate, crude oil and produced water, as applicable. Revenues are valued based on the rate in effect for the month of service when the fee is either the same rate per unit over the contract term or when the fee escalates and the escalation factor approximates inflation. Deficiency fees charged to customers that do not meet their minimum delivery requirements are recognized as services are performed based on an estimate of the fees that will be billed upon completion of the performance period. Because of its significant upfront capital investment, the Partnership may charge additional service fees to customers for only a portion of the contract term (i.e., for the first year of a contract or until reaching a volume threshold), and these fees are recognized as revenue over the expected period of customer benefit, which is generally the life of the related properties. The Partnership also recognizes revenue and cost of product expense from marketing services performed on behalf of its customers by Anadarko. The Partnership also receives Service revenues – fee based from contracts that have minimum volume commitment demand fees and fees that require periodic rate redeterminations based upon the related facility cost of service. These fees include fixed and variable consideration that are recognized on a consistent per-unit rate over the term of the contract. Annual adjustments are made to the cost of service rates charged to customers, and a cumulative catch-up revenue adjustment related to services already provided to the minimum volumes under the contract may be recorded in future periods, with revenues for the remaining term of the contract recognized on a consistent per-unit rate. Service revenues – product based includes service revenues from percent-of-proceeds gathering and processing contracts that are recognized net of the cost of product for purchases from the Partnership’s customers since it is acting as the agent in the product sale. Keep-whole and percent-of-product agreements result in Service revenues – product based being recognized when the natural gas and/or NGLs are received from the customer as noncash consideration for the services provided. Noncash consideration for these services is valued at the time the services are provided. Revenue from product sales is also recognized, along with the cost of product expense related to the sale, when the product received as noncash consideration is sold to either Anadarko or a third party. When the product is sold to Anadarko, Anadarko is acting as the Partnership’s agent in the product sale, with the Partnership recognizing revenue and related cost of product expense associated with these marketing activities based on the Anadarko sales price to the third party. The Partnership also purchases natural gas volumes from producers at the wellhead or from a production facility, typically at an index price, and charges the producer fees associated with the downstream gathering and processing services. When the fees relate to services performed after control of the product has transferred to the Partnership, the fees are treated as a reduction of the purchase cost. If the fees relate to services performed before control of the product has transferred to the Partnership, the fees are treated as Service revenues – fee based. Product sales revenue is recognized, along with cost of product expense related to the sale, when the purchased product is sold to either Anadarko or a third party. The Partnership receives aid in construction reimbursements for certain capital costs necessary to provide services to customers (i.e., connection costs, etc.) under certain service contracts. Aid in construction reimbursements are reflected as a contract liability upon receipt and amortized to Service revenues – fee based over the expected period of customer benefit, which is generally the life of the related properties.
Equity-based compensation policy	Equity-based compensation. 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, the Partnership’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, of which 2,241,980 units remained available for future issuance as of December 31, 2018 . Upon vesting of each phantom unit, the holder will receive common units of the Partnership or, at the discretion of the Board of Directors of its general partner (the “Board of Directors”), cash in an amount equal to the market value of common units of the Partnership 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. Equity-based compensation expense attributable to grants made under the WES LTIP is amortized over the vesting periods applicable to the awards. Additionally, general and administrative expenses include equity-based compensation costs allocated by Anadarko to the Partnership for grants made pursuant to (i) the Western Gas Equity Partners, LP 2012 Long-Term Incentive Plan (the “WGP LTIP”) and (ii) the Anadarko Petroleum Corporation 2012 Omnibus Incentive Compensation Plan, as amended and restated (the “Anadarko Incentive Plan”) 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 WGP LTIP and the Anadarko Incentive Plan 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	Income taxes. The Partnership 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. The Partnership routinely assesses the realizability of its deferred tax assets. If the Partnership 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 the Partnership assets prior to the Partnership’s acquisition of these assets from Anadarko. For periods beginning on and subsequent to the Partnership’s acquisition of the Partnership assets, the Partnership makes payments to Anadarko pursuant to the tax sharing agreement entered into between Anadarko and the Partnership for its estimated share of taxes from all forms of taxation, excluding income 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 the Partnership’s assets for financial and tax reporting purposes cannot be readily determined as the Partnership does not have access to information about each partner’s tax attributes in the Partnership. 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. The Partnership had no material uncertain tax positions at December 31, 2018 or 2017 . With respect to assets acquired from Anadarko, the Partnership recorded Anadarko’s historic deferred income taxes for the periods prior to the Partnership’s ownership of the assets. For periods on and subsequent to the Partnership’s acquisition, the Partnership 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. Net income (loss) attributable to the Partnership assets acquired from Anadarko for periods prior to the Partnership’s acquisition of the Partnership assets is not allocated to the unitholders for purposes of calculating net income (loss) per common unit. Net income (loss) attributable to Western Gas Partners, LP earned on and subsequent to the date of acquisition of the Partnership assets is allocated as follows: General partner. The general partner’s allocation is equal to cash distributions plus its portion of undistributed earnings or losses. Specifically, net income equal to the amount of available cash (as defined by the partnership agreement) is allocated to the general partner consistent with actual cash distributions and capital account allocations, including incentive distributions. Undistributed earnings (net income in excess of distributions) or undistributed losses (available cash in excess of net income) are then allocated to the general partner in accordance with its weighted-average ownership percentage during each period. Series A Preferred unitholders. The Series A Preferred units were not considered a participating security as they only had distribution rights up to the specified per-unit quarterly distribution and had no rights to the Partnership’s undistributed earnings and losses. As such, the Series A Preferred unitholders’ allocation was equal to their cash distribution plus the amortization of the Series A Preferred units beneficial conversion feature (see Series A Preferred units above). 5. EQUITY AND PARTNERS’ CAPITAL (CONTINUED) Common and Class C unitholders. The Class C units are considered a participating security because they participate in distributions with common units according to a predetermined formula (see Note 4 ). The common and Class C unitholders’ allocation is equal to their cash distributions plus their respective allocations of undistributed earnings or losses. Specifically, net income equal to the amount of available cash (as defined by the partnership agreement) is allocated to the common and Class C unitholders consistent with actual cash distributions and capital account allocations. Undistributed earnings or undistributed losses are then allocated to the common and Class C unitholders in accordance with their respective weighted-average ownership percentages during each period. The common unitholder allocation also includes the impact of the amortization of the Series A Preferred units and Class C units beneficial conversion features. The Class C unitholder allocation is similarly impacted by the amortization of the Class C units beneficial conversion feature (see Class C units above). Calculation of net income (loss) per unit. Basic net income (loss) per common unit is calculated by dividing the net income (loss) attributable to common unitholders by the weighted-average number of common units outstanding during the period. The common units issued in connection with acquisitions and equity offerings are included on a weighted-average basis for periods they were outstanding. Diluted net income (loss) per common unit is calculated by dividing the sum of (i) the net income (loss) attributable to common units adjusted for distributions on the Series A Preferred units and a reallocation of the common and Class C limited partners’ interest in net income (loss) assuming, prior to the actual conversion, conversion of the Series A Preferred units into common units, and (ii) the net income (loss) attributable to the Class C units as a participating security, by the sum of the weighted-average number of common units outstanding plus the dilutive effect of (i) the weighted-average number of outstanding Class C units and (ii) the weighted-average number of common units outstanding assuming, prior to the actual conversion, conversion of the Series A Preferred units.
New accounting standards policy	Recently adopted accounting standards. Accounting Standards Update (“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. The Partnership adopted this ASU using a retrospective approach on January 1, 2018, with no impact to the consolidated financial statements. Revenue from contracts with customers (Topic 606). The Partnership adopted Topic 606 on 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 was recognized in the opening balance of equity and partners’ capital was a decrease of $43.8 million . The comparative historical financial information has not been adjusted and continues to be reported under Revenue Recognition (Topic 605) (“Topic 605”). Effective January 1, 2018, the Partnership changed its accounting policy for revenue recognition as detailed below: • Fee-based gathering / processing. Under Topic 605, fee revenues were 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, deficiency fees were charged and recognized only when the customer did not meet the specified delivery minimums for the completed performance period. Under Topic 606, (i) revenues continue to be recognized based on the rate in effect when the fee is either the same rate per unit over the contract term or when the fee escalates and the escalation factor approximates inflation, (ii) deficiency fees are estimated and recognized during the performance period as the services are performed for the customer’s delivered volumes, and (iii) timing differences between Service revenues – fee based recognized and amounts billed to customers are recognized as contract assets or contract liabilities, as appropriate, which results in a change in the timing of revenue and changes to net income as a result of the revenue contract’s consideration provisions. In addition, under Topic 606, revenue associated with upfront or limited-term fees is recognized over the expected period of customer benefit, which is generally the life of the related properties. These revenues also include revenues earned for marketing services performed on behalf of the Partnership’s customers, and the expense associated with these marketing activities is recognized in cost of product expense, resulting in no impact to Operating income (loss). 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) • Cost of service rate adjustments. Under Topic 605, revenue was recognized based on the amounts billed to customers each period as Service revenues – fee based. Under Topic 606, fixed minimum volume commitment demand fees and variable fees that are also billed on these minimum volumes are recognized as Service revenues – fee based on a consistent per-unit rate over the term of the contract. Annual adjustments are made to the cost of service rates charged to customers, and, as a result, a cumulative catch-up revenue adjustment related to the services already provided under the contract may be recorded in future periods, with revenues for the remaining term of the contract recognized on a consistent per-unit rate. Fees received on volumes in excess of the minimum volumes are recognized as Service revenues – fee based as service is provided to the customer based on the billing rate in effect for the performance period. This revenue recognition timing does not affect billings to customers, and differences between amounts billed and revenue recognized are recorded as contract assets or liabilities, as appropriate. • Aid in construction. Under Topic 605, aid in construction reimbursements were reflected as a reduction to property, plant and equipment upon receipt (and a reduction to capital expenditures). Under Topic 606, reimbursement of capital costs received from customers is reflected as a contract liability (deferred revenue) upon receipt. The contract liability is amortized to Service revenues – fee based over the expected period of customer benefit, which is generally the life of the related properties. • Percent-of-proceeds gathering / processing. Under Topic 605, the Partnership recognized cost of product expense when the product was purchased from a producer to whom it provides services, and the Partnership recognized revenue when the product was sold to Anadarko or 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 is presented net within Service revenues – product based because the Partnership is acting as the producer’s agent in the product sale. • Noncash consideration - keep-whole and percent-of-product agreements. Under Topic 605, the Partnership recognized revenues only upon the sale of the related products. Under Topic 606, (i) Service revenues – product based is recognized for the products received as noncash consideration in exchange for the services provided, with the keep-whole noncash consideration value based on the net value of the NGLs over the replacement residue gas cost, and (ii) product sales revenue is recognized, along with cost of product expense related to the sale, when the product is sold to Anadarko or a third party. When the product is sold to Anadarko, Anadarko is acting as the Partnership’s agent in the product sale and the Partnership recognizes revenue, along with cost of product expense related to the sale, based on the Anadarko sales price to the third party, resulting in no impact to Operating income (loss). • Wellhead purchase / sale incorporated into gathering / processing. Under Topic 605, the natural gas purchase cost was recognized as cost of product expense and any specified gathering or processing fees charged to the producer were recognized as revenues. Under Topic 606, the fees charged to the producer under this contract type are recognized as adjustments to the amount recognized in cost of product expense instead of revenues when such fees relate to services performed after control of the product transfers to the Partnership. 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) The following tables summarize the impact of adopting Topic 606 on the impacted line items within the consolidated statement of operations and the consolidated balance sheet. The differences between revenue as reported following Topic 606 and revenue as it would have been reported under Topic 605 are due to the changes described above. Year Ended thousands As Reported Without Adoption of Topic 606 Effect of Change Increase / (Decrease) Revenues Service revenues – fee based $ 1,905,728 $ 1,751,242 $ 154,486 Service revenues – product based 88,785 — 88,785 Product sales 303,020 1,405,898 (1,102,878 ) Expenses Cost of product 415,505 1,338,100 (922,595 ) Operation and maintenance 480,861 480,668 193 Depreciation and amortization 389,164 386,179 2,985 Impairments 230,584 230,539 45 Income tax expense (benefit) 58,934 58,804 130 Net income attributable to noncontrolling interest 8,609 8,541 68 Net income (loss) attributable to Western Gas Partners, LP 627,917 568,350 59,567 December 31, 2018 thousands As Reported Without Adoption of Topic 606 Effect of Change Increase / (Decrease) Assets Other current assets $ 26,181 $ 20,782 $ 5,399 Net property, plant and equipment 8,410,353 8,291,554 118,799 Other assets 67,194 24,972 42,222 Liabilities Accrued liabilities 127,874 121,967 5,907 Deferred income taxes 280,017 254,939 25,078 Other liabilities 132,130 2,741 129,389 Equity and partners’ capital Total equity and partners’ capital 4,919,597 4,913,551 6,046 1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (CONTINUED) Accounting standards adopted in 2019. 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. This standard is effective for periods beginning after December 15, 2018, and in the first quarter of 2019, the Partnership fully adopted this standard using the modified retrospective method applied to all leases that existed on January 1, 2019. The Partnership made certain elections allowing the Partnership not to reassess contracts that commenced prior to adoption, to continue applying its current accounting policy for existing or expired land easements and not to recognize ROU assets or lease liabilities for short-term leases. Upon adoption, the Partnership recognized approximately $10.0 million of ROU assets and corresponding lease liabilities on the consolidated balance sheet. The adoption of this ASU did not have a material impact on the consolidated statement of operations or the consolidated statement of cash flows. The Partnership has implemented the necessary changes to its business processes, systems and controls to support accounting and disclosure requirements under this ASU.
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.
Derivatives policy	The Partnership does not apply hedge accounting and, therefore, gains and losses associated with the interest-rate swaps are recognized currently in earnings. For the year ended December 31, 2018 , the Partnership recognized a non-cash loss of $8.0 million , which is included in Other income (expense), net in the consolidated statements of operations. Valuation of the interest-rate swaps is based on similar transactions observable in active markets and industry standard models that primarily rely on market-observable inputs. Inputs used to estimate fair value in industry standard models are categorized as Level 2 inputs, because substantially all assumptions and inputs are observable in active markets throughout the full term of the instruments. Inputs used to estimate the fair value include market price curves, contract terms and prices, and credit risk adjustments. The fair value of the interest-rate swaps as of December 31, 2018 , was an $8.0 million liability, which is reported in Accrued liabilities on the consolidated balance sheets.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Assets and Investments Table	As of December 31, 2018 , the Partnership’s assets and investments, including AMA (as defined in Note 3 ), consisted of the following: Owned and Operated Operated Interests Non-Operated Interests Equity Interests Gathering systems (1) 17 2 3 2 Treating facilities 34 3 — 3 Natural gas processing plants/trains 23 3 — 5 NGLs pipelines 2 — — 4 Natural gas pipelines 5 — — — Oil pipelines 3 1 — 3 (1) Includes the DBM water systems.
Ownership Interests and Method of Consolidation Table	The following table outlines the Partnership’s ownership interests and the accounting method of consolidation used in the Partnership’s consolidated financial statements for entities not wholly owned: Percentage Interest Equity investments (1) Fort Union 14.81 % White Cliffs 10.00 % Rendezvous 22.00 % Mont Belvieu JV 25.00 % TEP 20.00 % TEG 20.00 % FRP 33.33 % Whitethorn 20.00 % Cactus II 15.00 % Saddlehorn 20.00 % Panola 15.00 % Mi Vida 50.00 % Ranch Westex 50.00 % Proportionate consolidation (2) Marcellus Interest systems 33.75 % Springfield system 50.10 % Full consolidation Chipeta (3) 75.00 % (1) Investments in non-controlled entities over which the Partnership exercises significant influence are accounted for under the equity method. “Equity investment throughput” refers to the Partnership’s share of average throughput for these investments. (2) The Partnership proportionately consolidates its 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 interest in the consolidated financial statements.
Impact of New Accounting Pronouncement Tables	The following tables summarize the impact of adopting Topic 606 on the impacted line items within the consolidated statement of operations and the consolidated balance sheet. The differences between revenue as reported following Topic 606 and revenue as it would have been reported under Topic 605 are due to the changes described above. Year Ended thousands As Reported Without Adoption of Topic 606 Effect of Change Increase / (Decrease) Revenues Service revenues – fee based $ 1,905,728 $ 1,751,242 $ 154,486 Service revenues – product based 88,785 — 88,785 Product sales 303,020 1,405,898 (1,102,878 ) Expenses Cost of product 415,505 1,338,100 (922,595 ) Operation and maintenance 480,861 480,668 193 Depreciation and amortization 389,164 386,179 2,985 Impairments 230,584 230,539 45 Income tax expense (benefit) 58,934 58,804 130 Net income attributable to noncontrolling interest 8,609 8,541 68 Net income (loss) attributable to Western Gas Partners, LP 627,917 568,350 59,567 December 31, 2018 thousands As Reported Without Adoption of Topic 606 Effect of Change Increase / (Decrease) Assets Other current assets $ 26,181 $ 20,782 $ 5,399 Net property, plant and equipment 8,410,353 8,291,554 118,799 Other assets 67,194 24,972 42,222 Liabilities Accrued liabilities 127,874 121,967 5,907 Deferred income taxes 280,017 254,939 25,078 Other liabilities 132,130 2,741 129,389 Equity and partners’ capital Total equity and partners’ capital 4,919,597 4,913,551 6,046

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Summary of Revenue from Contracts with Customers Table	The following table summarizes the Partnership’s revenue from contracts with customers: thousands Year Ended Revenue from customers Service revenues – fee based $ 1,905,728 Service revenues – product based 88,785 Product sales 310,895 Total revenue from customers 2,305,408 Revenue from other than customers Net gains (losses) on commodity price swap agreements (7,875 ) Other 2,125 Total revenues and other $ 2,299,658
Contract Assets and Liabilities Activity Tables	The following table summarizes the current period activity related to contract liabilities from contracts with customers: thousands Balance at December 31, 2017 $ — Cumulative effect of adopting Topic 606 120,309 Cash received or receivable, excluding revenues recognized during the period 55,786 Assets received from customer 12,933 Revenues recognized during the period that were included in the adoption effect (1) (21,556 ) Cumulative catch up adjustment for change in estimated consideration due to cost of service rate updates (21,848 ) Balance at December 31, 2018 $ 145,624 Contract liabilities at December 31, 2018 Accrued liabilities $ 16,235 Other liabilities 129,389 Total contract liabilities from contracts with customers $ 145,624 (1) Includes $(7.5) million from a performance obligation satisfied in a previous period related to the arbitration against SWEPI LP (see Note 14 ). The following table summarizes the current period activity related to contract assets from contracts with customers: thousands Balance at December 31, 2017 $ — Cumulative effect of adopting Topic 606 5,950 Amounts transferred to Accounts receivable, net from contract assets recognized in the adoption effect (4,952 ) Additional estimated revenues recognized 30,519 Cumulative catch up adjustment for change in estimated consideration due to cost of service rate updates 16,104 Balance at December 31, 2018 $ 47,621 Contract assets at December 31, 2018 Other current assets $ 5,399 Other assets 42,222 Total contract assets from contracts with customers $ 47,621
Expected Revenue Recognition from Satisfaction of Performance Obligations Table	Therefore, the following table represents only a portion of expected future revenues from existing contracts as most future revenues from customers are dependent on future variable customer volumes and, in some cases, variable commodity prices for those volumes. thousands 2019 $ 674,609 2020 847,045 2021 894,706 2022 947,310 2023 913,099 Thereafter 4,565,428 Total $ 8,842,197

Acquisitions and Divestitures (

Acquisitions and Divestitures (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Impact to Historical Consolidated Statements of Income Table	The following table presents the impact of AMA on Revenues and other, Equity income, net – affiliates and Net income (loss) as presented in the Partnership’s historical consolidated statements of operations: Year Ended December 31, 2018 thousands Partnership Historical AMA Eliminations Combined Revenues and other $ 1,990,276 $ 343,499 $ (34,117 ) $ 2,299,658 Equity income, net – affiliates 153,024 42,445 — 195,469 Net income (loss) 454,384 182,142 — 636,526 Year Ended December 31, 2017 thousands Partnership Historical AMA Eliminations Combined Revenues and other $ 2,248,356 $ 192,853 $ (11,595 ) $ 2,429,614 Equity income, net – affiliates 85,194 29,947 — 115,141 Net income (loss) 578,218 164,183 — 742,401 3. ACQUISITIONS AND DIVESTITURES (CONTINUED) Year Ended December 31, 2016 thousands Partnership Historical AMA Eliminations Combined Revenues and other $ 1,804,270 $ 138,269 $ (1,209 ) $ 1,941,330 Equity income, net – affiliates 78,717 22,975 — 101,692 Net income (loss) 602,294 61,306 — 663,600
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
	Dec. 31, 2018
Distribution Made to Limited Partner [Line Items]
Cash Distributions Table	The Board of Directors declared the following cash distributions to the Partnership’s common and general partner unitholders 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 $ 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 0.920 216,586 February 2018 2018 March 31 $ 0.935 $ 221,133 May 2018 June 30 0.950 225,691 August 2018 September 30 0.965 230,239 November 2018 December 31 (1) 0.980 234,787 February 2019 (1) The Board of Directors declared a cash distribution to the Partnership’s unitholders for the fourth quarter of 2018 of $0.980 per unit, or $234.8 million in aggregate, including incentive distributions, but excluding distributions on Class C units (see Class C unit distributions below). The cash distribution was paid on February 13, 2019 , to unitholders of record at the close of business on February 1, 2019 .
Series A Preferred Units [Member]
Distribution Made to Limited Partner [Line Items]
Cash Distributions Table	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 Series A Preferred units were outstanding during the first quarter of 2016. (2) Full quarterly per unit distribution on 14,030,611 Series A Preferred units and quarterly per unit distribution prorated for the 77 -day period during which 7,892,220 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
	Dec. 31, 2018
Partners' Capital Notes [Abstract]
Partnership Interests Table	The following table summarizes the Partnership’s units issued during the years ended December 31, 2018 and 2017: Common Units Class C Units Series A Preferred Units General Partner Units Total 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 PIK Class C units — 1,128,782 — — 1,128,782 Long-Term Incentive Plan award vestings 7,180 — — — 7,180 Balance at December 31, 2018 152,609,285 14,372,665 — 2,583,068 169,565,018
Calculation of Net Income (Loss) Per Unit Table	The following table illustrates the Partnership’s calculation of net income (loss) per common unit: Year Ended December 31, thousands except per-unit amounts 2018 2017 2016 Net income (loss) attributable to Western Gas Partners, LP $ 627,917 $ 731,666 $ 652,637 Pre-acquisition net (income) loss allocated to Anadarko (182,142 ) (164,183 ) (72,632 ) Series A Preferred units interest in net (income) loss (1) — (42,373 ) (76,893 ) General partner interest in net (income) loss (346,538 ) (303,835 ) (236,561 ) Common and Class C limited partners’ interest in net income (loss) $ 99,237 $ 221,275 $ 266,551 Net income (loss) allocable to common units (1) $ 84,334 $ 192,066 $ 226,611 Net income (loss) allocable to Class C units (1) 14,903 29,209 39,940 Common and Class C limited partners’ interest in net income (loss) $ 99,237 $ 221,275 $ 266,551 Net income (loss) per unit Common units – basic and diluted (2) $ 0.55 $ 1.30 $ 1.74 Weighted-average units outstanding Common units – basic and diluted 152,606 147,194 130,253 Excluded due to anti-dilutive effect: Class C units (2) 13,795 12,776 11,945 Series A Preferred units assuming conversion to common units (2) — 5,406 16,860 (1) Adjusted to reflect amortization of the beneficial conversion features. (2) The impact of Class C units would be anti-dilutive for all periods presented and the conversion of Series A Preferred units would be anti-dilutive for the years ended December 31, 2017 and 2016. On March 1, 2017, 50% of the outstanding Series A Preferred units converted into common units on a one -for-one basis, and on May 2, 2017, all remaining Series A Preferred units converted into common units on a one -for-one basis.

Transactions with Affiliates (T

Transactions with Affiliates (Tables)	12 Months Ended
	Dec. 31, 2018
Related Party Fees and Other Arrangements, Limited Liability Company (LLC) or Limited Partnership (LP) [Abstract]
Commodity Price Swap Agreements Tables	The tables below summarize the swap prices compared to the forward market prices: DJ Basin Complex per barrel except natural gas 2016 - 2018 Swap Prices 2016 Market Prices (1) 2017 Market Prices (1) 2018 Market Prices (1) Ethane $ 18.41 $ 0.60 $ 5.09 $ 5.41 Propane 47.08 10.98 18.85 28.72 Isobutane 62.09 17.23 26.83 32.92 Normal butane 54.62 16.86 26.20 32.71 Natural gasoline 72.88 26.15 41.84 48.04 Condensate 76.47 34.65 45.40 49.36 Natural gas (per MMBtu) 5.96 2.11 3.05 2.21 Hugoton System (2) per barrel except natural gas 2016 Swap Prices 2016 Market Prices (1) Condensate $ 78.61 $ 18.81 Natural gas (per MMBtu) 5.50 2.12 MGR Assets per barrel except natural gas 2016 - 2018 Swap Prices 2017 Market Prices (1) 2018 Market Prices (1) Ethane $ 23.11 $ 4.08 $ 2.52 Propane 52.90 19.24 25.83 Isobutane 73.89 25.79 30.03 Normal butane 64.93 25.16 29.82 Natural gasoline 81.68 45.01 47.25 Condensate 81.68 53.55 56.76 Natural gas (per MMBtu) 4.87 3.05 2.21 (1) Represents the New York Mercantile Exchange forward strip price as of December 8, 2015, December 1, 2016, and December 20, 2017, for the 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 3 .
Related Party Transactions Tables	The following table summarizes material affiliate transactions: Year ended December 31, thousands 2018 2017 2016 Revenues and other (1) $ 1,353,711 $ 1,539,105 $ 1,358,918 Equity income, net – affiliates (1) 195,469 115,141 101,692 Cost of product (1) 168,535 74,560 75,983 Operation and maintenance (2) 115,948 82,249 82,133 General and administrative (3) 48,819 42,411 41,176 Operating expenses 333,302 199,220 199,292 Interest income (4) 16,900 16,900 16,900 Interest expense (5) (6) 6,746 224 (7,747 ) APCWH Note Payable borrowings (6) 321,780 98,813 — Settlement of the Deferred purchase price obligation – Anadarko (7) — (37,346 ) — Proceeds from the issuance of common units, net of offering expenses (8) — — 25,000 Distributions to unitholders (9) 514,906 452,777 382,711 Above-market component of swap agreements with Anadarko 51,618 58,551 45,820 (1) Represents amounts earned or incurred on and subsequent to the date of the acquisition of Partnership assets, as well as amounts earned or incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets. (2) Represents expenses incurred on and subsequent to the date of the acquisition of Partnership assets, as well as expenses incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets. (3) Represents general and administrative expense incurred on and subsequent to the date of the acquisition of Partnership assets, as well as a management services fee for expenses incurred by Anadarko for periods prior to the acquisition of the Partnership assets by the Partnership. These amounts include equity-based compensation expense allocated to the Partnership by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plan within this Note 6 ) and amounts charged by Anadarko under the omnibus agreement. (4) Represents interest income recognized on the note receivable from Anadarko. (5) Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 3 and Note 13 ). (6) Includes amounts related to the APCWH Note Payable (see Note 13 and Note 15 ). (7) Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 3 ). (8) Represents proceeds from the issuance of 835,841 common units to WGP as partial funding for the acquisition of Springfield (see Note 3 ). (9) Represents distributions paid under the partnership agreement (see Note 4 and Note 5 ). The following table summarizes Anadarko’s contributions and distributions of other assets to the Partnership: Year Ended December 31, 2018 2017 2016 2018 2017 2016 thousands Purchases Sales Cash consideration $ (254 ) $ (3,910 ) $ (3,965 ) $ — $ — $ 623 Net carrying value 59,089 5,283 3,496 — — (605 ) Partners’ capital adjustment $ 58,835 $ 1,373 $ (469 ) $ — $ — $ 18 The following table summarizes the amounts the Partnership reimbursed to Anadarko: Year Ended December 31, thousands 2018 2017 2016 General and administrative expenses $ 35,077 $ 31,733 $ 29,360 Public company expenses 15,409 9,379 8,410 Total reimbursement $ 50,486 $ 41,112 $ 37,770
LTIP Award Activity Table	The following table summarizes WES LTIP award activity for the years ended December 31, 2018 , 2017 and 2016 : 2018 2017 2016 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 $ 55.73 7,180 $ 49.30 7,304 $ 68.78 5,477 Vested 55.73 (7,180 ) 49.30 (7,304 ) 68.78 (5,477 ) Granted 49.88 8,020 55.73 7,180 49.30 7,304 Phantom units outstanding at end of year 49.88 8,020 55.73 7,180 49.30 7,304

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Components of Income Tax Expense (Benefit) Table	The components of the Partnership’s income tax expense (benefit) are as follows: Year Ended December 31, thousands 2018 2017 2016 Current income tax expense (benefit) Federal income tax expense (benefit) $ (79,264 ) $ (9,207 ) $ (19,480 ) State income tax expense (benefit) (850 ) 2,422 1,257 Total current income tax expense (benefit) (80,114 ) (6,785 ) (18,223 ) Deferred income tax expense (benefit) Federal income tax expense (benefit) 133,044 (55,835 ) 49,855 State income tax expense (benefit) 6,004 2,697 1,337 Total deferred income tax expense (benefit) 139,048 (53,138 ) 51,192 Total income tax expense (benefit) $ 58,934 $ (59,923 ) $ 32,969
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 2018 2017 2016 Income (loss) before income taxes $ 695,460 $ 682,478 $ 696,569 Statutory tax rate — % — % — % Tax computed at statutory rate $ — $ — $ — Adjustments resulting from: U.S. federal tax reform — (87,306 ) — Federal taxes on income attributable to Partnership assets pre-acquisition 54,243 22,353 30,550 State taxes on income attributable to Partnership assets pre-acquisition (net of federal benefit) 1,745 164 326 Texas margin tax expense (benefit) 2,946 4,866 2,093 Income tax expense (benefit) $ 58,934 $ (59,923 ) $ 32,969 Effective tax rate 8 % (9 )% 5 %
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 2018 2017 Depreciable property $ (280,377 ) $ (139,902 ) Credit carryforwards 497 448 Other intangible assets (299 ) (189 ) Other 162 8 Net long-term deferred income tax liabilities $ (280,017 ) $ (139,635 )

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
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 2018 2017 Land n/a $ 5,298 $ 5,096 Gathering systems and processing complexes 3 to 49 years 10,441,574 7,851,458 Pipelines and equipment 6 to 45 years 172,497 137,644 Assets under construction n/a 604,265 954,719 Other 3 to 40 years 35,139 30,701 Total property, plant and equipment 11,258,773 8,979,618 Less accumulated depreciation 2,848,420 2,213,718 Net property, plant and equipment $ 8,410,353 $ 6,765,900

Goodwill and Intangibles (Table

Goodwill and Intangibles (Tables)	12 Months Ended
	Dec. 31, 2018
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 2018 2017 Gross carrying amount $ 979,863 $ 979,863 Accumulated amortization (138,455 ) (107,676 ) Other intangible assets $ 841,408 $ 872,187

Equity Investments (Tables)

Equity Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity Investments Tables	The following tables present the activity in the Partnership’s equity investments for the years ended December 31, 2018 and 2017: thousands Balance at December 31, 2016 Impairment expense (1) Acquisitions Equity income, net Contributions Distributions Distributions in excess of cumulative earnings (2) Balance at December 31, 2017 Fort Union $ 12,833 $ (3,110 ) $ — $ 3,821 $ — $ (4,217 ) $ (2,297 ) $ 7,030 White Cliffs 47,319 — — 12,547 277 (11,965 ) (3,233 ) 44,945 Rendezvous 46,739 — — 1,144 — (3,085 ) (2,270 ) 42,528 Mont Belvieu JV 112,805 — — 29,444 — (29,482 ) (2,468 ) 110,299 TEG 15,846 — — 3,350 — (3,317 ) — 15,879 TEP 189,194 — — 17,387 107 (17,639 ) (10,074 ) 178,975 FRP 169,472 — — 17,501 — (17,675 ) (2,743 ) 166,555 Saddlehorn 107,420 — — 10,001 2,454 (10,127 ) (521 ) 109,227 Panola 24,546 — — 2,230 46 (2,470 ) (727 ) 23,625 Mi Vida 67,738 — — 10,029 — (9,161 ) (3,618 ) 64,988 Ranch Westex 34,777 — 22,500 7,687 — (7,955 ) (3,708 ) 53,301 Total $ 828,689 $ (3,110 ) $ 22,500 $ 115,141 $ 2,884 $ (117,093 ) $ (31,659 ) $ 817,352 thousands Balance at December 31, 2017 Acquisitions Equity income, net Contributions (3) Distributions Distributions in excess of cumulative earnings (2) Balance at December 31, 2018 Fort Union $ 7,030 $ — $ (1,433 ) $ — $ (194 ) $ (3,144 ) $ 2,259 White Cliffs 44,945 — 11,841 1,278 (11,259 ) (3,785 ) 43,020 Rendezvous 42,528 — 767 — (2,709 ) (2,745 ) 37,841 Mont Belvieu JV 110,299 — 29,200 — (29,239 ) (5,311 ) 104,949 TEG 15,879 — 4,290 3,720 (4,368 ) (163 ) 19,358 TEP 178,975 — 37,963 11,980 (33,552 ) (2,168 ) 193,198 FRP 166,555 — 23,308 14,980 (23,481 ) (4,926 ) 176,436 Saddlehorn 109,227 — 15,833 294 (16,017 ) (830 ) 108,507 Panola 23,625 — 2,200 — (2,200 ) (856 ) 22,769 Mi Vida 64,988 — 13,734 — (14,000 ) (91 ) 64,631 Ranch Westex 53,301 — 10,678 — (10,876 ) (2,201 ) 50,902 Whitethorn — 150,563 47,088 7,069 (39,497 ) (3,365 ) 161,858 Cactus II — 12,052 — 94,308 — — 106,360 Total $ 817,352 $ 162,615 $ 195,469 $ 133,629 $ (187,392 ) $ (29,585 ) $ 1,092,088 (1) Recorded in Impairments in the consolidated statements of operations. (2) 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. (3) Includes capitalized interest of $1.4 million related to the construction of the Cactus II pipeline.
Summarized Equity Investments Financial Information Presented at 100 Percent Tables	The following tables present the summarized combined financial information for the Partnership’s equity investments (amounts represent 100% of investee financial information): Year Ended December 31, thousands 2018 2017 2016 Revenues $ 1,300,921 $ 877,020 $ 806,671 Operating income 876,910 542,390 503,239 Net income 874,587 540,538 502,260 December 31, thousands 2018 2017 Current assets $ 297,143 $ 214,473 Property, plant and equipment, net 4,251,020 3,366,754 Other assets 81,769 84,522 Total assets $ 4,629,932 $ 3,665,749 Current liabilities 101,729 112,143 Non-current liabilities 42,431 45,413 Equity 4,485,772 3,508,193 Total liabilities and equity $ 4,629,932 $ 3,665,749

Components of Working Capital (

Components of Working Capital (Tables)	12 Months Ended
	Dec. 31, 2018
Components Of Working Capital [Abstract]
Accounts Receivable, Net Table	A summary of accounts receivable, net is as follows: December 31, thousands 2018 2017 Trade receivables, net $ 221,328 $ 160,700 Other receivables, net 45 210 Total accounts receivable, net $ 221,373 $ 160,910
Other Current Assets Table	A summary of other current assets is as follows: December 31, thousands 2018 2017 NGLs inventory $ 6,466 $ 10,958 Imbalance receivables 9,035 2,063 Prepaid insurance 1,972 2,388 Contract assets 5,399 — Other 3,309 — Total other current assets $ 26,181 $ 15,409
Accrued Liabilities Table	A summary of accrued liabilities is as follows: December 31, thousands 2018 2017 Accrued interest expense $ 70,959 $ 40,632 Short-term asset retirement obligations 25,938 2,304 Short-term remediation and reclamation obligations 863 833 Income taxes payable 384 2,495 Contract liabilities 16,235 — Other 13,495 1,635 Total accrued liabilities $ 127,874 $ 47,899

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2018
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 2018 2017 Carrying amount of asset retirement obligations at beginning of year $ 154,571 $ 150,082 Liabilities incurred 34,558 17,932 Liabilities settled (12,432 ) (10,468 ) Accretion expense 7,909 7,339 Revisions in estimated liabilities 141,356 (10,314 ) Carrying amount of asset retirement obligations at end of year $ 325,962 $ 154,571

Debt and Interest Expense (Tabl

Debt and Interest Expense (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Instruments [Abstract]
Debt Outstanding and Debt Activity Tables	The following table presents the Partnership’s outstanding debt: December 31, 2018 December 31, 2017 thousands Principal Carrying Value Fair Value (1) Principal Carrying Value Fair Value (1) 2.600% Senior Notes due 2018 $ — $ — $ — $ 350,000 $ 349,684 $ 350,631 5.375% Senior Notes due 2021 500,000 496,959 515,990 500,000 495,815 530,647 4.000% Senior Notes due 2022 670,000 669,078 662,109 670,000 668,849 684,043 3.950% Senior Notes due 2025 500,000 492,837 466,135 500,000 491,885 500,885 4.650% Senior Notes due 2026 500,000 495,710 483,994 500,000 495,245 520,144 4.500% Senior Notes due 2028 400,000 394,631 377,475 — — — 4.750% Senior Notes due 2028 400,000 395,841 384,370 — — — 5.450% Senior Notes due 2044 600,000 593,349 522,386 600,000 593,234 637,827 5.300% Senior Notes due 2048 700,000 686,648 605,327 — — — 5.500% Senior Notes due 2048 350,000 342,328 311,536 — — — RCF 220,000 220,000 220,000 370,000 370,000 370,000 APCWH Note Payable 427,493 427,493 427,493 98,966 98,966 98,966 Total long-term debt $ 5,267,493 $ 5,214,874 $ 4,976,815 $ 3,588,966 $ 3,563,678 $ 3,693,143 (1) Fair value is measured using the market approach and Level 2 inputs. Debt activity. The following table presents the debt activity of the Partnership for the years ended December 31, 2018 and 2017: thousands Carrying Value Balance at December 31, 2016 $ 3,091,461 RCF borrowings 370,000 APCWH Note Payable borrowings 98,813 Other 3,404 Balance at December 31, 2017 $ 3,563,678 RCF borrowings 540,000 APCWH Note Payable borrowings 321,780 Issuance of 4.500% Senior Notes due 2028 400,000 Issuance of 5.300% Senior Notes due 2048 700,000 Issuance of 4.750% Senior Notes due 2028 400,000 Issuance of 5.500% Senior Notes due 2048 350,000 Repayment of 2.600% Senior Notes due 2018 (350,000 ) Repayments of RCF borrowings (690,000 ) Other (20,584 ) Balance at December 31, 2018 $ 5,214,874
Interest-Rate Swap Table	The following interest-rate swaps were outstanding as of December 31, 2018 : Notional Principal Amount Reference Period Mandatory Termination Date Fixed Interest Rate $250.0 million December 2019 - 2024 December 2019 2.730% $250.0 million December 2019 - 2029 December 2019 2.856% $250.0 million December 2019 - 2049 December 2019 2.905%
Interest Expense Table	The following table summarizes the amounts included in interest expense: Year Ended December 31, thousands 2018 2017 2016 Third parties Long-term debt $ (199,322 ) $ (142,525 ) $ (121,832 ) Amortization of debt issuance costs and commitment fees (8,207 ) (6,616 ) (6,398 ) Capitalized interest 32,479 9,074 12,918 Total interest expense – third parties (175,050 ) (140,067 ) (115,312 ) Affiliates Deferred purchase price obligation – Anadarko (1) — (71 ) 7,747 APCWH Note Payable (6,746 ) (153 ) — Total interest expense – affiliates (6,746 ) (224 ) 7,747 Interest expense $ (181,796 ) $ (140,291 ) $ (107,565 ) (1) See Note 3 for a discussion of the Deferred purchase price obligation - Anadarko.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 , that may be assigned or otherwise charged to the Partnership pursuant to the reimbursement provisions of the omnibus agreement: thousands Operating Leases 2019 $ 8,711 2020 2,236 2021 460 2022 467 2023 473 Thereafter 1,547 Total $ 13,894

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Assets and Investments Table (Details)	Dec. 31, 2018unit
Owned and Operated [Member] | Gathering Systems [Member]
Assets [Line Items]
Assets, number of units	17	[1]
Owned and Operated [Member] | Treating Facilities [Member]
Assets [Line Items]
Assets, number of units	34
Owned and Operated [Member] | Natural Gas Processing Plants/Trains [Member]
Assets [Line Items]
Assets, number of units	23
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
Owned and Operated [Member] | Oil Pipelines [Member]
Assets [Line Items]
Assets, number of units	3
Operated Interests [Member] | Gathering Systems [Member]
Assets [Line Items]
Assets, number of units	2	[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	3
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	5
Equity Interests [Member] | Natural Gas Liquids Pipelines [Member]
Assets [Line Items]
Assets, number of units	4
Equity Interests [Member] | Oil Pipelines [Member]
Assets [Line Items]
Assets, number of units	3
[1]	Includes the DBM water systems.

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Ownership Interests and Method of Consolidation Table (Details)	12 Months Ended
	Dec. 31, 2018
Chipeta [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest by noncontrolling interest owner	25.00%
Fort Union [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	14.81%
Equity Investments [Member] | Fort Union [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	14.81%	[1]
Equity Investments [Member] | White Cliffs [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	10.00%	[1]
Equity Investments [Member] | Rendezvous [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	22.00%	[1]
Equity Investments [Member] | Mont Belvieu JV [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	25.00%	[1]
Equity Investments [Member] | Texas Express Pipeline [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	20.00%	[1]
Equity Investments [Member] | Texas Express Gathering [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	20.00%	[1]
Equity Investments [Member] | Front Range Pipeline [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	33.33%	[1]
Equity Investments [Member] | Whitethorn [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	20.00%	[1]
Equity Investments [Member] | Cactus II [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	15.00%	[1]
Equity Investments [Member] | Saddlehorn [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	20.00%	[1]
Equity Investments [Member] | Panola [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	15.00%	[1]
Equity Investments [Member] | Mi Vida [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	50.00%	[1]
Equity Investments [Member] | Ranch Westex [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Equity investment ownership percentage	50.00%	[1]
Proportionate Consolidation [Member] | Marcellus Interest Systems [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	33.75%	[2]
Proportionate Consolidation [Member] | Springfield System [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	50.10%	[2]
Full Consolidation [Member] | Chipeta [Member]
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Percentage ownership interest	75.00%	[3]
[1]	Investments in non-controlled entities over which the Partnership exercises significant influence are accounted for under the equity method. “Equity investment throughput” refers to the Partnership’s share of average throughput for these investments.
[2]	The Partnership proportionately consolidates its 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 interest in the consolidated financial statements.

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Impact of New Accounting Pronouncement - Statements of Operations Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Revenues and other	[1]	$ 2,299,658	$ 2,429,614	$ 1,941,330
Expenses
Cost of product	[1],[2]	415,505	953,792	517,371
Operation and maintenance	[1],[2]	480,861	345,617	332,405
Depreciation and amortization	[1]	389,164	318,771	295,959
Impairments	[1]	230,584	180,051	17,822
Income tax expense (benefit)	[1]	58,934	(59,923)	32,969
Net income attributable to noncontrolling interest	[1]	8,609	10,735	10,963
Net income (loss) attributable to Western Gas Partners, LP	[1]	627,917	$ 731,666	$ 652,637
Service Revenues - Fee Based [Member]
Revenues
Revenues and other		1,905,728
Service Revenues - Product Based [Member]
Revenues
Revenues and other		88,785
Product Sales [Member]
Revenues
Revenues and other		303,020
Accounting Standards Update 2014-09 [Member] | Without Adoption of Topic 606 [Member]
Expenses
Cost of product		1,338,100
Operation and maintenance		480,668
Depreciation and amortization		386,179
Impairments		230,539
Income tax expense (benefit)		58,804
Net income attributable to noncontrolling interest		8,541
Net income (loss) attributable to Western Gas Partners, LP		568,350
Accounting Standards Update 2014-09 [Member] | Without Adoption of Topic 606 [Member] | Service Revenues - Fee Based [Member]
Revenues
Revenues and other		1,751,242
Accounting Standards Update 2014-09 [Member] | Without Adoption of Topic 606 [Member] | Service Revenues - Product Based [Member]
Revenues
Revenues and other		0
Accounting Standards Update 2014-09 [Member] | Without Adoption of Topic 606 [Member] | Product Sales [Member]
Revenues
Revenues and other		1,405,898
Accounting Standards Update 2014-09 [Member] | Effect of Change Increase / (Decrease) [Member]
Expenses
Cost of product		(922,595)
Operation and maintenance		193
Depreciation and amortization		2,985
Impairments		45
Income tax expense (benefit)		130
Net income attributable to noncontrolling interest		68
Net income (loss) attributable to Western Gas Partners, LP		59,567
Accounting Standards Update 2014-09 [Member] | Effect of Change Increase / (Decrease) [Member] | Service Revenues - Fee Based [Member]
Revenues
Revenues and other		154,486
Accounting Standards Update 2014-09 [Member] | Effect of Change Increase / (Decrease) [Member] | Service Revenues - Product Based [Member]
Revenues
Revenues and other		88,785
Accounting Standards Update 2014-09 [Member] | Effect of Change Increase / (Decrease) [Member] | Product Sales [Member]
Revenues
Revenues and other		$ (1,102,878)
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Cost of product includes product purchases from affiliates (as defined in Note 1) of $168.5 million, $74.6 million and $76.0 million for the years ended December 31, 2018, 2017 and 2016, respectively. Operation and maintenance includes charges from affiliates of $115.9 million, $82.2 million and $82.1 million for the years ended December 31, 2018, 2017 and 2016, respectively. General and administrative includes charges from affiliates of $48.8 million, $42.4 million and $41.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 6.

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Impact of New Accounting Pronouncement - Balance Sheet Table (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Other current assets	[1],[2]	$ 26,181	$ 15,409
Net property, plant and equipment	[1]	8,410,353	6,765,900
Other assets	[1],[3]	67,194	11,757
Liabilities
Accrued liabilities	[1],[4]	127,874	47,899
Deferred income taxes	[1]	280,017	139,635
Other liabilities	[1],[5]	132,130	3,494
Equity and partners' capital
Total equity and partners' capital	[1]	4,919,597	$ 5,021,182	$ 4,897,669	$ 4,643,386
Accounting Standards Update 2014-09 [Member] | Without Adoption of Topic 606 [Member]
Assets
Other current assets		20,782
Net property, plant and equipment		8,291,554
Other assets		24,972
Liabilities
Accrued liabilities		121,967
Deferred income taxes		254,939
Other liabilities		2,741
Equity and partners' capital
Total equity and partners' capital		4,913,551
Accounting Standards Update 2014-09 [Member] | Effect of Change Increase / (Decrease) [Member]
Assets
Other current assets		5,399
Net property, plant and equipment		118,799
Other assets		42,222
Liabilities
Accrued liabilities		5,907
Deferred income taxes		25,078
Other liabilities		129,389
Equity and partners' capital
Total equity and partners' capital		$ 6,046
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Other current assets includes affiliate amounts of $3.7 million and zero as of December 31, 2018 and 2017, respectively.
[3]	Other assets includes affiliate amounts of $42.2 million and zero as of December 31, 2018 and 2017, respectively.
[4]	Accrued liabilities includes affiliate amounts of $2.2 million and $0.2 million as of December 31, 2018 and 2017, respectively.
[5]	Other liabilities includes affiliate amounts of $47.8 million and $0.7 million as of December 31, 2018 and 2017, respectively.

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Jan. 01, 2018
Revenues and other	[1]		$ 2,299,658	$ 2,429,614	$ 1,941,330
Cost of product	[1],[2]		415,505	953,792	517,371
Impairments	[1]		230,584	180,051	17,822
Imbalance receivables			9,035	2,063
Imbalance payables			9,600	3,100
Loss on divestiture and other, net	[1],[3]		(1,312)	(132,388)	14,641
Proceeds from property insurance claims	[1]		0	22,977	17,465
Cumulative effect of accounting change	[1],[4]		$ (43,750)
Accounting Standards Update 2014-09 [Member]
Cumulative effect of accounting change							$ (43,750)
Accounting Standards Update 2016-02 [Member] | Subsequent Event [Member]
Right-of-use assets						$ 10,000
Lease liabilities						$ 10,000
Western Gas Partners Long-Term Incentive Plan [Member]
Units authorized under LTIP			2,250,000
Units available under LTIP			2,241,980
Kitty Draw and Third Creek Gathering Systems [Member]
Impairments			$ 134,000
Delaware Basin Midstream Complex [Member]
Loss on divestiture and other, net				5,700
Proceeds from insurance claims, total				52,900	33,800
Proceeds from business interruption insurance claims				29,882	16,270
Proceeds from property insurance claims				22,977	17,465
Affiliates [Member]
Revenues and other	[1],[5]		1,353,711	1,539,105	1,358,918
Cost of product	[5]		168,535	74,560	75,983
Service Revenues - Fee Based [Member]
Revenues and other			1,905,728
Service Revenues - Fee Based [Member] | Affiliates [Member]
Revenues and other	[1]		1,070,066	769,305	853,837
Product Sales [Member]
Revenues and other			303,020
Product Sales [Member] | Affiliates [Member]
Revenues and other	[1]		280,306	$ 753,724	$ 505,081
Product Sales [Member] | Affiliates [Member] | Kitty Draw and Third Creek Gathering Systems [Member]
Revenues and other			$ (10,900)
Prior Period Adjustment [Member]
Cost of product		$ 56,400
Prior Period Adjustment [Member] | Service Revenues - Fee Based [Member]
Revenues and other		42,600
Prior Period Adjustment [Member] | Product Sales [Member]
Revenues and other		$ 13,800
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Cost of product includes product purchases from affiliates (as defined in Note 1) of $168.5 million, $74.6 million and $76.0 million for the years ended December 31, 2018, 2017 and 2016, respectively. Operation and maintenance includes charges from affiliates of $115.9 million, $82.2 million and $82.1 million for the years ended December 31, 2018, 2017 and 2016, respectively. General and administrative includes charges from affiliates of $48.8 million, $42.4 million and $41.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 6.
[3]	Includes losses related to an incident at the DBM complex for the year ended December 31, 2017. See Note 1.
[4]	See Note 1.
[5]	Represents amounts earned or incurred on and subsequent to the date of the acquisition of Partnership assets, as well as amounts earned or incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Revenue From Contracts With Customers Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue from customers		$ 2,305,408
Total revenues and other	[1]	2,299,658	$ 2,429,614	$ 1,941,330
Service Revenues - Fee Based [Member]
Disaggregation of Revenue [Line Items]
Revenue from customers		1,905,728
Total revenues and other		1,905,728
Service Revenues - Product Based [Member]
Disaggregation of Revenue [Line Items]
Revenue from customers		88,785
Total revenues and other		88,785
Product Sales [Member]
Disaggregation of Revenue [Line Items]
Revenue from customers		310,895
Total revenues and other		303,020
Commodity Price Swap Agreement [Member]
Disaggregation of Revenue [Line Items]
Revenue from other than customers		(7,875)
Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from other than customers		$ 2,125
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Contract Assets Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Change in Contracts with Customer, Asset [Roll Forward]
Balance at December 31, 2017	$ 0
Cumulative effect of adopting Topic 606	5,950
Amounts transferred to Accounts receivable, net from contract assets recognized in the adoption effect	(4,952)
Additional estimated revenues recognized	30,519
Cumulative catch up adjustment for change in estimated consideration due to cost of service rate updates	16,104
Balance at December 31, 2018	47,621
Contract assets at December 31, 2018
Other current assets		$ 5,399	$ 0
Other assets		42,222
Total contract assets from contracts with customers	$ 0	$ 47,621	$ 0

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Contract Liabilities Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Change in Contracts with Customer, Liability [Roll Forward]
Balance at December 31, 2017		$ 0
Cumulative effect of adopting Topic 606		120,309
Cash received or receivable, excluding revenues recognized during the period		55,786
Assets received from customer		12,933
Revenues recognized during the period that were included in the adoption effect	[1]	(21,556)
Cumulative catch up adjustment for change in estimated consideration due to cost of service rate updates		(21,848)
Balance at December 31, 2018		145,624
Contract liabilities at December 31, 2018
Accrued liabilities			$ 16,235	$ 0
Other liabilities			129,389
Total contract liabilities from contracts with customers		0	$ 145,624	$ 0
Change in Contract with Customer, Asset and Liability [Abstract]
Performance obligation satisfied in previous period		$ (7,500)
[1]	Includes $(7.5) million from a performance obligation satisfied in a previous period related to the arbitration against SWEPI LP (see Note 14).

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Expected Revenues Table (Details) $ in Thousands	Dec. 31, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected to be satisfied	$ 674,609
Performance obligation expected to be satisfied, expected timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected to be satisfied	$ 847,045
Performance obligation expected to be satisfied, expected timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected to be satisfied	$ 894,706
Performance obligation expected to be satisfied, expected timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected to be satisfied	$ 947,310
Performance obligation expected to be satisfied, expected timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected to be satisfied	$ 913,099
Performance obligation expected to be satisfied, expected timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected to be satisfied	$ 8,842,197
Performance obligation expected to be satisfied, expected timing

Revenue from Contracts with C_7

Revenue from Contracts with Customers - Additional Information (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Revenue from Contracts with Customer [Line Items]
Accounts receivable, net	[1],[2]	$ 221,373	$ 160,910
Customers [Member]
Revenue from Contracts with Customer [Line Items]
Accounts receivable, net		$ 214,300	$ 244,900
[1]	Accounts receivable, net includes amounts receivable from affiliates (as defined in Note 1) of $72.8 million and $36.3 million as of December 31, 2018 and 2017, respectively.
[2]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Acquisitions and Divestitures -

Acquisitions and Divestitures - Impact to Historical Consolidated Statements of Operations Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues and other	[1]	$ 2,299,658	$ 2,429,614	$ 1,941,330
Equity income, net – affiliates	[1],[2]	195,469	115,141	101,692
Net income (loss)	[1]	636,526	742,401	663,600
Anadarko Midstream Assets [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues and other		343,499	192,853	138,269
Equity income, net – affiliates		42,445	29,947	22,975
Net income (loss)		182,142	164,183	61,306
Anadarko Midstream Assets [Member] | Eliminations [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues and other		(34,117)	(11,595)	(1,209)
Equity income, net – affiliates		0	0	0
Net income (loss)		0	0	0
Historical financial data [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Revenues and other		1,990,276	2,248,356	1,804,270
Equity income, net – affiliates		153,024	85,194	78,717
Net income (loss)		$ 454,384	$ 578,218	$ 602,294
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Represents amounts earned or incurred on and subsequent to the date of the acquisition of Partnership assets, as well as amounts earned or incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.

Acquisitions and Divestitures_2

Acquisitions and Divestitures - Impact of Deferred Purchase Price Obligation - Anadarko Table (Details) - Affiliates [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Settlement of the Deferred purchase price obligation - Anadarko	[1],[2]	$ 0	$ (37,346)		$ 0
Deferred Purchase Price Obligation - Anadarko [Member]
Property, Plant and Equipment [Line Items]
Accretion revision/expense	[3]	0	71		(7,747)
Settlement of the Deferred purchase price obligation - Anadarko	[4]	$ 0	(37,346)		0
Delaware Basin JV Gathering LLC [Member] | Deferred Purchase Price Obligation - Anadarko [Member]
Property, Plant and Equipment [Line Items]
Deferred purchase price obligation - Anadarko			0		41,440		$ 188,674
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	[8]		$ 0		$ 56,455		$ 282,807
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	See Note 3.
[3]	See Note 3 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 3).
[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 Divestitures_3

Acquisitions and Divestitures - Additional Information (Details) $ in Thousands		Feb. 28, 2019MBbls / dMcf / dmibbl	Jan. 18, 2019USD ($)	Dec. 14, 2018USD ($)	Jun. 27, 2018USD ($)	Jun. 01, 2018USD ($)	Mar. 17, 2017USD ($)	Mar. 14, 2016USD ($)shares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)
Property, Plant and Equipment [Line Items]
Acquisition, net investment									$ 162,615	$ 22,500
Units issued | shares									1,128,782	885,760
Newcastle System [Member]
Property, Plant and Equipment [Line Items]
Proceeds from the sale of assets				$ 3,200
Gain (loss) on sale of assets									$ 600
Helper and Clawson Systems [Member]
Property, Plant and Equipment [Line Items]
Gain (loss) on sale of assets										$ 16,300
Hugoton System [Member]
Property, Plant and Equipment [Line Items]
Gain (loss) on sale of assets											$ (12,000)
Goodwill allocated to divestiture											1,600
Affiliates [Member]
Property, Plant and Equipment [Line Items]
Cash payment	[1]								254	3,910	716,465
Settlement of the Deferred purchase price obligation - Anadarko	[1],[2]								0	37,346	0
Proceeds from the sale of assets	[1]								0	0	623
Deferred Purchase Price Obligation - Anadarko [Member] | Affiliates [Member]
Property, Plant and Equipment [Line Items]
Settlement of the Deferred purchase price obligation - Anadarko	[3]								$ 0	$ 37,346	$ 0
Ranch Westex [Member]
Property, Plant and Equipment [Line Items]
Equity investment ownership percentage										50.00%	33.00%
Non-Operated Marcellus Interest [Member]
Property, Plant and Equipment [Line Items]
Percentage ownership interest							33.75%
Newcastle System [Member] | Newcastle System [Member]
Property, Plant and Equipment [Line Items]
Percentage ownership interest				50.00%
Ranch Westex [Member]
Property, Plant and Equipment [Line Items]
Acquisition, net investment										$ 22,500
Red Bluff Express [Member] | Subsequent Event [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired			30.00%
Acquisition, net investment			$ 92,500
Whitethorn [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired						20.00%
Acquisition, net investment						$ 150,600
Cactus II [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired					15.00%
Acquisition, net investment					$ 12,100
Delaware Basin JV Gathering LLC [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired							50.00%
Cash payment							$ 155,000
Net gain from property exchange										125,700
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
Delaware Basin JV Gathering LLC [Member] | Delaware Basin JV Gathering LLC [Member]
Property, Plant and Equipment [Line Items]
Percentage ownership interest							50.00%
Springfield [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired								50.10%
Acquisition price								$ 750,000
Cash payment for acquisition								712,500
Springfield [Member] | Revolving Credit Facility [Member]
Property, Plant and Equipment [Line Items]
Borrowings - revolving credit facility								$ 247,500
Springfield [Member] | Anadarko [Member] | Common Units [Member]
Property, Plant and Equipment [Line Items]
Units issued | shares								1,253,761
Springfield [Member] | Western Gas Equity Partners, LP [Member] | Common Units [Member]
Property, Plant and Equipment [Line Items]
Units issued | shares								835,841
Scenario, Forecast [Member] | Wattenberg Processing Plant [Member] | Cryogenic Train [Member]
Property, Plant and Equipment [Line Items]
Gas processing capacity | Mcf / d		190,000
Scenario, Forecast [Member] | Wattenberg Processing Plant [Member] | Refrigeration Train [Member]
Property, Plant and Equipment [Line Items]
Gas processing capacity | Mcf / d		100,000
Scenario, Forecast [Member] | DJ Basin Oil System [Member] | Pipelines [Member]
Property, Plant and Equipment [Line Items]
Pipeline miles | mi		12
Scenario, Forecast [Member] | DJ Basin Oil System [Member] | Storage Tank [Member]
Property, Plant and Equipment [Line Items]
Storage capacity - barrels | bbl		500,000
Scenario, Forecast [Member] | DJ Basin Oil System Trains I Through 6 [Member]
Property, Plant and Equipment [Line Items]
Oil processing capacity | MBbls / d		155
Scenario, Forecast [Member] | DJ Basin Oil System Train 6 [Member]
Property, Plant and Equipment [Line Items]
Oil processing capacity | MBbls / d		30
Scenario, Forecast [Member] | DBM Oil System [Member] | Pipelines [Member]
Property, Plant and Equipment [Line Items]
Pipeline miles | mi		14
Scenario, Forecast [Member] | DBM Oil System [Member] | Storage Tank [Member]
Property, Plant and Equipment [Line Items]
Storage capacity - barrels | bbl		30,000
Scenario, Forecast [Member] | DBM Oil System [Member] | Central Production Facilities [Member]
Property, Plant and Equipment [Line Items]
Oil processing capacity | MBbls / d		75
Scenario, Forecast [Member] | DBM Oil System [Member] | Regional Oil Treating Facilities [Member]
Property, Plant and Equipment [Line Items]
Oil processing capacity | MBbls / d		120
Scenario, Forecast [Member] | APC Water System 1 [Member]
Property, Plant and Equipment [Line Items]
Produced water processing capacity | MBbls / d		30
Scenario, Forecast [Member] | APC Water Systems 1-5 [Member]
Property, Plant and Equipment [Line Items]
Produced water processing capacity | MBbls / d		565
Scenario, Forecast [Member] | Saddlehorn [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired		20.00%
Scenario, Forecast [Member] | Saddlehorn [Member] | Pipelines [Member]
Property, Plant and Equipment [Line Items]
Pipeline miles | mi		600
Scenario, Forecast [Member] | Saddlehorn [Member] | Storage Tank [Member]
Property, Plant and Equipment [Line Items]
Storage capacity - barrels | bbl		300,000
Scenario, Forecast [Member] | Panola [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired		15.00%
Scenario, Forecast [Member] | Panola [Member] | Pipelines [Member]
Property, Plant and Equipment [Line Items]
Pipeline miles | mi		248
Scenario, Forecast [Member] | Mi Vida [Member]
Property, Plant and Equipment [Line Items]
Gas processing capacity | Mcf / d		200,000
Ownership percentage acquired		50.00%
Scenario, Forecast [Member] | Ranch Westex [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage acquired		50.00%
Scenario, Forecast [Member] | Ranch Westex [Member] | Cryogenic Train [Member]
Property, Plant and Equipment [Line Items]
Gas processing capacity | Mcf / d		100,000
Scenario, Forecast [Member] | Ranch Westex [Member] | Refrigeration Train [Member]
Property, Plant and Equipment [Line Items]
Gas processing capacity | Mcf / d		25,000
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	See Note 3.
[3]	Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 3).

Partnership Distributions - Cas

Partnership Distributions - Cash Distributions Table (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Dec. 31, 2018	[1]	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016
Distributions Made to Members or Limited Partners [Abstract]
Total quarterly distribution per unit	$ 0.980		$ 0.965	$ 0.950	$ 0.935	$ 0.920	$ 0.905	$ 0.890	$ 0.875	$ 0.860	$ 0.845	$ 0.830	$ 0.815
Total quarterly cash distribution	$ 234,787		$ 230,239	$ 225,691	$ 221,133	$ 216,586	$ 212,038	$ 207,491	$ 188,753	$ 170,657	$ 166,742	$ 162,827	$ 158,905
[1]	The Board of Directors declared a cash distribution to the Partnership’s unitholders for the fourth quarter of 2018 of $0.980 per unit, or $234.8 million in aggregate, including incentive distributions, but excluding distributions on Class C units (see Class C unit distributions below). The cash distribution was paid on February 13, 2019, to unitholders of record at the close of business on February 1, 2019.

Partnership Distributions - Ser

Partnership Distributions - Series A Preferred Unit Distributions Table (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended							12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Distribution Made to Limited Partner [Line Items]
Units issued								1,128,782	885,760
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				21,922,831
Series A Preferred Units [Member] | Private Investor [Member] | Over-Allotment Option [Member]
Distribution Made to Limited Partner [Line Items]
Units issued				7,892,220
[1]	Full quarterly per unit distribution on 14,030,611 Series A Preferred units and quarterly per unit distribution prorated for the 77-day period during which 7,892,220 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 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, 2018
Distribution Made to Limited Partner [Line Items]
Partnership agreement day requirement of distribution of available cash										45 days
Incentive distributions percentage										48.00%
Minimum [Member]
Distribution Made to Limited Partner [Line Items]
Distribution sharing percentage										1.50%
Maximum [Member]
Distribution Made to Limited Partner [Line Items]
Distribution sharing percentage										49.50%
Class C Units [Member]
Distribution Made to Limited Partner [Line Items]
Class C units, discount rate percentage on distribution										6.00%
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
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
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 Series A Preferred units and quarterly per unit distribution prorated for the 77-day period during which 7,892,220 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 Series A Preferred units were outstanding during the first quarter of 2016.

Equity and Partners' Capital -

Equity and Partners' Capital - Partnership Interests Table (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Change In Units [Roll Forward]
Balance	168,429,056	167,535,992
Units issued	1,128,782	885,760
Conversion of Series A Preferred units		0
Long-Term Incentive Plan award vestings	7,180	7,304
Balance	169,565,018	168,429,056
Common Units [Member]
Change In Units [Roll Forward]
Balance	152,602,105	130,671,970
Conversion of Series A Preferred units		21,922,831
Long-Term Incentive Plan award vestings	7,180	7,304
Balance	152,609,285	152,602,105
Class C Units [Member]
Change In Units [Roll Forward]
Balance	13,243,883	12,358,123
Units issued	1,128,782	885,760
Balance	14,372,665	13,243,883
Series A Preferred Units [Member]
Change In Units [Roll Forward]
Balance	0	21,922,831
Conversion of Series A Preferred units		(21,922,831)
Balance	0	0
General Partner [Member]
Change In Units [Roll Forward]
Balance	2,583,068	2,583,068
Balance	2,583,068	2,583,068

Equity and Partners' Capital _2

Equity and Partners' Capital - Calculation of Net Income (Loss) Per Unit Table (Details) - USD ($) $ / shares in Units, $ in Thousands		May 02, 2017	Mar. 01, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Unit [Line Items]
Net income (loss) attributable to Western Gas Partners, LP	[1]			$ 627,917	$ 731,666	$ 652,637
Pre-acquisition net (income) loss allocated to Anadarko	[1]			(182,142)	(164,183)	(72,632)
General partner interest in net (income) loss	[1],[2]			(346,538)	(303,835)	(236,561)
Series A Preferred Units [Member]
Earnings Per Unit [Line Items]
Limited partners’ interest in net income (loss)	[1],[2],[3]			$ 0	$ 42,373	$ 76,893
Anti-dilutive units excluded from computation of earnings per unit	[4]			0	5,406,000	16,860,000
Series A Preferred Units [Member] | Series A Preferred Units March 2017 Conversion [Member]
Earnings Per Unit [Line Items]
Series A Preferred units, percentage converted			50.00%
Series A Preferred units, common units issued upon conversion			1
Series A Preferred Units [Member] | Series A Preferred Units May 2017 Conversion [Member]
Earnings Per Unit [Line Items]
Series A Preferred units, percentage converted		50.00%
Series A Preferred units, common units issued upon conversion		1
Common and Class C Units [Member]
Earnings Per Unit [Line Items]
Limited partners’ interest in net income (loss)	[1],[2]			$ 99,237	$ 221,275	$ 266,551
Common Units [Member]
Earnings Per Unit [Line Items]
Limited partners’ interest in net income (loss)	[3]			$ 84,334	$ 192,066	$ 226,611
Net income (loss) per common unit – basic and diluted	[1],[2],[4]			$ 0.55	$ 1.30	$ 1.74
Weighted-average units outstanding - basic and diluted				152,606,000	147,194,000	130,253,000
Class C Units [Member]
Earnings Per Unit [Line Items]
Limited partners’ interest in net income (loss)	[3]			$ 14,903	$ 29,209	$ 39,940
Anti-dilutive units excluded from computation of earnings per unit	[4]			13,795,000	12,776,000	11,945,000
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	See Note 5 for the calculation of net income (loss) per common unit.
[3]	Adjusted to reflect amortization of the beneficial conversion features.
[4]	The impact of Class C units would be anti-dilutive for all periods presented and the conversion of Series A Preferred units would be anti-dilutive for the years ended December 31, 2017 and 2016. On March 1, 2017, 50% of the outstanding Series A Preferred units converted into common units on a one-for-one basis, and on May 2, 2017, all remaining Series A Preferred units converted into common units on a one-for-one basis.

Equity and Partners' Capital _3

Equity and Partners' Capital - Additional Information (Details) - USD ($) $ in Thousands		May 02, 2017	Mar. 01, 2017	Nov. 30, 2014	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014	Jul. 31, 2017
Schedule Of Investments [Line Items]
Units issued							1,128,782	885,760
Beneficial conversion feature	[1]								$ 0
Series A Preferred units, amortization of beneficial conversion feature	[1]						$ 0	$ 0	0
General partner units owned							2,583,068	2,583,068
Western Gas Partners, LP [Member] | Western Gas Equity Partners, LP [Member]
Schedule Of Investments [Line Items]
General partner units owned							2,583,068
General partner's interest							1.50%
Class C Units [Member]
Schedule Of Investments [Line Items]
Units issued							1,128,782	885,760
Class C units, common units issued upon conversion							1
Beneficial conversion feature										$ 34,800
Limited partner units owned							14,372,665	13,243,883
Class C Units [Member] | Western Gas Partners, LP [Member] | Other Subsidiaries of Anadarko [Member]
Schedule Of Investments [Line Items]
Limited partner units owned							14,372,665
Class C Units [Member] | Other Subsidiaries of Anadarko [Member]
Schedule Of Investments [Line Items]
Units issued				10,913,853
Series A Preferred Units [Member]
Schedule Of Investments [Line Items]
Beneficial conversion feature									93,409
Series A Preferred units, proceeds from issuance	[1]						$ 0	$ 0	$ 686,937
Series A Preferred units, amortization of beneficial conversion feature								$ 62,299
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			1
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		1
Series A Preferred Units [Member] | Private Investor [Member]
Schedule Of Investments [Line Items]
Units issued					14,030,611	14,030,611			21,922,831
Series A Preferred units, proceeds from issuance									$ 686,937
Series A Preferred units, transaction fee percentage									2.00%
Common Units [Member]
Schedule Of Investments [Line Items]
Limited partner units owned							152,609,285	152,602,105
Common Units [Member] | Western Gas Partners, LP [Member] | Public [Member]
Schedule Of Investments [Line Items]
Limited partner units owned							100,465,859
Limited partner ownership interest							59.20%
Common Units [Member] | Western Gas Partners, LP [Member] | Western Gas Equity Partners, LP [Member]
Schedule Of Investments [Line Items]
Limited partner units owned							50,132,046
Limited partner ownership interest							29.60%
Common Units [Member] | Western Gas Partners, LP [Member] | Other Subsidiaries of Anadarko [Member]
Schedule Of Investments [Line Items]
Limited partner units owned							2,011,380
Incentive Distribution Rights [Member] | Western Gas Partners, LP [Member] | Western Gas Equity Partners, LP [Member]
Schedule Of Investments [Line Items]
General partner's interest							100.00%
Common and Class C Units [Member] | Western Gas Partners, LP [Member] | Other Subsidiaries of Anadarko [Member]
Schedule Of Investments [Line Items]
Limited partner ownership interest							9.70%
July 2017 COP [Member]
Schedule Of Investments [Line Items]
Maximum aggregate principal of common units											$ 500,000
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Transactions with Affiliates -

Transactions with Affiliates - Commodity Price Swap Agreements Tables (Details)		Dec. 31, 2018$ / MMBTU$ / bbl	Dec. 20, 2017$ / MMBTU$ / bbl	Dec. 31, 2016$ / MMBTU$ / bbl	Dec. 01, 2016$ / MMBTU$ / bbl	Dec. 08, 2015$ / MMBTU$ / bbl
DJ Basin Complex [Member] | Years 2016 - 2018 [Member] | Ethane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		18.41
DJ Basin Complex [Member] | Years 2016 - 2018 [Member] | Propane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		47.08
DJ Basin Complex [Member] | Years 2016 - 2018 [Member] | Isobutane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		62.09
DJ Basin Complex [Member] | Years 2016 - 2018 [Member] | Normal Butane [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		54.62
DJ Basin Complex [Member] | Years 2016 - 2018 [Member] | Natural Gasoline [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		72.88
DJ Basin Complex [Member] | Years 2016 - 2018 [Member] | Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price		76.47
DJ Basin Complex [Member] | Years 2016 - 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 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] | Year 2016 [Member] | Condensate [Member]
Commodity Price Risk Swap [Line Items]
Commodity swap fixed price	[2]			78.61
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 swap fixed price | $ / MMBTU	[2]			5.50
Commodity market price | $ / MMBTU	[1],[2]					2.12
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 December 8, 2015, December 1, 2016, and December 20, 2017, for the 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 3.

Transactions with Affiliates _2

Transactions with Affiliates - Omnibus Agreement Table (Details) - Omnibus Agreement [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Allocated costs from Anadarko	$ 50,486	$ 41,112	$ 37,770
General and Administrative Expenses [Member]
Related Party Transaction [Line Items]
Allocated costs from Anadarko	35,077	31,733	29,360
Public Company Expenses [Member]
Related Party Transaction [Line Items]
Allocated costs from Anadarko	$ 15,409	$ 9,379	$ 8,410

Transactions with Affiliates _3

Transactions with Affiliates - LTIP Award Activity Table (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Fees and Other Arrangements, Limited Liability Company (LLC) or Limited Partnership (LP) [Abstract]
Value per unit of phantom units outstanding at beginning of year	$ 55.73	$ 49.30	$ 68.78
Value per unit of phantom units vested during the period	55.73	49.30	68.78
Value per unit of phantom units granted during the period	49.88	55.73	49.30
Value per unit of phantom units outstanding at end of year	$ 49.88	$ 55.73	$ 49.30
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	7,180	7,304	5,477
Phantom units vested	(7,180)	(7,304)	(5,477)
Phantom units granted	8,020	7,180	7,304
Phantom units outstanding at end of year	8,020	7,180	7,304

Transactions with Affiliates _4

Transactions with Affiliates - Affiliate Asset Contributions and Distributions Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Partners’ capital adjustment	[1],[2]	$ (58,835)	$ (3,189)	$ 451
Affiliates [Member] | Purchases [Member]
Related Party Transaction [Line Items]
Cash consideration - purchases		(254)	(3,910)	(3,965)
Net carrying value		59,089	5,283	3,496
Partners’ capital adjustment		58,835	1,373	(469)
Affiliates [Member] | Sales [Member]
Related Party Transaction [Line Items]
Cash consideration - sales		0	0	623
Net carrying value		0	0	(605)
Partners’ capital adjustment		$ 0	$ 0	$ 18
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	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 6.

Transactions with Affiliates _5

Transactions with Affiliates - Summary of Affiliate Transactions Table (Details) - USD ($) $ in Thousands		Mar. 14, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Revenues and other	[1]		$ 2,299,658	$ 2,429,614	$ 1,941,330
Equity income, net – affiliates	[1],[2]		195,469	115,141	101,692
Cost of product	[1],[3]		415,505	953,792	517,371
Operation and maintenance	[1],[3]		480,861	345,617	332,405
General and administrative	[1],[3]		63,166	51,077	48,701
Operating expenses	[1]		1,631,128	1,902,455	1,257,896
Interest income	[1],[4]		16,900	16,900	16,900
Interest expense	[1],[5]		181,796	140,291	107,565
Proceeds from the issuance of common units, net of offering expenses	[1]		0	(183)	25,000
Distributions to unitholders	[1],[6]		893,649	801,300	671,938
Above-market component of swap agreements with Anadarko	[1],[6]		$ 51,618	$ 58,551	45,820
Units issued			1,128,782	885,760
Affiliates [Member]
Related Party Transaction [Line Items]
Revenues and other	[1],[2]		$ 1,353,711	$ 1,539,105	1,358,918
Cost of product	[2]		168,535	74,560	75,983
Operation and maintenance	[7]		115,948	82,249	82,133
General and administrative	[8]		48,819	42,411	41,176
Operating expenses			333,302	199,220	199,292
Interest expense	[9],[10]		6,746	224	(7,747)
APCWH Note Payable borrowings	[9]		321,780	98,813	0
Settlement of the Deferred purchase price obligation - Anadarko	[1],[11]		0	(37,346)	0
Proceeds from the issuance of common units, net of offering expenses	[12]		0	0	25,000
Distributions to unitholders	[13]		514,906	452,777	382,711
Affiliates [Member] | Deferred Purchase Price Obligation - Anadarko [Member]
Related Party Transaction [Line Items]
Settlement of the Deferred purchase price obligation - Anadarko	[14]		$ 0	$ (37,346)	$ 0
Springfield [Member] | Western Gas Equity Partners, LP [Member] | Common Units [Member]
Related Party Transaction [Line Items]
Units issued		835,841
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Represents amounts earned or incurred on and subsequent to the date of the acquisition of Partnership assets, as well as amounts earned or incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.
[3]	Cost of product includes product purchases from affiliates (as defined in Note 1) of $168.5 million, $74.6 million and $76.0 million for the years ended December 31, 2018, 2017 and 2016, respectively. Operation and maintenance includes charges from affiliates of $115.9 million, $82.2 million and $82.1 million for the years ended December 31, 2018, 2017 and 2016, respectively. General and administrative includes charges from affiliates of $48.8 million, $42.4 million and $41.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 6.
[4]	Represents interest income recognized on the note receivable from Anadarko.
[5]	Includes affiliate (as defined in Note 1) amounts of $(6.7) million, $(0.2) million and $7.7 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 3 and Note 13.
[6]	See Note 6.
[7]	Represents expenses incurred on and subsequent to the date of the acquisition of Partnership assets, as well as expenses incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.
[8]	Represents general and administrative expense incurred on and subsequent to the date of the acquisition of Partnership assets, as well as a management services fee for expenses incurred by Anadarko for periods prior to the acquisition of the Partnership assets by the Partnership. These amounts include equity-based compensation expense allocated to the Partnership by Anadarko (see WES LTIP and WGP LTIP and Anadarko Incentive Plan within this Note 6) and amounts charged by Anadarko under the omnibus agreement.
[9]	Includes amounts related to the APCWH Note Payable (see Note 13 and Note 15).
[10]	Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 3 and Note 13).
[11]	See Note 3.
[12]	Represents proceeds from the issuance of 835,841 common units to WGP as partial funding for the acquisition of Springfield (see Note 3).
[13]	Represents distributions paid under the partnership agreement (see Note 4 and Note 5).
[14]	Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 3).

Transactions with Affiliates _6

Transactions with Affiliates - Additional Information (Details) - USD ($)		1 Months Ended	12 Months Ended
		May 31, 2008	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Note receivable - Anadarko	[1]		$ 260,000,000	$ 260,000,000
Above-market component of swap agreements with Anadarko	[1],[2]		51,618,000	58,551,000	$ 45,820,000
Contributions of equity-based compensation from Anadarko	[1]		$ 5,727,000	4,563,000	4,214,000
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	400,000
Unvested equity-based compensation expense			$ 100,000
Weighted-average term of unvested awards			5 months
Western Gas Equity Partners Long-Term Incentive Plan [Member] | Anadarko Incentive Plan [Member]
Related Party Transaction [Line Items]
Equity-based compensation expense			$ 6,600,000	4,600,000	5,200,000
Contributions of equity-based compensation from Anadarko			5,727,000	$ 4,563,000	$ 4,214,000
Unvested equity-based compensation expense			$ 12,500,000
Weighted-average term of unvested awards			2 years
Natural Gas [Member] | Gathering, Treating, Transportation and Disposal [Member]
Related Party Transaction [Line Items]
Affiliate throughput percent			7.00%	34.00%	37.00%
Natural Gas [Member] | Processing [Member]
Related Party Transaction [Line Items]
Affiliate throughput percent			40.00%	41.00%	53.00%
Crude Oil, NGLs and Produced Water [Member] | Gathering, Treating, Transportation and Disposal [Member]
Related Party Transaction [Line Items]
Affiliate throughput percent			85.00%	81.00%	86.00%
Commodity Price Swap Agreement [Member]
Related Party Transaction [Line Items]
Net gains (losses) on commodity price swap agreements			$ (7,875,000)
Affiliates [Member]
Related Party Transaction [Line Items]
Note receivable - Anadarko		$ 260,000,000
Note receivable, due date		May 14, 2038
Fixed annual rate for note receivable bearing interest		6.50%
Affiliates [Member] | Commodity Price Swap Agreement [Member]
Related Party Transaction [Line Items]
Net gains (losses) on commodity price swap agreements			(7,875,000)	$ 600,000	$ 28,500,000
Affiliates [Member] | Level 2 Inputs [Member] | Valuation, Market Approach [Member]
Related Party Transaction [Line Items]
Fair value of the note receivable			$ 279,600,000	$ 325,200,000
Independent Director [Member] | Western Gas Partners Long-Term Incentive Plan [Member]
Related Party Transaction [Line Items]
Units vesting period			1 year
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	See Note 6.

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Benefit) Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income tax expense (benefit)
Federal income tax expense (benefit)		$ (79,264)	$ (9,207)	$ (19,480)
State income tax expense (benefit)		(850)	2,422	1,257
Total current income tax expense (benefit)		(80,114)	(6,785)	(18,223)
Deferred income tax expense (benefit)
Federal income tax expense (benefit)		133,044	(55,835)	49,855
State income tax expense (benefit)		6,004	2,697	1,337
Total deferred income tax expense (benefit)	[1]	139,048	(53,138)	51,192
Total income tax expense (benefit)	[1]	$ 58,934	$ (59,923)	$ 32,969
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Income Taxes - Tax Rate Reconci

Income Taxes - Tax Rate Reconciliation Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Income (loss) before income taxes	[1]	$ 695,460	$ 682,478	$ 696,569
Statutory tax rate		0.00%	0.00%	0.00%
Adjustments resulting from:
U.S. federal tax reform		$ 0	$ (87,306)	$ 0
Federal taxes on income		0	0	0
State taxes on income (net of federal benefit) and Texas margin tax expense (benefit)		2,946	4,866	2,093
Income tax expense (benefit)	[1]	$ 58,934	$ (59,923)	$ 32,969
Effective tax rate		8.00%	(9.00%)	5.00%
Pre Acquisition From Parent [Member]
Adjustments resulting from:
Federal taxes on income		$ 54,243	$ 22,353	$ 30,550
State taxes on income (net of federal benefit) and Texas margin tax expense (benefit)		$ 1,745	$ 164	$ 326
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Income Taxes - Income Tax Tempo

Income Taxes - Income Tax Temporary Differences Table (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Depreciable property		$ (280,377)	$ (139,902)
Credit carryforwards		497	448
Other intangible assets		(299)	(189)
Other		162	8
Net long-term deferred income tax liabilities	[1]	$ (280,017)	$ (139,635)
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
U.S. federal tax reform	$ 0	$ 87,306	$ 0
Statutory tax rate	0.00%	0.00%	0.00%
Credit carryforwards	$ 497	$ 448
Tax credit carryforward, expiration date	Dec. 31, 2026
Anadarko Midstream Assets [Member]
Related Party Transaction [Line Items]
U.S. federal tax reform		$ 87,306
Statutory tax rate	21.00%	35.00%

Property, Plant and Equipment -

Property, Plant and Equipment - Historical Cost Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment	[1]	$ 11,258,773	$ 8,979,618
Less accumulated depreciation	[1]	2,848,420	2,213,718
Net property, plant and equipment	[1]	8,410,353	6,765,900
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment		5,298	5,096
Gathering Systems and Processing Complexes [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment		$ 10,441,574	7,851,458
Gathering Systems and Processing Complexes [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life		15 years
Gathering Systems and Processing Complexes [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life		40 years
Pipelines and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment		$ 172,497	137,644
Pipelines and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life		6 years
Pipelines and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life		45 years
Assets Under Construction [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment		$ 604,265	954,719
Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment		$ 35,139	$ 30,701
Other [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life		3 years
Other [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life		40 years
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Property, Plant and Equipment_2

Property, Plant and Equipment - Additional Information (Details) - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Impairments	[1]	$ 230,584,000	$ 180,051,000		$ 17,822,000
Equity investment impairment loss	[2]		3,110,000
Fort Union [Member]
Property, Plant and Equipment [Line Items]
Equity investment impairment loss			3,110,000	[2]	3,000,000
Third Creek Gathering System [Member]
Property, Plant and Equipment [Line Items]
Impairments		125,900,000
Third Creek Gathering System [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Market Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated salvage value		1,800,000
Kitty Draw Gathering System [Member]
Property, Plant and Equipment [Line Items]
Impairments		8,100,000
Kitty Draw Gathering System [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Market Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated salvage value		0
Hilight System [Member]
Property, Plant and Equipment [Line Items]
Impairments		38,700,000	8,200,000
Hilight System [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Income Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated fair value		4,900,000
MIGC System [Member]
Property, Plant and Equipment [Line Items]
Impairments		34,600,000
MIGC System [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Income Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated fair value		15,200,000
Equipment [Member]
Property, Plant and Equipment [Line Items]
Impairments		23,300,000	21,300,000		11,700,000
GNB NGL Pipeline [Member]
Property, Plant and Equipment [Line Items]
Impairments		10,900,000
GNB NGL Pipeline [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Income Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated fair value		10,000,000
Chipeta Complex [Member]
Property, Plant and Equipment [Line Items]
Impairments		5,600,000
Chipeta Complex [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Market Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated salvage value		$ 1,500,000
Granger Complex [Member]
Property, Plant and Equipment [Line Items]
Impairments			158,800,000
Granger Complex [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Income Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated fair value			48,500,000
Granger Straddle Plant [Member]
Property, Plant and Equipment [Line Items]
Impairments			3,700,000
Granger Straddle Plant [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Income Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated salvage value			600,000
Northeast Wyoming Facility [Member]
Property, Plant and Equipment [Line Items]
Impairments			2,000,000
Northeast Wyoming Facility [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Market Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated salvage value			$ 400,000
Newcastle System [Member]
Property, Plant and Equipment [Line Items]
Impairments					6,100,000
Newcastle System [Member] | Fair Value, Measurements, Nonrecurring [Member] | Level 3 Inputs [Member] | Valuation, Income Approach [Member]
Property, Plant and Equipment [Line Items]
Estimated fair value					$ 3,100,000
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Recorded in Impairments in the consolidated statements of operations.

Goodwill and Intangibles - Othe

Goodwill and Intangibles - Other Intangible Assets Table (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Gross carrying amount		$ 979,863	$ 979,863
Accumulated amortization		(138,455)	(107,676)
Other intangible assets	[1]	$ 841,408	$ 872,187
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Goodwill and Intangibles - Addi

Goodwill and Intangibles - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Goodwill, impairment loss	$ 0
Intangible assets (excluding goodwill), impairment loss	0
Amortization of intangible assets	30,800,000	$ 30,700,000	$ 30,700,000
Estimated amortization expense 2019	32,000,000
Estimated amortization expense 2020	32,000,000
Estimated amortization expense 2021	32,000,000
Estimated amortization expense 2022	32,000,000
Estimated amortization expense 2023	$ 31,700,000
Platte Valley [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	38 years
Wattenberg Processing Plant [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	38 years
Chipeta [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	10 years
Delaware Basin Midstream LLC [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset, useful life	30 years

Equity Investments - Equity Inv

Equity Investments - Equity Investments Tables (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Balance		$ 817,352	[1]	$ 828,689
Impairment expense	[2]			(3,110)
Acquisitions		162,615		22,500
Equity income, net	[1],[3]	195,469		115,141		$ 101,692
Contributions	[1]	133,629	[4]	2,884		58,726
Distributions	[1]	(187,392)		(117,093)		(104,948)
Distributions in excess of cumulative earnings	[1]	(29,585)	[5]	(31,659)	[5]	(29,725)
Balance		1,092,088	[1]	817,352	[1]	828,689
Fort Union [Member]
Schedule of Equity Method Investments [Line Items]
Balance		7,030		12,833
Impairment expense				(3,110)	[2]	(3,000)
Acquisitions		0		0
Equity income, net		(1,433)		3,821
Contributions		0	[4]	0
Distributions		(194)		(4,217)
Distributions in excess of cumulative earnings	[5]	(3,144)		(2,297)
Balance		2,259		7,030		12,833
White Cliffs [Member]
Schedule of Equity Method Investments [Line Items]
Balance		44,945		47,319
Impairment expense	[2]			0
Acquisitions		0		0
Equity income, net		11,841		12,547
Contributions		1,278	[4]	277
Distributions		(11,259)		(11,965)
Distributions in excess of cumulative earnings	[5]	(3,785)		(3,233)
Balance		43,020		44,945		47,319
Rendezvous [Member]
Schedule of Equity Method Investments [Line Items]
Balance		42,528		46,739
Impairment expense	[2]			0
Acquisitions		0		0
Equity income, net		767		1,144
Contributions		0	[4]	0
Distributions		(2,709)		(3,085)
Distributions in excess of cumulative earnings	[5]	(2,745)		(2,270)
Balance		37,841		42,528		46,739
Mont Belvieu JV [Member]
Schedule of Equity Method Investments [Line Items]
Balance		110,299		112,805
Impairment expense	[2]			0
Acquisitions		0		0
Equity income, net		29,200		29,444
Contributions		0	[4]	0
Distributions		(29,239)		(29,482)
Distributions in excess of cumulative earnings	[5]	(5,311)		(2,468)
Balance		104,949		110,299		112,805
Texas Express Gathering [Member]
Schedule of Equity Method Investments [Line Items]
Balance		15,879		15,846
Impairment expense	[2]			0
Acquisitions		0		0
Equity income, net		4,290		3,350
Contributions		3,720	[4]	0
Distributions		(4,368)		(3,317)
Distributions in excess of cumulative earnings	[5]	(163)		0
Balance		19,358		15,879		15,846
Texas Express Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Balance		178,975		189,194
Impairment expense	[2]			0
Acquisitions		0		0
Equity income, net		37,963		17,387
Contributions		11,980	[4]	107
Distributions		(33,552)		(17,639)
Distributions in excess of cumulative earnings	[5]	(2,168)		(10,074)
Balance		193,198		178,975		189,194
Front Range Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Balance		166,555		169,472
Impairment expense	[2]			0
Acquisitions		0		0
Equity income, net		23,308		17,501
Contributions		14,980	[4]	0
Distributions		(23,481)		(17,675)
Distributions in excess of cumulative earnings	[5]	(4,926)		(2,743)
Balance		176,436		166,555		169,472
Saddlehorn [Member]
Schedule of Equity Method Investments [Line Items]
Balance		109,227		107,420
Impairment expense	[2]			0
Acquisitions		0		0
Equity income, net		15,833		10,001
Contributions		294	[4]	2,454
Distributions		(16,017)		(10,127)
Distributions in excess of cumulative earnings	[5]	(830)		(521)
Balance		108,507		109,227		107,420
Panola [Member]
Schedule of Equity Method Investments [Line Items]
Balance		23,625		24,546
Impairment expense	[2]			0
Acquisitions		0		0
Equity income, net		2,200		2,230
Contributions		0	[4]	46
Distributions		(2,200)		(2,470)
Distributions in excess of cumulative earnings	[5]	(856)		(727)
Balance		22,769		23,625		24,546
Mi Vida [Member]
Schedule of Equity Method Investments [Line Items]
Balance		64,988		67,738
Impairment expense	[2]			0
Acquisitions		0		0
Equity income, net		13,734		10,029
Contributions		0	[4]	0
Distributions		(14,000)		(9,161)
Distributions in excess of cumulative earnings	[5]	(91)		(3,618)
Balance		64,631		64,988		67,738
Ranch Westex [Member]
Schedule of Equity Method Investments [Line Items]
Balance		53,301		34,777
Impairment expense	[2]			0
Acquisitions		0		22,500
Equity income, net		10,678		7,687
Contributions		0	[4]	0
Distributions		(10,876)		(7,955)
Distributions in excess of cumulative earnings	[5]	(2,201)		(3,708)
Balance		50,902		53,301		$ 34,777
Whitethorn [Member]
Schedule of Equity Method Investments [Line Items]
Balance		0
Acquisitions		150,563
Equity income, net		47,088
Contributions	[4]	7,069
Distributions		(39,497)
Distributions in excess of cumulative earnings	[5]	(3,365)
Balance		161,858		0
Cactus II [Member]
Schedule of Equity Method Investments [Line Items]
Balance		0
Acquisitions		12,052
Equity income, net		0
Contributions	[4]	94,308
Distributions		0
Distributions in excess of cumulative earnings	[5]	0
Balance		106,360		$ 0
Capitalized interest		$ 1,400
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Recorded in Impairments in the consolidated statements of operations.
[3]	Represents amounts earned or incurred on and subsequent to the date of the acquisition of Partnership assets, as well as amounts earned or incurred by Anadarko on a historical basis related to the Partnership assets prior to the acquisition of such assets.
[4]	Includes capitalized interest of $1.4 million related to the construction of the Cactus II pipeline.
[5]	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.

Equity Investments - Summarized

Equity Investments - Summarized Combined Financial Data For Equity Investments - Income Statement Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]
Revenues	$ 1,300,921	$ 877,020	$ 806,671
Operating income	876,910	542,390	503,239
Net income	$ 874,587	$ 540,538	$ 502,260

Equity Investments - Summariz_2

Equity Investments - Summarized Combined Financial Data For Equity Investments - Balance Sheet Table (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Current assets	$ 297,143	$ 214,473
Property, plant and equipment, net	4,251,020	3,366,754
Other assets	81,769	84,522
Total assets	4,629,932	3,665,749
Current liabilities	101,729	112,143
Non-current liabilities	42,431	45,413
Equity	4,485,772	3,508,193
Total liabilities and equity	$ 4,629,932	$ 3,665,749

Equity Investments - Additional

Equity Investments - Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Equity investment impairment loss	[1]	$ 3,110
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]	$ 3,000
Rendezvous [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value					$ 34,300
Equity investment impairment loss	[1]	0
White Cliffs [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value					$ (6,400)
Equity investment impairment loss	[1]	$ 0
White Cliffs [Member] | Affiliates [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment ownership percentage					0.40%
Whitethorn [Member]
Schedule of Equity Method Investments [Line Items]
Equity investment difference between carrying and underlying value					$ (39,100)
[1]	Recorded in Impairments in the consolidated statements of operations.

Components of Working Capital -

Components of Working Capital - Accounts Receivable, Net Table (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Trade receivables, net		$ 221,328	$ 160,700
Other receivables, net		45	210
Total accounts receivable, net	[1],[2]	$ 221,373	$ 160,910
[1]	Accounts receivable, net includes amounts receivable from affiliates (as defined in Note 1) of $72.8 million and $36.3 million as of December 31, 2018 and 2017, respectively.
[2]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Components of Working Capital_2

Components of Working Capital - Other Current Assets Table (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Other Current Assets [Line Items]
Natural gas liquids inventory		$ 6,466	$ 10,958
Imbalance receivables		9,035	2,063
Prepaid insurance		1,972	2,388
Contract assets		5,399	0
Other		3,309	0
Total other current assets	[1],[2]	$ 26,181	$ 15,409
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Other current assets includes affiliate amounts of $3.7 million and zero as of December 31, 2018 and 2017, respectively.

Components of Working Capital_3

Components of Working Capital - Accrued Liabilities Table (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Components Of Working Capital [Abstract]
Accrued interest expense		$ 70,959	$ 40,632
Short-term asset retirement obligations		25,938	2,304
Short-term remediation and reclamation obligations		863	833
Income taxes payable		384	2,495
Contract liabilities		16,235	0
Other		13,495	1,635
Total accrued liabilities	[1],[2]	$ 127,874	$ 47,899
[1]	Accrued liabilities includes affiliate amounts of $2.2 million and $0.2 million as of December 31, 2018 and 2017, respectively.
[2]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Asset Retirement Obligations -

Asset Retirement Obligations - Asset Retirement Obligations Table (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Carrying amount of asset retirement obligations at beginning of year	$ 154,571	$ 150,082
Liabilities incurred	34,558	17,932
Liabilities settled	(12,432)	(10,468)
Accretion expense	7,909	7,339
Revisions in estimated liabilities	141,356	(10,314)
Carrying amount of asset retirement obligations at end of year	$ 325,962	$ 154,571

Asset Retirement Obligations _2

Asset Retirement Obligations - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Revisions in estimated liabilities	$ 141,356	$ (10,314)
Gathering Systems and Processing Complexes [Member]
Property, Plant and Equipment [Line Items]
Revisions in estimated liabilities	71,800
Third Creek Gathering System [Member]
Property, Plant and Equipment [Line Items]
Revisions in estimated liabilities	$ 43,400

Debt and Interest Expense - Deb

Debt and Interest Expense - Debt Outstanding Table (Details) - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Carrying value	[1]	$ 4,787,381,000	$ 3,464,712,000
WES RCF [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Principal		220,000,000	370,000,000
Carrying value		220,000,000	370,000,000
WES RCF [Member] | Revolving Credit Facility [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 220,000,000	$ 370,000,000
APCWH Note Payable [Member]
Debt Instrument [Line Items]
Interest rate		3.04%	2.09%
Principal		$ 427,493,000	$ 98,966,000
Carrying value		427,493,000	98,966,000
APCWH Note Payable [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 427,493,000	98,966,000
Senior Notes [Member] | 2.600% Senior Notes due 2018 [Member]
Debt Instrument [Line Items]
Interest rate		2.60%
Debt instrument, maturity date		Aug. 15, 2018
Principal		$ 0	350,000,000
Carrying value		0	349,684,000
Senior Notes [Member] | 2.600% Senior Notes due 2018 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 0	350,631,000
Senior Notes [Member] | 5.375% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Interest rate		5.375%
Debt instrument, maturity date		Jun. 1, 2021
Principal		$ 500,000,000	500,000,000
Carrying value		496,959,000	495,815,000
Senior Notes [Member] | 5.375% Senior Notes due 2021 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 515,990,000	530,647,000
Senior Notes [Member] | 4.000% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Interest rate		4.00%
Debt instrument, maturity date		Jul. 1, 2022
Principal		$ 670,000,000	670,000,000
Carrying value		669,078,000	668,849,000
Senior Notes [Member] | 4.000% Senior Notes due 2022 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 662,109,000	684,043,000
Senior Notes [Member] | 3.950% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Interest rate		3.95%
Debt instrument, maturity date		Jun. 1, 2025
Principal		$ 500,000,000	500,000,000
Carrying value		492,837,000	491,885,000
Senior Notes [Member] | 3.950% Senior Notes due 2025 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 466,135,000	500,885,000
Senior Notes [Member] | 4.650% Senior Notes due 2026 [Member]
Debt Instrument [Line Items]
Interest rate		4.65%
Debt instrument, maturity date		Jul. 1, 2026
Principal		$ 500,000,000	500,000,000
Carrying value		495,710,000	495,245,000
Senior Notes [Member] | 4.650% Senior Notes due 2026 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 483,994,000	520,144,000
Senior Notes [Member] | 4.500% Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Interest rate		4.50%
Debt instrument, maturity date		Mar. 1, 2028
Principal		$ 400,000,000	0
Carrying value		394,631,000	0
Senior Notes [Member] | 4.500% Senior Notes due 2028 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 377,475,000	0
Senior Notes [Member] | 4.750% Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Interest rate		4.75%
Debt instrument, maturity date		Aug. 15, 2028
Principal		$ 400,000,000	0
Carrying value		395,841,000	0
Senior Notes [Member] | 4.750% Senior Notes due 2028 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 384,370,000	0
Senior Notes [Member] | 5.450% Senior Notes due 2044 [Member]
Debt Instrument [Line Items]
Interest rate		5.45%
Debt instrument, maturity date		Apr. 1, 2044
Principal		$ 600,000,000	600,000,000
Carrying value		593,349,000	593,234,000
Senior Notes [Member] | 5.450% Senior Notes due 2044 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 522,386,000	637,827,000
Senior Notes [Member] | 5.300% Senior Notes due 2048 [Member]
Debt Instrument [Line Items]
Interest rate		5.30%
Debt instrument, maturity date		Mar. 1, 2048
Principal		$ 700,000,000	0
Carrying value		686,648,000	0
Senior Notes [Member] | 5.300% Senior Notes due 2048 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	$ 605,327,000	0
Senior Notes [Member] | 5.500% Senior Notes due 2048 [Member]
Debt Instrument [Line Items]
Interest rate		5.50%
Debt instrument, maturity date		Aug. 15, 2048
Principal		$ 350,000,000	0
Carrying value		342,328,000	0
Senior Notes [Member] | 5.500% Senior Notes due 2048 [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value	[2]	311,536,000	0
Long Term Debt Obligations [Member]
Debt Instrument [Line Items]
Total long-term debt, principal		5,267,493,000	3,588,966,000
Carrying value		5,214,874,000	3,563,678,000	$ 3,091,461,000
Long Term Debt Obligations [Member] | Valuation, Market Approach [Member] | Level 2 Inputs [Member]
Debt Instrument [Line Items]
Fair value		$ 4,976,815,000	$ 3,693,143,000
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Fair value is measured using the market approach and Level 2 inputs.

Debt and Interest Expense - D_2

Debt and Interest Expense - Debt Activity Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Changes in Debt Outstanding [Roll Forward]
Beginning balance	[1]	$ 3,464,712
Other		(20,584)	$ 3,404
Ending balance	[1]	4,787,381	3,464,712
WES RCF [Member] | Revolving Credit Facility [Member]
Changes in Debt Outstanding [Roll Forward]
Beginning balance		370,000
RCF borrowings		540,000	370,000
Repayments of RCF borrowings		(690,000)
Ending balance		220,000	370,000
APCWH Note Payable [Member]
Changes in Debt Outstanding [Roll Forward]
Beginning balance		98,966
APCWH Note Payable borrowings		321,780	98,813
Ending balance		427,493	98,966
Senior Notes [Member] | 4.500% Senior Notes due 2028 [Member]
Changes in Debt Outstanding [Roll Forward]
Beginning balance		0
Issuance of senior notes		400,000
Ending balance		394,631	0
Senior Notes [Member] | 5.300% Senior Notes due 2048 [Member]
Changes in Debt Outstanding [Roll Forward]
Beginning balance		0
Issuance of senior notes		700,000
Ending balance		686,648	0
Senior Notes [Member] | 4.750% Senior Notes due 2028 [Member]
Changes in Debt Outstanding [Roll Forward]
Beginning balance		0
Issuance of senior notes		400,000
Ending balance		395,841	0
Senior Notes [Member] | 5.500% Senior Notes due 2048 [Member]
Changes in Debt Outstanding [Roll Forward]
Beginning balance		0
Issuance of senior notes		350,000
Ending balance		342,328	0
Senior Notes [Member] | 2.600% Senior Notes due 2018 [Member]
Changes in Debt Outstanding [Roll Forward]
Beginning balance		349,684
Repayment of senior notes		(350,000)
Ending balance		0	349,684
Long Term Debt Obligations [Member]
Changes in Debt Outstanding [Roll Forward]
Beginning balance		3,563,678	3,091,461
Ending balance		$ 5,214,874	$ 3,563,678
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Debt and Interest Expense - Int

Debt and Interest Expense - Interest-Rate Swap Table (Details) - Not Designated as Hedging Instrument [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Interest-Rate Swap 1 [Member]
Derivative [Line Items]
Interest-rate swap, notional amount	$ 250
Interest-rate swap, reference period start date	Dec. 31, 2019
Interest-rate swap, reference period end date	Dec. 31, 2024
Interest-rate swap, maturity date	Dec. 31, 2019
Interest-rate swap, fixed interest rate	2.73%
Interest-Rate Swap 2 [Member]
Derivative [Line Items]
Interest-rate swap, notional amount	$ 250
Interest-rate swap, reference period start date	Dec. 31, 2019
Interest-rate swap, reference period end date	Dec. 31, 2029
Interest-rate swap, maturity date	Dec. 31, 2019
Interest-rate swap, fixed interest rate	2.856%
Interest-Rate Swap 3 [Member]
Derivative [Line Items]
Interest-rate swap, notional amount	$ 250
Interest-rate swap, reference period start date	Dec. 31, 2019
Interest-rate swap, reference period end date	Dec. 31, 2049
Interest-rate swap, maturity date	Dec. 31, 2019
Interest-rate swap, fixed interest rate	2.905%

Debt and Interest Expense - I_2

Debt and Interest Expense - Interest Expense Table (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Interest expense	[1],[2]	$ (181,796)	$ (140,291)	$ (107,565)
Third Parties [Member]
Debt Instrument [Line Items]
Long-term debt		(199,322)	(142,525)	(121,832)
Amortization of debt issuance costs and commitment fees		(8,207)	(6,616)	(6,398)
Capitalized interest		32,479	9,074	12,918
Interest expense		(175,050)	(140,067)	(115,312)
Affiliates [Member]
Debt Instrument [Line Items]
Interest expense	[3],[4]	(6,746)	(224)	7,747
Affiliates [Member] | APCWH Note Payable [Member]
Debt Instrument [Line Items]
Affiliate interest expense		(6,746)	(153)	0
Affiliates [Member] | Deferred Purchase Price Obligation - Anadarko [Member]
Debt Instrument [Line Items]
Affiliate interest expense	[5]	$ 0	$ (71)	$ 7,747
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.
[2]	Includes affiliate (as defined in Note 1) amounts of $(6.7) million, $(0.2) million and $7.7 million for the years ended December 31, 2018, 2017 and 2016, respectively. See Note 3 and Note 13.
[3]	Includes amounts related to the APCWH Note Payable (see Note 13 and Note 15).
[4]	Includes amounts related to the Deferred purchase price obligation - Anadarko (see Note 3 and Note 13).
[5]	See Note 3 for a discussion of the Deferred purchase price obligation - Anadarko.

Debt and Interest Expense - Add

Debt and Interest Expense - Additional Information (Details) - USD ($)

Feb. 15, 2019

Dec. 19, 2018

Feb. 16, 2018

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Mar. 31, 2019

Aug. 31, 2018

Mar. 31, 2018

Jun. 30, 2017

Feb. 25, 2014

Debt Instrument [Line Items]

APCWH Note Payable

[1],[2]

$ 427,493,000

$ 98,966,000

Long-term debt

[1]

4,787,381,000

3,464,712,000

Gain (loss) on interest-rate swaps

[1]

(7,972,000)

$ 0

$ 0

Interest-Rate Swap [Member]

Debt Instrument [Line Items]

Gain (loss) on interest-rate swaps

(7,972,000)

Interest-Rate Swap [Member] | Not Designated as Hedging Instrument [Member]

Debt Instrument [Line Items]

Interest-rate swap, collateral posted if credit risk related provision triggered

2,700,000

Interest-rate swap, aggregate fair value of swaps with credit risk related features for which a net liability position existed

5,700,000

Interest-Rate Swap [Member] | Not Designated as Hedging Instrument [Member] | Accrued Liabilities [Member]

Debt Instrument [Line Items]

Interest-rate swap, liability fair value

$ 8,000,000

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

Debt Instrument [Line Items]

Facility, maximum borrowing capacity

$ 1,500,000,000

$ 1,200,000,000

Facility, expandable maximum borrowing capacity

$ 2,000,000,000

Facility, expiration date

Feb. 15, 2023

Facility, fee rate

0.20%

0.20%

Facility, outstanding borrowings

$ 220,000,000

Facility, outstanding letters of credit

4,600,000

Facility, available borrowing capacity

$ 1,300,000,000

Facility, interest rate at period end

3.74%

2.87%

Long-term debt

$ 220,000,000

$ 370,000,000

WES RCF [Member] | Revolving Credit Facility [Member] | Scenario, Forecast [Member]

Debt Instrument [Line Items]

Facility, maximum borrowing capacity

$ 2,000,000,000

Facility, accordion feature amount

$ 500,000,000

WES RCF [Member] | Revolving Credit Facility [Member] | Subsequent Event [Member]

Debt Instrument [Line Items]

Facility, expiration date

Feb. 15, 2024

WES RCF [Member] | Revolving Credit Facility [Member] | Minimum [Member]

Debt Instrument [Line Items]

Facility, fee rate

0.125%

WES RCF [Member] | Revolving Credit Facility [Member] | Maximum [Member]

Debt Instrument [Line Items]

Facility, fee rate

0.25%

WES RCF [Member] | Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Alternate Base Rate [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

1.00%

WES RCF [Member] | Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

1.00%

WES RCF [Member] | Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

1.50%

WES RCF [Member] | Revolving Credit Facility [Member] | Percentage Above Federal Funds Effective Rate [Member] | Alternate Base Rate [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

0.50%

WES RCF [Member] | Revolving Credit Facility [Member] | Base Rate [Member] | Minimum [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

0.00%

WES RCF [Member] | Revolving Credit Facility [Member] | Base Rate [Member] | Maximum [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

0.50%

364-Day Facility [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Facility, maximum borrowing capacity

$ 2,000,000,000

Facility, fee rate

0.175%

364-Day Facility [Member] | Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Alternate Base Rate [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

1.00%

364-Day Facility [Member] | Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

1.00%

364-Day Facility [Member] | Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

1.625%

364-Day Facility [Member] | Revolving Credit Facility [Member] | Percentage Above Federal Funds Effective Rate [Member] | Alternate Base Rate [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

0.50%

364-Day Facility [Member] | Revolving Credit Facility [Member] | Base Rate [Member] | Minimum [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

0.00%

364-Day Facility [Member] | Revolving Credit Facility [Member] | Base Rate [Member] | Maximum [Member]

Debt Instrument [Line Items]

Facility, applicable margin added

0.625%

APCWH Note Payable [Member]

Debt Instrument [Line Items]

Interest rate

3.04%

2.09%

Long-term debt

$ 427,493,000

$ 98,966,000

APCWH Note Payable [Member] | Maximum [Member]

Debt Instrument [Line Items]

APCWH Note Payable

$ 500,000,000

Senior Notes [Member] | 4.750% Senior Notes due 2028 [Member]

Debt Instrument [Line Items]

Interest rate

4.75%

Senior note, offering percent

99.818%

Senior note, effective interest rate

4.885%

Long-term debt

$ 395,841,000

0

Senior Notes [Member] | 5.500% Senior Notes due 2048 [Member]

Debt Instrument [Line Items]

Interest rate

5.50%

Senior note, offering percent

98.912%

Senior note, effective interest rate

5.652%

Long-term debt

$ 342,328,000

0

Senior Notes [Member] | 4.500% Senior Notes due 2028 [Member]

Debt Instrument [Line Items]

Interest rate

4.50%

Senior note, offering percent

99.435%

Senior note, effective interest rate

4.682%

Long-term debt

$ 394,631,000

0

Senior Notes [Member] | 5.300% Senior Notes due 2048 [Member]

Debt Instrument [Line Items]

Interest rate

5.30%

Senior note, offering percent

99.169%

Senior note, effective interest rate

5.431%

Long-term debt

$ 686,648,000

$ 0

[1]

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

[2]

See Note 6 and Note 15.

Commitments and Contingencies -

Commitments and Contingencies - Operating Lease Obligations Table (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019	$ 8,711
2020	2,236
2021	460
2022	467
2023	473
Thereafter	1,547
Total	$ 13,894

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands		Mar. 17, 2017	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies				$ 1,700	$ 1,800
Contract liabilities				16,235	0
Revenues and other	[1]			2,299,658	2,429,614	$ 1,941,330
Rent expense associated with office, warehouse and equipment leases				56,500	$ 45,500	$ 37,800
Service Revenues - Fee Based [Member]
Loss Contingencies [Line Items]
Revenues and other				$ 1,905,728
DBJV Arbitration [Member] | Pending Litigation [Member]
Loss Contingencies [Line Items]
Contract liabilities							$ 7,500
DBJV Arbitration [Member] | Settled Litigation [Member] | Service Revenues - Fee Based [Member]
Loss Contingencies [Line Items]
Revenues and other			$ 7,500
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%
[1]	Financial information has been recast to include the financial position and results attributable to AMA. See Note 1 and Note 3.

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($) $ in Thousands	Feb. 28, 2019	Dec. 31, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Units issued		1,128,782	885,760
Acquisitions		$ 162,615	$ 22,500
General partner units owned		2,583,068	2,583,068
Conversion of units			0
Anadarko [Member] | Anadarko Midstream Assets [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Cash consideration	$ 1,814,000
Acquisitions	$ 193,900
Class C Units [Member]
Subsequent Event [Line Items]
Units issued		1,128,782	885,760
Class C units, common units issued upon conversion		1
Units outstanding		14,372,665	13,243,883
Class C Units [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Class C units, common units issued upon conversion	1
Common Units [Member]
Subsequent Event [Line Items]
Conversion of units			21,922,831
Units outstanding		152,609,285	152,602,105
Common Units [Member] | Anadarko [Member] | Anadarko Midstream Assets [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Units issued	45,760,201
Western Gas Partners, LP [Member] | Common Units [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Conversion of units	105,624,704
Anadarko [Member] | Western Gas Partners, LP [Member] | Common Units [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Units outstanding	6,375,284
Western Gas Equity Partners, LP [Member] | Common Units [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
Conversion of units	55,360,984
Western Gas Equity Partners, LP [Member] | Western Gas Partners, LP [Member]
Subsequent Event [Line Items]
General partner units owned		2,583,068
Western Gas Equity Partners, LP [Member] | Western Gas Partners, LP [Member] | Scenario, Forecast [Member]
Subsequent Event [Line Items]
General partner units owned	2,583,068
Western Gas Equity Partners, LP [Member] | Western Gas Partners, LP [Member] | Common Units [Member]
Subsequent Event [Line Items]
Units outstanding		50,132,046