Western Midstream Partners 10-Q 7 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Nov. 04, 2013
Document And Entity Information [Abstract]	'	'
Entity Registrant Name	'WESTERN GAS PARTNERS LP	'
Entity Central Index Key	'0001414475	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-13	'
Amendment Flag	'false	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock Shares Outstanding	'	112,380,764

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	3 Months Ended				9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Revenues	'		'		'		'
Total revenues	$278,001		$234,734	[1]	$762,874		$679,720	[1]
Operating expenses	'		'		'		'
Cost of product	93,516	[2]	89,107	[1],[2]	270,059	[2]	254,719	[1],[2]
Operation and maintenance	42,757	[2]	35,493	[1],[2]	121,165	[2]	103,304	[1],[2]
General and administrative	7,276	[2]	15,039	[1],[2]	22,228	[2]	35,623	[1],[2]
Property and other taxes	6,649		5,328	[1]	18,520		14,998	[1]
Depreciation, amortization and impairments	37,615		28,455	[1]	106,551		83,263	[1]
Total operating expenses	187,813		173,422	[1]	538,523		491,907	[1]
Operating income	90,188		61,312	[1]	224,351		187,813	[1]
Interest income, net - affiliates	4,225		4,225	[1]	12,675		12,675	[1]
Interest expense	-13,018	[3]	-10,977	[1],[3]	-37,483	[3]	-30,118	[1],[3]
Other income (expense), net	439		522	[1]	1,612		-287	[1]
Income before income taxes	81,834		55,082	[1]	201,155		170,083	[1]
Income tax expense	58		5,080	[1]	4,431		14,588	[1]
Net income	81,776		50,002	[1]	196,724		155,495	[1]
Net income attributable to noncontrolling interests	3,376		3,423	[1]	7,467		11,956	[1]
Net income attributable to Western Gas Partners, LP	78,400		46,579	[1]	189,257		143,539	[1]
Limited partners' interest in net income:	'		'		'		'
Pre-acquisition net (income) loss allocated to Anadarko	0		-7,062	[1]	-4,637		-19,582	[1]
General partner interest in net (income) loss	-18,693	[4]	-8,042	[1],[4]	-47,733	[4]	-18,508	[1],[4]
Limited partners' interest in net income	59,707	[4]	31,475	[1],[4]	136,887	[4]	105,449	[1],[4]
Affiliated Entity [Member]	'		'		'		'
Revenues	'		'		'		'
Gathering, processing and transportation of natural gas and natural gas liquids	83,606		61,388	[1]	218,680		182,448	[1]
Natural gas, natural gas liquids and condensate sales	129,411		115,132	[1]	371,077		324,793	[1]
Equity income and Other, net	4,607		4,085	[1]	13,457		12,219	[1]
Total revenues	217,624	[5]	180,605	[1],[5]	603,214	[5]	519,460	[1],[5]
Operating expenses	'		'		'		'
Cost of product	33,753	[5]	42,839	[5]	97,801	[5]	115,603	[5]
Operation and maintenance	13,469	[6]	12,638	[6]	41,021	[6]	38,040	[6]
General and administrative	5,867	[7]	14,227	[7]	17,325	[7]	30,811	[7]
Total operating expenses	53,089		69,704		156,147		184,454
Interest expense	0	[5],[8]	-81	[8]	0	[8]	-2,684	[9]
Third Parties [Member]	'		'		'		'
Revenues	'		'		'		'
Gathering, processing and transportation of natural gas and natural gas liquids	47,175		32,545	[1]	124,791		96,518	[1]
Natural gas, natural gas liquids and condensate sales	11,915		20,974	[1]	31,539		62,025	[1]
Equity income and Other, net	1,287		610	[1]	3,330		1,717	[1]
Total revenues	60,377		54,129	[1]	159,660		160,260	[1]
Operating expenses	'		'		'		'
Interest expense	($13,018)		($10,896)		($37,483)		($27,434)
Limited Partners [Member] | Common Units [Member]	'		'		'		'
Limited partners' interest in net income:	'		'		'		'
Net income per common unit - basic and diluted	$0.53		$0.33	[1]	$1.26		$1.14	[1]
Weighted average common units outstanding - basic and diluted	112,143		95,883	[1]	108,540		92,627	[1]
[1]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.
[2]	Cost of product includes product purchases from Anadarko (as defined in Note 1) of $33.8 million and $97.8 million for the three and nine months ended September 30, 2013, respectively, and $42.8 million and $115.6 million for the three and nine months ended September 30, 2012, respectively. Operation and maintenance includes charges from Anadarko of $13.5 million and $41.0 million for the three and nine months ended September 30, 2013, respectively, and $12.6 million and $38.0 million for the three and nine months ended September 30, 2012, respectively. General and administrative includes charges from Anadarko of $5.9 million and $17.3 million for the three and nine months ended September 30, 2013, respectively, and $14.2 million and $30.8 million for the three and nine months ended September 30, 2012, respectively. See Note 5.
[3]	Includes affiliate (as defined in Note 1) interest expense of zero for the three and nine months ended September 30, 2013, and $0.1 million and $2.7 million for the three and nine months ended September 30, 2012, respectively. See Note 8.
[4]	Represents net income for periods including and subsequent to the acquisition of the Partnership assets (as defined in Note 1). See Note 4.
[5]	Represents amounts recognized under gathering, treating or processing agreements, and purchase and sale agreements.
[6]	Represents expenses incurred on and subsequent to the date of the acquisition of the 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 by the Partnership.
[7]	Represents general and administrative expense incurred on and subsequent to the date of the Partnership’s acquisition of the Partnership assets, as well as a management services fee for reimbursement of 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 Equity incentive plan and Anadarko incentive plans within this Note 5).
[8]	For the three and nine months ended September 30, 2012, includes interest expense recognized on the note payable to Anadarko (see Note 8) and interest imputed on the reimbursement payable to Anadarko for certain expenditures Anadarko incurred in 2011 related to the construction of the Brasada and Lancaster plants. The Partnership repaid the note payable to Anadarko in June 2012, and repaid the reimbursement payable to Anadarko related to the construction of the Brasada and Lancaster plants in the fourth quarter of 2012. See Note receivable from and amounts payable to Anadarko within this Note 5.
[9]	Represents interest income recognized on the note receivable from Anadarko.

Consolidated_Statements_of_Inc1

Consolidated Statements of Income (Parenthetical) (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Cost of product	$93,516	[1]	$89,107	[1],[2]	$270,059	[1]	$254,719	[1],[2]
Operation and maintenance	42,757	[1]	35,493	[1],[2]	121,165	[1]	103,304	[1],[2]
General and administrative	7,276	[1]	15,039	[1],[2]	22,228	[1]	35,623	[1],[2]
Interest expense	13,018	[3]	10,977	[2],[3]	37,483	[3]	30,118	[2],[3]
Affiliated Entity [Member]	'		'		'		'
Cost of product	33,753	[4]	42,839	[4]	97,801	[4]	115,603	[4]
Operation and maintenance	13,469	[5]	12,638	[5]	41,021	[5]	38,040	[5]
General and administrative	5,867	[6]	14,227	[6]	17,325	[6]	30,811	[6]
Interest expense	$0	[4],[7]	$81	[7]	$0	[7]	$2,684	[8]
[1]	Cost of product includes product purchases from Anadarko (as defined in Note 1) of $33.8 million and $97.8 million for the three and nine months ended September 30, 2013, respectively, and $42.8 million and $115.6 million for the three and nine months ended September 30, 2012, respectively. Operation and maintenance includes charges from Anadarko of $13.5 million and $41.0 million for the three and nine months ended September 30, 2013, respectively, and $12.6 million and $38.0 million for the three and nine months ended September 30, 2012, respectively. General and administrative includes charges from Anadarko of $5.9 million and $17.3 million for the three and nine months ended September 30, 2013, respectively, and $14.2 million and $30.8 million for the three and nine months ended September 30, 2012, respectively. See Note 5.
[2]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.
[3]	Includes affiliate (as defined in Note 1) interest expense of zero for the three and nine months ended September 30, 2013, and $0.1 million and $2.7 million for the three and nine months ended September 30, 2012, respectively. See Note 8.
[4]	Represents amounts recognized under gathering, treating or processing agreements, and purchase and sale agreements.
[5]	Represents expenses incurred on and subsequent to the date of the acquisition of the 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 by the Partnership.
[6]	Represents general and administrative expense incurred on and subsequent to the date of the Partnership’s acquisition of the Partnership assets, as well as a management services fee for reimbursement of 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 Equity incentive plan and Anadarko incentive plans within this Note 5).
[7]	For the three and nine months ended September 30, 2012, includes interest expense recognized on the note payable to Anadarko (see Note 8) and interest imputed on the reimbursement payable to Anadarko for certain expenditures Anadarko incurred in 2011 related to the construction of the Brasada and Lancaster plants. The Partnership repaid the note payable to Anadarko in June 2012, and repaid the reimbursement payable to Anadarko related to the construction of the Brasada and Lancaster plants in the fourth quarter of 2012. See Note receivable from and amounts payable to Anadarko within this Note 5.
[8]	Represents interest income recognized on the note receivable from Anadarko.

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2013		Dec. 31, 2012
Current assets	'		'
Cash and cash equivalents	$38,364,000		$419,981,000	[1]
Accounts receivable, net	75,788,000	[2]	50,233,000	[1],[2]
Other current assets	8,763,000	[3]	6,998,000	[1],[3]
Total current assets	122,915,000		477,212,000	[1]
Note receivable - Anadarko	260,000,000		260,000,000	[1]
Property, plant and equipment	'		'
Cost	4,061,389,000		3,432,392,000	[1]
Less accumulated depreciation	817,489,000		714,436,000	[1]
Net property, plant and equipment	3,243,900,000		2,717,956,000	[1]
Goodwill	105,336,000		105,336,000	[1]
Other intangible assets	54,436,000		55,490,000	[1]
Equity investments	227,566,000		106,130,000	[1]
Other assets	28,078,000		27,798,000	[1]
Total assets	4,042,231,000		3,749,922,000	[1]
Current liabilities	'		'
Accounts and natural gas imbalance payables	19,131,000	[4]	25,154,000	[1],[4]
Accrued ad valorem taxes	18,472,000		11,949,000	[1]
Income taxes payable	190,000		552,000	[1]
Accrued liabilities	140,166,000	[5]	147,651,000	[1],[5]
Total current liabilities	177,959,000		185,306,000	[1]
Long-term debt - third parties	1,518,110,000		1,168,278,000	[1]
Deferred income taxes	1,830,000		47,153,000	[1]
Asset retirement obligations and other	76,336,000		68,749,000	[1]
Total long-term liabilities	1,596,276,000		1,284,180,000	[1]
Total liabilities	1,774,235,000		1,469,486,000	[1]
Equity and partners' capital	'		'
Common units (112,174,911 and 104,660,553 units issued and outstanding at September 30, 2013, and December 31, 2012, respectively)	2,127,040,000		1,957,066,000	[1]
General partner units (2,288,573 and 2,135,930 units issued and outstanding at September 30, 2013, and December 31, 2012, respectively)	68,585,000		52,752,000	[1]
Net investment by Anadarko	0		199,960,000	[1]
Total partners' capital	2,195,625,000		2,209,778,000	[1]
Noncontrolling interests	72,371,000		70,658,000	[1]
Total equity and partners' capital	2,267,996,000		2,280,436,000	[1]
Total liabilities, equity and partners' capital	4,042,231,000		3,749,922,000	[1]
Affiliated Entity [Member]	'		'
Current assets	'		'
Accounts receivable, net	40,100,000		19,100,000
Other current assets	100,000		400,000
Current liabilities	'		'
Accounts and natural gas imbalance payables	2,800,000		2,500,000
Accrued liabilities	$100,000		$100,000
[1]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.
[2]	Accounts receivable, net includes amounts receivable from affiliates (as defined in Note 1) of $40.1 million and $19.1 million as of September 30, 2013, and December 31, 2012, respectively.
[3]	Other current assets includes natural gas imbalance receivables from affiliates of $0.1 million and $0.4 million as of September 30, 2013, and December 31, 2012, respectively.
[4]	Accounts and natural gas imbalance payables includes amounts payable to affiliates of $2.8 million and $2.5 million as of September 30, 2013, and December 31, 2012, respectively.
[5]	Accrued liabilities include amounts payable to affiliates of $0.1 million as of September 30, 2013 and December 31, 2012.

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
GP units issued	2,288,573		2,135,930
General partner units outstanding	2,288,573		2,135,930
Accounts receivable, net	$75,788	[1]	$50,233	[1],[2]
Other current assets	8,763	[3]	6,998	[2],[3]
Accounts and natural gas imbalance payables	19,131	[4]	25,154	[2],[4]
Accrued liabilities	140,166	[5]	147,651	[2],[5]
Affiliated Entity [Member]	'		'
Accounts receivable, net	40,100		19,100
Other current assets	100		400
Accounts and natural gas imbalance payables	2,800		2,500
Accrued liabilities	$100		$100
Common Units [Member]	'		'
Common units issued	112,174,911		104,660,553
Units outstanding	112,174,911		104,660,553
[1]	Accounts receivable, net includes amounts receivable from affiliates (as defined in Note 1) of $40.1 million and $19.1 million as of September 30, 2013, and December 31, 2012, respectively.
[2]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.
[3]	Other current assets includes natural gas imbalance receivables from affiliates of $0.1 million and $0.4 million as of September 30, 2013, and December 31, 2012, respectively.
[4]	Accounts and natural gas imbalance payables includes amounts payable to affiliates of $2.8 million and $2.5 million as of September 30, 2013, and December 31, 2012, respectively.
[5]	Accrued liabilities include amounts payable to affiliates of $0.1 million as of September 30, 2013 and December 31, 2012.

Consolidated_Statement_of_Equi

Consolidated Statement of Equity and Partners' Capital (USD $)		Total	Net Investment by Anadarko [Member]	Common Units [Member]	General Partner [Member]	Noncontrolling Interest [Member]
In Thousands
Balance at Dec. 31, 2012	[1]	$2,280,436	$199,960	$1,957,066	$52,752	$70,658
Net income		196,724	4,637	136,887	47,733	7,467
Issuance of common and general partner units, net of offering expenses		427,795	'	418,517	9,278	'
Contributions from noncontrolling interest owners		2,247	'	'	'	2,247
Distributions to noncontrolling interest owners		-8,001	'	'	'	-8,001
Distributions to unitholders		-215,115	'	-173,976	-41,139	'
Acquisitions from affiliates		-465,500	-255,635	-209,865	'	'
Contributions of equity-based compensation from Anadarko		2,144	'	2,101	43	'
Net pre-acquisition contributions from (distributions to) Anadarko		4,508	4,508	'	'	'
Net distributions of other assets to Anadarko		-4,080	'	-3,998	-82	'
Elimination of net deferred tax liabilities		46,530	46,530	'	'	'
Other		308	'	308	'	'
Balance at Sep. 30, 2013		$2,267,996	'	$2,127,040	$68,585	$72,371
[1]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012
Cash flows from operating activities	'		'
Net income	$196,724		$155,495	[1]
Adjustments to reconcile net income to net cash provided by operating activities:	'		'
Depreciation, amortization and impairments	106,551		83,263	[1]
Non-cash equity-based compensation expense	2,564		2,769	[1]
Deferred income taxes	1,207		21,565	[1]
Debt-related amortization and other items, net	1,756		1,728	[1]
Changes in assets and liabilities:	'		'
(Increase) decrease in accounts receivable, net	-27,387		47,272	[1]
Increase (decrease) in accounts and natural gas imbalance payables and accrued liabilities, net	6,818		29,261	[1]
Change in other items, net	836		2,234	[1]
Net cash provided by operating activities	289,069		343,587	[1]
Cash flows from investing activities	'		'
Capital expenditures	-469,678		-403,949	[1]
Investments in equity affiliates	-45,126		-147	[1]
Other	-1,524		0	[1]
Net cash used in investing activities	-1,226,404		-1,009,296	[1]
Cash flows from financing activities	'		'
Borrowings, net of debt issuance costs	842,566		885,291	[1]
Repayments of debt	-495,000		-549,000	[1]
Increase (decrease) in outstanding checks	-3,335		2,534	[1]
Proceeds from issuance of common and general partner units, net of offering expenses	427,848		216,462	[1]
Distributions to unitholders	-215,115		-141,505	[1]
Contributions from noncontrolling interest owners	2,247		26,888	[1]
Distributions to noncontrolling interest owners	-8,001		-14,303	[1]
Net contributions from Anadarko	4,508		60,277	[1]
Net cash provided by financing activities	555,718		486,644	[1]
Net increase (decrease) in cash and cash equivalents	-381,617		-179,065	[1]
Cash and cash equivalents at beginning of period	419,981	[1]	226,559	[1]
Cash and cash equivalents at end of period	38,364		47,494	[1]
Supplemental disclosures	'		'
Net distributions to Anadarko of other assets	4,080		10,790	[1]
Interest paid, net of capitalized interest	34,974		16,460	[1]
Taxes paid	0		495	[1]
Affiliated Entity [Member]	'		'
Cash flows from investing activities	'		'
Acquisitions	-469,884		-605,960	[1]
Proceeds from sale of assets	82		760	[1]
Third Parties [Member]	'		'
Cash flows from investing activities	'		'
Acquisitions	($240,274)		$0	[1]
[1]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Description_of_Business_and_Ba

Description of Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Description of Business and Basis of Presentation	'
	1. DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION
	General. Western Gas Partners, LP is a growth-oriented Delaware master limited partnership formed by Anadarko Petroleum Corporation in 2007 to own, operate, acquire and develop midstream energy 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” or “GP”), is owned by Western Gas Equity Partners, LP (“WGP”), a Delaware master limited partnership 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 (see Western Gas Equity Partners, LP below). 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 consolidated subsidiaries, excluding the Partnership and the general partner, and “affiliates” refers to wholly owned and partially owned subsidiaries of Anadarko, excluding the Partnership, and includes the interests in Fort Union Gas Gathering, LLC (“Fort Union”), White Cliffs Pipeline, LLC (“White Cliffs”), Rendezvous Gas Services, LLC (“Rendezvous”), and a joint venture, Enterprise EF78 LLC (“Mont Belvieu JV”). See Note 2. “Equity investment throughput” refers to the Partnership’s 14.81% share of Fort Union and 22% share of Rendezvous gross volumes.
	The Partnership is engaged in the business of gathering, processing, compressing, treating and transporting natural gas, condensate, NGLs and crude oil for Anadarko, as well as third-party producers and customers. As of September 30, 2013, the Partnership’s assets, exclusive of interests in Fort Union, White Cliffs, Rendezvous and the Mont Belvieu JV accounted for under the equity method, consisted of the following:
		Owned and	Operated	Non-Operated
		Operated	Interests	Interests
	Natural gas gathering systems	13	1	5
	Natural gas treating facilities	8	—	—
	Natural gas processing facilities	8	3	—
	NGL pipelines	3	—	—
	Natural gas pipelines	3	—	—
	These assets are located in South, East and West Texas, the Rocky Mountains (Colorado, Utah and Wyoming), north-central Pennsylvania, and the Mid-Continent (Kansas and Oklahoma). The Partnership was also constructing the Lancaster processing facility in Northeast Colorado at the end of the third quarter of 2013.
	Western Gas Equity Partners, LP. In December 2012, WGP completed its initial public offering (“IPO”) of 19,758,150 common units representing limited partner interests in WGP at a price of $22.00 per common unit. WGP used the net proceeds from the offering to purchase common and general partner units of the Partnership resulting in aggregate proceeds to the Partnership of approximately $409.4 million, which was used by the Partnership for general partnership purposes, including the funding of capital expenditures.
	WGP owns the following types of interests in the Partnership: (i) the 2.0% general partner interest and all of the incentive distribution rights (“IDRs”) in the Partnership, both owned through WGP’s 100% ownership of the Partnership’s general partner and (ii) a significant limited partner interest (see Holdings of Partnership equity in Note 4). WGP has no independent operations or material assets other than its partnership interests in WES.
	1. DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (CONTINUED)
	Basis of presentation. 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. Investments in noncontrolled entities over which the Partnership exercises significant influence are accounted for under the equity method. The Partnership proportionately consolidates its 33.75% share of the assets, liabilities, revenues and expenses attributable to the Non-Operated Marcellus Interest and Anadarko-Operated Marcellus Interest (see Note 2) and its 50% share of the assets, liabilities, revenues and expenses attributable to the Newcastle system in the accompanying consolidated financial statements.
	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, utilizing historical experience and other methods considered reasonable under the particular circumstances. Changes in facts and circumstances or additional information may result in revised estimates and actual results may differ from these estimates. Effects on the business, financial condition and results of operations resulting from revisions to estimates are recognized when the facts that give rise to the revisions become known. The information furnished herein reflects all normal recurring adjustments which are, in the opinion of management, necessary for a fair presentation of the consolidated financial statements, and certain prior-period amounts have been reclassified to conform to the current-year presentation.
	For the nine months ended September 30, 2012, operating cash inflows and investing cash outflows in the Partnership’s unaudited consolidated statements of cash flows include a reduction of $35.7 million attributable to the correction of an error discovered during analysis of accounts payable balances. This analysis revealed that certain 2012 invoices received, but not yet paid, were properly attributable to ongoing capital projects rather than to operating expenses. Management concluded that this misstatement was not material relative to the nine months ended September 30, 2012, and has corrected the error within the unaudited statement of cash flows for the nine months ended September 30, 2012, as included in this report.
	Certain information and note disclosures commonly included in annual financial statements have been condensed or omitted pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Accordingly, the accompanying consolidated financial statements and notes should be read in conjunction with the Partnership’s 2012 Form 10-K, as filed with the SEC on February 28, 2013, certain sections of which were recast in the Partnership’s Current Report on Form 8-K, as filed with the SEC on May 13, 2013, to reflect the results of the Non-Operated Marcellus Interest acquisition (as defined in Note 2). Management believes that the disclosures made are adequate to make the information not misleading.
	In July 2009, the Partnership acquired a 51% interest in Chipeta Processing LLC (“Chipeta”) and became party to Chipeta’s limited liability company agreement. On August 1, 2012, the Partnership acquired Anadarko’s then remaining 24% membership interest in Chipeta (the “additional Chipeta interest”). Prior to this transaction, the interests in Chipeta held by Anadarko and a third-party member were reflected as noncontrolling interests in the consolidated financial statements. The acquisition of Anadarko’s then remaining 24% interest was accounted for on a prospective basis as the Partnership acquired an additional interest in an already-consolidated entity. As such, effective August 1, 2012, noncontrolling interest excludes the financial results and operations of the additional Chipeta interest. The remaining 25% membership interest held by the third-party member is reflected within noncontrolling interests in the consolidated financial statements for all periods presented. See Note 2.
	Presentation of Partnership assets. References to the “Partnership assets” refer collectively to the assets owned by the Partnership as of September 30, 2013. Because Anadarko controls the Partnership through its ownership and control of WGP, which owns the Partnership’s general partner, each of the Partnership’s acquisitions of 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 may be required to recast its financial statements to include the activities of such assets as of the date of common control. See Note 2.
	1. DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (CONTINUED)
	For those periods requiring recast, the consolidated financial statements for periods prior to the Partnership’s acquisition of Partnership assets from Anadarko, including the Non-Operated Marcellus Interest, 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 the assets during the periods reported. Net income attributable to the Partnership assets for periods prior to the Partnership’s acquisition of such assets is not allocated to the limited partners for purposes of calculating net income per common unit.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
Acquisitions	'
	2. ACQUISITIONS
	The following table presents the acquisitions completed by the Partnership during 2012 and 2013, and identifies the funding sources for such acquisitions:
	thousands except unit and		Acquisition		Percentage			Borrowings			Cash		Common	GP Units
	percent amounts		Date		Acquired						On Hand		Units Issued	Issued
	MGR (1)		1/13/12		100	%		$	299,000		$	159,587	632,783	12,914
	Chipeta (2)		8/1/12		24	%		—			128,250		151,235	3,086
	Non-Operated Marcellus Interest (3)		3/1/13		33.75	%		250,000			215,500		449,129	—
	Anadarko-Operated Marcellus Interest (4)		3/8/13		33.75	%		133,500			—		—	—
	Mont Belvieu JV (5)		6/5/13		25	%		—			78,129		—	—
	OTTCO (6)		9/3/13		100	%		27,500			—		—	—
	(1)	The assets acquired from Anadarko consist of (i) the Red Desert complex, which is located in the greater Green River Basin in southwestern Wyoming, and includes the Patrick Draw processing plant, the Red Desert processing plant, gathering lines, and related facilities, (ii) a 22% interest in Rendezvous, which owns a gathering system serving the Jonah and Pinedale Anticline fields in southwestern Wyoming, and (iii) certain additional midstream assets and equipment. These assets are collectively referred to as the “MGR assets” and the acquisition as the “MGR acquisition.”
	(2)	The Partnership acquired Anadarko’s then remaining 24% membership interest in Chipeta (as described in Note 1). The Partnership received distributions related to the additional interest beginning July 1, 2012. This transaction brought the Partnership’s total membership interest in Chipeta to 75%. The remaining 25% membership interest in Chipeta held by a third-party member is reflected as noncontrolling interests in the consolidated financial statements for all periods presented.
	(3)	The Partnership acquired Anadarko’s 33.75% interest (non-operated) in the Liberty and Rome gas gathering systems, serving production from the Marcellus shale in north-central Pennsylvania. The interest acquired is referred to as the “Non-Operated Marcellus Interest” and the acquisition as the “Non-Operated Marcellus Interest acquisition.” In connection with the issuance of the common units, the Partnership’s general partner purchased 9,166 general partner units for consideration of $0.5 million in order to maintain its 2.0% general partner interest in the Partnership. See Non-Operated Marcellus Interest acquisition below for further information.
	(4)	The interest acquired from a third party consisted of a 33.75% interest in each of the Larry’s Creek, Seely and Warrensville gas gathering systems, which are operated by Anadarko and serve production from the Marcellus shale in north-central Pennsylvania. The interest acquired is referred to as the “Anadarko-Operated Marcellus Interest” and the acquisition as the “Anadarko-Operated Marcellus Interest acquisition.” See Anadarko-Operated Marcellus Interest acquisition below for further information, including the final allocation of the purchase price as of September 30, 2013.
	(5)	The acquisition from a third party consisted of a 25% interest in Enterprise EF78 LLC, an entity formed to design, construct, and own two fractionators located in Mont Belvieu, Texas. The interest acquired is accounted for under the equity method of accounting and is referred to as the “Mont Belvieu JV” and the acquisition as the “Mont Belvieu JV acquisition.” See Mont Belvieu JV acquisition below for further information.
	(6)	The Partnership acquired Overland Trail Transmission, LLC (“OTTCO”), a Delaware limited liability company, from a third party. OTTCO owns and operates an intrastate pipeline which connects the Partnership’s Red Desert and Granger complexes in southwestern Wyoming. The assets acquired are referred to as the “OTTCO pipeline” and the acquisition as the “OTTCO acquisition.”
	2. ACQUISITIONS (CONTINUED)
	Non-Operated Marcellus Interest acquisition. Because the Non-Operated Marcellus Interest acquisition was a transfer of net assets between entities under common control, the Partnership’s historical financial statements previously filed with the SEC have been recast in this Form 10-Q to include the results attributable to the Non-Operated Marcellus Interest as if the Partnership owned such assets for all periods presented. The consolidated financial statements for periods prior to the Partnership’s acquisition of the Partnership assets from Anadarko, including the Non-Operated Marcellus Interest, 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 the assets during the periods reported.
	The following table presents the revenue and net income impact of the Non-Operated Marcellus Interest on revenue and net income as presented in the Partnership’s historical consolidated statements of income:
			Three Months Ended September 30, 2012
	thousands		Partnership Historical				Non-Operated Marcellus Interest			Combined
	Revenues		$	219,020			$	15,714		$	234,734
	Net income		42,940				7,062			50,002
			Nine Months Ended September 30, 2012
	thousands		Partnership Historical				Non-Operated Marcellus Interest			Combined
	Revenues		$	636,603			$	43,117		$	679,720
	Net income		135,913				19,582			155,495
	Anadarko-Operated Marcellus Interest acquisition. The Anadarko-Operated Marcellus Interest acquisition has been accounted for under the acquisition method of accounting. The assets acquired and liabilities assumed in the Anadarko-Operated Marcellus Interest acquisition were recorded in the consolidated balance sheet at their estimated fair values as of the acquisition date. Results of operations attributable to the Anadarko-Operated Marcellus Interest were included in the Partnership’s consolidated statements of income beginning on the acquisition date in the first quarter of 2013.
	The following is the final allocation of the purchase price as of September 30, 2013, including $1.1 million of post-closing purchase price adjustments, to the assets acquired and liabilities assumed in the Anadarko-Operated Marcellus Interest acquisition as of the acquisition date:
	thousands
	Property, plant and equipment		$	134,819
	Asset retirement obligations		(174		)
	Total purchase price		$	134,645
	The purchase price allocation is based on an assessment of the fair value of the assets acquired and liabilities assumed in the Anadarko-Operated Marcellus Interest acquisition. The fair values of the interests in the land, right-of-way contracts, and gathering systems were based on the market and income approaches. All fair-value measurements of assets acquired and liabilities assumed are based on inputs that are not observable in the market and thus represent Level 3 inputs.
	2. ACQUISITIONS (CONTINUED)
	The following table presents the pro forma condensed financial information of the Partnership as if the Anadarko-Operated Marcellus Interest acquisition had occurred on January 1, 2012:
			Nine Months Ended
			September 30,
	thousands except per-unit amounts		2013				2012
	Revenues		$	764,128			$	682,820
	Net income		196,872				153,423
	Net income attributable to Western Gas Partners, LP		189,405				141,467
	Net income per common unit - basic and diluted		$	1.26			$	1.12
	The pro forma information is presented for illustration purposes only and is not necessarily indicative of the operating results that would have occurred had the Anadarko-Operated Marcellus Interest acquisition been completed at the assumed date, nor is it necessarily indicative of future operating results of the combined entity. The Partnership’s pro forma information in the table above includes $8.1 million of revenues and $0.5 million of operating expenses, excluding depreciation, amortization and impairments, attributable to the Anadarko-Operated Marcellus Interest that are included in the Partnership’s consolidated statement of income for the nine months ended September 30, 2013. The pro forma adjustments reflect pre-acquisition results of the Anadarko-Operated Marcellus Interest including (a) estimated revenues and expenses; (b) estimated depreciation and amortization based on the purchase price allocated to property, plant and equipment and estimated useful lives; and (c) interest on the Partnership’s borrowings under its revolving credit facility to finance the Anadarko-Operated Marcellus Interest acquisition. The pro forma adjustments include estimates and assumptions based on currently available information. Management believes the estimates and assumptions are reasonable, and the relative effects of the transaction are properly reflected. The pro forma information does not reflect any cost savings or other synergies anticipated as a result of the Anadarko-Operated Marcellus Interest acquisition, nor any future acquisition related expenses.
	Mont Belvieu JV acquisition. The acquisition purchase price represented the Partnership’s 25% share of construction costs incurred by the joint venture partner and 25% of the capitalized interest charged to the financial statements of the Mont Belvieu JV up to the date of acquisition. The allocated capitalized interest is reflected as a component of the equity investment balance recorded upon acquisition. Based on the total estimated net project cost, the construction of the fractionation facilities owned by the Mont Belvieu JV is considered a significant project and satisfies criteria for capitalization of interest. Capitalization of interest subsequent to the acquisition is treated as a basis difference between the cost of the investment and the underlying equity in the net assets of the Mont Belvieu JV. The Partnership will begin to amortize the capitalized interest recognized subsequent to the acquisition upon completion of the facilities, and will reflect the amortization as an adjustment to equity earnings from the Mont Belvieu JV.

Partnership_Distributions

Partnership Distributions	9 Months Ended
	Sep. 30, 2013
Distributions Made to Members or Limited Partners [Abstract]	'
Partnership Distributions	'
	3. PARTNERSHIP DISTRIBUTIONS
	The partnership agreement of Western Gas Partners, LP 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 of the general partner declared the following cash distributions to the Partnership’s unitholders for the periods presented:
	thousands except per-unit amounts		Total Quarterly		Total Quarterly		Date of
	Quarters Ended		Distribution		Cash Distribution		Distribution
			per Unit
	2012
	31-Mar		$	0.46	$	46,053	May-12
	30-Jun		$	0.48	$	52,425	August 2012
	30-Sep		$	0.5	$	56,346	Nov-12
	2013
	31-Mar		$	0.54	$	70,143	May 2013
	30-Jun		$	0.56	$	79,315	Aug-13
	September 30 (1)		$	0.58	$	83,986	Nov-13
	(1)	On October 16, 2013, the board of directors of the Partnership’s general partner declared a cash distribution to the Partnership’s unitholders of $0.58 per unit, or $84.0 million in aggregate, including incentive distributions. The cash distribution is payable on November 12, 2013, to unitholders of record at the close of business on October 31, 2013.

Equity_and_Partners_Capital

Equity and Partners' Capital	9 Months Ended
	Sep. 30, 2013
Partners' Capital Notes [Abstract]	'
Equity and Partners' Capital	'
	4. EQUITY AND PARTNERS’ CAPITAL
	Equity offerings. The Partnership completed the following public offerings of its common units during 2012 and 2013:
	thousands except unit	Common		GP Units		Price Per		Underwriting		Net
	and per-unit amounts	Units Issued (1)		Issued (2)		Unit		Discount and		Proceeds
								Other Offering
								Expenses
	June 2012 equity offering	5,000,000		102,041		$	43.88	$	7,468	$	216,409
	May 2013 equity offering	7,015,000		143,163		61.18		13,203		424,733
	(1)	Includes the issuance of 915,000 common units pursuant to the full exercise of the underwriters’ over-allotment option granted in connection with the May 2013 equity offering.
	(2)	Represents general partner units issued to the general partner in exchange for the general partner’s proportionate capital contribution to maintain its 2.0% general partner interest.
	In addition, pursuant to the Partnership’s registration statement filed with the SEC in August 2012 authorizing the issuance of up to an aggregate of $125.0 million of common units (the “Continuous Offering Program”), the Partnership initiated trades totaling 218,750 common units during the three and nine months ended September 30, 2013, at an average price per unit of $58.22, generating gross proceeds of $12.7 million (including the general partner’s proportionate capital contribution and before $0.1 million of invoiced offering expenses), of which $2.7 million had been received as of September 30, 2013.
	4. EQUITY AND PARTNERS’ CAPITAL (CONTINUED)
	Common and general partner units. The Partnership’s common units are listed on the New York Stock Exchange under the symbol “WES.”
	The following table summarizes common and general partner units issued during the nine months ended September 30, 2013:
			Common		General		Total
			Units		Partner Units
	Balance at December 31, 2012		104,660,553		2,135,930		106,796,483
	Non-Operated Marcellus Interest acquisition		449,129		9,166		458,295
	Long-Term Incentive Plan awards		6,879		140		7,019
	May 2013 equity offering		7,015,000		143,163		7,158,163
	Continuous Offering Program		43,350		174		43,524
	Balance at September 30, 2013		112,174,911		2,288,573		114,463,484
	Holdings of Partnership equity. As of September 30, 2013, WGP held 49,296,205 common units, representing a 43.1% limited partner interest in the Partnership, and, through its ownership of the general partner, WGP indirectly held 2,288,573 general partner units, representing a 2.0% general partner interest in the Partnership, and 100% of the Partnership’s IDRs. As of September 30, 2013, Anadarko Marcellus Midstream, L.L.C. (“AMM”), a subsidiary of Anadarko, separately held 449,129 common units, representing a 0.4% limited partner interest in the Partnership. As of September 30, 2013, the public held 62,429,577 common units, representing a 54.5% limited partner interest in the Partnership.
	The Partnership’s net income for periods including and subsequent to the acquisition of the Partnership assets (as defined in Note 1) is allocated to the general partner and the limited partners consistent with actual cash distributions, including incentive distributions allocable to the general partner. 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 and the limited partners in accordance with their respective ownership percentages.
	Basic and diluted net income per common unit are calculated by dividing the limited partners’ interest in net income 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.

Transactions_With_Affiliates

Transactions With Affiliates	9 Months Ended
	Sep. 30, 2013
Related Party Fees and Other Arrangements, Limited Liability Company (LLC) or Limited Partnership (LP) [Abstract]	'
Transactions with Affiliates	'
	5. TRANSACTIONS WITH AFFILIATES
	Affiliate transactions. Revenues from affiliates include amounts earned by the Partnership from services provided to Anadarko as well as from the sale of residue, condensate and NGLs to Anadarko. In addition, the Partnership purchases natural gas from an affiliate of Anadarko pursuant to gas purchase agreements. Operating 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. See Note 2 for further information related to contributions of assets to the Partnership by Anadarko.
	Cash management. Anadarko operates a cash management system whereby excess cash from most of its subsidiaries’ separate bank accounts is generally swept to centralized accounts. Prior to the 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. Anadarko charged or credited the Partnership interest at a variable rate on outstanding affiliate balances for the periods these balances remained outstanding. 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, and affiliate-based interest expense on current intercompany balances is not charged. Chipeta cash settles its transactions directly with third parties and Anadarko, as well as with the other subsidiaries of the Partnership.
	Note receivable from and amounts payable to Anadarko. Concurrently with the closing of the Partnership’s May 2008 IPO, 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 approximately $301.5 million and $334.8 million at September 30, 2013, and December 31, 2012, 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.
	In 2008, the Partnership entered into a five-year $175.0 million term loan agreement with Anadarko, which was repaid in full in June 2012 using the proceeds from the issuance of 4.000% Senior Notes due 2022. See Note 8.
	Commodity price swap agreements. The Partnership has commodity price swap agreements with Anadarko to mitigate exposure to commodity price volatility that would otherwise be present as a result of the purchase and sale of natural gas, condensate or NGLs. Notional volumes for each of the commodity price swap agreements are not specifically defined; instead, the commodity price swap agreements apply to the actual volume of natural gas, condensate and NGLs purchased and sold at the Granger, Hilight, Hugoton, Newcastle, MGR and Wattenberg assets, with various expiration dates through December 2016. The commodity price swap agreements do not satisfy the definition of a derivative financial instrument and, therefore, are not required to be measured at fair value. The Partnership has not entered into any new commodity price swap agreements since the fourth quarter of 2011.
	5. TRANSACTIONS WITH AFFILIATES (CONTINUED)
	Below is a summary of the fixed price ranges on the Partnership’s outstanding commodity price swap agreements as of September 30, 2013:
	per barrel except natural gas		2013							2014							2015				2016
	Ethane		$	18.32		−	30.1			$	18.36		−	30.53			$	18.41	−	23.41	$	23.11
	Propane		$	45.9		−	55.84			$	46.47		−	53.78			$	47.08	−	52.99	$	52.9
	Isobutane		$	60.44		−	77.66			$	61.24		−	75.13			$	62.09	−	74.02	$	73.89
	Normal butane		$	53.2		−	68.24			$	53.89		−	66.01			$	54.62	−	65.04	$	64.93
	Natural gasoline		$	70.89		−	92.23			$	71.85		−	83.04			$	72.88	−	81.82	$	81.68
	Condensate		$	74.04		−	85.84			$	75.22		−	83.04			$	76.47	−	81.82	$	81.68
	Natural gas (per MMbtu)		$	3.75		−	6.09			$	4.45		−	6.2			$	4.66	−	5.96	$	4.87
	The following table summarizes realized gains and losses on commodity price swap agreements:
			Three Months Ended								Nine Months Ended
			September 30,								September 30,
	thousands		2013				2012				2013				2012
	Gains (losses) on commodity price swap agreements related to sales: (1)
	Natural gas sales		$	6,923			$	9,132			$	14,707			$	30,728
	Natural gas liquids sales		27,541				25,986				83,049				46,020
	Total		34,464				35,118				97,756				76,748
	Losses on commodity price swap agreements related to purchases (2)		(23,902		)		(25,803		)		(66,613		)		(70,342		)
	Net gains (losses) on commodity price swap agreements		$	10,562			$	9,315			$	31,143			$	6,406
	(1)	Reported in affiliate natural gas, NGLs and condensate sales in the consolidated statements of income in the period in which the related sale is recorded.
	(2)	Reported in cost of product in the consolidated statements of income in the period in which the related purchase is recorded.
	Gas gathering and processing agreements. The Partnership has significant gas gathering and processing arrangements with affiliates of Anadarko on a majority of its systems. Approximately 56% and 63% of the Partnership’s gathering, transportation and treating throughput (excluding equity investment throughput and volumes measured in barrels) for the three months ended September 30, 2013 and 2012, respectively, and 58% and 64% for the nine months ended September 30, 2013 and 2012, respectively, was attributable to natural gas production owned or controlled by Anadarko. Approximately 58% and 61% of the Partnership’s processing throughput (excluding equity investment throughput and volumes measured in barrels) for the three months ended September 30, 2013 and 2012, respectively, and 56% and 59% for the nine months ended September 30, 2013 and 2012, respectively, was attributable to natural gas production owned or controlled by Anadarko.
	5. TRANSACTIONS WITH AFFILIATES (CONTINUED)
	Equipment purchases and sales. The following table summarizes the Partnership’s purchases from and sales to Anadarko of pipe and equipment:
			Nine Months Ended September 30,
			2013				2012				2013				2012
	thousands		Purchases								Sales
	Consideration (1)		$	6,167			$	18,946			$	82			$	760
	Net carrying value		2,039				6,765				34				392
	Partners’ capital adjustment		$	4,128			$	12,181			$	48			$	368
	-1	Includes a payable of $1.8 million for pipe and equipment purchased in September 2013.
	Long-term incentive plan. The general partner awards phantom units under the Western Gas Partners, LP 2008 Long-Term Incentive Plan (“LTIP”), primarily to its independent directors and its Chief Executive Officer. 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 $0.1 million and $0.4 million for the three and nine months ended September 30, 2013, respectively, and $0.1 million and $0.3 million for the three and nine months ended September 30, 2012, respectively.
	Equity incentive plan and Anadarko incentive plans. The Partnership’s general and administrative expenses include equity-based compensation costs allocated by Anadarko to the Partnership for grants made pursuant to (i) the Western Gas Holdings, LLC Equity Incentive Plan, as amended and restated (the “Incentive Plan”) and (ii) the Anadarko Petroleum Corporation 2008 and 2012 Omnibus Incentive Compensation Plans (“Anadarko Incentive Plans”).
	The Partnership’s general and administrative expenses included $0.8 million and $2.2 million for the three and nine months ended September 30, 2013, respectively, and $0.8 million and $2.4 million for the three and nine months ended September 30, 2012, respectively, of equity-based compensation expense for awards granted to the executive officers of the general partner and other employees under the Anadarko Incentive Plans, which was allocated to the Partnership by Anadarko.
	For the three and nine months ended September 30, 2012, the Partnership’s general and administrative expenses included $8.6 million and $13.9 million, respectively, of compensation expense for grants of Unit Value Rights, Unit Appreciation Rights (“UARs”) and Distribution Equivalent Rights under the Incentive Plan to certain executive officers of the general partner as a component of their compensation, which was allocated to the Partnership by Anadarko. Awards outstanding under the Incentive Plan at September 30, 2012, were valued at $1,053 per UAR. WGP’s IPO in December 2012 resulted in the vesting of all then unvested Incentive Plan awards and the effective termination of the Incentive Plan.
	5. TRANSACTIONS WITH AFFILIATES (CONTINUED)
	Summary of affiliate transactions. The following table summarizes affiliate transactions, which include revenue from affiliates, reimbursement of operating expenses and purchases of natural gas:
			Three Months Ended								Nine Months Ended
			September 30,								September 30,
	thousands		2013				2012				2013				2012
	Revenues (1)		$	217,624			$	180,605			$	603,214			$	519,460
	Cost of product (1)		33,753				42,839				97,801				115,603
	Operation and maintenance (2)		13,469				12,638				41,021				38,040
	General and administrative (3)		5,867				14,227				17,325				30,811
	Operating expenses		53,089				69,704				156,147				184,454
	Interest income, net (4)		4,225				4,225				12,675				12,675
	Interest expense (5)		—				81				—				2,684
	Distributions to unitholders (6)		44,378				25,852				121,493				69,615
	Contributions from noncontrolling interest owners (7)		—				2,148				—				12,588
	Distributions to noncontrolling interest owners (7)		—				1,464				—				6,528
	(1)	Represents amounts recognized under gathering, treating or processing agreements, and purchase and sale agreements.
	(2)	Represents expenses incurred on and subsequent to the date of the acquisition of the 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 by the Partnership.
	(3)	Represents general and administrative expense incurred on and subsequent to the date of the Partnership’s acquisition of the Partnership assets, as well as a management services fee for reimbursement of 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 Equity incentive plan and Anadarko incentive plans within this Note 5).
	(4)	Represents interest income recognized on the note receivable from Anadarko.
	(5)	For the three and nine months ended September 30, 2012, includes interest expense recognized on the note payable to Anadarko (see Note 8) and interest imputed on the reimbursement payable to Anadarko for certain expenditures Anadarko incurred in 2011 related to the construction of the Brasada and Lancaster plants. The Partnership repaid the note payable to Anadarko in June 2012, and repaid the reimbursement payable to Anadarko related to the construction of the Brasada and Lancaster plants in the fourth quarter of 2012. See Note receivable from and amounts payable to Anadarko within this Note 5.
	(6)	Represents distributions paid under the partnership agreement.
(7)	As described in Note 2, the Partnership acquired Anadarko’s then remaining 24% membership interest in Chipeta on August 1, 2012, and accounted for the acquisition on a prospective basis. As such, contributions from noncontrolling interest owners and distributions to noncontrolling interest owners subsequent to the acquisition date no longer reflect contributions from or distributions to Anadarko.
Concentration of credit risk. Anadarko was the only customer from whom revenues exceeded 10% of the Partnership’s consolidated revenues for all periods presented on the consolidated statements of income.

Property_Plant_and_Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2013
Property, Plant and Equipment [Abstract]	'
Property, Plant and Equipment	'
	6. PROPERTY, PLANT AND EQUIPMENT
	A summary of the historical cost of the Partnership’s property, plant and equipment is as follows:
	thousands	Estimated Useful Life	30-Sep-13		December 31, 2012
	Land	n/a	$	2,584	$	501
	Gathering systems	3 to 47 years	3,610,879		2,911,572
	Pipelines and equipment	15 to 45 years	119,278		91,126
	Assets under construction	n/a	318,107		422,002
	Other	3 to 25 years	10,541		7,191
	Total property, plant and equipment		4,061,389		3,432,392
	Accumulated depreciation		817,489		714,436
	Net property, plant and equipment		$	3,243,900	$	2,717,956
	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. See Note 7.
	During the second quarter of 2013, the Partnership recognized a $1.0 million impairment primarily related to the cancellation of various capital projects by the third-party operator of the Non-Operated Marcellus Interest.

Components_of_Working_Capital

Components of Working Capital	9 Months Ended
	Sep. 30, 2013
Components Of Working Capital [Abstract]	'
Components of Working Capital	'
	7. COMPONENTS OF WORKING CAPITAL
	A summary of other current assets is as follows:
	thousands	September 30,		December 31,
		2013		2012
	Natural gas liquids inventory	$	2,438	$	1,678
	Natural gas imbalance receivables	2,729		1,663
	Prepaid insurance	1,934		1,897
	Other	1,662		1,760
	Total other current assets	$	8,763	$	6,998
	A summary of accrued liabilities is as follows:
	thousands	September 30,		December 31,
		2013		2012
	Accrued capital expenditures	$	100,876	$	112,311
	Accrued plant purchases	20,738		16,350
	Accrued interest expense	16,620		15,868
	Short-term asset retirement obligations	1,187		1,711
	Short-term remediation and reclamation obligations	609		799
	Other	136		612
	Total accrued liabilities	$	140,166	$	147,651

Debt_and_Interest_Expense

Debt and Interest Expense	9 Months Ended
	Sep. 30, 2013
Debt Instruments [Abstract]	'
Debt and Interest Expense	'
	8. DEBT AND INTEREST EXPENSE
	The following table presents the Partnership’s outstanding debt as of September 30, 2013, and December 31, 2012:
			30-Sep-13									31-Dec-12
	thousands		Principal			Carrying			Fair			Principal			Carrying		Fair
						Value			Value (1)						Value		Value (1)
	4.000% Senior Notes due 2022		$	670,000		$	673,363		$	651,580		$	670,000		$	673,617	$	669,928
	5.375% Senior Notes due 2021		500,000			495,042			531,210			500,000			494,661		499,946
	Revolving credit facility		100,000			100,000			100,000			—			—		—
	2.600% Senior Notes due 2018		250,000			249,705			249,134			—			—		—
	Total debt outstanding		$	1,520,000		$	1,518,110		$	1,531,924		$	1,170,000		$	1,168,278	$	1,169,874
	(1)	Fair value is measured using Level 2 inputs.
	Debt activity. The following table presents the debt activity of the Partnership for the nine months ended September 30, 2013:
	thousands		Carrying Value
	Balance as of December 31, 2012		$	1,168,278
	Revolving credit facility borrowings		595,000
	Repayments of revolving credit facility		(495,000		)
	Issuance of 2.600% Senior Notes due 2018		250,000
	Other		(168		)
	Balance as of September 30, 2013		$	1,518,110
	Senior Notes. In August 2013, the Partnership completed the offering of $250.0 million aggregate principal amount of 2.600% Senior Notes due 2018 (the “2018 Notes”) at a price to the public of 99.879% of the face amount. Including the effects of the issuance and underwriting discounts, the effective interest rate of the 2018 Notes is 2.806%. Interest will be paid semi-annually on February 15 and August 15 of each year, commencing on February 15, 2014. The 2018 Notes will mature on August 15, 2018, unless redeemed, in whole or in part, prior to maturity. Proceeds (net of underwriting discount of $1.5 million, original issue discount and debt issuance costs) were used to repay amounts then outstanding under the Partnership’s $800.0 million senior unsecured revolving credit facility (“RCF”).
	In June 2012, the Partnership completed the offering of $520.0 million aggregate principal amount of 4.000% Senior Notes due 2022 at a price to the public of 99.194% of the face amount. In October 2012, the Partnership issued an additional $150.0 million in aggregate principal amount of 4.000% Senior Notes due 2022 at a price to the public of 105.178% of the face amount. The October 2012 notes and the June 2012 notes were issued under the same indenture and are considered a single class of securities, collectively referred to as the “2022 Notes.”
	In May 2011, the Partnership completed the offering of $500.0 million aggregate principal amount of 5.375% Senior Notes due 2021 (the “2021 Notes”) at a price to the public of 98.778% of the face amount.
	At September 30, 2013, the Partnership was in compliance with all covenants under the indentures governing the 2021 Notes, 2022 Notes and the 2018 Notes.
	8. DEBT AND INTEREST EXPENSE (CONTINUED)
	Interest rate agreements. In May 2012, the Partnership entered into U.S. Treasury Rate lock agreements to mitigate the risk of rising interest rates prior to the issuance of the 2022 Notes. The Partnership settled the rate lock agreements simultaneously with the June 2012 offering of the 2022 Notes, realizing a loss of $1.7 million, which is included in other income (expense), net in the consolidated statements of income.
	Note payable to Anadarko. In 2008, the Partnership entered into a five-year $175.0 million term loan agreement with Anadarko. The interest rate was fixed at 2.82% prior to June 2012 when the note payable to Anadarko was repaid in full with proceeds from the June 2012 offering of the 2022 Notes.
	Revolving credit facility. At September 30, 2013, and December 31, 2012, the interest rate on the RCF was 1.68% and 1.71%, respectively. The Partnership is required to pay a quarterly facility fee currently ranging from 0.20% to 0.35% of the commitment amount (whether used or unused), based upon the Partnership’s senior unsecured debt rating. The facility fee rate was 0.25% at September 30, 2013, and December 31, 2012.
	At September 30, 2013, the Partnership had $100.0 million of outstanding borrowings, $12.8 million in outstanding letters of credit issued and $687.2 million available for borrowing under the RCF. At September 30, 2013, the Partnership was in compliance with all covenants under the RCF.
	The 2021 Notes, the 2022 Notes, the 2018 Notes and obligations under the RCF are recourse to the Partnership’s general partner, and as of December 31, 2012, the Partnership’s general partner was indemnified by a wholly owned subsidiary of Anadarko, Western Gas Resources, Inc. (“WGRI”), against any claims made against the general partner under the 2022 Notes, the 2021 Notes and/or the RCF.
	In connection with the acquisition of the Non-Operated Marcellus Interest in March 2013, the general partner and another wholly owned subsidiary of Anadarko entered into an indemnification agreement (the “2013 Indemnification Agreement”) whereby such subsidiary agreed to indemnify the Partnership’s general partner for any recourse liability it may have for RCF borrowings, or other debt financing, attributable to the acquisitions of the Non-Operated Marcellus Interest or the Anadarko-Operated Marcellus Interest. As of September 30, 2013, the 2013 Indemnification Agreement applied to the $250.0 million of 2018 Notes. The Partnership’s general partner and WGRI also amended and restated the existing indemnity agreement between them to reduce the amount for which WGRI would indemnify the Partnership’s general partner by an amount equal to any amounts payable to the Partnership’s general partner under the 2013 Indemnification Agreement.
	8. DEBT AND INTEREST EXPENSE (CONTINUED)
	Interest expense. The following table summarizes the amounts included in interest expense:
			Three Months Ended						Nine Months Ended
			September 30,						September 30,
	thousands		2013			2012			2013			2012
	Third parties
	Interest expense on long-term debt		$	14,994		$	11,919		$	43,783		$	28,036
	Amortization of debt issuance costs and commitment fees (1)		1,135			1,201			3,252			3,225
	Capitalized interest		(3,111		)	(2,224		)	(9,552		)	(3,827		)
	Total interest expense – third parties		13,018			10,896			37,483			27,434
	Affiliates
	Interest expense on note payable to Anadarko (2)		—			—			—			2,440
	Interest expense on affiliate balances (3)		—			81			—			244
	Total interest expense – affiliates		—			81			—			2,684
	Interest expense		$	13,018		$	10,977		$	37,483		$	30,118
	(1)	For the three and nine months ended September 30, 2013, includes $0.3 million and $0.8 million, respectively, of amortization of (i) the original issue discount for the June 2012 offering of the 2022 Notes, partially offset by the original issue premium for the October 2012 offering of the 2022 Notes, (ii) original issue discount for the 2021 Notes and 2018 Notes and (iii) underwriters’ fees. For the three and nine months ended September 30, 2012, includes $0.4 million and $0.8 million, respectively, of amortization of the original issue discount and underwriters’ fees for the 2022 Notes issued in June 2012 and the 2021 Notes.
	(2)	In June 2012, the note payable to Anadarko was repaid in full. See Note payable to Anadarko within this Note 8.
	(3)	Imputed interest expense on the reimbursement payable to Anadarko for certain expenditures Anadarko incurred in 2011 related to the construction of the Brasada and Lancaster plants. In the fourth quarter of 2012, the Partnership repaid the reimbursement payable to Anadarko associated with the construction of the Brasada and Lancaster plants.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	9. COMMITMENTS AND CONTINGENCIES
	Litigation and legal proceedings. In March 2011, DCP Midstream LP (“DCP”) filed a lawsuit against Anadarko and others, including a Partnership subsidiary, Kerr-McGee Gathering LLC, in Weld County District Court (the “Court”) in Colorado, alleging that Anadarko and its affiliates diverted gas from DCP’s gathering and processing facilities in breach of certain dedication agreements. In addition to various claims against Anadarko, DCP is claiming unjust enrichment and other damages against Kerr-McGee Gathering LLC, the entity which holds the Wattenberg assets. Anadarko countersued DCP asserting that DCP has not properly allocated values and charges to Anadarko for the gas that DCP gathers and/or processes, and seeks a judgment that DCP has no valid gathering or processing rights to much of the gas production it is claiming, in addition to other claims.
	In July 2011, the Court denied the defendants’ motion to dismiss without ruling on the merits and the case is in the discovery phase. Trial is set for April 2014. Management does not believe the outcome of this proceeding will have a material effect on the Partnership’s financial condition, results of operations or cash flows. The Partnership intends to vigorously defend this litigation. Furthermore, without regard to the merit of DCP’s claims, management believes that the Partnership has adequate contractual indemnities covering the claims against it in this lawsuit.
	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 a final disposition could have a material adverse effect on the Partnership’s financial condition, results of operations or cash flows.
	9. 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. As of September 30, 2013, the Partnership had unconditional payment obligations for services to be rendered or products to be delivered in connection with its capital projects of approximately $61.3 million, the majority of which is expected to be paid in the next twelve months. These commitments relate primarily to the continued construction of the Lancaster plant and an expansion project at the Fort Lupton compressor station in the Wattenberg system. In addition, as of September 30, 2013, and in conjunction with the Mont Belvieu JV acquisition, the Partnership is committed to fund 25%, or approximately $13.6 million, of the total remaining estimated net project cost to complete the construction of the fractionation facilities over the next six months (see Note 2).
	Lease commitments. Anadarko, on behalf of the Partnership, has entered into lease agreements for corporate offices, shared field offices and a warehouse supporting the Partnership’s operations. The leases for the corporate offices and shared field offices extend through 2017 and 2018, respectively, and the lease for the warehouse extends through February 2014 and includes an early termination clause.
	Rent expense associated with the office, warehouse and equipment leases was $0.6 million and $2.0 million for the three and nine months ended September 30, 2013, respectively, and $0.8 million and $2.3 million for the three and nine months ended September 30, 2012, respectively.

Summary_of_Significant_Account

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Business combinations policy	'
	Presentation of Partnership assets. References to the “Partnership assets” refer collectively to the assets owned by the Partnership as of September 30, 2013. Because Anadarko controls the Partnership through its ownership and control of WGP, which owns the Partnership’s general partner, each of the Partnership’s acquisitions of 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 may be required to recast its financial statements to include the activities of such assets as of the date of common control. See Note 2.
	For those periods requiring recast, the consolidated financial statements for periods prior to the Partnership’s acquisition of Partnership assets from Anadarko, including the Non-Operated Marcellus Interest, 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 the assets during the periods reported. Net income attributable to the Partnership assets for periods prior to the Partnership’s acquisition of such assets is not allocated to the limited partners for purposes of calculating net income per common unit.
	Anadarko-Operated Marcellus Interest acquisition. The Anadarko-Operated Marcellus Interest acquisition has been accounted for under the acquisition method of accounting. The assets acquired and liabilities assumed in the Anadarko-Operated Marcellus Interest acquisition were recorded in the consolidated balance sheet at their estimated fair values as of the acquisition date. Results of operations attributable to the Anadarko-Operated Marcellus Interest were included in the Partnership’s consolidated statements of income beginning on the acquisition date in the first quarter of 2013.
Net income per common unit policy	'
	The Partnership’s net income for periods including and subsequent to the acquisition of the Partnership assets (as defined in Note 1) is allocated to the general partner and the limited partners consistent with actual cash distributions, including incentive distributions allocable to the general partner. 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 and the limited partners in accordance with their respective ownership percentages.
Fair value policy	'
	Note receivable from and amounts payable to Anadarko. Concurrently with the closing of the Partnership’s May 2008 IPO, 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 approximately $301.5 million and $334.8 million at September 30, 2013, and December 31, 2012, 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.
Capitalized interest policy	'
	Mont Belvieu JV acquisition. The acquisition purchase price represented the Partnership’s 25% share of construction costs incurred by the joint venture partner and 25% of the capitalized interest charged to the financial statements of the Mont Belvieu JV up to the date of acquisition. The allocated capitalized interest is reflected as a component of the equity investment balance recorded upon acquisition. Based on the total estimated net project cost, the construction of the fractionation facilities owned by the Mont Belvieu JV is considered a significant project and satisfies criteria for capitalization of interest. Capitalization of interest subsequent to the acquisition is treated as a basis difference between the cost of the investment and the underlying equity in the net assets of the Mont Belvieu JV. The Partnership will begin to amortize the capitalized interest recognized subsequent to the acquisition upon completion of the facilities, and will reflect the amortization as an adjustment to equity earnings from the Mont Belvieu JV.

Description_of_Business_and_Ba1

Description of Business and Basis of Presentation (tables)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Assets Table	'
	As of September 30, 2013, the Partnership’s assets, exclusive of interests in Fort Union, White Cliffs, Rendezvous and the Mont Belvieu JV accounted for under the equity method, consisted of the following:
		Owned and	Operated	Non-Operated
		Operated	Interests	Interests
	Natural gas gathering systems	13	1	5
	Natural gas treating facilities	8	—	—
	Natural gas processing facilities	8	3	—
	NGL pipelines	3	—	—
	Natural gas pipelines	3	—	—

Acquisitions_tables

Acquisitions (tables)	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
Acquisitions Table	'
	The following table presents the acquisitions completed by the Partnership during 2012 and 2013, and identifies the funding sources for such acquisitions:
	thousands except unit and		Acquisition		Percentage			Borrowings			Cash		Common	GP Units
	percent amounts		Date		Acquired						On Hand		Units Issued	Issued
	MGR (1)		1/13/12		100	%		$	299,000		$	159,587	632,783	12,914
	Chipeta (2)		8/1/12		24	%		—			128,250		151,235	3,086
	Non-Operated Marcellus Interest (3)		3/1/13		33.75	%		250,000			215,500		449,129	—
	Anadarko-Operated Marcellus Interest (4)		3/8/13		33.75	%		133,500			—		—	—
	Mont Belvieu JV (5)		6/5/13		25	%		—			78,129		—	—
	OTTCO (6)		9/3/13		100	%		27,500			—		—	—
	(1)	The assets acquired from Anadarko consist of (i) the Red Desert complex, which is located in the greater Green River Basin in southwestern Wyoming, and includes the Patrick Draw processing plant, the Red Desert processing plant, gathering lines, and related facilities, (ii) a 22% interest in Rendezvous, which owns a gathering system serving the Jonah and Pinedale Anticline fields in southwestern Wyoming, and (iii) certain additional midstream assets and equipment. These assets are collectively referred to as the “MGR assets” and the acquisition as the “MGR acquisition.”
	(2)	The Partnership acquired Anadarko’s then remaining 24% membership interest in Chipeta (as described in Note 1). The Partnership received distributions related to the additional interest beginning July 1, 2012. This transaction brought the Partnership’s total membership interest in Chipeta to 75%. The remaining 25% membership interest in Chipeta held by a third-party member is reflected as noncontrolling interests in the consolidated financial statements for all periods presented.
	(3)	The Partnership acquired Anadarko’s 33.75% interest (non-operated) in the Liberty and Rome gas gathering systems, serving production from the Marcellus shale in north-central Pennsylvania. The interest acquired is referred to as the “Non-Operated Marcellus Interest” and the acquisition as the “Non-Operated Marcellus Interest acquisition.” In connection with the issuance of the common units, the Partnership’s general partner purchased 9,166 general partner units for consideration of $0.5 million in order to maintain its 2.0% general partner interest in the Partnership. See Non-Operated Marcellus Interest acquisition below for further information.
	(4)	The interest acquired from a third party consisted of a 33.75% interest in each of the Larry’s Creek, Seely and Warrensville gas gathering systems, which are operated by Anadarko and serve production from the Marcellus shale in north-central Pennsylvania. The interest acquired is referred to as the “Anadarko-Operated Marcellus Interest” and the acquisition as the “Anadarko-Operated Marcellus Interest acquisition.” See Anadarko-Operated Marcellus Interest acquisition below for further information, including the final allocation of the purchase price as of September 30, 2013.
	(5)	The acquisition from a third party consisted of a 25% interest in Enterprise EF78 LLC, an entity formed to design, construct, and own two fractionators located in Mont Belvieu, Texas. The interest acquired is accounted for under the equity method of accounting and is referred to as the “Mont Belvieu JV” and the acquisition as the “Mont Belvieu JV acquisition.” See Mont Belvieu JV acquisition below for further information.
	(6)	The Partnership acquired Overland Trail Transmission, LLC (“OTTCO”), a Delaware limited liability company, from a third party. OTTCO owns and operates an intrastate pipeline which connects the Partnership’s Red Desert and Granger complexes in southwestern Wyoming. The assets acquired are referred to as the “OTTCO pipeline” and the acquisition as the “OTTCO acquisition.”
Impact to Historical Consolidated Statement of Income Table	'
	The following table presents the revenue and net income impact of the Non-Operated Marcellus Interest on revenue and net income as presented in the Partnership’s historical consolidated statements of income:
			Three Months Ended September 30, 2012
	thousands		Partnership Historical				Non-Operated Marcellus Interest			Combined
	Revenues		$	219,020			$	15,714		$	234,734
	Net income		42,940				7,062			50,002
			Nine Months Ended September 30, 2012
	thousands		Partnership Historical				Non-Operated Marcellus Interest			Combined
	Revenues		$	636,603			$	43,117		$	679,720
	Net income		135,913				19,582			155,495
Purchase Price Allocation Table	'
	The following is the final allocation of the purchase price as of September 30, 2013, including $1.1 million of post-closing purchase price adjustments, to the assets acquired and liabilities assumed in the Anadarko-Operated Marcellus Interest acquisition as of the acquisition date:
	thousands
	Property, plant and equipment		$	134,819
	Asset retirement obligations		(174		)
	Total purchase price		$	134,645
Pro Forma Condensed Financial Information Table	'
	The following table presents the pro forma condensed financial information of the Partnership as if the Anadarko-Operated Marcellus Interest acquisition had occurred on January 1, 2012:
			Nine Months Ended
			September 30,
	thousands except per-unit amounts		2013				2012
	Revenues		$	764,128			$	682,820
	Net income		196,872				153,423
	Net income attributable to Western Gas Partners, LP		189,405				141,467
	Net income per common unit - basic and diluted		$	1.26			$	1.12

Partnership_Distributions_tabl

Partnership Distributions (tables)	9 Months Ended
	Sep. 30, 2013
Distributions Made to Members or Limited Partners [Abstract]	'
Cash Distributions Table	'
	The board of directors of the general partner declared the following cash distributions to the Partnership’s unitholders for the periods presented:
	thousands except per-unit amounts		Total Quarterly		Total Quarterly		Date of
	Quarters Ended		Distribution		Cash Distribution		Distribution
			per Unit
	2012
	31-Mar		$	0.46	$	46,053	May-12
	30-Jun		$	0.48	$	52,425	August 2012
	30-Sep		$	0.5	$	56,346	Nov-12
	2013
	31-Mar		$	0.54	$	70,143	May 2013
	30-Jun		$	0.56	$	79,315	Aug-13
	September 30 (1)		$	0.58	$	83,986	Nov-13
	(1)	On October 16, 2013, the board of directors of the Partnership’s general partner declared a cash distribution to the Partnership’s unitholders of $0.58 per unit, or $84.0 million in aggregate, including incentive distributions. The cash distribution is payable on November 12, 2013, to unitholders of record at the close of business on October 31, 2013.

Equity_and_Partners_Capital_ta

Equity and Partners' Capital (tables)	9 Months Ended
	Sep. 30, 2013
Partners' Capital Notes [Abstract]	'
Equity Offerings Table	'
	The Partnership completed the following public offerings of its common units during 2012 and 2013:
	thousands except unit	Common		GP Units		Price Per		Underwriting		Net
	and per-unit amounts	Units Issued (1)		Issued (2)		Unit		Discount and		Proceeds
								Other Offering
								Expenses
	June 2012 equity offering	5,000,000		102,041		$	43.88	$	7,468	$	216,409
	May 2013 equity offering	7,015,000		143,163		61.18		13,203		424,733
	(1)	Includes the issuance of 915,000 common units pursuant to the full exercise of the underwriters’ over-allotment option granted in connection with the May 2013 equity offering.
	(2)	Represents general partner units issued to the general partner in exchange for the general partner’s proportionate capital contribution to maintain its 2.0% general partner interest.
Limited Partner and General Partner Units Table	'
	The following table summarizes common and general partner units issued during the nine months ended September 30, 2013:
			Common		General		Total
			Units		Partner Units
	Balance at December 31, 2012		104,660,553		2,135,930		106,796,483
	Non-Operated Marcellus Interest acquisition		449,129		9,166		458,295
	Long-Term Incentive Plan awards		6,879		140		7,019
	May 2013 equity offering		7,015,000		143,163		7,158,163
	Continuous Offering Program		43,350		174		43,524
	Balance at September 30, 2013		112,174,911		2,288,573		114,463,484

Transactions_With_Affiliates_t

Transactions With Affiliates (tables)	9 Months Ended
	Sep. 30, 2013
Related Party Fees and Other Arrangements, Limited Liability Company (LLC) or Limited Partnership (LP) [Abstract]	'
Commodity Price Swap Agreements Table	'
	Below is a summary of the fixed price ranges on the Partnership’s outstanding commodity price swap agreements as of September 30, 2013:
	per barrel except natural gas		2013							2014							2015				2016
	Ethane		$	18.32		−	30.1			$	18.36		−	30.53			$	18.41	−	23.41	$	23.11
	Propane		$	45.9		−	55.84			$	46.47		−	53.78			$	47.08	−	52.99	$	52.9
	Isobutane		$	60.44		−	77.66			$	61.24		−	75.13			$	62.09	−	74.02	$	73.89
	Normal butane		$	53.2		−	68.24			$	53.89		−	66.01			$	54.62	−	65.04	$	64.93
	Natural gasoline		$	70.89		−	92.23			$	71.85		−	83.04			$	72.88	−	81.82	$	81.68
	Condensate		$	74.04		−	85.84			$	75.22		−	83.04			$	76.47	−	81.82	$	81.68
	Natural gas (per MMbtu)		$	3.75		−	6.09			$	4.45		−	6.2			$	4.66	−	5.96	$	4.87
Gains (Losses) on Commodity Price Swap Agreements Table	'
	The following table summarizes realized gains and losses on commodity price swap agreements:
			Three Months Ended								Nine Months Ended
			September 30,								September 30,
	thousands		2013				2012				2013				2012
	Gains (losses) on commodity price swap agreements related to sales: (1)
	Natural gas sales		$	6,923			$	9,132			$	14,707			$	30,728
	Natural gas liquids sales		27,541				25,986				83,049				46,020
	Total		34,464				35,118				97,756				76,748
	Losses on commodity price swap agreements related to purchases (2)		(23,902		)		(25,803		)		(66,613		)		(70,342		)
	Net gains (losses) on commodity price swap agreements		$	10,562			$	9,315			$	31,143			$	6,406
	(1)	Reported in affiliate natural gas, NGLs and condensate sales in the consolidated statements of income in the period in which the related sale is recorded.
	(2)	Reported in cost of product in the consolidated statements of income in the period in which the related purchase is recorded.
Equipment Purchase and Sale	'
	The following table summarizes the Partnership’s purchases from and sales to Anadarko of pipe and equipment:
			Nine Months Ended September 30,
			2013				2012				2013				2012
	thousands		Purchases								Sales
	Consideration (1)		$	6,167			$	18,946			$	82			$	760
	Net carrying value		2,039				6,765				34				392
	Partners’ capital adjustment		$	4,128			$	12,181			$	48			$	368
	-1	Includes a payable of $1.8 million for pipe and equipment purchased in September 2013.
Summary of Affiliate Transactions Table	'
	The following table summarizes affiliate transactions, which include revenue from affiliates, reimbursement of operating expenses and purchases of natural gas:
			Three Months Ended								Nine Months Ended
			September 30,								September 30,
	thousands		2013				2012				2013				2012
	Revenues (1)		$	217,624			$	180,605			$	603,214			$	519,460
	Cost of product (1)		33,753				42,839				97,801				115,603
	Operation and maintenance (2)		13,469				12,638				41,021				38,040
	General and administrative (3)		5,867				14,227				17,325				30,811
	Operating expenses		53,089				69,704				156,147				184,454
	Interest income, net (4)		4,225				4,225				12,675				12,675
	Interest expense (5)		—				81				—				2,684
	Distributions to unitholders (6)		44,378				25,852				121,493				69,615
	Contributions from noncontrolling interest owners (7)		—				2,148				—				12,588
	Distributions to noncontrolling interest owners (7)		—				1,464				—				6,528
	(1)	Represents amounts recognized under gathering, treating or processing agreements, and purchase and sale agreements.
	(2)	Represents expenses incurred on and subsequent to the date of the acquisition of the 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 by the Partnership.
	(3)	Represents general and administrative expense incurred on and subsequent to the date of the Partnership’s acquisition of the Partnership assets, as well as a management services fee for reimbursement of 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 Equity incentive plan and Anadarko incentive plans within this Note 5).
	(4)	Represents interest income recognized on the note receivable from Anadarko.
	(5)	For the three and nine months ended September 30, 2012, includes interest expense recognized on the note payable to Anadarko (see Note 8) and interest imputed on the reimbursement payable to Anadarko for certain expenditures Anadarko incurred in 2011 related to the construction of the Brasada and Lancaster plants. The Partnership repaid the note payable to Anadarko in June 2012, and repaid the reimbursement payable to Anadarko related to the construction of the Brasada and Lancaster plants in the fourth quarter of 2012. See Note receivable from and amounts payable to Anadarko within this Note 5.
	(6)	Represents distributions paid under the partnership agreement.
	(7)	As described in Note 2, the Partnership acquired Anadarko’s then remaining 24% membership interest in Chipeta on August 1, 2012, and accounted for the acquisition on a prospective basis. As such, contributions from noncontrolling interest owners and distributions to noncontrolling interest owners subsequent to the acquisition date no longer reflect contributions from or distributions to Anadarko.

Property_Plant_and_Equipment_t

Property, Plant and Equipment (table)	9 Months Ended
	Sep. 30, 2013
Property, Plant and Equipment [Abstract]	'
Property, Plant and Equipment Table	'
	A summary of the historical cost of the Partnership’s property, plant and equipment is as follows:
	thousands	Estimated Useful Life	30-Sep-13		December 31, 2012
	Land	n/a	$	2,584	$	501
	Gathering systems	3 to 47 years	3,610,879		2,911,572
	Pipelines and equipment	15 to 45 years	119,278		91,126
	Assets under construction	n/a	318,107		422,002
	Other	3 to 25 years	10,541		7,191
	Total property, plant and equipment		4,061,389		3,432,392
	Accumulated depreciation		817,489		714,436
	Net property, plant and equipment		$	3,243,900	$	2,717,956

Components_of_Working_Capital_

Components of Working Capital (tables)	9 Months Ended
	Sep. 30, 2013
Components Of Working Capital [Abstract]	'
Other Current Assets Table	'
	A summary of other current assets is as follows:
	thousands	September 30,		December 31,
		2013		2012
	Natural gas liquids inventory	$	2,438	$	1,678
	Natural gas imbalance receivables	2,729		1,663
	Prepaid insurance	1,934		1,897
	Other	1,662		1,760
	Total other current assets	$	8,763	$	6,998
Accrued Liabilities Table	'
	A summary of accrued liabilities is as follows:
	thousands	September 30,		December 31,
		2013		2012
	Accrued capital expenditures	$	100,876	$	112,311
	Accrued plant purchases	20,738		16,350
	Accrued interest expense	16,620		15,868
	Short-term asset retirement obligations	1,187		1,711
	Short-term remediation and reclamation obligations	609		799
	Other	136		612
	Total accrued liabilities	$	140,166	$	147,651

Debt_and_Interest_Expense_tabl

Debt and Interest Expense (tables)	9 Months Ended
	Sep. 30, 2013
Debt Instruments [Abstract]	'
Debt Outstanding and Debt Activity Tables	'
	The following table presents the Partnership’s outstanding debt as of September 30, 2013, and December 31, 2012:
			30-Sep-13									31-Dec-12
	thousands		Principal			Carrying			Fair			Principal			Carrying		Fair
						Value			Value (1)						Value		Value (1)
	4.000% Senior Notes due 2022		$	670,000		$	673,363		$	651,580		$	670,000		$	673,617	$	669,928
	5.375% Senior Notes due 2021		500,000			495,042			531,210			500,000			494,661		499,946
	Revolving credit facility		100,000			100,000			100,000			—			—		—
	2.600% Senior Notes due 2018		250,000			249,705			249,134			—			—		—
	Total debt outstanding		$	1,520,000		$	1,518,110		$	1,531,924		$	1,170,000		$	1,168,278	$	1,169,874
	(1)	Fair value is measured using Level 2 inputs.
	Debt activity. The following table presents the debt activity of the Partnership for the nine months ended September 30, 2013:
	thousands		Carrying Value
	Balance as of December 31, 2012		$	1,168,278
	Revolving credit facility borrowings		595,000
	Repayments of revolving credit facility		(495,000		)
	Issuance of 2.600% Senior Notes due 2018		250,000
	Other		(168		)
	Balance as of September 30, 2013		$	1,518,110
Interest Expense Table	'
	The following table summarizes the amounts included in interest expense:
			Three Months Ended						Nine Months Ended
			September 30,						September 30,
	thousands		2013			2012			2013			2012
	Third parties
	Interest expense on long-term debt		$	14,994		$	11,919		$	43,783		$	28,036
	Amortization of debt issuance costs and commitment fees (1)		1,135			1,201			3,252			3,225
	Capitalized interest		(3,111		)	(2,224		)	(9,552		)	(3,827		)
	Total interest expense – third parties		13,018			10,896			37,483			27,434
	Affiliates
	Interest expense on note payable to Anadarko (2)		—			—			—			2,440
	Interest expense on affiliate balances (3)		—			81			—			244
	Total interest expense – affiliates		—			81			—			2,684
	Interest expense		$	13,018		$	10,977		$	37,483		$	30,118
	(1)	For the three and nine months ended September 30, 2013, includes $0.3 million and $0.8 million, respectively, of amortization of (i) the original issue discount for the June 2012 offering of the 2022 Notes, partially offset by the original issue premium for the October 2012 offering of the 2022 Notes, (ii) original issue discount for the 2021 Notes and 2018 Notes and (iii) underwriters’ fees. For the three and nine months ended September 30, 2012, includes $0.4 million and $0.8 million, respectively, of amortization of the original issue discount and underwriters’ fees for the 2022 Notes issued in June 2012 and the 2021 Notes.
	(2)	In June 2012, the note payable to Anadarko was repaid in full. See Note payable to Anadarko within this Note 8.
	(3)	Imputed interest expense on the reimbursement payable to Anadarko for certain expenditures Anadarko incurred in 2011 related to the construction of the Brasada and Lancaster plants. In the fourth quarter of 2012, the Partnership repaid the reimbursement payable to Anadarko associated with the construction of the Brasada and Lancaster plants.

Description_of_Business_and_Ba2

Description of Business and Basis of Presentation - Asset Table (details)	Sep. 30, 2013
Gathering System [Member] | Operated [Member]	'
Assets [Line Items]	'
Assets, number of units	13
Gathering System [Member] | Operated Interest [Member]	'
Assets [Line Items]	'
Assets, number of units	1
Gathering System [Member] | Non Operated Interest [Member]	'
Assets [Line Items]	'
Assets, number of units	5
Natural Gas Treating Facilities [Member] | Operated [Member]	'
Assets [Line Items]	'
Assets, number of units	8
Natural Gas Processing Plant [Member] | Operated [Member]	'
Assets [Line Items]	'
Assets, number of units	8
Natural Gas Processing Plant [Member] | Operated Interest [Member]	'
Assets [Line Items]	'
Assets, number of units	3
Natural Gas Liquids Pipeline [Member] | Operated [Member]	'
Assets [Line Items]	'
Assets, number of units	3
Natural Gas Pipelines [Member] | Operated [Member]	'
Assets [Line Items]	'
Assets, number of units	3

Description_of_Business_and_Ba3

Description of Business and Basis of Presentation - Additional Information (details) (USD $)

31-May-13

Jun. 30, 2012

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Jul. 31, 2009

Sep. 30, 2013

Aug. 31, 2012

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

In Millions, except Share data, unless otherwise specified

Statement Of Cash Flow [Member]

Fort Union [Member]

Rendezvous [Member]

Non-Operated Marcellus Interest [Member]

Anadarko-Operated Marcellus Interest [Member]

Newcastle [Member]

Chipeta Processing Limited Liability Company [Member]

Chipeta Processing Limited Liability Company [Member]

Chipeta Processing Limited Liability Company [Member]

Western Gas Equity Partners [Member]

Western Gas Equity Partners [Member]

Western Gas Equity Partners [Member]

Incentive Distribution Rights [Member]

Equity method investment ownership

'

'

'

14.81%

22.00%

'

'

'

'

'

'

'

'

'

Ownership interest

'

'

'

'

'

33.75%

33.75%

50.00%

51.00%

'

'

'

100.00%

'

Percentage ownership of general partner

'

'

'

'

'

'

'

'

'

'

'

'

2.00%

'

General partner's interest

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

Common units issued

'

'

'

'

'

'

'

'

'

'

'

19,758,150

'

'

Price per unit

$61.18

$43.88

'

'

'

'

'

'

'

'

'

$22

'

'

Proceeds From Issuance of Private Placement

'

'

'

'

'

'

'

'

'

'

'

$409.40

'

'

Correction of error

'

'

$35.70

'

'

'

'

'

'

'

'

'

'

'

Ownership interest by noncontrolling owners

'

'

'

'

'

'

'

'

'

25.00%

24.00%

'

'

'

Acquisitions_Acquisitions_Tabl

Acquisitions - Acquisitions Table (details) (USD $)

9 Months Ended

1 Months Ended

1 Months Ended

9 Months Ended

1 Months Ended

1 Months Ended

In Thousands, except Share data, unless otherwise specified

Sep. 30, 2013

Sep. 30, 2012

Dec. 31, 2012

Jan. 31, 2012

Jan. 31, 2012

Aug. 31, 2012

Sep. 30, 2013

Mar. 31, 2013

Mar. 31, 2013

Jun. 30, 2013

Jun. 30, 2013

Sep. 30, 2013

Jan. 31, 2012

Aug. 31, 2012

Mar. 31, 2013

Jan. 31, 2012

Aug. 31, 2012

Mountain Gas Resources [Member]

Mountain Gas Resources [Member]

Chipeta Processing Limited Liability Company [Member]

Chipeta Processing Limited Liability Company [Member]

Non-Operated Marcellus Interest [Member]

Anadarko-Operated Marcellus Interest [Member]

Mont Belvieu JV [Member]

Mont Belvieu JV [Member]

Overland Trail Transmission Limited Liability Company [Member]

Common Units [Member]

Common Units [Member]

Common Units [Member]

General Partner [Member]

General Partner [Member]

Rendezvous [Member]

Fractionator [Member]

Mountain Gas Resources [Member]

Chipeta Processing Limited Liability Company [Member]

Non-Operated Marcellus Interest [Member]

Mountain Gas Resources [Member]

Chipeta Processing Limited Liability Company [Member]

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage acquired

'

'

'

100.00%

[1]

'

24.00%

[2]

75.00%

33.75%

[3]

33.75%

[4]

'

'

100.00%

[5]

'

'

'

'

'

Equity method investment ownership

'

'

'

'

22.00%

'

'

'

'

25.00%

[6]

'

'

'

'

'

'

'

Borrowings

$842,566

$885,291

[7]

'

$299,000

[1]

'

'

'

$250,000

[3]

$133,500

[4]

'

'

$27,500

[5]

'

'

'

'

'

Cash on hand

'

'

'

159,587

[1]

'

128,250

[2]

'

215,500

[3]

'

78,129

[6]

'

'

'

'

'

'

'

Units issued

'

'

'

'

'

'

'

'

'

'

'

'

632,783

[1]

151,235

[2]

449,129

[3]

12,914

[1]

3,086

[2]

Table Text Block Supplement [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest by noncontrolling owners

'

'

'

'

'

'

25.00%

'

'

'

'

'

'

'

'

'

'

GP units issued

2,288,573

'

2,135,930

'

'

'

'

9,166

'

'

'

'

'

'

'

'

'

Proceeds from issuance of common and general partner units, net of offering expenses

$427,848

$216,462

[7]

'

'

'

'

'

$500

'

'

'

'

'

'

'

'

'

General partner's interest

'

'

'

'

'

'

'

2.00%

'

'

'

'

'

'

'

'

'

Assets, number of units

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

[1]

The assets acquired from Anadarko consist of (i) the Red Desert complex, which is located in the greater Green River Basin in southwestern Wyoming, and includes the Patrick Draw processing plant, the Red Desert processing plant, gathering lines, and related facilities, (ii) a 22% interest in Rendezvous, which owns a gathering system serving the Jonah and Pinedale Anticline fields in southwestern Wyoming, and (iii) certain additional midstream assets and equipment. These assets are collectively referred to as the “MGR assets” and the acquisition as the “MGR acquisition.”

[2]

The Partnership acquired Anadarko’s then remaining 24% membership interest in Chipeta (as described in Note 1). The Partnership received distributions related to the additional interest beginning July 1, 2012. This transaction brought the Partnership’s total membership interest in Chipeta to 75%. The remaining 25% membership interest in Chipeta held by a third-party member is reflected as noncontrolling interests in the consolidated financial statements for all periods presented.

[3]

The Partnership acquired Anadarko’s 33.75% interest (non-operated) in the Liberty and Rome gas gathering systems, serving production from the Marcellus shale in north-central Pennsylvania. The interest acquired is referred to as the “Non-Operated Marcellus Interest” and the acquisition as the “Non-Operated Marcellus Interest acquisition.” In connection with the issuance of the common units, the Partnership’s general partner purchased 9,166 general partner units for consideration of $0.5 million in order to maintain its 2.0% general partner interest in the Partnership. See Non-Operated Marcellus Interest acquisition below for further information.

[4]

The interest acquired from a third party consisted of a 33.75% interest in each of the Larry’s Creek, Seely and Warrensville gas gathering systems, which are operated by Anadarko and serve production from the Marcellus shale in north-central Pennsylvania. The interest acquired is referred to as the “Anadarko-Operated Marcellus Interest” and the acquisition as the “Anadarko-Operated Marcellus Interest acquisition.” See Anadarko-Operated Marcellus Interest acquisition below for further information, including the final allocation of the purchase price as of September 30, 2013.

[5]

The Partnership acquired Overland Trail Transmission, LLC (“OTTCO”), a Delaware limited liability company, from a third party. OTTCO owns and operates an intrastate pipeline which connects the Partnership’s Red Desert and Granger complexes in southwestern Wyoming. The assets acquired are referred to as the “OTTCO pipeline” and the acquisition as the “OTTCO acquisition.”

[6]

The acquisition from a third party consisted of a 25% interest in Enterprise EF78 LLC, an entity formed to design, construct, and own two fractionators located in Mont Belvieu, Texas. The interest acquired is accounted for under the equity method of accounting and is referred to as the “Mont Belvieu JV” and the acquisition as the “Mont Belvieu JV acquisition.” See Mont Belvieu JV acquisition below for further information.

[7]

Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Acquisitions_Impact_to_Histori

Acquisitions - Impact to Historical Consolidated Statement of Income Table (details) (USD $)	3 Months Ended			9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012		Sep. 30, 2013	Sep. 30, 2012
Revenues	$278,001	$234,734	[1]	$762,874	$679,720	[1]
Net income	81,776	50,002	[1]	196,724	155,495	[1]
Partnership Historical [Member]	'	'		'	'
Revenues	'	219,020		'	636,603
Net income	'	42,940		'	135,913
Non-Operated Marcellus Interest [Member]	'	'		'	'
Revenues	'	15,714		'	43,117
Net income	'	$7,062		'	$19,582
[1]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Acquisitions_Purchase_Price_Al

Acquisitions - Purchase Price Allocation Table (details) (Anadarko-Operated Marcellus Interest [Member], USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Anadarko-Operated Marcellus Interest [Member]	'
Business Acquisition [Line Items]	'
Property, plant and equipment	$134,819
Asset retirement obligations	-174
Total purchase price	$134,645

Acquisitions_Pro_Forma_Condens

Acquisitions - Pro Forma Condensed Financial Information Table (details) (Anadarko-Operated Marcellus Interest [Member], USD $)	9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Anadarko-Operated Marcellus Interest [Member]	'	'
Business Acquisition [Line Items]	'	'
Revenues	$764,128	$682,820
Net income	196,872	153,423
Net income attributable to Western Gas Partners, LP	$189,405	$141,467
Net income per common unit - basic and diluted	$1.26	$1.12

Acquisitions_Additional_Inform

Acquisitions - Additional Information (details) (USD $)	3 Months Ended			9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012		Sep. 30, 2013	Sep. 30, 2012
Business Acquisition [Line Items]	'	'		'	'
Revenues	$278,001	$234,734	[1]	$762,874	$679,720	[1]
Operating expenses	187,813	173,422	[1]	538,523	491,907	[1]
Anadarko-Operated Marcellus Interest [Member]	'	'		'	'
Business Acquisition [Line Items]	'	'		'	'
Revenues	'	'		8,100	'
Operating expenses	'	'		500	'
Purchase price adjustment	134,645	'		134,645	'
Anadarko-Operated Marcellus Interest [Member] | Purchase Price Allocation Adjustments [Member]	'	'		'	'
Business Acquisition [Line Items]	'	'		'	'
Purchase price adjustment	$1,100	'		$1,100	'
[1]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Partnership_Distributions_Cash

Partnership Distributions - Cash Distributions Table (details) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013		Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012
Distributions Made to Members or Limited Partners [Abstract]	'		'	'	'	'	'
Total Quarterly Distribution per Unit	$0.58	[1]	$0.56	$0.54	$0.50	$0.48	$0.46
Total Quarterly Cash Distribution	$83,986	[1]	$79,315	$70,143	$56,346	$52,425	$46,053
[1]	On October 16, 2013, the board of directors of the Partnership’s general partner declared a cash distribution to the Partnership’s unitholders of $0.58 per unit, or $84.0 million in aggregate, including incentive distributions. The cash distribution is payable on November 12, 2013, to unitholders of record at the close of business on October 31, 2013.

Partnership_Distributions_Addi

Partnership Distributions - Additional Information (details)	9 Months Ended
	Sep. 30, 2013
Distributions Made to Members or Limited Partners [Abstract]	'
Partnership agreement day requirement of distribution of available cash	'45 days

Equity_and_Partners_Capital_Eq

Equity and Partners' Capital - Equity Offerings Table (details) (USD $)

1 Months Ended

9 Months Ended

In Thousands, except Share data, unless otherwise specified

31-May-13

Jun. 30, 2012

31-May-13

Jun. 30, 2012

31-May-13

31-May-13

Jun. 30, 2012

Sep. 30, 2013

Common Units [Member]

Common Units [Member]

Common Units [Member]

General Partner [Member]

General Partner [Member]

Western Gas Equity Partners [Member]

Option On Securities [Member]

Capital Unit [Line Items]

'

'

'

'

'

'

'

'

Common units issued

'

'

7,015,000

[1]

5,000,000

[1]

915,000

'

'

'

General partner units issued

'

'

'

'

'

143,163

[2]

102,041

[2]

'

Price per unit

$61.18

$43.88

'

'

'

'

'

'

Underwriting discount and other offering expenses

$13,203

$7,468

'

'

'

'

'

'

Net proceeds

$424,733

$216,409

'

'

'

'

'

'

Table Text Block Supplement [Abstract]

'

'

'

'

'

'

'

'

General partner's interest

'

'

'

'

'

'

'

2.00%

[1]

Includes the issuance of 915,000 common units pursuant to the full exercise of the underwriters’ over-allotment option granted in connection with the May 2013 equity offering.

[2]

Represents general partner units issued to the general partner in exchange for the general partner’s proportionate capital contribution to maintain its 2.0% general partner interest.

Equity_and_Partners_Capital_Li

Equity and Partners' Capital - Limited Partner and General Partner Units (details)	1 Months Ended				9 Months Ended
	31-May-13		Jun. 30, 2012		Sep. 30, 2013
Capital Unit [Line Items]	'		'		'
Balance	'		'		106,796,483
Long-Term Incentive Plan Awards	'		'		7,019
Balance	'		'		114,463,484
Non-Operated Marcellus Interest [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Acquisition	'		'		458,295
May 2013 Equity Offering [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Offering	'		'		7,158,163
Continuous Offering Program [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Offering	'		'		43,524
Common Units [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Balance	'		'		104,660,553
Long-Term Incentive Plan Awards	'		'		6,879
Common units issued	7,015,000	[1]	5,000,000	[1]	'
Balance	'		'		112,174,911
Common Units [Member] | Non-Operated Marcellus Interest [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Acquisition	'		'		449,129
Common Units [Member] | May 2013 Equity Offering [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Common units issued	'		'		7,015,000
Common Units [Member] | Continuous Offering Program [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Common units issued	'		'		43,350
General Partner [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Balance	'		'		2,135,930
Long-Term Incentive Plan Awards	'		'		140
Offering	143,163	[2]	102,041	[2]	'
Balance	'		'		2,288,573
General Partner [Member] | Non-Operated Marcellus Interest [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Acquisition	'		'		9,166
General Partner [Member] | May 2013 Equity Offering [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Offering	'		'		143,163
General Partner [Member] | Continuous Offering Program [Member]	'		'		'
Capital Unit [Line Items]	'		'		'
Offering	'		'		174
[1]	Includes the issuance of 915,000 common units pursuant to the full exercise of the underwriters’ over-allotment option granted in connection with the May 2013 equity offering.
[2]	Represents general partner units issued to the general partner in exchange for the general partner’s proportionate capital contribution to maintain its 2.0% general partner interest.

Equity_and_Partners_Capital_Ad

Equity and Partners' Capital - Additional Information (details) (USD $)

Sep. 30, 2013

31-May-13

Dec. 31, 2012

Jun. 30, 2012

Sep. 30, 2013

31-May-13

Jun. 30, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Aug. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Western Gas Equity Partners [Member]

Common Units [Member]

Common Units [Member]

Common Units [Member]

Common Units [Member]

Common Units [Member]

Common Units [Member]

Common Units [Member]

Incentive Distribution Rights [Member]

Continuous Offering Program [Member]

Continuous Offering Program [Member]

Continuous Offering Program [Member]

Continuous Offering Program [Member]

Western Gas Equity Partners [Member]

Anadarko Marcellus Midstream [Member]

Public [Member]

Western Gas Equity Partners [Member]

Initiated Trade [Member]

Common Units [Member]

Schedule Of Investments [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Maximum aggregate principal of common stock

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$125,000,000

'

'

Common units issued

'

'

'

'

'

7,015,000

[1]

5,000,000

[1]

'

'

'

'

'

'

'

'

218,750

43,350

Average price per unit

'

$61.18

'

$43.88

'

'

'

'

'

'

'

'

'

$58.22

'

'

'

Offering expenses

'

13,203,000

'

7,468,000

'

'

'

'

'

'

'

'

'

100,000

'

'

'

Gross proceeds

'

'

'

'

'

'

'

'

'

'

'

'

'

$2,700,000

'

$12,700,000

'

Units owned

'

'

'

'

'

'

'

112,174,911

104,660,553

49,296,205

449,129

62,429,577

'

'

'

'

'

Ownership interest

'

'

'

'

'

'

'

'

'

43.10%

0.40%

54.50%

'

'

'

'

'

General partner units owned

2,288,573

'

2,135,930

'

2,288,573

'

'

'

'

'

'

'

'

'

'

'

'

General partner's interest

'

'

'

'

2.00%

'

'

'

'

'

'

'

100.00%

'

'

'

'

[1]

Includes the issuance of 915,000 common units pursuant to the full exercise of the underwriters’ over-allotment option granted in connection with the May 2013 equity offering.

Transactions_With_Affiliates_C

Transactions With Affiliates - Commodity Price Per Unit Table (details)	Sep. 30, 2013
Ethane [Member] | Year 2016 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	23.11
Ethane [Member] | Minimum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	18.32
Ethane [Member] | Minimum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	18.36
Ethane [Member] | Minimum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	18.41
Ethane [Member] | Maximum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	30.1
Ethane [Member] | Maximum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	30.53
Ethane [Member] | Maximum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	23.41
Propane [Member] | Year 2016 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	52.9
Propane [Member] | Minimum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	45.9
Propane [Member] | Minimum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	46.47
Propane [Member] | Minimum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	47.08
Propane [Member] | Maximum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	55.84
Propane [Member] | Maximum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	53.78
Propane [Member] | Maximum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	52.99
Isobutane [Member] | Year 2016 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	73.89
Isobutane [Member] | Minimum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	60.44
Isobutane [Member] | Minimum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	61.24
Isobutane [Member] | Minimum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	62.09
Isobutane [Member] | Maximum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	77.66
Isobutane [Member] | Maximum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	75.13
Isobutane [Member] | Maximum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	74.02
Normal Butane [Member] | Year 2016 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	64.93
Normal Butane [Member] | Minimum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	53.2
Normal Butane [Member] | Minimum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	53.89
Normal Butane [Member] | Minimum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	54.62
Normal Butane [Member] | Maximum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	68.24
Normal Butane [Member] | Maximum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	66.01
Normal Butane [Member] | Maximum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	65.04
Natural Gasoline [Member] | Year 2016 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	81.68
Natural Gasoline [Member] | Minimum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	70.89
Natural Gasoline [Member] | Minimum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	71.85
Natural Gasoline [Member] | Minimum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	72.88
Natural Gasoline [Member] | Maximum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	92.23
Natural Gasoline [Member] | Maximum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	83.04
Natural Gasoline [Member] | Maximum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	81.82
Condensate [Member] | Year 2016 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	81.68
Condensate [Member] | Minimum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	74.04
Condensate [Member] | Minimum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	75.22
Condensate [Member] | Minimum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	76.47
Condensate [Member] | Maximum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	85.84
Condensate [Member] | Maximum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	83.04
Condensate [Member] | Maximum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	81.82
Natural Gas (per MMbtu) [Member] | Year 2016 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	4.87
Natural Gas (per MMbtu) [Member] | Minimum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	3.75
Natural Gas (per MMbtu) [Member] | Minimum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	4.45
Natural Gas (per MMbtu) [Member] | Minimum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	4.66
Natural Gas (per MMbtu) [Member] | Maximum [Member] | Year 2013 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	6.09
Natural Gas (per MMbtu) [Member] | Maximum [Member] | Year 2014 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	6.2
Natural Gas (per MMbtu) [Member] | Maximum [Member] | Year 2015 [Member]	'
Commodity Price Risk Swap [Line Items]	'
Commodity Swap Fixed Price	5.96

Transactions_With_Affiliates_G

Transactions With Affiliates - Gains Losses Commodity Price Swap Table (details) (USD $)	3 Months Ended				9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Gains (losses) on commodity price swap	'		'		'		'
Net gains (losses) on commodity price swap agreements	$10,562		$9,315		$31,143		$6,406
Sales [Member]	'		'		'		'
Gains (losses) on commodity price swap	'		'		'		'
Net gains (losses) on commodity price swap agreements	34,464	[1]	35,118	[1]	97,756	[1]	76,748	[1]
Cost Of Sales [Member]	'		'		'		'
Gains (losses) on commodity price swap	'		'		'		'
Net gains (losses) on commodity price swap agreements	-23,902	[2]	-25,803	[2]	-66,613	[2]	-70,342	[2]
Natural Gas Per Thousand Cubic Feet [Member] | Sales [Member]	'		'		'		'
Gains (losses) on commodity price swap	'		'		'		'
Net gains (losses) on commodity price swap agreements	6,923	[1]	9,132	[1]	14,707	[1]	30,728	[1]
Natural Gas Liquids [Member] | Sales [Member]	'		'		'		'
Gains (losses) on commodity price swap	'		'		'		'
Net gains (losses) on commodity price swap agreements	$27,541	[1]	$25,986	[1]	$83,049	[1]	$46,020	[1]
[1]	Reported in affiliate natural gas, NGLs and condensate sales in the consolidated statements of income in the period in which the related sale is recorded.
[2]	Reported in cost of product in the consolidated statements of income in the period in which the related purchase is recorded.

Transactions_With_Affiliates_E

Transactions With Affiliates - Equipment Purchase and Sale Table (details) (USD $)

9 Months Ended

9 Months Ended

In Thousands, unless otherwise specified

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Affiliated Entity [Member]

Affiliated Entity [Member]

Affiliated Entity [Member]

Affiliated Entity [Member]

Affiliated Entity [Member]

Affiliated Entity [Member]

Purchases [Member]

Purchases [Member]

Sales [Member]

Sales [Member]

Related Party Transaction [Line Items]

'

'

'

'

'

'

'

'

Consideration given for equipment

'

'

'

'

$6,167

[1]

$18,946

[1]

'

'

Consideration received for equipment

'

'

'

'

'

'

82

[1]

760

[1]

Net carrying value

'

'

'

'

2,039

6,765

34

392

Partners' capital adjustment

308

'

'

'

4,128

12,181

48

368

Table Text Block Supplement [Abstract]

'

'

'

'

'

'

'

'

Accounts payable

$19,131

[2]

$25,154

[2],[3]

$2,800

$2,500

$1,800

'

'

'

[1]

Includes a payable of $1.8 million for pipe and equipment purchased in September 2013.

[2]

Accounts and natural gas imbalance payables includes amounts payable to affiliates of $2.8 million and $2.5 million as of September 30, 2013, and December 31, 2012, respectively.

[3]

Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Transactions_With_Affiliates_S

Transactions With Affiliates - Summary Table (details) (USD $)

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

In Thousands, unless otherwise specified

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Aug. 31, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Chipeta Processing Limited Liability Company [Member]

Chipeta Processing Limited Liability Company [Member]

Affiliated Entity [Member]

Affiliated Entity [Member]

Affiliated Entity [Member]

Affiliated Entity [Member]

Related Party Transaction [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Revenues

$278,001

'

'

$234,734

[1]

'

'

$762,874

$679,720

[1]

'

'

$217,624

[2]

$180,605

[1],[2]

$603,214

[2]

$519,460

[1],[2]

Cost of product

93,516

[3]

'

'

89,107

[1],[3]

'

'

270,059

[3]

254,719

[1],[3]

'

'

33,753

[2]

42,839

[2]

97,801

[2]

115,603

[2]

Operation and maintenance

42,757

[3]

'

'

35,493

[1],[3]

'

'

121,165

[3]

103,304

[1],[3]

'

'

13,469

[4]

12,638

[4]

41,021

[4]

38,040

[4]

General and administrative

7,276

[3]

'

'

15,039

[1],[3]

'

'

22,228

[3]

35,623

[1],[3]

'

'

5,867

[5]

14,227

[5]

17,325

[5]

30,811

[5]

Operating expenses

187,813

'

'

173,422

[1]

'

'

538,523

491,907

[1]

'

'

53,089

69,704

156,147

184,454

Interest income, net

4,225

[6]

'

'

4,225

[6]

'

'

12,675

[6]

12,675

[6]

'

'

'

'

'

'

Interest expense

13,018

[7]

'

'

10,977

[1],[7]

'

'

37,483

[7]

30,118

[1],[7]

'

'

0

[2],[8]

81

[8]

0

[8]

2,684

[6]

Distributions to unitholders

83,986

[9]

79,315

70,143

56,346

52,425

46,053

'

'

'

'

44,378

[10]

25,852

[10]

121,493

[10]

69,615

[10]

Contributions from noncontrolling interest owners

'

'

'

'

'

'

2,247

'

'

'

0

[11]

2,148

[11]

0

[11]

12,588

[11]

Distributions to noncontrolling interest owners

'

'

'

'

'

'

$8,001

'

'

'

$0

[11]

$1,464

[11]

$0

[11]

$6,528

[11]

Table Text Block Supplement [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest by noncontrolling owners

'

'

'

'

'

'

'

'

25.00%

24.00%

'

'

'

'

[1]

Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

[2]

Represents amounts recognized under gathering, treating or processing agreements, and purchase and sale agreements.

[3]

Cost of product includes product purchases from Anadarko (as defined in Note 1) of $33.8 million and $97.8 million for the three and nine months ended September 30, 2013, respectively, and $42.8 million and $115.6 million for the three and nine months ended September 30, 2012, respectively. Operation and maintenance includes charges from Anadarko of $13.5 million and $41.0 million for the three and nine months ended September 30, 2013, respectively, and $12.6 million and $38.0 million for the three and nine months ended September 30, 2012, respectively. General and administrative includes charges from Anadarko of $5.9 million and $17.3 million for the three and nine months ended September 30, 2013, respectively, and $14.2 million and $30.8 million for the three and nine months ended September 30, 2012, respectively. See Note 5.

[4]

Represents expenses incurred on and subsequent to the date of the acquisition of the 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 by the Partnership.

[5]

Represents general and administrative expense incurred on and subsequent to the date of the Partnership’s acquisition of the Partnership assets, as well as a management services fee for reimbursement of 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 Equity incentive plan and Anadarko incentive plans within this Note 5).

[6]

Represents interest income recognized on the note receivable from Anadarko.

[7]

Includes affiliate (as defined in Note 1) interest expense of zero for the three and nine months ended September 30, 2013, and $0.1 million and $2.7 million for the three and nine months ended September 30, 2012, respectively. See Note 8.

[8]

For the three and nine months ended September 30, 2012, includes interest expense recognized on the note payable to Anadarko (see Note 8) and interest imputed on the reimbursement payable to Anadarko for certain expenditures Anadarko incurred in 2011 related to the construction of the Brasada and Lancaster plants. The Partnership repaid the note payable to Anadarko in June 2012, and repaid the reimbursement payable to Anadarko related to the construction of the Brasada and Lancaster plants in the fourth quarter of 2012. See Note receivable from and amounts payable to Anadarko within this Note 5.

[9]

On October 16, 2013, the board of directors of the Partnership’s general partner declared a cash distribution to the Partnership’s unitholders of $0.58 per unit, or $84.0 million in aggregate, including incentive distributions. The cash distribution is payable on November 12, 2013, to unitholders of record at the close of business on October 31, 2013.

[10]

Represents distributions paid under the partnership agreement.

[11]

As described in Note 2, the Partnership acquired Anadarko’s then remaining 24% membership interest in Chipeta on August 1, 2012, and accounted for the acquisition on a prospective basis. As such, contributions from noncontrolling interest owners and distributions to noncontrolling interest owners subsequent to the acquisition date no longer reflect contributions from or distributions to Anadarko.

Transactions_With_Affiliates_A

Transactions With Affiliates - Additional Information (details) (USD $)

Sep. 30, 2013

Dec. 31, 2012

31-May-08

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2008

Jun. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2012

Sep. 30, 2012

Sep. 30, 2012

Sep. 30, 2013

Note Receivable From Anadarko [Member]

Note Receivable From Anadarko [Member]

Note Receivable From Anadarko [Member]

Note Payable To Anadarko [Member]

Note Payable To Anadarko [Member]

Senior Notes 4 Percent Due 2022 [Member]

Gathering Transportation And Treating [Member]

Gathering Transportation And Treating [Member]

Gathering Transportation And Treating [Member]

Gathering Transportation And Treating [Member]

Processing [Member]

Processing [Member]

Processing [Member]

Processing [Member]

Long Term Incentive Plan [Member]

Long Term Incentive Plan [Member]

Long Term Incentive Plan [Member]

Long Term Incentive Plan [Member]

Anadarko Incentive Plans [Member]

Anadarko Incentive Plans [Member]

Anadarko Incentive Plans [Member]

Anadarko Incentive Plans [Member]

Incentive Plan [Member]

Incentive Plan [Member]

Incentive Plan [Member]

Independent Director [Member]

Unit Appreciation Right [Member]

Long Term Incentive Plan [Member]

Related Party Transaction [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Note receivable, due date

'

'

'

14-May-38

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Note receivable - Anadarko

$260,000,000

$260,000,000

[1]

$260,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt instrument, maturity date

'

'

'

'

'

2-Aug-13

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fixed annual rate for note receivable bearing interest

'

'

6.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

The fair value of the note receivable

'

'

'

301,500,000

334,800,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal

1,520,000,000

1,170,000,000

'

'

'

'

175,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fixed interest rate

'

'

'

'

'

'

'

4.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

AffiliateThroughput Percent

'

'

'

'

'

'

'

'

56.00%

63.00%

58.00%

64.00%

58.00%

61.00%

56.00%

59.00%

'

'

'

'

'

'

'

'

'

'

'

'

Phantom units vesting term

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 years

'

'

'

'

'

'

'

'

'1 year

Equity based compensation expense

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$100,000

$100,000

$400,000

$300,000

$800,000

$800,000

$2,200,000

$2,400,000

$8,600,000

$13,900,000

'

'

UVR, UAR and DER Valuation

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$1,053

'

[1]

Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Recovered_Sheet1

Property, Plant and Equipment Table (details) (USD $)

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

In Thousands, unless otherwise specified

Land [Member]

Land [Member]

Gathering systems [Member]

Gathering systems [Member]

Gathering systems [Member]

Gathering systems [Member]

Pipelines And Equipment [Member]

Pipelines And Equipment [Member]

Pipelines And Equipment [Member]

Pipelines And Equipment [Member]

Asset Under Construction [Member]

Asset Under Construction [Member]

Other [Member]

Other [Member]

Other [Member]

Other [Member]

Minimum [Member]

Maximum [Member]

Minimum [Member]

Maximum [Member]

Minimum [Member]

Maximum [Member]

Property Plant And Equipment [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Property, plant and equipment

$4,061,389

$3,432,392

[1]

$2,584

$501

$3,610,879

$2,911,572

'

'

$119,278

$91,126

'

'

$318,107

$422,002

$10,541

$7,191

'

'

Accumulated depreciation

817,489

714,436

[1]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net property, plant and equipment

$3,243,900

$2,717,956

[1]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Estimated useful life

'

'

'

'

'

'

'3 years

'47 years

'

'

'15 years

'45 years

'

'

'

'

'3 years

'25 years

[1]

Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Property_Plant_and_Equipment_A

Property, Plant and Equipment - Additional Information (details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013
Property, Plant and Equipment [Abstract]	'
Impairment	$1

Components_of_Working_Capital_1

Components of Working Capital - Other Current Assets Table (details) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Other Current Assets [Line Items]	'		'
Natural gas liquids inventory	$2,438		$1,678
Natural gas imbalance receivables	2,729		1,663
Prepaid insurance	1,934		1,897
Other	1,662		1,760
Other current assets	$8,763	[1]	$6,998	[1],[2]
[1]	Other current assets includes natural gas imbalance receivables from affiliates of $0.1 million and $0.4 million as of September 30, 2013, and December 31, 2012, respectively.
[2]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Components_of_Working_Capital_2

Components of Working Capital - Accrued Liabilities Table (details) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Thousands, unless otherwise specified
Accrued Liabilities [Line Items]	'		'
Other accrued liabilities	$136		$612
Accrued interest expense	16,620		15,868
Short-term asset retirement obligations	1,187		1,711
Short-term remediation and reclamation obligations	609		799
Accrued liabilities	140,166	[1]	147,651	[1],[2]
Accrued Capital Expenditures [Member]	'		'
Accrued Liabilities [Line Items]	'		'
Other accrued liabilities	100,876		112,311
Accrued Plant Purchases [Member]	'		'
Accrued Liabilities [Line Items]	'		'
Other accrued liabilities	$20,738		$16,350
[1]	Accrued liabilities include amounts payable to affiliates of $0.1 million as of September 30, 2013 and December 31, 2012.
[2]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Debt_and_Interest_Expense_Debt

Debt and Interest Expense - Debt Outstanding Table (details) (USD $)

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Oct. 31, 2012

Jun. 30, 2012

Sep. 30, 2013

Dec. 31, 2012

31-May-11

Sep. 30, 2013

Aug. 31, 2013

Dec. 31, 2012

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Senior Notes 4 Percent Due 2022 [Member]

Senior Notes 4 Percent Due 2022 [Member]

Senior Notes 4 Percent Due 2022 [Member]

Senior Notes 4 Percent Due 2022 [Member]

Senior Notes 5 Point 375 Percent Due 2021 [Member]

Senior Notes 5 Point 375 Percent Due 2021 [Member]

Senior Notes 5 Point 375 Percent Due 2021 [Member]

Senior Notes 2 Point 6 Percent Due 2018 [Member]

Senior Notes 2 Point 6 Percent Due 2018 [Member]

Senior Notes 2 Point 6 Percent Due 2018 [Member]

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal

$1,520,000,000

$1,170,000,000

$100,000,000

$0

$670,000,000

$670,000,000

$150,000,000

$520,000,000

$500,000,000

$500,000,000

$500,000,000

$250,000,000

$250,000,000

$0

Carrying Value

1,518,110,000

1,168,278,000

[1]

100,000,000

0

673,363,000

673,617,000

'

'

495,042,000

494,661,000

'

249,705,000

'

0

Fair Value

$1,531,924,000

[2]

$1,169,874,000

[2]

$100,000,000

[2]

$0

[2]

$651,580,000

[2]

$669,928,000

[2]

'

'

$531,210,000

[2]

$499,946,000

[2]

'

$249,134,000

[2]

'

$0

[2]

[1]

Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

[2]

Fair value is measured using Level 2 inputs.

Debt_and_Interest_Expense_Debt1

Debt and Interest Expense - Debt Activity Table (details) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013
Debt Instrument [Line Items]	'
Beginning Balance	$1,168,278	[1]
Other	-168
Ending Balance	1,518,110
Revolving Credit Facility [Member]	'
Debt Instrument [Line Items]	'
Beginning Balance	0
Borrowings	595,000
Repayments	-495,000
Ending Balance	100,000
Senior Notes 2 Point 6 Percent Due 2018 [Member]	'
Debt Instrument [Line Items]	'
Beginning Balance	0
Borrowings	250,000
Ending Balance	$249,705
[1]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.

Debt_and_Interest_Expense_Inte

Debt and Interest Expense - Interest Expense Table (details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Debt Instrument [Line Items]	'		'		'		'
Interest Expense	$13,018,000	[1]	$10,977,000	[1],[2]	$37,483,000	[1]	$30,118,000	[1],[2]
Senior Notes 5 Point 375 Percent Due 2021 [Member] | Senior Notes 4 Percent Due 2022 [Member]	'		'		'		'
Table Text Block Supplement [Abstract]	'		'		'		'
Amortization related to Senior Notes	'		400,000		'		800,000
Third Parties [Member]	'		'		'		'
Debt Instrument [Line Items]	'		'		'		'
Interest expense on long-term debt	14,994,000		11,919,000		43,783,000		28,036,000
Amortization of debt issuance costs and commitment fees	1,135,000	[3]	1,201,000	[3]	3,252,000	[3]	3,225,000	[3]
Capitalized interest	-3,111,000		-2,224,000		-9,552,000		-3,827,000
Interest Expense	13,018,000		10,896,000		37,483,000		27,434,000
Affiliated Entity [Member]	'		'		'		'
Debt Instrument [Line Items]	'		'		'		'
Interest expense on note payable to Anadarko	0	[4]	0	[4]	0	[4]	2,440,000	[4]
Interest expense on affiliate balances	0	[5]	81,000	[5]	0	[5]	244,000	[5]
Interest Expense	0	[6],[7]	81,000	[6]	0	[6]	2,684,000	[8]
Senior Notes 2 Point 6 Percent Due 2018 [Member] | Senior Notes 5 Point 375 Percent Due 2021 [Member] | Senior Notes 4 Percent Due 2022 [Member]	'		'		'		'
Table Text Block Supplement [Abstract]	'		'		'		'
Amortization related to Senior Notes	$300,000		'		$800,000		'
[1]	Includes affiliate (as defined in Note 1) interest expense of zero for the three and nine months ended September 30, 2013, and $0.1 million and $2.7 million for the three and nine months ended September 30, 2012, respectively. See Note 8.
[2]	Financial information has been recast to include the financial position and results attributable to the Non-Operated Marcellus Interest. See Note 2.
[3]	For the three and nine months ended September 30, 2013, includes $0.3 million and $0.8 million, respectively, of amortization of (i) the original issue discount for the June 2012 offering of the 2022 Notes, partially offset by the original issue premium for the October 2012 offering of the 2022 Notes, (ii) original issue discount for the 2021 Notes and 2018 Notes and (iii) underwriters’ fees. For the three and nine months ended September 30, 2012, includes $0.4 million and $0.8 million, respectively, of amortization of the original issue discount and underwriters’ fees for the 2022 Notes issued in June 2012 and the 2021 Notes.
[4]	In June 2012, the note payable to Anadarko was repaid in full. See Note payable to Anadarko within this Note 8.
[5]	Imputed interest expense on the reimbursement payable to Anadarko for certain expenditures Anadarko incurred in 2011 related to the construction of the Brasada and Lancaster plants. In the fourth quarter of 2012, the Partnership repaid the reimbursement payable to Anadarko associated with the construction of the Brasada and Lancaster plants.
[6]	For the three and nine months ended September 30, 2012, includes interest expense recognized on the note payable to Anadarko (see Note 8) and interest imputed on the reimbursement payable to Anadarko for certain expenditures Anadarko incurred in 2011 related to the construction of the Brasada and Lancaster plants. The Partnership repaid the note payable to Anadarko in June 2012, and repaid the reimbursement payable to Anadarko related to the construction of the Brasada and Lancaster plants in the fourth quarter of 2012. See Note receivable from and amounts payable to Anadarko within this Note 5.
[7]	Represents amounts recognized under gathering, treating or processing agreements, and purchase and sale agreements.
[8]	Represents interest income recognized on the note receivable from Anadarko.

Debt_and_Interest_Expense_Addi

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

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2013

Mar. 31, 2011

Mar. 31, 2011

Aug. 31, 2013

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Jun. 30, 2012

Sep. 30, 2013

Dec. 31, 2012

Oct. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

31-May-11

Sep. 30, 2013

Dec. 31, 2010

Dec. 31, 2008

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Minimum [Member]

Maximum [Member]

Senior Notes 2 Point 6 Percent Due 2018 [Member]

Senior Notes 2 Point 6 Percent Due 2018 [Member]

Senior Notes 2 Point 6 Percent Due 2018 [Member]

Senior Notes 2 Point 6 Percent Due 2018 [Member]

Senior Notes 4 Percent Due 2022 [Member]

Senior Notes 4 Percent Due 2022 [Member]

Senior Notes 4 Percent Due 2022 [Member]

Senior Notes 4 Percent Due 2022 [Member]

Senior Notes 5 Point 375 Percent Due 2021 [Member]

Senior Notes 5 Point 375 Percent Due 2021 [Member]

Senior Notes 5 Point 375 Percent Due 2021 [Member]

Note Payable To Anadarko [Member]

Note Payable To Anadarko [Member]

Note Payable To Anadarko [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Indemnification Guarantee [Member]

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal

$1,520,000,000

$1,170,000,000

$0

$100,000,000

'

'

$250,000,000

$250,000,000

$0

'

$520,000,000

$670,000,000

$670,000,000

$150,000,000

$500,000,000

$500,000,000

$500,000,000

'

'

$175,000,000

Fixed interest rate

'

'

'

'

'

'

2.60%

'

'

'

4.00%

'

'

4.00%

'

'

5.38%

'

2.82%

'

Offering Percent

'

'

'

'

'

'

99.88%

'

'

'

99.19%

'

'

105.18%

'

'

98.78%

'

'

'

Effective interest rate

'

'

'

'

'

'

2.81%

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt instrument, maturity date

'

'

'

'

'

'

'

15-Aug-18

'

'

'

1-Jul-22

'

'

1-Jun-21

'

'

2-Aug-13

'

'

Underwriting discount

'

'

'

'

'

'

1,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Realized loss on terminated swap agreement

'

'

'

'

'

'

'

'

'

'

1,700,000

'

'

'

'

'

'

'

'

'

Line of credit, expiration date

'

'

'

24-Mar-16

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Revolving Credit Facility, current maximum borrowing capacity

'

'

'

800,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Revolving Credit Facility, interest rate at period end

'

'

1.71%

1.68%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Facility fee

'

'

0.25%

0.25%

0.20%

0.35%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding borrowings

'

'

'

100,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding letters of credit

'

'

'

12,800,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available borrowing capacity

'

'

'

687,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt financings

'

'

'

'

'

'

'

'

'

$250,000,000

'

'

'

'

'

'

'

'

'

'

Commitments_and_Contingencies_

Commitments and Contingencies - Additional Information (details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2013	Jun. 30, 2013
					Purchase Commitment [Member]	Mont Belvieu JV [Member]	Mont Belvieu JV [Member]
Commitments and Contingencies [Line Items]	'	'	'	'	'	'	'
Committed capital	$61.30	'	$61.30	'	'	$13.60	'
Term of instrument or obligation	'	'	'	'	'12 months	'6 months	'
Equity method investment ownership	'	'	'	'	'	'	25.00%
Rent expense associated with office and equipment leases	$0.60	$0.80	$2	$2.30	'	'	'