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

[1] See Note 2.

[2] See Note 2.

[3] See Note 2 for a discussion of the Deferred purchase price obligation - Anadarko.

[4] Represents the cash payment to Anadarko for the settlement of the Deferred purchase price obligation - Anadarko (see Note 2).

[5] Accretion expense was recorded as a charge to Interest expense in the consolidated statements of operations.

[6] Financing-related accretion revisions were recorded in Interest expense in the consolidated statements of operations.

[7] Recorded as revisions within Common units in the consolidated balance sheets and consolidated statements of equity and partners’ capital.

[8] Calculated using Level 3 inputs.