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

[1] Represents amounts earned or incurred on and subsequent to the date of the acquisition of WES assets, as well as amounts earned or incurred by Anadarko on a historical basis related to WES assets prior to the acquisition of such assets by WES, recognized under gathering, treating or processing agreements, and purchase and sale agreements.

[2] Recorded in Impairments in the consolidated statements of operations.

[3] Distributions in excess of cumulative earnings, classified as investing cash flows in the consolidated statements of cash flows, are calculated on an individual investment basis.

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

[5] WES has a 10% interest in White Cliffs, a limited liability company that owns a crude oil pipeline that originates in Platteville, Colorado and terminates in Cushing, Oklahoma. The third-party majority owner is the manager of the White Cliffs operations. Certain business decisions, including, but not limited to, approval of annual budgets and decisions with respect to significant expenditures, contractual commitments, acquisitions, material financings, dispositions of assets or admitting new members, require more than 75% approval of the members.

[6] WES has a 22% interest in Rendezvous, a limited liability company that operates gas gathering facilities in Southwestern Wyoming. Certain business decisions, including, but not limited to, decisions with respect to significant expenditures or contractual commitments, annual budgets, material financings, dispositions of assets or amending the members’ gas servicing agreements, require unanimous approval of the members.

[7] WES has a 25% interest in the Mont Belvieu JV, an entity formed to design, construct, and own two fractionation trains located in Mont Belvieu, Texas. A third party is the operator of the Mont Belvieu JV fractionation trains. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require 50% or unanimous approval of the owners.

[8] WES has a 20% interest in TEG, which owns two NGL gathering systems that link natural gas processing plants to TEP. Midcoast Energy Partners, L.P., a wholly-owned subsidiary of Enbridge, Inc., is the operator of the two gathering systems. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the delegation, creation, appointment, or removal of officer positions require more than 50% approval of the members.

[9] WES has a 20% interest in TEP, which owns an NGL pipeline that originates in Skellytown, Texas and extends to Mont Belvieu, Texas. Enterprise Products Operating LLC (“Enterprise”) is the operator of TEP. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require more than 50% approval of the members.

[10] WES has a 33.33% interest in FRP, which owns an NGL pipeline that extends from Weld County, Colorado to Skellytown, Texas. Enterprise is the operator of FRP. Certain business decisions, including, but not limited to, decisions with respect to the execution of contracts, settlements, disposition of assets, or the creation, appointment, or removal of officer positions require more than 50% approval of the members.