Equity Investments - Equity Investments Table (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018		Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Balance		$ 566,211
Investment earnings (loss), net of amortization	[1]	20,424		$ 19,461
Distributions		(20,941)		(19,114)
Distributions in excess of cumulative earnings		(8,013)	[2]	$ (3,453)
Balance		557,681
Western Gas Partners, LP [Member] | Fort Union [Member]
Schedule of Equity Method Investments [Line Items]
Balance		7,030
Investment earnings (loss), net of amortization		144
Distributions		(144)
Distributions in excess of cumulative earnings	[2]	(741)
Balance		6,289
Western Gas Partners, LP [Member] | White Cliffs [Member]
Schedule of Equity Method Investments [Line Items]
Balance		44,945
Investment earnings (loss), net of amortization		2,673
Distributions		(2,527)
Distributions in excess of cumulative earnings	[2]	(1,228)
Balance		43,863
Western Gas Partners, LP [Member] | Rendezvous [Member]
Schedule of Equity Method Investments [Line Items]
Balance		42,528
Investment earnings (loss), net of amortization		225
Distributions		(710)
Distributions in excess of cumulative earnings	[2]	(1,162)
Balance		40,881
Western Gas Partners, LP [Member] | Mont Belvieu JV [Member]
Schedule of Equity Method Investments [Line Items]
Balance		110,299
Investment earnings (loss), net of amortization		7,090
Distributions		(7,100)
Distributions in excess of cumulative earnings	[2]	(1,325)
Balance		108,964
Western Gas Partners, LP [Member] | Texas Express Gathering LLC [Member]
Schedule of Equity Method Investments [Line Items]
Balance		15,879
Investment earnings (loss), net of amortization		1,066
Distributions		(1,127)
Distributions in excess of cumulative earnings	[2]	(20)
Balance		15,798
Western Gas Partners, LP [Member] | Texas Express Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Balance		178,975
Investment earnings (loss), net of amortization		4,417
Distributions		(4,480)
Distributions in excess of cumulative earnings	[2]	(2,168)
Balance		176,744
Western Gas Partners, LP [Member] | Front Range Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Balance		166,555
Investment earnings (loss), net of amortization		4,809
Distributions		(4,853)
Distributions in excess of cumulative earnings	[2]	(1,369)
Balance		$ 165,142

[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] 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.