Equity Investments - Equity Investments Table (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017
Schedule of Equity Method Investments [Line Items]
Balance				$ 566,211
Acquisitions				161,858
Investment earnings (loss), net of amortization	[1]	$ 43,110	$ 21,519	102,752		$ 62,708
Contributions				67,463
Capitalized interest				516
Distributions				(93,827)		(64,313)
Distributions in excess of cumulative earnings				(18,097)	[2]	$ (16,255)
Balance		786,876		786,876
Western Gas Partners, LP [Member] | Fort Union [Member]
Schedule of Equity Method Investments [Line Items]
Balance				7,030
Acquisitions				0
Investment earnings (loss), net of amortization				(892)
Contributions				0
Capitalized interest				0
Distributions				(194)
Distributions in excess of cumulative earnings	[2]			(2,889)
Balance		3,055		3,055
Western Gas Partners, LP [Member] | White Cliffs [Member]
Schedule of Equity Method Investments [Line Items]
Balance				44,945
Acquisitions				0
Investment earnings (loss), net of amortization				8,547
Contributions				1,278
Capitalized interest				0
Distributions				(8,111)
Distributions in excess of cumulative earnings	[2]			(3,109)
Balance		43,550		43,550
Western Gas Partners, LP [Member] | Rendezvous [Member]
Schedule of Equity Method Investments [Line Items]
Balance				42,528
Acquisitions				0
Investment earnings (loss), net of amortization				635
Contributions				0
Capitalized interest				0
Distributions				(2,091)
Distributions in excess of cumulative earnings	[2]			(2,015)
Balance		39,057		39,057
Western Gas Partners, LP [Member] | Mont Belvieu JV [Member]
Schedule of Equity Method Investments [Line Items]
Balance				110,299
Acquisitions				0
Investment earnings (loss), net of amortization				22,916
Contributions				0
Capitalized interest				0
Distributions				(22,945)
Distributions in excess of cumulative earnings	[2]			(3,305)
Balance		106,965		106,965
Western Gas Partners, LP [Member] | TEFR Interests [Member]
Schedule of Equity Method Investments [Line Items]
Balance				361,409
Acquisitions				0
Investment earnings (loss), net of amortization				47,736
Contributions				24,680
Capitalized interest				0
Distributions				(43,989)
Distributions in excess of cumulative earnings	[2]			(6,779)
Balance		383,057		383,057
Western Gas Partners, LP [Member] | Whitethorn [Member]
Schedule of Equity Method Investments [Line Items]
Balance				0
Acquisitions				150,563
Investment earnings (loss), net of amortization				23,810
Contributions				7,069
Capitalized interest				0
Distributions				(16,497)
Distributions in excess of cumulative earnings	[2]			0
Balance		164,945		164,945
Western Gas Partners, LP [Member] | Cactus II [Member]
Schedule of Equity Method Investments [Line Items]
Balance				0
Acquisitions				11,295
Investment earnings (loss), net of amortization				0
Contributions				34,436
Capitalized interest				516
Distributions				0
Distributions in excess of cumulative earnings	[2]			0
Balance		$ 46,247		$ 46,247

[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.