Transactions with Affiliates - Gains (Losses) on Commodity Price Swap Agreements Table (Details) - Affiliates [Member] - Western Gas Partners, LP [Member] - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements		$ 648	$ 28,457	$ 66,292
Sales [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[1]	(1,798)	71,034	191,236
Sales [Member] | Natural Gas [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[1]	19,924	11,116	45,978
Sales [Member] | Natural Gas Liquids [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[1]	(21,722)	59,918	145,258
Purchases [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[2]	$ 2,446	$ (42,577)	$ (124,944)

[1] Reported in affiliate Natural gas and natural gas liquids sales in the consolidated statements of operations in the period in which the related sale is recorded.

[2] Reported in Cost of product in the consolidated statements of operations in the period in which the related purchase is recorded.