Transactions with Affiliates - Gains (Losses) on Commodity Price Swap Agreements Table (Details) - Affiliates [Member] - Western Gas Partners, LP [Member] - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements		$ (1,043)	$ 7,410	$ (586)	$ 24,419
Sales [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[1]	(926)	16,658	2,342	69,451
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]	6,284	719	12,022	12,962
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]	(7,210)	15,939	(9,680)	56,489
Purchases [Member]
Gains (losses) on commodity price swap agreements related to sales and purchases
Gains (losses) on commodity price swap agreements	[2]	$ (117)	$ (9,248)	$ (2,928)	$ (45,032)

[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.