Acquisitions - Purchase Price Allocation Table (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill	$ 393,035	$ 389,087	[1]
Western Gas Partners [Member] | Delaware Basin Midstream Limited Liability Company [Member]
Business Acquisition [Line Items]
Current assets	63,020
Property, plant and equipment	467,171
Goodwill	282,999
Other intangible assets	811,048
Accounts payables	(17,679)
Accrued liabilities	(38,684)
Deferred income taxes	(1,342)
Asset retirement obligations and other	(9,060)
Total purchase price	$ 1,557,473

[1] Financial information has been recast to include the financial position and results attributable to the DBJV system. See Note 1 and Note 2.