Acquisitions - Purchase Price Allocation Table (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Goodwill	$ 384,387us-gaap_Goodwill	$ 105,336us-gaap_Goodwill
Western Gas Partners [Member] \| Delaware Basin Midstream Limited Liability Company [Member]
Business Acquisition [Line Items]
Current assets	46,358
Property, plant and equipment	440,971
Goodwill	279,051
Other intangible assets	835,566
Accounts payables	(13,064)
Accrued liabilities	(24,824)
Deferred income taxes	(1,450)
Asset retirement obligations and other	(8,649)
Total purchase price	$ 1,553,959

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Amount of assets that are expected to be realized or consumed within one year or the normal operating cycle, if longer, acquired at the acquisition date.

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Amount of deferred tax liability attributable to taxable temporary differences due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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Amount of intangible assets, excluding goodwill, acquired at the acquisition date.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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The amount of property, plant, and equipment recognized as of the acquisition date.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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