Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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The estimate of the lease property's economic value at the end of the direct financing lease term excluding any amounts guaranteed by either the lessee or a third-party.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Property, Plant and Equipment - Additional Information (details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2014
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 5,424,699,000us-gaap_PropertyPlantAndEquipmentGross	$ 4,239,100,000us-gaap_PropertyPlantAndEquipmentGross
Natural Gas Processing Plant [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	4,600,000
Western Gas Partners [Member]
Property, Plant and Equipment [Line Items]
Unguaranteed residual value		4,600,000
Impairment	3,100,000	1,200,000
Western Gas Partners [Member] \| Natural Gas Processing Plant [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment				4,600,000
Western Gas Partners [Member] \| Equipment [Member]
Property, Plant and Equipment [Line Items]
Impairment			600,000
Estimated fair value	2,400,000
Western Gas Partners [Member] \| Natural Gas Gathering Systems [Member]
Property, Plant and Equipment [Line Items]
Impairment			$ 6,000,000