Commitments and Contingencies Commitments and Contingencies - Additional Information (Details) (Western Gas Partners [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Purchase Commitment [Member]	Sep. 30, 2013 Mont Belvieu JV [Member]	Jun. 30, 2013 Mont Belvieu JV [Member]
Loss Contingencies [Line Items]
Committed capital	$ 61.3		$ 61.3			$ 13.6
Term of instrument or obligation					12 months	6 months
Equity method investment ownership							25.00%	[1]
Rent expense associated with office and equipment leases	$ 0.6	$ 0.8	$ 2.0	$ 2.3

[1] The acquisition from a third party consisted of a 25% interest in Enterprise EF78 LLC, an entity formed to design, construct, and own two fractionators located in Mont Belvieu, Texas. The interest acquired is accounted for under the equity method of accounting and is referred to as the “Mont Belvieu JV” and the acquisition as the “Mont Belvieu JV acquisition.” See Mont Belvieu JV acquisition below for further information.