Divestiture (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Divestiture
Gain on sale of asset	$ 37,736,000	$ (1,342,000)	$ 37,598,000	$ (2,328,000)
Summit | Sherwood
Divestiture
Proceeds from divestiture			207,900,000
Number of compressor stations			2
Carrying value of assets			169,700,000
Gain on sale of asset			$ 38,200,000
Summit | Minimum | Sherwood
Divestiture
Length of gas gathering pipelines (in miles)	40		40
Power of compressor stations			21,000