Divestiture (Details) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2013 Summit Sherwood item	Jun. 30, 2013 Summit Minimum Sherwood hp mi
Divestiture
Proceeds from divestiture					$ 207,900,000
Length of gas gathering pipelines (in miles)						40
Number of compressor stations					2
Power of compressor stations						21,000
Carrying value of assets					169,000,000
Gain on sale of asset	$ (1,840,000)	$ (655,000)	$ 35,758,000	$ (2,983,000)	$ 38,900,000