Divestiture (Details) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	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				168,200,000
Gain on sale of asset	$ 33,763,000	$ (6,254,000)	$ (8,797,000)	$ 39,700,000