Investments in Unconsolidated Affiliates (Details)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Webb/Duval Gatherers ("Webb Duval")
Investments in Unconsolidated Affiliates
Ownership %	62.50%
Eagle Ford Gathering LLC ("Eagle Ford Gathering")
Investments in Unconsolidated Affiliates
Ownership %	50.00%	50.00%	50.00%
Liberty Pipeline Group, LLC ("Liberty Pipeline Group")
Investments in Unconsolidated Affiliates
Ownership %	50.00%
Double Eagle Pipeline LLC ("Double Eagle Pipeline")
Investments in Unconsolidated Affiliates
Ownership %	50.00%
Southern Dome, LLC ("Southern Dome")
Investments in Unconsolidated Affiliates
Ownership %	69.50%
Bighorn Gas Gathering, L.L.C. ("Bighorn")
Investments in Unconsolidated Affiliates
Ownership %	51.00%	51.00%	51.00%
Fort Union Gas Gathering, L.L.C. ("Fort Union")
Investments in Unconsolidated Affiliates
Ownership %	37.04%	37.04%	37.04%