Investments in Unconsolidated Affiliates (Details)	Sep. 30, 2011	Sep. 30, 2010
Webb/Duval Gatherers ("Webb Duval") [Member] | Texas general partnership [Member] | Texas [Member]
Investments in unconsolidated affiliates
Ownership Percentage	62.50%
Eagle Ford Gathering LLC ("Eagle Ford Gathering") [Member]
Investments in unconsolidated affiliates
Ownership Percentage	50.00%	50.00%
Eagle Ford Gathering LLC ("Eagle Ford Gathering") [Member] | Delaware limited liability company [Member] | Texas [Member]
Investments in unconsolidated affiliates
Ownership Percentage	50.00%
Liberty Pipeline Group, LLC ("Liberty Pipeline Group") [Member] | Delaware limited liability company [Member] | Texas [Member]
Investments in unconsolidated affiliates
Ownership Percentage	50.00%
Southern Dome, LLC ("Southern Dome") [Member] | Delaware limited liability company [Member] | Oklahoma [Member]
Investments in unconsolidated affiliates
Ownership Percentage	69.50%
Bighorn Gas Gathering, L.L.C. ("Bighorn") [Member] | Delaware limited liability company [Member] | Rocky Mountains [Member]
Investments in unconsolidated affiliates
Ownership Percentage	51.00%
Fort Union Gas Gathering, L.L.C. ("Fort Union") [Member] | Delaware limited liability company [Member] | Rocky Mountains [Member]
Investments in unconsolidated affiliates
Ownership Percentage	37.04%