Commitments And Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2012 mi in
Schedule Of Commitments And Contingencies [Line Items]
Purchase commitments expected to occur over next twelve months	22.2
Marc I Pipeline
Schedule Of Commitments And Contingencies [Line Items]
Length of pipeline	39
Pipeline diameter	30
Expected transportation capacity of firm	550
Marc I Pipeline | Anadarko
Schedule Of Commitments And Contingencies [Line Items]
Option to acquire ownership interest	25.00%
Watkins Glen NGL Development Project
Schedule Of Commitments And Contingencies [Line Items]
Barrels of NGL storage	2,100,000