Commitments and Contingencies (Contingencies) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended
	Sep. 30, 2012 Environmental Issue [Member]	Sep. 30, 2012 CPG Manufactured Gas Plant Properties and PNG Manufactured Gas Plant Properties [Member] Environmental Remediation Expense [Member]	Sep. 30, 2011 CPG Manufactured Gas Plant Properties and PNG Manufactured Gas Plant Properties [Member] Environmental Remediation Expense [Member]	Sep. 30, 2012 CPG MGP [Member] Environmental Remediation Expense [Member]	Sep. 30, 2012 PNG MGP [Member] Environmental Remediation Expense [Member]	Sep. 30, 2012 PNG MGP [Member] Environmental Issue [Member]
Contingencies [Line Items]
Environmental expenditures				$ 1,800	$ 1,100
Option to termination agreement by either party effective at end of any period						2 years
Accrued liabilities for environmental investigation and remediation costs related to CPG-COA and PNG-COA		$ 14,979	$ 17,917
Base Year for Determination of Investigation and Remediation Cost	5 years