Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended		3 Months Ended	6 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Environmental Issue [Member]	Mar. 31, 2013 Environmental Issue [Member] PNG MGP [Member]	Mar. 31, 2013 Environmental Remediation Expense [Member] CPG MGP [Member]	Mar. 31, 2013 Environmental Remediation Expense [Member] PNG MGP [Member]	Mar. 31, 2013 CPG and PNG COAs [Member]	Mar. 31, 2012 CPG and PNG COAs [Member]	Jun. 06, 2006 Key Span [Member]	Jun. 24, 2004 Key Span [Member]	Feb. 09, 2011 Allentown, Pennsylvania Natural Gas Explosion [Member] Damage from Natural Gas Explosion [Member] Persons
Commitments and Contingencies [Line Items]
Environmental expenditures cap during calendar year				$ 1,800	$ 1,100
Option to termination agreement by either party effective at end of any two-year period beginning with the original effective date in March 2004 (in years)			2 years
Accrual for environmental loss contingencies						14,338	16,789
Base year for determination of investigation and remediation cost (in years)		5 years
Alleged Percentage of Liability (as a percent)									50.00%
Approximate remediation cost spent by claimant									2,300
Environmental exit cost anticipated by claimant									11,000
Environmental exit cost based on third party estimate								10,000
Additional environment exit cost based on claimant estimate								20,000
Deaths from natural gas explosion (in persons)										5
Liability insurance deductible	$ 500