Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								3 Months Ended		3 Months Ended
	Dec. 31, 2012 Environmental Issue [Member]	Dec. 31, 2012 Environmental Issue [Member] PNG MGP [Member]	Dec. 31, 2012 Environmental Remediation Expense [Member] CPG MGP [Member]	Dec. 31, 2012 Environmental Remediation Expense [Member] PNG MGP [Member]	Dec. 31, 2012 CPG and PNG COAs [Member]	Dec. 31, 2011 CPG and PNG COAs [Member]	Jun. 06, 2006 Key Span [Member]	Jun. 24, 2004 Key Span [Member]	Dec. 31, 2012 Allentown, Pennsylvania Natural Gas Explosion [Member] Damage from Natural Gas Explosion [Member]	Feb. 09, 2011 Allentown, Pennsylvania Natural Gas Explosion [Member] Damage from Natural Gas Explosion [Member] Persons	Dec. 31, 2012 Minimum [Member] Allentown, Pennsylvania Natural Gas Explosion [Member] Damage from Natural Gas Explosion [Member] Claims
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					14,965	17,751
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
Property claims (in claims)											100
Liability insurance deductible									$ 500