Regulatory Assets and Liabilities and Regulatory Matters Textual (Details) (USD $) In Thousands, unless otherwise specified			3 Months Ended		12 Months Ended				0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Deferral Fuel and Power [Member]	Dec. 31, 2011 Deferral Fuel and Power [Member]	Sep. 30, 2012 Deferral Fuel and Power [Member]	Dec. 31, 2012 Electric Utility Electric Supply Contracts [Member]	Sep. 30, 2012 Electric Utility Electric Supply Contracts [Member]	Dec. 31, 2011 Electric Utility Electric Supply Contracts [Member]	Oct. 03, 2012 Damage from Natural Gas Explosion [Member] Allentown, Pennsylvania Natural Gas Explosion [Member]	Feb. 09, 2011 Damage from Natural Gas Explosion [Member] Allentown, Pennsylvania Natural Gas Explosion [Member] Persons	Dec. 31, 2012 Allentown Incident [Member]	Dec. 31, 2012 Revised Penalty [Member] Allentown Incident [Member]
Regulatory Assets [Line Items]
Site Contingency, Accelerated Time Frame Replacing Remainder of Cast-Iron Mains									14 years
Unrealized gains (losses) on derivative financial instrument contracts			$ (440)	$ (2,589)	$ 5,303
Fair value of electric utility electricity supply contracts	(39,453)	(37,782)				8,182	9,207	13,529
Deaths from natural gas explosion (in persons)										5
Penalty Assessed											$ 386	$ 500
Loss Contingency, Agreement Permitted To Retain Current Timeframe for Replacing The Remainder of Their Bare Steel Mains									30 years