Risk Management and Derivative Financial Instruments (Details 2) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Electric
Gain / (Loss) on derivatives
Unrealized losses applicable to financial instruments which will settle in next twelve months	$ 3,400,000		$ 3,400,000		$ 3,400,000
Period within which financial instruments will settle (in months)	12 months		12 months		12 months
Amount of Gain/(Loss) on Derivative recognized as Regulatory (assets)/Liabilities	474,000	(1,367,000)	(1,828,000)	(735,000)	(8,057,000)	(2,959,000)
Amount of Gain / (Loss) Recognized in Income on Derivative	83,000	(552,000)	59,000	(392,000)	(1,781,000)	(1,008,000)
Gas
Gain / (Loss) on derivatives
Amount of Gain/(Loss) on Derivative recognized as Regulatory (assets)/Liabilities	164,000	(175,000)	(491,000)	(271,000)	(2,136,000)	(717,000)
Commodity contracts | Electric
Gain / (Loss) on derivatives
Amount of Gain/(Loss) on Derivative recognized as Regulatory (assets)/Liabilities	474,000	(1,367,000)	(1,828,000)	(735,000)	(8,057,000)	(2,959,000)
Amount of Gain / (Loss) Recognized in Income on Derivative	83,000	(552,000)	59,000	(392,000)	(1,781,000)	(1,008,000)
Commodity contracts | Gas
Gain / (Loss) on derivatives
Amount of Gain/(Loss) on Derivative recognized as Regulatory (assets)/Liabilities	164,000	(175,000)	(491,000)	(271,000)	(2,136,000)	(717,000)
Derivatives in Cash Flow Hedging Relationships | Electric
Gain / (Loss) on derivatives
Amount of Gain / (Loss) Reclassed from OCI into Income (Effective portion)						(4,864,000)
Amount of Gain / (Loss) Recognized in OCI on Derivative (Effective portion)						1,037,000
Derivatives in Cash Flow Hedging Relationships | Commodity contracts | Electric
Gain / (Loss) on derivatives
Amount of Gain / (Loss) Reclassed from OCI into Income (Effective portion)						(4,864,000)
Amount of Gain / (Loss) Recognized in OCI on Derivative (Effective portion)						$ 1,037,000