Risk Management and Derivative Financial Instruments (Details) (USD $) In Thousands	6 Months Ended			6 Months Ended
	Jun. 30, 2010	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 Electric Non-designated as hedging instruments due to regulatory accounting Commodity contracts	Dec. 31, 2010 Electric Non-designated as hedging instruments due to regulatory accounting Commodity contracts	Jun. 30, 2011 Gas Non-designated as hedging instruments due to regulatory accounting Commodity contracts	Dec. 31, 2010 Gas Non-designated as hedging instruments due to regulatory accounting Commodity contracts
Fair value of derivative financial instruments
Current assets						$ 28	$ 39
Non-current assets and deferred charges				52	77	6	117
Total derivatives assets		86	233
Current liabilities		1,264	760	1,197	508	67	252
Non-current liabilities and deferred credits		3,392	3,564	3,377	3,562	15	2
Total derivatives liabilities		4,656	4,324
Unrealized losses are applicable to financial instruments	$ (652)			$ 1,200
Period within which financial instruments will settle (in months)				twelve months