Risk Management and Derivative Financial Instruments (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Fair value of derivative financial instruments
Total derivatives assets		$ 233
Current liabilities	3,402	760
Non-current liabilities and deferred credits	2,985	3,564
Total derivatives liabilities	6,387	4,324
Electric | Non-designated as hedging instruments due to regulatory accounting | Commodity contracts
Fair value of derivative financial instruments
Non-current assets and deferred charges		77
Current liabilities	2,933	508
Non-current liabilities and deferred credits	2,912	3,562
Period within which financial instruments will settle (in months)	twelve months
Gas | Non-designated as hedging instruments due to regulatory accounting | Commodity contracts
Fair value of derivative financial instruments
Current assets		39
Non-current assets and deferred charges		117
Current liabilities	469	252
Non-current liabilities and deferred credits	$ 73	$ 2