Risk Management and Derivative Financial Instruments (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Fair value of derivative financial instruments
Current assets	$ 900,000	$ 96,000
Total derivatives assets	1,156,000	287,000
Current liabilities	1,905,000	3,403,000
Non-current liabilities and deferred credits	3,307,000	3,819,000
Total derivatives liabilities	5,212,000	7,222,000
Margin deposit liabilities	0	0
Contingent Features
Margin deposit assets	3,100,000	4,200,000
Non-designated as hedging instruments due to regulatory accounting | Commodity contracts | Gas
Fair value of derivative financial instruments
Current assets	79,000	3,000
Non-current assets and deferred charges- Other		17,000
Current liabilities		104,000
Non-designated as hedging instruments due to regulatory accounting | Commodity contracts | Electric
Fair value of derivative financial instruments
Current assets	821,000	93,000
Non-current assets and deferred charges- Other	256,000	174,000
Current liabilities	1,905,000	3,299,000
Non-current liabilities and deferred credits	$ 3,307,000	$ 3,819,000