Derivative and Hedging Instruments (Details-3) (USD $)			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Commodity Derivative Contracts [Member] Regulated Gas Revenues [Member]	Sep. 30, 2011 Commodity Derivative Contracts [Member] Regulated Gas Revenues [Member]	Sep. 30, 2012 Commodity Derivative Contracts [Member] Regulated Gas Revenues [Member]	Sep. 30, 2011 Commodity Derivative Contracts [Member] Regulated Gas Revenues [Member]	Sep. 30, 2012 Commodity Derivative Contracts [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2011 Commodity Derivative Contracts [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2012 Commodity Derivative Contracts [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2011 Commodity Derivative Contracts [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2012 Commodity Derivative Contracts [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2011 Commodity Derivative Contracts [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2012 Commodity Derivative Contracts [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2011 Commodity Derivative Contracts [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2012 Financial Transmission Rights [Member] Regulated Gas Revenues [Member]	Sep. 30, 2011 Financial Transmission Rights [Member] Regulated Gas Revenues [Member]	Sep. 30, 2012 Financial Transmission Rights [Member] Regulated Gas Revenues [Member]	Sep. 30, 2011 Financial Transmission Rights [Member] Regulated Gas Revenues [Member]	Sep. 30, 2012 Financial Transmission Rights [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2011 Financial Transmission Rights [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2012 Financial Transmission Rights [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2011 Financial Transmission Rights [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2012 Financial Transmission Rights [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2011 Financial Transmission Rights [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2012 Financial Transmission Rights [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2011 Financial Transmission Rights [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2012 Purchased Power Agreement [Member] Regulated Gas Revenues [Member]	Sep. 30, 2011 Purchased Power Agreement [Member] Regulated Gas Revenues [Member]	Sep. 30, 2012 Purchased Power Agreement [Member] Regulated Gas Revenues [Member]	Sep. 30, 2011 Purchased Power Agreement [Member] Regulated Gas Revenues [Member]	Sep. 30, 2012 Purchased Power Agreement [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2011 Purchased Power Agreement [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2012 Purchased Power Agreement [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2011 Purchased Power Agreement [Member] Fuel For Electric Generation Purchased Power [Member]	Sep. 30, 2012 Purchased Power Agreement [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2011 Purchased Power Agreement [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2012 Purchased Power Agreement [Member] Cost Of Gas Sold Expense [Member]	Sep. 30, 2011 Purchased Power Agreement [Member] Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement			$ 0	$ 0	$ 0	$ 0	$ 176,000	$ (94,000)	$ 2,685,000	$ (465,000)	$ 0	$ 0	$ 3,090,000	$ 1,315,000	$ 0	$ 0	$ 0	$ 0	$ (256,000)	$ (23,000)	$ (93,000)	$ 5,000	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 3,655,000	$ 0	$ 4,874,000	$ 0	$ 0	$ 0	$ 0	$ 0
Derivative collateral required to be posted for ten-year PPA [Abstract]
Minimum collateral required	20,000,000
Maximum collateral required	40,000,000
Required collateral posted	0
Counterparties in net liability position [Abstract]
Counterparties in net liability position	$ 0	$ 0