Derivative and Hedging Instruments (Details-4) (USD $)			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Commodity Derivative Contracts [Member] Regulated Gas Revenues [Member]	Mar. 31, 2012 Commodity Derivative Contracts [Member] Regulated Gas Revenues [Member]	Mar. 31, 2013 Commodity Derivative Contracts [Member] Fuel For Electric Generation Purchased Power [Member]	Mar. 31, 2012 Commodity Derivative Contracts [Member] Fuel For Electric Generation Purchased Power [Member]	Mar. 31, 2013 Commodity Derivative Contracts [Member] Cost Of Gas Sold Expense [Member]	Mar. 31, 2012 Commodity Derivative Contracts [Member] Cost Of Gas Sold Expense [Member]	Mar. 31, 2013 Financial Transmission Rights [Member] Regulated Gas Revenues [Member]	Mar. 31, 2012 Financial Transmission Rights [Member] Regulated Gas Revenues [Member]	Mar. 31, 2013 Financial Transmission Rights [Member] Fuel For Electric Generation Purchased Power [Member]	Mar. 31, 2012 Financial Transmission Rights [Member] Fuel For Electric Generation Purchased Power [Member]	Mar. 31, 2013 Financial Transmission Rights [Member] Cost Of Gas Sold Expense [Member]	Mar. 31, 2012 Financial Transmission Rights [Member] Cost Of Gas Sold Expense [Member]	Mar. 31, 2013 Purchased Power Agreement [Member] Regulated Gas Revenues [Member]	Mar. 31, 2012 Purchased Power Agreement [Member] Regulated Gas Revenues [Member]	Mar. 31, 2013 Purchased Power Agreement [Member] Fuel For Electric Generation Purchased Power [Member]	Mar. 31, 2012 Purchased Power Agreement [Member] Fuel For Electric Generation Purchased Power [Member]	Mar. 31, 2013 Purchased Power Agreement [Member] Cost Of Gas Sold Expense [Member]	Mar. 31, 2012 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	$ 22,000	$ 1,928,000	$ 608,000	$ 3,090,000	$ 0	$ 0	$ (158,000)	$ 66,000	$ 0	$ 0	$ 0	$ 0	$ 1,278,000	$ 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