Derivative and Hedging Instruments (Details-5) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) counterparty	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) counterparty	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Counterparties in net liability position or default [Abstract]
Derivative, net liability position of counterparties (less than $0.1 million)	$ 100		$ 100		$ 100
Number of counterparties in default | counterparty	0		0
Commodity Derivative Contracts [Member] | Fuel For Electric Generation Purchased Power [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	$ 578	$ (1,061)	$ 998	$ (5,856)
Commodity Derivative Contracts [Member] | Cost Of Gas Sold Expense [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	(2)	(128)	1,759	(1,349)
Financial Transmission Rights [Member] | Fuel For Electric Generation Purchased Power [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	(255)	(196)	(374)	(832)
Financial Transmission Rights [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
Purchased Power Agreement [Member]
Derivative collateral required to be posted for PPA [Abstract]
Minimum collateral that may be required to be posted	20,000		20,000
Maximum collateral that may be required to be posted	40,000		40,000
Collateral posted	0		0
Purchased Power Agreement [Member] | Fuel For Electric Generation Purchased Power [Member]
Realized losses (gains) on income statement [Line Items]
Realized losses (gains) on income statement	570	602	1,591	(607)
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