Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Offsetting Liabilities [Line Items]
Collateral posted against derivative positions	$ (900)	$ (2,200)
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	1,436	2,433
Gross amounts offset in balance sheet	(525)	(223)
Collateral posted against derivative positions	(908)	(2,179)
Net amount presented in balance sheet	3	31
Purchased Power Agreement [Member]
Offsetting Liabilities [Line Items]
Gross amounts	55,950	53,430
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 55,950	$ 53,430