Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Collateral posted against derivative positions	$ (1,000)	$ (1,000)
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	1,487	1,336
Gross amounts offset in balance sheet	(494)	(290)
Collateral posted against derivative positions	(989)	(1,038)
Net amount presented in balance sheet	4	8
Purchased Power Agreement [Member]
Offsetting Liabilities [Line Items]
Gross amounts	55,910	53,270
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 55,910	$ 53,270