Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Offsetting Liabilities [Line Items]
Collateral posted against derivative positions	$ (1,000)	$ (2,200)
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	1,336	2,433
Gross amounts offset in balance sheet	(290)	(223)
Collateral posted against derivative positions	(1,038)	(2,179)
Net amount presented in the balance sheet	8	31
PPA [Member]
Offsetting Liabilities [Line Items]
Gross amounts	53,270	53,430
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in the balance sheet	$ 53,270	$ 53,430