Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Collateral posted against derivative positions	$ 0	$ (1,000)
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	218	1,336
Gross amounts offset in balance sheet	(218)	(290)
Collateral posted against derivative positions	0	(1,038)
Net amount presented in the balance sheet	0	8
PPA [Member]
Offsetting Liabilities [Line Items]
Gross amounts	50,590	53,270
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in the balance sheet	$ 50,590	$ 53,270