Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	$ 342	$ 793
Gross amounts offset in balance sheet	(342)	(654)
Collateral posted against derivative positions	0	(139)
Net amount presented in the balance sheet	0	0
PPA [Member]
Offsetting Liabilities [Line Items]
Gross amounts	32,530	42,170
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in the balance sheet	$ 32,530	$ 42,170

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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