Derivative and Hedging Instruments (Details-3) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Commodity Derivative Contracts [Member]
Offsetting Liabilities [Line Items]
Gross amounts	$ 212	$ 342
Gross amounts offset in balance sheet	(212)	(342)
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	0	0
Purchased Power Agreement [Member]
Offsetting Liabilities [Line Items]
Gross amounts	31,610	32,530
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 31,610	$ 32,530

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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Fair value of asset associated with 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.

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