Derivative and Hedging Instruments (Details-2) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Commodity Derivative Contracts [Member]
Offsetting Assets [Line Items]
Gross amounts	$ 676	$ 1,384
Gross amounts offset in balance sheet	(654)	(218)
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	22	1,166
Financial Transmission Rights [Member]
Offsetting Assets [Line Items]
Gross amounts	329	143
Gross amounts offset in balance sheet	0	0
Collateral posted against derivative positions	0	0
Net amount presented in balance sheet	$ 329	$ 143

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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