Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Current and Long-Term Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 36,924	$ 45,316	$ 41,958	$ 49,281
Unrealized loss (gain)	(2,007)	(1,277)	(5,906)	(3,698)
Realized (loss) gain reclassified to a deferred account	(316)	(313)	(837)	(935)
Realized gain (loss) reclassified to income statement	29	(1,450)	(585)	(2,372)
Ending balance,	34,630	42,276	34,630	42,276
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	640	618	806	230
Unrealized loss (gain)	0	0	0	0
Realized (loss) gain reclassified to a deferred account	316	313	837	935
Realized gain (loss) reclassified to income statement	(62)	(57)	(749)	(291)
Ending balance,	$ 894	$ 874	$ 894	$ 874

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- Definition

Change in realized derivative gains and losses deferred.

+ References

No definition available.

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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