Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Current and Long-Term Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 56,884	$ 53,966	$ 54,082	$ 54,998
Unrealized (gain) loss	(4,580)	3,160	1,791	4,478
Realized gain (loss) reclassified to a deferred account	17	(231)	(1,434)	(1,292)
Realized (loss) gain reclassified to income statement	(1,800)	(847)	(3,918)	(2,136)
Ending balance,	50,521	56,048	50,521	56,048
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	655	268	1,208	1,001
Unrealized (gain) loss	0	0	0	0
Realized gain (loss) reclassified to a deferred account	(17)	231	1,434	1,292
Realized (loss) gain reclassified to income statement	21	(44)	(1,983)	(1,838)
Ending balance,	$ 659	$ 455	$ 659	$ 455