Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Current and Long-Term Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 50,521	$ 56,048	$ 54,082	$ 54,998
Unrealized (gain) loss	(663)	4,036	1,128	8,514
Realized gain (loss) reclassified to a deferred account	17	(408)	(1,417)	(1,700)
Realized (loss) gain reclassified to income statement	(304)	(2,278)	(4,222)	(4,414)
Ending balance,	49,571	57,398	49,571	57,398
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	659	455	1,208	1,001
Unrealized (gain) loss	0	0	0	0
Realized gain (loss) reclassified to a deferred account	(17)	408	1,417	1,700
Realized (loss) gain reclassified to income statement	46	(91)	(1,937)	(1,929)
Ending balance,	$ 688	$ 772	$ 688	$ 772