Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Current and Long-Term Regulatory Asset [Member]
Change in Derivative Fair Value [Roll Forward]
Beginning balance	$ 54,998	$ 63,893
Unrealized loss (gain)	8,586	(14,518)
Realized (loss) gain reclassified to a deferred account	(2,953)	595
Realized (loss) gain reclassified to income statement	(6,549)	5,028
Ending balance	54,082	54,998
Other Current Assets [Member]
Change in Derivative Fair Value [Roll Forward]
Beginning balance	1,001	411
Unrealized loss (gain)	0	0
Realized (loss) gain reclassified to a deferred account	2,953	(595)
Realized (loss) gain reclassified to income statement	(2,746)	1,185
Ending balance	$ 1,208	$ 1,001