Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Current and Long-Term Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 54,083	$ 54,998
Unrealized loss	6,370	1,318
Realized gain (loss) reclassified to a deferred account	(1,451)	(1,061)
Realized loss reclassified to income statement	(2,118)	(1,289)
Ending balance,	56,884	53,966
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	1,208	1,001
Unrealized loss	0	0
Realized gain (loss) reclassified to a deferred account	1,451	1,061
Realized loss reclassified to income statement	(2,004)	(1,794)
Ending balance,	$ 655	$ 268