Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Current and Long-Term Regulatory Asset [Member]
Change in Derivative Fair Value [Roll Forward]
Beginning balance	$ 54,082	$ 54,998
Unrealized loss	1,575	8,586
Realized (loss) gain reclassified to a deferred account	(1,060)	(2,953)
Realized loss reclassified to income statement	(5,316)	(6,549)
Ending balance	49,281	54,082
Other Current Assets [Member]
Change in Derivative Fair Value [Roll Forward]
Beginning balance	1,208	1,001
Unrealized loss	0	0
Realized (loss) gain reclassified to a deferred account	1,060	2,953
Realized loss reclassified to income statement	(2,038)	(2,746)
Ending balance	$ 230	$ 1,208