Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Current and Long-Term Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 49,281	$ 54,082
Unrealized (gain) loss	(689)	6,371
Realized (loss) gain reclassified to a deferred account	(78)	(1,451)
Realized loss reclassified to income statement	(441)	(2,118)
Ending balance,	48,073	56,884
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	230	1,208
Unrealized (gain) loss	0	0
Realized (loss) gain reclassified to a deferred account	78	1,451
Realized loss reclassified to income statement	(166)	(2,004)
Ending balance,	$ 142	$ 655