Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 53,966	$ 58,213	$ 54,998	$ 63,893
Unrealized loss (gain)	3,160	(9,817)	4,478	(23,418)
Realized gain (loss) reclassified to a deferred account	(231)	(101)	(1,292)	1,434
Realized gain (loss) reclassified to income statement	(847)	559	(2,136)	6,945
Ending balance,	56,048	48,854	56,048	48,854
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	268	351	1,001	411
Unrealized loss (gain)	0	0	0	0
Realized gain (loss) reclassified to a deferred account	231	101	1,292	(1,434)
Realized gain (loss) reclassified to income statement	(44)	224	(1,838)	1,699
Ending balance,	$ 455	$ 676	$ 455	$ 676