Derivative and Hedging Instruments (Details-4) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Regulatory Asset [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	$ 56,048	$ 48,853	$ 54,998	$ 63,893
Unrealized loss (gain)	4,036	5,329	8,514	(18,090)
Realized gain (loss) reclassified to a deferred account	(408)	(314)	(1,700)	1,120
Realized gain (loss) reclassified to income statement	(2,278)	(1,184)	(4,414)	5,761
Ending balance,	57,398	52,684	57,398	52,684
Other Current Assets [Member]
Change In Derivative Fair Value [Roll Forward]
Beginning balance,	455	676	1,001	411
Unrealized loss (gain)	0	0	0	0
Realized gain (loss) reclassified to a deferred account	408	314	1,700	(1,120)
Realized gain (loss) reclassified to income statement	(91)	(249)	(1,929)	1,450
Ending balance,	$ 772	$ 741	$ 772	$ 741