Derivative and Hedging Instruments (Details-3) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Regulatory Asset [Member]
Derivative Unrealized Realized Gains Losses On Balance Sheet [Line Items]
Beginning balance,	$ 66,649	$ 79,362	$ 72,329	$ 42,356
Change in unrealized loss (gain)	2,330	(468)	(1,330)	42,633
Realized loss reclassified to a deferred account	(275)	(223)	(953)	(3,103)
Realized gain (loss) reclassified to income statement	(621)	(3,414)	(1,963)	(6,629)
Ending balance,	68,083	75,257	68,083	75,257
Other Current Assets [Member]
Derivative Unrealized Realized Gains Losses On Balance Sheet [Line Items]
Beginning balance,	658	718	574	1,604
Change in unrealized loss (gain)	0	0	0	0
Realized loss reclassified to a deferred account	275	223	953	3,103
Realized gain (loss) reclassified to income statement	(111)	(161)	(705)	(3,927)
Ending balance,	$ 822	$ 780	$ 822	$ 780