Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net income	$ 54,971	$ 47,396	$ 41,296
Reclassification adjustments for loss included in net income or reclassified to regulatory asset or liability		5,814	13,568
Net change in fair market value of open derivative contracts for period		(6,362)	(9,576)
Income taxes		209	(1,521)
Comprehensive income	$ 54,971	$ 47,057	$ 43,767