CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Comprehensive income:
Net income	$ 22,200	$ 19,973	$ 42,820	$ 43,094
Derivative instruments:
Reclassification of losses to net income, net of tax of $12, $13, $37 and $38, respectively	20	19	58	57
Other comprehensive income	20	19	58	57
Comprehensive income	$ 22,220	$ 19,992	$ 42,878	$ 43,151