CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Comprehensive income:
Net income	$ 166,266	$ 192,443	$ 380,170	$ 381,135
Derivative instruments:
Net fair value increase (decrease), net of tax of $5, $(2,197), $(2), and $(5,710), respectively	11	(3,574)	(2)	(9,311)
Reclassification of gains to net income, net of tax of $(76), $(186), $(221), and $(646), respectively	(119)	(304)	(355)	(1,055)
Other comprehensive loss	(108)	(3,878)	(357)	(10,366)
Comprehensive income	$ 166,158	$ 188,565	$ 379,813	$ 370,769