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	$ 192,443	$ 140,718	$ 381,135	$ 308,366
Derivative instruments:
Net fair value decrease, net of tax of $(2,197), $(8,839), $(5,710) and $(8,788), respectively	(3,574)	(14,428)	(9,311)	(14,346)
Reclassification of gains to net income, net of tax of $(186), $(233), $(646) and $(691), respectively	(304)	(381)	(1,055)	(1,127)
Total derivative instruments, net of tax	(3,878)	(14,809)	(10,366)	(15,473)
Other comprehensive loss	(3,878)	(14,809)	(10,366)	(15,473)
Comprehensive income	$ 188,565	$ 125,909	$ 370,769	$ 292,893