CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Comprehensive income:
Net income	$ 97,299	$ 95,407	$ 213,904	$ 188,692
Derivative instruments:
Net fair value decrease, net of tax of $(11), $(11,485), $(7), and $(3,513), respectively	(20)	(18,757)	(13)	(5,737)
Reclassification of gains to net income, net of tax of $(71), $(230), $(145), and $(460), respectively	(118)	(376)	(236)	(751)
Other comprehensive loss	(138)	(19,133)	(249)	(6,488)
Comprehensive income	$ 97,161	$ 76,274	$ 213,655	$ 182,204