CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Comprehensive income:
Net income	$ 116,605	$ 93,285
Derivative instruments:
Net fair value increase, net of tax of $4 and $7,972, respectively	7	13,020
Reclassification of gains to net income, net of tax of $(74) and $(230), respectively	(118)	(375)
Total derivative instruments, net of tax	(111)	12,645
Other comprehensive (loss) income	(111)	12,645
Comprehensive income	$ 116,494	$ 105,930