CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Other comprehensive income (loss)
Net income	$ 93,285	$ 96,630
Derivative instruments:
Net fair value increase, net of tax of $7,972 and $60, respectively	13,020	98
Reclassification of gains to net income, net of tax of $(230) and $(219), respectively	(375)	(357)
Total derivative instruments, net of tax	12,645	(259)
Other comprehensive income (loss)	12,645	(259)
Comprehensive income	$ 105,930	$ 96,371