Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components of Comprehensive Income
Net income	$ 585,746	$ 507,673	$ 419,373
Unrealized losses on cash flow hedges, net of tax	0	0	4,992
Reclassification adjustment for unrealized losses on cash flow hedges, net of tax, included in net income	0	2,970	0
Other comprehensive income	0	2,970	4,992
Total comprehensive income	$ 585,746	$ 510,643	$ 424,365