Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Components of comprehensive income:
Net income	$ 507,673	$ 419,373	$ 307,498
Unrealized losses on cash flow hedges, net of tax	0	4,992	3,551
Reclassification adjustment for unrealized losses on cash flow hedges, net of tax, included in net income	2,970	0	0
Other comprehensive income	2,970	4,992	3,551
Total comprehensive income	$ 510,643	$ 424,365	$ 311,049