Comprehensive Income Differences Between Net Income And Comprehensive Income (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Net income	$ 42,302	$ 40,494	$ 85,610	$ 83,298
Other Comprehensive Income (Loss), Net of Tax
Settlement of forward starting interest rate swap agreement	0	(8,663)	0	(8,663)
Amortization of loss on cash flow hedge	215	117	646	117
Foreign currency translation adjustment, net	(1,167)	1,851	(164)	668
Actuarial pension loss, net of tax	0	0	(10)	0
Other comprehensive income (loss), net of tax	(952)	(6,695)	472	(7,878)
Comprehensive income	$ 41,350	$ 33,799	$ 86,082	$ 75,420