Summary Of Quarterly Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary Of Quarterly Data [Abstract]
Revenue	$ 354,073	$ 338,297	$ 352,583	$ 332,106	$ 319,538	$ 315,475	$ 335,649	$ 322,676	$ 1,377,058	$ 1,293,338	$ 1,218,689
Gross profit	188,665	185,783	197,698	183,974	169,050	170,635	184,689	174,774	756,118	699,148	646,506
Operating income	61,328	65,485	78,763	61,188	63,427	62,912	75,817	60,407	266,762	262,563	236,225
Net income attributable to stockholders	$ 43,258	$ 45,688	$ 53,995	$ 44,860	$ 43,354	$ 42,853	$ 51,317	$ 40,743	$ 187,800	$ 178,267	$ 161,786
Earnings per Share:
Basic	$ 0.83	$ 0.87	$ 1.01	$ 0.82	$ 0.79	$ 0.78	$ 0.93	$ 0.74	$ 3.53	$ 3.24	$ 2.85
Diluted	$ 0.82	$ 0.86	$ 0.99	$ 0.81	$ 0.78	$ 0.76	$ 0.91	$ 0.72	$ 3.48	$ 3.17	$ 2.78