Summary Of Quarterly Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary Of Quarterly Data [Abstract]
Revenue	$ 351,959	$ 383,523	$ 390,122	$ 360,203	$ 354,073	$ 338,297	$ 352,583	$ 332,106	$ 1,485,807	$ 1,377,058	$ 1,293,338
Gross profit	182,165	213,336	218,518	202,097	188,665	185,783	197,698	183,974	816,116	756,118	699,148
Operating income	34,801	72,189	83,219	70,046	61,328	65,485	78,763	61,188	260,255	266,762	262,563
Net income attributable to stockholders	$ 25,961	$ 52,142	$ 57,218	$ 46,585	$ 43,258	$ 45,688	$ 53,995	$ 44,860	$ 181,906	$ 187,800	$ 178,267
Earnings per Share:
Basic	$ 0.54	$ 1.05	$ 1.12	$ 0.90	$ 0.83	$ 0.87	$ 1.01	$ 0.82	$ 3.63	$ 3.53	$ 3.24
Diluted	$ 0.54	$ 1.03	$ 1.10	$ 0.89	$ 0.82	$ 0.86	$ 0.99	$ 0.81	$ 3.58	$ 3.48	$ 3.17