Unaudited Quarterly Financial Data (Schedule Of Quarterly Financial Data) (Details) (USD $) In Thousands, except Per Share data	3 Months Ended								12 Months Ended
	Aug. 31, 2011	May 31, 2011	Feb. 28, 2011	Nov. 30, 2010	Aug. 31, 2010	May 31, 2010	Feb. 28, 2010	Nov. 30, 2009	Aug. 31, 2011		Aug. 31, 2010		Aug. 31, 2009
Unaudited Quarterly Financial Data [Abstract]
Revenues	$ 191,939	$ 183,647	$ 177,635	$ 173,289	$ 168,234	$ 160,301	$ 157,281	$ 155,243	$ 726,510	[1]	$ 641,059	[1]	$ 622,023	[1]
Cost of services	65,477	62,224	60,137	56,785	53,918	51,355	50,870	50,407	244,623		206,550		209,364
Selling, general and administrative	67,472	59,600	59,405	57,075	56,886	53,262	51,938	50,789	243,552		212,875		201,629
Operating income	58,990	61,823	58,093	59,429	57,430	55,684	54,473	54,047	238,335		221,634		211,030
Net income	$ 40,880	$ 43,311	$ 45,254	$ 41,601	$ 39,291	$ 38,658	$ 36,119	$ 36,143	$ 171,046		$ 150,211		$ 144,950
Diluted earnings per common share	$ 0.88	$ 0.92	$ 0.95	$ 0.88	$ 0.83	$ 0.81	$ 0.75	$ 0.74	$ 3.61		$ 3.13		$ 2.97
Weighted average common shares (diluted)	46,595	47,154	47,427	47,487	47,280	47,725	48,066	48,876	47,355		48,004		48,789

[1] Revenues are attributed to countries based on the location of the client.