Employee Stock Option And Retirement Plans (Summary Of Stock Option Activity) (Details) (USD $)	3 Months Ended	12 Months Ended						12 Months Ended
	May 31, 2010	Aug. 31, 2011	Aug. 31, 2010		Aug. 31, 2009	Aug. 31, 2008	Aug. 31, 2007	Aug. 31, 2011 Non-Performance Based [Member]	Aug. 31, 2010 Non-Performance Based [Member]	Aug. 31, 2009 Non-Performance Based [Member]		Aug. 31, 2011 Performance Based [Member]	Aug. 31, 2010 Performance Based [Member]	Aug. 31, 2011 Non-Employee Directors Grant [Member]	Aug. 31, 2010 Non-Employee Directors Grant [Member]	Aug. 31, 2009 Non-Employee Directors Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number Outstanding, Beginning Balance		6,451,000	7,553,000			8,916,000
Weighted Average Exercise Price Per Share, Beginning Balance		$ 47.73	$ 39.51			$ 40.11
Stock options granted to existing employees	0							91,000	329,000	330,000		892,000	1,721,000	15,000	19,000	69,000
Weighted Average Exercise Price Per Share, Granted		$ 89.39	$ 66.35		$ 36.00			$ 89.45	$ 63.42	$ 36.00		$ 89.39	$ 66.91	$ 95.05	$ 66.81	$ 42.09
Number Outstanding, Exercised		(1,209,000)	(1,980,000)							(797,000)
Weighted Average Exercise Price Per Share, Exercised		$ 32.08	$ 25.77							$ 22.23
Number Outstanding, Forfeited		(108,000)	(1,191,000)	[1]						(965,000)	[2]
Weighted Average Exercise Price Per Share, Forfeited		$ 66.55	$ 64.47	[1]						$ 58.31	[2]
Number outstanding, Ending Balance		6,132,000	6,451,000			8,916,000
Weighted Average Exercise Price Per Share, Ending Balance		$ 57.28	$ 47.73			$ 40.11
Number of shares available for grant						1,058,981	896,194

[1] In August 2008, the Company granted 1,058,981 performance-based employee stock options. None of these performance-based stock options granted vested because FactSet did not achieve certain performance levels for both organic ASV and diluted earnings per share during the two fiscal years ended August 31, 2010. As such, these performance-based stock options were recorded as forfeitures in August 2010.

[2] In August 2007, the Company granted 896,194 performance-based employee stock options. None of these performance-based stock options granted vested because FactSet did not achieve certain performance levels for both organic ASV and diluted earnings per share during the two fiscal years ended August 31, 2009. As such, these performance-based stock options were recorded as forfeitures in August 2009.