Employee Stock Option And Retirement Plans (Summary Of Share-Based Awards Available For Grant) (Details)	3 Months Ended			12 Months Ended																															12 Months Ended
	May 31, 2010	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 Non-Performance Based [Member] Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]	Aug. 31, 2010 Non-Performance Based [Member] Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]	Aug. 31, 2009 Non-Performance Based [Member] Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]	Aug. 31, 2011 Non-Performance Based [Member] Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]	Aug. 31, 2010 Non-Performance Based [Member] Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]	Aug. 31, 2009 Non-Performance Based [Member] Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]	Aug. 31, 2011 Performance Based [Member]	Aug. 31, 2010 Performance Based [Member]	Aug. 31, 2011 Performance Based [Member] Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]	Aug. 31, 2010 Performance Based [Member] Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]	Aug. 31, 2011 Performance Based [Member] Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]	Aug. 31, 2010 Performance Based [Member] Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [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]	Aug. 31, 2011 Non-Employee Directors Grant [Member] Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]	Aug. 31, 2010 Non-Employee Directors Grant [Member] Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]	Aug. 31, 2009 Non-Employee Directors Grant [Member] Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]	Aug. 31, 2011 Non-Employee Directors Grant [Member] Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]	Aug. 31, 2010 Non-Employee Directors Grant [Member] Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]	Aug. 31, 2009 Non-Employee Directors Grant [Member] Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]	Aug. 31, 2011 2004 Stock Option And Award Plan [Member]	Dec. 14, 2010 2004 Stock Option And Award Plan [Member]	Nov. 30, 2009 2004 Stock Option And Award Plan [Member]	Aug. 31, 2011 2004 Stock Option And Award Plan [Member] Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]		Aug. 31, 2011 2004 Stock Option And Award Plan [Member] Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]		Aug. 31, 2011 Restricted Stock [Member]	Aug. 31, 2011 Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]		Aug. 31, 2010 Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]		Aug. 31, 2009 Share-Based Awards Available For Grant Under Employee Stock Option Plans [Member]		Aug. 31, 2011 Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]		Aug. 31, 2010 Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]		Aug. 31, 2009 Share-Based Awards Available For Grant Under Non-Employee Stock Option Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant		1,058,981	896,194																											1,000,000						2,216,000		4,124,000		3,489,000		162,000		181,000		0
Performance-based employee stock options granted	0			91,000	329,000	330,000	(91,000)	(329,000)	(330,000)		0	0	892,000	1,721,000	(892,000)	(1,721,000)		0	15,000	19,000	69,000	0	0	0	(15,000)	(19,000)	(69,000)													0						250,000
Restricted stock awards granted																																			2.5	(386,000)	[1]	(667,000)	[1]	0	[1]		[1]	0	[1]	0	[1]
Share-based awards canceled/forfeited																																				130,000		1,204,000		965,000				0		0
Share-based awards expired																																						(395,000)	[2]					0	[2]
Number of shares available for grant		1,058,981	896,194																											1,000,000						4,977,000		2,216,000		4,124,000		147,000		162,000		181,000
Common stock reserved for issuance																												4,000,000	4,000,000		4,000,000	[3]	0	[3]

[1] For each share awarded as restricted stock under the Company's Option Plans, an equivalent of 2.5 shares were deducted from the available share-based awards balance.

[2] Represents the remaining stock options available for grant within the Company's 2000 Stock Option plan that expired in January 2010 because they were never granted.

[3] As of November 30, 2010, 1.0 million shares remained available for future grant of share-based awards under the Company's 2004 Stock Option and Award Plan, a number that the Company believed to be insufficient to meet its anticipated needs over the next 12 to 18 months. Therefore, the Company's Board of Directors approved, subject to stockholder approval, an amendment to increase the maximum number of shares of FactSet common stock issuable under the 2004 Stock Option and Award Plan by 4,000,000 shares. The stockholders of FactSet voted on and approved the Amended and Restated FactSet Research Systems Inc. 2004 Stock Option and Award Plan at the Company's annual meeting held on December 14, 2010, including the reservation of an additional 4,000,000 shares of common stock for issuance.