Note 13 - Employee Stock Option and Retirement Plans (Details) (USD $)	1 Months Ended	0 Months Ended			1 Months Ended		3 Months Ended				12 Months Ended						3 Months Ended	0 Months Ended		12 Months Ended			3 Months Ended	7 Months Ended	12 Months Ended		0 Months Ended				1 Months Ended	4 Months Ended	12 Months Ended		14 Months Ended			12 Months Ended				1 Months Ended					3 Months Ended	1 Months Ended			12 Months Ended
	Apr. 30, 2013	Jan. 15, 2013	Jan. 13, 2012	Jan. 14, 2011	Jul. 31, 2012	Nov. 30, 2010	Aug. 31, 2013	May 31, 2013	May 31, 2012	Feb. 29, 2012	Aug. 31, 2013		Aug. 31, 2012		Aug. 31, 2011	Dec. 16, 2008	Aug. 31, 2013 Unamortized [Member]	Feb. 09, 2010 Awards Granted Between June 2010 and July 2011 [Member] Restricted Stock [Member]	Aug. 31, 2013 Awards Granted Between June 2010 and July 2011 [Member] Restricted Stock [Member]	Aug. 31, 2013 Awards Granted on October 23, 2009 [Member] Restricted Stock [Member]	Aug. 31, 2013 In-The-Money Stock Options [Member]	Aug. 31, 2012 In-The-Money Stock Options [Member]	Aug. 31, 2013 July 2012 Performance Based Option Grant Review [Member]	Jul. 31, 2011 Other Performace-Based Options [Member]	Aug. 31, 2013 Other Performace-Based Options [Member]	Aug. 31, 2012 Other Performace-Based Options [Member]	Apr. 08, 2013 Restricted Stock [Member]	Apr. 14, 2011 Restricted Stock [Member]	Nov. 08, 2010 Restricted Stock [Member]	Feb. 09, 2010 Restricted Stock [Member]	Jan. 27, 2011 Restricted Stock [Member]	Aug. 31, 2012 Restricted Stock [Member]	Aug. 31, 2013 Restricted Stock [Member]	Aug. 31, 2012 Restricted Stock [Member]	Jul. 31, 2011 Restricted Stock [Member]	Feb. 09, 2013 Restricted Stock [Member]	Oct. 23, 2012 Restricted Stock [Member]	Aug. 31, 2013 Granted Without Performance Conditions [Member] Minimum [Member]	Aug. 31, 2013 Granted Without Performance Conditions [Member] Maximum [Member]	Aug. 31, 2013 Majority of Options Granted with Performance Conditions [Member] Minimum [Member]	Aug. 31, 2013 Majority of Options Granted with Performance Conditions [Member] Maximum [Member]	Jun. 30, 2010 Other Performace-Based Options [Member]	Aug. 31, 2013 Financial Performance Level One [Member]	Aug. 31, 2013 Financial Performance Level Two [Member]	Aug. 31, 2013 Financial Performance Level Three [Member]	Aug. 31, 2013 Financial Performance Level Four [Member]	Feb. 28, 2013 Additional Stock-Based Compensation [Member]	Nov. 30, 2010 November 2010 Annual Employee Performance-based Option Grant Review [Member]	Nov. 30, 2011 November 2011 Annual Employee Performance-based Option Grant Review [Member]	Nov. 30, 2012 November 2012 Annual Employee Performance-based Option Grant Review [Member]	Aug. 31, 2013 November 2012 Annual Employee Performance-based Option Grant Review [Member]	Aug. 31, 2013 Employee Stock Purchase Plan [Member]	Aug. 31, 2012 Employee Stock Purchase Plan [Member]	Aug. 31, 2011 Employee Stock Purchase Plan [Member]
Note 13 - Employee Stock Option and Retirement Plans (Details) [Line Items]
Stock Option Expiration Term																																						7 years	10 years	7 years	10 years
Stock Option Vesting Rate After First Year of Grant Date											20.00%
Stock Option Vesting Rate Per Month from Two Years through Five Years of Grant Date											1.67%
Stock Option Vesting Rate for First Two Years for Grant Date											40.00%
Stock Option Vesting Rate Per Month from Three Years through Five Years											1.67%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		18,781	20,976	14,514	241,546		0	0	0	0	1,674,966		1,468,513		998,038									229,635																		746,415						734,334	665,551	1,011,510
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit (in Dollars per share)											$ 88.40
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit (in Dollars per share)											$ 103.30
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value (in Dollars)							$ 82,082,000				$ 82,082,000										$ 82,100,000	$ 125,400,000
Share-Based Compensation Arrangement by Share-Based Payment Award Options Closing Share Price (in Dollars per share)							$ 102.35				$ 102.35
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value (in Dollars)											99,100,000		43,000,000		71,300,000
Vesting Percentage																			25.00%														40.00%			100.00%	60.00%						0.00%	20.00%	60.00%	100.00%
ASV Growth Rate													0.00%
Share-Based Compensation Expense Reversed (in Dollars)													1,400,000
Percent of Performance-Based Stock Options Expected to Vest																																																			20.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number							48,314				48,314														7,964																										202,302
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized (in Dollars)							10,400,000				10,400,000		39,200,000																																						3,600,000
Share-based Compensation (in Dollars)							2,600,000				39,951,000		21,982,000		25,773,000		1,200,000								100,000																						15,700,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition											4 years 219 days		3 years 36 days										4 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage											20.00%
Share-based Compensation Options Vested in Period																										133,958
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value (in Dollars)											53,285
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period											(743,000)		(786,000)		(108,000)										9,301
Performance Based Stock Options Outstanding Expected to be Forfeited							25,127				25,127
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period											150,000	[1]	14,000	[2]	0			6,411		87,758												14,258	149,741	14,258	21,102
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	131,702										132,000		0		154,000												131,702	30,090	117,723	55,572	366		131,702	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in Dollars per share)		$ 24.23	$ 24.79	$ 26.87																										$ 63.09
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in Dollars per share)	$ 85.80										$ 85.80		$ 0		$ 87.55												$ 85.80	$ 99.75	$ 84.38		$ 95.24
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant						1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized						4,000,000
Common Stock, Capital Shares Reserved for Future Issuance																500,000																																				119,770
Stock Issued During Period, Shares, Employee Stock Purchase Plans											2,459,000		825,000		1,283,000																																					75,281	85,487	75,718
Defined Contribution Plan, Employer Discretionary Contribution Amount (in Dollars)											$ 7,500,000		$ 6,700,000		$ 5,900,000

[1] Of the total 149,741 restricted stock awards that vested during fiscal 2013, 87,758 related to awards granted on October 23, 2009. These restricted stock awards cliff vested 60% after three years (on October 23, 2012) and the remaining 40% will vest after five years (on October 23, 2014). An additional 55,572 awards that vested in fiscal 2013 related to awards granted on February 9, 2010 at a price of $63.09. These restricted stock awards cliff vested 100% after three years (on February 9, 2013). The remaining 6,411 restricted stock awards that vested were previously granted between June 2010 and July 2011 and vesting occured when certain ASV targets were met in fiscal 2013.

[2] * Between June 2010 and July 2011, FactSet granted 21,102 restricted stock units which entitled the holder to shares of common stock as the awards vest. A restricted stock unit is a promise to deliver shares to the employee at a future date if certain vesting conditions are met. These restricted stock units are performance-based and cliff vest 25% when certain ASV targets are met. Of the total 21,102 units granted, 14,258 units vested during the fourth quarter of fiscal 2012 because FactSet achieved three of the four ASV growth targets.