Note 15 - Income Taxes (Details) (USD $)	3 Months Ended			6 Months Ended
	Feb. 28, 2015		Feb. 28, 2014	Feb. 28, 2015		Feb. 28, 2014	Aug. 31, 2014
Income Tax Disclosure [Abstract]
Tax Adjustments, Settlements, and Unusual Provisions	$ (5,100,000)
Effective Income Tax Rate Reconciliation, Percent	24.10%	[1]	30.50%	27.40%	[1]	30.50%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				35.00%		35.00%
Unrecognized Tax Benefits	6,907,000			6,907,000			5,501,000
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	1,400,000			1,400,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 500,000			$ 500,000

[1] On December 16, 2014, the U.S. Congress passed the Tax Increase Prevention Act of 2014 (the "ACT"), which President Obama signed into law on December 19, 2014. The ACT reinstated the U.S. Federal R&D tax credit, which had previously expired on December 31, 2013. The reenactment of the credit was retroactive to January 1, 2014 and extended through the end of the 2014 calendar year. Prior to the reenactment of the tax credit, FactSet had not been permitted to factor it into its effective tax rate because it was not currently enacted tax law. The reenactment resulted in a discrete income tax benefit of $5.1 million during the second quarter of fiscal 2015 and reduced the Company's annual effective tax rate to 30.4%.