Note 17 - Income Taxes - Percentage of Income Before Income Taxes (Details)		12 Months Ended
		Aug. 31, 2018	Aug. 31, 2018 Rate	Dec. 31, 2017	Aug. 31, 2017	Aug. 31, 2017 Rate		Aug. 31, 2016	Aug. 31, 2016 Rate
Tax at U.S. Federal statutory tax rate (Rate)		25.70%	25.70%	35.00%		35.00%			35.00%
Increase (decrease) in taxes resulting from:
State and local taxes, net of U.S. federal income tax benefit (Rate)			2.90%			1.80%			1.50%
Foreign income at other than U.S. rates (Rate)			(3.20%)			(7.00%)	[1]		(5.00%)	[2]
Domestic production activities deduction (Rate)			(1.60%)			(2.10%)			(1.50%)
Income tax benefits from R&D tax credits (Rate)			(3.70%)			(3.30%)			(3.60%)
Income tax benefits from foreign tax credits (Rate)						(0.30%)			(0.20%)
Share-Based Payments(1) (Rate)	[3]		(2.70%)
One-time transition tax from TCJA(2) (Rate)	[4]		6.60%
Other, net (Rate)			0.10%			0.90%			0.30%
Effective Income Tax Rate Reconciliation, Percent, Total		24.10%	24.10%		25.00%	25.00%		26.50%	26.50%	[5]

[1] Includes a 200 basis point benefit as a result of FactSet's global realignment. Effective September 1, 2016, FactSet realigned certain aspects of its global operations from FactSet Research Systems Inc., its U.S. parent company, to FactSet UK Limited, a U.K. operating company, to better position the Company to serve its growing client base outside the U.S. This realignment allows the Company to further implement strategic corporate objectives and helps achieve operational and financial efficiencies, while complementing FactSet's increasing global growth and reach.

[2] Includes a portion of the gain from the sale of the Market Metrics business that was not taxable in the UK

[3] During the first quarter of fiscal 2018, FactSet adopted an accounting standard that requires all excess tax benefits or deficiencies related to share-based payments to be reported within the consolidated statement of income that were previously reported within equity. The adoption of this standard resulted in the recognition of $9.5 million of excess tax benefits to FactSet's provision for income taxes during fiscal 2018.

[4] The enactment of the TCJA resulted in a one-time transition tax expense of $23.2 million during the second quarter of fiscal 2018.

[5] The fiscal 2016 effective tax rate of 26.5% includes income tax benefits of $10.5 million primarily from the permanent reenactment of the U.S. Federal R&D Tax Credit ("R&D tax credit") in December 2015, finalizing the fiscal 2015 tax returns and other discrete items. The reenactment of the R&D tax credit was retroactive to January 1, 2015, and eliminates the yearly uncertainty surrounding the extension of the credit.