Cover - shares	6 Months Ended
	Feb. 28, 2021	Mar. 31, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Feb. 28, 2021
Document Transition Report	false
Entity File Number	1-11869
Entity Registrant Name	FACTSET RESEARCH SYSTEMS INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-3362547
Entity Address, Address Line One	45 Glover Avenue
Entity Address, City or Town	Norwalk
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06850
City Area Code	203
Local Phone Number	810-1000
Title of 12(b) Security	Common Stock, $0.01 Par Value
Trading Symbol	FDS
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		37,852,172
Entity Central Index Key	0001013237
Current Fiscal Year End Date	--08-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false
New York Stock Exchange LLC
Entity Information [Line Items]
Security Exchange Name	NYSE
The Nasdaq Stock Market
Entity Information [Line Items]
Security Exchange Name	NASDAQ