Document And Entity Information	12 Months Ended
	Aug. 31, 2019	Oct. 24, 2019 shares	Feb. 28, 2019 USD ($)	Nov. 08, 2016
Document Information [Line Items]
Entity Central Index Key	0001013237
Entity Registrant Name	FACTSET RESEARCH SYSTEMS INC
Amendment Flag	false
Current Fiscal Year End Date	--08-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2019
Document Type	10-K
Document Annual Report	true
Document Period End Date	Aug. 31, 2019
Document Transition Report	false
Entity File Number	1-11869
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-3362547
Entity Address, Address Line One	601 Merritt 7
Entity Address, City or Town	Norwalk
Entity Address, State or Province	CT
Entity Address, Postal Zip Code	06851
City Area Code	203
Local Phone Number	810-1000
Title of 12(b) Security	Common Stock
Trading Symbol	FDS
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
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 Public Float | $			$ 8,808,676,952
Entity Common Stock, Shares Outstanding | shares		37,944,709
Vermilion Holdings Limited [Member]
Document Information [Line Items]
Entity Number of Employees				59