Document And Entity Information - USD ($)	12 Months Ended
	Aug. 31, 2018	Oct. 24, 2018	Feb. 28, 2018
Document Information [Line Items]
Entity Registrant Name	FACTSET RESEARCH SYSTEMS INC
Entity Central Index Key	0001013237
Trading Symbol	fds
Current Fiscal Year End Date	--08-31
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding (in shares)		38,037,295
Entity Public Float			$ 7,767,417,390
Document Type	10-K
Document Period End Date	Aug. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Shell Company	false