Document And Entity Information - USD ($)	12 Months Ended
	Aug. 31, 2017	Oct. 25, 2017	Feb. 28, 2017
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 Common Stock, Shares Outstanding (in shares)		39,109,746
Entity Public Float			$ 6,862,902,916
Document Type	10-K
Document Period End Date	Aug. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Amendment Flag	false