Document And Entity Information (USD $)	12 Months Ended
	Aug. 31, 2012	Oct. 22, 2012	Feb. 29, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	FACTSET RESEARCH SYSTEMS INC
Document Type	10-K
Current Fiscal Year End Date	--08-31
Entity Common Stock, Shares Outstanding		44,259,635
Entity Public Float			$ 3,598,639,975
Amendment Flag	false
Entity Central Index Key	0001013237
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Document Period End Date	Aug. 31, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	FY