Document and Entity Information (USD $)	12 Months Ended
	Sep. 30, 2011	Oct. 31, 2011	Mar. 31, 2011
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	FY
Trading Symbol	FICO
Entity Registrant Name	Fair Isaac Corporation
Entity Central Index Key	0000814547
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		35,701,425
Entity Public Float			$ 540,420,207