v3.8.0.1
Document and Entity Information - shares
6 Months Ended
Mar. 31, 2018
Apr. 13, 2018
Document And Entity Information [Abstract]    
Entity Registrant Name FAIR ISAAC CORP  
Trading Symbol FICO  
Entity Central Index Key 0000814547  
Current Fiscal Year End Date --09-30  
Entity Filer Category Large Accelerated Filer  
Document Type 10-Q  
Document Period End Date Mar. 31, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Entity Common Stock, Shares Outstanding   29,840,374