Document and Entity Information Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2017
Feb. 19, 2018
Dec. 29, 2017
Document and Entity Information [Abstract]      
Entity Registrant Name FORESCOUT TECHNOLOGIES, INC    
Entity Central Index Key 0001145057    
Current Fiscal Year End Date --12-31    
Entity Filer Category Non-accelerated Filer    
Document Type 10-K    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Common Stock, Shares Outstanding   38,367,757  
Entity Public Float     $ 493,541,535