Document and Entity Information - shares
9 Months Ended
Sep. 30, 2018
Oct. 31, 2018
Document and Entity Information [Abstract]    
Entity Registrant Name FIREEYE, INC.  
Entity Central Index Key 0001370880  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Document Type 10-Q  
Document Period End Date Sep. 30, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q3  
Emerging Growth Company false  
Small Business false  
Amendment Flag false  
Entity Common Stock, Shares Outstanding   197,014,986