v3.25.1
Cover Page - shares
shares in Millions
3 Months Ended
Mar. 31, 2025
Apr. 30, 2025
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2025  
Document Transition Report false  
Entity File Number 001-38897  
Entity Registrant Name FASTLY, INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 27-5411834  
Entity Address, Address Line One 475 Brannan Street, Suite 300  
Entity Address, City or Town San Francisco  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 94107  
City Area Code 844  
Local Phone Number 432-7859  
Title of 12(b) Security Class A Common Stock, $0.00002 par value  
Trading Symbol FSLY  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   144.8
Entity Central Index Key 0001517413  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q1  
Amendment Flag false