Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Nov. 05, 2019
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Trading Symbol SYBX  
Entity Registrant Name SYNLOGIC, INC.  
Security Exchange Name NASDAQ  
Entity Central Index Key 0001527599  
Entity Current Reporting Status Yes  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Shell Company false  
Entity Small Business true  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Title of 12(b) Security Common Stock  
Entity Common Stock, Shares Outstanding   32,290,814
Entity Address, State or Province MA  
Entity File Number 001-37566  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 26-1824804  
Entity Address, Address Line One 301 Binney St.  
Entity Address, Address Line Two Suite 402  
Entity Address, City or Town Cambridge  
Entity Address, Postal Zip Code 02142  
City Area Code 617  
Local Phone Number 401-9975  
Entity Interactive Data Current Yes  
Document Quarterly Report true  
Document Transition Report false