Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Aug. 08, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Trading Symbol STRO  
Entity Registrant Name SUTRO BIOPHARMA, INC.  
Entity Central Index Key 0001382101  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity Current Reporting Status Yes  
Entity Shell Company false  
Entity File Number 001-38662  
Entity Tax Identification Number 470926186  
Entity Address, Address Line One 310 Utah Avenue  
Entity Address, Address Line Two Suite 150  
Entity Address, City or Town South San Francisco  
Entity Address, State or Province California  
Entity Address, Postal Zip Code 94080  
City Area Code 650  
Local Phone Number 392-8412  
Entity Common Stock, Shares Outstanding   22,927,863