v3.10.0.1
Document and Entity Information - shares
6 Months Ended
Jun. 30, 2018
Aug. 10, 2018
Document And Entity Information [Abstract]    
Trading Symbol SESN  
Entity Registrant Name Sesen Bio, Inc.  
Entity Central Index Key 0001485003  
Current Fiscal Year End Date --12-31  
Entity Filer Category Smaller Reporting Company  
Document Type 10-Q  
Document Period End Date Jun. 30, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Entity Common Stock, Shares Outstanding   77,010,999