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Document and Entity Information - shares
 6 Months Ended
Jun. 30, 2019
Jul. 26, 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 CBIO  
Entity Registrant Name CATALYST BIOSCIENCES, INC.  
Entity Central Index Key 0001124105  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
Entity Common Stock, Shares Outstanding   12,015,921
Entity Current Reporting Status Yes  
Entity Shell Company false  
Entity File Number 000-51173  
Entity Tax Identification Number 562020050  
Entity Address, Address Line One 611 Gateway Blvd.  
Entity Address, Address Line Two Suite 710  
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 871-0761