Quarterly report pursuant to Section 13 or 15(d)

Document and Entity Information

Document and Entity Information - shares
9 Months Ended
Sep. 30, 2019
Oct. 31, 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 CBAY  
Entity Registrant Name CYMABAY THERAPEUTICS, INC.  
Entity Central Index Key 0001042074  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Current Reporting Status Yes  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Common Stock, Shares Outstanding   68,701,043
Entity Shell Company false  
Entity File Number 001-36500  
Entity Tax Identification Number 94-3103561  
Entity Address, Address Line One 7575 Gateway Blvd  
Entity Address, Address Line Two Suite 110  
Entity Address, City or Town Newark  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 94560  
City Area Code 510  
Local Phone Number 293-8800  
Entity Interactive Data Current Yes  
Title of 12(b) Security Common stock, $0.0001 par value per share  
Security Exchange Name NASDAQ  
Entity Incorporation, State or Country Code DE  
Document Quarterly Report true  
Document Transition Report false