Annual report pursuant to Section 13 and 15(d)

Cover Page

Cover Page - USD ($)
12 Months Ended
Dec. 31, 2020
Feb. 28, 2021
Jun. 30, 2020
Document Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2020    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Trading Symbol CBAY    
Entity Registrant Name CYMABAY THERAPEUTICS, INC.    
Entity Central Index Key 0001042074    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer No    
Entity Filer Category Non-accelerated Filer    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Small Business true    
Entity Emerging Growth Company false    
Entity Common Stock, Shares Outstanding   68,946,092  
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 Annual Report true    
Document Transition Report false    
Entity Public Float     $ 238,474,701
ICFR Auditor Attestation Flag false