Annual report pursuant to Section 13 and 15(d)

Cover Page

Cover Page - USD ($)
12 Months Ended
Dec. 31, 2019
Feb. 29, 2020
Jun. 28, 2019
Document Information [Line Items]      
Document Type 10-K/A    
Amendment Flag true    
Document Period End Date Dec. 31, 2019    
Document Fiscal Year Focus 2019    
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 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   68,882,459  
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     $ 487,988,477
Amendment Description CymaBay Therapeutics, Inc. (“CymaBay,” “the Company,” “we,” “us,” or “our”) filed its Annual Report on Form 10-K for the fiscal year ended December 31, 2019 (the “Form 10-K”) with the U.S. Securities and Exchange Commission (the “SEC”) on March 16, 2020. The Company is filing this Amendment No. 1 on Form 10-K/A (the “Form 10-K/A”) for the purpose of including in Part III the information that was to be incorporated by reference from its definitive proxy statement for the 2020 annual meeting of stockholders. This Form 10-K/A amends and restates in their entirety Items 10 through 14 of Part III of the Form 10-K. In addition, the reference on the cover of the Form 10-K to the incorporation by reference of the Company’s Proxy Statement for its 2020 Annual Meeting of Stockholders into Part III of the Form 10-K is hereby amended to delete that reference. In addition, Item 15 of Part IV of the Form 10-K is amended and restated in its entirety to file new certifications by our principal executive officer and principal financial officer as required by Rule 12b-15 under the Securities Exchange Act of 1934, as amended.Except as expressly noted in this Form 10-K/A, this Form 10-K/A does not reflect events occurring after the original filing of the Form 10-K or modify or update in any way any of the other disclosures contained in the Form 10-K including, without limitation, the financial statements. Accordingly, this Form 10-K/A should be read in conjunction with the Form 10-K and the Company’s other filings with the SEC.