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Cover Page
Jan. 11, 2021
Jan. 10, 2021
Cover [Abstract]    
Document Type 8-K  
Document Period End Date   Jan. 10, 2021
Entity Registrant Name EXELIXIS, INC.  
Entity Incorporation, State or Country Code DE  
Entity File Number 000-30235  
Entity Tax Identification Number 04-3257395  
Entity Address, Address Line One 1851 Harbor Bay Parkway  
Entity Address, City or Town Alameda  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 94502  
City Area Code 650  
Local Phone Number 837-7000  
Written Communications false  
Soliciting Material false  
Pre-commencement Tender Offer false  
Pre-commencement Issuer Tender Offer false  
Title of 12(b) Security Common Stock $.001 Par Value per Share  
Trading Symbol EXEL  
Security Exchange Name NASDAQ  
Entity Emerging Growth Company false  
Amendment Flag false  
Entity Central Index Key 0000939767