Quarterly report pursuant to Section 13 or 15(d)

Document and Entity Information

Document and Entity Information - shares
6 Months Ended
Jun. 30, 2021
Aug. 06, 2021
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2021  
Document Fiscal Year Focus 2021  
Document Fiscal Period Focus Q2  
Trading Symbol KZR  
Entity Registrant Name Kezar Life Sciences, Inc.  
Entity Central Index Key 0001645666  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Emerging Growth Company true  
Entity Small Business true  
Entity Ex Transition Period true  
Entity Common Stock, Shares Outstanding   48,192,840
Entity Current Reporting Status Yes  
Entity Shell Company false  
Entity File Number 001-38542  
Entity Tax Identification Number 47-3366145  
Entity Address, Address Line One 4000 Shoreline Court  
Entity Address, Address Line Two Suite 300  
Entity Address, City or Town South San Francisco  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 94080  
City Area Code 650  
Local Phone Number 822-5600  
Document Quarterly Report true  
Document Transition Report false  
Entity Interactive Data Current Yes  
Title of 12(b) Security Common Stock, $0.001 par value  
Security Exchange Name NASDAQ  
Entity Incorporation, State or Country Code DE