v3.26.1
Cover - shares
 3 Months Ended
Mar. 31, 2026
May 07, 2026
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2026  
Document Transition Report false  
Entity File Number 001-38542  
Entity Registrant Name Kezar Life Sciences, Inc.  
Entity Incorporation, State or Country Code DE  
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  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   7,387,701
Entity Central Index Key 0001645666  
Current Fiscal Year End Date --12-31  
Amendment Flag false  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Common Stock    
Document Information [Line Items]    
Title of 12(b) Security Common Stock, $0.001 par value  
Trading Symbol KZR  
Security Exchange Name NASDAQ  
Preferred Share Purchase Right    
Document Information [Line Items]    
Title of 12(b) Security Preferred Share Purchase Rights  
No Trading Symbol Flag true  
Security Exchange Name NASDAQ