v3.19.1
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2018
Mar. 04, 2019
Jun. 30, 2018
Document and Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus Q4    
Trading Symbol GH    
Entity Registrant Name Guardant Health, Inc.    
Entity Central Index Key 0001576280    
Current Fiscal Year End Date --12-31    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company true    
Entity Ex Transition Period false    
Entity Shell Company false    
Entity Common Stock, Shares Outstanding   85,928,193  
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 0