Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2024	Aug. 01, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
Entity Registrant Name	Personalis, Inc.
Entity Central Index Key	0001527753
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		53,074,698
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38943
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-5411038
Entity Address, Address Line One	6600 Dumbarton Circle
Entity Address, City or Town	Fremont
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94555
City Area Code	650
Local Phone Number	752-1300
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, par value $0.0001
Trading Symbol	PSNL
Security Exchange Name	NASDAQ