Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 12, 2021
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Entity File Number	001-39787
Entity Registrant Name	BIOATLA, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	85-1922320
Entity Address, Address Line One	11085 Torreyana Road
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	858
Local Phone Number	558-0708
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	BCAB
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Central Index Key	0001826892
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Common Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		1,492,059
Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		35,343,790