Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022
Related Party Transaction [Line Items]
Research and development expense	$ 21,697	$ 16,923
Himalaya Therapeutics SEZC
Related Party Transaction [Line Items]
Description of agreement with related party	In April 2022, the Company entered into a Clinical Trial Agreement with Himalaya Therapeutics SEZC. Under the agreement, Himalaya Therapeutics SEZC agreed to provide services related to the initiation of clinical trials for BA3011 in the People’s Republic of China. For the first year following effectiveness of the agreement, the Company has agreed to pay Himalaya Therapeutics SEZC for the full-time use of two of its personnel. Payments are due and payable by BioAtla to Himalaya Therapeutics SEZC on a quarterly calendar basis and are non-refundable. For the three months ended March 31, 2023, the Company recognized $0.1 million in research and development expense related to the Clinical Trial Agreement. The Company did not have any amounts due from or due to Himalaya Therapeutics SEZC as of March 31, 2023.
Research and development expense	$ 100

The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 912
-SubTopic 730
-Section 25
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6472174&loc=d3e58812-109433

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 10
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

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