Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Mar. 23, 2021	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Related Party Transaction [Line Items]
Related party transaction, terms and manner of settlement				(i) a lump sum payment equal to 18 months of Ms. Anderson Short’s then-current base salary, (ii) a payment at her targeted bonus rate for 2021, pro-rated to the date of her termination of employment, and (iii) full accelerated vesting of her equity awards including 7,747 stock options and 138,461 restricted stock units. The modification of these equity awards resulted in an incremental fair value of $7.0 million which was recognized on a straight-line basis over the transition service period which ended on the separation date. For the three and six months ended June 30, 2021, the Company recognized $0.8 million and $1.0 million, respectively, related to the lump sum salary payment and target bonus. The Company also recognized non-cash stock-based compensation charges of $8.4 million and $9.4 million related to the modified equity awards for the three and six months ended June 30, 2021, respectively. No unrecognized stock-based compensation remained as of June 30, 2021.
Non-cash stock-based compensation charges		$ 3,842	$ 12,298	$ 7,474	$ 16,941
Research and development expense		20,711	14,850	$ 37,634	25,273
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 BA3021 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 and six months ended June 30, 2022, 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 June 30, 2022.
Research and development expense		$ 100		$ 100
Carolyn Anderson Short
Related Party Transaction [Line Items]
Number of accelerated full vesting equity awards including stock options	7,747
Number of accelerated full vesting equity awards including restricted stock units	138,461
Incremental Fair Value				$ 7,000
Expense related to Lump Sum Salary Payment and Target Bonus			800		1,000
Non-cash stock-based compensation charges			8,400		9,400
Unrecognized stock-based compensation			$ 0		$ 0