Common Stock Shares Reserved for Issuance.

No definition available.

Name:	bcab_CommonSharesReservedForIssuance
Namespace Prefix:	bcab_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair Value Of Vested Liability Assumed Additional Paid In Capital.

+ References

No definition available.

+ Details

Name:	bcab_FairValueOfVestedLiabilityAssumedAdditionalPaidInCapital
Namespace Prefix:	bcab_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair Value Of Vested Liability Assumed by Himalaya Parent LLC

+ References

No definition available.

+ Details

Name:	bcab_FairValueOfVestedLiabilityAssumedByHimalayaParentLlc
Namespace Prefix:	bcab_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Increase (Decrease) In Profits Interest Liability

+ References

No definition available.

+ Details

Name:	bcab_IncreaseDecreaseInProfitsInterestLiability
Namespace Prefix:	bcab_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reduction to aggregate profits interest liability

+ References

No definition available.

+ Details

Name:	bcab_ReductionToAggregateProfitsInterestLiability
Namespace Prefix:	bcab_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Stock Based Compensation Expense And Additional Paid-In Capital Related To Fair Value Of Unvested Liability

+ References

No definition available.

+ Details

Name:	bcab_StockBasedCompensationExpenseAndAdditionalPaidInCapitalRelatedToFairValueOfUnvestedLiability
Namespace Prefix:	bcab_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=122041274&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Profits interest incentive plan - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of vested Class B units assumed by BioAtla Holdings and Inversagen		$ (991,000)
Share-based payment arrangement, expense		(6,852,000)	$ (6,403,000)
Reduction to aggregate profits interest liability as part of LLC Division			(900,000)
Increase (decrease) in profits interest liability			(7,400,000)
Class B Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair Value Of Vested Liability Assumed by Himalaya Parent LLC		1,000,000.0
Fair value of vested Class B units assumed by BioAtla Holdings and Inversagen			800,000
Stock-based compensation expense and additional paid-in capital related to fair value of unvested liability			$ 200,000
Class B Units reserved for issuance			16,665,977
Share-based payment arrangement, expense		$ 700,000
Vesting period	4 years