Marketable Securities - Narrative (Details) - debtSecurity	Jun. 30, 2026	Dec. 31, 2025
Investments, Debt and Equity Securities [Abstract]
Number of securities held in unrealized loss position	19	0

Debt Securities, Available-for-Sale, Number Of Securities In Unrealized Loss Position

No definition available.

Name:	bcax_DebtSecuritiesAvailableForSaleNumberOfSecuritiesInUnrealizedLossPosition
Namespace Prefix:	bcax_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant