Segment Information - Schedule of Segment expenses reviewed by the CDMO (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Segment Reporting Information [Line Items]
Collaboration and other revenue	$ 0	$ 11,000	$ 0	$ 11,000
Research and development expense	9,539	16,395	35,578	51,445
General and administrative expense	4,250	5,875	14,472	17,254
Net loss and comprehensive loss	(15,778)	(10,586)	(49,823)	(54,892)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Collaboration and other revenue	0	11,000	0	11,000
Research and development expense	9,539	16,395	35,578	51,445
General and administrative expense	4,250	5,875	14,472	17,254
Interest and other income (loss)	(1,989)	684	227	2,807
Net loss and comprehensive loss	(15,778)	(10,586)	(49,823)	(54,892)
Operating Segments [Member] | Total program expenses
Segment Reporting Information [Line Items]
Research and development expense	6,231	11,425	23,607	35,511
Operating Segments [Member] | Personnel and related
Segment Reporting Information [Line Items]
Research and development expense	2,109	2,970	7,712	9,740
General and administrative expense	1,577	1,951	5,257	5,857
Operating Segments [Member] | Equity-based compensation
Segment Reporting Information [Line Items]
Research and development expense	491	1,071	1,833	3,314
General and administrative expense	801	1,123	2,481	3,676
Operating Segments [Member] | Facilities and other
Segment Reporting Information [Line Items]
Research and development expense	708	929	2,426	2,880
General and administrative expense	1,872	2,801	6,734	7,721
Operating Segments [Member] | Mecbotamab vedotin, BA3011 | Total program expenses
Segment Reporting Information [Line Items]
Research and development expense	1,315	2,770	7,307	11,603
Operating Segments [Member] | Ozuriftamab vedotin, BA3021 | Total program expenses
Segment Reporting Information [Line Items]
Research and development expense	824	2,593	4,109	7,157
Operating Segments [Member] | Evalstotug, BA3071 | Total program expenses
Segment Reporting Information [Line Items]
Research and development expense	734	2,095	3,958	7,150
Operating Segments [Member] | BA3182 | Total program expenses
Segment Reporting Information [Line Items]
Research and development expense	2,384	1,352	5,460	3,728
Operating Segments [Member] | Other CAB Programs | Total program expenses
Segment Reporting Information [Line Items]
Research and development expense	$ 974	$ 2,615	$ 2,773	$ 5,873