401(k) Plan (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
401 (k) Plan
Employer contribution (as a percent)			100.00%
Amount up to which the employer matches 100 percent contribution			$ 5,000
Total matching contributions	$ 100,000	$ 100,000	$ 500,000	$ 500,000

Maximum amount up to which the employer matches 100 percent contribution to employee's contribution, under a defined contribution plan.

No definition available.

Name:	bcel_DefinedContributionPlanEmployeeMatchingContributionThresholdAmount
Namespace Prefix:	bcel_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration