Significant agreements - Revenue recognition due to changes in contract assets and liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Significant agreements
Revenue recognized based on proportional performance	$ 9,652	$ 6,326	$ 429
Revenue recognized based on expiration of material rights	1,876	1,702	9,984
Revenue recognized based on changes in transaction price	169
Total	$ 11,697	$ 8,028	$ 10,413

Amount of revenue recognized based on proportional performance that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

No definition available.

Name:	bcyc_ContractWithCustomerLiabilityRevenueRecognizedProportionalPerformanceObligation
Namespace Prefix:	bcyc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration