Significant agreements - Revenue recognition due to changes in contract assets and liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Significant agreements
Revenue recognized based on proportional performance	$ 19,160	$ 12,358	$ 9,652
Revenue recognized based on expiration of material rights	7,816	1,433	1,876
Revenue recognized based on changes in transaction price		672	169
Total	$ 26,976	$ 14,463	$ 11,697

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