Amount payable to other party on first anniversary in settlement of litigation agreement.

No definition available.

Name:	bcyc_LitigationSettlementAmountPayableOnFirstAnniversary
Namespace Prefix:	bcyc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount payable to for the achievement of various milestones.

+ References

No definition available.

+ Details

Name:	bcyc_SettlementAgreementMilestonePayments
Namespace Prefix:	bcyc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of litigation expense, including but not limited to legal, forensic, accounting, and investigative fees.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of cash paid for the settlement of litigation or for other legal issues during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3536-108585

+ Details

Name:	us-gaap_PaymentsForLegalSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Commitments and Contingencies - Legal proceedings (Details) € in Millions, $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2020 EUR (€)	Dec. 31, 2020 USD ($)	Dec. 31, 2021 EUR (€)	Dec. 31, 2021 USD ($)
Commitments and Contingencies
Payments for Legal Settlements \| €	€ 3
Settlement payable on first anniversary \| €			€ 1
Milestone payments \| $				$ 92.4
Litigation settlement amount \| $		$ 4.7