Number of collaboration targets under the collaboration agreement.

No definition available.

Name:	bcyc_CollaborationAgreementNumberOfTargets
Namespace Prefix:	bcyc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of upfront cash payment received from collaborative arrangement.

+ References

No definition available.

+ Details

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

- Definition

The number of payments of a mid-single-digit million dollar, failing to achieve the specified development diligence.

+ References

No definition available.

+ Details

Name:	bcyc_NumberOfPaymentsOfMidSingleDigitMillionDollarFailingToAchieveSpecifiedDevelopmentDiligenceMilestone
Namespace Prefix:	bcyc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents number of years over which royalty is payable.

+ References

No definition available.

+ Details

Name:	bcyc_NumberOfYearsOverWhichRoyaltyIsPayable
Namespace Prefix:	bcyc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period for which the company will perform research and discovery activities including a baseline level of effort for no additional consideration, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	bcyc_PeriodForWhichResearchAndDiscoveryActivitiesWillBePerformedWithNoAdditionalConsideration
Namespace Prefix:	bcyc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 808
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479402/808-10-50-1

+ Details

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

- Details

Name:	us-gaap_TypeOfArrangementAxis=bcyc_IonisCollaborationAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=bcyc_AmendedIonisCollaborationAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=bcyc_ThirdIonisAmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Significant agreements - Ionis Collaboration Agreement (Details) $ in Millions		1 Months Ended
	Jul. 09, 2021 USD ($) item	Apr. 30, 2023 USD ($)	Dec. 31, 2021 USD ($)
Ionis
Significant agreements.
Period for which research and discovery activities will be performed with no additional consideration	3 years
Upfront cash payment	$ 31.0
Number of payments of a mid-single-digit million dollar, failing to achieve the specified development diligence \| item	3
Number of collaboration targets \| item	4
Number of years over which royalty is payable	10 years
Amended Ionis
Significant agreements.
Upfront cash payment			$ 1.6
Third Ionis Amendment
Significant agreements.
Upfront cash payment		$ 0.8