Represents the threshold period of notice required for termination of agreement.

No definition available.

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

- Definition

Amount to be paid upon exercise of an option by the customer.

+ References

No definition available.

+ Details

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

- Definition

Amount of milestone payment under revenue from contract with customer.

+ References

No definition available.

+ Details

Name:	bcyc_RevenueFromContractWithCustomerMilestonePayment
Namespace Prefix:	bcyc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

No definition available.

+ Details

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

- Definition

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=126919976&loc=SL49130531-203044

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130549-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=126919976&loc=SL49130532-203044

+ Details

Name:	us-gaap_ContractWithCustomerLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of revenue recognized 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130549-203045

+ Details

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

- Details

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

- Details

Name:	bcyc_AchievementOfMilestoneAxis=bcyc_DevelopmentMilestoneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	bcyc_AchievementOfMilestoneAxis=bcyc_RegulatoryMilestoneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	bcyc_AchievementOfMilestoneAxis=bcyc_GrantingFirstRegulatoryApprovalOrFirstIndicationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Significant agreements - Oxurion Collaboration Agreement (Details) € in Millions	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2022 EUR (€)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2022 EUR (€)
Significant agreements.
Deferred revenue \| $	$ 61,873,000		$ 71,340,000	$ 35,156,000
Oxurion
Significant agreements.
Threshold period of notice required for termination of agreement	90 days	90 days
Revenue recognized \| $	$ 0		$ 0	$ 2,400,000
Deferred revenue \| $	$ 0
Oxurion \| Development milestone
Significant agreements.
Potential milestone payments					€ 8.3
Revenue under contracts with customer from milestone payment		€ 3.8
Oxurion \| Regulatory milestone
Significant agreements.
Potential milestone payments					16.5
Oxurion \| Granting first regulatory approval or first indication
Significant agreements.
Potential milestone payments					€ 5.0