Additional research term.

No definition available.

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

- Definition

AstraZeneca research term.

+ References

No definition available.

+ Details

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

- Definition

Bicycle research term.

+ References

No definition available.

+ Details

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

- Definition

Amount of regulatory, development, commercialization or sales milestone payments, receivable by the entity.

+ References

No definition available.

+ Details

Name:	bcyc_CollaborationAgreementSalesMilestonePaymentsReceivable
Namespace Prefix:	bcyc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the number of biological targets.

+ References

No definition available.

+ Details

Name:	bcyc_CollaborativeArrangementNumberOfBiologicalTargets
Namespace Prefix:	bcyc_
Data Type:	xbrli:integerItemType
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

Represents the number of FTE required to be funded by counterparty.

+ References

No definition available.

+ Details

Name:	bcyc_NumberOfFte
Namespace Prefix:	bcyc_
Data Type:	xbrli:integerItemType
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_OptionFeeForDevelopmentAndExploitationRights
Namespace Prefix:	bcyc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Research term.

+ References

No definition available.

+ Details

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

- Definition

Amount of allocated determined transaction price under revenue recognition arrangement.

+ References

No definition available.

+ Details

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

- 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, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8906-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9031-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9038-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130543-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8736-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130545-203045

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI https://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

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

- Details

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

- Details

Name:	us-gaap_GainContingenciesByNatureAxis=us-gaap_ResearchAndDevelopmentArrangementMember
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:	us-gaap_GainContingenciesByNatureAxis=us-gaap_FavorableRegulatoryActionMember
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:	us-gaap_GainContingenciesByNatureAxis=bcyc_CommercialMilestoneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis=bcyc_RespiratoryCardiovascularAndMetabolicMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis=bcyc_AdditionalFourTargetsOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	bcyc_AchievementOfMilestoneAxis=us-gaap_LicenseAgreementTermsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=bcyc_TargetThreeResearchLicenseAndRelatedServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=bcyc_TargetThreeMaterialRightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=bcyc_TargetFourMaterialRightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=bcyc_TargetFiveMaterialRightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=bcyc_TargetSixMaterialRightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Significant agreements - AstraZeneca Collaboration Agreement (Details) $ in Thousands		1 Months Ended		12 Months Ended
	May 31, 2018 USD ($)	May 31, 2018 USD ($) item	Nov. 30, 2016 item	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2019 USD ($)
Significant agreements.
Collaboration revenues				$ 14,463	$ 11,697	$ 10,390
Deferred revenue				61,873	71,340	35,156
AstraZeneca
Significant agreements.
Option fee for development and exploitation rights		$ 5,000
Research term	3 years
Bicycle research term	1 year
AstraZeneca research	2 years
Additional research term	12 months
Transaction price	$ 5,700	5,700
Collaboration revenues				1,165	1,404	2,696
Deferred revenue				1,076	$ 2,361	$ 3,756
AstraZeneca \| Development Milestone
Significant agreements.
Transaction price	700	700
AstraZeneca \| Development Milestone \| Development milestone
Significant agreements.
Milestone payments, receivable	29,000	29,000
AstraZeneca \| Regulatory Milestone \| Regulatory milestone
Significant agreements.
Milestone payments, receivable	23,000	23,000
AstraZeneca \| Commercial milestone \| Commercial milestone
Significant agreements.
Milestone payments, receivable	$ 110,000	110,000
AstraZeneca \| Maximum
Significant agreements.
Additional research term	15 months
AstraZeneca \| 2016 Collaboration Agreement
Significant agreements.
Biological Targets \| item			2
AstraZeneca \| May 2018 Option Exercise
Significant agreements.
Option fee for development and exploitation rights		$ 5,000
Number of FTE \| item		2
Transaction price				5,650			$ 6,300
AstraZeneca \| May 2018 Option Exercise \| Commercialization license per candidate
Significant agreements.
Customer option payment	$ 8,000	$ 8,000
AstraZeneca \| May 2018 Option Exercise \| Target Three Research License and Related Services
Significant agreements.
Transaction price				650
AstraZeneca \| May 2018 Option Exercise \| Target 3 Material Right
Significant agreements.
Transaction price				1,504
AstraZeneca \| May 2018 Option Exercise \| Target 4 Material Right
Significant agreements.
Transaction price				1,204
AstraZeneca \| May 2018 Option Exercise \| Target 5 Material Right
Significant agreements.
Transaction price				1,165
AstraZeneca \| May 2018 Option Exercise \| Target 6 Material Right
Significant agreements.
Transaction price				$ 1,127