Long-term debt (Details) $ in Millions	9 Months Ended
Sep. 30, 2020 USD ($)
Debt Instrument [Line Items]
Borrowing option to prepay subject to minimum debt outstanding	$ 5.0
End term charge rate	5.00%
Additional interest rate event of default	5.00%
Prepayment occurs in first year
Debt Instrument [Line Items]
Prepayment rate	2.00%
Prepayment occurs in second year
Debt Instrument [Line Items]
Prepayment rate	1.50%
Prepayment occurs in after year two
Debt Instrument [Line Items]
Prepayment rate	1.00%
Prime Rate
Debt Instrument [Line Items]
Debt instrument stated percentage	8.85%
Basis spread variable rate	5.60%
Initial Term Loan
Debt Instrument [Line Items]
Fees and transaction costs	$ 0.6
Debt instrument effective percentage	12.10%
Loan and Security Agreement \| Term Loan
Debt Instrument [Line Items]
Maximum borrowing	$ 40.0
Loan and Security Agreement \| Initial Term Loan
Debt Instrument [Line Items]
Term loan	15.0
Loan and Security Agreement \| Additional Term Loan One
Debt Instrument [Line Items]
Term loan	15.0
Loan and Security Agreement \| Additional Term Loan Two
Debt Instrument [Line Items]
Term loan	$ 10.0

The rate at which additional interest charged on the outstanding principle and interest in the event of default.

No definition available.

Name:	bcyc_DebtInstrumentAdditionalInterestRateEventOfDefault
Namespace Prefix:	bcyc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The rate at which entity has to pay end term charge on the principle amount.

+ References

No definition available.

+ Details

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Namespace Prefix:	bcyc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The minimum outstanding amount should be required for the borrower has the option to prepay the liability.

+ References

No definition available.

+ Details

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

- Definition

The rate at which entity has to repay on the outstanding debt.

+ References

No definition available.

+ Details

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Namespace Prefix:	bcyc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

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

- Definition

Amount of the fee that accompanies borrowing money under the debt instrument.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentFeeAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 835
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-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Details

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- Details

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- Details

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- Details

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Data Type:	na
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Data Type:	na
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- Details

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- Details

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