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

No definition available.

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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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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

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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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- Definition

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

+ References

No definition available.

+ Details

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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
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+ Details

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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
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-Paragraph 1
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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
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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
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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

Aggregate amount of interest paid or due on all long-term debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.8)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

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Name:	us-gaap_InterestExpenseLongTermDebt
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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
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-SubTopic 10
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-Paragraph 1
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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Long-term debt (Details) - USD ($) $ in Millions	12 Months Ended
Long-term debt (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
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 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	12.20%
Interest expense	$ 0.4
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