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Summary of Warrant Activity (Parenthetical) (Detail) - shares | 1 Months Ended | 12 Months Ended
--- | --- | ---
Nov. 30, 2018 | Apr. 30, 2018 | Dec. 31, 2018
Class Of Warrant Or Right [Line Items] |  |  |
Number of shares of warrants forfeited/cancelled |  | 4,250 | 6,095
Healthcare Ventures VIII |  |  |
Class Of Warrant Or Right [Line Items] |  |  |
Number of shares of warrants forfeited/cancelled | 1,845 |  |

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- Definition Class of warrant or right, forfeited during period. + References No definition available. + Details
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Namespace Prefix: | cbio_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- 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

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- Details
Name: | dei_LegalEntityAxis=cbio_HealthcareVenturesVIIIMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |