Commercial milestone payments.

No definition available.

Name:	cbio_CommercialMilestonePayments
Namespace Prefix:	cbio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Commitments and contingencies disclosure.

+ References

No definition available.

+ Details

Name:	cbio_CommitmentsAndContingenciesDisclosureLineItems
Namespace Prefix:	cbio_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

License fees payable.

+ References

No definition available.

+ Details

Name:	cbio_LicenseFeesPayable
Namespace Prefix:	cbio_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Milestone and royalty payments obligation.

+ References

No definition available.

+ Details

Name:	cbio_MilestoneAndRoyaltyPaymentsObligation
Namespace Prefix:	cbio_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Milestone payments.

+ References

No definition available.

+ Details

Name:	cbio_MilestonePayments
Namespace Prefix:	cbio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Operating lease commencement date.

+ References

No definition available.

+ Details

Name:	cbio_OperatingLeaseCommencementDate
Namespace Prefix:	cbio_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Potential milestone payment.

+ References

No definition available.

+ Details

Name:	cbio_PotentialMilestonePayment
Namespace Prefix:	cbio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Regulatory and development milestone payment.

+ References

No definition available.

+ Details

Name:	cbio_RegulatoryAndDevelopmentMilestonePayment
Namespace Prefix:	cbio_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

+ References

No definition available.

+ Details

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

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Net rentable area for properties owned.

+ References

No definition available.

+ Details

Name:	us-gaap_NetRentableArea
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41499-112717

+ Details

Name:	us-gaap_OperatingLeasesRentExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	srt_StatementGeographicalAxis=cbio_SouthSanFranciscoCaliforniaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=cbio_NewOfficeLeaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LeaseArrangementTypeAxis=cbio_OfficeLeaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=cbio_PfizerIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=us-gaap_CollaborativeArrangementMember
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:	srt_CounterpartyNameAxis=cbio_AGCBiologicsIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	srt_CounterpartyNameAxis=cbio_IsuAbxisMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended			12 Months Ended
	Dec. 31, 2018 USD ($)	Feb. 28, 2018 USD ($)	Nov. 30, 2017 ft²	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2013 USD ($)	Aug. 10, 2018 ft²	Dec. 08, 2016 USD ($)	May 20, 2016 USD ($)
Commitments And Contingencies Disclosure [Line Items]
Operating lease rent expense				$ 400,000	$ 800,000
License fees payable						$ 100,000
South San Francisco, California \| New Office Lease Agreement
Commitments And Contingencies Disclosure [Line Items]
Leased area \| ft²			8,606
Operating lease term of contract			5 years 2 months
Operating lease commencement date			Feb. 16, 2018
South San Francisco, California \| Office Lease Agreement
Commitments And Contingencies Disclosure [Line Items]
Leased area \| ft²							4,626
Pfizer Inc \| Collaboration Agreement
Commitments And Contingencies Disclosure [Line Items]
Milestone payment		$ 1,000,000
Pfizer Inc \| Collaboration Agreement \| Maximum
Commitments And Contingencies Disclosure [Line Items]
Obligated to make milestone and royalty payments upon achievement of clinical, regulatory and commercial milestones								$ 17,500,000
AGC Biologics, Inc \| Dalcinonacog alfa (“DalcA”)
Commitments And Contingencies Disclosure [Line Items]
Contractual obligation payments	$ 3,400,000			3,400,000					$ 5,600,000
AGC Biologics, Inc \| MarzAA
Commitments And Contingencies Disclosure [Line Items]
Contractual obligation payments	300,000			300,000					$ 3,800,000
ISU Abxis \| Maximum
Commitments And Contingencies Disclosure [Line Items]
Potential milestone payments				$ 2,000,000
ISU Abxis \| Amended and Restated License Agreement
Commitments And Contingencies Disclosure [Line Items]
Regulatory and development milestone payment	2,500,000
ISU Abxis \| Amended and Restated License Agreement \| Maximum
Commitments And Contingencies Disclosure [Line Items]
Milestone payment	19,500,000
Commercial milestone payments	$ 17,000,000