Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Contract revenue				$ 6
Type of Revenue [Extensible List]	cbio:ContractMember	cbio:ContractMember	cbio:ContractMember	cbio:ContractMember
Operating expenses:
Research and development	$ 11,111	$ 3,889	$ 23,138	$ 7,660
General and administrative	3,270	3,225	6,956	6,139
Total operating expenses	14,381	7,114	30,094	13,799
Loss from operations	(14,381)	(7,114)	(30,094)	(13,793)
Interest and other income, net	601	632	1,232	2,269
Net loss	$ (13,780)	$ (6,482)	$ (28,862)	$ (11,524)
Net loss per share attributable to common stockholders, basic and diluted	$ (1.15)	$ (0.54)	$ (2.41)	$ (1.10)
Shares used to compute net loss per share attributable to common stockholders, basic and diluted	11,989,866	11,938,401	11,976,799	10,472,180

Interest and other income (expense), net.

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.

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The net result for the period of deducting operating expenses from operating revenues.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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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.

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Indicates type of revenue from product and service.

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Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

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