Summary of Significant Accounting Polices - Grant Awards (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Significant Accounting Policies
Grants from Muscular Dystrophy Association	$ 376,000	$ 100,000	$ 0

Grants recorded as reduction in research and development expenses

No definition available.

Name:	catb_GrantOffsettingResearchAndDevelopmentExpenses
Namespace Prefix:	catb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant