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Summary of Significant Accounting Polices - Grant Awards (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Summary of Significant Accounting Policies |  |  |
Grants from Muscular Dystrophy Association | $ 124,000 | $ 376,000 | $ 100,000
Grants utilized to offset related expenses | $ 205,000 | $ 224,000 | $ 100,000

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- Definition Grants recorded as reduction in research and development expenses + References No definition available. + Details
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Namespace Prefix: | catb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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- Definition Revenue earned during the period from non-repayable sum of money awarded to an entity to carry out a specific purpose as provided in grant agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1(e)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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Period Type: | duration