v2.4.1.9

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] |  |  |
Balance at beginning of year | $ 2,196us-gaap_UnrecognizedTaxBenefits | $ 1,159us-gaap_UnrecognizedTaxBenefits | $ 1,130us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions related to current year | 83us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 177us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 53us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions
Additions (reductions) based on tax positions related to prior years | (225)cdna_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions | 860cdna_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions | (24)cdna_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions
Balance at end of year | $ 2,054us-gaap_UnrecognizedTaxBenefits | $ 2,196us-gaap_UnrecognizedTaxBenefits | $ 1,159us-gaap_UnrecognizedTaxBenefits

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- Definition Unrecognized tax benefits increase decrease resulting from prior period tax positions. + References No definition available. + Details
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Namespace Prefix: | cdna_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Unrecognized Tax Benefit -URI http://asc.fasb.org/extlink&oid=6527854 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
Name: | us-gaap_UnrecognizedTaxBenefits
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Balance Type: | credit
Period Type: | instant

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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
Name: | us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration