v2.4.1.9

Fair Value Measurements - Additional Information (Detail) (USD $) | 3 Months Ended | 12 Months Ended | 0 Months Ended | 1 Months Ended
--- | --- | --- | --- | ---
Jun. 30, 2014 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2014 CommercialTests | Jun. 30, 2014 | Apr. 17, 2014 | Jul. 31, 2014
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |  |  |  |  |  |
Transfers between Level 1, Level 2 and Level 3 categories during the periods |  | $ 0cdna_FairValueMeasurementsInterTransfersBetweenLevels |  |  |  |  |  |
Estimated fair value of embedded derivative liabilities | 239,000us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeNet |  |  |  |  | 239,000us-gaap_EmbeddedDerivativeFairValueOfEmbeddedDerivativeNet |  |
Fair value of derivative | 120,000us-gaap_DerivativeFairValueOfDerivativeNet |  |  |  |  | 120,000us-gaap_DerivativeFairValueOfDerivativeNet |  |
Gain on derivative | 119,000us-gaap_DerivativeGainLossOnDerivativeNet | (118,000)us-gaap_DerivativeGainLossOnDerivativeNet | 0us-gaap_DerivativeGainLossOnDerivativeNet | 0us-gaap_DerivativeGainLossOnDerivativeNet |  |  |  |
Illumina, Inc. [Member] |  |  |  |  |  |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |  |  |  |  |  |
Subordinated convertible promissory note issued |  |  |  |  |  |  | 5,000,000us-gaap_ConvertibleSubordinatedDebt / dei_LegalEntityAxis = cdna_IlluminaIncMember |
ImmuMetrix, Inc. [Member] |  |  |  |  |  |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |  |  |  |  |  |
Number of commercial tests involving the measurement of cfDNA to be completed |  | 2,500cdna_NumberOfCommercialTests / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember |  |  | 2,500cdna_NumberOfCommercialTests / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember |  |  |
Milestone description |  | The milestone will be achieved if the Company completes 2,500 commercial tests involving the measurement of cfDNA in organ transplant recipients in the United States no later than six years after the closing date of the acquisition. |  |  |  |  |  |
Contingent consideration maturity date |  | Jun. 10, 2020 |  |  |  |  |  |
IPO [Member] |  |  |  |  |  |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |  |  |  |  |  |
Change in control for repayment |  |  |  |  |  | 5.00%cdna_ChangeInControlForRepayment / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember | 10.00%cdna_ChangeInControlForRepayment / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember |
Fair value of derivative |  |  |  |  |  |  |  | 0us-gaap_DerivativeFairValueOfDerivativeNet / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember
Gain on derivative |  |  |  |  |  |  |  | $ 120,000us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember
Contingent consideration [Member] | ImmuMetrix, Inc. [Member] |  |  |  |  |  |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |  |  |  |  |  |
Contingent obligation to issue common stock |  |  |  |  | 227,845us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember / us-gaap_ContingentConsiderationByTypeAxis = cdna_ContingentPaymentMember |  |  |
Milestone description |  | The issuance will occur if the Company completes 2,500 commercial tests involving the measurement of cfDNA in organ transplant recipients in the United States by June 10, 2020. |  |  |  |  |  |
Probability of the achievement |  |  |  |  | 65.00%cdna_FairValueInputProbabilityOfAchievement / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember / us-gaap_ContingentConsiderationByTypeAxis = cdna_ContingentPaymentMember |  |  |

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