v2.4.1.9

Organization and Description of Business - Additional Information (Detail) (USD $) | 0 Months Ended | 1 Months Ended | 12 Months Ended | 0 Months Ended
--- | --- | --- | --- | ---
Aug. 13, 2014 | Jul. 22, 2014 | Jul. 31, 2013 | Dec. 31, 2014 Segment | Dec. 31, 2013 | Dec. 31, 2012 | Jul. 01, 2014
Schedule of Capitalization, Equity [Line Items] |  |  |  |  |  |  |
Number of operating segment |  |  |  | 1us-gaap_NumberOfOperatingSegments |  |  |
Common stock, shares authorized |  |  |  | 100,000,000us-gaap_CommonStockSharesAuthorized | 7,737,226us-gaap_CommonStockSharesAuthorized |  |
Common stock, par value |  |  |  | $ 0.001us-gaap_CommonStockParOrStatedValuePerShare | $ 0.001us-gaap_CommonStockParOrStatedValuePerShare |  |
Convertible preferred stock, shares authorized |  |  |  | 0us-gaap_TemporaryEquitySharesAuthorized | 6,417,954us-gaap_TemporaryEquitySharesAuthorized |  |
Convertible preferred stock, par value |  |  |  | $ 0.001us-gaap_TemporaryEquityParOrStatedValuePerShare | $ 0.001us-gaap_TemporaryEquityParOrStatedValuePerShare |  |
Issuance of additional shares pursuant to exercise of underwriters' overallotment option | 220,000cdna_SaleOfStockPursuantToExerciseOfUnderwritersOverAllotmentOption |  |  |  |  |  |
Underwriting discounts and commissions |  |  |  | $ 3,733,000us-gaap_PaymentsOfStockIssuanceCosts | $ 0us-gaap_PaymentsOfStockIssuanceCosts | $ 0us-gaap_PaymentsOfStockIssuanceCosts |
Proceeds from initial public offering net of underwriting discounts and commissions |  |  |  | 39,246,000us-gaap_ProceedsFromIssuanceInitialPublicOffering | 0us-gaap_ProceedsFromIssuanceInitialPublicOffering | 0us-gaap_ProceedsFromIssuanceInitialPublicOffering |
Net proceeds from issuance of initial public offering |  |  | 467,000us-gaap_SaleOfStockConsiderationReceivedOnTransaction |  |  |  |
Shares issued upon conversion |  | 510,777us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities |  |  |  |  |
IPO [Member] |  |  |  |  |  |  |
Schedule of Capitalization, Equity [Line Items] |  |  |  |  |  |  |
Common stock shares issued from IPO |  | 4,000,000us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember |  |  |  |  |
Public offering price per share |  | 10.00us-gaap_SaleOfStockPricePerShare / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember |  |  |  |  |
Underwriting discounts and commissions |  | 3,000,000us-gaap_PaymentsOfStockIssuanceCosts / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember |  |  |  |  |
Proceeds from initial public offering net of underwriting discounts and commissions |  | 39,200,000us-gaap_ProceedsFromIssuanceInitialPublicOffering / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember |  |  |  |  |
Offering expenses |  | 3,700,000us-gaap_NoninterestExpenseOfferingCost / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember |  |  |  |  |
Net proceeds from issuance of initial public offering |  | 35,500,000us-gaap_SaleOfStockConsiderationReceivedOnTransaction / us-gaap_SubsidiarySaleOfStockAxis = us-gaap_IPOMember |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |
Schedule of Capitalization, Equity [Line Items] |  |  |  |  |  |  |
Common stock shares issued from IPO |  |  |  | 510,777us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |
Shares issued upon conversion |  | 6,048,220us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |  |
Convertible Subordinated Debt [Member] |  |  |  |  |  |  |
Schedule of Capitalization, Equity [Line Items] |  |  |  |  |  |  |
Shares issued upon conversion |  | 510,777us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities / us-gaap_LongtermDebtTypeAxis = us-gaap_ConvertibleSubordinatedDebtMember |  |  |  |  |
Convertible note principal amount |  | 5,000,000us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities / us-gaap_LongtermDebtTypeAxis = us-gaap_ConvertibleSubordinatedDebtMember |  |  |  |  |
Amendment [Member] |  |  |  |  |  |  |
Schedule of Capitalization, Equity [Line Items] |  |  |  |  |  |  |
Reverse stock split, ratio |  |  |  |  |  |  | 0.145985401us-gaap_StockholdersEquityNoteStockSplitConversionRatio1 / us-gaap_StatementScenarioAxis = cdna_AmendmentMember
Reverse stock split |  |  |  | 1 for 6.85 |  |  |
Common stock, shares authorized |  | 100,000,000us-gaap_CommonStockSharesAuthorized / us-gaap_StatementScenarioAxis = cdna_AmendmentMember |  |  |  |  | 10,000,000us-gaap_CommonStockSharesAuthorized / us-gaap_StatementScenarioAxis = cdna_AmendmentMember
Reverse Stock Split effective date |  |  |  | Jul. 14, 2014 |  |  |
Common stock, par value |  | 0.001us-gaap_CommonStockParOrStatedValuePerShare / us-gaap_StatementScenarioAxis = cdna_AmendmentMember |  |  |  |  |
Convertible preferred stock, shares authorized |  | 10,000,000us-gaap_TemporaryEquitySharesAuthorized / us-gaap_StatementScenarioAxis = cdna_AmendmentMember |  |  |  |  |
Convertible preferred stock, par value |  | 0.001us-gaap_TemporaryEquityParOrStatedValuePerShare / us-gaap_StatementScenarioAxis = cdna_AmendmentMember |  |  |  |  |

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- Definition Face amount or stated value per share of common stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 30 -Article 5 + Details
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- Definition Includes offering costs of open-end investment companies, and closed-end funds with a continuous offering period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.14) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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- Definition Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues. + References No definition available. + Details
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- Definition Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Stock Split -URI http://asc.fasb.org/extlink&oid=6525746 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB TOPIC 4.C) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770 + Details
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