v2.4.1.9

Stock Incentive Plans - Additional Information (Detail) (USD $) | 12 Months Ended | 0 Months Ended |
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Jan. 01, 2014 | Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Fair market value of Company's common stock | $ 7.25us-gaap_SharePrice | $ 8.97us-gaap_SharePrice |  |  | $ 7.03us-gaap_SharePrice
Weighted average fair value of options to purchase common stock granted | $ 4.81us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue | $ 0.21us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue | $ 0.27us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue |  |
Non-vested stock option awards not yet recognized | $ 2,200,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions |  |  |  |
Non-vested stock option awards weighted average remaining period of recognition | 3 years 1 month 6 days |  |  |  |
Share based compensation, Total expensed | 535,000us-gaap_AllocatedShareBasedCompensationExpense | 72,000us-gaap_AllocatedShareBasedCompensationExpense | 69,000us-gaap_AllocatedShareBasedCompensationExpense |  |
Share-based compensation expense, tax benefit recognized | 0us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense | 0us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense | 0us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense |  |
Share-based compensation costs, capitalized | 0us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount | 0us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount | 0us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount |  |
General and administrative [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share based compensation, Total expensed | 390,000us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_IncomeStatementLocationAxis = us-gaap_GeneralAndAdministrativeExpenseMember | 59,000us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_IncomeStatementLocationAxis = us-gaap_GeneralAndAdministrativeExpenseMember | 49,000us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_IncomeStatementLocationAxis = us-gaap_GeneralAndAdministrativeExpenseMember |  |
2014 Equity Incentive Plan [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares reserved for issuance of common stock | 838,695us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_PlanNameAxis = cdna_TwoThousandAndFourteenEquityIncentivePlanMember |  |  | 357,075us-gaap_CommonStockCapitalSharesReservedForFutureIssuance / us-gaap_PlanNameAxis = cdna_TwoThousandAndFourteenEquityIncentivePlanMember |
Maximum number of shares may be added to the plan hereunder | 865,252us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod / us-gaap_PlanNameAxis = cdna_TwoThousandAndFourteenEquityIncentivePlanMember |  |  |  |
Outstanding shares of common stock, in percentage |  |  |  | 4.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum / us-gaap_PlanNameAxis = cdna_TwoThousandAndFourteenEquityIncentivePlanMember |
Non Vested Stock Options [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Share based compensation, Total expensed | $ 0us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_DeferredCompensationArrangementWithIndividualShareBasedPaymentsByTypeOfDeferredCompensationAxis = cdna_NonvestedStockOptionsMember |  |  |  |

X
- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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Balance Type: | debit
Period Type: | duration

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- Definition Aggregate number of common shares reserved for future issuance. + 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 + Details
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Balance Type: | na
Period Type: | instant

X
- Definition Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(ii) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Unrecognized cost of unvested options awarded to employees as compensation. + References No definition available. + Details
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- Definition The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Details
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- Definition The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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Balance Type: | na
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- Definition The addition or reduction in the number of reserved shares that could potentially be issued under the option plan attributable to reasons other than grants, exercises, forfeitures, and expirations during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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Balance Type: | na
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- Definition Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock. + References No definition available. + Details
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- Definition Price of a single share of a number of saleable stocks of a company. + References No definition available. + Details
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- Details
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- Details
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- Details
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