v2.4.1.9

Stock Incentive Plans - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended
	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



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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

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-Publisher FASB

-Name Accounting Standards Codification

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-Section 50

-Paragraph 2

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-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

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X

- 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

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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

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X

- 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

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X

- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

+ References

No definition available.

+ Details

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X

- 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

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X

- 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)

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Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

X

- 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

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- 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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X

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

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X

- Details

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X

- Details

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X

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