v2.4.1.9

Summary of Significant Accounting Policies - Additional Information - Concentration of Credit Risk (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Services Revenue [Member] | Customer Concentration Risk [Member] | Minimum [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_RangeAxis = us-gaap_MinimumMember	10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_RangeAxis = us-gaap_MinimumMember	10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Services Revenue [Member] | Customer Concentration Risk [Member] | Medicare [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	51.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = cdna_MedicareMember	53.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = cdna_MedicareMember	52.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueServicesNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = cdna_MedicareMember
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Minimum [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CreditConcentrationRiskMember / us-gaap_RangeAxis = us-gaap_MinimumMember	10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CreditConcentrationRiskMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Medicare [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	78.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CreditConcentrationRiskMember / us-gaap_MajorCustomersAxis = cdna_MedicareMember	72.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CreditConcentrationRiskMember / us-gaap_MajorCustomersAxis = cdna_MedicareMember

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

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