v2.4.1.9

Business Combination - Schedule of Pro Forma Results of Operations (Detail) (ImmuMetrix, Inc. [Member], USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
ImmuMetrix, Inc. [Member]
Business Acquisition [Line Items]
Net revenue	$ 27,306us-gaap_BusinessAcquisitionsProFormaRevenue / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember	$ 22,098us-gaap_BusinessAcquisitionsProFormaRevenue / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember
Net loss	$ (1,080)us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember	$ (3,768)us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember
Net loss per common share-basic	$ (0.19)us-gaap_BusinessAcquisitionProFormaEarningsPerShareBasic / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember	$ (3.73)us-gaap_BusinessAcquisitionProFormaEarningsPerShareBasic / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember
Net loss per common share-diluted	$ (0.19)us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember	$ (3.73)us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted / us-gaap_BusinessAcquisitionAxis = cdna_ImmumetrixIncMember

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- Definition

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

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- Definition

The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

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- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

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- Definition

The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

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