v2.4.1.9

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 2,196us-gaap_UnrecognizedTaxBenefits	$ 1,159us-gaap_UnrecognizedTaxBenefits	$ 1,130us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions related to current year	83us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	177us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	53us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions
Additions (reductions) based on tax positions related to prior years	(225)cdna_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions	860cdna_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions	(24)cdna_UnrecognizedTaxBenefitsIncreaseDecreaseResultingFromPriorPeriodTaxPositions
Balance at end of year	$ 2,054us-gaap_UnrecognizedTaxBenefits	$ 2,196us-gaap_UnrecognizedTaxBenefits	$ 1,159us-gaap_UnrecognizedTaxBenefits

X

- Definition

Unrecognized tax benefits increase decrease resulting from prior period tax positions.

+ References

No definition available.

+ Details

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Namespace Prefix:	cdna_
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Balance Type:	credit
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X

- Details

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

X

- Definition

Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

-URI http://asc.fasb.org/extlink&oid=6527854



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

+ Details

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Balance Type:	credit
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X

- Definition

Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

+ Details

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