v2.4.1.9

Warrants - Additional Information (Detail) (USD $) | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2013 | Dec. 31, 2014 | Sep. 30, 2014 | Oct. 31, 2011
Class of Warrant or Right [Line Items] |  |  |  |
Common stock price | $ 8.97us-gaap_SharePrice | $ 7.25us-gaap_SharePrice | $ 7.03us-gaap_SharePrice |
Dividend yield | 0.00%us-gaap_FairValueAssumptionsExpectedDividendRate |  |  |
Warrants to purchase convertible preferred stock |  |  |  | 82,190cdna_WarrantsToPurchaseConvertiblePreferredStock
Minimum [Member] |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |
Expected volatility | 40.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |
Risk-free interest rate | 0.80%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |
Maximum [Member] |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |
Expected volatility | 45.00%us-gaap_FairValueAssumptionsExpectedVolatilityRate / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |
Risk-free interest rate | 2.10%us-gaap_FairValueAssumptionsRiskFreeInterestRate / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |

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- Definition Warrants To Purchase Convertible Preferred Stock + References No definition available. + Details
Name: | cdna_WarrantsToPurchaseConvertiblePreferredStock
Namespace Prefix: | cdna_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

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- Details
Name: | us-gaap_ClassOfWarrantOrRightLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Expected dividends to be paid to holders of the underlying shares or financial instruments (expressed as a percentage of the share or instrument's price). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueAssumptionsExpectedDividendRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueAssumptionsExpectedVolatilityRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Risk-free interest rate assumption used in valuing an instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueAssumptionsRiskFreeInterestRate
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Price of a single share of a number of saleable stocks of a company. + References No definition available. + Details
Name: | us-gaap_SharePrice
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |