v2.4.1.9

Stock Incentive Plans - Summary of Options Outstanding Vested and Expected to Vest (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of Shares, Vested	415,401cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedOutstandingNumber
Number of Shares, Expected to vest	616,403cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedToVestOutstandingNumber
Number of Shares, Total	1,031,804us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber
Weighted-average Exercise Price, Vested	$ 2.68cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedWeightedAverageExercisePrice
Weighted-average Exercise Price, Expected to vest	$ 10.51cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedToVestWeightedAverageExercisePrice
Weighted-average Exercise Price, Total	$ 7.36us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice
Weighted-average Remaining Contractual Life (Years), Vested	6 years 2 months 1 day
Weighted-average Remaining Contractual Life (Years), Expected to vest	9 years 2 months 9 days
Weighted-average Remaining Contractual Life (Years), Total	7 years 11 months 23 days
Aggregate Intrinsic Value, Vested	$ 1,994cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedOutstandingAggregateIntrinsicValue
Aggregate Intrinsic Value, Expected to vest	457cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedToVestOutstandingAggregateIntrinsicValue
Aggregate Intrinsic Value, Total	$ 2,451us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue

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- Definition

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- Definition

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- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of fully vested and expected to vest options outstanding.

+ 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 (e)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

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-Section 50

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- Definition

As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

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-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

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