v2.4.1.9

Income Taxes - Schedule of Reconciliation of Difference between Benefit for Income Taxes and Income Taxes at Statutory U.S. Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depreciation and Amortization, Percent [Abstract]
Federal tax at statutory rate	34.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	34.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	34.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Stock based compensation	(9.50%)us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	(11.40%)us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	0.00%us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost
Change in valuation allowance	190.60%us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	(8.60%)us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	(30.90%)us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance
Change in unrecognized tax benefits	0.00%cdna_EffectiveIncomeTaxRateReconciliationChangeInUnrecognizedTaxBenefits	(8.40%)cdna_EffectiveIncomeTaxRateReconciliationChangeInUnrecognizedTaxBenefits	0.00%cdna_EffectiveIncomeTaxRateReconciliationChangeInUnrecognizedTaxBenefits
Preferred stock warrant revaluation	(0.70%)cdna_EffectiveIncomeTaxRateReconciliationPreferredStockWarrantRevaluation	(5.00%)cdna_EffectiveIncomeTaxRateReconciliationPreferredStockWarrantRevaluation	0.00%cdna_EffectiveIncomeTaxRateReconciliationPreferredStockWarrantRevaluation
Interest expense	(5.80%)cdna_EffectiveIncomeTaxRateReconciliationInterestExpense	0.00%cdna_EffectiveIncomeTaxRateReconciliationInterestExpense	(2.30%)cdna_EffectiveIncomeTaxRateReconciliationInterestExpense
Contingent liability for IMX acquisition	38.20%cdna_EffectiveIncomeTaxRateReconciliationLiabilityContingentForUnconsolidatedSubsidiaryPercent	0.00%cdna_EffectiveIncomeTaxRateReconciliationLiabilityContingentForUnconsolidatedSubsidiaryPercent	0.00%cdna_EffectiveIncomeTaxRateReconciliationLiabilityContingentForUnconsolidatedSubsidiaryPercent
IMX acquisition costs	(36.70%)cdna_EffectiveIncomeTaxRateReconciliationAcquisitionCosts	0.00%cdna_EffectiveIncomeTaxRateReconciliationAcquisitionCosts	0.00%cdna_EffectiveIncomeTaxRateReconciliationAcquisitionCosts
Other	(1.30%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments	(0.60%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments	(0.80%)us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments
Effective income tax rate	208.80%us-gaap_EffectiveIncomeTaxRateContinuingOperations	0.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations	0.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations

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- Definition

Effective income tax rate reconciliation acquisition costs.

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Effective income tax rate reconciliation change in unrecognized tax benefits.

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Effective income tax rate reconciliation interest expense.

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Effective income tax rate reconciliation, Liability contingent for unconsolidated subsidiary, percent.

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Effective income tax rate reconciliation, preferred stock warrant revaluation.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to equity-based compensation costs.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other adjustments.

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