v2.4.1.9
Subsequent Events - Additional Information (Detail) (USD $)
12 Months Ended 0 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Jan. 30, 2015
Subsequent Event [Line Items]        
Pay-off of term debt $ 4,528,000us-gaap_RepaymentsOfDebt $ 58,000us-gaap_RepaymentsOfDebt $ 12,994,000us-gaap_RepaymentsOfDebt  
Interest rate, description Draw A and Draw B each bear interest at a floating rate equal to 2.00%, plus the greater of (i) 3.25% or (ii) the prime rate published by the lender.      
Loan agreement description The Company agreed to issue to the lender warrants to purchase shares of the Company's common stock upon the drawdown of each advance in an amount equal to 1.5% of the amount drawn, divided by the exercise price per share for that tranche.      
Loan agreement initiation date Jan. 30, 2015      
Subsequent Event [Member]        
Subsequent Event [Line Items]        
Aggregate principal amount       20,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Interest rate basis spread       2.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Subsequent Event [Member] | Common Stock [Member]        
Subsequent Event [Line Items]        
Warrant to purchase of common stock, shares       34,483us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Warrant to purchase of common stock, per share       $ 6.96us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Subsequent Event [Member] | Draw A [Member]        
Subsequent Event [Line Items]        
Loan agreement, amount borrowed       16,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= cdna_TrancheATermLoanFacilityMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Pay-off of term debt       11,300,000us-gaap_RepaymentsOfDebt
/ us-gaap_CreditFacilityAxis
= cdna_TrancheATermLoanFacilityMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Subsequent Event [Member] | Draw B [Member]        
Subsequent Event [Line Items]        
Loan agreement, amount available to borrow       $ 4,000,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= cdna_TrancheBTermLoanFacilityMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember