v2.4.1.9
Commitments and Contingencies - Additional Information (Detail) (USD $)
 12 Months Ended 6 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Sep. 30, 2014
Loss Contingencies [Line Items]          
Operating lease agreement expiry date 2020-12        
Rent expense under non-cancelable operating leases $ 1,007,000us-gaap_OperatingLeasesRentExpenseNet $ 1,020,000us-gaap_OperatingLeasesRentExpenseNet $ 1,016,000us-gaap_OperatingLeasesRentExpenseNet    
Past due royalties 0us-gaap_AccruedRoyaltiesCurrentAndNoncurrent 2,804,000us-gaap_AccruedRoyaltiesCurrentAndNoncurrent      
Royalty revenues 221,000us-gaap_RoyaltyRevenue 94,000us-gaap_RoyaltyRevenue 34,000us-gaap_RoyaltyRevenue    
July 1, 2011 through June 30, 2014 [Member]          
Loss Contingencies [Line Items]          
Settlement and payment 2,800,000us-gaap_PaymentsForLegalSettlements
/ us-gaap_StatementScenarioAxis
= cdna_ScenarioOneMember		        
Decrease in cost of testing 566,000cdna_IncreaseDecreaseInServicerPayables
/ us-gaap_StatementScenarioAxis
= cdna_ScenarioOneMember		        
Decrease in interest expense 132,000us-gaap_IncreaseDecreaseInInterestPayableNet
/ us-gaap_StatementScenarioAxis
= cdna_ScenarioOneMember		        
Unpaid Royalties [Member]          
Loss Contingencies [Line Items]          
Settlement and mutual release agreement, counter party name Roche        
Settlement and mutual release agreement, date September 2014        
Maximum number of days from end of calendar quarter for royalty payment 45 days        
Settlement and mutual release agreement, terms of agreement In September 2014, the Company entered into a settlement and mutual release agreement with Roche whereby: (i) for the period beginning July 1, 2011 through June 30, 2014, the Company agreed to pay the amount of $2,827,220 in settlement of past royalties due; (ii) for the period beginning July 1, 2014 through September 30, 2014, the Company agreed to pay royalties based on the same combination services percentage used to determine the past royalties due; (iii) for the period beginning October 1, 2014 through September 30, 2017, Roche and the Company agreed to a downward adjustment of the combination services percentage used to determine the portion of the AlloMap testing revenue that is royalty bearing under the terms of the license; (iv) the Company agreed to report and pay quarterly royalties within 45 days of the end of each calendar quarter; (v) Roche agreed that, subject to the Company’s timely payment of all applicable royalties through such date, no further royalties will be payable by the Company for periods after September 30, 2017;        
Royalty expenses 650,000us-gaap_RoyaltyExpense
/ us-gaap_RelatedPartyTransactionAxis
= cdna_RoyaltyAgreementLiabilityMember		 1,200,000us-gaap_RoyaltyExpense
/ us-gaap_RelatedPartyTransactionAxis
= cdna_RoyaltyAgreementLiabilityMember		 1,100,000us-gaap_RoyaltyExpense
/ us-gaap_RelatedPartyTransactionAxis
= cdna_RoyaltyAgreementLiabilityMember		    
Unpaid Royalties [Member] | July 1, 2011 through June 30, 2014 [Member]          
Loss Contingencies [Line Items]          
Past due royalties         2,827,220us-gaap_AccruedRoyaltiesCurrentAndNoncurrent
/ us-gaap_RelatedPartyTransactionAxis
= cdna_RoyaltyAgreementLiabilityMember
/ us-gaap_StatementScenarioAxis
= cdna_ScenarioOneMember
AlloMap [Member] | July 1, 2011 through June 30, 2014 [Member]          
Loss Contingencies [Line Items]          
Royalty revenues $ 600,000us-gaap_RoyaltyRevenue
/ us-gaap_RelatedPartyTransactionAxis
= cdna_AllomapMember
/ us-gaap_StatementScenarioAxis
= cdna_ScenarioOneMember		 $ 1,000,000us-gaap_RoyaltyRevenue
/ us-gaap_RelatedPartyTransactionAxis
= cdna_AllomapMember
/ us-gaap_StatementScenarioAxis
= cdna_ScenarioOneMember		 $ 900,000us-gaap_RoyaltyRevenue
/ us-gaap_RelatedPartyTransactionAxis
= cdna_AllomapMember
/ us-gaap_StatementScenarioAxis
= cdna_ScenarioOneMember		 $ 400,000us-gaap_RoyaltyRevenue
/ us-gaap_RelatedPartyTransactionAxis
= cdna_AllomapMember
/ us-gaap_StatementScenarioAxis
= cdna_ScenarioOneMember