v2.4.1.9
Organization and Description of Business - Additional Information (Detail) (USD $)
 0 Months Ended 1 Months Ended 12 Months Ended 0 Months Ended
Aug. 13, 2014
Jul. 22, 2014
Jul. 31, 2013
Dec. 31, 2014
Segment
Dec. 31, 2013
Dec. 31, 2012
Jul. 01, 2014
Schedule of Capitalization, Equity [Line Items]              
Number of operating segment       1us-gaap_NumberOfOperatingSegments      
Common stock, shares authorized       100,000,000us-gaap_CommonStockSharesAuthorized 7,737,226us-gaap_CommonStockSharesAuthorized    
Common stock, par value       $ 0.001us-gaap_CommonStockParOrStatedValuePerShare $ 0.001us-gaap_CommonStockParOrStatedValuePerShare    
Convertible preferred stock, shares authorized       0us-gaap_TemporaryEquitySharesAuthorized 6,417,954us-gaap_TemporaryEquitySharesAuthorized    
Convertible preferred stock, par value       $ 0.001us-gaap_TemporaryEquityParOrStatedValuePerShare $ 0.001us-gaap_TemporaryEquityParOrStatedValuePerShare    
Issuance of additional shares pursuant to exercise of underwriters' overallotment option 220,000cdna_SaleOfStockPursuantToExerciseOfUnderwritersOverAllotmentOption            
Underwriting discounts and commissions       $ 3,733,000us-gaap_PaymentsOfStockIssuanceCosts $ 0us-gaap_PaymentsOfStockIssuanceCosts $ 0us-gaap_PaymentsOfStockIssuanceCosts  
Proceeds from initial public offering net of underwriting discounts and commissions       39,246,000us-gaap_ProceedsFromIssuanceInitialPublicOffering 0us-gaap_ProceedsFromIssuanceInitialPublicOffering 0us-gaap_ProceedsFromIssuanceInitialPublicOffering  
Net proceeds from issuance of initial public offering     467,000us-gaap_SaleOfStockConsiderationReceivedOnTransaction        
Shares issued upon conversion   510,777us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities          
IPO [Member]              
Schedule of Capitalization, Equity [Line Items]              
Common stock shares issued from IPO   4,000,000us-gaap_StockIssuedDuringPeriodSharesNewIssues
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember		          
Public offering price per share   10.00us-gaap_SaleOfStockPricePerShare
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember		          
Underwriting discounts and commissions   3,000,000us-gaap_PaymentsOfStockIssuanceCosts
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember		          
Proceeds from initial public offering net of underwriting discounts and commissions   39,200,000us-gaap_ProceedsFromIssuanceInitialPublicOffering
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember		          
Offering expenses   3,700,000us-gaap_NoninterestExpenseOfferingCost
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember		          
Net proceeds from issuance of initial public offering   35,500,000us-gaap_SaleOfStockConsiderationReceivedOnTransaction
/ us-gaap_SubsidiarySaleOfStockAxis
= us-gaap_IPOMember		          
Common Stock [Member]              
Schedule of Capitalization, Equity [Line Items]              
Common stock shares issued from IPO       510,777us-gaap_StockIssuedDuringPeriodSharesNewIssues
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember		      
Shares issued upon conversion   6,048,220us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_CommonStockMember		          
Convertible Subordinated Debt [Member]              
Schedule of Capitalization, Equity [Line Items]              
Shares issued upon conversion   510,777us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleSubordinatedDebtMember		          
Convertible note principal amount   5,000,000us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_ConvertibleSubordinatedDebtMember		          
Amendment [Member]              
Schedule of Capitalization, Equity [Line Items]              
Reverse stock split, ratio             0.145985401us-gaap_StockholdersEquityNoteStockSplitConversionRatio1
/ us-gaap_StatementScenarioAxis
= cdna_AmendmentMember
Reverse stock split       1 for 6.85      
Common stock, shares authorized   100,000,000us-gaap_CommonStockSharesAuthorized
/ us-gaap_StatementScenarioAxis
= cdna_AmendmentMember		         10,000,000us-gaap_CommonStockSharesAuthorized
/ us-gaap_StatementScenarioAxis
= cdna_AmendmentMember
Reverse Stock Split effective date       Jul. 14, 2014      
Common stock, par value   0.001us-gaap_CommonStockParOrStatedValuePerShare
/ us-gaap_StatementScenarioAxis
= cdna_AmendmentMember		          
Convertible preferred stock, shares authorized   10,000,000us-gaap_TemporaryEquitySharesAuthorized
/ us-gaap_StatementScenarioAxis
= cdna_AmendmentMember		          
Convertible preferred stock, par value   0.001us-gaap_TemporaryEquityParOrStatedValuePerShare
/ us-gaap_StatementScenarioAxis
= cdna_AmendmentMember