v2.4.1.9
Stock Incentive Plans - Schedule of Outstanding, Exercisable and Vested Stock Options (Detail) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Range of Exercise Prices $ 7.36us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 1.99us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 2.67us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 3.70us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Options Outstanding & Exercisable, Number of Options Outstanding 1,031,804cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptions      
Options Outstanding & Exercisable, Weighted Average Remaining Contractual Life (Years) 8 years      
Options Outstanding & Exercisable, Weighted Average Exercise Price $ 7.36cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptionsWeightedAverageExercisePrice      
Options Vested, Number of Options 415,401cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedOutstandingNumber      
Number of Options vested, Weighted Average Exercise Price $ 2.68cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedWeightedAverageExercisePrice      
$0.27-0.55 [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding & Exercisable, Number of Options Outstanding 200,002cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptions
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeOneMember
     
Options Outstanding & Exercisable, Weighted Average Remaining Contractual Life (Years) 7 years 9 months 18 days      
Options Outstanding & Exercisable, Weighted Average Exercise Price $ 0.55cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptionsWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeOneMember
     
Options Vested, Number of Options 136,560cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedOutstandingNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeOneMember
     
Number of Options vested, Weighted Average Exercise Price $ 0.55cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeOneMember
     
$0.27-0.55 [Member] | Minimum [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Range of Exercise Prices $ 0.27us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeOneMember
     
$0.27-0.55 [Member] | Maximum [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Range of Exercise Prices $ 0.55us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeOneMember
     
$2.05-3.01 [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding & Exercisable, Number of Options Outstanding 153,469cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptions
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeTwoMember
     
Options Outstanding & Exercisable, Weighted Average Remaining Contractual Life (Years) 6 years 4 months 10 days      
Options Outstanding & Exercisable, Weighted Average Exercise Price $ 2.78cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptionsWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeTwoMember
     
Options Vested, Number of Options 147,641cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedOutstandingNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeTwoMember
     
Number of Options vested, Weighted Average Exercise Price $ 2.77cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeTwoMember
     
$2.05-3.01 [Member] | Minimum [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Range of Exercise Prices $ 2.05us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeTwoMember
     
$2.05-3.01 [Member] | Maximum [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Range of Exercise Prices $ 3.01us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeTwoMember
     
$3.36-3.97 [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding & Exercisable, Number of Options Outstanding 110,188cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptions
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeThreeMember
     
Options Outstanding & Exercisable, Weighted Average Remaining Contractual Life (Years) 3 years 6 months 18 days      
Options Outstanding & Exercisable, Weighted Average Exercise Price $ 3.47cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptionsWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeThreeMember
     
Options Vested, Number of Options 110,188cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedOutstandingNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeThreeMember
     
Number of Options vested, Weighted Average Exercise Price $ 3.47cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeThreeMember
     
$3.36-3.97 [Member] | Minimum [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Range of Exercise Prices $ 3.36us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeThreeMember
     
$3.36-3.97 [Member] | Maximum [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Range of Exercise Prices $ 3.97us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeThreeMember
     
$7.03-12.40 [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding & Exercisable, Number of Options Outstanding 568,145cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptions
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeFourMember
     
Options Outstanding & Exercisable, Weighted Average Remaining Contractual Life (Years) 9 years 4 months 17 days      
Options Outstanding & Exercisable, Weighted Average Exercise Price $ 11.75cdna_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingAndExercisableOptionsWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeFourMember
     
Options Vested, Number of Options 21,012cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedOutstandingNumber
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeFourMember
     
Number of Options vested, Weighted Average Exercise Price $ 11.82cdna_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedWeightedAverageExercisePrice
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeFourMember
     
$7.03-12.40 [Member] | Minimum [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Range of Exercise Prices $ 7.03us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeFourMember
     
$7.03-12.40 [Member] | Maximum [Member]        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Options Outstanding, Range of Exercise Prices $ 12.40us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis
= cdna_ExercisePriceRangeFourMember