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v3.21.1

Summary of Significant Accounting Policies - Leases (Detail) | 3 Months Ended
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Mar. 31, 2021
Minimum |
Summary Of Significant Accounting Policies [Line Items] |
Remaining lease terms | 2 months 15 days
Maximum |
Summary Of Significant Accounting Policies [Line Items] |
Remaining lease terms | 7 years 11 months 1 day

X
- Definition Remaining operating and finance lease term. + References No definition available. + Details
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Namespace Prefix: | cdna_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Summary Of Significant Accounting Policies [Line Items] + References No definition available. + Details
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Namespace Prefix: | cdna_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |