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v3.20.1

Stock-Based Compensation - Summary of RSU Activity (Parenthetical) (Details) shares in Thousands | 3 Months Ended
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Mar. 31, 2020 shares
RSUs |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |
RSUs vested but not yet delivered | 80

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- Definition Share based compensation arrangement by share based payment award equity instruments other than options vested but not yet delivered. + References No definition available. + Details
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Namespace Prefix: | cars_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |