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Other Income (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2018 USD ($)
Other Income and Expenses [Abstract] |
One-time enrollment fee in program | $ 9,850
Percentage of first accelerated Dealer Holdback payment retained | 50.00%

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- Definition Payment Holdback Percentage + References No definition available. + Details
Name: | cacc_PaymentHoldbackPercentage
Namespace Prefix: | cacc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Revenue From Enrollment And Registration Fees In Program + References No definition available. + Details
Name: | cacc_RevenueFromEnrollmentAndRegistrationFeesInProgram
Namespace Prefix: | cacc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_OtherIncomeAndExpensesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration