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Description of Business (Percentage of Consumer Loans Assigned with FICO Score of Less Than 650 or No FICO Score)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Percentage Of Contracts With FICO Score Lower Than 650 Or No FICO Score [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Percentage Of Contracts	94.30%	96.50%

X

- Definition

Percentage Of Contracts

+ References

No definition available.

+ Details

Name:	cacc_PercentageOfContracts
Namespace Prefix:	cacc_
Data Type:	num:percentItemType
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_FinancingReceivableRecordedInvestmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_CreditScoreFicoAxis=cacc_FICOScoreLowerThan650OrNoFICOScoreMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: