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Loans Receivable (Narrative) (Details)	6 Months Ended
	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Age of Consumer Loans contractual payments due with no forecasted future net cash flows	120 months

X

- Definition

Period After Consumer Loans With No Forecasted Future Net Cash Flows

+ References

No definition available.

+ Details

Name:	cacc_PeriodAfterConsumerLoansWithNoForecastedFutureNetCashFlows
Namespace Prefix:	cacc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- 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_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration