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Description of Business (Percentage of Consumer Loans Assigned Based on Unit Volumes) (Details) | 3 Months Ended
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Mar. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014
Description Of Business [Line Items] |  |  |  |  |
Financing Receivable, Credit Quality, Additional Information | 0.967 |  |  |  | 0.963
Portfolio Program [Member] |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |
Percentage of new consumer loans | 88.60%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PortfolioProgramMember | 89.00%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PortfolioProgramMember | 90.50%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PortfolioProgramMember | 91.40%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PortfolioProgramMember | 91.70%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PortfolioProgramMember
Purchase Program [Member] |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |
Percentage of new consumer loans | 11.40%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PurchaseProgramMember | 11.00%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PurchaseProgramMember | 9.50%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PurchaseProgramMember | 8.60%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PurchaseProgramMember | 8.30%cacc_PercentageOfNewConsumerLoanAssignments / cacc_PaymentsForProceedsFromLoansReceivableProgramsAxis = cacc_PurchaseProgramMember

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- Definition Includes any additional disclosures related to the credit quality of financing receivables. This may include a description of a credit quality indicator or a description of how the internal risk ratings used by a company relate to the likelihood of loss. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 29 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953659-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953664-111524 + Details
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