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v2.4.1.9

Loans Receivable (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2013 | Dec. 31, 2014 | Dec. 31, 2012 | Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Age of Consumer Loans contractual payments due with no forecasted future net cash flows |  | 120 months |  |
Increase in provision for credit losses | $ 3.0 us-gaap_AllowanceForLoanAndLeaseLossesPeriodIncreaseDecrease |  | $ 2.8 us-gaap_AllowanceForLoanAndLeaseLossesPeriodIncreaseDecrease |
Increase in finance charges |  |  | 0.8 cacc_IncreaseDecreaseInFinanceCharges |
Dealer Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Increase in provision for credit losses |  |  |  | 1.2 us-gaap_AllowanceForLoanAndLeaseLossesPeriodIncreaseDecrease / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = cacc_DealerLoansMember
Purchased Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Increase in provision for credit losses |  |  |  | $ 1.8 us-gaap_AllowanceForLoanAndLeaseLossesPeriodIncreaseDecrease / us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis = cacc_PurchasedLoansMember

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- Definition Increase (Decrease) In Finance Charges + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- 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

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- Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- Definition Amount of increase (decrease) of allowance reserve for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5212-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph d -Article 9 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |