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v3.20.4

Loans Receivable (Summary of Changes in Expected Future Net Cash Flows) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Balance, beginning of period | $ 9,005.2 | $ 9,005.2 | $ 7,828.8 | $ 6,285.1
New Consumer Loan Assignments |  | 5,131.6 | 5,305.0 | 5,074.4
Realized Net Cash Flows |  | (4,552.9) | (4,152.2) | (3,580.8)
Forecast changes | (206.5) | (46.3) | 14.6 | 42.3
Transfers |  | 6.8 | 9.0 | 7.8
Balance, end of period |  | 9,544.4 | 9,005.2 | 7,828.8
Dealer Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Balance, beginning of period | 5,577.0 | 5,577.0 | 5,045.9 | 4,240.7
New Consumer Loan Assignments |  | 3,113.4 | 3,396.1 | 3,405.0
Realized Net Cash Flows |  | (2,870.6) | (2,749.7) | (2,507.8)
Forecast changes |  | (41.1) | (7.9) | 2.0
Transfers |  | (114.4) | (107.4) | (94.0)
Balance, end of period |  | 5,664.3 | 5,577.0 | 5,045.9
Purchased Loans [Member] |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Balance, beginning of period | $ 3,428.2 | 3,428.2 | 2,782.9 | 2,044.4
New Consumer Loan Assignments |  | 2,018.2 | 1,908.9 | 1,669.4
Realized Net Cash Flows |  | (1,682.3) | (1,402.5) | (1,073.0)
Forecast changes |  | (5.2) | 22.5 | 40.3
Transfers |  | 121.2 | 116.4 | 101.8
Balance, end of period |  | $ 3,880.1 | $ 3,428.2 | $ 2,782.9

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- Definition Change in the estimate of cash flows expected to be collected, after acquisition of a loan, which results in an increase in accretable yield (for example, if actual cash flows are significantly greater than previously expected). This relates to loans with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable. + References No definition available. + Details
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Namespace Prefix: | cacc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Expected Future Net Cash Flows + References No definition available. + Details
Name: | cacc_ExpectedFutureNetCashFlows
Namespace Prefix: | cacc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Loans Receivable Expected Net Cash Flows At Assignment + References No definition available. + Details
Name: | cacc_LoansReceivableExpectedNetCashFlowsAtAssignment
Namespace Prefix: | cacc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Realized Net Cash Flows + References No definition available. + Details
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Namespace Prefix: | cacc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Transfer of Expected Future Net Cash Flows between Programs + References No definition available. + Details
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Namespace Prefix: | cacc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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
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- Details
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |