Loans Receivable (Summary Of Changes In Accretable Yield) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes	$ (206.3)	$ (59.7)	$ 326.1
Dealer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes	(125.3)	(41.6)	87.7
Purchased Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecast changes	$ (81.0)	$ (18.1)	$ 238.4

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.

No definition available.

Name:	cacc_CertainLoansAcquiredInTransferAccountedForAsLoansAccretableYieldReclassificationsFromNonaccretableDifferenceForecastChanges
Namespace Prefix:	cacc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration