Loans Receivable (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Loans Receivable [Abstract]
Increase in provision for credit losses	$ 2.8
Increased finance charges	$ 0.8

Increased (Decrease) in Provision for Credit Losses

No definition available.

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