Other Income (Narrative) (Details)	12 Months Ended
Dec. 31, 2018 USD ($)
Other Income and Expenses [Abstract]
One-time enrollment fee in program	$ 9,850
Percentage of first accelerated Dealer Holdback payment retained	50.00%

Revenue From Enrollment And Registration Fees In Program

No definition available.

Name:	cacc_RevenueFromEnrollmentAndRegistrationFeesInProgram
Namespace Prefix:	cacc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration