Other Income (Narrative) (Details)	3 Months Ended
Mar. 31, 2018 USD ($)
Other Income and Expenses [Abstract]
Payment Holdback Percentage	50.00%
One-time enrollment fee in program	$ 9,850

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