Commitments and Contingencies (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Significant change in legal and regulatory proceedings	$ 0.0

Represents the amount of significant change in legal and regulatory proceedings during the reporting period.

No definition available.

Name:	kar_SignificantChangeInLegalAndRegulatoryProceedings
Namespace Prefix:	kar_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration