Consolidated Statements of Stockholders Equity (Deficit) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings (Deficit)	Net Parent Investment	Net Parent Investment Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Beginning balance at Dec. 31, 2017	$ 571.3	$ 0.0	$ 0.0	$ 0.0	$ 582.6	$ (3.0)	$ (11.3)
Beginning balance (in shares) at Dec. 31, 2017		0
Increase (Decrease) in Stockholders' Equity
Net income	183.7				183.7
Foreign currency translation adjustments, net of tax	(1.7)						(1.7)
Stock-based compensation expense	3.8				3.8
Net transfer to parent and affiliates	(190.9)				(190.9)
Ending balance at Dec. 30, 2018	563.2	$ 0.0	0.0	0.0	576.2	$ 1.1	(13.0)
Ending balance (in shares) at Dec. 30, 2018		0
Increase (Decrease) in Stockholders' Equity
Cumulative effect adjustment for adoption of ASC, net of tax	1.1
Net income	193.2			87.4	105.8
Foreign currency translation adjustments, net of tax	(1.9)						(1.9)
Stock-based compensation expense	4.7		2.8		1.9
Exercise of stock options	1.6		1.6
Exercise of stock options (in shares)		200,000
Withholding taxes on stock-based awards	(0.9)		(0.9)
Reclassification of net parent investment to common stock and additional paid-in capital	0.0	$ 1.3		(214.5)	213.2
Reclassification of net parent investment to common stock and additional paid-in capital (in shares)		133,400,000
Dividend paid to KAR	(1,278.0)				(1,278.0)
Net transfer to parent and affiliates	379.8				379.8
Ending balance at Dec. 29, 2019	$ (137.2)	$ 1.3	3.5	(127.1)	0.0		(14.9)
Ending balance (in shares) at Dec. 29, 2019	133,600,000	133,600,000
Increase (Decrease) in Stockholders' Equity
Net income	$ 194.8			194.8	0.0
Foreign currency translation adjustments, net of tax	3.3						3.3
Stock-based compensation expense	8.5		8.5		0.0
Common stock issued for exercise and vesting of stock-based awards	$ 8.1		8.1
Common stock issued for exercise and vesting of stock-based awards (in shares)		1,100,000
Exercise of stock options (in shares)	533,385
Common stock issued for employee stock purchase plan	$ 1.0		1.0
Withholding taxes on stock-based awards	(9.1)		(9.1)
Withholding taxes on stock-based awards (in shares)		(200,000)
Ending balance at Dec. 27, 2020	$ 69.4	$ 1.3	$ 12.0	$ 67.7	$ 0.0		$ (11.6)
Ending balance (in shares) at Dec. 27, 2020	134,500,000	134,500,000