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Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	$ 1,255.7	$ 1,095.7	$ 1,124.3
Other comprehensive income (loss) before reclassifications
Pre-tax	(54.2)	(13.5)	(15.5)
Tax effect	8.8	4.1	(2.1)
Amounts reclassified from accumulated other comprehensive income (loss)
Provision (benefit) for income taxes	(2.6)	(0.1)	(1.2)
Net current period other comprehensive income (loss)	(37.1)	(9.2)	(14.4)
Tax effects reclassified from accumulated other comprehensive income (loss)			(0.2)
BALANCE	1,449.6	1,255.7	1,095.7
Floorplan interest expense (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax	7.9	0.4	4.7
Other interest expense, net (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax	2.8	(0.2)	0.5
Realized (gain) loss on interest rate swap termination (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax	0.1		(0.7)
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	(147.0)	(137.8)	(123.2)
Amounts reclassified from accumulated other comprehensive income (loss)
Net current period other comprehensive income (loss)	(37.1)	(9.2)	(14.4)
BALANCE	(184.0)	(147.0)	(137.8)
Accumulated income (loss) on foreign currency translation
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	(142.9)	(146.7)	(122.6)
Other comprehensive income (loss) before reclassifications
Pre-tax	(8.7)	3.9	(24.2)
Tax effect	0.0	0.0	0.0
Amounts reclassified from accumulated other comprehensive income (loss)
Provision (benefit) for income taxes	0.0	0.0	0.0
Net current period other comprehensive income (loss)	(8.7)	3.9	(24.2)
Tax effects reclassified from accumulated other comprehensive income (loss)			0.0
BALANCE	(151.6)	(142.9)	(146.7)
Accumulated income (loss) on foreign currency translation | Floorplan interest expense (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax	0.0	0.0	0.0
Accumulated income (loss) on foreign currency translation | Other interest expense, net (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax	0.0	0.0	0.0
Accumulated income (loss) on foreign currency translation | Realized (gain) loss on interest rate swap termination (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax	0.0		0.0
Accumulated income (loss) on interest rate swaps
Increase (Decrease) in AOCI [Roll Forward]
BALANCE	(4.1)	8.9
Other comprehensive income (loss) before reclassifications
Pre-tax	(45.5)	(17.4)
Tax effect	8.8	4.1
Amounts reclassified from accumulated other comprehensive income (loss)
Provision (benefit) for income taxes	(2.6)	(0.1)
Net current period other comprehensive income (loss)	(28.4)	(13.0)
BALANCE	(32.5)	(4.1)	8.9
Accumulated income (loss) on interest rate swaps | Floorplan interest expense (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax	7.9	0.4
Accumulated income (loss) on interest rate swaps | Other interest expense, net (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax	2.8	(0.2)
Accumulated income (loss) on interest rate swaps | Realized (gain) loss on interest rate swap termination (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax	$ 0.1		(0.7)
Accumulated income (loss) on interest rate swaps
Increase (Decrease) in AOCI [Roll Forward]
BALANCE		$ 8.9	(0.7)
Other comprehensive income (loss) before reclassifications
Pre-tax			8.6
Tax effect			(2.1)
Amounts reclassified from accumulated other comprehensive income (loss)
Provision (benefit) for income taxes			(1.2)
Net current period other comprehensive income (loss)			9.8
Tax effects reclassified from accumulated other comprehensive income (loss)			(0.2)
BALANCE			8.9
Accumulated income (loss) on interest rate swaps | Floorplan interest expense (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax			4.7
Accumulated income (loss) on interest rate swaps | Other interest expense, net (pre-tax)
Amounts reclassified from accumulated other comprehensive income (loss)
Pre-tax			$ 0.5

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Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent.

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