Goodwill and Franchise Value - Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2008
Goodwill [Roll Forward]
Balance		$ 454.6	$ 434.9
Adjustments to purchase price allocations			5.1
Additions through acquisitions		144.9	17.4
Reductions through divestitures		(3.0)	(1.1)
Reductions from impairments	$ (4.4)	(3.5)	(1.7)
Balance		593.0	454.6
Accumulated impairment losses				$ 299.3
Goodwill acquired including purchase accounting adjustments			22.5
Domestic
Goodwill [Roll Forward]
Balance		171.8	164.5
Adjustments to purchase price allocations			1.6
Additions through acquisitions		33.3	6.2
Reductions through divestitures		(0.1)	(0.2)
Reductions from impairments		(0.5)	(0.3)
Balance		204.5	171.8
Import
Goodwill [Roll Forward]
Balance		197.3	188.9
Adjustments to purchase price allocations			1.6
Additions through acquisitions		94.3	9.0
Reductions through divestitures		(0.7)	(0.9)
Reductions from impairments		(3.0)	(1.3)
Balance		287.9	197.3
Luxury
Goodwill [Roll Forward]
Balance		85.5	81.5
Adjustments to purchase price allocations			1.9
Additions through acquisitions		17.3	2.2
Reductions through divestitures		(2.2)	0.0
Reductions from impairments		0.0	(0.1)
Balance		$ 100.6	$ 85.5