Goodwill and Franchise Value - Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2008
Goodwill [Roll Forward]
Balance	$ 434.9	$ 256.3
Adjustments to purchase price allocations	5.1	180.7
Additions through acquisitions	17.4
Reductions from impairments	(1.7)
Reductions through divestitures	(1.1)	(2.1)
Balance	454.6	434.9
Accumulated impairment losses			$ 299.3
Goodwill acquired including purchase accounting adjustments	22.5
Domestic
Goodwill [Roll Forward]
Balance	164.5	114.0
Adjustments to purchase price allocations	1.6	51.4
Additions through acquisitions	6.2
Reductions from impairments	(0.3)
Reductions through divestitures	(0.2)	(0.9)
Balance	171.8	164.5
Import
Goodwill [Roll Forward]
Balance	188.9	104.3
Adjustments to purchase price allocations	1.6	85.8
Additions through acquisitions	9.0
Reductions from impairments	(1.3)
Reductions through divestitures	(0.9)	(1.2)
Balance	197.3	188.9
Luxury
Goodwill [Roll Forward]
Balance	81.5	38.0
Adjustments to purchase price allocations	1.9	43.5
Additions through acquisitions	2.2
Reductions from impairments	(0.1)
Reductions through divestitures	0.0	0.0
Balance	$ 85.5	$ 81.5