Income Taxes - Net deferred tax assets (liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Differences in capitalization and depreciation and amortization of reacquired franchises and equipment	$ 0.0	$ 0.0
Differences in acquisition financing costs	0.0	0.1
Employee compensation	9.0	7.6
Deferred gain on sale of assets	0.0	0.7
Book/tax difference in revenue recognition	34.3	14.2
Other	16.8	42.2
Deferred tax assets	60.1	64.8
Valuation allowance	(0.4)	0.0
Total deferred tax assets after valuation allowance	59.7	64.8
Differences between financial and tax accounting in the recognition of franchise and equipment sales	(16.8)	(20.7)
Differences in capitalization and depreciation (1)	(139.2)	(147.5)
Differences in acquisition financing costs	(0.6)	0.0
Book/tax difference in revenue recognition	0.0	(2.4)
Differences between book and tax basis of property and equipment	(8.1)	(8.5)
Other	(0.8)	(3.5)
Deferred tax liabilities	(165.5)	(182.6)
Net deferred tax liabilities	$ (105.8)	$ (117.8)