Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 57.5		$ 69.2
Restricted cash included in Current Assets	1.4		1.9
Total cash, cash equivalents, and restricted cash	58.9	$ 57.6	$ 71.1	$ 65.4
Non-cash investing and financing activities related to property acquired under capital leases		2.2
Capital lease and deferred purchase price related to acquisitions		3.3
Accrued purchases of property and equipment	26.4	22.4
Interest payments, net of amounts capitalized and including interest on vehicle inventory financing	46.5	43.5
Income tax payments, net of income tax refunds	$ 84.6	$ 0.5