Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingency [Abstract]
Rent expense	$ 61.7	$ 58.6	$ 44.9
Letters of credit issued	78.7
Outstanding surety bonds	$ 582.6