Property and Equipment, Net (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Property and Equipment, Net [Abstract]
Depreciation expense	$ 68.1	$ 64.2	$ 133.1	$ 128.3
Non-cash capital expenditures			$ 10.9		$ 12.4