Goodwill - Schedule of Goodwill and Changes to Carrying Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Balance at the beginning of the period	$ 431.4	$ 431.3
Foreign currency translation	0.3	0.1
Balance at the end of the period	431.7	431.4
Region One
Goodwill [Roll Forward]
Balance at the beginning of the period	368.7	368.6
Foreign currency translation	0.3	0.1
Balance at the end of the period	369.0	368.7
Region Two
Goodwill [Roll Forward]
Balance at the beginning of the period	62.7	62.7
Foreign currency translation	0.0	0.0
Balance at the end of the period	$ 62.7	$ 62.7