Description of Business and Summary of Significant Accounting Policies - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 725.5	$ 705.2	$ 777.2
Translation adjustments	41.2	(23.0)	(29.1)
Unrealized gain on available-for-sale securities	0.0	0.1	0.1
Ending Balance	599.4	725.5	705.2
Cumulative Translation Adjustment
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(99.8)	(76.8)	(47.7)
Translation adjustments	41.2	(23.0)	(29.1)
Unrealized gain on available-for-sale securities		0.0	0.0
Ending Balance	(58.6)	(99.8)	(76.8)
Pension and other post-retirement benefits
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	5.2	5.2	5.2
Translation adjustments	0.0	0.0	0.0
Unrealized gain on available-for-sale securities		0.0	0.0
Ending Balance	5.2	5.2	5.2
Unrealized gain in available-for-sale securities
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	0.4	0.3	0.2
Translation adjustments	0.0	0.0	0.0
Unrealized gain on available-for-sale securities		0.1	0.1
Ending Balance	0.4	0.4	0.3
Total
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(94.2)	(71.3)	(42.3)
Translation adjustments	41.2	(23.0)	(29.1)
Unrealized gain on available-for-sale securities		0.1	0.1
Ending Balance	$ (53.0)	$ (94.2)	$ (71.3)