Fair Value Measurements (Details) - Recurring basis - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Fair value of assets and liabilities measured on recurring basis
Short-term investments	$ 15.0	$ 12.4
Forward contracts	0.4	2.4
Contingent consideration	(75.0)
Total	(59.6)	14.8
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair value of assets and liabilities measured on recurring basis
Short-term investments	15.0	12.4
Forward contracts	0.0	0.0
Contingent consideration	0.0
Total	15.0	12.4
Significant Observable Inputs (Level 2)
Fair value of assets and liabilities measured on recurring basis
Short-term investments	0.0	0.0
Forward contracts	0.4	2.4
Contingent consideration	0.0
Total	0.4	2.4
Significant Unobservable Inputs (Level 3)
Fair value of assets and liabilities measured on recurring basis
Short-term investments	0.0	0.0
Forward contracts	0.0	0.0
Contingent consideration	(75.0)
Total	$ (75.0)	$ 0.0