Fair Value - Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets and Liabilities Measured at Fair Value on a recurring basis
Cash and cash equivalents		$ 48.8
Restricted cash	$ 0.8	6.7
Short-term investments		0.1
Fair Value, Recurring
Assets and Liabilities Measured at Fair Value on a recurring basis
Cash and cash equivalents	320.3	160.7
Restricted cash	0.8	6.7
Short-term investments	37.6	25.7
Foreign currency hedges	1.1	7.6
Total Assets	359.8	249.6
Foreign currency hedges	8.1	1.4
Total Liabilities	8.1	1.4
Fair Value, Recurring | Level 1
Assets and Liabilities Measured at Fair Value on a recurring basis
Cash and cash equivalents	318.6	158.2
Restricted cash	0.8	6.7
Short-term investments	0.0	0.0
Foreign currency hedges	0.0	0.0
Total Assets	319.4	164.9
Foreign currency hedges	0.0	0.0
Total Liabilities	0.0	0.0
Fair Value, Recurring | Level 2
Assets and Liabilities Measured at Fair Value on a recurring basis
Cash and cash equivalents	1.7	2.5
Restricted cash	0.0	0.0
Short-term investments	37.6	25.7
Foreign currency hedges	1.1	7.6
Total Assets	40.4	35.8
Foreign currency hedges	8.1	1.4
Total Liabilities	8.1	1.4
Fair Value, Recurring | Level 3
Assets and Liabilities Measured at Fair Value on a recurring basis
Cash and cash equivalents	0.0	0.0
Restricted cash	0.0	0.0
Short-term investments	0.0	0.0
Foreign currency hedges	0.0	0.0
Total Assets	0.0	0.0
Foreign currency hedges	0.0	0.0
Total Liabilities	$ 0.0	$ 0.0