Segment Data - Schedule of long-lived assets by geographical areas (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 299.4	$ 313.8
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	191.5	216.9
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	45.7	40.5
All other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 62.2	$ 56.4