Geographic Information - Long-lived Assets by Selected Geographic Area Information (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 1,027.6	$ 985.9
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	637.2	602.6
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	181.8	187.5
Other foreign countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 208.6	$ 195.8