Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
U.S.
Defined Contribution Plan Disclosure [Line Items]
Employer contributions to plan	$ 26.2	$ 17.4	$ 15.2
U.K.
Defined Contribution Plan Disclosure [Line Items]
Employer contributions to plan	$ 9.2	$ 7.3	$ 7.7