Retirement Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Funded status of plan	$ (0.7)
Defined benefit plan, benefit obligation	2.1
Fair value of pension plan assets	1.4
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan	8.3	$ 7.5	$ 7.4
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan	$ 2.5	2.6	2.9
United Kingdom | Employees hired prior to November 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	15.00%
United Kingdom | Employees hired after November 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	12.00%
European, Outside of U.K.
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan	$ 0.5	0.3	0.5
European, Outside of U.K. | Minimum
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	2.10%
European, Outside of U.K. | Maximum
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	26.00%
Retirement Savings Contributions | United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan	$ 5.1	4.9	4.2
Non Discretionary Matching Contributions | United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan	$ 3.2	$ 2.6	$ 3.2