Defined Benefit Pension Plans - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost, non-service cost	$ (964,000)	$ (234,000)	$ (1,774,000)	$ (491,000)
U.S.
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			4,500,000	3,000,000
U.K. Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			$ 358,000	$ 288,000