Retirement Plans - Assumptions (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
U.S.
Defined Benefit Plan Disclosure [Line Items]
Discount rate used to compute benefit obligations	3.15%	4.30%
Discount rate used to compute periodic benefit cost	4.31%	3.63%
Expected long-term rates of return on plans' assets	6.10%	6.20%
U.K Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate used to compute benefit obligations	1.93%	2.77%
Discount rate used to compute periodic benefit cost	2.77%	2.61%
Expected long-term rates of return on plans' assets	3.28%	3.98%