U.K. Pension Plan Net Periodic Service Cost (Details) - Pension Plan [Member] - U.K. Pension [Member] $ in Thousands, £ in Millions	3 Months Ended
	Mar. 31, 2019 GBP (£)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 GBP (£)	Dec. 31, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Company contribution % required in shared cost arrangement	60.00%	60.00%
Defined benefit plan, contribution percent by participant	40.00%	40.00%
Net periodic benefit cost		$ 1,459	$ 1,523
Defined Benefit Plan, Contribution by Employer	£ 1.6	2,100
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year				£ 5.4	$ 7,000
Labor and Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		3,440	3,872
Other income/(loss), net [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost		2,366	2,556
Expected return on plan assets		(4,391)	(4,905)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		44	0
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component		$ (1,981)	$ (2,349)