U.K. Pension Plan Net Periodic Benefit Cost (Details) - Pension Plan [Member] - Foreign Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 5,613	$ 8,549	$ 9,620
Labor and Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	14,260	15,401	12,980
Nonoperating income, net [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	9,413	10,194	12,074
Expected return on plan assets	(18,060)	(17,046)	(15,434)
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component	$ (8,647)	$ (6,852)	$ (3,360)