Components Of Net Periodic Pension Benefit Cost (Details) - United Kingdom Subsidiary - UK Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 8,622	$ 10,320	$ 11,603
Expected return on plan assets	(13,508)	(14,227)	(16,181)
Amortization of unrecognized loss	2,942	2,047	2,526
Net periodic pension cost (income)	$ (1,944)	$ (1,860)	$ (2,052)