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Components Of Net Periodic Pension Benefit Cost (Details) - United Kingdom Subsidiary - UK Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 6,401	$ 7,961	$ 8,085
Expected return on plan assets	(12,023)	(12,165)	(13,797)
Amortization of unrecognized loss	2,389	2,342	2,630
Net periodic pension cost (income)	$ (3,233)	$ (1,862)	$ (3,082)

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