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Retirement Plans (Narrative) (Details)	3 Months Ended
	Mar. 31, 2021 USD ($) plan	Mar. 31, 2020 USD ($)
UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Number of plans | plan	3
Contributions to defined benefit pension plans	$ 0
Net periodic pension cost (income)	100,000	$ 100,000
UK Plan | United Kingdom Subsidiary [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions to defined benefit pension plans	1,200,000
Anticipated additional contribution	3,800,000
Net periodic pension cost (income)	$ (943,000)	$ (806,000)

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