Retirement Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, total costs	$ 2,800	$ 2,700
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Settlement charge	$ 0	$ 873