Retirement Benefit Plans (Fair Value Hierarchy) (Details) - Pension Plan - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	$ 41,099	$ 37,364	$ 34,954
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	41,099	37,364
Level 1 | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	18,640	16,862
Level 1 | Non-U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	8,335	7,482
Level 1 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	13,948	12,854
Level 1 | Money market
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	$ 176	$ 166