Retirement Benefit Plans (Fair Value Hierarchy) (Details) - Pension Plan - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	$ 38,527	$ 34,628	$ 37,162
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	38,527	34,628
Level 1 | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	18,175	16,054
Level 1 | Non-U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	8,120	6,792
Level 1 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	12,097	11,657
Level 1 | Money market
Defined Benefit Plan Disclosure [Line Items]
Fair value of each major category of U.S. plan assets	$ 135	$ 125