Retirement Benefit Plans (Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1,746	$ 1,757	$ 1,713
Expected return on plan assets	(2,843)	(2,789)	(2,733)
Amortization of actuarial loss	363	415	495
Amortization of prior service cost	58	58	50
Settlements	76	90	0
Net periodic pension income	(600)	(469)	(475)
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	50	70	70
Interest cost	101	116	113
Amortization of actuarial loss	97	132	91
Amortization of prior service cost	(17)	(107)	(107)
Net periodic pension income	$ 231	$ 211	$ 167