Retirement Benefit Plans (Schedule of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	$ 12
Interest cost	831	1,287
Expected return on plan assets	(1,275)	(1,844)
Amortization of net loss	433	724
Recognition of Settlement		2,889
Net periodic benefit cost	(7)	3,068
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	198	176
Interest cost	204	175
Amortization of prior service cost	406	364
Net periodic benefit cost	808	715
Hourly Employees’ Pension Plan | Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	8
Interest cost	0	401
Expected return on plan assets	0	(648)
Amortization of net loss	0	284
Recognition of Settlement	2,889	2,889
Net periodic benefit cost	0	2,934
Employees’ Retirement Plan | Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4
Interest cost	831	886
Expected return on plan assets	(1,275)	(1,196)
Amortization of net loss	433	440
Recognition of Settlement		0
Net periodic benefit cost	$ (7)	$ 134