Retirement Benefit Plans (Schedule of Assumptions Used) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Discount rate (percentage)	3.45%	3.85%
Composite rate of compensation increase (percentage)	3.00%	3.00%
Net periodic pension expense, discount rate (percentage)	3.85%	4.05%
Net periodic pension expense, rate of compensation increase (percentage)	3.00%	3.00%
Hourly Employees’ Pension Plan | Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension expense, discount rate (percentage)		4.30%
Net periodic pension expense, Long-term rate of return on plan assets (percentage)		7.25%
Employees’ Retirement Plan | Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Discount rate (percentage)	3.60%	4.10%
Net periodic pension expense, discount rate (percentage)	4.10%	4.40%
Net periodic pension expense, Long-term rate of return on plan assets (percentage)	7.25%	7.25%