Retirement Benefit Plans (Changes in Benefit Obligations and Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	$ 495,746	$ 646,832
Service cost	7,916	11,438	$ 11,616
Interest cost	$ 23,854	$ 14,639	$ 13,476
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Payroll Taxes Healthcare Costs Pension And Other Postretirement Benefit Expense	Payroll Taxes Healthcare Costs Pension And Other Postretirement Benefit Expense	Payroll Taxes Healthcare Costs Pension And Other Postretirement Benefit Expense
Net actuarial gain (loss)	$ 15,285	$ (152,009)
Benefits paid	(25,153)	(25,154)
Benefit obligation, end of year	517,648	495,746	$ 646,832
Fair value of plan assets at beginning of year	700,535	859,883
Actual return on plan assets	48,497	(133,843)
Employer contributions	1,136	1,150
Benefit payments	(25,153)	(25,154)
Expenses	(1,951)	(1,501)
Fair value of plan assets, end of year	723,064	700,535	859,883
Funded status at end of year - net asset (liability)	205,416	204,789
Unrecognized loss (gain) at beginning of year	135,243	108,121
Net actuarial loss (gain)	5,806	27,122
Unrecognized loss (gain) at end of year	141,049	135,243	108,121
Accumulated benefit obligation	493,800	472,843
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	13,796	20,282
Service cost	34	59	93
Interest cost	$ 622	$ 375	$ 348
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Payroll Taxes Healthcare Costs Pension And Other Postretirement Benefit Expense	Payroll Taxes Healthcare Costs Pension And Other Postretirement Benefit Expense	Payroll Taxes Healthcare Costs Pension And Other Postretirement Benefit Expense
Plan participants' contributions	$ 691	$ 794
Net actuarial gain (loss)	92	(5,906)
Benefits paid	(1,831)	(1,808)
Benefit obligation, end of year	13,404	13,796	$ 20,282
Employer contributions	1,140	1,015
Plan participants' contributions	691	793
Benefit payments	(1,831)	(1,808)
Funded status at end of year - net asset (liability)	(13,404)	(13,796)
Unrecognized loss (gain) at beginning of year	(8,837)	(3,581)
Net actuarial loss (gain)	935	(5,256)
Unrecognized loss (gain) at end of year	$ (7,902)	$ (8,837)	$ (3,581)