Retirement Benefit Plans (Summary of Fair Value of Plan Assets by Level) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 266,268	$ 239,621
Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	40,506	37,777
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	225,762	201,844
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Exchange traded funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	39,645	36,552
Exchange traded funds [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	39,645	36,552
Exchange traded funds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Exchange traded funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Defined Benefit Plan, Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	861	1,225
Defined Benefit Plan, Cash and Cash Equivalents [Member] | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	861	1,225
Defined Benefit Plan, Cash and Cash Equivalents [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Defined Benefit Plan, Cash and Cash Equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Defined Benefit Plan, Common Collective Trust
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	225,762	201,844
Defined Benefit Plan, Common Collective Trust | Quoted Prices In Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Defined Benefit Plan, Common Collective Trust | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	225,762	201,844
Defined Benefit Plan, Common Collective Trust | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0