Retirement Benefit Plans (Summary of Components of Accumulated Other Comprehensive Loss Related to Pensions and Postretirement Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain) included in AOCL	$ 56,555	$ 64,523
Deferred tax benefit	12,528	14,623
Amounts included in accumulated AOCL, net of tax	44,027	49,900
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain) included in AOCL	602	453
Deferred tax benefit	133	103
Amounts included in accumulated AOCL, net of tax	469	350
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Amounts included in accumulated AOCL, net of tax	(357)	(285)
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain) included in AOCL	(458)	(368)
Deferred tax benefit	$ (101)	$ (83)