Pensions and Other Postretirement Benefit Plans (Schedule of Net Periodic Benefit Plan Cost) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 545	$ 580
Interest cost	1,338	1,550
Expected return on assets	(1,606)	(1,723)
Amortization of prior service cost/(credit)	3	8
Amortization of net actuarial loss	544	596
Net periodic benefit cost	824	1,011
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	33	50
Interest cost	276	428
Expected return on assets	0	0
Amortization of prior service cost/(credit)	(1,122)	(1,122)
Amortization of net actuarial loss	565	648
Net periodic benefit cost	$ (248)	$ 4