Pensions and Other Postretirement Benefit Plans (Schedule of Net Periodic Benefit Plan Cost) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,090	$ 1,148
Interest cost	2,674	3,071
Expected return on assets	(3,211)	(3,415)
Settlement	0	145
Curtailment	0	233
Amortization of prior service cost/(credit)	7	16
Amortization of net actuarial loss	1,087	1,180
Net periodic benefit cost	1,647	2,378
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	66	100
Interest cost	551	857
Expected return on assets	0	0
Settlement	0	0
Curtailment	0	0
Amortization of prior service cost/(credit)	(2,244)	(2,244)
Amortization of net actuarial loss	1,130	1,296
Net periodic benefit cost	$ (497)	$ 9