Pensions and Other Postretirement Benefit Plans (Schedule of Funded Status of Plans and Composition of Accrued Pension Cost) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Noncurrent asset	$ 31,100	$ 21,300
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	239,051	211,755	$ 178,942
Benefit obligation	245,800	227,211	201,450
Funded status	(6,749)	(15,456)
Noncurrent asset	31,139	21,337
Current liability	(2,281)	(2,155)
Noncurrent liability	(35,607)	(34,638)
Net amount recognized	(6,749)	(15,456)
Net actuarial loss	53,065	63,240
Prior service cost/(credit)	393	639
Net amount recognized	53,458	63,879
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	0
Benefit obligation	47,977	54,384	$ 51,127
Funded status	(47,977)	(54,384)
Noncurrent asset	0	0
Current liability	(3,660)	(3,808)
Noncurrent liability	(44,317)	(50,576)
Net amount recognized	(47,977)	(54,384)
Net actuarial loss	20,736	28,119
Prior service cost/(credit)	(12,946)	(17,434)
Net amount recognized	$ 7,790	$ 10,685