Retirement Plans (Components of Net Periodic Benefits Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,620	$ 3,207	$ 8,996	$ 9,690
Interest cost	3,552	3,892	9,982	12,315
Expected return on plan assets	(11,463)	(12,047)	(34,854)	(36,144)
Amortization of net (gain) or loss and prior service costs	717	1,854	4,471	5,168
Special termination benefits			16,052
Net periodic benefit cost	(4,574)	(3,094)	4,647	(8,971)
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	23	28	71	78
Interest cost	91	106	257	377
Amortization of net (gain) or loss and prior service costs	(192)	(142)	(501)	(512)
Special termination benefits			4,137
Net periodic benefit cost	$ (78)	$ (8)	$ 3,964	$ (57)