Pension and Other Postretirement Benefit Plans (Schedule of Components of Net Periodic Benefit Obligation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,950	$ 1,150	$ 2,948
Interest cost	25,101	23,505	25,265
Expected return on plan assets	(40,457)	(40,370)	(42,383)
Amortization of prior service credits	(367)	(502)	(502)
Recognized net actuarial loss	5,958	8,715	8,896
Settlement loss	0	0	10,153
Net periodic benefit (credit) cost	(5,815)	(7,502)	4,377
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	18,320	18,706	23,945
Expected return on plan assets	0	0	0
Amortization of prior service credits	(2,405)	(2,405)	(2,405)
Recognized net actuarial loss	9,262	16,205	23,112
Settlement loss	0	0	0
Net periodic benefit (credit) cost	$ 25,177	$ 32,506	$ 44,652