Pension and Other Postretirement Benefit Plans (Schedule of Components of Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,150	$ 2,948	$ 1,533
Interest cost	23,505	25,265	25,048
Expected return on plan assets	(40,370)	(42,383)	(46,674)
Amortization of prior service credits	(502)	(502)	(502)
Recognized net actuarial loss	8,715	8,896	9,163
Settlement loss	0	10,153	22,196
Net periodic benefit (credit) cost	(7,502)	4,377	10,764
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	18,706	23,945	24,241
Expected return on plan assets	0	0	0
Amortization of prior service credits	(2,405)	(2,405)	0
Recognized net actuarial loss	16,205	23,112	19,168
Settlement loss	0	0	0
Net periodic benefit (credit) cost	$ 32,506	$ 44,652	$ 43,409