Employee Benefit Plans (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6,677	$ 7,440	$ 6,320
Interest cost	4,922	4,365	4,651
Amortization of other actuarial losses (gains)	0	0	0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	8,141	9,269	11,169
Curtailments	0	0	0
Settlements	(1,326)	(2,332)	(1,532)
Expected return on plan assets	(10,555)	(12,083)	(16,498)
Amortization of prior service credits	(24)	0	0
Amortization of other actuarial losses (gains)	(11)	0	0
Total occupational disease	(3,775)	(5,146)	(6,861)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	480	558	671
Interest cost	3,505	3,674	4,150
Curtailments	0	0	(520)
Settlements	0	0	0
Expected return on plan assets	0	0	0
Amortization of prior service credits	0	0	0
Amortization of other actuarial losses (gains)	(2,974)	0	0
Total occupational disease	$ 1,011	$ 4,232	$ 4,301