Employee Benefit Plans (Schedule of Net Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 7,564	$ 6,677	$ 7,440
Interest cost	5,115	4,922	4,365
Amortization of other actuarial losses (gains)	(1,189)	0	0
Defined benefit pension plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	5,498	8,141	9,269
Curtailments	0	0	0
Settlements	(896)	(1,326)	(2,332)
Expected return on plan assets	(8,283)	(10,555)	(12,083)
Amortization of prior service credits	(112)	(24)	0
Amortization of other actuarial losses (gains)	0	(11)	0
Net benefit cost (credit)	(3,793)	(3,775)	(5,146)
Other postretirement benefits plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	419	480	558
Interest cost	2,392	3,505	3,674
Curtailments	0	0	0
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)	(1,379)	(2,974)	0
Net benefit cost (credit)	$ 1,432	$ 1,011	$ 4,232