Employee Benefit Plans (Schedule of Defined Benefit Plans Disclosures) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Service cost	$ 7,564	$ 6,677	$ 7,440
Interest cost	5,115	4,922	4,365
Defined benefit pension plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligations at beginning of year	217,548	228,873
Service cost	0	0	0
Interest cost	5,498	8,141	9,269
Settlement gain	(896)	(1,326)
Curtailments	0	0
Benefits paid	(38,221)	(34,918)
Other-primarily actuarial (gain) loss	18,338	16,778
Benefit Obligations at end of year	202,267	217,548	228,873
CHANGE IN PLAN ASSETS
Value of Plan Assets at beginning of year	211,802	212,506
Actual return on plan assets	23,055	33,998
Employer contributions	2,612	216
Benefits paid	(38,221)	(34,918)
Value of Plan Assets at end of year	199,248	211,802	212,506
Accrued benefit cost	(3,019)	(5,746)
ITEMS NOT YET RECOGNIZED AS A COMPONENT OF NET PERIODIC BENEFIT COST
Prior service credit	880	992
Accumulated gain	10,790	14,537
Total not yet recognized as a component of net periodic benefit cost	11,670	15,529
BALANCE SHEET AMOUNTS
Current liability	(140)	(270)
Noncurrent liability	(2,879)	(5,476)
Liability, Defined Benefit Plan	(3,019)	(5,746)
Other postretirement benefits plan
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligations at beginning of year	87,867	88,563
Service cost	419	480	558
Interest cost	2,392	3,505	3,674
Settlement gain	0	0
Curtailments	284	30
Benefits paid	(6,507)	(7,304)
Other-primarily actuarial (gain) loss	16,443	2,593
Benefit Obligations at end of year	100,898	87,867	88,563
CHANGE IN PLAN ASSETS
Value of Plan Assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	6,507	7,304
Benefits paid	(6,507)	(7,304)
Value of Plan Assets at end of year	0	0	$ 0
Accrued benefit cost	(100,898)	(87,867)
ITEMS NOT YET RECOGNIZED AS A COMPONENT OF NET PERIODIC BENEFIT COST
Prior service credit	0	0
Accumulated gain	2,226	20,333
Total not yet recognized as a component of net periodic benefit cost	2,226	20,333
BALANCE SHEET AMOUNTS
Current liability	(6,510)	(7,300)
Noncurrent liability	(94,388)	(80,567)
Liability, Defined Benefit Plan	$ (100,898)	$ (87,867)