Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2007
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 32	$ 100,000
Funded status	289,030	157,902
Accumulated benefit obligation	$ 972,700	985,000
Percent of employer match (percent)	100.00%			4.50%
Percentage of employee compensation matched	6.00%
Additional contribution if employed at end of year	3.00%
Defined contribution plan cost	$ 36,200	35,600	$ 30,800
Deferred compensation cash-based arrangements, liability, current and noncurrent	84,000	68,200
BancShares Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 32	80,000
Bancorporation Plan
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		$ 20,000
401(k) Matching Range 1
Defined Benefit Plan Disclosure [Line Items]
Percent of employer match (percent)				100.00%
Percentage of employee compensation matched				3.00%
401(k) Matching Range 2
Defined Benefit Plan Disclosure [Line Items]
Percent of employer match (percent)				50.00%
Percentage of employee compensation matched				3.00%