Loans and Allowances for Credit Losses, Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 6,739,706	$ 6,633,234
Loans, variable rate of interest	17,328,293	17,126,265
Financing Receivable, Nonaccrual	(46,725)	(145,469)
Total	24,114,724	23,904,968
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	10,061	7,863
Credit Commitments [Abstract]
Outstanding commitments to extend credit	14,700,000
Outstanding commercial letters of credit	703,000
Geographic Concentration Risk [Member] | Texas [Member]
Loans receivables disclosure [Abstract]
Total	$ 7,800,000	$ 7,600,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)	32.00%	32.00%
Geographic Concentration Risk [Member] | Oklahoma [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,700,000	$ 3,300,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	15.00%	14.00%
Geographic Concentration Risk [Member] | Colorado [Member]
Loans receivables disclosure [Abstract]
Total	$ 2,900,000	$ 2,700,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Colorado (in hundredths)	12.00%	11.00%
Commercial [Member]
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 3,450,238	$ 3,558,563
Loans, variable rate of interest	11,565,251	11,135,075
Financing Receivable, Nonaccrual	(14,647)	(110,131)
Total	15,030,136	14,803,769
Commercial [Member] | Geographic Concentration Risk [Member] | Texas [Member]
Loans receivables disclosure [Abstract]
Total	$ 5,000,000	$ 4,800,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)	34.00%	33.00%
Commercial [Member] | Geographic Concentration Risk [Member] | Oklahoma [Member]
Loans receivables disclosure [Abstract]
Total	$ 2,300,000	$ 1,800,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	15.00%	12.00%
Commercial [Member] | Geographic Concentration Risk [Member] | Colorado [Member]
Loans receivables disclosure [Abstract]
Total	$ 1,700,000	$ 1,800,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Colorado (in hundredths)	12.00%	12.00%
Commercial [Member] | Healthcare [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,967,533	$ 4,143,233
Commercial [Member] | Healthcare [Member] | Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 4,000,000	$ 4,100,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	16.00%	17.00%
Commercial [Member] | Services [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,643,203	$ 3,576,223
Commercial [Member] | Services [Member] | Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,600,000	$ 3,600,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	15.00%	15.00%
Commercial [Member] | Energy [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,254,724	$ 3,437,101
Commercial [Member] | Energy [Member] | Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,300,000	$ 3,400,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	13.00%	14.00%
Commercial [Member] | Energy Producers [Member] | Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 2,600,000	$ 2,700,000
Loans receivable, other information [Abstract]
Percentage of committed energy production loans secured by oil	70.00%	69.00%
Percentage of committed energy production loans secured by natural gas	30.00%	31.00%
Commercial [Member] | General business [Member]
Loans receivables disclosure [Abstract]
Total	$ 4,164,676	$ 3,647,212
Commercial [Member] | General business [Member] | Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 4,200,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	17.00%
Commercial real estate [Member]
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 668,532	791,757
Loans, variable rate of interest	4,380,015	4,538,570
Financing Receivable, Nonaccrual	(9,905)	(7,320)
Total	$ 5,058,452	$ 5,337,647
Commercial real estate [Member] | Geographic Concentration Risk [Member]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in all other states (in hundredths)	10.00%	10.00%
Commercial real estate [Member] | Geographic Concentration Risk [Member] | Texas [Member]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)	29.00%	31.00%
Commercial real estate [Member] | Geographic Concentration Risk [Member] | Colorado [Member]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Colorado (in hundredths)	11.00%
Loans to individuals [Member]
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 2,620,936	$ 2,282,914
Loans, variable rate of interest	1,383,027	1,452,620
Financing Receivable, Nonaccrual	(22,173)	(28,018)
Total	$ 4,026,136	$ 3,763,552
Loans receivable, other information [Abstract]
Percentage of personal loans secured by collateral in our geographical footprint	90.00%