Loans and Allowances for Credit Losses, Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 6,633,234	$ 6,366,303
Loans, variable rate of interest	17,126,265	16,069,050
Loans, non-accrual	145,469	121,797
Total	23,904,968	22,557,150
Foregone interest on nonaccrual loans	7,863	6,796
Credit Commitments [Abstract]
Outstanding commitments to extend credit	14,800,000
Outstanding commercial letters of credit	711,000
Geographic Concentration Risk [Member] \| Texas [Member]
Loans receivables disclosure [Abstract]
Total	$ 7,600,000	$ 7,300,000
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	$ 3,300,000	$ 3,500,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	14.00%	16.00%
Geographic Concentration Risk [Member] \| Colorado [Member]
Loans receivables disclosure [Abstract]
Total	$ 2,700,000	$ 2,500,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Colorado (in hundredths)	11.00%	11.00%
Commercial [Member]
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 3,558,563	$ 3,392,422
Loans, variable rate of interest	11,135,075	10,759,780
Loans, non-accrual	110,131	60,297
Total	14,803,769	14,212,499
Commercial [Member] \| Geographic Concentration Risk [Member] \| Texas [Member]
Loans receivables disclosure [Abstract]
Total	$ 4,800,000	$ 4,700,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)	33.00%	33.00%
Commercial [Member] \| Geographic Concentration Risk [Member] \| Oklahoma [Member]
Loans receivables disclosure [Abstract]
Total	$ 1,800,000	$ 2,100,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	12.00%	15.00%
Commercial [Member] \| Geographic Concentration Risk [Member] \| Colorado [Member]
Loans receivables disclosure [Abstract]
Total	$ 1,800,000	$ 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] \| Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 4,100,000	$ 3,800,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	17.00%	17.00%
Commercial [Member] \| Services [Member]
Loans receivable, other information [Abstract]
Amount of loans with individual balances less than $10 million	$ 1,600,000	$ 1,600,000
Commercial [Member] \| Services [Member] \| Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,600,000	$ 3,400,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	15.00%	15.00%
Commercial [Member] \| Energy [Member] \| Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,400,000	$ 3,400,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	14.00%	15.00%
Commercial [Member] \| Energy Producers [Member] \| Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 2,700,000	$ 2,700,000
Loans receivable, other information [Abstract]
Percentage of committed energy production loans secured by oil	69.00%	72.00%
Percentage of committed energy production loans secured by natural gas	31.00%	28.00%
Commercial real estate [Member]
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 791,757	$ 874,716
Loans, variable rate of interest	4,538,570	3,715,491
Loans, non-accrual	7,320	16,570
Total	$ 5,337,647	$ 4,606,777
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)	31.00%	30.00%
Loans to individuals [Member]
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 2,282,914	$ 2,099,165
Loans, variable rate of interest	1,452,620	1,593,779
Loans, non-accrual	28,018	44,930
Total	$ 3,763,552	$ 3,737,874
Loans receivable, other information [Abstract]
Percentage of personal loans secured by collateral in our geographical footprint	91.00%

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Maximum dollar amount of loans in this category with individual loan amount less than specified threshold.

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Percentage of committed energy production loans secured by properties producing natural gas

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Percentage of committed energy production loans secured by properties primarily producing oil

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Reflects the percentage of the loan portfolio secured by property in all other states outside of Texas.

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Reflects the percentage of the loan in portfolio secured by property in the state of Oklahoma.

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Reflects the percentage of the loan in portfolio secured by property in the state of Texas.

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Percentage Of Loan Portfolio Secured By Property in Colorado

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Percentage of personal loans secured by collateral in our geographical footprint

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Represents percentage of given loan class to total loans.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-2

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Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 310
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481746/310-40-50-1

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Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of loan with fixed rate of interest.

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Amount of loan with variable or adjustable rate of interest.

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Unused amount of commitments to extend credit to customers.

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