Loans and Allowances for Credit Losses, Loans by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 6,603,265	$ 8,078,873
Loans, variable rate of interest	13,468,356	14,693,954
Loans, non-accrual	134,059	234,693
Total	20,205,680	23,007,520
Foregone interest on nonaccrual loans	14,102	22,870
Credit Commitments [Abstract]
Outstanding commitments to extend credit	12,500,000
Outstanding standby letters of credit	700,000
Geographic Concentration Risk [Member] \| Texas [Member]
Loans receivables disclosure [Abstract]
Total	$ 6,800,000	$ 7,200,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)	34.00%	31.00%
Geographic Concentration Risk [Member] \| Oklahoma [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,200,000	$ 3,800,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	16.00%	17.00%
Geographic Concentration Risk [Member] \| Colorado [Member]
Loans receivables disclosure [Abstract]
Total	$ 2,500,000	$ 2,800,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Colorado (in hundredths)	12.00%	12.00%
Commercial [Member]
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 3,360,117	$ 3,174,203
Loans, variable rate of interest	9,072,244	9,736,173
Loans, non-accrual	74,104	167,159
Total	12,506,465	13,077,535
Commercial [Member] \| Geographic Concentration Risk [Member] \| Texas [Member]
Loans receivables disclosure [Abstract]
Total	$ 4,400,000	$ 4,300,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)	35.00%	33.00%
Commercial [Member] \| Geographic Concentration Risk [Member] \| Oklahoma [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 Oklahoma (in hundredths)	13.00%	14.00%
Commercial [Member] \| Geographic Concentration Risk [Member] \| Colorado [Member]
Loans receivables disclosure [Abstract]
Total	$ 1,600,000	$ 1,700,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Colorado (in hundredths)	13.00%	13.00%
Commercial [Member] \| Services [Member]
Loans receivable, other information [Abstract]
Amount of loans with individual balances less than $10 million	$ 1,700,000	$ 1,500,000
Commercial [Member] \| Services [Member] \| Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,400,000	$ 3,500,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	17.00%	15.00%
Commercial [Member] \| Energy [Member] \| Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,000,000	$ 3,500,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	15.00%	15.00%
Commercial [Member] \| Energy Producers [Member] \| Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 2,200,000	$ 2,600,000
Loans receivable, other information [Abstract]
Percentage of committed energy production loans secured by oil	67.00%	58.00%
Percentage of committed energy production loans secured by natural gas	33.00%	42.00%
Commercial [Member] \| Healthcare [Member] \| Credit Concentration Risk [Member]
Loans receivables disclosure [Abstract]
Total	$ 3,400,000	$ 3,300,000
Loans receivable, other information [Abstract]
Percentage of loan class to total loans	17.00%	14.00%
Commercial real estate [Member]
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 929,015	$ 1,047,486
Loans, variable rate of interest	2,888,048	3,623,806
Loans, non-accrual	14,262	27,246
Total	$ 3,831,325	$ 4,698,538
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)	30.00%	27.00%
Commercial real estate [Member] \| Geographic Concentration Risk [Member] \| Oklahoma [Member]
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	12.00%	10.00%
Paycheck Protection Program
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	$ 276,341	$ 1,682,310
Loans, variable rate of interest	0	0
Loans, non-accrual	0	0
Total	276,341	1,682,310
Loans to individuals [Member]
Loans receivables disclosure [Abstract]
Loans, fixed rate of interest	2,037,792	2,174,874
Loans, variable rate of interest	1,508,064	1,333,975
Loans, non-accrual	45,693	40,288
Total	$ 3,591,549	$ 3,549,137
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 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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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
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-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
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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
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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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