Mortgage Banking Activities, Components of Loans Held For Sale (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
Number of days for past due for loan to be considered nonperforming (in days)	90		90
Residential mortgage loans held for sale, nonperforming	$ 0		$ 0
Credit losses recognized on residential mortgage loans held for sale	0	$ 0
Components of Residential Mortgage Loans Held for Sale [Abstract]
Unpaid principal balance	260,005		227,161
Residential mortgage loans held for sale, Fair value	262,333		236,444
Residential mortgage loans held for sale	$ 284,447		$ 252,316
Residential Mortgage Loan Commitments [Member] \| Not Designated as Hedging Instrument [Member]
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
General number of days outstanding for residential mortgage commitments, minimum (in days)	60		60
General number of days outstanding for residential mortgage commitments, maximum (in days)	90		90
Components of Residential Mortgage Loans Held for Sale [Abstract]
Derivative, Notional Amount	$ 387,465		$ 380,637
Derivative, Net fair value	$ 11,455		$ 20,435
Forward sales contracts [Member] \| Not Designated as Hedging Instrument [Member]
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
General number of days for delivery of loans, for which the price is set by forward sales contracts, minimum (in days)	60		60
General number of days for delivery for loans, for which the price is set by forward sales contracts, maximum (in days)	90		90
Components of Residential Mortgage Loans Held for Sale [Abstract]
Derivative, Notional Amount	$ 584,743		$ 549,414
Derivative, Net fair value	$ 10,659		$ (4,563)

Represents the individual components of residential mortgage loans held for sale

No definition available.

Name:	bokf_ComponentsofResidentialMortgageLoansHeldforSaleAbstract
Namespace Prefix:	bokf_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Credit losses recognized on residential mortgage loans held for sale

+ References

No definition available.

+ Details

Name:	bokf_CreditLossesRecognizedOnResidentialMortgageLoansHeldForSale
Namespace Prefix:	bokf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the fair value of residential mortgage loans held for sale as of the balance sheet, exclusive of mortgage commitments and forward sales contracts

+ References

No definition available.

+ Details

Name:	bokf_FairValueofResidentialMortgageLoansHeldforSale
Namespace Prefix:	bokf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents represents the typical maximum period for commitment to originate a residential mortgage loan to when the closed loan is sold to an investor.

+ References

No definition available.

+ Details

Name:	bokf_MaximumNumberofDaysOutstandingForResidentialMortgageCommitments
Namespace Prefix:	bokf_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents represents the typical maximum number of days from the point pricing is set to delivery of forward sales contracts.

+ References

No definition available.

+ Details

Name:	bokf_MaximumNumberofDaysforDeliveryofForwardSalesContracts
Namespace Prefix:	bokf_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents represents the typical minimum period for commitment to originate a residential mortgage loan to when the closed loan is sold to an investor.

+ References

No definition available.

+ Details

Name:	bokf_MinimumNumberofDaysOutstandingForResidentialMortgageCommitments
Namespace Prefix:	bokf_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the minimum number of days from the point of pricing being set to delivery of forward sales contracts.

+ References

No definition available.

+ Details

Name:	bokf_MinimumNumberofDaysforDeliveryofForwardSalesContracts
Namespace Prefix:	bokf_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of days past due for residential mortgage loans held for sale to be reported as delinquent.

+ References

No definition available.

+ Details

Name:	bokf_NumberOfDaysForPastDueResidentialMortgageLoansHeldforSale
Namespace Prefix:	bokf_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Residential mortgage loans held for sale, 90 days past due or impaired.

+ References

No definition available.

+ Details

Name:	bokf_ResidentialMortgageLoansHeldForSaleNonperforming
Namespace Prefix:	bokf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unpaid principal balance of loans held for sale.

+ References

No definition available.

+ Details

Name:	bokf_ResidentialMortgageLoansHeldForSaleUnpaidPrincipalBalanceGross
Namespace Prefix:	bokf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	bokf_ScheduleOfResidentialMortgageLoansHeldForSaleLineItems
Namespace Prefix:	bokf_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=120238483&loc=d3e48678-111004

+ Details

Name:	us-gaap_LoansReceivableHeldForSaleNetNotPartOfDisposalGroup
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=bokf_ResidentialMortgageLoanCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=bokf_ForwardSalesContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: