Loans and Allowances for Credit Losses Loans and Allowances for Credit Losses, Nonaccrual (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	$ 179,636	$ 234,693
Financing Receivable, Nonaccrual, No Allowance	153,630	167,878
Financing Receivable, Nonaccrual, With Allowance	26,006	66,815
Financing Receivable, Nonaccrual, Related Allowance	13,775	22,441
Commercial [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	112,604	167,159
Financing Receivable, Nonaccrual, No Allowance	99,333	113,945
Financing Receivable, Nonaccrual, With Allowance	13,271	53,214
Financing Receivable, Nonaccrual, Related Allowance	10,076	19,052
Commercial [Member] \| Energy [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	70,341	125,059
Financing Receivable, Nonaccrual, No Allowance	70,341	76,633
Financing Receivable, Nonaccrual, With Allowance	0	48,426
Financing Receivable, Nonaccrual, Related Allowance	0	16,478
Commercial [Member] \| Healthcare [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	527	3,645
Financing Receivable, Nonaccrual, No Allowance	527	3,645
Financing Receivable, Nonaccrual, With Allowance	0	0
Financing Receivable, Nonaccrual, Related Allowance	0	0
Commercial [Member] \| Services [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	29,913	25,598
Financing Receivable, Nonaccrual, No Allowance	21,484	20,810
Financing Receivable, Nonaccrual, With Allowance	8,429	4,788
Financing Receivable, Nonaccrual, Related Allowance	5,234	2,574
Commercial [Member] \| General business [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	11,823	12,857
Financing Receivable, Nonaccrual, No Allowance	6,981	12,857
Financing Receivable, Nonaccrual, With Allowance	4,842	0
Financing Receivable, Nonaccrual, Related Allowance	4,842	0
Commercial real estate [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	26,123	27,246
Financing Receivable, Nonaccrual, No Allowance	13,388	13,645
Financing Receivable, Nonaccrual, With Allowance	12,735	13,601
Financing Receivable, Nonaccrual, Related Allowance	3,699	3,389
Loans to individuals [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	40,909	40,288
Financing Receivable, Nonaccrual, No Allowance	40,909	40,288
Financing Receivable, Nonaccrual, With Allowance	0	0
Financing Receivable, Nonaccrual, Related Allowance	0	0
Loans to individuals [Member] \| Residential mortgage [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	31,473	32,228
Financing Receivable, Nonaccrual, No Allowance	31,473	32,228
Financing Receivable, Nonaccrual, With Allowance	0	0
Financing Receivable, Nonaccrual, Related Allowance	0	0
Loans to individuals [Member] \| Personal [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	229	319
Financing Receivable, Nonaccrual, No Allowance	229	319
Financing Receivable, Nonaccrual, With Allowance	0	0
Financing Receivable, Nonaccrual, Related Allowance	0	0
US Government Agency Insured Loans [Member] \| Loans to individuals [Member] \| Residential mortgage [Member]
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual	9,207	7,741
Financing Receivable, Nonaccrual, No Allowance	9,207	7,741
Financing Receivable, Nonaccrual, With Allowance	0	0
Financing Receivable, Nonaccrual, Related Allowance	$ 0	$ 0

Amount of financing receivable on nonaccrual status with a related allowance.

No definition available.

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

- Definition

Amount of financing receivable on nonaccrual status with an allowance.

+ References

No definition available.

+ Details

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

- Definition

Amount of financing receivable on nonaccrual status with no allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919258-210447

+ Details

Name:	us-gaap_FinancingReceivableNonaccrualNoAllowance
Namespace Prefix:	us-gaap_
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:	us-gaap_FinancingReceivableNonaccrualStatusLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919258-210447

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bokf_EnergyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HealthCareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bokf_ServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bokf_GeneralbusinessmemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bokf_LoanstoindividualsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=us-gaap_UsGovernmentAgencyInsuredLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: