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Employee Benefits (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
BOK Financial Pension Plan [Member] |  |  |
BOK Financial Pension Plan [Abstract] |  |  |
Interest percentage added to the five-year trailing average of five-year Treasury Securities | 1.50% |  |
Interest percentage accrued on employee account balances, Minimum | 3.00% |  |
Interest percentage accrued on employee account balances, Maximum | 5.00% |  |
Quarterly variable interest percentage accrued on employee account balances, minimum | 3.28% |  |
Quarterly variable interest percentage accrued on employee account balances, maximum | 3.40% |  |
Defined Benefit Plan, Benefit Obligation | $ 24,000,000 | $ 25,000,000 |
Defined Benefit Plan, Plan Assets, Amount | 38,000,000 | 36,000,000 |
Net periodic benefit cost (credit) | (1,300,000) | $ (815,000) | $ (583,000)
Total estimated future benefit payments | $ 26,600,000 |  |
BOK Financial Pension Plan Weighted-average Assumptions [Abstract] |  |  |
Discount rate (in hundredths) | 2.69% | 4.10% |
Expected return on plan assets (in hundredths) | 5.50% | 5.50% |
BOK Financial Pension Plan [Member] | Equity Securities [Member] |  |  |
BOK Financial Pension Plan [Abstract] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 60.00% |  |
BOK Financial Pension Plan [Member] | Bonds [Member] |  |  |
BOK Financial Pension Plan [Abstract] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 40.00% |  |
BOK Financial 401(k) Plan [Member] |  |  |
BOK Financial 401(k) Plan [Abstract] |  |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay | 6.00% |  |
Defined Contribution Plan, Minimum Years of Service for Employees to Obtain Maximum Employer Matching | 4 |  |
Defined Contribution Plan, Maximum Years of Service for Employees to Obtain Minimum Employer Matching | 15 |  |
Contributions Non-Elective Annual Contributions For Qualified Employees | $ 750 |  |
Defined Contribution Plan, Annual Base Employee Compensation to Qualify for Non-Elective Employer Contributions, Maximum | $ 40,000 |  |
Defined Contribution Plan, Vesting Period for Employer Contributions | five years |  |
Defined Contribution Plan, Cost | $ 29,900,000 | $ 27,600,000 | $ 25,100,000
BOK Financial 401(k) Plan [Member] | Minimum [Member] |  |  |
BOK Financial 401(k) Plan [Abstract] |  |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Match | 50.00% |  |
BOK Financial 401(k) Plan [Member] | Maximum [Member] |  |  |
BOK Financial 401(k) Plan [Abstract] |  |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Match | 200.00% |  |

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- Definition The total amount of expected future benefit payments under a defined benefit plan. + References No definition available. + Details
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- Definition Defined Benefit Plan Interest Percentage Accrued on Employee Account Balances (Maximum) + References No definition available. + Details
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- Definition Represents the minimum interest rate used to accrued to employee account balances. + References No definition available. + Details
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- Definition Represents percentage added to five-year trailing average of five-year Treasury securities used in determining the interest accrued on employees' account balances. + References No definition available. + Details
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- Definition Represents the lower end of the range of variable interest rates used to accrued on employee account balances during the current year. + References No definition available. + Details
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- Definition The maximum annual base employee compensation to qualify for non-elective employer contributions under the deferred compensation plan. + References No definition available. + Details
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- Definition The minimum years of service for employees to obtain maximum employer matching under a defined contribution plan. + References No definition available. + Details
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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920 + Details
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- Definition Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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