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Investment (Held-to-Maturity) Securities (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Sep. 30, 2011
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investment Securities, Amortized Cost $ 651,745,000bokf_HeldToMaturitySecuritiesAmortizedCost $ 676,047,000bokf_HeldToMaturitySecuritiesAmortizedCost  
Investment Securities, Debt Maturities, Carrying Value 652,360,000us-gaap_HeldToMaturitySecurities [1] 677,878,000us-gaap_HeldToMaturitySecurities [2]  
Investment Securities, Fair Value 673,626,000us-gaap_HeldToMaturitySecuritiesFairValue 687,127,000us-gaap_HeldToMaturitySecuritiesFairValue  
Investment Securities, Gross Unrealized Gain 22,874,000us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain [3] 12,687,000us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain [3]  
Investment Securities, Gross Unrealized Loss (1,608,000)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss [3] (3,438,000)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss [3]  
Investment Securities, Debt Maturities, Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Carrying Value 652,360,000us-gaap_HeldToMaturitySecurities [1] 677,878,000us-gaap_HeldToMaturitySecurities [2]  
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]      
Investment Securities, Fair Value 673,626,000us-gaap_HeldToMaturitySecuritiesFairValue 687,127,000us-gaap_HeldToMaturitySecuritiesFairValue  
Investment Securities, Debt Maturities, Nominal Yield [Abstract]      
Investment Securities, Debt Maturities, Nominal Yield 3.28%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield    
Investment Securities, Pledged as Collateral [Abstract]      
Investment Securities, Pledged as Collateral, Carrying Value 63,495,000us-gaap_HeldToMaturitySecuritiesPledgedAsCollateral 89,087,000us-gaap_HeldToMaturitySecuritiesPledgedAsCollateral  
Investment Securities, Pledged as Collateral, Fair Value 65,855,000bokf_HeldToMaturityCollateralFairValue 91,804,000bokf_HeldToMaturityCollateralFairValue  
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]      
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities 162us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions 139us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions  
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 143,951,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue 192,538,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue  
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 60,837,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue 53,850,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue  
Investment Securities, Continuous Unrealized Loss Position, Fair Value 204,788,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue 246,388,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue  
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses 1,063,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss 2,526,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss  
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses 545,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss 912,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss  
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss 1,608,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss 3,438,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss  
Other than Temporary Impairment Losses, Investment Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Lowest Current Credit Rating [Abstract]      
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Carrying Value 35,750,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationUsGovtGseSecuritiesNotRatedCarryingValue [4]    
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value 37,463,000bokf_HeldToMaturityPortfolioConcentrationRatedUsGovernmentOrGseFairValue [4]    
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value 424,679,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaCarryingValue    
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value 441,566,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaFairValue    
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value 13,676,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbCarryingValue    
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value 13,806,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbFairValue    
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedBelowInvestmentGradeCarryingValue    
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedBelowInvestmentGradeFairValue    
Investment Securities, Portfolio Concentration Not Rated, Carrying Value 178,255,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedCarryingValue    
Investment Securities, Portfolio Concentration Not Rated, Fair Value 180,791,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedFairValue    
Fixed maturity securities [Member]      
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investment Securities, Debt Maturities, Carrying Value 616,610,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Fair Value 636,163,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Less than One Year, Carrying Value 60,173,000bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Carrying Value 337,660,000bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Carrying Value 80,767,000bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Carrying Value 138,010,000bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Carrying Value 616,610,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]      
Investment Securities, Debt Maturities, Less than One Year, Fair Value 60,306,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Fair Value 338,943,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value 84,096,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Fair Value 152,818,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Fair Value 636,163,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Nominal Yield [Abstract]      
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield 2.14%bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield 2.10%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield 4.83%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield 5.91%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Nominal Yield 3.31%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Weighted Average Maturity 5.65bokf_HeldToMaturitySecuritiesDebtMaturitiesWeightedAverageMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		 [5]    
Municipal and other tax-exempt securities [Member]      
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investment Securities, Amortized Cost 405,090,000bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 440,187,000bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Investment Securities, Debt Maturities, Carrying Value 405,090,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [1] 440,187,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [2]  
Investment Securities, Fair Value 408,344,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 439,870,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Investment Securities, Gross Unrealized Gain 4,205,000us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [3] 2,452,000us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [3]  
Investment Securities, Gross Unrealized Loss (951,000)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [3] (2,769,000)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [3]  
Investment Securities, Debt Maturities, Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Less than One Year, Carrying Value 44,255,000bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, One to Five Years, Carrying Value 299,934,000bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Carrying Value 22,429,000bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Over Ten Years, Carrying Value 38,472,000bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Carrying Value 405,090,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [1] 440,187,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [2]  
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]      
Investment Securities, Debt Maturities, Less than One Year, Fair Value 44,381,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, One to Five Years, Fair Value 300,434,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value 22,666,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Over Ten Years, Fair Value 40,863,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Fair Value 408,344,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 439,870,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Investment Securities, Debt Maturities, Nominal Yield [Abstract]      
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield 1.71%bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [6]    
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield 1.74%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [6]    
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield 3.91%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [6]    
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield 5.37%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [6]    
Investment Securities, Debt Maturities, Nominal Yield 2.20%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [6]    
Investment Securities, Debt Maturities, Weighted Average Maturity 3.80bokf_HeldToMaturitySecuritiesDebtMaturitiesWeightedAverageMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [5]    
Investment Securities, Debt Maturities, Effective tax rate for nominal yield calculation 39.00%bokf_HeldtoMaturitySecuritiesDebtMaturitiesEffectivetaxratefornominalyieldcalculation
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]      
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities 78us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 107us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 112,677,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 166,382,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 60,076,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 53,073,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Investment Securities, Continuous Unrealized Loss Position, Fair Value 172,753,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 219,455,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses 426,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 1,921,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses 525,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 848,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss 951,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 2,769,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
Other than Temporary Impairment Losses, Investment Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Lowest Current Credit Rating [Abstract]      
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationUsGovtGseSecuritiesNotRatedCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [4]    
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value 0bokf_HeldToMaturityPortfolioConcentrationRatedUsGovernmentOrGseFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [4]    
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value 264,326,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value 264,651,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value 13,676,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value 13,806,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedBelowInvestmentGradeCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedBelowInvestmentGradeFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Not Rated, Carrying Value 127,088,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Not Rated, Fair Value 129,887,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Other debt securities [Member]      
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investment Securities, Amortized Cost 211,520,000bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 187,509,000bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Investment Securities, Debt Maturities, Carrying Value 211,520,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [1] 187,509,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [2]  
Investment Securities, Fair Value 227,819,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 195,393,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Investment Securities, Gross Unrealized Gain 16,956,000us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [3] 8,497,000us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [3]  
Investment Securities, Gross Unrealized Loss (657,000)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [3] (613,000)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [3]  
Investment Securities, Debt Maturities, Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Less than One Year, Carrying Value 15,918,000bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Carrying Value 37,726,000bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Carrying Value 58,338,000bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Carrying Value 99,538,000bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Carrying Value 211,520,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [1] 187,509,000us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [2]  
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]      
Investment Securities, Debt Maturities, Less than One Year, Fair Value 15,925,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Fair Value 38,509,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value 61,430,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Fair Value 111,955,000us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Fair Value 227,819,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 195,393,000us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Investment Securities, Debt Maturities, Nominal Yield [Abstract]      
Investment Securities, Debt Maturities, Less Than One Year, Nominal Yield 3.32%bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield 4.96%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield 5.19%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield 6.12%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Nominal Yield 5.45%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Weighted Average Maturity 9.18bokf_HeldToMaturitySecuritiesDebtMaturitiesWeightedAverageMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [5]    
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]      
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities 84us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 30us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 31,274,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 10,932,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 761,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 777,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Investment Securities, Continuous Unrealized Loss Position, Fair Value 32,035,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 11,709,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses 637,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 549,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses 20,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 64,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss 657,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 613,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		  
Other than Temporary Impairment Losses, Investment Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Lowest Current Credit Rating [Abstract]      
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationUsGovtGseSecuritiesNotRatedCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [4]    
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value 0bokf_HeldToMaturityPortfolioConcentrationRatedUsGovernmentOrGseFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [4]    
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value 160,353,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value 176,915,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedBelowInvestmentGradeCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedBelowInvestmentGradeFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Portfolio Concentration Not Rated, Carrying Value 51,167,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Portfolio Concentration Not Rated, Fair Value 50,904,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
U.S. government agency residential mortgage-backed securities [Member] | Other [Member]      
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investment Securities, Amortized Cost 35,135,000bokf_HeldToMaturitySecuritiesAmortizedCost
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 48,351,000bokf_HeldToMaturitySecuritiesAmortizedCost
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Investment Securities, Debt Maturities, Carrying Value 35,750,000us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [1] 50,182,000us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [2]  
Investment Securities, Fair Value 37,463,000us-gaap_HeldToMaturitySecuritiesFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 51,864,000us-gaap_HeldToMaturitySecuritiesFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Investment Securities, Gross Unrealized Gain 1,713,000us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [3] 1,738,000us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [3]  
Investment Securities, Gross Unrealized Loss 0us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [3] (56,000)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [3]  
Investments Securities, Transfers [Abstract]      
Investment Securities, Transferred From Available For Sale Securities Portfolio, Fair Value     131,000,000bokf_InvestmentSecuritiesTransferredFromAvailableForSaleSecuritiesPortfolioFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Investment Securities, Transferred From Available For Sale Securities Portfolio, Amortized Cost     118,000,000bokf_InvestmentSecuritiesTransferredFromAvailableForSaleSecuritiesPortfolioAmortizedCost
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Investment Securities, Transferred From Available For Sale Securities Portfolio, Net Unrealized Gain 615,000bokf_InvestmentSecuritiesTransferredFromAvailableForSaleSecuritiesPortfolioNetUnrealizedGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 1,800,000bokf_InvestmentSecuritiesTransferredFromAvailableForSaleSecuritiesPortfolioNetUnrealizedGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 13,000,000bokf_InvestmentSecuritiesTransferredFromAvailableForSaleSecuritiesPortfolioNetUnrealizedGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Investment Securities, Debt Maturities, Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Carrying Value 35,750,000us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [1] 50,182,000us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [2]  
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]      
Investment Securities, Fair Value 37,463,000us-gaap_HeldToMaturitySecuritiesFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 51,864,000us-gaap_HeldToMaturitySecuritiesFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Investment Securities, Debt Maturities, Nominal Yield [Abstract]      
Investment Securities, Debt Maturities, Nominal Yield 2.74%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [7]    
Investment Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities 2 years 10 months    
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]      
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities   2us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value   15,224,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value   0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Investment Securities, Continuous Unrealized Loss Position, Fair Value   15,224,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses   56,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses   0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss   56,000us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
Other than Temporary Impairment Losses, Investment Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Lowest Current Credit Rating [Abstract]      
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Carrying Value 35,750,000bokf_HeldToMaturitySecuritiesPortfolioConcentrationUsGovtGseSecuritiesNotRatedCarryingValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [4]    
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value 37,463,000bokf_HeldToMaturityPortfolioConcentrationRatedUsGovernmentOrGseFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [4]    
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaCarryingValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		    
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		    
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbCarryingValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		    
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
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[1] Carrying value includes $615 thousand of net unrealized gain which remains in Accumulated other comprehensive income (“AOCI”) in the Consolidated Balance Sheets related to certain securities transferred from the Available for Sale securities portfolio to the Investment securities portfolio as discussed in greater detail following.
[2] Carrying value includes $1.8 million of net unrealized gain which remains in AOCI in the Consolidated Balance Sheets related to certain securities transferred from the Available for Sale securities portfolio to the Investment securities portfolio as discussed in greater detail following.
[3] Gross unrealized gains and losses are not recognized in AOCI in the Consolidated Balance Sheets.
[4] 1 U.S. government and government sponsored enterprises are not rated by the nationally-recognized rating agencies as these securities are guaranteed by agencies of the U.S. government or government-sponsored enterprises.
[5] Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty.
[6] Calculated on a taxable equivalent basis using a 39% effective tax rate.
[7] The nominal yield on residential mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary - Unaudited for current yields on the investment securities portfolio.