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Investment (Held-to-Maturity) Securities (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investment Securities, Amortized Cost $ 634,151bokf_HeldToMaturitySecuritiesAmortizedCost $ 651,745bokf_HeldToMaturitySecuritiesAmortizedCost $ 667,548bokf_HeldToMaturitySecuritiesAmortizedCost
Investments Securities, Carrying Value 634,587us-gaap_HeldToMaturitySecurities [1] 652,360us-gaap_HeldToMaturitySecurities [2] 668,976us-gaap_HeldToMaturitySecurities [3]
Investment securities, fair value 657,971us-gaap_HeldToMaturitySecuritiesFairValue 673,626us-gaap_HeldToMaturitySecuritiesFairValue 685,063us-gaap_HeldToMaturitySecuritiesFairValue
Investment Securities, Gross Unrealized Gain 24,651us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain [4] 22,874us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain [4] 18,253us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain [4]
Investment Securities, Gross Unrealized Loss (1,267)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss [4] (1,608)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss [4] (2,166)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss [4]
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Net Carrying Value 634,587us-gaap_HeldToMaturitySecurities [1] 652,360us-gaap_HeldToMaturitySecurities [2] 668,976us-gaap_HeldToMaturitySecurities [3]
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]      
Investment Securities, Debt Maturities, Fair value 657,971us-gaap_HeldToMaturitySecuritiesFairValue 673,626us-gaap_HeldToMaturitySecuritiesFairValue 685,063us-gaap_HeldToMaturitySecuritiesFairValue
Investment Securities, Debt Maturities, Nominal Yield [Abstract]      
Investment Securities, Debt Maturities, Nominal Yield 3.26%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield    
Investment Securities, Pledged as Collateral [Abstract]      
Investment Securities, Pledged as Collateral, Carrying Value 63,425us-gaap_HeldToMaturitySecuritiesPledgedAsCollateral 63,495us-gaap_HeldToMaturitySecuritiesPledgedAsCollateral 87,757us-gaap_HeldToMaturitySecuritiesPledgedAsCollateral
Investment Securities, Pledged as Collateral, Fair Value 65,723bokf_HeldToMaturityCollateralFairValue 65,855bokf_HeldToMaturityCollateralFairValue 90,765bokf_HeldToMaturityCollateralFairValue
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]      
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 134us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions 162us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions 128us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 72,499us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue 143,951us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue 100,994us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 56,140us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue 60,837us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue 118,707us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Investment Securities, Continuous Unrealized Loss Position, Fair Value 128,639us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue 204,788us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue 219,701us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 1,019us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss 1,063us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss 771us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 248us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss 545us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss 1,395us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss 1,267us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss 1,608us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss 2,166us-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 33,545bokf_HeldToMaturitySecuritiesPortfolioConcentrationUsGovtGseSecuritiesNotRatedCarryingValue [5]    
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value 35,253bokf_HeldToMaturityPortfolioConcentrationRatedUsGovernmentOrGseFairValue [5]    
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value 408,301bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaCarryingValue    
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value 427,251bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaFairValue    
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value 13,078bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbCarryingValue    
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value 13,198bokf_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 179,663bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedCarryingValue    
Investment Securities, Portfolio Concentration Not Rated, Fair Value 182,269bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedFairValue    
Fixed Maturity Securities [Member]      
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investments Securities, Carrying Value 601,042us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment securities, fair value 622,718us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value 65,434bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value 326,886bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value 105,018bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value 103,704bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Net Carrying Value 601,042us-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 65,622us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Fair Value 329,374us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value 112,752us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Fair Value 114,970us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Fair value 622,718us-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 2.07%bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield 2.12%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield 5.33%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield 5.65%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Nominal Yield 3.28%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		    
Investment Securities, Debt Maturities, Weighted Average Maturity 5.56bokf_HeldToMaturitySecuritiesDebtMaturitiesWeightedAverageMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_FixedIncomeSecuritiesMember		 [6]    
Municipal and other tax-exempt securities [Member]      
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investment Securities, Amortized Cost 396,063bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 405,090bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 440,303bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Investments Securities, Carrying Value 396,063us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [1] 405,090us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [2] 440,303us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [3]
Investment securities, fair value 400,112us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 408,344us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 441,532us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Investment Securities, Gross Unrealized Gain 4,443us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [4] 4,205us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [4] 3,182us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [4]
Investment Securities, Gross Unrealized Loss (394)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [4] (951)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [4] (1,953)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [4]
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value 51,635bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value 287,099bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value 19,461bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value 37,868bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Net Carrying Value 396,063us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [1] 405,090us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [2] 440,303us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [3]
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]      
Investment Securities, Debt Maturities, Less Than One Year, Fair Value 51,726us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, One to Five Years, Fair Value 288,383us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value 19,757us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Over Ten Years, Fair Value 40,246us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Debt Maturities, Fair value 400,112us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 408,344us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 441,532us-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 1.72%bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [7]    
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield 1.76%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [7]    
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield 4.04%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [7]    
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield 5.36%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [7]    
Investment Securities, Debt Maturities, Nominal Yield 2.21%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [7]    
Investment Securities, Debt Maturities, Weighted Average Maturity 3.62bokf_HeldToMaturitySecuritiesDebtMaturitiesWeightedAverageMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [6]    
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 Positions 37us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 78us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 96us-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 41,048us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 112,677us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 78,833us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 53,662us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 60,076us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 117,909us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Investment Securities, Continuous Unrealized Loss Position, Fair Value 94,710us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 172,753us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 196,742us-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, Accumulated Loss 173us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 426us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 601us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 221us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 525us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 1,352us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss 394us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 951us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 1,953us-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		 [5]    
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value 0bokf_HeldToMaturityPortfolioConcentrationRatedUsGovernmentOrGseFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 [5]    
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value 256,859bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value 257,878bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value 13,078bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value 13,198bokf_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 126,126bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Investment Securities, Portfolio Concentration Not Rated, Fair Value 129,036bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		    
Other debt securities [Member]      
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investment Securities, Amortized Cost 204,979bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 211,520bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 182,756bokf_HeldToMaturitySecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember
Investments Securities, Carrying Value 204,979us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [1] 211,520us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [2] 182,756us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [3]
Investment securities, fair value 222,606us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 227,819us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 195,697us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember
Investment Securities, Gross Unrealized Gain 18,500us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [4] 16,956us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [4] 13,114us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [4]
Investment Securities, Gross Unrealized Loss (873)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [4] (657)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [4] (173)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [4]
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Less than One Year, Net Carrying Value 13,799bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Net Carrying Value 39,787bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Net Carrying Value 85,557bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Net Carrying Value 65,836bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNetCarryingAmount
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Net Carrying Value 204,979us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [1] 211,520us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [2] 182,756us-gaap_HeldToMaturitySecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [3]
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]      
Investment Securities, Debt Maturities, Less Than One Year, Fair Value 13,896us-gaap_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Fair Value 40,991us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Fair Value 92,995us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Fair Value 74,724us-gaap_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Fair value 222,606us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 227,819us-gaap_HeldToMaturitySecuritiesFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 195,697us-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 3.36%bokf_HeldToMaturitySecuritiesDebtMaturitiesNextRollingTwelveMonthsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, One to Five Years, Nominal Yield 4.70%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearTwoThroughFiveNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Six to Ten Years, Nominal Yield 5.62%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingYearSixThroughTenNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Over Ten Years, Nominal Yield 5.83%bokf_HeldToMaturitySecuritiesDebtMaturitiesRollingAfterTenYearsNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Nominal Yield 5.35%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Debt Maturities, Weighted Average Maturity 9.31bokf_HeldToMaturitySecuritiesDebtMaturitiesWeightedAverageMaturity
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [6]    
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]      
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 97us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 84us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 31us-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 31,451us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 31,274us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 12,516us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember
Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 2,478us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 761us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 798us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember
Investment Securities, Continuous Unrealized Loss Position, Fair Value 33,929us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 32,035us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 13,314us-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, Accumulated Loss 846us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 637us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 130us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember
Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 27us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 20us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 43us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember
Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss 873us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 657us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 173us-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		 [5]    
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value 0bokf_HeldToMaturityPortfolioConcentrationRatedUsGovernmentOrGseFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		 [5]    
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value 151,442bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value 169,373bokf_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 53,537bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedCarryingValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
Investment Securities, Portfolio Concentration Not Rated, Fair Value 53,233bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_OtherDebtSecuritiesMember		    
U.S. agency residential mortgage-backed securities [Member] | Other [Member]      
Schedule of Investment (Held-to-Maturity) Securities [Line Items]      
Investment Securities, Amortized Cost 33,109bokf_HeldToMaturitySecuritiesAmortizedCost
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 35,135bokf_HeldToMaturitySecuritiesAmortizedCost
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 44,489bokf_HeldToMaturitySecuritiesAmortizedCost
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Investments Securities, Carrying Value 33,545us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [1] 35,750us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [2] 45,917us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [3]
Investment securities, fair value 35,253us-gaap_HeldToMaturitySecuritiesFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 37,463us-gaap_HeldToMaturitySecuritiesFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 47,834us-gaap_HeldToMaturitySecuritiesFairValue
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Investment Securities, Gross Unrealized Gain 1,708us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [4] 1,713us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [4] 1,957us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [4]
Investment Securities, Gross Unrealized Loss 0us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [4] 0us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [4] (40)us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [4]
Investments Securities, Transfers [Abstract]      
Investment Securities, Transferred From Available For Sale Securities Portfolio, Net Unrealized Gain 436bokf_InvestmentSecuritiesTransferredFromAvailableForSaleSecuritiesPortfolioNetUnrealizedGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 615bokf_InvestmentSecuritiesTransferredFromAvailableForSaleSecuritiesPortfolioNetUnrealizedGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 1,400bokf_InvestmentSecuritiesTransferredFromAvailableForSaleSecuritiesPortfolioNetUnrealizedGain
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Investment Securities, Debt Maturities, Net Carrying Value [Abstract]      
Investment Securities, Debt Maturities, Net Carrying Value 33,545us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [1] 35,750us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [2] 45,917us-gaap_HeldToMaturitySecurities
/ bokf_GuarantorOfSecurityAxis
= bokf_USAgencyResidentalMortgageBackedSecuritiesOtherMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [3]
Investment Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]      
Investment Securities, Debt Maturities, Fair value 35,253us-gaap_HeldToMaturitySecuritiesFairValue
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 47,834us-gaap_HeldToMaturitySecuritiesFairValue
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Investment Securities, Debt Maturities, Nominal Yield [Abstract]      
Investment Securities, Debt Maturities, Nominal Yield 2.74%bokf_HeldToMaturitySecuritiesDebtMaturitiesNominalYield
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [8]    
Investment Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities 2.7    
Investment Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]      
Investment Securities, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions 0us-gaap_HeldToMaturitySecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
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Investment Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 9,645us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
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Investment Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
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Investment Securities, Continuous Unrealized Loss Position, Fair Value 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 9,645us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
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Investment Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]      
Investment Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 40us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
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Investment Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
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Investment Securities, Continuous Unrealized Loss Position, Accumulated Loss 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 0us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 40us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
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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 33,545bokf_HeldToMaturitySecuritiesPortfolioConcentrationUsGovtGseSecuritiesNotRatedCarryingValue
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [5]    
Investment Securities, Portfolio Concentration US Govt or GSE Securities Not Rated, Fair Value 35,253bokf_HeldToMaturityPortfolioConcentrationRatedUsGovernmentOrGseFairValue
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= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		 [5]    
Investment Securities, Portfolio Concentration Rated AAA to AA, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaCarryingValue
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Investment Securities, Portfolio Concentration Rated AAA to AA, Fair Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedAaaToAaFairValue
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Investment Securities, Portfolio Concentration Rated A to BBB, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbCarryingValue
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Investment Securities, Portfolio Concentration Rated A to BBB, Fair Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedToBbbFairValue
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Investment Securities, Portfolio Concentration Rated Below Investment Grade, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedBelowInvestmentGradeCarryingValue
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Investment Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationRatedBelowInvestmentGradeFairValue
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Investment Securities, Portfolio Concentration Not Rated, Carrying Value 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedCarryingValue
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Investment Securities, Portfolio Concentration Not Rated, Fair Value $ 0bokf_HeldToMaturitySecuritiesPortfolioConcentrationNotRatedFairValue
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[1] Carrying value includes $436 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 in 2011.
[2] 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 in 2011.
[3] Carrying value includes $1.4 million 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 in 2011.
[4] Gross unrealized gains and losses are not recognized in AOCI in the Consolidated Balance Sheets.
[5] 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.
[6] Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty.
[7] Calculated on a taxable equivalent basis using a 39% effective tax rate.
[8] 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.