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Mortgage Banking Activities, Loan Servicing Portfolio (Details) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Stratification of Mortgage Loan Servicing Portfolio [Line Items]        
Fair value $ 171,976,000us-gaap_ServicingAssetAtFairValueAmount $ 153,333,000us-gaap_ServicingAssetAtFairValueAmount $ 100,812,000us-gaap_ServicingAssetAtFairValueAmount $ 86,783,000us-gaap_ServicingAssetAtFairValueAmount
Outstanding principal of loans serviced others 16,162,887,000bokf_LoansServicedForOthers      
Weighted average prepayment rate (in hundredths) 10.26%bokf_WeightedAveragePrepaymentRate [1]      
Economic hedge threshold for interest rate sensitivity for mortgage servicing rights and securities held (in basis points) 50bokf_EconomicHedgeThresholdForInterestRateSensitivityForMortgageServicingRightsAndSecuritiesHeld      
Dollar increase in fair value, net of economic hedge, of mortgage servicing rights due to 50 basis point increase in mortgage interest rates 4,700,000bokf_IncreaseInFairValueOfMortgageServicingRightsDueTo50BasisPointIncreaseInMortgageInterestRates      
Dollar decrease in fair value, net of economic hedge, of mortgage servicing rights due to 50 basis point decrease in mortgage interest rates 4,600,000bokf_DecreaseInFairValueOfMortgageServicingRightsDueTo50BasisPointDecreaseInMortgageInterestRates      
Interest Rate Range Less than 4.00% [Member]        
Stratification of Mortgage Loan Servicing Portfolio [Line Items]        
Fair value 67,412,000us-gaap_ServicingAssetAtFairValueAmount
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRangeLessThan400Member		      
Outstanding principal of loans serviced others 6,332,112,000bokf_LoansServicedForOthers
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRangeLessThan400Member		      
Weighted average prepayment rate (in hundredths) 7.70%bokf_WeightedAveragePrepaymentRate
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRangeLessThan400Member		 [1]      
Interest Rate Range 4.00% to 4.99% [Member]        
Stratification of Mortgage Loan Servicing Portfolio [Line Items]        
Fair value 80,405,000us-gaap_ServicingAssetAtFairValueAmount
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRange400To499Member		      
Outstanding principal of loans serviced others 6,882,025,000bokf_LoansServicedForOthers
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRange400To499Member		      
Weighted average prepayment rate (in hundredths) 8.58%bokf_WeightedAveragePrepaymentRate
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRange400To499Member		 [1]      
Interest Rate Range 5.00% to 5.99% [Member]        
Stratification of Mortgage Loan Servicing Portfolio [Line Items]        
Fair value 19,383,000us-gaap_ServicingAssetAtFairValueAmount
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRange500To599Member		      
Outstanding principal of loans serviced others 1,989,977,000bokf_LoansServicedForOthers
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRange500To599Member		      
Weighted average prepayment rate (in hundredths) 14.50%bokf_WeightedAveragePrepaymentRate
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRange500To599Member		 [1]      
Interest Rate Range Greater than 5.99% [Member]        
Stratification of Mortgage Loan Servicing Portfolio [Line Items]        
Fair value 4,776,000us-gaap_ServicingAssetAtFairValueAmount
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRangeGreaterThan599Member		      
Outstanding principal of loans serviced others $ 958,773,000bokf_LoansServicedForOthers
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRangeGreaterThan599Member		      
Weighted average prepayment rate (in hundredths) 30.44%bokf_WeightedAveragePrepaymentRate
/ bokf_MortgageLoanServicingPortfolioByInterestRateRangeAxis
= bokf_InterestRateRangeGreaterThan599Member		 [1]      
[1] Annual prepayment estimates based upon loan interest rate, original term and loan type. Weighted average prepayment rate is determined by weighting the prepayment speed for each loan by its unpaid principal balance.