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Fair Value Measurements Fair Value Measurement, Measured On Non-Recurring Basis, Signfiicant Unobservable Inputs, Quantitative Information (Details) (Fair Value, Measurements, Nonrecurring [Member], Fair Value, Inputs, Level 3 [Member], USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2014
Mar. 31, 2015
Impaired Loans [Member]
   
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Assets, Fair Value Disclosure, Nonrecurring $ 1,541us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByAssetClassAxis
= bokf_FairValueImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
$ 0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByAssetClassAxis
= bokf_FairValueImpairedLoansMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
Fair Value Measurements, Valuation Techniques Appraised value, as adjusted  
Fair Value Measurements, Significant Unobservable Input Broker quotes and management's knowledge of industry and collateral.  
Real estate and other repossessed assets [Member]
   
Fair Value Inputs, Assets, Quantitative Information [Line Items]    
Assets, Fair Value Disclosure, Nonrecurring $ 0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByAssetClassAxis
= bokf_FairValueRealEstateAndOtherRepossessedAssetsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember
$ 0us-gaap_AssetsFairValueDisclosureNonrecurring
/ us-gaap_FairValueByAssetClassAxis
= bokf_FairValueRealEstateAndOtherRepossessedAssetsMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
/ us-gaap_FairValueByMeasurementFrequencyAxis
= us-gaap_FairValueMeasurementsNonrecurringMember