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Commitments and Contingent Liabilities Guarantor Obligations (Details) (Property Lease Guarantee [Member], USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Property Lease Guarantee [Member]
  
Guarantor Obligations [Line Items]  
Total amount of guaranteed rents $ 29bokf_TotalAmountOfGuaranteedRents
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_PropertyLeaseGuaranteeMember
Contingent Obligation For Guaranteed Rents 7.7us-gaap_GuaranteeObligationsMaximumExposure
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_PropertyLeaseGuaranteeMember
Guaranteed Percentage To Be Received (in hundredths) 80.00%bokf_GuaranteedPercentageToBeReceived
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_PropertyLeaseGuaranteeMember
Maximum Amount To Be Received Under Rent Agreement With City Of Tulsa $ 4.5bokf_MaximumAmountToBeReceivedUnderRentAgreementWithCityOfTulsa
/ us-gaap_GuaranteeObligationsByNatureAxis
= us-gaap_PropertyLeaseGuaranteeMember