Mortgage Banking Activities, Components of Loans Held For Sale (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of Residential Mortgage Loans Held for Sale [Abstract]
Residential mortgages loans held for sale, Fair Value	$ 304,182us-gaap_LoansHeldForSaleMortgages	$ 200,546us-gaap_LoansHeldForSaleMortgages
Mortgage Banking Revenue [Abstract]
Net realized gains on sales of mortgage loans	56,696us-gaap_GainLossOnSaleOfMortgageLoans	95,309us-gaap_GainLossOnSaleOfMortgageLoans	115,879us-gaap_GainLossOnSaleOfMortgageLoans
Net change in unrealized gain on mortgage loans held for sale	5,357	(10,899)	4,720
Change in fair value of mortgage loan commitments	7,315	(10,077)	6,136
Change in the fair value of forward sales commitments	(8,307)	5,212	2,382
Total production revenue	61,061bokf_MortgageProductionRevenue	79,545bokf_MortgageProductionRevenue	129,117bokf_MortgageProductionRevenue
Servicing revenue	48,032us-gaap_ServicingFeesNet	42,389us-gaap_ServicingFeesNet	40,185us-gaap_ServicingFeesNet
Total mortgage banking revenue	109,093bokf_MortgageBankingRevenue	121,934bokf_MortgageBankingRevenue	169,302bokf_MortgageBankingRevenue
Residential mortgage loans held for sale [Member]
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
Number of days for past due for loan to be considered nonperforming (in days)	90 days	90 days
Residential mortgage loans held for sale, nonperforming	0	0
Credit losses recognized on residential mortgage loans held for sale	0	0
Components of Residential Mortgage Loans Held for Sale [Abstract]
Residential mortgage loans held for sale, Unpaid Principal Balance	291,537	192,266
Residential mortgages loans held for sale, Fair Value	298,212	193,584
Residential mortgage loan commitments [Member]
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
General number of days outstanding for residential mortgage commitments, minimum (in days)	60 days	60 days
General number of days outstanding for residential mortgage commitments, maximum (in days)	90 days	90 days
Components of Residential Mortgage Loans Held for Sale [Abstract]
Residential mortgage loans held for sale, Derivative contracts, Notional	520,829	258,873
Residential mortgages loans held for sale, Fair Value	9,971	2,656
Forward sales contracts [Member]
Schedule of Residential Mortgage Loans Held For Sale [Line Items]
General number of days for delivery of loans, for which the price is set by forward sales contracts, minimum (in days)	60 days	60 days
General number of days for delivery of loans, for which the price is set by forward sales contracts, maximum (in days)	90 days	90 days
Components of Residential Mortgage Loans Held for Sale [Abstract]
Residential mortgage loans held for sale, Derivative contracts, Notional	701,066	435,867
Residential mortgages loans held for sale, Fair Value	$ (4,001)	$ 4,306

Represents the change in fair value of mortgage loan commitments during the period.

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Represents the change in the fair value of forward sales commitments considered to be derivative instruments during the period.

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Credit losses recognized on residential mortgage loans held for sale

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Maximum number of days for delivery of forward sales contracts.

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Maximum number of days outstanding for residential mortgage commitments to purchase.

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Minimum number of days for delivery of forward sales contracts.

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Minimum number of days outstanding for residential mortgage commitments to purchase.

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Noninterest income derived from the sale and changes in fair value of residential mortgage loans held for sale and fees for servicing of residential mortgage loans held by third parties. Also includes changes in the fair value of residential mortgage loan commitments and forward sales commitments considered to be derivative instruments.

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Total gain (loss) on mortgage loans held for sale, including mortgage loan commitments and forward sales contracts.

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Represents the net change in unrealized gain on mortgage loans held for sale under fair value option.

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No definition available.

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Number of days past due for residential mortgage loans

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Residential mortgage loans held for sale, 90 days past due or impaired.

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- Definition

Unpaid principal balance of loans held for sale.

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Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

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The gains (losses) included in earnings that represent the difference between the sale price and the carrying value of loans made to finance real estate acquisitions. This element refers to the gain (loss) and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

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-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 45

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Amount classified as mortgage loans attributable to disposal group held for sale or disposed of. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.

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Amount of revenue from servicing real estate mortgages, credit cards, and other financial assets held by others. Includes premiums received in lieu of regular servicing fees.

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