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Fair Value Measurements, Fair Value Measured On a Nonrecurring Basis (Details) - Fair Value, Measurements, Nonrecurring [Member] - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Impaired Loans [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Gross charge-offs against allowance for loan losses | $ 6,701 | $ 232 | $ 7,198 | $ 676
Net losses and expenses of repossessed assets, net | 0 | 0 | 0 | 0
Real estate and other repossessed assets [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Gross charge-offs against allowance for loan losses | 0 | 0 | 0 | 0
Net losses and expenses of repossessed assets, net | 118 | 772 | 5,242 | 906
Fair Value, Inputs, Level 1 [Member] | Impaired Loans [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Carrying Value | 0 | 0 | 0 | 0
Fair Value, Inputs, Level 1 [Member] | Real estate and other repossessed assets [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Carrying Value | 0 | 0 | 0 | 0
Fair Value, Inputs, Level 2 [Member] | Impaired Loans [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Carrying Value | 1,045 | 464 | 1,045 | 464
Fair Value, Inputs, Level 2 [Member] | Real estate and other repossessed assets [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Carrying Value | 1,996 | 3,488 | 1,996 | 3,488
Fair Value, Inputs, Level 3 [Member] | Impaired Loans [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Carrying Value | 11,763 | 3,570 | 11,763 | 3,570
Fair Value, Inputs, Level 3 [Member] | Real estate and other repossessed assets [Member] |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Carrying Value | $ 6,838 | $ 530 | $ 6,838 | $ 530

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- Definition Amount of expense and net losses recognized during the period for repossessed assets. + References No definition available. + Details
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Namespace Prefix: | bokf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7(d)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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Balance Type: | debit
Period Type: | duration

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- Definition This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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