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Acquisition Acquisitions (Details) | 3 Months Ended
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Jun. 30, 2018 USD ($) shares
Cobiz Financial Inc. [Member] |
Business Acquisition [Line Items] |
Business Acquisition, Date of Acquisition Agreement | Jun. 18, 2018
Cobiz Financial Assets | $ 3,800,000,000
Number of BOKF Shares Given for Each Existing Cobiz Share | shares | 0.17
Amount of Cash Paid for Each Exisitng Share of Cobiz Stock | $ 5.70
Switchgrass Holdings LLC [Member] |
Business Acquisition [Line Items] |
Business Acquisition, Effective Date of Acquisition | May 01, 2018
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Consideration Transferred | $ 14,000,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Goodwill | $ 6,100,000

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- Definition Amount of Cash Paid for Each Exisitng Share of Cobiz Stock + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Goodwill + References No definition available. + Details
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Balance Type: | debit
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- Definition Cobiz Financial 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 Number of BOKF Shares Given for Each Existing Cobiz Share + References No definition available. + Details
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Namespace Prefix: | bokf_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Definition Date when the business acquisition agreement was executed, in CCYY-MM-DD format. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

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- Definition Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e845-128460 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e848-128460 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463 + Details
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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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- Definition This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to items of consideration transferred in connection with a business combination for which the initial accounting was incomplete. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 4A -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=SL65897772-128472 + Details
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- Details
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Namespace Prefix: |
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |