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Mortgage Banking Activities, Mortgage Banking Revenue (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Mortgage Banking Revenue [Abstract] |  |  |
Net realized gains on sales of mortgage loans | $ 39,730 | $ 36,379 | $ 45,128
Net change in unrealized gain on mortgage loans held for sale | 672 | (674) | 2,031
Net change in fair value of mortgage loan commitments | (145) | (1,145) | (3,210)
Net change in the fair value of forward sales contracts | 2,463 | (2,870) | (5,451)
Total mortgage production revenue | 42,720 | 31,690 | 38,498
Servicing revenue | 64,821 | 66,097 | 66,221
Total mortgage banking revenue | $ 107,541 | $ 97,787 | $ 104,719

X
- Definition Represents the change in fair value of mortgage loan commitments during the period. + References No definition available. + Details
Name: | bokf_Changeinfairvalueofmortgageloancommitments
Namespace Prefix: | bokf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the change in the fair value of forward sales commitments considered to be derivative instruments during the period. + References No definition available. + Details
Name: | bokf_Changeinthefairvalueofforwardsalescommitments
Namespace Prefix: | bokf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition 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. + References No definition available. + Details
Name: | bokf_MortgageBankingRevenue
Namespace Prefix: | bokf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Mortgage Banking Revenue [Abstract] + References No definition available. + Details
Name: | bokf_MortgageBankingRevenueAbstract
Namespace Prefix: | bokf_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Total gain (loss) on mortgage loans held for sale, including mortgage loan commitments and forward sales contracts. + References No definition available. + Details
Name: | bokf_MortgageProductionRevenue
Namespace Prefix: | bokf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Servicing fees for loans secured by real property. + References No definition available. + Details
Name: | bokf_MortgageServicingFees
Namespace Prefix: | bokf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the net change in unrealized gain on mortgage loans held for sale under fair value option. + References No definition available. + Details
Name: | bokf_Netchangeinunrealizedgainonmortgageloansheldforsale
Namespace Prefix: | bokf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=118959141&loc=d3e21310-158488 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118959141&loc=d3e21286-158488 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=117337389&loc=d3e21493-158490 + Details
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