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Goodwill and Other Intangibles - Additional Information (Detail) $ in Millions | 3 Months Ended
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Mar. 31, 2021 USD ($)
Goodwill And Intangible Assets Disclosure [Abstract] |
Disposition of goodwill | $ 6.3
Unamortized customer relationship intangibles | $ 1.9

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- Definition Unamortized customer relationship intangibles. + References No definition available. + Details
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Namespace Prefix: | umbf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121556970&loc=d3e13816-109267 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration