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PARENT COMPANY FINANCIAL INFORMATION (Narrative) (Details) - Parent Company $ in Millions | Dec. 31, 2019 USD ($)
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Aggregate amount of unrestricted funds | $ 383.7
Aggregate amount of unrestricted funds percentage | 15.27%

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- Definition Aggregate amount of unrestricted funds available for transfer to the Parent Company from the Bank. + References No definition available. + Details
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Namespace Prefix: | aub_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Percentage of aggregate amount of unrestricted funds available for transfer to the Parent Company from the Bank to consolidated net assets. + References No definition available. + Details
Name: | aub_PercentageOfAggregateAmountOfUnrestrictedFundsAvailableToConsolidatedNetAssets
Namespace Prefix: | aub_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Details
Name: | srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |