SECURITIES (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	$ 2,660,254	$ 3,204,361
Gross Unrealized Gains	233	293
Gross Unrealized (Losses)	(408,122)	(462,838)
Total AFS securities, Estimated Fair Value	2,252,365	2,741,816
U.S. government and agency securities
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	69,474	70,196
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(6,900)	(8,253)
Total AFS securities, Estimated Fair Value	62,574	61,943
Obligations of states and political subdivisions
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	650,328	959,999
Gross Unrealized Gains	20	137
Gross Unrealized (Losses)	(127,251)	(152,701)
Total AFS securities, Estimated Fair Value	523,097	807,435
Corporate and other bonds
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	171,899	243,979
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(19,893)	(17,599)
Total AFS securities, Estimated Fair Value	152,006	226,380
Commercial
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	300,856	349,598
Gross Unrealized Gains	156	75
Gross Unrealized (Losses)	(40,365)	(43,512)
Total AFS securities, Estimated Fair Value	260,647	306,161
Commercial \| Agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	220,617	250,186
Gross Unrealized Gains	156	75
Gross Unrealized (Losses)	(37,729)	(39,268)
Total AFS securities, Estimated Fair Value	183,044	210,993
Commercial \| Non-agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	80,239	99,412
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(2,636)	(4,244)
Total AFS securities, Estimated Fair Value	77,603	95,168
Residential
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	1,466,016	1,578,925
Gross Unrealized Gains	57	81
Gross Unrealized (Losses)	(213,713)	(240,773)
Total AFS securities, Estimated Fair Value	1,252,360	1,338,233
Residential \| Agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	1,394,464	1,510,110
Gross Unrealized Gains	57	81
Gross Unrealized (Losses)	(207,355)	(233,961)
Total AFS securities, Estimated Fair Value	1,187,166	1,276,230
Residential \| Non-agency
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	71,552	68,815
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(6,358)	(6,812)
Total AFS securities, Estimated Fair Value	65,194	62,003
Other securities
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract]
Total AFS securities	1,681	1,664
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	0	0
Total AFS securities, Estimated Fair Value	$ 1,681	$ 1,664

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAmortizedCostAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_AgencySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=aub_NonAgencySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CollateralizedSecuritiesOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: