XML 56 R44.htm IDEA: XBRL DOCUMENT
v3.25.3

SECURITIES AND OTHER INVESTMENTS (Amortized Cost, Gross Unrealized Gains and Losses, and Estimated Fair Values of Investment Securities) (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | $ 4,595,098 | $ 2,844,763
Gross Unrealized Gains | 16,587 | 3,378
Gross Unrealized (Losses) | (344,162) | (405,975)
Total AFS securities, Estimated Fair Value | 4,267,523 | 2,442,166
US Government Agencies Debt Securities [Member] |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 128,592 | 65,650
Gross Unrealized Gains | 723 | 390
Gross Unrealized (Losses) | (34) | (27)
Total AFS securities, Estimated Fair Value | 129,281 | 66,013
US States and Political Subdivisions Debt Securities [Member] |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 598,767 | 597,956
Gross Unrealized Gains | 186 | 84
Gross Unrealized (Losses) | (117,438) | (129,703)
Total AFS securities, Estimated Fair Value | 481,515 | 468,337
Corporate Bond Securities [Member] |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 250,663 | 253,526
Gross Unrealized Gains | 686 | 505
Gross Unrealized (Losses) | (5,194) | (9,319)
Total AFS securities, Estimated Fair Value | 246,155 | 244,712
Commercial Mortgage-Backed Securities [Member] |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 462,479 | 347,501
Gross Unrealized Gains | 1,370 | 352
Gross Unrealized (Losses) | (42,929) | (46,788)
Total AFS securities, Estimated Fair Value | 420,920 | 301,065
Commercial Mortgage-Backed Securities [Member] | Agency Securities [Member] |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 359,154 | 285,949
Gross Unrealized Gains | 1,148 | 348
Gross Unrealized (Losses) | (40,826) | (44,678)
Total AFS securities, Estimated Fair Value | 319,476 | 241,619
Commercial Mortgage-Backed Securities [Member] | Non-agency |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 103,325 | 61,552
Gross Unrealized Gains | 222 | 4
Gross Unrealized (Losses) | (2,103) | (2,110)
Total AFS securities, Estimated Fair Value | 101,444 | 59,446
Residential Mortgage-Backed Securities [Member] |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 3,152,665 | 1,578,270
Gross Unrealized Gains | 13,622 | 2,047
Gross Unrealized (Losses) | (178,567) | (220,138)
Total AFS securities, Estimated Fair Value | 2,987,720 | 1,360,179
Residential Mortgage-Backed Securities [Member] | Agency Securities [Member] |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 2,968,326 | 1,478,648
Gross Unrealized Gains | 12,772 | 1,375
Gross Unrealized (Losses) | (175,713) | (216,754)
Total AFS securities, Estimated Fair Value | 2,805,385 | 1,263,269
Residential Mortgage-Backed Securities [Member] | Non-agency |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 184,339 | 99,622
Gross Unrealized Gains | 850 | 672
Gross Unrealized (Losses) | (2,854) | (3,384)
Total AFS securities, Estimated Fair Value | 182,335 | 96,910
Collateralized Securities, Other [Member] |  |
Debt Securities, Available-for-sale Securities, Amortized Cost Basis [Abstract] |  |
Total AFS securities | 1,932 | 1,860
Gross Unrealized Gains | 0 | 0
Gross Unrealized (Losses) | 0 | 0
Total AFS securities, Estimated Fair Value | $ 1,932 | $ 1,860

X
- Definition 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). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-2 + Details
Name: | us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-2 + Details
Name: | us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- 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 -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479130/326-30-45-1 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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 -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479130/326-30-45-1 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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

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

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

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

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

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

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