The number of branch offices operated by the entity.

No definition available.

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Namespace Prefix:	abtx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of banking branches which will be sold under a definitive purchase and assumption agreement pending regulatory approval and certain other customary conditions.

+ References

No definition available.

+ Details

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Namespace Prefix:	abtx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The total amount of proceeds for the sale of deposits.

+ References

No definition available.

+ Details

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Namespace Prefix:	abtx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Amount of gain (loss) on sale or disposal of assets utilized in financial service operations.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow associated with the sale of loans receivables arising from the financing of goods and services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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Namespace Prefix:
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Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=abtx_EnterpriseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=abtx_HoustonTexasMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_StatementGeographicalAxis=abtx_CentralTexasMember
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ACQUISITIONS (Details) $ in Thousands	3 Months Ended			9 Months Ended
ACQUISITIONS (Details) $ in Thousands	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Mar. 31, 2016 USD ($) branch	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jan. 01, 2015 branch
Business Acquisition [Line Items]
Gain on sale of branch assets \| $	$ 0	$ 0		$ 0	$ 2,050
Acquisition of F&M
Business Acquisition [Line Items]
Proceeds from sale of loans receivable \| $			$ 18,200
Proceeds for sale of deposits \| $			26,600
Gain on sale of branch assets \| $			$ 2,100
Disposed of by Sale
Business Acquisition [Line Items]
Number of branches agreed to be sold \| branch			2
Enterprise
Business Acquisition [Line Items]
Number of branches \| branch						9
Enterprise \| Houston, Texas
Business Acquisition [Line Items]
Number of branches \| branch						7
Enterprise \| Central Texas
Business Acquisition [Line Items]
Number of branches \| branch						2