NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING AND REPORTING POLICIES (Details)	Sep. 30, 2017 office
Accounting Policies [Abstract]
Number of offices in which entity operates	16
Number of loan production offices in which entity operates	1

Number of Loan Production Offices in which Entity Operates

No definition available.

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