REGULATORY CAPITAL MATTERS - Actual and Required Capital (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Total Capital
Capital	$ 292,639	$ 268,155
Capital to Risk Weighted Assets	12.04%	12.57%
Capital Required for Capital Adequacy	$ 194,407	$ 170,690
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Plus Capital Conservation Buffer	$ 224,783	$ 184,025
Plus Capital Conservation Buffer to Risk Weighted Assets	9.25%	8.625%
Common Equity Tier 1 Capital
Common Equity Tier One Risk Based Capital	$ 259,640	$ 241,048
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	10.68%	11.30%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy	$ 109,354	$ 96,013
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Plus Common Equity Tier One Risk Based Capital	$ 139,730	$ 109,348
Plus Common Equity Tier One Risk Based Capital to Risk Weighted Assets	5.75%	5.125%
Tier I Capital
Tier One Risk Based Capital	$ 268,917	$ 250,244
Tier One Risk Based Capital to Risk Weighted Assets	11.07%	11.73%
Tier One Risk Based Capital Required for Capital Adequacy	$ 145,805	$ 128,018
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%	6.00%
Plus Tier One Risk Based Capital	$ 176,181	$ 141,353
Plus Tier One Risk Based Capital to Risk Weighted Assets	7.25%	6.625%
Tier I Capital
Tier One Leverage Capital	$ 268,917	$ 250,244
Tier One Leverage Capital to Average Assets	9.90%	10.35%
Tier One Leverage Capital Required for Capital Adequacy	$ 108,673	$ 96,708
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%	4.00%
Plus Tier One Leverage Capital	$ 108,673	$ 96,708
Plus Tier One Leverage Capital to Average Assets	4.00%	4.00%
Allegiance Bank
Total Capital
Capital	$ 289,178	$ 247,606
Capital to Risk Weighted Assets	11.90%	11.61%
Capital Required for Capital Adequacy	$ 194,316	$ 170,630
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Plus Capital Conservation Buffer	$ 224,678	$ 183,960
Plus Capital Conservation Buffer to Risk Weighted Assets	9.25%	8.625%
Capital Required to be Well Capitalized	$ 242,895	$ 213,288
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00%	10.00%
Common Equity Tier 1 Capital
Common Equity Tier One Risk Based Capital	$ 265,456	$ 229,694
Common Equity Tier One Risk Based Capital to Risk Weighted Assets	10.93%	10.77%
Common Equity Tier One Risk Based Capital Required for Capital Adequacy	$ 109,303	$ 95,979
Common Equity Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Plus Common Equity Tier One Risk Based Capital	$ 139,664	$ 109,310
Plus Common Equity Tier One Risk Based Capital to Risk Weighted Assets	5.75%	5.125%
Common Equity Tier One Risk Based Capital Required to be Well Capitalized	$ 157,882	$ 138,637
Common Equity Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	6.50%	6.50%
Tier I Capital
Tier One Risk Based Capital	$ 265,456	$ 229,694
Tier One Risk Based Capital to Risk Weighted Assets	10.93%	10.77%
Tier One Risk Based Capital Required for Capital Adequacy	$ 145,737	$ 127,973
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%	6.00%
Plus Tier One Risk Based Capital	$ 176,099	$ 141,303
Plus Tier One Risk Based Capital to Risk Weighted Assets	7.25%	6.625%
Tier One Risk Based Capital Required to be Well Capitalized	$ 194,316	$ 170,630
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets	8.00%	8.00%
Tier I Capital
Tier One Leverage Capital	$ 265,456	$ 229,694
Tier One Leverage Capital to Average Assets	9.77%	9.50%
Tier One Leverage Capital Required for Capital Adequacy	$ 108,630	$ 96,679
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%	4.00%
Plus Tier One Leverage Capital	$ 108,630	$ 96,679
Plus Tier One Leverage Capital to Average Assets	4.00%	4.00%
Tier One Leverage Capital Required to be Well Capitalized	$ 135,788	$ 120,849
Tier One Leverage Capital Required to be Well Capitalized to Average Assets	5.00%	5.00%

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The amount of total capital as defined in the regulations.

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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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Tier 1 Risk Based Capital as defined in the regulations.

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