Note 15 - Stockholders' Equity and Regulatory Matters - Actual Capital Amounts and Ratios (Details) $ in Thousands	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Total Capital, Amount	$ 754,990	$ 704,840
Total Capital to Risk-Weighted Assets Ratio	0.1285	0.1275
Total Capital Required for Capital Adequacy, Amount	$ 470,215	$ 442,391
Total Capital Required for Capital Adequacy, Ratio	0.08	0.08
Total Capital to be Well Capitalized, Amount	$ 587,769	$ 552,988
Total Capital to be Well Capitalized, Ratio	0.10	0.10
Tier I Capital, Amount	$ 614,975	$ 557,088
Tier I Capital to Risk-Weighted Assets Ratio	0.1046	0.1007
Tier I Capital Required for Capital Adequacy, Amount	$ 352,661	$ 331,793
Tier I Capital Required for Capital Adequacy, Ratio	0.06	0.06
Tier I Capital to be Well Capitalized, Amount	$ 470,215	$ 442,391
Tier I Capital to be Well Capitalized, Ratio	0.08	0.08
Common Equity Tier 1 Capital, Amount	$ 538,045	$ 480,158
Common Equity Tier 1 Capital to Risk-Weighted Assets Ratio	0.0915	0.0868
Common Equity Tier 1 Capital Required for Capital Adequacy, Amount	$ 264,496	$ 248,845
Common Equity Tier 1 Capital Required for Capital Adequacy, Ratio	4.50%	4.50%
Common Equity Tier 1 Capital to be Well Capitalized, Amount	$ 382,050	$ 359,442
Common Equity Tier 1 Capital to be Well Capitalized, Ratio	6.50%	6.50%
Tier 1 Leveraged Capital (to Average Assets)	$ 614,975	$ 557,088
Tier 1 Leveraged Capital (to Average Assets) Ratio	0.0952	0.0949
Tier I Leveraged Capital Required for Capital Adequacy, Amount	$ 258,407	$ 234,859
Tier I Leveraged Capital Capital Required for Capital Adequacy, Ratio	0.04	0.04
Tier I Leveraged Capital to be Well Capitalized, Amount	$ 323,008	$ 293,574
Tier I Leveraged Capital to be Well Capitalized, Ratio	0.05	0.05
Business First Bank [Member]
Total Capital, Amount	$ 730,117	$ 657,588
Total Capital to Risk-Weighted Assets Ratio	0.1243	0.1191
Total Capital Required for Capital Adequacy, Amount	$ 469,751	$ 441,833
Total Capital Required for Capital Adequacy, Ratio	0.08	0.08
Total Capital to be Well Capitalized, Amount	$ 587,188	$ 552,292
Total Capital to be Well Capitalized, Ratio	0.10	0.10
Tier I Capital, Amount	$ 686,379	$ 618,805
Tier I Capital to Risk-Weighted Assets Ratio	0.1169	0.112
Tier I Capital Required for Capital Adequacy, Amount	$ 352,313	$ 331,375
Tier I Capital Required for Capital Adequacy, Ratio	0.06	0.06
Tier I Capital to be Well Capitalized, Amount	$ 469,751	$ 441,833
Tier I Capital to be Well Capitalized, Ratio	0.08	0.08
Common Equity Tier 1 Capital, Amount	$ 686,379	$ 618,805
Common Equity Tier 1 Capital to Risk-Weighted Assets Ratio	0.1169	0.112
Common Equity Tier 1 Capital Required for Capital Adequacy, Amount	$ 264,235	$ 248,531
Common Equity Tier 1 Capital Required for Capital Adequacy, Ratio	4.50%	4.50%
Common Equity Tier 1 Capital to be Well Capitalized, Amount	$ 381,672	$ 358,989
Common Equity Tier 1 Capital to be Well Capitalized, Ratio	6.50%	6.50%
Tier 1 Leveraged Capital (to Average Assets)	$ 686,379	$ 618,805
Tier 1 Leveraged Capital (to Average Assets) Ratio	0.1063	0.1055
Tier I Leveraged Capital Required for Capital Adequacy, Amount	$ 258,203	$ 234,679
Tier I Leveraged Capital Capital Required for Capital Adequacy, Ratio	0.04	0.04
Tier I Leveraged Capital to be Well Capitalized, Amount	$ 322,754	$ 293,348
Tier I Leveraged Capital to be Well Capitalized, Ratio	0.05	0.05