Note 15 - Stockholders' Equity and Regulatory Matters - Actual Capital Amounts and Ratios (Details) $ in Thousands	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Total Capital, Amount	$ 478,794
Total Capital to Risk-Weighted Assets Ratio	0.1194
Total Capital Required for Capital Adequacy, Amount	$ 320,715
Total Capital Required for Capital Adequacy, Ratio	0.0800
Total Capital to be Well Capitalized, Amount	$ 400,894
Total Capital to be Well Capitalized, Ratio	0.1000
Tier I Capital, Amount	$ 367,431
Tier I Capital to Risk-Weighted Assets Ratio	0.0917
Tier I Capital Required for Capital Adequacy, Amount	$ 240,537
Tier I Capital Required for Capital Adequacy, Ratio	0.0600
Tier I Capital to be Well Capitalized, Amount	$ 320,715
Tier I Capital to be Well Capitalized, Ratio	0.0800
Common Equity Tier 1 Capital, Amount	$ 362,431
Common Equity Tier 1 Capital to Risk-Weighted Assets Ratio	0.0904
Common Equity Tier 1 Capital Required for Capital Adequacy, Amount	$ 180,402
Common Equity Tier 1 Capital Required for Capital Adequacy, Ratio	4.50%
Common Equity Tier 1 Capital to be Well Capitalized, Amount	$ 260,581
Common Equity Tier 1 Capital to be Well Capitalized, Ratio	6.50%
Tier I Leveraged Capital, Amount	$ 367,431	$ 340,715
Tier I Leveraged Capital to Average Assets Ratio	0.0814	0.0879
Tier I Leveraged Capital Required for Capital Adequacy, Amount	$ 180,604	$ 310,151
Tier I Leveraged Capital Capital Required for Capital Adequacy, Ratio	0.0400	0.0800
Tier I Leveraged Capital to be Well Capitalized, Amount	$ 225,755
Tier I Leveraged Capital to be Well Capitalized, Ratio	0.0500
Business First Bank [Member]
Total Capital, Amount	$ 468,834
Total Capital to Risk-Weighted Assets Ratio	0.1171
Total Capital Required for Capital Adequacy, Amount	$ 320,411
Total Capital Required for Capital Adequacy, Ratio	0.0800
Total Capital to be Well Capitalized, Amount	$ 400,514
Total Capital to be Well Capitalized, Ratio	0.1000
Tier I Capital, Amount	$ 438,898
Tier I Capital to Risk-Weighted Assets Ratio	0.1096
Tier I Capital Required for Capital Adequacy, Amount	$ 240,308
Tier I Capital Required for Capital Adequacy, Ratio	0.0600
Tier I Capital to be Well Capitalized, Amount	$ 320,411
Tier I Capital to be Well Capitalized, Ratio	0.0800
Common Equity Tier 1 Capital, Amount	$ 438,898
Common Equity Tier 1 Capital to Risk-Weighted Assets Ratio	0.1096
Common Equity Tier 1 Capital Required for Capital Adequacy, Amount	$ 180,231
Common Equity Tier 1 Capital Required for Capital Adequacy, Ratio	4.50%
Common Equity Tier 1 Capital to be Well Capitalized, Amount	$ 260,334
Common Equity Tier 1 Capital to be Well Capitalized, Ratio	6.50%
Tier I Leveraged Capital, Amount	$ 438,898	$ 358,083
Tier I Leveraged Capital to Average Assets Ratio	0.0973	0.0924
Tier I Leveraged Capital Required for Capital Adequacy, Amount	$ 180,453	$ 310,091
Tier I Leveraged Capital Capital Required for Capital Adequacy, Ratio	0.0400	0.0800
Tier I Leveraged Capital to be Well Capitalized, Amount	$ 225,566
Tier I Leveraged Capital to be Well Capitalized, Ratio	0.0500