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Note 17 - Regulatory Matters - Summary of Company and Bank Continue to Exceed Regulatory Capital Minimum Requirements and Bank Continues to Exceed Well Capitalized Standards (Details) $ in Thousands | Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($)
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RBB Bancorp [Member] |  |  |
Tier 1 Leverage Ratio, Amount |  | $ 469,785 | $ 472,152
Tier 1 Leverage Ratio, Ratio |  | 0.1192 | 0.1199
Tier 1 Leverage Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 157,660 | $ 157,526
Tier 1 Leverage Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 0.04 | 0.04
Tier 1 Leverage Ratio, Minimum Required Plus Capital Conservation Buffer Fully Phased-In Amount |  | $ 197,075 | $ 196,907
Tier 1 Leverage Ratio, Minimum Required Plus Capital Conservation Buffer Fully Phased-In Ratio |  | 5.00% | 5.00%
Common Equity Tier 1 Risk-Based Capital Ratio, Amount |  | $ 455,084 | $ 457,214
Common Equity Tier 1 Risk-Based Capital Ratio, Ratio |  | 0.1794 | 0.1907
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 114,133 | $ 107,886
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 4.50% | 4.50%
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Amount |  | $ 164,859 | $ 155,836
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Ratio |  | 0.065 | 0.065
Tier 1 Risk-Based Capital Ratio, Amount |  | $ 469,785 | $ 472,152
Tier 1 Risk-Based Capital Ratio, Ratio |  | 0.1852 | 0.1969
Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 152,178 | $ 143,849
Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 0.06 | 0.06
Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Amount |  | $ 202,903 | $ 191,798
Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Ratio |  | 8.00% | 8.00%
Total Risk-Based Capital Ratio, Amount |  | $ 621,225 | $ 621,423
Total Risk-Based Capital Ratio, Ratio |  | 0.2449 | 0.2592
Total Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 202,903 | $ 191,798
Total Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 0.08 | 0.08
Total Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Amount |  | $ 253,629 | $ 239,748
Total Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Ratio |  | 10.00% | 10.00%
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 114,133 | $ 107,886
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 4.50% | 4.50%
Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes, Amount |  | $ 152,178 | $ 143,849
Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 0.06 | 0.06
Royal Business Bank [Member] |  |  |
Tier 1 Leverage Ratio, Amount |  | $ 549,889 | $ 535,952
Tier 1 Leverage Ratio, Ratio |  | 0.1396 | 0.1362
Tier 1 Leverage Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 157,529 | $ 157,454
Tier 1 Leverage Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 0.04 | 0.04
Tier 1 Leverage Ratio, Minimum Required Plus Capital Conservation Buffer Fully Phased-In Amount |  | $ 196,912 | $ 196,818
Tier 1 Leverage Ratio, Minimum Required Plus Capital Conservation Buffer Fully Phased-In Ratio |  | 5.00% | 5.00%
Common Equity Tier 1 Risk-Based Capital Ratio, Amount |  | $ 549,889 | $ 535,952
Common Equity Tier 1 Risk-Based Capital Ratio, Ratio |  | 0.2174 | 0.2241
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 113,843 | $ 107,598
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 4.50% | 4.50%
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Amount |  | $ 164,440 | $ 155,419
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Ratio |  | 0.065 | 0.065
Tier 1 Risk-Based Capital Ratio, Amount |  | $ 549,889 | $ 535,952
Tier 1 Risk-Based Capital Ratio, Ratio |  | 0.2174 | 0.2241
Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 151,791 | $ 143,464
Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 0.06 | 0.06
Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Amount |  | $ 202,388 | $ 191,285
Tier 1 Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Ratio |  | 8.00% | 8.00%
Total Risk-Based Capital Ratio, Amount |  | $ 581,720 | $ 565,997
Total Risk-Based Capital Ratio, Ratio |  | 0.2299 | 0.2367
Total Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 202,388 | $ 191,285
Total Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 0.08 | 0.08
Total Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Amount |  | $ 252,985 | $ 239,106
Total Risk-Based Capital Ratio, Minimum Required Plus Capital Conversation Buffer Fully Phased-In, Ratio |  | 10.00% | 10.00%
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Amount |  | $ 113,843 | $ 107,598
Common Equity Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 4.50% | 4.50%
Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes, Amount |  | $ 151,791 | $ 143,464
Tier 1 Risk-Based Capital Ratio, Minimum Required for Capital Adequacy Purposes Ratio | [1] | 0.06 | 0.06
[1] | These ratios are exclusive of the 2.5% capital conservation buffer.

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