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Regulatory Capital Requirements (Details) $ in Thousands | Sep. 30, 2025 USD ($) | Dec. 31, 2024 USD ($)
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Total Capital (to Risk-Weighted Assets) |  |
Total Capital (to Risk-Weighted Assets), Actual Amount | $ 785,198 | $ 814,505
Total Capital (to Risk-Weighted Assets), Actual Ratio | 0.156 | 0.174
Total Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Amount | $ 403,006 | $ 374,650
Total Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Ratio | 0.08 | 0.08
Total Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Amount | $ 503,757 | $ 468,313
Total Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Ratio | 0.10 | 0.10
Tier I Capital (to Risk-Weighted Assets) |  |
Tier I Capital (to Risk-Weighted Assets), Actual Amount | $ 739,460 | $ 772,558
Tier I Capital (to Risk-Weighted Assets), Actual Ratio | 0.147 | 0.165
Tier I Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Amount | $ 302,254 | $ 280,988
Tier I Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Ratio | 0.06 | 0.06
Tier I Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Amount | $ 403,006 | $ 374,650
Tier I Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Ratio | 0.08 | 0.08
Common Equity Tier I Capital (to Risk-Weighted Assets) |  |
Common Equity Tier I Capital (to Risk-Weighted Assets), Actual Amount | $ 739,460 | $ 772,558
Common Equity Tier I Capital (to Risk-Weighted Assets), Actual Ratio | 0.147 | 0.165
Common Equity Tier I Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Amount | $ 226,691 | $ 210,741
Common Equity Tier I Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Ratio | 0.045 | 0.045
Common Equity Tier I Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Amount | $ 327,442 | $ 304,403
Common Equity Tier I Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Ratio | 0.065 | 0.065
Tier I Capital (to Total Average Assets) |  |
Tier I Capital (to Total Average Assets), Actual Amount | $ 739,460 | $ 772,558
Tier I Capital (to Total Average Assets), Actual Ratio | 0.14 | 0.153
Tier I Capital (to Total Average Assets), For minimum capital adequacy purposes, Amount | $ 211,148 | $ 202,436
Tier I Capital (to Total Average Assets), For minimum capital adequacy purposes, Ratio | 0.04 | 0.04
Tier I Capital (to Total Average Assets), To be well capitalized under prompt corrective action provisions, Amount | $ 263,935 | $ 253,045
Tier I Capital (to Total Average Assets), To be well capitalized under prompt corrective action provisions, Ratio | 0.05 | 0.05
Needham Bank [Member] |  |
Total Capital (to Risk-Weighted Assets) |  |
Total Capital (to Risk-Weighted Assets), Actual Amount | $ 699,582 | $ 656,103
Total Capital (to Risk-Weighted Assets), Actual Ratio | 0.139 | 0.141
Total Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Amount | $ 401,533 | $ 372,083
Total Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Ratio | 0.08 | 0.08
Total Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Amount | $ 501,917 | $ 465,104
Total Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Ratio | 0.10 | 0.10
Tier I Capital (to Risk-Weighted Assets) |  |
Tier I Capital (to Risk-Weighted Assets), Actual Amount | $ 653,844 | $ 614,156
Tier I Capital (to Risk-Weighted Assets), Actual Ratio | 0.13 | 0.132
Tier I Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Amount | $ 301,150 | $ 279,063
Tier I Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Ratio | 0.06 | 0.06
Tier I Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Amount | $ 401,533 | $ 372,083
Tier I Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Ratio | 0.08 | 0.08
Common Equity Tier I Capital (to Risk-Weighted Assets) |  |
Common Equity Tier I Capital (to Risk-Weighted Assets), Actual Amount | $ 653,844 | $ 614,156
Common Equity Tier I Capital (to Risk-Weighted Assets), Actual Ratio | 0.13 | 0.132
Common Equity Tier I Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Amount | $ 225,862 | $ 209,297
Common Equity Tier I Capital (to Risk-Weighted Assets), For minimum capital adequacy purposes, Ratio | 0.045 | 0.045
Common Equity Tier I Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Amount | $ 326,246 | $ 302,318
Common Equity Tier I Capital (to Risk-Weighted Assets), To be well capitalized under prompt corrective action provisions, Ratio | 0.065 | 0.065
Tier I Capital (to Total Average Assets) |  |
Tier I Capital (to Total Average Assets), Actual Amount | $ 653,844 | $ 614,156
Tier I Capital (to Total Average Assets), Actual Ratio | 0.126 | 0.125
Tier I Capital (to Total Average Assets), For minimum capital adequacy purposes, Amount | $ 207,685 | $ 196,435
Tier I Capital (to Total Average Assets), For minimum capital adequacy purposes, Ratio | 0.04 | 0.04
Tier I Capital (to Total Average Assets), To be well capitalized under prompt corrective action provisions, Amount | $ 259,606 | $ 245,544
Tier I Capital (to Total Average Assets), To be well capitalized under prompt corrective action provisions, Ratio | 0.05 | 0.05

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