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Summary of Significant Accounting Policies (Detail) | 6 Months Ended
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Jun. 30, 2025 USD ($) segment trust office county | Jun. 30, 2024 USD ($)
Significant Accounting Policies [Line Items] |  |
Number of subsidiary business trusts (in trusts) | trust | 5 |
Number of loan production offices (in offices) | trust | 2 |
Company's investments in the trusts | $ | $ 1,800,000 |
Number of operating segments (in segments) | segment | 1 |
Number of reportable segments (in segments) | segment | 1 |
Loans contractual past due | 90 days |
Security credit losses recognized | $ | $ 0 | $ 0
North Valley Bancorp |  |
Significant Accounting Policies [Line Items] |  |
Number of subsidiary business trusts (in trusts) | office | 3 |
California |  |
Significant Accounting Policies [Line Items] |  |
Number of counties (in counties) | county | 31 |

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- Definition Amount of credit loss expense on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) transferred into available-for-sale out of investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 8B -Publisher FASB -URI https://asc.fasb.org/1943274/2147481830/320-10-45-8B + Details
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