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Benefit Plans - Defined Contribution Plan and Employee Stock Ownership Plan (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer matching contribution percentage | 70.00% |  |
Employer matching contribution maximum amount | $ 5,000 |  |
Stock issued to employee stock ownership plan | $ 1,315,000 | $ 1,233,000 | $ 1,330,000
Defined Contribution Plan (the 401k Plan) |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Minimum age of eligible employee for 401(k) plan | 18 years |  |
Minimum employment period to qualify for 401(k) plan | 90 days |  |
Minimum annual contribution per employee, percent of eligible compensation | 1.00% |  |
Maximum annual contribution per employee, percent of eligible compensation | 50.00% |  |
Annual vesting percentage | 20.00% |  |
Defined contribution plan, number of years to be fully vested | 5 years |  |
Employer contributions | $ 871,000 | 949,000 | 991,000
Bank of Marin Employee Stock Ownership and Savings Plan (the Plan) |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Defined contribution plan, number of years to be fully vested | 5 years |  |
Stock issued to employee stock ownership plan | $ 1,300,000 | $ 1,200,000 | $ 1,300,000

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- Definition Defined Contribution Plan, Employer Matching Contribution, Maximum Amount + References No definition available. + Details
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- Definition Schedule of Defined Contribution Plans Disclosures [Line Items] + References No definition available. + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480794/715-70-50-1 + Details
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