Benefit Plans	12 Months Ended
Dec. 31, 2017
Retirement Benefits [Abstract]
Benefit Plans	Benefit Plans In 2003, we established a Deferred Compensation Plan that allows certain key Management personnel designated by the Board of Directors of the Bank to defer up to 80% of their salary and 100% of their annual bonus. The plan was amended in 2007 in order to comply with the most recent Internal Revenue Code Section 409A changes. Under the amended plan, amounts deferred earn interest that is equal to the prime rate as published in the Wall Street Journal, on the first business day of the year, which was 3.75% on January 1, 2017, 3.50% on January 1, 2016 and 3.25% on January 1, 2015. Our deferred compensation obligation totaled $3.4 million and $3.2 million at December 31, 2017 and 2016, respectively, and is included in interest payable and other liabilities. Our 401(k) Defined Contribution Plan (the “401(k) Plan”) commenced in May 1990 and is available to all regular employees at least eighteen years of age who complete ninety days of service, and enter the plan during one of the four open enrollment dates (January 1, April 1, July 1, and October 1) of each year. Under the 401(k) Plan, employees can defer between 1% and 50% of their eligible compensation, up to the maximum amount allowed by the Internal Revenue Code. Contributions to the 401(k) Plan for the employer match are vested at a rate of 20% per year over a five year period. In 2015 and 2016, the Bank matched 60% of each participant's contribution, with a maximum of $4 thousand of matching contribution per participant per year. In 2017, the Bank increased the match to 70% of each participant's contribution, with a maximum of $5 thousand of matching contribution per participant per year. Employer contributions totaled $765 thousand, $589 thousand and $555 thousand for the years ended December 31, 2017, 2016 and 2015, respectively. In 1999, the 401(k) Plan was amended to include an employee stock ownership component and was renamed the Bank of Marin Employee Stock Ownership and Savings Plan (the “Plan”). Under the terms of the Plan, as amended, the Board of Directors determines a specific portion of the Bank's profits to be contributed to the employee stock ownership each year either in common stock or in cash for the purchase of Bancorp stock to be allocated to all eligible employees based on a percentage of their salaries, regardless of whether an employee is participating in the 401(k) plan or not. In January 2010, the Bank of Marin Employee Stock Ownership and Savings Plan was split into two plans: Bank of Marin 401(k) Plan and Bank of Marin Employee Stock Ownership Plan ("ESOP"). The same eligibility criteria apply under the ESOP, while employees' contributions are not permitted. For all participants, employer contributions vest over a five year period of service. After five years of service, all employer contributions vest immediately. The Bank of Marin 401(k) Plan was amended in early 2016 to incorporate recent changes in the pension laws, and was amended again in November 2016 to include a Roth 401(k) option. The Bank contributed cash in the amount of $1.2 million in 2016 and $1.1 million in 2015 to the ESOP, which purchased Bancorp stock at market prices. Starting in 2017, Bancorp issued shares of common stock and contributed them to the ESOP and recognized $1.2 million in expense, based on the quoted market price on the date of contribution. Cash dividends paid on Bancorp stock held by the ESOP are used to purchase additional shares in the open market. All shares of Bancorp stock held by the ESOP are included in the calculations of basic and diluted earnings per share. The employer contributions to the ESOP and the 401(k) Plan are included in salaries and benefits expense. On January 1, 2011, we established a Salary Continuation Plan for a select group of Executive Management, who will receive twenty-five percent of their estimated salary at retirement as salary continuation benefit payments upon retirement. Each participant will need to participate in this plan for five years before vesting begins. After five years, the participant will vest ratably in the benefit over the remaining period until age 65. This Plan is unfunded and nonqualified for tax purposes and for purposes of Title I of the Employee Retirement Income Security Act of 1974. As part of the acquisition of Bank of Napa in November 2017, we assumed the salary continuation agreements for four former executive officers of Bank of Napa. Under these agreements, fixed annual retirement benefit payments will be made for ten years beginning the first day of the month following the executive reaching the age of 65. At December 31, 2017 and 2016, respectively, our liability under the Salary Continuation Plan was $2.5 million (including $1.2 million assumed from Bank of Napa) and $1.0 million recorded in interest payable and other liabilities.

Benefit Plans

In 2003, we established a Deferred Compensation Plan that allows certain key Management personnel designated by the Board of Directors of the Bank to defer up to 80% of their salary and 100% of their annual bonus. The plan was amended in 2007 in order to comply with the most recent Internal Revenue Code Section 409A changes. Under the amended plan, amounts deferred earn interest that is equal to the prime rate as published in the Wall Street Journal, on the first business day of the year, which was 3.75% on January 1, 2017, 3.50% on January 1, 2016 and 3.25% on January 1, 2015. Our deferred compensation obligation totaled $3.4 million and $3.2 million at December 31, 2017 and 2016, respectively, and is included in interest payable and other liabilities.

Our 401(k) Defined Contribution Plan (the “401(k) Plan”) commenced in May 1990 and is available to all regular employees at least eighteen years of age who complete ninety days of service, and enter the plan during one of the four open enrollment dates (January 1, April 1, July 1, and October 1) of each year. Under the 401(k) Plan, employees can defer between 1% and 50% of their eligible compensation, up to the maximum amount allowed by the Internal Revenue Code. Contributions to the 401(k) Plan for the employer match are vested at a rate of 20% per year over a five year period. In 2015 and 2016, the Bank matched 60% of each participant's contribution, with a maximum of $4 thousand of matching contribution per participant per year. In 2017, the Bank increased the match to 70% of each participant's contribution, with a maximum of $5 thousand of matching contribution per participant per year. Employer contributions totaled $765 thousand, $589 thousand and $555 thousand for the years ended December 31, 2017, 2016 and 2015, respectively.

In 1999, the 401(k) Plan was amended to include an employee stock ownership component and was renamed the Bank of Marin Employee Stock Ownership and Savings Plan (the “Plan”). Under the terms of the Plan, as amended, the Board of Directors determines a specific portion of the Bank's profits to be contributed to the employee stock ownership each year either in common stock or in cash for the purchase of Bancorp stock to be allocated to all eligible employees based on a percentage of their salaries, regardless of whether an employee is participating in the 401(k) plan or not. In January 2010, the Bank of Marin Employee Stock Ownership and Savings Plan was split into two plans: Bank of Marin 401(k) Plan and Bank of Marin Employee Stock Ownership Plan ("ESOP"). The same eligibility criteria apply under the ESOP, while employees' contributions are not permitted. For all participants, employer contributions vest over a five year period of service. After five years of service, all employer contributions vest immediately. The Bank of Marin 401(k) Plan was amended in early 2016 to incorporate recent changes in the pension laws, and was amended again in November 2016 to include a Roth 401(k) option.

The Bank contributed cash in the amount of $1.2 million in 2016 and $1.1 million in 2015 to the ESOP, which purchased Bancorp stock at market prices. Starting in 2017, Bancorp issued shares of common stock and contributed them to the ESOP and recognized $1.2 million in expense, based on the quoted market price on the date of contribution. Cash dividends paid on Bancorp stock held by the ESOP are used to purchase additional shares in the open market. All shares of Bancorp stock held by the ESOP are included in the calculations of basic and diluted earnings per share. The employer contributions to the ESOP and the 401(k) Plan are included in salaries and benefits expense.

On January 1, 2011, we established a Salary Continuation Plan for a select group of Executive Management, who will receive twenty-five percent of their estimated salary at retirement as salary continuation benefit payments upon retirement. Each participant will need to participate in this plan for five years before vesting begins. After five years, the participant will vest ratably in the benefit over the remaining period until age 65. This Plan is unfunded and nonqualified for tax purposes and for purposes of Title I of the Employee Retirement Income Security Act of 1974. As part of the acquisition of Bank of Napa in November 2017, we assumed the salary continuation agreements for four former executive officers of Bank of Napa. Under these agreements, fixed annual retirement benefit payments will be made for ten years beginning the first day of the month following the executive reaching the age of 65. At December 31, 2017 and 2016, respectively, our liability under the Salary Continuation Plan was $2.5 million (including $1.2 million assumed from Bank of Napa) and $1.0 million recorded in interest payable and other liabilities.