Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2019
Equity [Abstract]
Stockholders' Equity	Stockholders' Equity Preferred Stock The Company is authorized to issue 50,000,000 shares of serial preferred stock, par value $0.01 per share, from time to time in one or more series subject to limitations of law. The Board of Directors is authorized to fix the designations, powers, preferences, limitations and rights of the shares of each such series. As of December 31, 2019, there were no shares of preferred stock issued. Capital Distributions and Restrictions Thereon The Company is a legal entity separate and distinct from each of the Banks and Brookline Securities Corp. The Company's primary source of revenue is dividends paid to it by the Banks and Brookline Securities Corp. The FRB has authority to prohibit the Company from paying dividends to the Company's shareholders if such payment is deemed to be an unsafe or unsound practice. The FRB has indicated generally that it may be an unsafe or unsound practice for bank holding companies to pay dividends unless the bank holding company's net income over the preceding year is sufficient to fund the dividends and the expected rate of earnings retention is consistent with the organization's capital needs, asset quality and overall financial condition. The FRB also has the authority to use its enforcement powers to prohibit the Banks from paying dividends to the Company if, in its opinion, the payment of dividends would constitute an unsafe or unsound practice. Federal law also prohibits the payment of dividends by a bank that will result in the bank failing to meet its applicable capital requirements on a pro forma basis. In addition, a state bank that is a member of the Federal Reserve System may not declare or pay a dividend if the total of all dividends declared during the calendar year, including the proposed dividend, exceeds the sum of the bank's net income (as reportable in its Reports of Condition and Income) during the current calendar year and the retained net income of the prior two calendar years, unless the dividend has been approved by the FRB. Payment of dividends by a bank is also restricted pursuant to various state regulatory limitations, including the Massachusetts Division of Banks in the case of Brookline Bank and the Banking Division of the Rhode Island Department of Business Regulation in the case of BankRI. Common Stock Repurchases On February 4, 2016, the Company's Board of Directors authorized a stock repurchase program to acquire up to $10.0 million of the Company's common stock over a period of twelve months ending on January 31, 2017 (the "2016 Stock Repurchase Plan"). No shares were purchased under the 2016 Stock Repurchase Plan. On December 5, 2018, the Company’s Board of Directors authorized a stock repurchase program to acquire up to $10.0 million of the Company’s common stock over a period of twelve months ending on December 31, 2019 (the “2018 Stock Repurchase Plan”). As of December 31, 2018, 725,583 shares of the Company's common stock were repurchased under the 2018 Stock Repurchase Plan. On January 30, 2019, the Company’s Board of Directors authorized a stock repurchase program to acquire up to $10.0 million of the Company’s common stock over a period of eleven months ending on December 31, 2019 (the “2019 Stock Repurchase Plan”). As of December 31, 2019, 103,758 shares of the Company’s common stock were repurchased under the 2019 Stock Repurchase Plan. On December 4, 2019, the Company’s Board of Directors authorized a stock repurchase program to acquire up to $10.0 million of the Company’s common stock over a period of twelve months ending on December 31, 2020 (the “2020 Stock Repurchase Plan”). There is no guarantee as to the exact number of shares, if any, to be repurchased by the Company under the 2020 Stock Repurchase Plan. Repurchases may be made from time to time depending on market conditions and other factors, and will be conducted through open market or private transactions, through block trades, and pursuant to any trading plan that may be adopted in accordance with the Securities and Exchange Commission Rule 10b5-1. There is no guarantee as to the exact number of shares, if any, to be repurchased by the Company. Common Stock Issuance On, April 27, 2017, the Company entered into an underwriting agreement with Piper Jaffray & Co., as representative of the underwriters named therein (collectively, the “Underwriters”), to offer and sell 5,175,000 shares of the Company’s common stock, $0.01 par value per share at a public offering price of $14.50 per share in an underwritten public offering (the “Offering”). In conjunction with the Offering, the Company granted the Underwriters a 30-day option to purchase up to an additional 776,250 shares of its common stock. On May 2, 2017, the Company and the Underwriters closed the Offering. The Underwriters exercised their option resulting in a new issuance in the aggregate of 5,951,250 shares of the Company’s common stock at a price to the public of $14.50 per share. The Company received net proceeds of $82.0 million after deductions for underwriting discounts, commissions, and expenses. Restricted Retained Earnings As part of the stock offering in 2002 and as required by regulation, Brookline Bank established a liquidation account for the benefit of eligible account holders and supplemental eligible account holders who maintain their deposit accounts at Brookline Bank after the stock offering. In the unlikely event of a complete liquidation of Brookline Bank (and only in that event), eligible depositors who continue to maintain deposit accounts at Brookline Bank shall be entitled to receive a distribution from the liquidation account. Accordingly, retained earnings of the Company are deemed to be restricted up to the balance of the liquidation account. The liquidation account balance is reduced annually to the extent that eligible depositors have reduced their qualifying deposits as of each anniversary date. Subsequent increases in deposit account balances do not restore an account holder's interest in the liquidation account. The liquidation account totaled $11.9 million (unaudited), $13.0 million (unaudited), and $15.1 million (unaudited) at December 31, 2019, 2018 and 2017, respectively.