Basis of Presentation	3 Months Ended
Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Overview Brookline Bancorp, Inc. (the “Company”) is a bank holding company (within the meaning of the Bank Holding Company Act of 1956, as amended) and the parent of Brookline Bank, a Massachusetts-chartered savings bank; Bank Rhode Island (“BankRI”), a Rhode Island-chartered financial institution; and First Ipswich Bank (“First Ipswich”), a Massachusetts-chartered trust company (collectively referred to as the “Banks”). The Banks are all members of the Federal Reserve System. The Company is also the parent of Brookline Securities Corp. The Company’s primary business is to provide commercial, business and retail banking services to its corporate, municipal, and individual customers through the Banks and its non-bank subsidiaries. Brookline Bank, which includes its wholly-owned subsidiaries BBS Investment Corp., Longwood Securities Corp. and its 84.4%-owned subsidiary, Eastern Funding LLC ("Eastern Funding"), operates 25 full-service banking offices in the greater Boston metropolitan area. BankRI, which includes its wholly-owned subsidiaries, Acorn Insurance Agency, BRI Realty Corp., Macrolease Corporation ("Macrolease"), BRI Investment Corp. and its wholly-owned subsidiary, BRI MSC Corp., operates 19 full-service banking offices in the greater Providence area. First Ipswich, which includes its wholly-owned subsidiaries, First Ipswich Insurance Agency and First Ipswich Securities II Corp., operates five full-service banking offices on the north shore of eastern Massachusetts. The Company’s activities include acceptance of commercial, municipal and retail deposits, origination of mortgage loans on commercial and residential real estate located principally in Massachusetts and Rhode Island, origination of commercial loans and leases to small and mid-sized businesses, investment in debt and equity securities, and the offering of cash management and investment advisory services. The Company also provides specialty equipment financing through its subsidiaries Eastern Funding, which is based in New York, New York, and Macrolease, which is based in Plainview, New York. The Company and the Banks are supervised, examined and regulated by the Board of Governors of the Federal Reserve System ("FRB"). As a Massachusetts-chartered saving bank and trust company, Brookline Bank and First Ipswich, respectively, are also subject to regulation under the laws of the Commonwealth of Massachusetts and the jurisdiction of the Massachusetts Division of Banks. As a Rhode Island-chartered financial institution, BankRI is also subject to regulation under the laws of the State of Rhode Island and the jurisdiction of the Banking Division of the Rhode Island Department of Business Regulation. The Federal Deposit Insurance Corporation (“FDIC”) offers insurance coverage on all deposits up to $250,000 per depositor at each of the three Banks. As FDIC-insured depository institutions, all three Banks are also secondarily subject to supervision, examination and regulation by the FDIC. Additionally, as a Massachusetts-chartered savings bank, Brookline Bank is insured by the Depositors Insurance Fund (“DIF”), a private industry-sponsored insurance company. The DIF insures savings bank deposits in excess of the FDIC insurance limits. As such, Brookline Bank offers 100% insurance on all deposits as a result of a combination of insurance from the FDIC and the DIF. Brookline Bank is required to file reports with the DIF. Basis of Financial Statement Presentation The unaudited consolidated financial statements of the Company presented herein have been prepared pursuant to the rules of the Securities and Exchange Commission (“SEC”) for quarterly reports on Form 10-Q and do not include all of the information and note disclosures required by U.S. generally accepted accounting principles (“GAAP”). In the opinion of Management, all adjustments (consisting of normal recurring adjustments) and disclosures considered necessary for the fair presentation of the accompanying consolidated financial statements have been included. Interim results are not necessarily reflective of the results of the entire year. The accompanying unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the fiscal year ended December 31, 2015. The unaudited consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany transactions and balances are eliminated in consolidation. In preparing these consolidated financial statements, Management is required to make significant estimates and assumptions that affect the reported amounts of assets, liabilities, income, expenses and disclosure of contingent assets and liabilities. Actual results could differ from those estimates based upon changing conditions, including economic conditions and future events. Material estimates that are particularly susceptible to significant change in the near-term include the determination of the allowance for loan and lease losses, the determination of fair market values of assets and liabilities, including acquired loans and leases, the review of goodwill and intangibles for impairment and the review of deferred tax assets for valuation allowances. The judgments used by Management in applying these critical accounting policies may be affected by a further and prolonged deterioration in the economic environment, which may result in changes to future financial results. For example, subsequent evaluations of the loan and lease portfolio, in light of the factors then prevailing, may result in significant changes in the allowance for loan and lease losses in future periods, and the inability to collect outstanding principal may result in increased loan and lease losses.

Basis of Presentation

Overview

Brookline Bancorp, Inc. (the “Company”) is a bank holding company (within the meaning of the Bank Holding Company Act of 1956, as amended) and the parent of Brookline Bank, a Massachusetts-chartered savings bank; Bank Rhode Island (“BankRI”), a Rhode Island-chartered financial institution; and First Ipswich Bank (“First Ipswich”), a Massachusetts-chartered trust company (collectively referred to as the “Banks”). The Banks are all members of the Federal Reserve System. The Company is also the parent of Brookline Securities Corp. The Company’s primary business is to provide commercial, business and retail banking services to its corporate, municipal, and individual customers through the Banks and its non-bank subsidiaries.

Brookline Bank, which includes its wholly-owned subsidiaries BBS Investment Corp., Longwood Securities Corp. and its 84.4%-owned subsidiary, Eastern Funding LLC ("Eastern Funding"), operates 25 full-service banking offices in the greater Boston metropolitan area. BankRI, which includes its wholly-owned subsidiaries, Acorn Insurance Agency, BRI Realty Corp., Macrolease Corporation ("Macrolease"), BRI Investment Corp. and its wholly-owned subsidiary, BRI MSC Corp., operates 19 full-service banking offices in the greater Providence area. First Ipswich, which includes its wholly-owned subsidiaries, First Ipswich Insurance Agency and First Ipswich Securities II Corp., operates five full-service banking offices on the north shore of eastern Massachusetts.

The Company’s activities include acceptance of commercial, municipal and retail deposits, origination of mortgage loans on commercial and residential real estate located principally in Massachusetts and Rhode Island, origination of commercial loans and leases to small and mid-sized businesses, investment in debt and equity securities, and the offering of cash management and investment advisory services. The Company also provides specialty equipment financing through its subsidiaries Eastern Funding, which is based in New York, New York, and Macrolease, which is based in Plainview, New York.

The Company and the Banks are supervised, examined and regulated by the Board of Governors of the Federal Reserve System ("FRB"). As a Massachusetts-chartered saving bank and trust company, Brookline Bank and First Ipswich, respectively, are also subject to regulation under the laws of the Commonwealth of Massachusetts and the jurisdiction of the Massachusetts Division of Banks. As a Rhode Island-chartered financial institution, BankRI is also subject to regulation under the laws of the State of Rhode Island and the jurisdiction of the Banking Division of the Rhode Island Department of Business Regulation.

The Federal Deposit Insurance Corporation (“FDIC”) offers insurance coverage on all deposits up to $250,000 per depositor at each of the three Banks. As FDIC-insured depository institutions, all three Banks are also secondarily subject to supervision, examination and regulation by the FDIC. Additionally, as a Massachusetts-chartered savings bank, Brookline Bank is insured by the Depositors Insurance Fund (“DIF”), a private industry-sponsored insurance company. The DIF insures savings bank deposits in excess of the FDIC insurance limits. As such, Brookline Bank offers 100% insurance on all deposits as a result of a combination of insurance from the FDIC and the DIF. Brookline Bank is required to file reports with the DIF.

Basis of Financial Statement Presentation

The unaudited consolidated financial statements of the Company presented herein have been prepared pursuant to the rules of the Securities and Exchange Commission (“SEC”) for quarterly reports on Form 10-Q and do not include all of the information and note disclosures required by U.S. generally accepted accounting principles (“GAAP”). In the opinion of Management, all adjustments (consisting of normal recurring adjustments) and disclosures considered necessary for the fair presentation of the accompanying consolidated financial statements have been included. Interim results are not necessarily reflective of the results of the entire year. The accompanying unaudited consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Annual Report on Form 10-K for the fiscal year ended December 31, 2015.

The unaudited consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany transactions and balances are eliminated in consolidation.

In preparing these consolidated financial statements, Management is required to make significant estimates and assumptions that affect the reported amounts of assets, liabilities, income, expenses and disclosure of contingent assets and liabilities. Actual results could differ from those estimates based upon changing conditions, including economic conditions and future events. Material estimates that are particularly susceptible to significant change in the near-term include the determination of the allowance for loan and lease losses, the determination of fair market values of assets and liabilities, including acquired loans and leases, the review of goodwill and intangibles for impairment and the review of deferred tax assets for valuation allowances.

The judgments used by Management in applying these critical accounting policies may be affected by a further and prolonged deterioration in the economic environment, which may result in changes to future financial results. For example, subsequent evaluations of the loan and lease portfolio, in light of the factors then prevailing, may result in significant changes in the allowance for loan and lease losses in future periods, and the inability to collect outstanding principal may result in increased loan and lease losses.