Brookline Bancorp (BRKL) 10-K 28 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 28, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	BROOKLINE BANCORP INC
Entity Central Index Key	1,049,782
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 1,093.5
Entity Common Stock, Shares Outstanding		76,827,247
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and due from banks		$ 25,622	$ 36,055
Short-term investments		35,383	31,602
Total cash and cash equivalents		61,005	67,657
Investment securities available-for-sale		540,124	523,634
Investment securities held-to-maturity (fair value of $108,523 and $85,271, respectively)		109,730	87,120
Total investment securities		649,854	610,754
Loans held-for-sale		2,628	13,078
Total loans and leases		5,730,679	5,398,864
Allowance for loan and lease losses		(58,592)	(53,666)
Net loans and leases		5,672,087	5,345,198
Restricted equity securities		59,369	64,511
Premises and equipment, net of accumulated depreciation of $63,423 and $58,790, respectively		80,283	76,176
Deferred tax asset		15,061	25,247
Goodwill		137,890	137,890
Identified intangible assets, net of accumulated amortization of $33,738 and $31,649, respectively		6,044	8,133
Other real estate owned (OREO) and repossessed assets, net		4,419	1,399
Other assets	[1]	91,609	88,086
Total assets		6,780,249	6,438,129
Non-interest-bearing deposits:
Demand checking accounts		942,583	900,474
Interest-bearing deposits:
NOW accounts		350,568	323,160
Savings accounts		646,359	613,061
Money market accounts		1,724,363	1,733,359
Certificate of deposit accounts		1,207,470	1,041,022
Total interest-bearing deposits		3,928,760	3,710,602
Total deposits		4,871,343	4,611,076
Borrowed funds:
Advances from the Federal Home Loan Bank of Boston (FHLBB)		889,909	910,774
Subordinated debentures and notes		83,271	83,105
Other borrowed funds		47,639	50,207
Total borrowed funds		1,020,819	1,044,086
Mortgagors' escrow accounts		7,686	7,645
Accrued expenses and other liabilities		67,818	72,573
Total liabilities		5,967,666	5,735,380
Commitments and contingencies
Brookline Bancorp, Inc. stockholders' equity:
Common stock, $0.01 par value; 200,000,000 shares authorized; 81,695,695 shares issued and 75,744,445 shares issued, respectively		817	757
Additional paid-in capital		699,976	616,734
Retained earnings, partially restricted	[1]	161,217	136,671
Accumulated other comprehensive loss		(5,950)	(3,818)
Treasury stock, at cost; 4,440,665 shares and 4,707,096 shares, respectively		(51,454)	(53,837)
Unallocated common stock held by Employee Stock Ownership Plan (ESOP); 142,332 shares and 176,688 shares, respectively		(776)	(963)
Total Brookline Bancorp, Inc. stockholders' equity	[1]	803,830	695,544
Noncontrolling interest in subsidiary		8,753	7,205
Total stockholders' equity	[1]	812,583	702,749
Total liabilities and stockholders' equity	[1]	6,780,249	6,438,129
Commercial real estate loans
ASSETS
Total loans and leases		3,075,777	2,918,567
Commercial loans and leases
ASSETS
Total loans and leases		1,624,111	1,495,408
Consumer loans
ASSETS
Total loans and leases		$ 1,030,791	$ 984,889
[1]	Previously reported amounts prior to January 1, 2015 have been restated to reflect a retrospective change in accounting principle for investments in qualified affordable housing projects, in accordance with ASU 2014-01. Refer to Note 10, "Other Assets".

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Investment securities held to maturity, fair value	$ 108,523	$ 85,271
Premises and equipment, accumulated depreciation and amortization	63,423	58,790
Identified intangible assets, accumulated amortization	$ 33,738	$ 31,649
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	81,695,695	75,744,445
Treasury stock, shares	4,440,665	4,707,096
Unallocated common stock held by ESOP, shares	142,332	176,688

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest and dividend income:
Loans and leases		$ 247,022	$ 224,721	$ 212,604
Debt securities		12,524	11,710	11,416
Marketable and restricted equity securities		3,062	2,975	2,762
Short-term investments		442	242	128
Total interest and dividend income		263,050	239,648	226,910
Interest expense:
Deposits		23,288	20,070	17,480
Borrowed funds		16,581	15,914	15,065
Total interest expense		39,869	35,984	32,545
Net interest income		223,181	203,664	194,365
Provision for credit losses		18,988	10,353	7,451
Net interest income after provision for credit losses		204,193	193,311	186,914
Non-interest income:
Deposit fees		10,050	9,467	9,269
Loan fees		1,110	1,299	1,186
Loan level derivative income, net		2,187	3,962	3,397
Gain on sales of investment securities, net		11,393	0	0
Gain on sales of loans and leases held-for-sale		2,644	3,256	2,208
Other		4,789	4,683	4,124
Total non-interest income		32,173	22,667	20,184
Non-interest expense:
Compensation and employee benefits		82,413	77,836	71,272
Occupancy		14,546	13,882	13,926
Equipment and data processing		16,854	15,496	14,837
Professional services		4,315	3,852	4,192
FDIC insurance		3,326	3,332	3,510
Advertising and marketing		3,369	3,381	3,352
Amortization of identified intangible assets		2,089	2,500	2,911
Merger and acquisition expense		411	0	0
Other		11,788	10,083	11,377
Total non-interest expense		139,111	130,362	125,377
Income before provision for income taxes		97,255	85,616	81,721
Provision for income taxes		43,636	30,392	29,353
Net income before noncontrolling interest in subsidiary	[1]	53,619	55,224	52,368
Less net income attributable to noncontrolling interest in subsidiary		3,101	2,862	2,586
Net income attributable to Brookline Bancorp, Inc.	[2]	$ 50,518	$ 52,362	$ 49,782
Earnings per common share:
Basic (in dollars per share)		$ 0.68	$ 0.74	$ 0.71
Diluted (in dollars per share)		$ 0.68	$ 0.74	$ 0.71
Weighted average common shares outstanding during the year:
Basic (in shares)		74,459,508	70,261,954	70,098,561
Diluted (in shares)		74,811,408	70,444,083	70,235,868
Dividends declared per common share (in dollars per share)		$ 0.36	$ 0.360	$ 0.355
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Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income before noncontrolling interest in subsidiary	[1]	$ 53,619	$ 55,224	$ 52,368
Other comprehensive loss, net of taxes:
Unrealized securities holding losses		(1,274)	(2,167)	(1,573)
Income tax benefit		457	781	479
Net unrealized securities holding losses before reclassification adjustments		(817)	(1,386)	(1,094)
Postretirement benefits:
Adjustment of accumulated obligation for postretirement benefits		(422)	69	353
Income tax benefit (expense)		170	(25)	(113)
Net adjustment of accumulated obligation for postretirement benefits		(252)	44	240
Other comprehensive loss, net of taxes		(1,069)	(1,342)	(854)
Comprehensive income	[1]	52,550	53,882	51,514
Net income attributable to noncontrolling interest in subsidiary		3,101	2,862	2,586
Comprehensive income attributable to Brookline Bancorp, Inc.	[1]	$ 49,449	$ 51,020	$ 48,928
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Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total		Total Brookline Bancorp, Inc. Stockholders' Equity	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	Unallocated Common Stock Held by ESOP	Noncontrolling Interest in Subsidiary
Balance at Dec. 31, 2014	$ 646,605		$ 641,818	$ 757	$ 617,475	$ 84,860	$ (1,622)	$ (58,282)	$ (1,370)	$ 4,787
Increase (Decrease) in Stockholders' Equity
Net income attributable to Brookline Bancorp, Inc.	49,782		49,782			49,782
Net income attributable to noncontrolling interest in subsidiary	2,586									2,586
Issuance of noncontrolling units	65									65
Other comprehensive income (loss)	(854)		(854)				(854)
Common stock dividends	(24,967)		(24,967)			(24,967)
Dividend distribution to owners of noncontrolling interest in subsidiary	(1,437)									(1,437)
Compensation under recognition and retention plan	1,311		1,311		(763)			2,074
Common stock held by ESOP committed to be released	395		395		187				208
Balance at Dec. 31, 2015	673,486		667,485	757	616,899	109,675	(2,476)	(56,208)	(1,162)	6,001
Increase (Decrease) in Stockholders' Equity
Net income attributable to Brookline Bancorp, Inc.	52,362		52,362			52,362
Net income attributable to noncontrolling interest in subsidiary	2,862									2,862
Issuance of noncontrolling units	76									76
Other comprehensive income (loss)	(1,342)		(1,342)				(1,342)
Common stock dividends	(25,366)		(25,366)			(25,366)
Dividend distribution to owners of noncontrolling interest in subsidiary	(1,734)									(1,734)
Compensation under recognition and retention plan	2,010		2,010		(361)			2,371
Common stock held by ESOP committed to be released	395		395		196				199
Balance at Dec. 31, 2016	702,749	[1]	695,544	757	616,734	136,671	(3,818)	(53,837)	(963)	7,205
Increase (Decrease) in Stockholders' Equity
Reclassification due to the adoption of ASU No. 2018-02						1,063	(1,063)
Net income attributable to Brookline Bancorp, Inc.	50,518		50,518			50,518
Net income attributable to noncontrolling interest in subsidiary	3,101									3,101
Issuance of common stock	81,943		81,943	60	81,883
Issuance of noncontrolling units	118									118
Other comprehensive income (loss)	(1,069)		(1,069)				(1,069)
Common stock dividends	(27,035)		(27,035)			(27,035)
Dividend distribution to owners of noncontrolling interest in subsidiary	(1,671)									(1,671)
Compensation under recognition and retention plan	3,428		3,428		1,045			2,383
Common stock held by ESOP committed to be released	501		501		314				187
Balance at Dec. 31, 2017	$ 812,583	[1]	$ 803,830	$ 817	$ 699,976	$ 161,217	$ (5,950)	$ (51,454)	$ (776)	$ 8,753
[1]	Previously reported amounts prior to January 1, 2015 have been restated to reflect a retrospective change in accounting principle for investments in qualified affordable housing projects, in accordance with ASU 2014-01. Refer to Note 10, "Other Assets".

Consolidated Statements of Cha7

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Common stock dividends, per share (in dollars per share)	$ 0.36	$ 0.360	$ 0.355
Common stock held by ESOP committed to be released, shares	34,356	36,372	38,316

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income attributable to Brookline Bancorp, Inc.	[1]	$ 50,518	$ 52,362	$ 49,782
Adjustments to reconcile net income to net cash provided from operating activities:
Net income attributable to noncontrolling interest in subsidiary		3,101	2,862	2,586
Provision for credit losses		18,988	10,353	7,451
Origination of loans and leases held-for-sale		(27,425)	(56,080)	(74,841)
Proceeds from sales of loans and leases held-for-sale, net		32,073	55,636	64,398
Deferred income tax expense		10,798	2,322	1,239
Depreciation of premises and equipment		7,232	7,080	7,074
Amortization of investment securities premiums and discounts, net		2,042	2,158	1,841
Amortization of deferred loan and lease origination costs, net		6,695	5,883	4,775
Amortization of identified intangible assets		2,089	2,500	2,911
Amortization of debt issuance costs		100	101	100
Accretion of acquisition fair value adjustments, net		(1,583)	(3,960)	(7,242)
Gain on sales of investment securities, net		(11,393)	0	0
Gain on sales of loans and leases held-for-sale		(2,644)	(3,256)	(2,208)
Loss on sales of OREO and other repossessed assets, net		(79)	(84)	102
Write-down of OREO and other repossessed assets		458	190	229
Compensation under recognition and retention plans		2,308	1,844	1,276
ESOP shares committed to be released		501	395	395
Net change in:
Cash surrender value of bank-owned life insurance		(1,041)	(1,050)	(1,049)
Other assets	[1]	(2,413)	(287)	(5,135)
Accrued expenses and other liabilities		(5,378)	(1,039)	10,920
Net cash provided from operating activities	[1]	84,947	77,930	64,604
Cash flows from investing activities:
Proceeds from maturities, calls, and principal repayments of investment securities available-for-sale		71,611	100,957	97,771
Purchases of investment securities available-for-sale		(90,971)	(115,403)	(63,615)
Proceeds from maturities, calls, and principal repayments of investment securities held to maturity		3,817	42,492	9,579
Purchases of investment securities held-to-maturity		(26,873)	(36,167)	(102,847)
Proceeds from redemption/sales of restricted equity securities		24,462	5,623	9,924
Purchase of restricted equity securities		(7,927)	(4,017)	(1,237)
Proceeds from sales of loans and leases held-for-investment, net		28,608	45,979	273,688
Net increase in loans and leases		(378,906)	(465,527)	(457,460)
Purchase of premises and equipment, net		(11,557)	(5,262)	(4,775)
Proceeds from sales of OREO and other repossessed assets		3,762	3,530	7,152
Net cash used for investing activities		(383,974)	(427,795)	(231,820)
Cash flows from financing activities:
Increase in demand checking, NOW, savings and money market accounts		93,819	351,908	206,748
(Decrease) increase in certificates of deposit		166,448	(46,752)	141,338
Proceeds from FHLBB advances		4,685,706	5,905,511	4,018,000
Repayment of FHLBB advances		(4,705,543)	(5,854,019)	(4,157,392)
Increase (decrease) in other borrowed funds, net		(2,568)	11,980	(1,388)
Increase (decrease) in mortgagors' escrow accounts, net		41	129	(985)
Proceeds from exercise of stock options		1,469	300	0
Proceeds from issuance of common stock		81,943	0	0
Payment of dividends on common stock		(27,035)	(25,366)	(24,967)
Payment of income taxes for shares withheld in share based activity		(352)	0	0
Proceeds from issuance of noncontrolling units		118	76	65
Payment of dividends to owners of noncontrolling interest in subsidiary		(1,671)	(1,734)	(1,437)
Net cash provided from (used for) financing activities		292,375	342,033	179,982
Net (decrease) increase in cash and cash equivalents		(6,652)	(7,832)	12,766
Cash and cash equivalents at beginning of year		67,657	75,489	62,723
Cash and cash equivalents at end of year		61,005	67,657	75,489
Cash paid during the year for:
Interest on deposits, borrowed funds and subordinated debt		40,785	38,620	35,522
Income taxes		34,026	29,770	26,694
Non-cash investing activities:
Transfer from loans and leases to loan and leases held-for-sale		7,500	2,500	0
Transfer from loans to other real estate owned		$ 7,161	$ 3,692	$ 7,370
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Basis of Presentation

Basis of Presentation	12 Months Ended
	Dec. 31, 2017
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. ("BSC"). The Company's primary business is to provide commercial, business and retail banking services to its corporate, municipal and retail customers through its banks and non-bank subsidiaries. Brookline Bank, which includes its wholly-owned subsidiaries BBS Investment Corp., Longwood Securities Corp. and its 84.2% -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 20 full-service banking offices in the greater Providence area, Rhode Island area. First Ipswich, which includes its wholly-owned subsidiaries, First Ipswich Insurance Agency and First Ipswich Securities II Corp., operates six 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 City, 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 Massachusetts-chartered savings 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 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 Banks. As FDIC-insured depository institutions, the Banks are also secondarily subject to supervision, examination and regulation by the FDIC. Additionally, as a Massachusetts-chartered savings bank, Brookline Bank is also 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 Company's consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles ("GAAP") as set forth by the Financial Accounting Standards Board ("FASB") in its Accounting Standards Codification and through the rules and interpretive releases of the Securities and Exchange Commission ("SEC") under the authority of federal securities laws. The 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, the review of goodwill and intangibles for impairment and the review of deferred tax assets for valuation allowance. 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. Reclassification Certain previously reported amounts have been reclassified to conform to the current year's presentation. Cash and Cash Equivalents For purposes of reporting asset balances and cash flows, cash and cash equivalents includes cash on hand and due from banks (including cash items in process of clearing), interest-bearing deposits with banks, federal funds sold, money market mutual funds and other short-term investments with original maturities of three months or less. Investment Securities Investment securities, other than those reported as short-term investments, are classified at the time of purchase as "available-for-sale," or "held-to-maturity." Classification is periodically re-evaluated for consistency with the Company's goals and objectives. Equity investments in the Federal Home Loan Bank of Boston ("FHLBB"), the Federal Reserve Bank of Boston and other restricted equities are discussed in more detail in Note 5, "Restricted Equity Securities." Investment Securities Available-for-Sale and Held-to-Maturity Investment securities for which the Company has the positive intent and ability to hold to maturity are classified as held-to-maturity and carried at amortized cost. Those investment securities held for indefinite periods of time but not necessarily to maturity are classified as available-for-sale. Investment securities held for indefinite periods of time include investment securities that management intends to use as part of its asset/liability, liquidity, and/or capital management strategies and may be sold in response to changes in interest rates, maturities, asset/liability mix, liquidity needs, regulatory capital needs or other business factors. Investment securities available-for-sale are carried at estimated fair value, primarily obtained from a third-party pricing service, with unrealized gains and losses reported on an after-tax basis in stockholders' equity as accumulated other comprehensive income or loss. As of December 31, 2017 and 2016 , the Company did not make any adjustments to the prices provided by the third-party pricing service. Security transactions are recorded on the trade date. Realized gains and losses are determined using the specific identification method and are recorded in non-interest income. Interest and dividends on securities are recorded using the accrual method. Premiums and discounts on securities are amortized or accreted into interest income using the level-yield method over the remaining period to contractual maturity, adjusted for the effect of actual prepayments in the case of mortgage-backed securities ("MBSs") and collateralized mortgage obligations ("CMOs"). These estimates of prepayment assumptions are made based upon the actual performance of the underlying security, current interest rates, the general market consensus regarding changes in mortgage interest rates, the contractual repayment terms of the underlying loans, the priority rights of the investors to the cash flows from the mortgage securities and other economic conditions. When differences arise between anticipated prepayments and actual prepayments, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. Unamortized premium or discount is adjusted to the amount that would have existed had the new effective yield been applied since purchase, with a corresponding charge or credit to interest income. Management evaluates securities for other-than-temporary impairment ("OTTI") on a periodic basis. Factors considered in determining whether an impairment is OTTI include: (1) the length of time and the extent to which the fair value has been less than amortized cost, (2) projected future cash flows, (3) the financial condition and near-term prospects of the issuers, and (4) the intent and ability of the Company to hold the investment for a period of time sufficient to allow for any anticipated recovery in fair value. The Company records an OTTI loss in an amount equal to the entire difference between the fair value and amortized cost if: (1) the Company intends to sell an impaired investment security, (2) it is more likely than not that the Company will be required to sell the investment security before its amortized cost, or (3) for debt securities, the present value of expected future cash flows is not sufficient to recover the entire amortized cost basis. If an investment security is determined to be OTTI but the Company does not intend to sell the investment security, only the credit portion of the estimated loss is recognized in earnings, with the non credit portion of the loss recognized in other comprehensive income. Restricted Equity Securities The Company invests in the stock of the FHLBB, the Federal Reserve Bank of Boston and a small amount of other restricted securities. No ready market exists for these stocks, and they have no quoted market values. The Banks, as members of the FHLBB, are required to maintain investments in the capital stock of the FHLBB equal to their membership base investments plus an activity-based investment determined according to the Banks' level of outstanding FHLBB advances. Federal Reserve Bank of Boston stock was purchased and is redeemable at par. The Company reviews for impairment of these securities based on the ultimate recoverability of the cost basis in the stock. As of December 31, 2017 and 2016 , no impairment has been recognized. Loans Originated Loans Loans the Company originates for the portfolio, and for which it has the intent and ability to hold to maturity, are reported at amortized cost, inclusive of deferred loan origination fees and expenses, less unadvanced funds due borrowers on loans and the allowance for loan and lease losses. Interest income on loans and leases originated for the portfolio is accrued on unpaid principal balances as earned. Loan origination fees and direct loan origination costs are deferred, and the net fee or cost is recognized in interest income using the interest method. Deferred amounts are recognized for fixed-rate loans over the contractual life of the loans and for adjustable-rate loans over the period of time required to adjust the contractual interest rate to a yield approximating a market rate at the origination date. If a loan is prepaid, the unamortized portion of the loan origination costs, including third party referral related costs not subject to rebate from the dealer, is charged to income. Loans and Leases Held-for-Sale Management identifies and designates certain newly originated loans and leases for sale to specific financial institutions, subject to the underwriting criteria of those financial institutions. These loans and leases are held for sale and are carried at the lower of cost or market as determined in the aggregate. Deferred loan fees and costs are included in the determination of the gain or loss on sale. Acquired Loans Acquired loans that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all contractually required payments receivable are initially recorded at fair value (as determined by the present value of expected future cash flows) with no valuation allowance. The difference between the undiscounted cash flows expected at acquisition and the recorded fair value of the loan, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment or as a loss accrual or a valuation allowance. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition (meaning the present value of all cash flows expected at acquisition that ultimately are not to be received). Nonperforming Loans Nonaccrual Loans Accrual of interest on loans generally is discontinued when contractual payment of principal or interest becomes past due 90 days or, if in management's judgment, reasonable doubt exists as to the full timely collection of interest. Exceptions may be made if the loan has matured and is in the process of renewal or is well-secured and in the process of collection. When a loan is placed on nonaccrual status, interest accruals cease and uncollected accrued interest is reversed and charged against current interest income. Interest payments on nonaccrual loans are generally applied to principal. If collection of the principal is reasonably assured, interest payments are recognized as income on the cash basis. Loans are generally returned to accrual status when principal and interest payments are current, full collectability of principal and interest is reasonably assured and a consistent record of at least six consecutive months of performance has been achieved. Impaired Loans A loan is considered to be impaired when, based on current information and events, it is probable that the Company will be unable to collect all amounts due (both interest and principal) according to the contractual terms of the loan agreement. Smaller-balance, homogeneous loans that are evaluated collectively for impairment, such as residential, home equity and other consumer loans are specifically excluded from the impaired loan portfolio except where the loan is classified as a troubled debt restructuring. The Company has defined the population of impaired loans to include nonaccrual loans and troubled debt restructured ("TDR") loans. When the ultimate collectability of the total principal of an impaired loan or lease is in doubt and the loan is on nonaccrual status, all payments are applied to principal, under the cost recovery method. When the ultimate collectability of the total principal of an impaired loan or lease is not in doubt and the loan or lease is on nonaccrual status, contractual interest is credited to interest income when received, under the cash basis method. The value of an impaired loan is measured based upon the present value of expected future cash flows discounted at the loan's effective interest rate, or the fair value of the collateral if the loan is collateral-dependent and its payment is expected solely based on the underlying collateral. For impaired loans deemed collateral dependent, where impairment is measured using the fair value of the collateral, the Company will either obtain a new appraisal or use another available source of collateral assessment to determine a reasonable estimate of the fair value of the collateral. Interest collected on impaired loans is either applied against principal or reported as income according to management's judgment as to the collectability of principal. If management does not consider a loan ultimately collectible within an acceptable time frame, payments are applied as principal to reduce the loan balance. If full collection of the remaining recorded investment should subsequently occur, interest receipts are recorded as interest income on a cash basis. Troubled Debt Restructured Loans In cases where a borrower experiences financial difficulties and the Company makes certain concessionary modifications to contractual terms, the loan is classified as a TDR loan. In determining whether a debtor is experiencing financial difficulties, the Company considers, among other factors, whether the debtor is in payment default or is likely to be in payment default in the foreseeable future without the modification, if the debtor declared or is in the process of declaring bankruptcy, there is substantial doubt that the debtor will continue as a going concern, the debtor's entity-specific projected cash flows will not be sufficient to service its debt, or the debtor cannot obtain funds from sources other than the existing creditors at market terms for debt with similar risk characteristics. Large groups of small-balance homogeneous loans such as residential real estate, residential construction, home equity and other consumer portfolios are collectively evaluated for impairment. As such, the Company does not typically identify individual loans within these groupings as impaired loans or for impairment evaluation and disclosure. However, the Company evaluates all TDRs for impairment on an individual loan basis regardless of loan type. Modifications may include interest-rate reductions, short-term (defined as one year or less) changes in payment structure to interest-only payments, short-term extensions of the loan's original contractual term, or less frequently, principal forgiveness, interest capitalization, forbearance and other actions intended to minimize economic loss and avoid foreclosure or repossession of collateral. Typically, TDRs are placed on nonaccrual status and reported as nonperforming loans. Generally, a nonaccrual loan that is restructured remains on nonaccrual for a period of six months to demonstrate that the borrower can meet the restructured terms; however, performance prior to the restructuring, or significant events that coincide with the restructuring, are considered in assessing whether the borrower can meet the new terms and may result in the loan being returned to accrual status at the time of restructuring or after a shorter performance period. If the borrower's ability to meet the revised payment schedule is not reasonably assured, the loan remains classified as a nonaccrual loan. Loans restructured at an interest rate equal to or greater than that of a new loan with comparable risk at the time the loan agreement is modified may be excluded from restructured loan disclosures in years subsequent to the restructuring if they are in compliance with the modified terms. Allowance for Loan and Lease Losses Management has established a methodology to determine the adequacy of the allowance for loan and lease losses that assesses the risks and losses inherent in the loan and lease portfolio. Additions to the allowance for loan and lease losses are made by charges to the provision for credit losses. Losses on loans and leases are charged off against the allowance when all or a portion of a loan or lease is considered uncollectible. Subsequent recoveries on loans previously charged off, if any, are credited to the allowance when realized. Management uses a consistent and systematic process and methodology to evaluate the adequacy of the allowance for loan and lease losses on a quarterly basis. For purposes of determining the allowance for loan and lease losses, the Company has segmented certain loans and leases in the portfolio by product type into the following segments: (1) commercial real estate loans, (2) commercial loans and leases, (3) and consumer loans. Portfolio segments are further disaggregated into classes based on the associated risks within the segments. Commercial real estate loans are divided into three classes: commercial real estate mortgage loans, multi-family mortgage loans, and construction loans. Commercial loans and leases are divided into three classes: commercial loans which includes taxi medallion loans, equipment financing, and loans to condominium associations. Consumer loans are divided into three classes: residential mortgage loans, home equity loans, and other consumer loans. A formula-based credit evaluation approach is applied to each group, coupled with an analysis of certain loans for impairment. The general allowance related to loans collectively evaluated for impairment is determined using a formula-based approach utilizing the risk ratings of individual credits and loss factors derived from historic portfolio loss rates, which include estimates of incurred losses over an estimated loss emergence period (“LEP”). The LEP was generated utilizing a charge-off look-back analysis which studied the time from the first indication of elevated risk of repayment (or other early event indicating a problem) to eventual charge-off to support the LEP considered in the allowance calculation. This reserving methodology established the approximate number of months of LEP that represents incurred losses for each portfolio. In addition to quantitative measures, relevant qualitative factors include, but are not limited to: (1) levels and trends in past due and impaired loans, (2) levels and trends in charge-offs, (3) changes in underwriting standards, policy exceptions, and credit policy, (4) experience of lending management and staff, (5) economic trends, (6) industry conditions, (7) effects of changes in credit concentrations, (8) interest rate environment, and (9) regulatory and other changes. The general allowance related to the acquired loans collectively evaluated for impairment is determined based upon the degree, if any, of deterioration in the pooled loans subsequent to acquisition. The qualitative factors used in the determination are the same as those used for originated loans. During 2015, the Company enhanced and refined its general allowance methodology. Under the enhanced methodology, management combined the historical loss histories of the Banks to generate a single set of historical loss ratios. Management believes it is appropriate to aggregate the ratios as the Banks share common environmental factors, operate in similar geographic markets, and utilize common underwriting standards in accordance with the Company's Credit Policy. In prior periods, a historical loss history applicable to each Bank was used. Management employed a similar analysis for the consolidation of the qualitative factors as it did for the quantitative factors. Again, management believes the realignment of the existing nine qualitative factors used at each of the Banks into a single group of factors used for the Company is appropriate based on the commonality of environmental factors, markets and underwriting standards among the Banks. Prior to 2015, each of the Banks utilized a set of qualitative factors applicable to each Bank. The Company’s December 31, 2017 allowance calculation included a further segmentation of the commercial loans and leases to reflect the increased risk in the Company’s taxi medallion portfolio. As of December 31, 2017 , this portfolio is approximately $19.7 million . Based on industry conditions, management established a loss factor for this portfolio that best represents the changing risks associated with it. Based on the refinements to the Company’s allowance methodology discussed above, management determined that the potential risks anticipated by the unallocated allowance are now incorporated into the allowance methodology, making the unallocated allowance unnecessary. Prior to 2015, the unallocated allowance was used to recognize the estimated risk associated with the allocated general and specific allowances. It incorporated management’s evaluation of existing conditions that were not included in the allocated allowance determinations and provided for losses that arise outside of the ordinary course of business. Specific valuation allowances are established for impaired originated loans with book values greater than the discounted present value of expected future cash flows or, in the case of collateral-dependent impaired loans, for any excess of a loan's book balance and the fair value of its underlying collateral. Specific valuation allowances are established for acquired loans with deterioration in the discounted present value of expected future cash flows since acquisitions or, in the case of collateral dependent impaired loans, for any increase in the excess of a loan's book balance greater than the fair value of its underlying collateral. A specific valuation allowance for losses on TDR loans is determined by comparing the net carrying amount of the troubled debt restructured loan with the restructured loan's cash flows discounted at the original effective rate. Impaired loans are reviewed quarterly with adjustments made to the calculated reserve as necessary. As of December 31, 2017 , management believes that the methodology for calculating the allowance is sound and that the allowance provides a reasonable basis for determining and reporting on probable losses in the Company’s loan portfolios. Liability for Unfunded Commitments In the ordinary course of business, the Company enters into commitments to extend credit, commercial letters of credit, and standby letters of credit. Such financial instruments are recorded in the financial statements when they become payable. The credit risk associated with these commitments is evaluated in a manner similar to the allowance for loan losses. Premises and Equipment Premises and equipment are carried at cost less accumulated depreciation and amortization, except for land which is carried at cost. Premises and equipment are depreciated using the straight-line method over the estimated useful life of the assets. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or the estimated useful life of the improvements. Costs related to internal-use software development projects that provide significant new functionality are capitalized. Internal-use software is software acquired or modified solely to meet the Company's needs and for which there is no plan to market the software externally. Direct and indirect costs associated with the application development stage of internal use software are capitalized until such time that the software is substantially complete and ready for its intended use. Capitalized costs are amortized on a straight-line basis over the remaining estimated life of the software. Computer software and development costs incurred in the preliminary project stage, as well as training and maintenance costs, are expensed as incurred. Leases The Company leases properties for offices and branches in the states of Massachusetts, Rhode Island and New York. Lease terms range from five years to over 25 years with options to renew. Management performs an analysis to determine proper lease accounting at lease inception and for each renewal. If a lease meets any of the following four criteria, the lease is classified as capital lease. The four criteria are: transfer of ownership by the end of lease term; contains bargain purchase option; lease term is at least 75% of the property’s estimated remaining economic life; or present value of the minimum lease payment is at least 90% of the fair value of the leased property. All leases are classified as operating leases and rental payments are expensed as incurred. Certain leases contain rent escalation clauses which are amortized over the life of the lease under the straight-line method. Bank-Owned Life Insurance The Company acquired bank-owned life insurance ("BOLI") plans as part of its acquisitions of First Ipswich and BankRI. BOLI represents life insurance on the lives of certain current and former employees who have provided positive consent allowing their employer to be the beneficiary of such policies. BankRI and First Ipswich are the beneficiaries of their respective policies. BankRI and First Ipswich utilize BOLI as tax-efficient financing for their benefit obligations to their employees, including their retirement obligations and Supplemental Executive Retirement Plans ("SERPs"). Since BankRI and First Ipswich are the primary beneficiaries of their respective insurance policies, increases in the cash value of the policies, as well as insurance proceeds received, are recorded in non-interest income and are not subject to income taxes. BOLI is recorded at the cash value of the policies, less any applicable cash surrender charges, and is reflected as an asset in the accompanying consolidated balance sheets. Cash proceeds, if any, are classified as cash flows from investing activities. The Company reviews the financial strength of the insurance carriers prior to the purchase of BOLI to ensure minimum credit ratings of at least investment grade. The financial strength of the carriers is reviewed at least annually, and BOLI with any individual carrier is limited to 10% of the Company's capital. Total BOLI is limited to 25% of the Company's capital. Goodwill and Other Identified Intangible Assets Goodwill represents the excess of the cost of an acquisition over the fair value of the net assets acquired. Goodwill and indefinite-lived identified intangible assets are not subject to amortization. Definite-lived identified intangible assets are assets resulting from acquisitions that are being amortized over their estimated useful lives. The recoverability of goodwill and identified intangible assets is evaluated for impairment at least annually. As part of this evaluation, the Company makes a qualitative assessment of whether it is more likely than not that the fair value of an acquired asset is greater than its carrying amount. If the Company qualitatively concludes that it is more likely than not that the fair value of an acquired asset is greater than its carrying amount, no further testing is necessary. If, however, the Company qualitatively concludes that the fair value of an acquired asset is less than its carrying value, the Company should recognize an impairment charge for the amount by which the carrying amount exceeds the fair value. The Company did not have any impairment of Goodwill and other identified intangible assets as of December 31, 2017 and 2016 . OREO and Other Repossessed Assets OREO and other repossessed assets consists of properties acquired through foreclosure, real estate acquired through acceptance of a deed in lieu of foreclosure and loans determined to be substantively repossessed. Real estate loans that are substantively repossessed include only those loans for which the Company has taken possession of the collateral. OREO and other repossessed assets which consist of vehicles and equipment, if any, are recorded initially at estimated fair value less costs to sell, resulting in a new cost basis. The amount by which the recorded investment in the loan exceeds the fair value (net of estimated cost to sell) of the foreclosed or repossessed asset is charged to the allowance for loan and lease losses. Such evaluations are based on an analysis of individual properties/assets as well as a general assessment of current real estate market conditions. Subsequent declines in the fair value of the foreclosed or repossessed asset below the new cost basis are recorded through the use of a valuation allowance. Subsequent increases in the fair value are recorded as reductions in the allowance, but not below zero. Rental revenue received on foreclosed or repossessed assets is included in other non-interest income, whereas operating expenses and changes in the valuation allowance relating to foreclosed and repossessed assets are included in other non-interest expense. Certain costs used to improve such properties are capitalized. Gains and losses from the sale of OREO and other repossessed assets are reflected in non-interest expense when realized

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisitions	Acquisitions First Commons Bank, N.A. On September 20, 2017, the Company and First Commons Bank, N.A. (“First Commons Bank”) entered into a definitive agreement and plan of merger (the “Merger Agreement”) pursuant to which First Commons Bank will merge with and into Brookline Bank. The Company expects to consummate the transaction during the first quarter of 2018, subject to approval by First Commons Bank shareholders, the Board of Governors of the Federal Reserve System and the Massachusetts Division of Banks. Under the terms of the Merger Agreement, the Company will pay $16.70 per share for the outstanding shares and warrants of First Commons Bank representing a total transaction value of approximately $56.0 million . First Commons Bank stockholders will receive 1.171 shares of the Company's common stock for each First Commons Bank share they own, subject to adjustment based on Company's ten-day, volume-weighted average stock price between $13.19 and $15.33 . First Commons Bank is a national banking association which was organized in 2009 and is headquartered in Newton and Wellesley, Massachusetts. First Commons Bank operates its business from two banking offices located in Massachusetts. First Commons Bank is engaged principally in the business of attracting deposits from the general public and investing those deposits in residential, commercial real estate loans, consumer and small business loans. At December 31, 2017 , First Commons Bank had total assets of approximately $324.8 million (unaudited), loans of approximately $263.0 million (unaudited), deposits of approximately $282.8 million (unaudited) and stockholders’ equity of approximately $35.7 million (unaudited). The Company recorded $411.0 thousand of merger and acquisition expense in connection with the proposed acquisition of First Commons Bank for the year ended December 31, 2017 .

Cash, Cash Equivalents and Shor

Cash, Cash Equivalents and Short-Term Investments	12 Months Ended
	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents and Short-Term Investments	Cash, Cash Equivalents and Short-Term Investments The Banks are required to maintain average reserve balances with the FRB based upon a percentage of certain of the Banks' deposits. As of December 31, 2017 and 2016 , the average amount required to be held before a credit for vault cash was $5.9 million and $6.9 million , respectively. Aggregate reserve balances included in cash and cash equivalents were $40.0 million and $30.9 million , respectively, as of December 31, 2017 and 2016 . Short-term investments are summarized as follows: At December 31, 2017 2016 (In Thousands) FRB interest bearing reserve $ 28,263 $ 19,952 FHLB overnight deposits 4,676 2,142 Federal funds sold 2,444 9,508 Total short-term investments $ 35,383 $ 31,602 Short-term investments are stated at cost which approximates market value.

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities The following tables set forth investment securities available-for-sale and held-to-maturity at the dates indicated: At December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In Thousands) Investment securities available-for-sale: GSE debentures $ 151,483 $ 70 $ 1,629 $ 149,924 GSE CMOs 131,082 27 4,087 127,022 GSE MBSs 191,281 354 2,322 189,313 SBA commercial loan asset-backed securities 73 — 1 72 Corporate debt obligations 62,811 110 238 62,683 U.S. treasury bonds 8,785 7 62 8,730 Trust preferred securities 1,471 — 73 1,398 Marketable equity securities 978 13 9 982 Total investment securities available-for-sale $ 547,964 $ 581 $ 8,421 $ 540,124 Investment securities held-to-maturity: GSE debentures $ 41,612 $ — $ 811 $ 40,801 GSEs MBSs 13,923 — 218 13,705 Municipal obligations 53,695 159 337 53,517 Foreign government obligations 500 — — 500 Total investment securities held-to-maturity $ 109,730 $ 159 $ 1,366 $ 108,523 At December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In Thousands) Investment securities available-for-sale: GSE debentures $ 98,122 $ 188 $ 1,290 $ 97,020 GSE CMOs 161,483 37 3,480 158,040 GSE MBSs 214,946 794 2,825 212,915 SBA commercial loan asset-backed securities 107 — — 107 Corporate debt obligations 48,308 360 183 48,485 U.S. treasury bonds 4,801 — 64 4,737 Trust preferred securities 1,469 — 111 1,358 Marketable equity securities 966 15 9 972 Total investment securities available-for-sale $ 530,202 $ 1,394 $ 7,962 $ 523,634 Investment securities held-to-maturity: GSE debentures $ 14,735 $ — $ 634 $ 14,101 GSEs MBSs 17,666 — 187 17,479 Municipal obligations 54,219 5 1,020 53,204 Foreign government obligations 500 — 13 487 Total investment securities held-to-maturity $ 87,120 $ 5 $ 1,854 $ 85,271 As of December 31, 2017 , the fair value of all investment securities available-for-sale was $540.1 million , with net unrealized losses of $7.8 million , compared to a fair value of $523.6 million and net unrealized losses of $6.6 million as of December 31, 2016 . As of December 31, 2017 , $469.2 million , or 86.9% of the portfolio, had gross unrealized losses of $8.4 million , compared to $ 389.0 million , or 74.3% of the portfolio, with gross unrealized losses of $8.0 million as of December 31, 2016 . As of December 31, 2017 , the fair value of all investment securities held-to-maturity was $108.5 million , with net unrealized losses of $1.2 million , compared to a fair value of $85.3 million with net unrealized losses of $1.8 million as of December 31, 2016 . As of December 31, 2017 , $92.9 million , or 85.6% of the portfolio, had gross unrealized losses of $1.4 million . As of December 31, 2016 , $82.0 million , or 96.1% of the portfolio had gross unrealized losses $1.9 million . Investment Securities as Collateral As of December 31, 2017 and 2016 , respectively, $431.2 million and $429.1 million of investment securities were pledged as collateral for repurchase agreements; municipal deposits; treasury, tax and loan deposits (TT&L); swap agreements; and FHLBB borrowings. The Banks did not have any outstanding FRB borrowings as of December 31, 2017 and 2016 . Other-Than-Temporary Impairment ("OTTI") Investment securities as of December 31, 2017 and 2016 that have been in a continuous unrealized loss position for less than twelve months or twelve months or longer are as follows: At December 31, 2017 Less than Twelve Months Twelve Months or Longer Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses (In Thousands) Investment securities available-for-sale: GSE debentures $ 120,409 $ 1,263 $ 12,481 $ 366 $ 132,890 $ 1,629 GSE CMOs 2,862 34 123,548 4,053 126,410 4,087 GSE MBSs 94,985 753 74,782 1,569 169,767 2,322 SBA commercial loan asset-backed securities 34 — 33 1 67 1 Corporate debt obligations 30,978 154 2,423 84 33,401 238 U.S. Treasury bonds 4,767 62 — — 4,767 62 Trust preferred securities — — 1,398 73 1,398 73 Marketable equity securities — — 503 9 503 9 Temporarily impaired investment securities available-for-sale 254,035 2,266 215,168 6,155 469,203 8,421 Investment securities held-to-maturity: GSE debentures 26,594 281 14,208 530 40,802 811 GSEs MBSs 1,996 15 11,674 203 13,670 218 Municipal obligations 30,542 235 7,408 102 37,950 337 Foreign government obligations — — 500 — 500 — Temporarily impaired investment securities held-to-maturity 59,132 531 33,790 835 92,922 1,366 Total temporarily impaired investment securities $ 313,167 $ 2,797 $ 248,958 $ 6,990 $ 562,125 $ 9,787 At December 31, 2016 Less than Twelve Months Twelve Months or Longer Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses (In Thousands) Investment securities available-for-sale: GSE debentures $ 67,216 $ 1,291 $ — $ — $ 67,216 $ 1,291 GSE CMOs 118,450 2,162 38,852 1,318 157,302 3,480 GSE MBSs 149,687 2,821 198 3 149,885 2,824 SBA commercial loan asset-backed securities — — 72 — 72 — Corporate debt obligations 7,953 183 — — 7,953 183 U.S. Treasury bonds 4,737 64 — — 4,737 64 Trust preferred securities — — 1,358 111 1,358 111 Marketable equity securities 503 9 — — 503 9 Temporarily impaired investment securities available-for-sale 348,546 6,530 40,480 1,432 389,026 7,962 Investment securities held-to-maturity: GSE debentures 14,101 634 — — 14,101 634 GSEs MBSs 17,289 187 — — 17,289 187 Municipal obligations 50,098 1,020 — — 50,098 1,020 Foreign government obligations 487 13 — — 487 13 Temporarily impaired investment securities held-to-maturity 81,975 1,854 — — 81,975 1,854 Total temporarily impaired investment securities $ 430,521 $ 8,384 $ 40,480 $ 1,432 $ 471,001 $ 9,816 The Company performs regular analysis on the investment securities available-for-sale portfolio to determine whether a decline in fair value indicates that an investment security is OTTI. In making these OTTI determinations, management considers, among other factors, the length of time and extent to which the fair value has been less than amortized cost; projected future cash flows; credit subordination and the creditworthiness; capital adequacy and near-term prospects of the issuers. Management also considers the Company's capital adequacy, interest-rate risk, liquidity and business plans in assessing whether it is more likely than not that the Company will sell or be required to sell the investment securities before recovery. If the Company determines that a decline in fair value is OTTI and that it is more likely than not that the Company will not sell or be required to sell the investment security before recovery of its amortized cost, the credit portion of the impairment loss is recognized in the Company's consolidated statement of income and the noncredit portion is recognized in accumulated other comprehensive income. The credit portion of the OTTI impairment represents the difference between the amortized cost and the present value of the expected future cash flows of the investment security. If the Company determines that a decline in fair value is OTTI and it is more likely than not that it will sell or be required to sell the investment security before recovery of its amortized cost, the entire difference between the amortized cost and the fair value of the security will be recognized in the Company's consolidated statement of income. Investment Securities Available-For-Sale Impairment Analysis The following discussion summarizes, by investment security type, the basis for evaluating if the applicable investment securities within the Company’s available-for-sale portfolio were OTTI as of December 31, 2017 . Based on the analysis below and the determination that, it is more likely than not that the Company will not sell or be required to sell the investment securities before recovery of its amortized cost. The Company's ability and intent to hold these investment securities until recovery is supported by the Company's strong capital and liquidity positions as well as its historically low portfolio turnover. As such, management has determined that the investment securities are not OTTI as of December 31, 2017 . If market conditions for investment securities worsen or the creditworthiness of the underlying issuers deteriorates, it is possible that the Company may recognize additional OTTI in future periods. U.S. Government-Sponsored Enterprises The Company invests in securities issued by U.S. Government-sponsored enterprises ("GSEs"), including GSE debentures, mortgage-backed securities ("MBSs"), and collateralized mortgage obligations ("CMOs"). GSE securities include obligations issued by the Federal National Mortgage Association ("FNMA"), the Federal Home Loan Mortgage Corporation ("FHLMC"), the Government National Mortgage Association ("GNMA"), the Federal Home Loan Banks ("FHLB") and the Federal Farm Credit Bank. As of December 31, 2017 , only GNMA MBSs and CMOs, and Small Business Administration ("SBA") commercial loan asset-backed securities in our available-for-sale portfolio with an estimated fair value of $23.7 million were backed explicitly by the full faith and credit of the U.S. Government, compared to $26.2 million as of December 31, 2016 . As of December 31, 2017 , the Company owned 48 GSE debentures with a total fair value of $149.9 million , and a net unrealized loss of $1.6 million . As of December 31, 2016 , the Company held 29 GSE debentures with a total fair value of $97.0 million , and a net unrealized loss of $1.1 million . As of December 31, 2017 , 43 of the 48 securities in this portfolio were in an unrealized loss position. As of December 31, 2016 , 21 of the 29 securities in this portfolio were in an unrealized loss position. All securities are performing and backed by the implicit (FHLB/FNMA/FHLMC) or explicit (GNMA/SBA) guarantee of the U.S Government. For the years ended December 31, 2017 and 2016, the Company purchased a total of $54.2 million and $65.7 million , respectively, of GSE debentures. As of December 31, 2017 , the Company owned 62 GSE CMOs with a total fair value of $127.0 million and a net unrealized loss of $4.1 million . As of December 31, 2016 , the Company held 62 GSE CMOs with a total fair value of $158.0 million with a net unrealized loss of $3.4 million . As of December 31, 2017 and 2016 , 47 of the 62 securities in this portfolio were in an unrealized loss position. All securities are performing and backed by the implicit (FHLB/FNMA/FHLMC) or explicit (GNMA) guarantee of the U.S Government. For the year ended December 31, 2017 , the Company did no t purchase any GSE CMOs. During the year ended December 31, 2016 , the Company purchased $3.1 million of GSE CMOs. As of December 31, 2017 , the Company owned 194 GSE MBSs with a total fair value of $189.3 million and a net unrealized loss of $2.0 million . As of December 31, 2016 , the Company held 195 GSE MBSs with a total fair value of $212.9 million with a net unrealized loss of $2.0 million . As of December 31, 2017 , 82 of the 194 securities in this portfolio were in an unrealized loss position. As of December 31, 2016 , 60 of the 195 securities in this portfolio were in an unrealized loss position. All securities are performing and backed by the implicit (FHLB/FNMA/FHLMC) or explicit (GNMA) guarantee of the U.S Government. For the years ended December 31, 2017 and 2016 , the Company purchased a total of $18.3 million and $36.6 million , respectively, of GSE MBSs. SBA Commercial Loan Asset-Backed As of December 31, 2017 and December 31, 2016 , the Company owned SBA securities with a total fair value of $0.1 million , which approximated amortized cost. As of December 31, 2017 , four of the five securities in this portfolio were in an unrealized loss position. As of December 31, 2016 , four of the six securities in this portfolio were in an unrealized loss position. All securities are performing and backed by the explicit (SBA) guarantee of the U.S Government. Corporate Obligations From time to time, the Company may invest in high-quality corporate obligations to provide portfolio diversification and improve the overall yield on the portfolio. As of December 31, 2017 , the Company owned 19 corporate obligation securities with a total fair value of $62.7 million and a net unrealized loss of $0.1 million . This compares to 16 corporate obligation securities with a total fair value of $48.5 million and a net unrealized gain of $0.2 million as of December 31, 2016 . As of December 31, 2017 , nine of the 19 securities in this portfolio were in an unrealized loss position. As of December 31, 2016 , three of the 16 securities in this portfolio was in an unrealized loss position. Full collection of the obligations is expected because the financial condition of the issuers is sound, they have not defaulted on scheduled payments, the obligations are rated investment grade, and the Company has the ability and intent to hold the obligations for a period of time to recover the amortized cost. For the years ended December 31, 2017 and 2016 , the Company purchased $14.5 million and $5.1 million , respectively, of corporate obligations. U.S. Treasury Bonds The Company invests in securities issued by the U.S. government. As of December 31, 2017 , the Company owned two U.S. Treasury bonds with a total fair value of $8.7 million and a net unrealized loss of $0.1 million . As of December 31, 2016 , the Company owned one U.S. Treasury bond with a total fair value of $4.7 million and a net unrealized loss of $0.1 million . As of December 31, 2017 and 2016 , all of the securities in this portfolio were in unrealized loss positions. For the year ended December 31, 2017 and 2016, the Company purchased $4.0 million and $4.8 million in U.S. Treasury bonds, respectively. Trust Preferred Securities Trust preferred securities represent subordinated debt issued by financial institutions. As of December 31, 2017 , the Company owned two trust preferred securities with a total fair value of $1.4 million and a net unrealized loss of $0.1 million . This compares to two trust preferred securities with a total fair value of $1.4 million and a net unrealized loss of $0.1 million as of December 31, 2016 . As of December 31, 2017 and 2016 , both of the securities in this portfolio were in an unrealized loss position. Full collection of the obligations is expected because the financial condition of the issuers is sound, neither of the issuers has defaulted on scheduled payments, the obligations are rated investment grade, and the Company has the ability and intent to hold the obligations for a period of time to recover the amortized cost. Marketable Equity Securities As of December 31, 2017 , the Company owned two marketable equity securities with a fair value of $1.0 million , which approximated amortized cost, compared to a fair value of $1.0 million , which approximated cost as of December 31, 2016 . As of December 31, 2017 and December 31, 2016 , one of the two securities in this portfolio was in an unrealized loss position. Investment Securities Held-to-Maturity Impairment Analysis The following discussion summarizes by investment security type, the basis for evaluating if the applicable investment securities within the Company's held-to-maturity portfolio were OTTI at December 31, 2017 . Management does not intend to sell these securities prior to maturity. U.S. Government-Sponsored Enterprises As of December 31, 2017 , the Company owned fourteen GSE debentures with a total fair value of $40.8 million and a net unrealized loss of $0.8 million . As of December 31, 2016 , the Company owned five GSE debentures with a total fair value of $14.1 million and a net unrealized loss of $0.6 million . As of December 31, 2017 , all securities in this portfolio were in an unrealized loss position. At December 31, 2016 , all securities in this portfolio were in an unrealized loss position. All securities are performing and backed by the implicit (FHLB/FNMA/FHLMC) or explicit (GNMA) guarantee of the U.S Government. During the years ended December 31, 2017 and December 31, 2016 , the Company purchased a total of $26.9 million and $17.7 million in GSE debentures, respectively. As of December 31, 2017 , the Company owned eleven GSE MBSs with a total fair value of $13.7 million and a net unrealized loss of $0.2 million . As of December 31, 2016 , the Company owned eleven GSE MBSs with a total fair value of $17.5 million and an unrealized loss of $0.2 million . As of December 31, 2017 , eight of the eleven securities in this portfolio were in an unrealized loss position. At December 31, 2016 , eight of the eleven securities were in an unrealized loss position. All securities are performing and backed by the implicit (FHLB/FNMA/FHLMC) or explicit (GNMA) guarantee of the U.S Government. During the year ended December 31, 2017 , the Company did no t purchase any GSE MBSs. During the year ended December 31, 2016, the Company purchased $2.3 million in GSE MBSs. Municipal Obligations As of December 31, 2017 , the Company owned 100 municipal obligation securities with a total fair value and total amortized cost of $53.5 million and $53.7 million , respectively. As of December 31, 2016 , the Company owned 100 municipal obligation securities with a total fair value and total amortized cost of $53.2 million and $54.2 million , respectively. As of December 31, 2017 , 69 of the 100 securities in this portfolio were in an unrealized loss position as compared to December 31, 2016 , when 93 of the 100 securities were in an unrealized loss position. During the year ended December 31, 2017 , the Company did no t purchase any of municipal obligations. During the year ended December 31, 2016 , the Company purchased $15.6 million in municipal obligations. Foreign Government Obligations As of December 31, 2017 and 2016, the Company owned one foreign government obligation security with a fair value and amortized cost of $0.5 million . As of December 31, 2017 , the security was in an unrealized loss position. As of December 31, 2016 , the security was in an unrealized loss position. During the year ended December 31, 2017 , the Company did not purchase any foreign government obligation securities. During the year ended December 31, 2016 , the Company repurchased the foreign government obligation security that matured during the first quarter of 2016. Portfolio Maturities The final stated maturities of the debt securities are as follows for the periods indicated: At December 31, 2017 2016 Amortized Cost Estimated Fair Value Weighted Average Rate Amortized Cost Estimated Fair Value Weighted Average Rate (Dollars in Thousands) Investment securities available-for-sale: Within 1 year $ 23,612 $ 23,652 2.27% $ 13 $ 13 0.17% After 1 year through 5 years 142,772 142,029 2.05% 81,524 81,833 2.14% After 5 years through 10 years 136,746 134,978 2.06% 128,956 127,952 2.03% Over 10 years 243,856 238,483 2.06% 318,743 312,864 2.03% $ 546,986 $ 539,142 2.07% $ 529,236 $ 522,662 2.04% Investment securities held-to-maturity: Within 1 year $ 918 $ 916 0.78% $ 190 $ 190 1.00% After 1 year through 5 years 58,335 57,939 1.74% 23,012 22,750 1.30% After 5 years through 10 years 36,589 35,998 1.79% 46,442 45,042 1.75% Over 10 years 13,888 13,670 1.98% 17,476 17,289 2.11% $ 109,730 $ 108,523 1.78% $ 87,120 $ 85,271 1.70% Actual maturities of debt securities will differ from those presented above since certain obligations amortize and may also provide the issuer the right to call or prepay the obligation prior to scheduled maturity without penalty. MBSs and CMOs are included above based on their final stated maturities; the actual maturities, however, may occur earlier due to anticipated prepayments and stated amortization of cash flows. As of December 31, 2017 , issuers of debt securities with an estimated fair value of $58.8 million had the right to call or prepay the obligations. Of the $58.8 million , approximately $32.7 million matures in 1 - 5 years, $25.2 million matures in 6 - 10 years, and $0.9 million matures after ten years. As of December 31, 2016 , issuers of debt securities with an estimated fair value of approximately $27.9 million had the right to call or prepay the obligations. Of the $27.9 million , $3.0 million matures in 1-5 years, $23.5 million matures in 6-10 years, and $1.4 million matures after ten years. Security Sales Security transactions are recorded on the trade date. When securities are sold, the adjusted cost of the specific security sold is used to compute the gain or loss on the sale. On February 3, 2017, the Company, through its wholly owned subsidiary, Brookline Securities Corp. ("Brookline Securities"), received $319.04 in cash and 14.876 shares of Community Bank Systems, Inc. (“CBU”) common stock in exchange for each of the 9,721 shares of Northeast Retirement Services, Inc. (“NRS”) stock held by Brookline Securities. The exchange was completed in accordance with the merger agreement entered into between NRS and CBU. As part of the merger agreement, the Company was restricted to selling 5,071 shares of CBU per day in the open market. During the quarter ended March 31, 2017, the Company completed the sale of all of the CBU shares. Brookline Securities recognized a gain on the sale of securities of $11.4 million for the year end December 31, 2017. On July 26, 2017, the Savings Bank Life Insurance Company of Massachusetts ("SBLI") converted from a Massachusetts stock insurance company to a Massachusetts mutual insurance company and, as a result, the Company, through its wholly owned subsidiary, Brookline Securities received $500 for the one share of Class A Common Stock and $128 per share for its 2,070 shares of Class B Common Stock held of SBLI, in exchange for $265.5 thousand in cash. Brookline Securities recognized a nominal gain on the exchange for the year end December 31, 2017. Sales of investment and restricted equity securities are summarized as follows: Year Ended December 31, 2017 (In Thousands) Sales of debt securities $ — Sales of marketable and restricted equity securities 11,393 Gross gains from sales 11,612 Gross losses from sales (219 ) Gain on sales of securities, net $ 11,393 There were no sales of investment and restricted equity securities in 2016 and 2015.

Restricted Equity Securities

Restricted Equity Securities	12 Months Ended
	Dec. 31, 2017
Restricted Investments Note [Abstract]
Restricted Equity Securities	Restricted Equity Securities Investments in the restricted equity securities of various entities are as follows: At December 31, 2017 2016 (In Thousands) FHLBB stock $ 42,427 $ 47,284 FRB stock 16,842 16,752 Other restricted equity securities 100 475 $ 59,369 $ 64,511 The Company invests in the stock of FHLBB as one of the requirements to borrow. As of December 31, 2017 and 2016 , FHLBB stock is recorded at its carrying value, which is equal to cost and which management believes approximates its fair value. The FHLBB stated that it remained in compliance with all regulatory capital ratios as of December 31, 2017 and was classified as "adequately capitalized" by its regulator, based on the FHLBB's financial information as of September 30, 2017. The FHLBB paid a dividend to member banks at an annualized rate of 363 basis points in 2016. The FHLBB increased its dividend from 394 basis points in the first quarter of 2017 to 433 basis points in the fourth quarter of 2017 . As of December 31, 2017 , the Company's investment in FHLBB stock exceeded its required investment which provides for additional borrowing capacity. The Company invests in the stock of the Federal Reserve Bank of Boston as required by its the Banks' membership in the Federal Reserve system. As of December 31, 2017 and 2016 , Federal Reserve Bank of Boston stock is recorded at its carrying value, which is equal to cost and which management believes approximates its fair value. The Company, through its wholly owned subsidiary, Brookline Securities Corp., ("Brookline Securities") held 9,721 shares of restricted equity securities of Northeast Retirement Services, Inc. ("NRS"). This investment was recorded at cost of $122 thousand as no readily determinable fair value was available. On December 5, 2016, Community Bank Systems, Inc. ("CBU") announced entry into a merger agreement to acquire NRS. After receiving stockholder and regulatory approvals, CBU completed the acquisition of NRS on February 3, 2017. The Company exchanged the 9,721 shares of NRS and received $319.04 in cash and 14.876 shares of CBU common stock for each share of NRS held. As part of the merger agreement, the Company was restricted to selling 5,071 shares per day in the open market. The Company completed the sale of all CBU shares during the first quarter of 2017. The Company recognized a gain on the sale of securities of $11.4 million for the quarter ending March 31, 2017. Brookline Securities held one Class A Common Stock share and 2,070 Class B Common Stock shares of the Savings Bank Life Insurance Company of Massachusetts ("SBLI"). In July 2017, SBLI converted from a Massachusetts stock insurance company to a Massachusetts mutual insurance company and, as a result, Brookline Securities received $500 for one share of Class A Common Stock and $128 per share for its 2,070 shares of Class B Common Stock of SBLI, in exchange for $265.5 thousand in cash. Brookline Securities recognized a nominal gain on the exchange.

Loans and Leases

Loans and Leases	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Loans and Leases	Loans and Leases The following tables present loan and lease balances and weighted average coupon rates for the originated and acquired loan and lease portfolios at the dates indicated: At December 31, 2017 Originated Acquired Total Balance Weighted Average Coupon Balance Weighted Average Coupon Balance Weighted Average Coupon (Dollars In Thousands) Commercial real estate loans: Commercial real estate $ 2,069,392 4.17 % $ 105,577 4.37 % $ 2,174,969 4.18 % Multi-family mortgage 735,921 4.09 % 24,749 4.48 % 760,670 4.10 % Construction 140,138 4.58 % — — % 140,138 4.58 % Total commercial real estate loans 2,945,451 4.17 % 130,326 4.39 % 3,075,777 4.18 % Commercial loans and leases: Commercial 696,825 4.35 % 8,179 5.77 % 705,004 4.37 % Equipment financing 861,974 7.28 % 4,514 5.92 % 866,488 7.27 % Condominium association 52,619 4.49 % — — % 52,619 4.49 % Total commercial loans and leases 1,611,418 5.92 % 12,693 5.82 % 1,624,111 5.92 % Consumer loans: Residential mortgage 604,897 3.81 % 55,168 4.28 % 660,065 3.85 % Home equity 314,189 4.16 % 41,765 4.62 % 355,954 4.21 % Other consumer 14,667 5.51 % 105 18.00 % 14,772 5.60 % Total consumer loans 933,753 3.95 % 97,038 4.44 % 1,030,791 4.00 % Total loans and leases $ 5,490,622 4.65 % $ 240,057 4.49 % $ 5,730,679 4.64 % At December 31, 2016 Originated Acquired Total Balance Weighted Average Coupon Balance Weighted Average Coupon Balance Weighted Average Coupon (Dollars In Thousands) Commercial real estate loans: Commercial real estate $ 1,907,254 3.95 % $ 143,128 4.24 % $ 2,050,382 3.97 % Multi-family mortgage 701,450 3.79 % 29,736 4.53 % 731,186 3.82 % Construction 136,785 3.79 % 214 3.67 % 136,999 3.79 % Total commercial real estate loans 2,745,489 3.90 % 173,078 4.29 % 2,918,567 3.92 % Commercial loans and leases: Commercial 621,285 4.11 % 14,141 5.44 % 635,426 4.14 % Equipment financing 793,702 7.06 % 6,158 5.86 % 799,860 7.05 % Condominium association 60,122 4.39 % — — % 60,122 4.39 % Total commercial loans and leases 1,475,109 5.71 % 20,299 5.57 % 1,495,408 5.71 % Consumer loans: Residential mortgage 555,430 3.67 % 68,919 3.98 % 624,349 3.70 % Home equity 289,361 3.50 % 52,880 4.26 % 342,241 3.62 % Other consumer 18,171 5.48 % 128 17.92 % 18,299 5.57 % Total consumer loans 862,962 3.65 % 121,927 4.12 % 984,889 3.71 % Total loans and leases $ 5,083,560 4.38 % $ 315,304 4.31 % $ 5,398,864 4.38 % The net unamortized deferred loan origination fees and costs included in total loans and leases were $15.5 million and $14.2 million as of December 31, 2017 and 2016 , respectively. The Company's Banks and subsidiaries lend primarily in eastern Massachusetts, southern New Hampshire and Rhode Island, with the exception of equipment financing, 28.0% of which is in the greater New York and New Jersey metropolitan area and 72.0% of which is in other areas in the United States of America as of December 31, 2017 , as compared to 29.6% of which is in the greater New York and New Jersey metropolitan area and 70.4% of which is in other areas in the United States of America as of December 31, 2016 . Competition for indirect automobile loans increased significantly in recent years as credit unions and large national banks entered indirect automobile lending. That competition drove interest rates down and, in some cases, changed the manner in which interest rates are developed, from including a dealer-shared spread to imposing a dealer-based fee to originate the loan. Given this market condition, management ceased the Company's origination of indirect automobile loans in December 2014. For the quarter ended March 31, 2015, the Company sold over 90% of the portfolio for $255.2 million , which resulted in a loss of $11.8 thousand excluding the impact on the allowance for loan and lease losses. Accretable Yield for the Acquired Loan Portfolio The following table summarizes activity in the accretable yield for the acquired loan portfolio for the periods indicated: Year Ended December 31, 2017 2016 2015 (In Thousands) Balance at beginning of year $ 14,353 $ 20,796 $ 32,044 Accretion (7,801 ) (6,781 ) (10,467 ) Reclassification from/(to) nonaccretable difference as a result from changes in expected cash flows 3,970 338 (781 ) Balance at end of year $ 10,522 $ 14,353 $ 20,796 On a quarterly basis, subsequent to acquisition, management reforecasts the expected cash flows for acquired ASC 310-30 loans, taking into account prepayment speeds, probability of default and loss given defaults. Management compares cash flow projections per the reforecast to the original cash flow projections and determines whether any reduction in cash flow expectations are due to deterioration, or if the change in cash flow expectation is related to noncredit events. This cash flow analysis is used to evaluate the need for a provision for loan and lease losses and/or prospective yield adjustments. During the years ended December 31, 2017 , 2016 and 2015 , accretable yield adjustments totaling $4.0 million , $0.3 million , and $(0.8) million , respectively, were made for certain loan pools. These accretable yield adjustments, which are subject to continued re-assessment, will be recognized over the remaining lives of those pools. Related Party Loans The Banks' authority to extend credit to their respective directors and executive officers, as well as to entities controlled by such persons, is currently governed by the requirements of the Sarbanes-Oxley Act and Regulation O of the FRB. Among other things, these provisions require that extensions of credit to insiders (1) be made on terms that are substantially the same as, and follow credit underwriting procedures that are not less stringent than, those prevailing for comparable transactions with unaffiliated persons and that do not involve more than the normal risk of repayment or present other unfavorable features; and (2) not exceed certain limitations on the amount of credit extended to such persons, individually and in the aggregate, which limits are based, in part, on the amount of the Banks' capital. In addition, the extensions of credit to insiders must be approved by the applicable Bank's Board of Directors. The following table summarizes the change in the total amounts of loans and advances, to directors, executive officers and their affiliates for the periods indicated. All loans were performing as of December 31, 2017 . Year Ended December 31, 2017 2016 (In Thousands) Balance at beginning of year $ 43,458 $ 37,375 New loans granted during the year 13,554 8,352 Advances on lines of credit 473 26 Repayments (9,544 ) (2,295 ) Balance at end of year $ 47,941 $ 43,458 Unfunded commitments on extensions of credit to related parties totaled $15.7 million and $8.7 million as of December 31, 2017 and 2016 , respectively. Loans and Leases Pledged as Collateral As of December 31, 2017 and 2016 , there were $2.3 billion and $2.1 billion , respectively, of loans and leases pledged as collateral for repurchase agreements; municipal deposits; treasury, tax and loan deposits; swap agreements; and FHLBB borrowings. The Banks did not have any outstanding FRB borrowings as of December 31, 2017 and 2016 .

Allowance for Loan and Lease Lo

Allowance for Loan and Lease Losses	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Allowance for Loan and Lease Losses	Allowance for Loan and Lease Losses The following tables present the changes in the allowance for loan and lease losses and the recorded investment in loans and leases by portfolio segment for the periods indicated: Year Ended December 31, 2017 Commercial Real Estate Commercial Consumer Total (In Thousands) Balance at December 31, 2016 $ 27,645 $ 20,906 $ 5,115 $ 53,666 Charge-offs (494 ) (14,914 ) (403 ) (15,811 ) Recoveries 476 1,158 319 1,953 (Credit) provision for loan and lease losses (515 ) 19,183 116 18,784 Balance at December 31, 2017 $ 27,112 $ 26,333 $ 5,147 $ 58,592 Year Ended December 31, 2016 Commercial Real Estate Commercial Consumer Total (In Thousands) Balance at December 31, 2015 $ 30,151 $ 22,018 $ 4,570 $ 56,739 Charge-offs (2,169 ) (10,516 ) (1,982 ) (14,667 ) Recoveries — 642 750 1,392 (Credit) provision for loan and lease losses (337 ) 8,762 1,777 10,202 Balance at December 31, 2016 $ 27,645 $ 20,906 $ 5,115 $ 53,666 Year Ended December 31, 2015 Commercial Real Estate Commercial Consumer Unallocated Total (In Thousands) Balance at December 31, 2014 $ 29,594 $ 15,957 $ 5,690 $ 2,418 $ 53,659 Charge-offs (550 ) (3,634 ) (2,370 ) — (6,554 ) Recoveries — 667 1,544 — 2,211 Provision (credit) for loan and lease losses 1,107 9,028 (294 ) (2,418 ) 7,423 Balance at December 31, 2015 $ 30,151 $ 22,018 $ 4,570 $ — $ 56,739 The liability for unfunded credit commitments, which is included in other liabilities, was $1.7 million , and $1.5 million , at December 31, 2017 , and 2016 , respectively. The changes in the liability for unfunded credit commitments reflect changes in the estimate of loss exposure associated with certain unfunded credit commitments. No credit commitments were charged off against the liability account in the years ended December 31, 2017 , and 2016 . Provision for Credit Losses The provisions for credit losses are set forth below for the periods indicated: Originated Acquired Total Year Ended December 31, Year Ended December 31, Year Ended December 31, 2017 2016 2015 2017 2016 2015 2017 2016 2015 (In Thousands) Provision (credit) for loan and lease losses: Commercial real estate $ (343 ) $ (750 ) $ 1,459 $ (172 ) $ 413 $ (352 ) $ (515 ) $ (337 ) $ 1,107 Commercial 18,899 8,469 9,077 284 293 (49 ) 19,183 8,762 9,028 Consumer 273 1,263 (763 ) (157 ) 514 469 116 1,777 (294 ) Unallocated — — (2,418 ) — — — — — (2,418 ) Total provision for loan and lease losses 18,829 8,982 7,355 (45 ) 1,220 68 18,784 10,202 7,423 Unfunded credit commitments 204 151 28 — — — 204 151 28 Total provision (credit) for credit losses $ 19,033 $ 9,133 $ 7,383 $ (45 ) $ 1,220 $ 68 $ 18,988 $ 10,353 $ 7,451 Allowance for Loan and Lease Losses Methodology Management has established a methodology to determine the adequacy of the allowance for loan and lease losses that assesses the risks and losses inherent in the loan and lease portfolio. Additions to the allowance for loan and lease losses are made by charges to the provision for credit losses. Losses on loans and leases are charged off against the allowance when all or a portion of a loan or lease is considered uncollectible. Subsequent recoveries on loans previously charged off, if any, are credited to the allowance when realized. Management uses a consistent and systematic process and methodology to evaluate the adequacy of the allowance for loan and lease losses on a quarterly basis. For purposes of determining the allowance for loan and lease losses, the Company has segmented certain loans and leases in the portfolio by product type into the following segments: (1) commercial real estate loans, (2) commercial loans and leases, (3) consumer loans. Portfolio segments are further disaggregated into classes based on the associated risks within the segments. Commercial real estate loans are divided into three classes: commercial real estate loans, multi-family mortgage loans, and construction loans. Commercial loans and leases are divided into three classes: commercial loans which includes taxi medallion loans, equipment financing, and loans to condominium associations. Consumer loans are divided into three classes: residential mortgage loans, home equity loans, and other consumer loans. A formula-based credit evaluation approach is applied to each group, coupled with an analysis of certain loans for impairment. For each class of loan, management makes significant judgments in selecting the estimation method that fits the credit characteristics of its class and portfolio segment as set forth below. Also refer to Note 1, "Basis of Presentation," in the consolidated financial statements for more information on the Company's allowance of loan and lease losses methodology. The general allowance related to loans collectively evaluated for impairment is determined using a formula-based approach utilizing the risk ratings of individual credits and loss factors derived from historic portfolio loss rates, which include estimates of incurred losses over an estimated loss emergence period (“LEP”). The LEP was generated utilizing a charge-off look-back analysis which studied the time from the first indication of elevated risk of repayment (or other early event indicating a problem) to eventual charge-off to support the LEP considered in the allowance calculation. This reserving methodology established the approximate number of months of LEP that represents incurred losses for each portfolio. In addition to quantitative measures, relevant qualitative factors include, but are not limited to: (1) levels and trends in past due and impaired loans, (2) levels and trends in charge-offs, (3) changes in underwriting standards, policy exceptions, and credit policy, (4) experience of lending management and staff, (5) economic trends, (6) industry conditions, (7) effects of changes in credit concentrations, (8) interest rate environment, and (9) regulatory and other changes. The general allowance related to the acquired loans collectively evaluated for impairment is determined based upon the degree, if any, of deterioration in the pooled loans subsequent to acquisition. The qualitative factors used in the determination are the same as those used for originated loans. During the third quarter of 2015, the Company enhanced and refined its general allowance methodology to provide further quantification of probable losses in the portfolio. Under the enhanced methodology, management combined the historical loss histories of the Banks to generate a single set of ratios. Management believes it is appropriate to aggregate the ratios as the Banks share common environmental factors, operate in similar geographic markets, and utilize common underwriting standards in accordance with the Company's Credit Policy. In prior periods to the three months ended September 30, 2015, a historical loss history applicable to each Bank was used. Management employed a similar analysis for the consolidation of the qualitative factors as it did for the quantitative factors. Again, management believes the realignment of the existing nine qualitative factors used at each of the Banks into a single group of factors for use across the Company is appropriate based on the commonality of environmental factors, markets and underwriting standards among the Banks. In prior periods to the three months ended September 30, 2015, each of the Banks utilized a set of qualitative factors applicable to each Bank. Based on the refinements to the Company’s allowance methodology discussed above, management determined that the potential risks anticipated by the unallocated allowance are now incorporated into the allowance methodology, making the unallocated allowance unnecessary. In prior periods, the unallocated allowance was used to recognize the estimated risk associated with the allocated general and specific allowances. It incorporated management’s evaluation of existing conditions that were not included in the allocated allowance determinations and provided for losses that arise outside of the ordinary course of business. Specific valuation allowances are established for impaired originated loans with book values greater than the discounted present value of expected future cash flows or, in the case of collateral-dependent impaired loans, for any excess of a loan's book balance and the fair value of its underlying collateral. Specific valuation allowances are established for acquired loans with deterioration in the discounted present value of expected future cash flows since acquisitions or, in the case of collateral dependent impaired loans, for any increase in the excess of a loan's book balance greater than the fair value of its underlying collateral. A specific valuation allowance for losses on TDR loans is determined by comparing the net carrying amount of the troubled debt restructured loan with the restructured loan's cash flows discounted at the original effective rate. Impaired loans are reviewed quarterly with adjustments made to the calculated reserve as necessary. As of December 31, 2017 , management believes that the methodology for calculating the allowance provides a reasonable basis for determining and reporting on probable losses in the Company’s loan portfolios. As of December 31, 2017 , the Company had a portfolio of approximately $19.7 million in loans secured by taxi medallions issued by the cities of Boston and Cambridge. As of December 31, 2016 , this portfolio was approximately $31.1 million . Application-based mobile ride services, such as Uber and Lyft, have generated increased competition in the transportation sector, resulting in a reduction in taxi utilization and, as a result, a reduction in the collateral value and credit quality of taxi medallion loans. This has increased the likelihood that loans secured by taxi medallions may default, or that the borrowers may be unable to repay these loans at maturity, resulting in an increase in past due loans, troubled debt restructurings, and charge-offs. Therefore, beginning with the three months ended September 30, 2015, the Company’s allowance calculation included an enhanced segmentation of the commercial loans and leases to reflect the increased risk in the Company’s taxi medallion portfolio. This allowance calculation segmentation represents management’s estimations of the special risks associated with the taxi portfolio. As of December 31, 2017 , the Company had an allowance for loan and lease losses associated with taxi medallion loans of $3.8 million of which $2.7 million were specific reserves and $1.1 million was a general reserve. As of December 31, 2016 , the Company had a reserve for loan and lease losses associated with taxi medallion loans of $1.3 million of which $0.1 million were specific reserves and $1.2 million was a general reserve.The increase in the allowance for loan and leases associated with taxi medallion loans was primarily driven by the increase in specific reserves due to changes in the underlying collateral value of taxi medallions and the increase in general reserve due to the increase in the historical loss factor applied to the taxi medallion loans. The total troubled debt restructured loans and leases secured by taxi medallions decreased by $2.4 million from $6.1 million at December 31, 2016 to $3.7 million at December 31, 2017 . The total loans and leases secured by taxi medallions that were placed on nonaccrual decreased to $7.8 million at December 31, 2017 from $13.4 million at December 31, 2016 . However, further declines in demand for taxi services or further deterioration in the value of taxi medallions may result in higher delinquencies and losses beyond that provided for in the allowance for loan and lease losses. The general allowance for loan and lease losses was $55.5 million as of December 31, 2017 , compared to $53.5 million as of December 31, 2016 . The general portion of the allowance for loan and lease losses increased by $2.0 million during the year ended December 31, 2017 , as a result of the continued growth in the Company's loan portfolios, the increase in historical loss factors applied to the commercial loan portfolio and the improvement of credit risk ratings of loans within the commercial real estate and commercial portfolios. The specific allowance for loan and lease losses was $3.1 million as of December 31, 2017 , compared to $0.2 million as of December 31, 2016 . The specific allowance increased by $3.0 million during the year ended December 31, 2017 , primarily due to changes in the underlying collateral value of taxi medallions during the year ended December 31, 2017 . Credit Quality Assessment At the time of loan origination, a rating is assigned based on the capacity to pay and general financial strength of the borrower, the value of assets pledged as collateral, and the evaluation of third party support such as a guarantor. The Company periodically monitors the quality of the loan portfolio using all available information. The officer responsible for handling each loan is required to initiate changes to risk ratings when changes in facts and circumstances occur that warrant an upgrade or downgrade in a loan rating. Based on this information, loans demonstrating certain payment issues or other weaknesses may be categorized as delinquent, impaired, nonperforming and/or put on nonaccrual status. Additionally, in the course of resolving such loans, the Company may choose to restructure the contractual terms of certain loans to match the borrower's ability to repay the loan based on their current financial condition. If a restructured loan meets certain criteria, it may be categorized as a troubled debt restructuring. The Company reviews numerous credit quality indicators when assessing the risk in its loan portfolio. For all loans, the Company utilizes an eight-grade loan rating system, which assigns a risk rating to each borrower based on a number of quantitative and qualitative factors associated with a loan transaction. Factors considered include industry and market conditions; position within the industry; earnings trends; operating cash flow; asset/liability values; debt capacity; guarantor strength; management and controls; financial reporting; collateral; and other considerations. In addition, the Company's independent loan review group evaluates the credit quality and related risk ratings in all loan portfolios. The results of these reviews are reported to the Risk Committee of the Board of Directors on a periodic basis and annually to the Board of Directors. For the consumer loans, the Company heavily relies on payment status for calibrating credit risk. The ratings categories used for assessing credit risk in the commercial real estate, multi-family mortgage, construction, commercial, equipment financing, condominium association and other consumer loan and lease classes are defined as follows: 1 -4 Rating—Pass Loan rating grades "1" through "4" are classified as "Pass," which indicates borrowers are performing in accordance with the terms of the loan and are less likely to result in loss due to the capacity of the borrower to pay and the adequacy of the value of assets pledged as collateral. 5 Rating—Other Assets Especially Mentioned ("OAEM") Borrowers exhibit potential credit weaknesses or downward trends deserving management's attention. If not checked or corrected, these trends will weaken the Company's asset and position. While potentially weak, currently these borrowers are marginally acceptable; no loss of principal or interest is envisioned. 6 Rating—Substandard Borrowers exhibit well defined weaknesses that jeopardize the orderly liquidation of debt. Substandard loans may be inadequately protected by the current net worth and paying capacity of the obligors or by the collateral pledged, if any. Normal repayment from the borrower is in jeopardy. Although no loss of principal is envisioned, there is a distinct possibility that a partial loss of interest and/or principal will occur if the deficiencies are not corrected. Collateral coverage may be inadequate to cover the principal obligation. 7 Rating—Doubtful Borrowers exhibit well-defined weaknesses that jeopardize the orderly liquidation of debt with the added provision that the weaknesses make collection of the debt in full, on the basis of currently existing facts, conditions, and values, highly questionable and improbable. Serious problems exist to the point where partial loss of principal is likely. 8 Rating—Definite Loss Borrowers deemed incapable of repayment. Loans to such borrowers are considered uncollectible and of such little value that continuation as active assets of the Company is not warranted. Assets rated as "OAEM," "substandard" or "doubtful" based on criteria established under banking regulations are collectively referred to as "criticized" assets. Credit Quality Information The following tables present the recorded investment in loans in each class as of December 31, 2017 by credit quality indicator. At December 31, 2017 Commercial Real Estate Multi- Family Mortgage Construction Commercial Equipment Financing Condominium Association Other Consumer Total (In Thousands) Originated: Loan rating: Pass $ 2,054,376 $ 735,313 $ 139,278 $ 670,265 $ 850,006 $ 52,619 $ 14,628 $ 4,516,485 OAEM 8,889 — — 7,691 3,630 — — 20,210 Substandard 5,926 608 860 17,681 5,012 — 39 30,126 Doubtful 201 — — 1,188 3,326 — — 4,715 Total originated 2,069,392 735,921 140,138 696,825 861,974 52,619 14,667 4,571,536 Acquired: Loan rating: Pass 94,244 24,459 — 6,643 4,501 — 104 129,951 OAEM 9,839 — — 265 — — 1 10,105 Substandard 1,494 290 — 1,271 13 — — 3,068 Doubtful — — — — — — — — Total acquired 105,577 24,749 — 8,179 4,514 — 105 143,124 Total loans $ 2,174,969 $ 760,670 $ 140,138 $ 705,004 $ 866,488 $ 52,619 $ 14,772 $ 4,714,660 As of December 31, 2017 , there were no loans categorized as definite loss. At December 31, 2017 Residential Mortgage Home Equity ($ In Thousands) Originated: Loan-to-value ratio: Less than 50% $ 153,373 23.2 % $ 148,137 41.6 % 50% - 69% 265,328 40.2 % 75,099 21.1 % 70% - 79% 168,272 25.5 % 63,742 17.9 % 80% and over 16,547 2.5 % 27,122 7.6 % Data not available* 1,377 0.2 % 89 — % Total originated 604,897 91.6 % 314,189 88.2 % Acquired: Loan-to-value ratio: Less than 50% 16,521 2.5 % 25,312 7.1 % 50%—69% 19,182 2.9 % 13,883 3.9 % 70%—79% 10,507 1.6 % 943 0.3 % 80% and over 7,893 1.2 % 582 0.2 % Data not available* 1,065 0.2 % 1,045 0.3 % Total acquired 55,168 8.4 % 41,765 11.8 % Total loans $ 660,065 100.0 % $ 355,954 100.0 % _______________________________________________________________________________ * Represents in process general ledger accounts for which data are not available. The following tables present the recorded investment in loans in each class as of December 31, 2016 by credit quality indicator. At December 31, 2016 Commercial Real Estate Multi- Family Mortgage Construction Commercial Equipment Financing Condominium Association Other Consumer Total (In Thousands) Originated: Loan rating: Pass $ 1,899,162 $ 700,046 $ 136,607 $ 583,940 $ 786,050 $ 60,122 $ 12,018 $ 4,177,945 OAEM 1,538 — 178 8,675 824 — — 11,215 Substandard 6,288 1,404 — 28,595 4,848 — 12 41,147 Doubtful 266 — — 75 1,980 — — 2,321 Total originated 1,907,254 701,450 136,785 621,285 793,702 60,122 12,030 4,232,628 Acquired: Loan rating: Pass 131,850 29,153 214 10,312 6,158 — 128 177,815 OAEM 1,408 270 — 249 — — — 1,927 Substandard 9,768 313 — 3,017 — — — 13,098 Doubtful 102 — — 563 — — — 665 Total acquired 143,128 29,736 214 14,141 6,158 — 128 193,505 Total loans $ 2,050,382 $ 731,186 $ 136,999 $ 635,426 $ 799,860 $ 60,122 $ 12,158 $ 4,426,133 As of December 31, 2016 , there were no loans categorized as definite loss. At December 31, 2016 Residential Mortgage Home Equity ($ In Thousands) Originated: Loan-to-value ratio: Less than 50% $ 138,030 22.1 % $ 153,679 44.9 % 50%—69% 229,799 36.9 % 61,553 18.1 % 70%—79% 162,614 26.0 % 49,987 14.6 % 80% and over 21,859 3.5 % 23,317 6.8 % Data not available* 3,128 0.5 % 825 0.2 % Total originated 555,430 89.0 % 289,361 84.6 % Acquired: Loan-to-value ratio: Less than 50% 17,809 2.9 % 32,334 9.4 % 50%—69% 24,027 3.8 % 15,059 4.4 % 70%—79% 14,030 2.2 % 3,069 0.9 % 80% and over 10,069 1.6 % 1,016 0.3 % Data not available* 2,984 0.5 % 1,402 0.4 % Total acquired 68,919 11.0 % 52,880 15.4 % Total loans $ 624,349 100.0 % $ 342,241 100.0 % _______________________________________________________________________________ * Represents in process general ledger accounts for which data are not available. The following table presents information regarding foreclosed residential real estate property for the periods indicated: At December 31, 2017 At December 31, 2016 (In Thousands) Foreclosed residential real estate property held by the creditor $ — $ 251 Recorded investment in mortgage loans collateralized by residential real estate property that are in the process of foreclosure 633 1,213 Age Analysis of Past Due Loans and Leases The following tables present an age analysis of the recorded investment in total loans and leases as of December 31, 2017 and 2016 . At December 31, 2017 Past Due Loans and Leases Past Due Greater Than 90 Days and Accruing 31-60 Days 61-90 Days Greater Than 90 Days Total Current Total Loans and Leases Nonaccrual Loans and Leases (In Thousands) Originated: Commercial real estate loans: Commercial real estate $ 3,294 $ 391 $ 1,843 $ 5,528 $ 2,063,864 $ 2,069,392 $ — $ 3,182 Multi-family mortgage 6,141 2,590 — 8,731 727,190 735,921 — 608 Construction 6,537 330 860 7,727 132,411 140,138 — 860 Total commercial real estate loans 15,972 3,311 2,703 21,986 2,923,465 2,945,451 — 4,650 Commercial loans and leases: Commercial 1,344 597 7,724 9,665 687,160 696,825 — 10,365 Equipment financing 3,214 2,494 3,203 8,911 853,063 861,974 224 8,106 Condominium association 857 262 — 1,119 51,500 52,619 — — Total commercial loans and leases 5,415 3,353 10,927 19,695 1,591,723 1,611,418 224 18,471 Consumer loans: Residential mortgage 1,256 166 728 2,150 602,747 604,897 — 1,979 Home equity 643 19 32 694 313,495 314,189 1 132 Other consumer 238 20 28 286 14,381 14,667 — 43 Total consumer loans 2,137 205 788 3,130 930,623 933,753 1 2,154 Total originated loans and leases $ 23,524 $ 6,869 $ 14,418 $ 44,811 $ 5,445,811 $ 5,490,622 $ 225 $ 25,275 (Continued) At December 31, 2017 Past Due Loans and Leases Past Due Greater Than 90 Days and Accruing 31-60 Days 61-90 Days Greater Than 90 Days Total Current Total Loans and Leases Nonaccrual Loans and Leases (In Thousands) Acquired: Commercial real estate loans: Commercial real estate $ 1,008 $ — $ 656 $ 1,664 $ 103,913 $ 105,577 $ 586 $ 131 Multi-family mortgage — — 3 3 24,746 24,749 3 — Total commercial real estate loans 1,008 — 659 1,667 128,659 130,326 589 131 Commercial loans and leases: Commercial — 44 1,022 1,066 7,113 8,179 17 1,254 Equipment financing — — 13 13 4,501 4,514 13 — Total commercial loans and leases — 44 1,035 1,079 11,614 12,693 30 1,254 Consumer loans: Residential mortgage — 463 1,990 2,453 52,715 55,168 1,990 — Home equity 508 — 186 694 41,071 41,765 186 612 Other consumer — — — — 105 105 — — Total consumer loans 508 463 2,176 3,147 93,891 97,038 2,176 612 Total acquired loans and leases 1,516 507 3,870 5,893 234,164 240,057 2,795 1,997 Total loans and leases $ 25,040 $ 7,376 $ 18,288 $ 50,704 $ 5,679,975 $ 5,730,679 $ 3,020 $ 27,272 At December 31, 2016 Past Due Loans and Leases Past Due Greater Than 90 Days and Accruing 31-60 Days 61-90 Days Greater Than 90 Days Total Current Total Loans and Leases Nonaccrual Loans and Leases (In Thousands) Originated: Commercial real estate loans: Commercial real estate $ 1,525 $ 2,075 $ 429 $ 4,029 $ 1,903,225 $ 1,907,254 $ 2 $ 5,035 Multi-family mortgage 2,296 — 291 2,587 698,863 701,450 — 1,404 Construction 547 — — 547 136,238 136,785 — — Total commercial real estate loans 4,368 2,075 720 7,163 2,738,326 2,745,489 2 6,439 Commercial loans and leases: Commercial 5,396 815 10,014 16,225 605,060 621,285 — 20,587 Equipment financing 2,983 1,444 5,341 9,768 783,934 793,702 — 6,758 Condominium association 266 — — 266 59,856 60,122 — — Total commercial loans and leases 8,645 2,259 15,355 26,259 1,448,850 1,475,109 — 27,345 Consumer loans: Residential mortgage 3,745 2,294 163 6,202 549,228 555,430 — 2,455 Home equity 25 219 5 249 289,112 289,361 3 128 Other consumer 549 87 16 652 17,519 18,171 — 149 Total consumer loans 4,319 2,600 184 7,103 855,859 862,962 3 2,732 Total originated loans and leases $ 17,332 $ 6,934 $ 16,259 $ 40,525 $ 5,043,035 $ 5,083,560 $ 5 $ 36,516 (Continued) At December 31, 2016 Past Due Loans and Leases Past Due Greater Than 90 Days and Accruing 31-60 Days 61-90 Days Greater Than 90 Days Total Current Total Loans and Leases Nonaccrual Loans and Leases (In Thousands) Acquired: Commercial real estate loans: Commercial real estate $ 925 $ — $ 4,011 $ 4,936 $ 138,192 $ 143,128 $ 3,786 $ 305 Multi-family mortgage — — — — 29,736 29,736 — — Construction — — — — 214 214 — — Total commercial real estate loans 925 — 4,011 4,936 168,142 173,078 3,786 305 Commercial loans and leases: Commercial 306 — 2,651 2,957 11,184 14,141 264 2,387 Equipment financing — — — — 6,158 6,158 — — Total commercial loans and leases 306 — 2,651 2,957 17,342 20,299 264 2,387 Consumer loans: Residential mortgage — 318 2,865 3,183 65,736 68,919 2,820 46 Home equity 288 97 339 724 52,156 52,880 202 823 Other consumer — 1 — 1 127 128 — — Total consumer loans 288 416 3,204 3,908 118,019 121,927 3,022 869 Total acquired loans and leases 1,519 416 9,866 11,801 303,503 315,304 7,072 3,561 Total loans and leases $ 18,851 $ 7,350 $ 26,125 $ 52,326 $ 5,346,538 $ 5,398,864 $ 7,077 $ 40,077 Commercial Real Estate Loans —As of December 31, 2017 , loans outstanding in the three classes within this segment expressed as a percentage of total loans and leases outstanding were as follows: commercial real estate loans ( 38.0% ); multi-family mortgage loans ( 13.3% ); and construction loans ( 2.4% ). Loans in this portfolio that are on nonaccrual status and/or risk-rated "substandard" or worse are evaluated on an individual loan basis for impairment. For non-impaired commercial real estate loans, loss factors are applied to outstanding loans by risk rating for each of the three classes in the portfolio. The factors applied are based primarily on historic loan loss experience and an assessment of internal and external factors and other relevant information. Commercial Loans and Leases —As of December 31, 2017 , loans and leases outstanding in the three classes within this segment expressed as a percent of total loans and leases outstanding were as follows: commercial loans and leases ( 12.3% ); equipment financing loans ( 15.1% ); and loans to condominium associations ( 0.9% ). Loans and leases in this portfolio that are on nonaccrual status and/or risk-rated "substandard" or worse are evaluated on an individual basis for impairment. For non-impaired commercial loans and leases, loss factors are applied to outstanding loans by risk rating for each of the three classes in the portfolio. Consumer Loans —As of December 31, 2017 , loans outstanding within the three classes within this segment expressed as a percent of total loans and leases outstanding were as follows: residential mortgage loans ( 11.5% ), home equity loans ( 6.2% ), and other consumer loans ( 0.3% ). Significant risk characteristics related to the residential mortgage and home equity loan portfolios are the geographic concentration of the properties financed within selected communities in the greater Boston and Providence metropolitan areas. The payment status and loan-to-value ratio are the primary credit quality indicator used for residential mortgage loans and home equity loans. Generally, loans are not made when the loan-to-value ratio exceeds 80% unless private mortgage insurance is obtained and/or there is a financially strong guarantor. Consumer loans that become 90 days or more past due, or are placed on nonaccrual regardless of past due status, are reviewed on an individual basis for impairment by assessing the net realizable value of underlying collateral and the economic condition of the borrower. Impaired Loans and Leases A loan is considered to be impaired when, based on current information and events, it is probable that the Company will be unable to collect all amounts due (both interest and principal) according to the contractual terms of the loan agreement. The Company has defined the population of impaired loans to include nonaccrual loans and troubled debt restructured loans. When the ultimate collectability of the total principal of an impaired loan or lease is in doubt and the loan is on nonaccrual status, all payments are applied to principal, under the cost recovery method. When the ultimate collectability of the total principal of an impaired loan or lease is not in doubt and the loan or lease is on nonaccrual status, contractual interest is credited to interest income when received, under the cash basis method. The following tables include the recorded investment and unpaid principal balances of impaired loans and leases with the related allowance amount, if applicable, for the originated and acquired loan and lease portfolios at the dates indicated. Also presented are the average recorded investments in the impaired loans and leases and the related amount of interest recognized during the period that the impaired loans were impaired. At December 31, 2017 At December 31, 2016 Recorded (1) Unpaid Related Recorded Investment (2) Unpaid Related (In Thousands) Originated: With no related allowance recorded: Commercial real estate $ 9,978 $ 9,962 $ — $ 9,113 $ 9,104 $ — Commercial 24,906 25,040 — 39,269 39,210 — Consumer 3,508 3,500 — 4,823 4,815 — Total originated with no related allowance recorded 38,392 38,502 — 53,205 53,129 — With an allowance recorded: Commercial real estate 3,056 3,056 — 3,984 3,984 28 Commercial 8,912 8,862 3,105 605 605 97 Total originated with an allowance recorded 11,968 11,918 3,105 4,589 4,589 125 Total originated impaired loans and leases 50,360 50,420 3,105 57,794 57,718 125 Acquired: With no related allowance recorded: Commercial real estate 1,880 1,880 — 10,400 10,400 — Commercial 1,594 1,594 — 3,948 3,948 — Consumer 4,736 4,736 — 6,384 6,399 — Total acquired with no related allowance recorded 8,210 8,210 — 20,732 20,747 — With an allowance recorded: Consumer 115 115 22 253 253 27 Total acquired with an allowance recorded 115 115 22 253 253 27 Total acquired impaired loans and leases 8,325 8,325 22 20,985 21,000 27 Total impaired loans and leases $ 58,685 $ 58,745 $ 3,127 $ 78,779 $ 78,718 $ 152 ___________________________________________________________________________ (1) Includes originated and acquired nonaccrual loans of $24.9 million and $2.0 million , respectively as of December 31, 2017 . (2) Includes originated and acquired nonaccrual loans of $34.1 million and $3.6 million , respectively as of December 31, 2016 . Year Ended December 31, 2017 December 31, 2016 December 31, 2015 Average Interest Average Interest Average Interest (In Thousands) Originated: With no related allowance recorded: Commercial real estate $ 10,125 $ 72 $ 6,608 $ 152 $ 3,999 $ 86 Commercial 26,439 225 23,445 600 15,143 641 Consumer 3,565 14 4,126 76 4,267 65 Total originated with no related allowance recorded 40,129 311 34,179 828 23,409 792 With an allowance recorded: Commercial real estate 3,058 38 4,715 195 5,132 197 Commercial 13,604 — 9,915 6 5,650 10 Consumer — — 124 — 84 — Total originated with an allowance recorded 16,662 38 14,754 201 10,866 207 Total originated impaired loans and leases 56,791 349 48,933 1,029 34,275 999 Acquired: With no related allowance recorded: Commercial real estate 1,996 1 8,906 151 9,200 125 Commercial 1,610 5 4,255 75 4,428 65 Consumer 4,784 17 7,537 68 7,837 62 Total acquired with no related allowance recorded 8,390 23 20,698 294 21,465 252 With an allowance recorded: Commercial real estate — — 1,093 — 713 — Commercial — — 364 — 638 — Consumer 116 1 431 8 249 8 Total acquired with an allowance recorded 116 1 1,888 8 1,600 8 Total acquired impaired loans and leases 8,506 24 22,586 302 23,065 260 Total impaired loans and leases $ 65,297 $ 373 $ 71,519 $ 1,331 $ 57,340 $ 1,259 The following tables present information regarding impaired and non-impaired loans and leases at the dates indicated: At December 31, 2017 Commercial Real Estate Commercial Consumer Total (In Thousands) Allowance for Loan and Lease Losses: Originated: Individually evaluated for impairment $ — $ 3,105 $ — $ 3,105 Collectively evaluated for impairment 26,366 23

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Premises and Equipment	Premises and Equipment Premises and equipment consist of the following: At December 31, Estimated Useful Life 2017 2016 (In Thousands) (In Years) Land $ 11,057 $ 7,562 NA Fine art 495 472 NA Computer equipment 9,728 9,004 3 Vehicles 126 221 3 to 5 Core processing system and software 19,791 19,433 3 to 7.5 Furniture, fixtures and equipment 14,226 13,439 5 to 25 Office building and improvements 88,283 84,835 10 to 40 Total 143,706 134,966 Accumulated depreciation and amortization 63,423 58,790 Total premises and equipment $ 80,283 $ 76,176 Depreciation and amortization expense is calculated using the straight-line method and is included in occupancy and equipment and data processing expense in the Consolidated Statements of Income. For the years ended December 31, 2017 , 2016 and 2015 , depreciation and amortization expense related to premises and equipment totaled $7.4 million , $7.2 million , and $7.2 million , respectively. The increase in land is primarily the result of the purchase of previously leased land at a Brookline Bank branch in Waltham, Massachusetts in 2017. The increase in office buildings and improvements was primarily due to several branch renovations for Brookline Bank branches in Massachusetts and BankRI branches in Rhode Island and the addition of a new BankRI branch in Warwick, Rhode Island in 2017.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets The changes in the carrying value of goodwill for the periods indicated were as follows: Year Ended December 31, 2017 2016 2015 (In Thousands) Balance at beginning of year $ 137,890 $ 137,890 $ 137,890 Additions — — — Adjustments to original goodwill — — — Balance at end of year $ 137,890 $ 137,890 $ 137,890 The following is a summary of the Company's other intangible assets: At December 31, 2017 At December 31, 2016 Gross Accumulated Carrying Gross Accumulated Carrying (In Thousands) Other intangible assets: Core deposits $ 36,172 $ 31,217 $ 4,955 $ 36,172 $ 29,128 $ 7,044 Trade name 1,600 511 1,089 1,600 511 1,089 Trust relationship 1,568 1,568 — 1,568 1,568 — Other intangible 442 442 — 442 442 — Total other intangible assets $ 39,782 $ 33,738 $ 6,044 $ 39,782 $ 31,649 $ 8,133 At December 31, 2013, the Company concluded that the BankRI name would continue to be utilized in its marketing strategies; therefore, the trade name with carrying value of $1.1 million , has an indefinite life and ceased to amortize. The weighted-average amortization period for the core deposit intangible is 7.8 years. There were no impairment losses relating to other acquisition-related intangible assets recorded during the years ended December 31, 2017 , 2016 and 2015 . The estimated aggregate future amortization expense for other intangible assets for each of the next five years and thereafter is as follows: Year ended December 31: Amount (In Thousands) 2018 $ 1,669 2019 1,295 2020 944 2021 601 2022 299 Thereafter 147 Total $ 4,955

Other Assets

Other Assets	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Other Assets	Other Assets BOLI BOLI is recorded at the cash surrender value of the policies, less any applicable cash surrender charges, and is recorded in other assets. As of December 31, 2017 and 2016 , BankRI owned seven policies with a net cash surrender value of $38.9 million and $37.9 million , respectively. As of December 31, 2017 and 2016 , First Ipswich owned two policies with a net cash surrender value of $0.8 million and $0.8 million , respectively. The Company recorded a total of $1.0 million , $1.1 million , and $1.0 million of tax exempt income from these nine policies in 2017 , 2016 , and 2015 , respectively. They are included in the Company’s other non-interest income in the consolidated statements of income. Affordable Housing Investments The Company began investing in affordable housing projects that benefit low- and moderate-income individuals in 2009. As of December 31, 2017 , the Company had investments in twelve of these projects. The project sponsor or general partner controls the project's management. In each case, the Company is a limited partner with less than 50% of the outstanding equity interest in any single project. On January 1, 2015, the Company adopted ASU 2014-01, Accounting for Investments in Qualified Affordable Housing Projects , which required retrospective application and had an impact on net income for 2014 of $0.5 million and a cumulative effect on retained earnings of $1.1 million at January 1, 2015. Prior to the adoption of ASU 2014-01, the Company’s investments in qualified affordable housing projects were accounted for using the equity method. Under the equity method, operating losses or gains from these investments were included as a component of non-interest income in the Company's consolidated statements of income. ASU 2014-01 calls for the use of the proportional amortization method calculation and the operating losses or gains for these investments are included as a component of the provision for income taxes in the Company’s consolidated statements of income. Under the proportional amortization method, the initial costs of the investment in qualified affordable housing projects is amortized based on the tax credits and other benefits received. Further information regarding the Company's investments in affordable housing projects follows: At December 31, 2017 2016 (In Thousands) Investments in affordable housing projects included in other assets $ 11,432 $ 11,565 Unfunded commitments related to affordable housing projects included in other liabilities 1,933 1,686 Investment in affordable housing tax credits 1,745 1,753 Investment in affordable housing tax benefits 653 598 For the year ended December 31, 2017 2016 2015 (In Thousands) Investment amortization included in provision for income taxes $ 1,844 $ 1,726 $ 1,654 Amount recognized as income tax benefit 623 598 656

Deposits

Deposits	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Deposits	Deposits A summary of deposits follows: December 31, 2017 December 31, 2016 Amount Weighted Average Rate Amount Weighted Average Rate (Dollars in Thousands) Demand checking accounts $ 942,583 — % $ 900,474 — % NOW accounts 350,568 0.07 % 323,160 0.07 % Savings accounts 646,359 0.25 % 613,061 0.20 % Money market accounts 1,724,363 0.56 % 1,733,359 0.47 % Total core deposit accounts 3,663,873 0.31 % 3,570,054 0.27 % Certificate of deposit accounts maturing: Within six months 363,866 0.93 % 345,339 0.77 % After six months but within 1 year 342,500 1.09 % 233,470 0.83 % After 1 year but within 2 years 300,921 1.48 % 264,993 1.08 % After 2 years but within 3 years 90,805 1.87 % 84,673 1.56 % After 3 years but within 4 years 57,926 1.79 % 52,522 1.88 % After 4 years but within 5 years 50,380 2.02 % 59,910 1.78 % 5+ Years 1,072 1.03 % 115 1.66 % Total certificate of deposit accounts 1,207,470 1.27 % 1,041,022 1.04 % Total deposits $ 4,871,343 0.55 % $ 4,611,076 0.44 % Certificate of deposit accounts issued in amounts of $250,000 or more totaled $265.8 million and $196.7 million as of December 31, 2017 and 2016 , respectively. Interest expense on deposit balances is summarized as follows: Year Ended December 31, 2017 2016 2015 (In Thousands) Interest-bearing deposits: NOW accounts $ 225 $ 209 $ 179 Savings accounts 1,297 1,322 1,094 Money market accounts 8,863 7,549 6,935 Certificate of deposit accounts 12,903 10,990 9,272 Total interest-bearing deposits $ 23,288 $ 20,070 $ 17,480 Related Party Deposits Deposit accounts of directors, executive officers and their affiliates totaled $41.4 million and $39.5 million as of December 31, 2017 and 2016 , respectively. Collateral Pledged to Deposits As of December 31, 2017 and 2016 , $165.5 million and $160.9 million , respectively, of collateral was pledged for municipal deposits and TT&L.

Borrowed Funds

Borrowed Funds	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Borrowed Funds	Borrowed Funds Borrowed funds are comprised of the following: At December 31, 2017 2016 (In Thousands) Advances from the FHLBB $ 889,909 $ 910,774 Subordinated debentures and notes 83,271 83,105 Other borrowed funds 47,639 50,207 Total borrowed funds $ 1,020,819 $ 1,044,086 Interest expense on borrowed funds for the periods indicated is as follows: Year Ended December 31, 2017 2016 2015 (In Thousands) Advances from the FHLBB $ 11,330 $ 10,760 $ 9,950 Subordinated debentures and notes 5,081 5,038 5,001 Other borrowed funds 170 116 114 Total interest expense on borrowed funds $ 16,581 $ 15,914 $ 15,065 Collateral Pledged to Borrowed Funds As of December 31, 2017 and 2016 , $1.9 billion and $1.8 billion , respectively, of investment securities and loans and leases, were pledged as collateral for repurchase agreements, swap agreements, FHLBB borrowings, and municipal deposits and TT&L (Treasury Tax and Loan Deposits). The Banks did not have any outstanding FRB borrowings as of December 31, 2017 and 2016 . FHLBB Advances FHLBB advances mature as follows: At December 31, 2017 2016 Amount Callable Amount Weighted Average Rate Amount Callable Amount Weighted Average Rate (Dollars in Thousands) Within 1 year $ 514,314 $ 55,000 1.43 % $ 651,489 $ 75,705 1.22 % Over 1 year to 2 years 279,928 115,000 1.70 % 168,598 290,311 1.44 % Over 2 years to 3 years 16,026 — 0.47 % 14,354 — 0.09 % Over 3 years to 4 years 30,849 — 0.41 % 85 — 2.04 % Over 4 years to 5 years 33,217 — 0.30 % 1,110 — 3.07 % Over 5 years 15,575 — 3.95 % 75,138 — 1.08 % $ 889,909 $ 170,000 1.47 % $ 910,774 $ 366,016 1.24 % Actual maturities of the advances may differ from those presented above since the FHLBB has the right to call certain advances prior to the scheduled maturity. The FHLBB advances are secured by blanket pledge agreements which require the Banks to maintain certain qualifying assets as collateral. The Banks did not have any FRB borrowings as of December 31, 2017 . Total available borrowing capacity for advances from the FHLBB and FRB was $1.7 billion as of December 31, 2017 for the Banks. The total amount of qualifying collateral for FHLBB and FRB borrowings was $2.5 billion as of December 31, 2017 . Other Borrowed Funds Information concerning other borrowed funds is as follows for the periods indicated below: Year Ended December 31, 2017 2016 (Dollars In Thousands) Outstanding at end of year $ 47,639 $ 50,207 Average outstanding for the year 45,908 41,053 Maximum outstanding at any month-end 54,064 50,207 Weighted average rate at end of year 0.46 % 0.14 % Weighted average rate paid for the year 0.37 % 0.27 % In addition to advances from the FHLBB and subordinated debentures and notes, the Company utilizes other funding sources as part of the overall liquidity strategy. Those funding sources include repurchase agreements, committed and uncommitted lines of credit with several financial institutions. The Company periodically enters into repurchase agreements with its larger deposit and commercial customers as part of its cash management services which are typically overnight borrowings. Repurchase agreements with customers decreased $12.6 million million to $37.6 million million as of December 31, 2017 from $50.2 million as of December 31, 2016 . The Company has access to a $12.0 million committed line of credit as of December 31, 2017 . As of December 31, 2017 and December 31, 2016 , the Company did not have any borrowings on this committed line of credit outstanding. The Banks also have access to funding through several uncommitted lines of credit of $203.0 million . As of December 31, 2017 , the Company had $10.0 million in borrowings on outstanding uncommitted lines of credit as compared to December 31, 2016 , when the Company did not have any borrowings on these uncommitted lines of credit. Subordinated Debentures and Notes On September 15, 2014, the Company issued $75.0 million of 6.0% fixed-to-floating subordinated notes due September 15, 2029. The Company is obligated to pay 6.0% interest semiannually between September 2014 and September 2024. Subsequently, the Company is obligated to pay 3-month LIBOR plus 3.315% quarterly until the notes mature in September 2029. The following table summarizes the Company's subordinated debentures and notes at the dates indicated. Carrying Amount Issue Date Rate Maturity Date Next Call Date December 31, 2017 December 31, 2016 (Dollars in Thousands) June 26, 2003 Variable; 3-month LIBOR + 3.10% June 26, 2033 March 26, 2018 $ 4,778 $ 4,752 March 17, 2004 Variable; 3-month LIBOR + 2.79% March 17, 2034 March 19, 2018 4,668 4,628 September 15, 2014 6.0% Fixed-to-Variable; 3-month LIBOR + 3.315% September 15, 2029 September 15, 2024 73,825 73,725 Total $ 83,271 $ 83,105 The above carrying amounts of the acquired subordinated debentures included $0.6 million of accretion adjustments and $1.2 million of capitalized debt issuance costs as of December 31, 2017 . This compares to $0.6 million of accretion adjustments and $1.3 million of capitalized debt issuance costs as of December 31, 2016 .

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Off-Balance Sheet Financial Instruments The Company is party to off-balance sheet financial instruments in the normal course of business to meet the financing needs of its customers and to reduce its own exposure to fluctuations in interest rates. These financial instruments include loan commitments, standby and commercial letters of credits, and loan level derivatives. According to GAAP, these financial instruments are not recorded in the financial statements until they are funded or related fees are incurred or received. The contract amounts reflect the extent of the involvement the Company has in particular classes of these instruments. Such commitments involve, to varying degrees, elements of credit risk and interest-rate risk in excess of the amount recognized in the consolidated balance sheets. The Company's exposure to credit loss in the event of non-performance by the counterparty is represented by the fair value of the instruments. The Company uses the same policies in making commitments and conditional obligations as it does for on-balance sheet instruments. Financial instruments with off-balance-sheet risk at the dates indicated follow: At December 31, 2017 2016 (In Thousands) Financial instruments whose contract amounts represent credit risk: Commitments to originate loans and leases: Commercial real estate $ 76,653 $ 27,750 Commercial 83,270 71,716 Residential mortgage 28,745 28,179 Unadvanced portion of loans and leases 571,668 580,416 Unused lines of credit: Home equity 407,552 340,682 Other consumer 34,191 13,157 Other commercial 323 208 Unused letters of credit: Financial standby letters of credit 12,422 11,720 Performance standby letters of credit 736 516 Commercial and similar letters of credit 184 785 Loan level derivatives: Receive fixed, pay variable 494,659 383,780 Pay fixed, receive variable 494,659 383,780 Risk participation-out agreements 36,627 16,961 Risk participation-in agreements 3,825 — Foreign exchange contracts: Buys foreign currency, sells U.S. currency 1,495 195 Sells foreign currency, buys U.S. currency 1,502 195 Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract. Commitments generally have fixed expiration dates or other termination clauses and may require the payment of a fee by the customer. Since some of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily represent future cash requirements. The Company evaluates each customer's creditworthiness on a case-by-case basis. The amount of collateral obtained, if any, is based on management's credit evaluation of the borrower. Standby and commercial letters of credits are conditional commitments issued by the Company to guarantee performance of a customer to a third party. These standby and commercial letters of credit are primarily issued to support the financing needs of the Company's commercial customers. The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loans to customers. The liability for unfunded credit commitments, which is included in other liabilities, was $1.7 million and $1.5 million as of December 31, 2017 and December 31, 2016 , respectively. From time to time, the Company enters into loan level derivatives, risk participation agreements or foreign exchange contracts with commercial customers and third-party financial institutions. These derivatives allow the Company to offer long-term fixed-rate commercial loans while mitigating the interest-rate or foreign exchange risk of holding those loans. In a loan level derivative transaction, the Company lends to a commercial customer on a floating-rate basis and then enters into an loan level derivative with that customer. Concurrently, the Company enters into offsetting swaps with a third-party financial institution, effectively minimizing its net interest-rate risk exposure resulting from such transactions. The fair value of derivative assets and liabilities was $9.0 million and $8.9 million , respectively, as of December 31, 2017 . The fair value of derivative assets and liabilities was $9.7 million and $9.7 million , respectively, as of December 31, 2016 . Lease Commitments The Company leases certain office space under various noncancellable operating leases. These leases have original terms ranging from 5 years to over 25 years. Certain leases contain renewal options and escalation clauses which can increase rental expenses based principally on the consumer price index and fair market rental value provisions. A summary of future minimum rental payments under such leases at the dates indicated follows: Year ended December 31, Minimum Rental Payments (In Thousands) 2018 $ 4,921 2019 4,053 2020 3,497 2021 2,988 2022 2,743 Thereafter 10,138 Total $ 28,340 Certain leases contain escalation clauses for real estate taxes and other expenditures, which are not included above. Total rental expense was $5.5 million in 2017 , this increase was due to the opening of a new branch in Danvers, Massachusetts for First Ipswich Bank, and the relocation of a branch in Brookline, Massachusetts for Brookline Bank. This compares to total rent expense of $5.3 million in 2016 . In 2015 , total rent expense was $5.5 million , which included $0.2 million in lease acceleration related to the sale of $255.2 million of the indirect automobile loan portfolio in March 2015. A portion of the Company's headquarters was rented to third-party tenants which generated rental income of $0.4 million in 2017 , 2016 and 2015 respectively. Rental income was reported in non-interest income in the Company's consolidated statements of income. Legal Proceedings In the normal course of business, there are various outstanding legal proceedings. In the opinion of management, after consulting with legal counsel, the consolidated financial position and results of operations of the Company are not expected to be affected materially by the outcome of such proceedings.

Earnings per Share (EPS)

Earnings per Share (EPS)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings per Share (EPS)	Earnings per Share ("EPS") The following table is a reconciliation of basic EPS and diluted EPS: For the year ended December 31, 2017 2016 2015 Basic Fully Diluted Basic Fully Diluted Basic Fully Diluted (Dollars in Thousands, Except Per Share Amounts) Numerator: Net income $ 50,518 $ 50,518 $ 52,362 $ 52,362 $ 49,782 $ 49,782 Denominator: Weighted average shares outstanding 74,459,508 74,459,508 70,261,954 70,261,954 70,098,561 70,098,561 Effect of dilutive securities — 351,900 — 182,129 — 137,307 Adjusted weighted average shares outstanding 74,459,508 74,811,408 70,261,954 70,444,083 70,098,561 70,235,868 EPS $ 0.68 $ 0.68 $ 0.74 $ 0.74 $ 0.71 $ 0.71

Comprehensive Income_(Loss)

Comprehensive Income/(Loss)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Comprehensive Income/(Loss)	Comprehensive Income/(Loss) Comprehensive income (loss) represents the sum of net income (loss) and other comprehensive income (loss). For the years ended December 31, 2017 , 2016 and 2015 , the Company’s other comprehensive income (loss) include the following two components: (i) unrealized holding losses on investment securities available-for-sale; and (ii) adjustment of accumulated obligation for postretirement benefits. Changes in accumulated other comprehensive loss by component, net of tax, were as follows for the periods indicated: Year Ended December 31, 2017 Investment Securities Available-for-Sale Postretirement Benefits Accumulated Other Comprehensive Loss (In Thousands) Balance at December 31, 2016 $ (4,213 ) $ 395 $ (3,818 ) Other comprehensive loss (817 ) (252 ) (1,069 ) Balance at December 31, 2017 $ (5,030 ) $ 143 $ (4,887 ) Year Ended December 31, 2016 Investment Securities Available-for-Sale Postretirement Benefits Accumulated Other Comprehensive Loss (In Thousands) Balance at December 31, 2015 $ (2,827 ) $ 351 $ (2,476 ) Other comprehensive (loss) income (1,386 ) 44 (1,342 ) Balance at December 31, 2016 $ (4,213 ) $ 395 $ (3,818 ) Year Ended December 31, 2015 Investment Securities Available-for-Sale Postretirement Benefits Accumulated Other Comprehensive Loss (In Thousands) Balance at December 31, 2014 $ (1,733 ) $ 111 $ (1,622 ) Other comprehensive (loss) income (1,094 ) 240 (854 ) Balance at December 31, 2015 $ (2,827 ) $ 351 $ (2,476 )

Derivatives and Hedging Activit

Derivatives and Hedging Activities	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives and Hedging Activities	Derivatives and Hedging Activities The Company utilizes loan level derivatives which consist of interest-rate contracts (swaps, caps and floors), and risk participation agreements as part of the Company's interest-rate risk management strategy for certain assets and liabilities and not for speculative purposes. Based on the Company's intended use for the loan level derivatives at inception, the Company designates the derivative as either an economic hedge of an asset or liability, or a hedging instrument subject to the hedge accounting provisions of FASB ASC Topic 815, "Derivatives and Hedging". Interest-rate swap, cap and floor agreements are entered into as hedges against future interest-rate fluctuations on specifically identified assets or liabilities. The Company did not have derivative fair value hedges or derivative cash flow hedges as of December 31, 2017 or 2016 . Derivatives not designated as hedges are not speculative, but rather, result from a service the Company provides to certain customers for a fee. The Company executes loan level derivative products such as interest-rate swap agreements with commercial banking customers to aid them in managing their interest-rate risk. The interest-rate swap contracts allow the commercial banking customers to convert floating-rate loan payments to fixed-rate loan payments. The Company concurrently enters into offsetting swaps with a third party financial institution, effectively minimizing its net risk exposure resulting from such transactions. The third-party financial institution exchanges the customer's fixed-rate loan payments for floating-rate loan payments. As the interest-rate swap agreements associated with this program do not meet hedge accounting requirements, changes in the fair value are recognized directly in earnings. The Company utilizes risk participation agreements with other banks participating in commercial loan arrangements. Participating banks guarantee the performance on borrower-related interest rate swap contracts. Risk participation agreements are derivative financial instruments and are recorded at fair value. These derivatives are not designated as hedges and therefore, changes in fair value are recorded directly through earnings at each reporting period. Under a risk participation-out agreement, a derivative asset, the Company participates out a portion of the credit risk associated with the interest rate swap position executed with the commercial borrower, for a fee paid to the participating bank. Under a risk participation-in agreement, a derivative liability, the Company assumes, or participates in, a portion of the credit risk associated with the interest rate swap position with the commercial borrower, for a fee received from the other bank. The Company offers foreign exchange contracts to commercial borrowers to accommodate their business needs. These foreign exchange contracts do not qualify as hedges for accounting purposes. To mitigate the market and liquidity risk associated with these foreign exchange contracts, the Company enters into similar offsetting positions. Asset derivatives and liability derivatives are included in other assets and accrued expenses and other liabilities on the consolidated balance sheets. The following tables presents the Company's customer related derivative positions for the periods indicated below for those derivatives not designated as hedging. The following tables presents the Company's customer related derivative positions for the periods indicated below for those derivatives not designated as hedging. Notional Amount Maturing Number of Positions Less than 1 year Less than 2 years Less than 3 years Less than 4 years Thereafter Total Fair Value December 31, 2017 (Dollars In Thousands) Loan level derivatives Receive fixed, pay variable 66 $ 3,903 $ 2,036 $ 27,992 $ — $ 460,728 $ 494,659 $ 8,865 Pay fixed, receive variable 66 3,903 2,036 27,992 — 460,728 494,659 8,865 Risk participation-out agreements 8 — — 8,613 — 28,014 36,627 65 Risk participation-in agreements 1 — — — — 3,825 3,825 10 Foreign exchange contracts Buys foreign currency, sells U.S. currency 22 $ 1,495 $ — $ — $ — $ — $ 1,495 $ 65 Sells foreign currency, buys U.S. currency 44 1,502 — — — — 1,502 72 Notional Amount Maturing Number of Positions Less than 1 year Less than 2 years Less than 3 years Less than 4 years Thereafter Total Fair Value December 31, 2016 (Dollars In Thousands) Loan level derivatives Receive fixed, pay variable 54 $ — $ 4,025 $ 2,141 $ 29,501 $ 348,113 $ 383,780 $ 9,738 Pay fixed, receive variable 54 — 4,025 2,141 29,501 348,113 383,780 9,738 Risk participation-out agreements 5 — — — 9,078 7,883 16,961 20 Foreign exchange contracts Buys foreign currency, sells U.S. currency 3 $ 195 $ — $ — $ — $ — $ 195 $ — Sells foreign currency, buys U.S. currency 3 195 — — — — 195 — As of December 31, 2016 , the Company held no risk participation-in agreements and the fair value of the foreign exchange contracts was nominal. Refer also to Note 21, "Fair Value of Financial Instruments." Changes in the fair value are recognized directly in the Company's consolidated statements of income and are included in other non-interest income in the consolidated statements of income. The table below presents the gain (loss) recognized in income due to changes in the fair value for the year ended December 31, 2017 . There were no gains (losses) recognized in income due to changes in the fair value for the year ended December 31, 2016 . Year Ended December 31, 2017 (In Thousands) Gain recognized in income on: Loan level derivatives $ — Risk participation-out agreements 55 Foreign exchange contracts 7 Total $ 62 By using derivative financial instruments, the Company exposes itself to credit risk which is the risk of failure by the counterparty to perform under the terms of the derivative contract. When the fair value of a derivative contract is positive, the counterparty owes the Company, which creates credit risk for the Company. When the fair value of a derivative is negative, the Company owes the counterparty and, therefore, it does not possess credit risk. The credit risk in derivative instruments is mitigated by entering into transactions with highly-rated counterparties that management believes to be creditworthy and by limiting the amount of exposure to each counterparty by either cross collateralizing the underlying hedged loan or through bilateral posting of collateral to cover exposure. As the swaps are subject to master netting agreements, the Company had limited exposure relating to loan level derivatives with institutional counterparties as of December 31, 2017 and 2016 . The estimated net credit risk exposure for derivative financial instruments was zero as of December 31, 2017 , and 2016 . Certain derivative agreements contain provisions that require the Company to post collateral if the derivative exposure exceeds a threshold amount. The Company posted collateral of $26.7 million and $34.5 million in the normal course of business as of December 31, 2017 and 2016 , respectively. The tables below present the offsetting of derivatives and amounts subject to master netting agreements not offset in the consolidated balance sheet at the dates indicated. At December 31, 2017 Gross Gross Amounts Statement of Financial Position Net Amounts Presented in the Statement of Financial Position Gross Amounts Not Offset in the Statement of Financial Position Net Amount Financial Instruments Pledged Cash Collateral Pledged (In Thousands) Asset derivatives Loan level derivatives $ 8,865 $ — $ 8,865 $ — $ — $ 8,865 Risk participation-out agreements 65 — 65 — — 65 Foreign exchange contracts 72 — 72 — — 72 Total $ 9,002 $ — $ 9,002 $ — $ — $ 9,002 Liability derivatives Loan level derivatives $ 8,865 $ — $ 8,865 $ 25,159 $ 1,510 $ — Risk participation-in agreements 10 — 10 — — — Foreign exchange contracts 65 — 65 — — — Total $ 8,940 $ — $ 8,940 $ 25,159 $ 1,510 $ — At December 31, 2016 Gross Gross Amounts Statement of Financial Position Net Amounts Presented in the Statement of Financial Position Gross Amounts Not Offset in the Statement of Financial Position Net Amount Financial Instruments Pledged Cash Collateral Pledged (In Thousands) Asset derivatives Loan level derivatives $ 9,738 $ — $ 9,738 $ — $ — $ 9,738 Risk participation-out agreements 20 — 20 — — 20 Total $ 9,758 $ — $ 9,758 $ — $ — $ 9,758 Liability derivatives Loan level derivatives $ 9,738 $ — $ 9,738 $ 33,744 $ 720 $ — Total $ 9,738 $ — $ 9,738 $ 33,744 $ 720 $ — As of December 31, 2016 , the Company held no risk participation-in agreements and the fair value of the foreign exchange contracts was nominal. The Company has agreements with certain of its derivative counterparties that contain credit-risk-related contingent provisions. These provisions provide the counterparty with the right to terminate its derivative positions and require the Company to settle its obligations under the agreements if the Company defaults on certain of its indebtedness or if the Company fails to maintain its status as a well-capitalized institution.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income tax expense is comprised of the following amounts: Year Ended December 31, 2017 2016 2015 (In Thousands) Current provision: Federal $ 27,825 $ 22,954 $ 23,340 State 5,013 5,116 4,774 Total current provision 32,838 28,070 28,114 Deferred provision: Federal 10,209 2,271 679 State 589 51 560 Total deferred provision 10,798 2,322 1,239 Total provision for income taxes $ 43,636 $ 30,392 $ 29,353 Total provision for income taxes differed from the amounts computed by applying the statutory U.S. federal income tax rate 35.0% to income before tax expense as a result of the following: Year Ended December 31, 2017 2016 2015 (Dollars In Thousands) Expected income tax expense at statutory federal tax rate $ 34,039 $ 29,965 $ 28,603 State taxes, net of federal income tax benefit 3,641 3,358 3,467 Bank-owned life insurance (364 ) (368 ) (367 ) Tax-exempt interest income (873 ) (826 ) (622 ) Income attributable to noncontrolling interest in subsidiary (870 ) (1,163 ) (994 ) Merger and acquisition expense 138 — — Tax Reform Act Adjustment 8,965 — — Investments in affordable housing projects (653 ) (640 ) (526 ) Other, net (387 ) 66 (208 ) Total provision for income taxes $ 43,636 $ 30,392 $ 29,353 Effective income tax rate 44.9 % 35.5 % 35.9 % The Company's effective tax rate was 44.9% as of December 31, 2017 compared to 35.5% as of December 31, 2016 . The increase in the Company's effective tax rate from 2016 was primarily driven by $9.0 million related to the enactment of the Tax Reform Act and $138.0 thousand of nondeductible merger and acquisition expenses. On December 22, 2017, the Tax Reform Act was enacted, which represents the most comprehensive reform to the U.S. tax code in over thirty years. The majority of the provisions of the Tax Reform Act takes effect on January 1, 2018. The Tax Reform Act lowers the Company’s federal tax rate from 35% to 21%. The Tax Reform Act also contains other provisions that may affect the Company currently or in future years. Among these are changes to the deductibility of meals and entertainment, the deductibility of executive compensation, accelerated expensing of depreciable property for assets placed in service after September 27, 2017 and before 2023, limits the deductibility of net interest expense, eliminated the corporate alternative minimum tax, limited net operating loss carryforwards to 80% of taxable income and other provisions. As a result of the Tax Reform Act, management re-valued the carrying value of our net deferred tax asset and investments in low income housing tax credits. The impact of the Tax Reform Act resulted in a write down of the carrying balance of net deferred tax assets and investments in affordable housing projects of $8.6 million and $0.3 million , respectively. The tax effects of temporary differences that give rise to significant portions of the deferred tax assets and liabilities at the dates indicated are as follows: At December 31, 2017 2016 (In Thousands) Deferred tax assets: Allowance for loan and lease losses $ 15,618 $ 21,655 Deferred compensation 1,032 5,659 Supplemental Executive Retirement Plans 2,805 4,127 Unrealized loss on investment securities available-for-sale 1,728 2,355 Net operating loss carryforwards 415 999 Postretirement benefits 400 465 Nonaccrual interest 551 621 Accrued expense 563 828 Restricted stock and stock option plans 621 573 Employee stock ownership plan 124 147 Other 67 61 Total gross deferred tax assets 23,924 37,490 Deferred tax liabilities: Identified intangible assets and goodwill 2,778 4,660 Deferred loan origination costs, net 2,918 3,370 Depreciation 1,866 2,193 Prepaid expense 109 1,045 Acquisition fair value adjustments 1,192 975 Total gross deferred tax liabilities 8,863 12,243 Net deferred tax asset $ 15,061 $ 25,247 As of December 31, 2017 , the Company had net operating loss carryforwards for federal income tax purposes of $0.4 million which are available to offset future federal taxable income, if any, through 2020. According to Section 382 of the Internal Revenue Code, the net operating loss carryforwards and credit are subject to an annual limitation of $0.9 million . The Company has determined that a valuation allowance is not required for any of its deferred tax assets because it believes that it is more likely than not that these assets will reverse against future taxable income. For federal income tax purposes, the Company has a $1.8 million reserve for credit losses which remains subject to recapture. If any portion of the reserve is used for purposes other than to absorb the losses for which it was established, approximately 150% of the amount actually used (limited to the amount of the reserve) would be subject to taxation in the year in which used. As the Company intends to use the reserve only to absorb credit losses, no provision has been made for the $0.5 million liability that would result if 100% of the reserve were recaptured. The Company did not have any unrecognized tax benefits accrued as income tax receivables or as deferred tax items as of December 31, 2017 and 2016 . The Company files U.S. federal and state income tax returns. During the third quarter of 2017, the Company was notified by the Internal Revenue Service of its intent to examine the Company's 2015 consolidated federal income tax return. Management believes that this examination will conclude during the next 12 months. As of December 31, 2017 , the Company is subject to examination by the Massachusetts, Rhode Island and several other state tax authorities for tax years after December 31, 2013 .

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
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, 2017 , 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 First Ipswich, and the Banking Division of the Rhode Island Department of Business Regulation in the case of BankRI. Common Stock Repurchases In 2017 , 2016 and 2015 , no shares of the Company's common stock were repurchased by the Company. On February 4, 2016, the Company's Board of Directors authorized a stock repurchase program to acquire up to $10.0 million of total outstanding shares of the Company's common stock over a period of twelve months ending on January 31, 2017. 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. As of December 31, 2017 , no shares of stock were repurchased under the stock repurchase program. 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 $15.1 million (unaudited), $15.2 million (unaudited), and $16.6 million (unaudited) at December 31, 2017 , 2016 and 2015 , respectively.

Regulatory Capital Requirements

Regulatory Capital Requirements	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Regulatory Capital Requirements	Regulatory Capital Requirements The Company's primary source of cash is dividends from the Banks and Brookline Securities Corp. The Banks are subject to certain restrictions on the amount of dividends that they may declare without prior regulatory approval. In addition, the dividends declared cannot be in excess of the amount which would cause the Banks to fall below the minimum required for capital adequacy purposes. The Company is a bank holding company within the meaning of the Bank Holding Company Act of 1956, as amended (the "BHCA") and as such, must comply with the capital requirements of the Federal Reserve Bank (the "FRB") at the consolidated level. As member banks of the FRB, Brookline Bank, BankRI and First Ipswich are also required to comply with the regulatory capital requirement of the FRB. The FRB has promulgated regulations imposing minimum capital requirements for bank holding companies and state member banks as well as prompt corrective action regulations for state member banks that implement the system of prompt corrective action established by Section 38 of the Federal Deposit Insurance Act, as amended (the "FDIA"). Under the prompt corrective action regulations in effect as of December 31, 2017 , a bank is "well-capitalized" if it has: (1) a total risk-based capital ratio of 10.0% or greater; (2) a Tier 1 risk-based capital ratio of 8.0% or greater; (3) a common equity Tier 1 capital ratio of 6.5% or greater; (4) a Tier 1 leverage ratio of 5.0% or greater; and (5) is not subject to any written agreement, order, capital directive or prompt corrective action directive to meet and maintain a specific capital level for any capital measure. Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the Company's financial statements. Under capital adequacy guidelines, the Company and each of the Banks must meet specific capital guidelines that involve quantitative measures of the Company's and the Banks' assets, liabilities and certain off-balance sheet items as calculated under regulatory accounting practices. In addition, the prompt corrective action rules applicable to state member banks establish a framework of supervisory actions for state member banks that are not at least adequately capitalized. The Company's and the Banks' capital amounts and classification are also subject to qualitative judgments by the regulators about components, risk weightings, and other factors. Prompt corrective action provisions are not applicable to bank holding companies. Bank holding companies are not subject to prompt corrective action requirements. However, a bank holding company is considered "well capitalized" for purpose of the FRB's Regulation Y (which can affect eligibility for expedited application processes to make acquisitions and engage in new activities) if the bank holding company maintains on a consolidated basis a total risk-based capital ratio of 10.0% or greater and a Tier 1 risk-based capital ratio of 6.0% or greater and is not subject to any written agreement under capital directive or prompt correction action directive issued by the FRB to meet and maintain a specific capital level for any capital measure. As of December 31, 2017 , the Company and the Banks are each under the primary regulation of, and must comply with, the capital requirements of the FRB. As of December 31, 2017 , the Company and the Banks exceeded all regulatory capital requirements and were considered “well-capitalized” under prompt corrective action regulations, as amended to reflect the changes under Basel III Capital Rules. The following table presents actual and required capital ratios as of December 31, 2017 for the Company and the Banks under the Basel III Capital Rules based on the phase-in provision of the Basel III Capital Rules and the minimum required capital levels as of January 1, 2019 when the Basel III Capital Rules have been fully phased in. Actual Minimum Required for Capital Adequacy Purposes Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer Minimum Required to be Considered “Well-Capitalized” Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio Amount Ratio (Dollars in Thousands) At December 31, 2017: Brookline Bancorp, Inc. Common equity Tier 1 capital ratio (1) $ 669,238 12.02 % $ 250,547 4.50 % $ 389,739 7.00 % N/A N/A Tier 1 leverage capital ratio (2) 687,299 10.43 % 263,585 4.00 % 263,585 4.00 % N/A N/A Tier 1 risk-based capital ratio (3) 687,299 12.34 % 334,181 6.00 % 473,423 8.50 % N/A N/A Total risk-based capital ratio (4) 821,373 14.75 % 445,490 8.00 % 584,706 10.50 % N/A N/A Brookline Bank Common equity Tier 1 capital ratio (1) $ 414,282 11.56 % $ 161,269 4.50 % $ 250,863 7.00 % $ 232,944 6.50 % Tier 1 leverage capital ratio (2) 423,035 10.35 % 163,492 4.00 % 163,492 4.00 % 204,365 5.00 % Tier 1 risk-based capital ratio (3) 423,035 11.81 % 214,920 6.00 % 304,471 8.50 % 286,561 8.00 % Total risk-based capital ratio (4) 463,986 12.95 % 286,632 8.00 % 376,205 10.50 % 358,290 10.00 % BankRI Common equity Tier 1 capital ratio (1) $ 193,849 11.38 % $ 76,654 4.50 % $ 119,239 7.00 % $ 110,722 6.50 % Tier 1 leverage capital ratio (2) 193,849 9.16 % 84,650 4.00 % 84,650 4.00 % 105,813 5.00 % Tier 1 risk-based capital ratio (3) 193,849 11.38 % 102,205 6.00 % 144,791 8.50 % 136,273 8.00 % Total risk-based capital ratio (4) 210,025 12.33 % 136,269 8.00 % 178,853 10.50 % 170,337 10.00 % First Ipswich Common equity Tier 1 capital ratio (1) $ 37,502 13.38 % $ 12,613 4.50 % $ 19,620 7.00 % $ 18,218 6.50 % Tier 1 leverage capital ratio (2) 37,502 9.44 % 15,891 4.00 % 15,891 4.00 % 19,863 5.00 % Tier 1 risk-based capital ratio (3) 37,502 13.38 % 16,817 6.00 % 23,824 8.50 % 22,423 8.00 % Total risk-based capital ratio (4) 40,625 14.50 % 22,414 8.00 % 29,418 10.50 % 28,017 10.00 % _______________________________________________________________________________ (1) Common equity Tier 1 capital ratio is calculated by dividing common equity Tier 1 capital by risk-weighted assets. The ratio was established as part of the implementation of Basel III, effective January 1, 2015. (2) Tier 1 leverage capital ratio is calculated by dividing Tier 1 capital by average assets. (3) Tier 1 risk-based capital ratio is calculated by dividing Tier 1 capital by risk-weighted assets. (4) Total risk-based capital ratio is calculated by dividing total capital by risk-weighted assets. The following table presents actual and required capital ratios as of December 31, 2016 for the Company and the Banks under the regulatory capital rules then in effect. Actual Minimum Required for Capital Adequacy Purposes Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer Minimum Required to be Considered “Well-Capitalized” Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio Amount Ratio (Dollars in Thousands) At December 31, 2016: Brookline Bancorp, Inc. Common equity Tier 1 capital ratio (1) $ 559,644 10.48 % $ 240,305 4.50 % $ 373,808 7.00 % N/A N/A Tier 1 leverage capital ratio (2) 575,830 9.16 % 251,454 4.00 % 251,454 4.00 % N/A N/A Tier 1 risk-based capital ratio (3) 575,830 10.79 % 320,202 6.00 % 453,620 8.50 % N/A N/A Total risk-based capital ratio (4) 704,675 13.20 % 427,076 8.00 % 560,537 10.50 % N/A N/A Brookline Bank Common equity Tier 1 capital ratio (1) $ 384,759 11.31 % $ 153,087 4.50 % $ 238,136 7.00 % $ 221,126 6.50 % Tier 1 leverage capital ratio (2) 391,964 10.07 % 155,696 4.00 % 155,696 4.00 % 194,620 5.00 % Tier 1 risk-based capital ratio (3) 391,964 11.53 % 203,971 6.00 % 288,959 8.50 % 271,961 8.00 % Total risk-based capital ratio (4) 428,966 12.61 % 272,143 8.00 % 357,188 10.50 % 340,179 10.00 % BankRI Common equity Tier 1 capital ratio (1) $ 182,202 10.94 % $ 74,946 4.50 % $ 116,583 7.00 % $ 108,255 6.50 % Tier 1 leverage capital ratio (2) 182,202 8.97 % 81,249 4.00 % 81,249 4.00 % 101,562 5.00 % Tier 1 risk-based capital ratio (3) 182,202 10.94 % 99,928 6.00 % 141,565 8.50 % 133,237 8.00 % Total risk-based capital ratio (4) 197,702 11.87 % 133,245 8.00 % 174,884 10.50 % 166,556 10.00 % First Ipswich Common equity Tier 1 capital ratio (1) $ 33,433 12.61 % $ 11,931 4.50 % $ 18,559 7.00 % $ 17,234 6.50 % Tier 1 leverage capital ratio (2) 33,433 9.23 % 14,489 4.00 % 14,489 4.00 % 18,111 5.00 % Tier 1 risk-based capital ratio (3) 33,433 12.61 % 15,908 6.00 % 22,536 8.50 % 21,210 8.00 % Total risk-based capital ratio (4) 36,053 13.60 % 21,208 8.00 % 27,835 10.50 % 26,510 10.00 % _______________________________________________________________________________ (1) Common equity Tier 1 capital ratio is calculated by dividing common equity Tier 1 capital by risk-weighted assets. The ratio was established as part of the implementation of Basel III, effective January 1, 2015. (2) Tier 1 leverage capital ratio is calculated by dividing Tier 1 capital by average assets. (3) Tier 1 risk-based capital ratio is calculated by dividing Tier 1 capital by risk-weighted assets. (4) Total risk-based capital ratio is calculated by dividing total capital by risk-weighted assets.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans Postretirement Benefits Postretirement benefits are provided for part of the annual expense of health insurance premiums for certain retired employees and their dependents. No contributions are made by the Company to invest in assets allocated for the purpose of funding this benefit obligation. The following table presents the change in plan assets and change in benefit obligation: Year Ended December 31, 2017 2016 2015 (In Thousands) Change in plan assets: Fair value of plan assets at beginning of year $ — $ — $ — Employer contributions 19 21 25 Benefits paid (19 ) (21 ) (25 ) Fair value of plan assets at end of year $ — $ — $ — Change in benefit obligation: Benefit obligation at beginning of year $ 1,135 $ 1,188 $ 1,562 Service cost 49 48 55 Interest cost 43 45 49 Estimated benefits paid (19 ) (21 ) (25 ) Actuarial loss (gain) 326 (125 ) (453 ) Benefit obligation at end of year $ 1,534 $ 1,135 $ 1,188 The liability for the postretirement benefits included in accrued expenses and other liabilities was $1.5 million , $1.1 million , and $1.2 million as of December 31, 2017 , 2016 and 2015 , respectively. The following table presents the components of net periodic postretirement benefit cost and other amounts recognized in other comprehensive income: Year Ended December 31, 2017 2016 2015 (In Thousands) Net periodic benefit expense: Service cost $ 49 $ 48 $ 55 Interest cost 43 45 49 Prior service credit (21 ) (21 ) (21 ) Actuarial gain (47 ) (42 ) (20 ) Net periodic benefit expense $ 24 $ 30 $ 63 Changes in postretirement benefit obligation recognized in other comprehensive income: Net actuarial (loss) gain (401 ) $ 90 $ 374 Prior service credit (21 ) (21 ) (21 ) Total pre-tax changes in postretirement benefit obligation recognized in other comprehensive income $ (422 ) $ 69 $ 353 The discount rate used to determine the actuarial present value of projected postretirement benefit obligations was 3.62% in 2017 , 4.15% in 2016 and 4.35% in 2015 . The estimated prior service credit that will be amortized from accumulated other comprehensive income into net periodic benefit cost in 2018 is $0.1 million . The actual health care trend used to measure the accumulated postretirement benefit obligation in 2017 for plan participants below age 65 and for plan participants over age 65 was (14.7)% and 33.9% , respectively. In 2016 , the rate for plan participants below age 65 and for plan participants over age 65 was 7.5% and 8.3% , respectively. This decrease from 2016 is due to reductions in active and retiree head counts in 2017. The rates to be used in 2018 through 2022 are expected to be in the range of 6.5% to 5.5% and to decline gradually thereafter to 4.9% . Assumed health care trend rates may have a significant effect on the amounts reported for the postretirement benefit plan. A 1% change in assumed health care cost trend rates would have the following effects: Year Ended 1% Increase 1% Decrease (In Thousands) Effect on total service and interest cost components of net periodic postretirement benefit costs $ 23 $ (18 ) Effect on the accumulated postretirement benefit obligation 356 (277 ) 401(k) Plan The Company administers one 401(k) plan (the "Plan"), which is a qualified, tax-exempt profit-sharing plan with a salary deferral feature under Section 401(k) of the Internal Revenue Code. Each employee, excluding temporary employees, who has attained the age of 21 is eligible to participate in the plan by making voluntary contributions, subject to certain limits based on federal tax laws. In the Plan, the Company makes a matching contribution of the amount contributed by eligible employees, up to 5% of the employee's yearly compensation. Contributions to the Plan are subject to certain limits based on federal tax laws. Expenses associated with the plans were $2.6 million in 2017 , $2.8 million in 2016 , and $2.3 million in 2015 . Nonqualified Deferred Compensation Plan The Company also maintains a Nonqualified Deferred Compensation Plan (the "Nonqualified Plan") under which certain participants may contribute the amounts they are precluded from contributing to the Company's 401(k) plan because of the qualified plan limitations, and additional compensation deferrals that may be advantageous for personal income tax or other planning reasons. Expenses associated with the Nonqualified Plan were nominal in 2017 , 2016 and 2015 . Accrued liabilities associated with the Nonqualified Plan in 2017 , 2016 , and 2015 were $0.1 million , $0.2 million , and $0.2 million , respectively. Supplemental Executive Retirement Agreements The Company acquired two Supplemental Executive Retirement Plans (the "SERPs") as part of its acquisition of BankRI. The Company maintains the SERPs for certain senior executives under which participants are entitled to an annual retirement benefit. As of December 31, 2017 , there are 13 participants in the SERPs. The Company funded a Rabbi Trust to provide a partial funding source for the Company's liabilities under the SERPs. During 2016, a portion of the Company's BOLI assets were transferred into the Rabbi Trust as a replacement for the funds previously held in the Rabbi Trust. The Company records the liability for the SERPs based on an actuarial calculation in accordance with GAAP, and no actuarial gains and losses are recognized. Total expenses for benefits payable under the SERPs for the years ended December 31, 2017 , and 2016 was $0.8 million . Aggregate benefits payable included in accrued expenses and other liabilities as of December 31, 2017 and 2016 were $12.0 million and $11.6 million , respectively. The nominal discount rate used to determine the actuarial present value of projected benefits under the agreements was 4.00% in the year 2017 and 2016 . Employee Stock Ownership Plan Brookline Bank established an Employee Stock Ownership Plan ("ESOP") on November 1, 1997. The Company's ESOP loan to Brookline Bank to purchase 546,986 shares of Company common stock is payable in quarterly installments over 30 years, bears interest at 8.50% per annum, matures December 31, 2021, and can be prepaid without penalty. The loan is repaid to the Company in the form of cash contributions from Brookline Bank, subject to federal tax law limits. The outstanding balance of the loan as of December 31, 2017 and 2016 , was $1.3 million and $1.5 million , respectively, and is eliminated in consolidation. Shares of common stock used as collateral to secure the loan are released and available for allocation to eligible employees as the principal and interest on the loan is paid. The ESOP was amended in 2015 to permit all eligible participants in the ESOP as of July 1, 2015 or any eligible participants after July 1, 2015 to be fully vested in the ESOP upon the date of eligibility. Dividends on released shares are credited to the participants' ESOP accounts. Dividends on unallocated shares of common stock are generally applied towards payment of the loan. ESOP shares committed to be released are considered outstanding in determining earnings per share. As of December 31, 2017 and 2016 , the ESOP held 142,332 and 176,688 unallocated shares, respectively at an aggregate cost of $0.7 million and $0.9 million , respectively. The market value of such shares as of December 31, 2017 and 2016 was $2.3 million and $2.9 million , respectively. Compensation and employee benefits expense related to the ESOP was $0.5 million in 2017 and $0.4 million in 2016 , and 2015 , respectively, based on the commitment to release to eligible employees 34,356 shares in 2017 , 36,372 shares in 2016 and 38,316 shares in 2015 . Recognition and Retention Plans As of December 31, 2017 , the Company had three active recognition and retention plans: the 2003 Recognition and Retention Plan (the "2003 RRP") with 1,250,000 authorized shares, the 2011 Restricted Stock Award Plan ("2011 RSA") with 500,000 authorized shares and the 2014 Equity Incentive Plan ("2014 Plan") with 1,750,000 authorized shares. The 2003 RRP, the 2011 RSA and the 2014 Plan are collectively referred to as the "Plans". The purpose of the Plans is to promote the long-term financial success of the Company and its subsidiaries by providing a means to attract, retain and reward individuals who contribute to such success and to further align their interests with those of the Company's stockholders. Of the awarded shares, generally 50% vest ratably over three years with one-third of such shares vesting at each of the first, second and third anniversary dates of the awards. These are referred to as "time-based shares". The remaining 50% of each award has a cliff vesting schedule and will vest three years after the award date based on the level of the Company's achievement of identified performance targets in comparison to the level of achievement of such identified performance targets by a defined peer group comprised of 17 financial institutions. These are referred to as "performance-based shares". The specific performance measure targets relate to return on assets, return on tangible equity, asset quality and total stockholder return (share price appreciation from date of award plus dividends paid as a percent of the Company's common stock share price on the date of award). If a participant leaves the Company prior to the third anniversary date of an award, any unvested shares are forfeited. Dividends declared with respect to shares awarded will be held by the Company and paid to the participant only when the shares vest. Under all the Plans, shares of the Company's common stock were reserved for issuance as restricted stock awards to officers, employees, consultants and non-employee directors of the Company. Shares issued upon vesting may be either authorized but unissued shares or reacquired shares held by the Company as treasury shares. Any shares not issued because vesting requirements are not met will be retired back to treasury and be made available again for issuance under the Plans. Total expense for the Plans was $2.3 million in 2017 , $1.8 million in 2016 and $1.4 million in 2015 , respectively. Total income tax benefits on vested awards was $0.7 million in 2017 , $0.3 million in 2016 , and $0.3 million in 2015 . Dividends paid on unvested awards under the Plans, which are recognized as compensation expense, were $0.1 million in 2017 , $0.1 million in 2016 , and $0.1 million in 2015 . Activity under the recognition and retention plans was as follows: Restricted Stock Awards Outstanding Weighted Average Price per Share (Dollars in Thousands, Except Per Share Amounts) Recognition and Retention Plans: Outstanding at December 31, 2016 476,854 $ 10.90 Granted 186,782 14.65 Vested (193,267 ) 10.24 Forfeited / Canceled (15,086 ) 16.10 Outstanding at December 31, 2017 455,283 $ 12.64 Unrecognized compensation cost $ 3,022 Weighted average remaining recognition period (months) 30 Stock Option Plans The Company has an active equity incentive plan, the 2014 Plan. The prior plans, the "2003 Option Plan" and the "1999 Option Plan" were terminated on October 16, 2013 and April 19, 2009, respectively. The 2014 plan is an omnibus plan from which the Company may award up to 1,750,000 shares of restricted stock or stock options among other types of awards. Under all the stock option plans, shares of the Company's common stock were reserved for issuance to directors, employees, consultants and non-employee directors of the Company. Shares issued upon the exercise of a stock option may be either authorized but unissued shares or reacquired shares held by the Company as treasury shares. Any shares subject to an award which expire or are terminated unexercised will again be available for issuance under the plans. The exercise price of options awarded is the fair market value of the common stock of the Company on the date the award is made. Certain of the options include a reload feature whereby an optionee exercising an option by delivery of shares of common stock would automatically be granted an additional option at the fair market value of stock when such additional option is granted equal to the number of shares so delivered. If an individual to whom a stock option was granted ceases to maintain continuous service by reason of normal retirement, death or disability, or following a change in control, all options and rights granted and not fully exercisable become exercisable in full upon the happening of such an event and shall remain exercisable for a period ranging from 3 months to 5 years. No options were granted in 2017 , 2016 , or 2015 . There was no expense for the stock option plans in 2017 , 2016 , and 2015 . In accordance with the terms of the Plans, no dividend equivalent rights were paid to holders of unexercised vested options in 2017 , 2016 or 2015 . Activity under the option plans was as follows: Options Outstanding Weighted Average Exercise Price Per Share Aggregate Intrinsic Value Weighted Average Contractual Term (In Years) (Dollars in Thousands, Except Per Share Amounts) Employee Stock Options: Outstanding at December 31, 2016 197,345 $ 10.18 Granted — — Exercised (147,345 ) 10.53 Forfeited / Canceled — — Outstanding at December 31, 2017 50,000 $ 10.80 $ 245 2.8 Exercisable at December 31, 2017 50,000 $ 10.80 $ 245 2.8

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments A description of the valuation methodologies used for assets and liabilities measured at fair value on a recurring and non-recurring basis, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below. There were no changes in the valuation techniques used during 2017 and 2016 . Assets and Liabilities Recorded at Fair Value on a Recurring Basis The following table set forth the carrying value of assets and liabilities measured at fair value on a recurring basis at December 31, 2017 and 2016 : Carrying Value as of December 31, 2017 Level 1 Level 2 Level 3 Total (In Thousands) Assets: Investment securities available-for-sale: GSE debentures $ — $ 149,924 $ — $ 149,924 GSE CMOs — 127,022 — 127,022 GSE MBSs — 189,313 — 189,313 SBA commercial loan asset-backed securities — 72 — 72 Corporate debt obligations — 62,683 — 62,683 U.S. Treasury bonds — 8,730 — 8,730 Trust preferred securities — 1,398 — 1,398 Marketable equity securities 982 — — 982 Total investment securities available-for-sale $ 982 $ 539,142 $ — $ 540,124 Loan level derivatives $ — $ 8,865 $ — $ 8,865 Risk participation-out agreements — 65 — 65 Foreign exchange contracts — 72 — 72 Liabilities: Loan level derivatives $ — $ 8,865 $ — $ 8,865 Risk participation-in agreements — 10 — 10 Foreign exchange contracts — 65 — 65 Carrying Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (In Thousands) Assets: Investment securities available-for-sale: GSE debentures $ — $ 97,020 $ — $ 97,020 GSE CMOs — 158,040 — 158,040 GSE MBSs — 212,915 — 212,915 SBA commercial loan asset-backed securities — 107 — 107 Corporate debt obligations — 48,485 — 48,485 U.S. Treasury bonds — 4,737 — 4,737 Trust preferred securities — 1,358 — 1,358 Marketable equity securities 972 — — 972 Total investment securities available-for-sale $ 972 $ 522,662 $ — $ 523,634 Loan level derivatives $ — $ 9,738 $ — $ 9,738 Risk participation-out agreements — 20 — 20 Liabilities: Loan level derivatives $ — $ 9,738 $ — $ 9,738 As of December 31, 2016 , the Company held no risk participation-in agreements and the fair value of the foreign exchange contracts was nominal. Investment Securities Available-for-Sale The fair value of investment securities is based principally on market prices and dealer quotes received from third-party and nationally-recognized pricing services for identical investment securities such as U.S. Treasury and agency securities. The Company's marketable equity securities are priced this way and are included in Level 1. These prices are validated by comparing the primary pricing source with an alternative pricing source when available. When quoted market prices for identical securities are unavailable, the Company uses market prices provided by independent pricing services based on recent trading activity and other observable information, including but not limited to market interest-rate curves, referenced credit spreads and estimated prepayment speeds where applicable. These investments include GSE debentures, GSE mortgage-related securities, SBA commercial loan asset backed securities, corporate debt securities, and trust preferred securities, all of which are included in Level 2. As of December 31, 2017 and December 31, 2016 , no investment securities were valued using pricing models included in Level 3. Additionally, management reviews changes in fair value from period to period and performs testing to ensure that prices received from the third parties are consistent with management's expectation of the market. Changes in the prices obtained from the pricing service are analyzed from month to month, taking into consideration changes in market conditions including changes in mortgage spreads, changes in U.S. Treasury security yields and changes in generic pricing of 15 -year and 30 -year securities. Additional analysis may include a review of prices provided by other independent parties, a yield analysis, a review of average life changes using Bloomberg analytics and a review of historical pricing for a particular security. Loan Level Derivatives The fair values for the interest-rate swap assets and liabilities represent a Level 2 valuation and are based on settlement values adjusted for credit risks associated with the counterparties and the Company and observable market interest rate curves. Credit risk adjustments consider factors such as the likelihood of default by the Company and its counterparties, its net exposures and remaining contractual life. To date, the Company has not realized any losses due to a counterparty's inability to pay any net uncollateralized position. Refer also to Note 16, "Derivatives and Hedging Activities." There are no assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the year ended December 31, 2017 and December 31, 2016 . There were no transfers between levels for assets and liabilities recorded at fair value on a recurring basis during 2017 or 2016 . Assets and Liabilities Recorded at Fair Value on a Non-Recurring Basis Assets and liabilities measured at fair value on a non-recurring basis as of December 31, 2017 and 2016 are summarized below: Carrying Value as of December 31, 2017 Level 1 Level 2 Level 3 Total (In Thousands) Assets measured at fair value on a non-recurring basis: Collateral-dependent impaired loans and leases $ — $ — $ 21,195 $ 21,195 OREO — — 3,235 3,235 Repossessed assets — 1,184 — 1,184 Total assets measured at fair value on a non-recurring basis $ — $ 1,184 $ 24,430 $ 25,614 Carrying Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (In Thousands) Assets measured at fair value on a non-recurring basis: Collateral-dependent impaired loans and leases $ — $ — $ 27,282 $ 27,282 OREO — — 618 618 Repossessed assets — 781 — 781 Total assets measured at fair value on a non-recurring basis $ — $ 781 $ 27,900 $ 28,681 Collateral-Dependent Impaired Loans and Leases For nonperforming loans and leases where the credit quality of the borrower has deteriorated significantly, fair values of the underlying collateral were estimated using purchase and sales agreements (Level 2), or comparable sales or recent appraisals (Level 3), adjusted for selling costs and other expenses. Other Real Estate Owned The Company records OREO at the lower of cost or fair value. In estimating fair value, the Company utilizes purchase and sales agreements (Level 2) or comparable sales, recent appraisals or cash flows discounted at an interest rate commensurate with the risk associated with these cash flows (Level 3), adjusted for selling costs and other expenses. Repossessed Assets Repossessed assets are carried at estimated fair value less costs to sell based on auction pricing (Level 2). The table below presents quantitative information about significant unobservable inputs (Level 3) for assets measured at fair value on a recurring basis at the dates indicated. Fair Value Valuation Technique At December 31, 2017 At December 31, 2016 (Dollars in Thousands) Collateral-dependent impaired loans and leases $ 21,195 $ 27,282 Appraisal of collateral (1) Other real estate owned 3,235 618 Appraisal of collateral (1) _______________________________________________________________________________ (1) Fair value is generally determined through independent appraisals of the underlying collateral. The Company may also use another available source of collateral assessment to determine a reasonable estimate of the fair value of the collateral. Appraisals may be adjusted by management for qualitative factors such as economic factors and estimated liquidation expenses. The range of the unobservable inputs used may vary but is generally 0% - 10% on the discount for costs to sell and 0% - 15% on appraisal adjustments. Summary of Estimated Fair Values of Financial Instruments The following table presents the carrying amount, estimated fair value, and placement in the fair value hierarchy of the Company's financial instruments at the dates indicated. This table excludes financial instruments for which the carrying amount approximates fair value. Financial assets for which the fair value approximates carrying value include cash and cash equivalents, restricted equity securities, and accrued interest receivable. Financial liabilities for which the fair value approximates carrying value include non-maturity deposits, short-term borrowings, and accrued interest payable. There were no transfers between levels during 2017 . Fair Value Measurements Carrying Value Estimated Fair Value Level 1 Inputs Level 2 Inputs Level 3 Inputs (In Thousands) At December 31, 2017 Financial assets: Investment securities held-to-maturity: GSE debentures $ 41,612 $ 40,801 $ — $ 40,801 $ — GSE MBSs 13,923 13,705 — 13,705 — Municipal obligations 53,695 53,517 — 53,517 — Foreign government obligations 500 500 — 500 Loans held-for-sale 2,628 2,628 — 2,628 — Loans and leases, net 5,672,087 5,594,543 — — 5,594,543 Restricted equity securities 59,369 59,369 — — 59,369 Financial liabilities: Certificates of deposit 1,207,470 1,198,201 — 1,198,201 — Borrowed funds 1,020,819 995,335 — 995,335 — At December 31, 2016 Financial assets: Investment securities held-to-maturity: GSE debentures $ 14,735 $ 14,101 $ — $ 14,101 $ — GSE MBSs 17,666 17,479 — 17,479 — Municipal obligations 54,219 53,204 — 53,204 — Foreign government obligations 500 487 — — 487 Loans held-for-sale 13,078 13,078 — 13,078 — Loans and leases, net 5,345,198 5,195,312 — — 5,195,312 Restricted equity securities 64,511 75,589 — — 75,589 Financial liabilities: Certificates of deposit 1,041,022 1,042,653 — 1,042,653 — Borrowed funds 1,044,086 1,030,753 — 1,030,753 — Investment Securities Held-to-Maturity The fair values of certain investment securities held-to-maturity are estimated using market prices provided by independent pricing services based on recent trading activity and other observable information, including but not limited to market interest-rate curves, referenced credit spreads and estimated prepayment speeds where applicable. These investments include GSE debentures, GSE MBSs, and municipal obligations, all of which are included in Level 2. Additionally, fair values of foreign government obligations are based on comparisons to market prices of similar securities and are considered to be Level 3. Loans Held-for-Sale Fair value is measured using quoted market prices when available. These assets are typically categorized as Level 1. If quoted market prices are not available, comparable market values may be utilized. These assets are typically categorized as Level 2. Loans and Leases The fair values of performing loans and leases was estimated by segregating the portfolio into its primary loan and lease categories—commercial real estate mortgage, multi-family mortgage, construction, commercial, equipment financing, condominium association, residential mortgage, home equity and other consumer. These categories were further disaggregated based upon significant financial characteristics such as type of interest rate (fixed / variable) and payment status (current / past-due). The Company discounts the contractual cash flows for each loan category using interest rates currently being offered for loans with similar terms to borrowers of similar quality and incorporates estimates of future loan prepayments. This method of estimating fair value does not incorporate the exit price concept of fair value. Restricted Equity Securities The fair values of certain restricted equity securities are estimated using observable inputs adjusted for other unobservable information, including but not limited to probability assumptions and similar discounts where applicable. These restricted equity securities are considered to be Level 3. Deposits The fair values of deposit liabilities with no stated maturity (demand, NOW, savings and money market savings accounts) are equal to the carrying amounts payable on demand. The fair value of certificates of deposit represents contractual cash flows discounted using interest rates currently offered on deposits with similar characteristics and remaining maturities. The fair value estimates for deposits do not include the benefit that results from the low-cost funding provided by the Company's core deposit relationships (deposit-based intangibles). Borrowed Funds The fair value of federal funds purchased is equal to the amount borrowed. The fair value of FHLBB advances and repurchase agreements represents contractual repayments discounted using interest rates currently available for borrowings with similar characteristics and remaining maturities. The fair values reported for retail repurchase agreements are based on the discounted value of contractual cash flows. The discount rates used are representative of approximate rates currently offered on borrowings with similar characteristics and maturities. The fair values reported for subordinated deferrable interest debentures are based on the discounted value of contractual cash flows. The discount rates used are representative of approximate rates currently offered on instruments with similar terms and maturities.

Condensed Parent Company Financ

Condensed Parent Company Financial Statements	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Parent Company Financial Statements	Condensed Parent Company Financial Statements Condensed Parent Company Balance Sheets as of December 31, 2017 and 2016 and Statements of Income for the years ended December 31, 2017 , 2016 and 2015 are as follows. The Statement of Stockholders' Equity is not presented below as the parent company's stockholders' equity is that of the consolidated company. Balance Sheets At December 31, 2017 2016 (In Thousands) ASSETS Cash and due from banks $ 5,511 $ 32,220 Short-term investments 32 32 Total cash and cash equivalents 5,543 32,252 ESOP loan to Brookline Bank 1,252 1,502 Intercompany loan to Brookline Bank 80,000 — Restricted equity securities 100 100 Premises and equipment, net 6,032 6,946 Investment in subsidiaries, at equity 753,056 701,943 Goodwill 35,267 35,267 Other assets 6,627 8,259 Total assets $ 887,877 $ 786,269 LIABILITIES AND STOCKHOLDERS' EQUITY Borrowed funds $ 83,271 $ 83,105 Deferred tax liability 608 243 Accrued expenses and other liabilities 168 7,377 Total liabilities 84,047 90,725 Stockholders' equity: Common stock, $0.01 par value; 200,000,000 shares authorized; 81,695,695 shares issued and 75,744,445 shares issued, respectively 817 757 Additional paid-in capital 699,976 616,734 Retained earnings, partially restricted 161,217 136,671 Accumulated other comprehensive loss (5,950 ) (3,818 ) Treasury stock, at cost; 4,440,665 shares and 4,707,096 shares, respectively (51,454 ) (53,837 ) Unallocated common stock held by ESOP; 142,332 shares and 176,688 shares, respectively (776 ) (963 ) Total stockholders' equity 803,830 695,544 Total liabilities and stockholders' equity $ 887,877 $ 786,269 Statements of Income Year Ended December 31, 2017 2016 2015 (In Thousands) Interest and dividend income: Dividend income from subsidiaries $ 7,317 $ 109 $ — Marketable and restricted equity securities — — 97 ESOP loan to Brookline Bank 120 141 162 Intercompany loan to Brookline Bank 532 — — Total interest and dividend income 7,969 250 259 Interest expense: Borrowed funds 5,123 5,080 5,063 Net interest income 2,846 (4,830 ) (4,804 ) Non-interest income: Other — 15 5 Total non-interest income — 15 5 Non-interest expense: Compensation and employee benefits 391 82 205 Occupancy 1,584 1,582 22 Equipment and data processing (1) (1,011 ) (1,190 ) 687 Directors' fees 453 700 688 Franchise taxes 180 180 113 Insurance 528 490 490 Professional services 470 245 185 Advertising and marketing 4 — — Merger and acquisition expense 411 — — Other (2) (1,224 ) (1,300 ) (1,289 ) Total non-interest expense 1,786 789 1,101 Loss before income taxes 1,060 (5,604 ) (5,900 ) Credit for income taxes (1,944 ) (1,779 ) (1,854 ) Loss before equity in undistributed income of subsidiaries 3,004 (3,825 ) (4,046 ) Equity in undistributed income of subsidiaries 47,514 56,187 53,828 Net income $ 50,518 $ 52,362 $ 49,782 _______________________________________________________________________________ (1) The Parent Company received a net benefit in 2017 and 2016 from the intercompany allocation of expense that is eliminated in consolidation. (2) The Parent Company received a net benefit in 2017, 2016 and 2015 from the intercompany allocation of expense that is eliminated in consolidation. Statements of Cash Flows Year Ended December 31, 2017 2016 2015 (In Thousands) Cash flows from operating activities: Net income attributable to parent company $ 50,518 $ 52,362 $ 49,782 Adjustments to reconcile net income to net cash provided from operating activities: Equity in undistributed income of subsidiaries (47,514 ) (56,187 ) (53,828 ) Depreciation of premises and equipment 2,856 2,735 2,728 Amortization of debt issuance costs 100 101 100 Other operating activities, net (5,885 ) 30,895 2,479 Net cash provided from operating activities 75 29,906 1,261 Cash flows from investing activities: Repayment of ESOP loan by Brookline Bank 250 250 250 Issuance of intercompany loan to Brookline Bank (80,000 ) — — Purchase of premises and equipment (1,942 ) (641 ) (742 ) Net cash used for investing activities (81,692 ) (391 ) (492 ) Cash flows from financing activities: Proceeds from issuance of common stock 81,943 — — Payment of dividends on common stock (27,035 ) (25,366 ) (24,967 ) Net cash provided from (used for) financing activities 54,908 (25,366 ) (24,967 ) Net (decrease) increase in cash and cash equivalents (26,709 ) 4,149 (24,198 ) Cash and cash equivalents at beginning of year 32,252 28,103 52,301 Cash and cash equivalents at end of year $ 5,543 $ 32,252 $ 28,103

Quarterly Results of Operations

Quarterly Results of Operations (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results of Operations (Unaudited)	Quarterly Results of Operations (Unaudited) 2017 Quarters Fourth Third Second First (Dollars in Thousands Except Per Share Data) Interest and dividend income $ 68,337 $ 67,176 $ 65,186 $ 62,351 Interest expense 10,680 10,333 9,603 9,253 Net interest income 57,657 56,843 55,583 53,098 Provision for credit losses 1,802 2,911 873 13,402 Net interest income after provision for credit losses 55,855 53,932 54,710 39,696 Loan level derivative income, net 755 844 186 402 Gain on sales of investment securities, net — — — 11,393 Gain on sales of loans and leases held-for-sale 935 1,049 307 353 Other non-interest income 4,125 4,080 3,984 3,760 Amortization of identified intangible assets (519 ) (519 ) (519 ) (532 ) Other non-interest expense (34,633 ) (34,889 ) (34,276 ) (33,224 ) Income before provision for income taxes 26,518 24,497 24,392 21,848 Provision for income taxes 18,712 8,330 8,759 7,835 Net income before noncontrolling interest in subsidiary 7,806 16,167 15,633 14,013 Less net income attributable to noncontrolling interest in subsidiary 979 801 753 568 Net income attributable to Brookline Bancorp, Inc. $ 6,827 $ 15,366 $ 14,880 $ 13,445 Earnings per share: Basic $ 0.09 $ 0.20 $ 0.20 $ 0.19 Diluted 0.09 0.20 0.20 0.19 Average common shares outstanding: Basic 76,583,712 76,452,539 74,325,013 70,386,766 Diluted 76,868,307 76,961,948 74,810,088 70,844,096 Common stock price: High $ 16.35 $ 15.50 $ 15.95 $ 16.75 Low 14.50 13.75 13.75 14.50 Dividends per share $ 0.09 $ 0.09 $ 0.09 $ 0.09 2016 Quarters Fourth Third Second First (Dollars in Thousands Except Per Share Data) Interest and dividend income $ 60,983 $ 61,531 $ 59,236 $ 57,898 Interest expense 9,129 9,181 8,979 8,695 Net interest income 51,854 52,350 50,257 49,203 Provision for credit losses 3,215 2,215 2,545 2,378 Net interest income after provision for credit losses 48,639 50,135 47,712 46,825 Loan level derivative income, net 265 858 1,210 1,629 Gain on sales of loans and leases held-for-sale 1,270 588 345 905 Other non-interest income 3,895 3,883 3,820 3,935 Amortization of identified intangible assets (621 ) (623 ) (621 ) (635 ) Other non-interest expense (31,986 ) (32,765 ) (31,629 ) (31,418 ) Income before provision for income taxes 21,462 22,076 20,837 21,241 Provision for income taxes 7,524 7,804 7,465 7,599 Net income before noncontrolling interest in subsidiary 13,938 14,272 13,372 13,642 Less net income attributable to noncontrolling interest in subsidiary 659 655 718 830 Net income attributable to Brookline Bancorp, Inc. $ 13,279 $ 13,617 $ 12,654 $ 12,812 Earnings per share: Basic $ 0.19 $ 0.19 $ 0.18 $ 0.18 Diluted 0.19 0.19 0.18 0.18 Average common shares outstanding: Basic 70,362,702 70,299,722 70,196,950 70,186,921 Diluted 70,592,204 70,450,760 70,388,438 70,343,408 Common stock price: High $ 16.60 $ 12.19 $ 11.69 $ 11.21 Low 12.05 10.71 10.44 10.23 Dividends per share $ 0.09 $ 0.09 $ 0.09 $ 0.09

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events First Commons Bank Acquisition On January 17, 2018, the holders of approximately 89% of the outstanding shares of First Commons Bank voted in favor to approve the Merger Agreement among the Company, Brookline Bank, and First Commons Bank. The holders of the remaining 11% of the outstanding shares of First Commons Bank did not vote. In February of 2018, the Company received approval of the Merger Agreement from the Board of Governors of the Federal Reserve System and the Massachusetts Division of Banks. Refer to Note 2, "Acquisitions" to the consolidated financial statements for information regarding the Company's acquisition of First Commons Bank as of December 31, 2017 . The Company has evaluated subsequent events other than the matters described above and through the date of issuance.

Basis of Presentation (Policies

Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies
Basis of Accounting	The Company's consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles ("GAAP") as set forth by the Financial Accounting Standards Board ("FASB") in its Accounting Standards Codification and through the rules and interpretive releases of the Securities and Exchange Commission ("SEC") under the authority of federal securities laws.
Consolidation	The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All significant intercompany transactions and balances are eliminated in consolidation.
Use of Estimates	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, the review of goodwill and intangibles for impairment and the review of deferred tax assets for valuation allowance. 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.
Reclassification	Reclassification Certain previously reported amounts have been reclassified to conform to the current year's presentation.
Cash and Cash Equivalents	Cash and Cash Equivalents For purposes of reporting asset balances and cash flows, cash and cash equivalents includes cash on hand and due from banks (including cash items in process of clearing), interest-bearing deposits with banks, federal funds sold, money market mutual funds and other short-term investments with original maturities of three months or less.
Investment Securities	Investment Securities Investment securities, other than those reported as short-term investments, are classified at the time of purchase as "available-for-sale," or "held-to-maturity." Classification is periodically re-evaluated for consistency with the Company's goals and objectives. Equity investments in the Federal Home Loan Bank of Boston ("FHLBB"), the Federal Reserve Bank of Boston and other restricted equities are discussed in more detail in Note 5, "Restricted Equity Securities." Investment Securities Available-for-Sale and Held-to-Maturity Investment securities for which the Company has the positive intent and ability to hold to maturity are classified as held-to-maturity and carried at amortized cost. Those investment securities held for indefinite periods of time but not necessarily to maturity are classified as available-for-sale. Investment securities held for indefinite periods of time include investment securities that management intends to use as part of its asset/liability, liquidity, and/or capital management strategies and may be sold in response to changes in interest rates, maturities, asset/liability mix, liquidity needs, regulatory capital needs or other business factors. Investment securities available-for-sale are carried at estimated fair value, primarily obtained from a third-party pricing service, with unrealized gains and losses reported on an after-tax basis in stockholders' equity as accumulated other comprehensive income or loss. As of December 31, 2017 and 2016 , the Company did not make any adjustments to the prices provided by the third-party pricing service. Security transactions are recorded on the trade date. Realized gains and losses are determined using the specific identification method and are recorded in non-interest income. Interest and dividends on securities are recorded using the accrual method. Premiums and discounts on securities are amortized or accreted into interest income using the level-yield method over the remaining period to contractual maturity, adjusted for the effect of actual prepayments in the case of mortgage-backed securities ("MBSs") and collateralized mortgage obligations ("CMOs"). These estimates of prepayment assumptions are made based upon the actual performance of the underlying security, current interest rates, the general market consensus regarding changes in mortgage interest rates, the contractual repayment terms of the underlying loans, the priority rights of the investors to the cash flows from the mortgage securities and other economic conditions. When differences arise between anticipated prepayments and actual prepayments, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. Unamortized premium or discount is adjusted to the amount that would have existed had the new effective yield been applied since purchase, with a corresponding charge or credit to interest income. Management evaluates securities for other-than-temporary impairment ("OTTI") on a periodic basis. Factors considered in determining whether an impairment is OTTI include: (1) the length of time and the extent to which the fair value has been less than amortized cost, (2) projected future cash flows, (3) the financial condition and near-term prospects of the issuers, and (4) the intent and ability of the Company to hold the investment for a period of time sufficient to allow for any anticipated recovery in fair value. The Company records an OTTI loss in an amount equal to the entire difference between the fair value and amortized cost if: (1) the Company intends to sell an impaired investment security, (2) it is more likely than not that the Company will be required to sell the investment security before its amortized cost, or (3) for debt securities, the present value of expected future cash flows is not sufficient to recover the entire amortized cost basis. If an investment security is determined to be OTTI but the Company does not intend to sell the investment security, only the credit portion of the estimated loss is recognized in earnings, with the non credit portion of the loss recognized in other comprehensive income. Restricted Equity Securities The Company invests in the stock of the FHLBB, the Federal Reserve Bank of Boston and a small amount of other restricted securities. No ready market exists for these stocks, and they have no quoted market values. The Banks, as members of the FHLBB, are required to maintain investments in the capital stock of the FHLBB equal to their membership base investments plus an activity-based investment determined according to the Banks' level of outstanding FHLBB advances. Federal Reserve Bank of Boston stock was purchased and is redeemable at par.
Loans	Loans Originated Loans Loans the Company originates for the portfolio, and for which it has the intent and ability to hold to maturity, are reported at amortized cost, inclusive of deferred loan origination fees and expenses, less unadvanced funds due borrowers on loans and the allowance for loan and lease losses. Interest income on loans and leases originated for the portfolio is accrued on unpaid principal balances as earned. Loan origination fees and direct loan origination costs are deferred, and the net fee or cost is recognized in interest income using the interest method. Deferred amounts are recognized for fixed-rate loans over the contractual life of the loans and for adjustable-rate loans over the period of time required to adjust the contractual interest rate to a yield approximating a market rate at the origination date. If a loan is prepaid, the unamortized portion of the loan origination costs, including third party referral related costs not subject to rebate from the dealer, is charged to income. Loans and Leases Held-for-Sale Management identifies and designates certain newly originated loans and leases for sale to specific financial institutions, subject to the underwriting criteria of those financial institutions. These loans and leases are held for sale and are carried at the lower of cost or market as determined in the aggregate. Deferred loan fees and costs are included in the determination of the gain or loss on sale. Acquired Loans Acquired loans that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Company will be unable to collect all contractually required payments receivable are initially recorded at fair value (as determined by the present value of expected future cash flows) with no valuation allowance. The difference between the undiscounted cash flows expected at acquisition and the recorded fair value of the loan, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment or as a loss accrual or a valuation allowance. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition (meaning the present value of all cash flows expected at acquisition that ultimately are not to be received).
Non-Performing Loans	Nonperforming Loans Nonaccrual Loans Accrual of interest on loans generally is discontinued when contractual payment of principal or interest becomes past due 90 days or, if in management's judgment, reasonable doubt exists as to the full timely collection of interest. Exceptions may be made if the loan has matured and is in the process of renewal or is well-secured and in the process of collection. When a loan is placed on nonaccrual status, interest accruals cease and uncollected accrued interest is reversed and charged against current interest income. Interest payments on nonaccrual loans are generally applied to principal. If collection of the principal is reasonably assured, interest payments are recognized as income on the cash basis. Loans are generally returned to accrual status when principal and interest payments are current, full collectability of principal and interest is reasonably assured and a consistent record of at least six consecutive months of performance has been achieved. Impaired Loans A loan is considered to be impaired when, based on current information and events, it is probable that the Company will be unable to collect all amounts due (both interest and principal) according to the contractual terms of the loan agreement. Smaller-balance, homogeneous loans that are evaluated collectively for impairment, such as residential, home equity and other consumer loans are specifically excluded from the impaired loan portfolio except where the loan is classified as a troubled debt restructuring. The Company has defined the population of impaired loans to include nonaccrual loans and troubled debt restructured ("TDR") loans. When the ultimate collectability of the total principal of an impaired loan or lease is in doubt and the loan is on nonaccrual status, all payments are applied to principal, under the cost recovery method. When the ultimate collectability of the total principal of an impaired loan or lease is not in doubt and the loan or lease is on nonaccrual status, contractual interest is credited to interest income when received, under the cash basis method. The value of an impaired loan is measured based upon the present value of expected future cash flows discounted at the loan's effective interest rate, or the fair value of the collateral if the loan is collateral-dependent and its payment is expected solely based on the underlying collateral. For impaired loans deemed collateral dependent, where impairment is measured using the fair value of the collateral, the Company will either obtain a new appraisal or use another available source of collateral assessment to determine a reasonable estimate of the fair value of the collateral. Interest collected on impaired loans is either applied against principal or reported as income according to management's judgment as to the collectability of principal. If management does not consider a loan ultimately collectible within an acceptable time frame, payments are applied as principal to reduce the loan balance. If full collection of the remaining recorded investment should subsequently occur, interest receipts are recorded as interest income on a cash basis. Troubled Debt Restructured Loans In cases where a borrower experiences financial difficulties and the Company makes certain concessionary modifications to contractual terms, the loan is classified as a TDR loan. In determining whether a debtor is experiencing financial difficulties, the Company considers, among other factors, whether the debtor is in payment default or is likely to be in payment default in the foreseeable future without the modification, if the debtor declared or is in the process of declaring bankruptcy, there is substantial doubt that the debtor will continue as a going concern, the debtor's entity-specific projected cash flows will not be sufficient to service its debt, or the debtor cannot obtain funds from sources other than the existing creditors at market terms for debt with similar risk characteristics. Large groups of small-balance homogeneous loans such as residential real estate, residential construction, home equity and other consumer portfolios are collectively evaluated for impairment. As such, the Company does not typically identify individual loans within these groupings as impaired loans or for impairment evaluation and disclosure. However, the Company evaluates all TDRs for impairment on an individual loan basis regardless of loan type. Modifications may include interest-rate reductions, short-term (defined as one year or less) changes in payment structure to interest-only payments, short-term extensions of the loan's original contractual term, or less frequently, principal forgiveness, interest capitalization, forbearance and other actions intended to minimize economic loss and avoid foreclosure or repossession of collateral. Typically, TDRs are placed on nonaccrual status and reported as nonperforming loans. Generally, a nonaccrual loan that is restructured remains on nonaccrual for a period of six months to demonstrate that the borrower can meet the restructured terms; however, performance prior to the restructuring, or significant events that coincide with the restructuring, are considered in assessing whether the borrower can meet the new terms and may result in the loan being returned to accrual status at the time of restructuring or after a shorter performance period. If the borrower's ability to meet the revised payment schedule is not reasonably assured, the loan remains classified as a nonaccrual loan. Loans restructured at an interest rate equal to or greater than that of a new loan with comparable risk at the time the loan agreement is modified may be excluded from restructured loan disclosures in years subsequent to the restructuring if they are in compliance with the modified terms.
Allowance for Loan and Lease Losses	Allowance for Loan and Lease Losses Management has established a methodology to determine the adequacy of the allowance for loan and lease losses that assesses the risks and losses inherent in the loan and lease portfolio. Additions to the allowance for loan and lease losses are made by charges to the provision for credit losses. Losses on loans and leases are charged off against the allowance when all or a portion of a loan or lease is considered uncollectible. Subsequent recoveries on loans previously charged off, if any, are credited to the allowance when realized. Management uses a consistent and systematic process and methodology to evaluate the adequacy of the allowance for loan and lease losses on a quarterly basis. For purposes of determining the allowance for loan and lease losses, the Company has segmented certain loans and leases in the portfolio by product type into the following segments: (1) commercial real estate loans, (2) commercial loans and leases, (3) and consumer loans. Portfolio segments are further disaggregated into classes based on the associated risks within the segments. Commercial real estate loans are divided into three classes: commercial real estate mortgage loans, multi-family mortgage loans, and construction loans. Commercial loans and leases are divided into three classes: commercial loans which includes taxi medallion loans, equipment financing, and loans to condominium associations. Consumer loans are divided into three classes: residential mortgage loans, home equity loans, and other consumer loans. A formula-based credit evaluation approach is applied to each group, coupled with an analysis of certain loans for impairment. The general allowance related to loans collectively evaluated for impairment is determined using a formula-based approach utilizing the risk ratings of individual credits and loss factors derived from historic portfolio loss rates, which include estimates of incurred losses over an estimated loss emergence period (“LEP”). The LEP was generated utilizing a charge-off look-back analysis which studied the time from the first indication of elevated risk of repayment (or other early event indicating a problem) to eventual charge-off to support the LEP considered in the allowance calculation. This reserving methodology established the approximate number of months of LEP that represents incurred losses for each portfolio. In addition to quantitative measures, relevant qualitative factors include, but are not limited to: (1) levels and trends in past due and impaired loans, (2) levels and trends in charge-offs, (3) changes in underwriting standards, policy exceptions, and credit policy, (4) experience of lending management and staff, (5) economic trends, (6) industry conditions, (7) effects of changes in credit concentrations, (8) interest rate environment, and (9) regulatory and other changes. The general allowance related to the acquired loans collectively evaluated for impairment is determined based upon the degree, if any, of deterioration in the pooled loans subsequent to acquisition. The qualitative factors used in the determination are the same as those used for originated loans. During 2015, the Company enhanced and refined its general allowance methodology. Under the enhanced methodology, management combined the historical loss histories of the Banks to generate a single set of historical loss ratios. Management believes it is appropriate to aggregate the ratios as the Banks share common environmental factors, operate in similar geographic markets, and utilize common underwriting standards in accordance with the Company's Credit Policy. In prior periods, a historical loss history applicable to each Bank was used. Management employed a similar analysis for the consolidation of the qualitative factors as it did for the quantitative factors. Again, management believes the realignment of the existing nine qualitative factors used at each of the Banks into a single group of factors used for the Company is appropriate based on the commonality of environmental factors, markets and underwriting standards among the Banks. Prior to 2015, each of the Banks utilized a set of qualitative factors applicable to each Bank. The Company’s December 31, 2017 allowance calculation included a further segmentation of the commercial loans and leases to reflect the increased risk in the Company’s taxi medallion portfolio. As of December 31, 2017 , this portfolio is approximately $19.7 million . Based on industry conditions, management established a loss factor for this portfolio that best represents the changing risks associated with it. Based on the refinements to the Company’s allowance methodology discussed above, management determined that the potential risks anticipated by the unallocated allowance are now incorporated into the allowance methodology, making the unallocated allowance unnecessary. Prior to 2015, the unallocated allowance was used to recognize the estimated risk associated with the allocated general and specific allowances. It incorporated management’s evaluation of existing conditions that were not included in the allocated allowance determinations and provided for losses that arise outside of the ordinary course of business. Specific valuation allowances are established for impaired originated loans with book values greater than the discounted present value of expected future cash flows or, in the case of collateral-dependent impaired loans, for any excess of a loan's book balance and the fair value of its underlying collateral. Specific valuation allowances are established for acquired loans with deterioration in the discounted present value of expected future cash flows since acquisitions or, in the case of collateral dependent impaired loans, for any increase in the excess of a loan's book balance greater than the fair value of its underlying collateral. A specific valuation allowance for losses on TDR loans is determined by comparing the net carrying amount of the troubled debt restructured loan with the restructured loan's cash flows discounted at the original effective rate. Impaired loans are reviewed quarterly with adjustments made to the calculated reserve as necessary. As of December 31, 2017 , management believes that the methodology for calculating the allowance is sound and that the allowance provides a reasonable basis for determining and reporting on probable losses in the Company’s loan portfolios. Liability for Unfunded Commitments In the ordinary course of business, the Company enters into commitments to extend credit, commercial letters of credit, and standby letters of credit. Such financial instruments are recorded in the financial statements when they become payable. The credit risk associated with these commitments is evaluated in a manner similar to the allowance for loan losses.
Premises and Equipment	Premises and Equipment Premises and equipment are carried at cost less accumulated depreciation and amortization, except for land which is carried at cost. Premises and equipment are depreciated using the straight-line method over the estimated useful life of the assets. Leasehold improvements are amortized using the straight-line method over the shorter of the lease term or the estimated useful life of the improvements. Costs related to internal-use software development projects that provide significant new functionality are capitalized. Internal-use software is software acquired or modified solely to meet the Company's needs and for which there is no plan to market the software externally. Direct and indirect costs associated with the application development stage of internal use software are capitalized until such time that the software is substantially complete and ready for its intended use. Capitalized costs are amortized on a straight-line basis over the remaining estimated life of the software. Computer software and development costs incurred in the preliminary project stage, as well as training and maintenance costs, are expensed as incurred.
Leases	Leases The Company leases properties for offices and branches in the states of Massachusetts, Rhode Island and New York. Lease terms range from five years to over 25 years with options to renew. Management performs an analysis to determine proper lease accounting at lease inception and for each renewal. If a lease meets any of the following four criteria, the lease is classified as capital lease. The four criteria are: transfer of ownership by the end of lease term; contains bargain purchase option; lease term is at least 75% of the property’s estimated remaining economic life; or present value of the minimum lease payment is at least 90% of the fair value of the leased property. All leases are classified as operating leases and rental payments are expensed as incurred. Certain leases contain rent escalation clauses which are amortized over the life of the lease under the straight-line method.
Bank-Owned Life Insurance	Bank-Owned Life Insurance The Company acquired bank-owned life insurance ("BOLI") plans as part of its acquisitions of First Ipswich and BankRI. BOLI represents life insurance on the lives of certain current and former employees who have provided positive consent allowing their employer to be the beneficiary of such policies. BankRI and First Ipswich are the beneficiaries of their respective policies. BankRI and First Ipswich utilize BOLI as tax-efficient financing for their benefit obligations to their employees, including their retirement obligations and Supplemental Executive Retirement Plans ("SERPs"). Since BankRI and First Ipswich are the primary beneficiaries of their respective insurance policies, increases in the cash value of the policies, as well as insurance proceeds received, are recorded in non-interest income and are not subject to income taxes. BOLI is recorded at the cash value of the policies, less any applicable cash surrender charges, and is reflected as an asset in the accompanying consolidated balance sheets. Cash proceeds, if any, are classified as cash flows from investing activities. The Company reviews the financial strength of the insurance carriers prior to the purchase of BOLI to ensure minimum credit ratings of at least investment grade. The financial strength of the carriers is reviewed at least annually, and BOLI with any individual carrier is limited to 10% of the Company's capital. Total BOLI is limited to 25% of the Company's capital.
Goodwill and Other Identified Intangible Assets	Goodwill and Other Identified Intangible Assets Goodwill represents the excess of the cost of an acquisition over the fair value of the net assets acquired. Goodwill and indefinite-lived identified intangible assets are not subject to amortization. Definite-lived identified intangible assets are assets resulting from acquisitions that are being amortized over their estimated useful lives. The recoverability of goodwill and identified intangible assets is evaluated for impairment at least annually. As part of this evaluation, the Company makes a qualitative assessment of whether it is more likely than not that the fair value of an acquired asset is greater than its carrying amount. If the Company qualitatively concludes that it is more likely than not that the fair value of an acquired asset is greater than its carrying amount, no further testing is necessary. If, however, the Company qualitatively concludes that the fair value of an acquired asset is less than its carrying value, the Company should recognize an impairment charge for the amount by which the carrying amount exceeds the fair value. The Company did not have any impairment of Goodwill and other identified intangible assets as of December 31, 2017 and 2016 .
OREO and Other Repossessed Assets	OREO and Other Repossessed Assets OREO and other repossessed assets consists of properties acquired through foreclosure, real estate acquired through acceptance of a deed in lieu of foreclosure and loans determined to be substantively repossessed. Real estate loans that are substantively repossessed include only those loans for which the Company has taken possession of the collateral. OREO and other repossessed assets which consist of vehicles and equipment, if any, are recorded initially at estimated fair value less costs to sell, resulting in a new cost basis. The amount by which the recorded investment in the loan exceeds the fair value (net of estimated cost to sell) of the foreclosed or repossessed asset is charged to the allowance for loan and lease losses. Such evaluations are based on an analysis of individual properties/assets as well as a general assessment of current real estate market conditions. Subsequent declines in the fair value of the foreclosed or repossessed asset below the new cost basis are recorded through the use of a valuation allowance. Subsequent increases in the fair value are recorded as reductions in the allowance, but not below zero. Rental revenue received on foreclosed or repossessed assets is included in other non-interest income, whereas operating expenses and changes in the valuation allowance relating to foreclosed and repossessed assets are included in other non-interest expense. Certain costs used to improve such properties are capitalized. Gains and losses from the sale of OREO and other repossessed assets are reflected in non-interest expense when realized. Together with nonperforming loans, OREO and repossessed assets comprise nonperforming assets.
Derivatives	Derivatives The Company utilizes loan level derivatives which consists of interest rate swap agreements and risk participation agreements as part of the Company's interest-rate risk management strategy for certain assets and liabilities and not for speculative purposes. Based on the Company's intended use for the loan level derivatives at inception, the Company designates the derivative as either an economic hedge of an asset or liability, or a hedging instrument subject to the hedge accounting provisions of FASB ASC Topic 815, "Derivatives and Hedging." Loan level derivatives and foreign exchange contracts entered into on behalf of our customers are designated as economic hedges and are recorded at fair value within other assets or liabilities. Changes in the fair value of these non hedging derivatives are recorded directly through earnings at each reporting period.
Transfer of Financial Assets	Transfer of Financial Assets Transfers of financial assets are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when (1) the assets have been isolated from the Company, (2) the transferee obtains the right (free of conditions that constrain it from taking advantage of that right) to pledge or exchange the transferred assets, and (3) the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
Securities Sold under Agreements to Repurchase	Securities Sold under Agreements to Repurchase The Company enters into sales of securities under agreements to repurchase with the Banks' commercial customers. These agreements are treated as financings, and the obligations to repurchase securities sold are reflected as a liability in the consolidated balance sheets. Securities pledged as collateral under agreements to repurchase are reflected as assets in the accompanying consolidated balance sheets.
Employee Benefits	Employee Benefits Costs related to the Company's 401(k) plan are recognized in current earnings. Costs related to the Company's nonqualified deferred compensation plan, SERPs and postretirement benefits are recognized over the vesting period or the related service periods of the participating employees. Changes in the funded status of postretirement benefits are recognized through comprehensive income in the year in which changes occur. Compensation expense for the Company's Employee Stock Ownership Program ("ESOP") is recorded at an amount equal to the shares allocated by the ESOP multiplied by the average fair market value of the shares during the year. The Company recognizes compensation expense ratably over the year based upon the Company's estimate of the number of shares expected to be allocated by the ESOP. The difference between the average fair market value and the cost of the shares allocated by the ESOP is recorded as an adjustment to additional paid-in capital. The fair value of restricted stock awards and stock option grants are determined as of the grant date and are recorded as compensation expense over the period in which the shares of restricted stock awards and stock options vest. Forfeitures are accounted for as they occur.
Fair Value Measurements	Fair Value Measurements ASC 820-10, "Fair Value Measurements and Disclosures," defines fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. A fair value measurement assumes that the transaction to sell the asset or transfer the liability occurs in the principal market for the asset or liability or, in the absence of a principal market, the most advantageous market for the asset or liability. The price in the principal (or most advantageous) market used to measure the fair value of the asset or liability is not adjusted for transaction costs. An orderly transaction is a transaction that assumes exposure to the market for a period prior to the measurement date to allow for marketing activities that are usual and customary for transactions involving such assets and liabilities. It is not a forced transaction. Market participants are buyers and sellers in the principal market that are independent, knowledgeable, able to transact, and willing to transact. A fair-value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs are included in ASC 820. The fair value hierarchy is as follows: Level 1: Inputs are unadjusted quoted prices in active markets for assets and liabilities identical to those reported at fair value. Level 2: Inputs other than quoted prices included within Level 1. Level 2 inputs are observable either directly or indirectly. These inputs might include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (such as interest rates, volatilities, prepayment speeds, credit risks, etc.) or inputs that are derived principally from or corroborated by market data by correlation or other means. Level 3: Inputs are unobservable inputs for an asset or liability that reflect an entity's own assumptions about the assumptions that market participants would use in pricing the assets or liabilities. These inputs are used to determine fair value only when observable inputs are not available.
Earnings per Common Share	Earnings per Common Share Basic earnings per share ("EPS") is computed by dividing net income by the weighted average number of shares of common stock outstanding for the applicable period, exclusive of Treasury shares, unearned ESOP shares and unvested shares of restricted stock. Diluted EPS is calculated after adjusting the denominator of the basic EPS calculation for the effect of all potential dilutive common shares outstanding during the period. The dilutive effects of options and unvested restricted stock awards are computed using the "treasury stock" method. Management evaluated the "two class" method and concluded that the method did not apply to the Company's EPS calculation.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Tax positions that are more likely than not to be sustained upon a tax examination are recognized in the Company's financial statements to the extent that the benefit is greater than 50% likely of being recognized. Interest resulting from underpayment of income taxes is classified as income tax expense in the first period the interest would begin accruing according to the provision of the relevant tax law. Penalties resulting from underpayment of income taxes are classified as income tax expense in the period for which the Company claims or expects to claim an uncertain tax position or in the period in which the Company's judgment changes regarding an uncertain tax position.
Treasury Stock	Treasury Stock Any shares repurchased under the Company's share repurchase programs were purchased in open-market transactions and are held as treasury stock. Treasury stock also consists of common stock withheld to satisfy federal, state and local income tax withholding requirements for employee restricted stock awards upon vesting. All treasury stock is held at cost.
Segment Reporting	Segment Reporting An operating segment is defined as a component of a business for which separate financial information is available that is evaluated regularly by the chief operating decision-maker in deciding how to allocate resources and evaluate performance. The Company is a bank holding company with subsidiaries engaged in the business of banking and activities closely related to banking. The Company's banking business provided substantially all of its total revenues and pre-tax income in 2017 , 2016 and 2015 . Therefore, the Company has determined to be a single segment.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2018, the FASB issued Accounting Standards Update (ASU) No. 2018-02, "Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income" was issued to address a narrow-scope financial reporting issue that arose as a consequence of the change in the tax law. On December 22, 2017, the U.S. federal government enacted a tax bill, H.R.1, An Act to Provide for Reconciliation Pursuant to Titles II and V of the Concurrent Resolution on the Budget for Fiscal Year 2018 (the “Tax Reform Act”). The ASU No. 2018-02 requires a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the newly enacted federal corporate income tax rate. The amount of the reclassification would be the difference between the historical corporate income tax rate of 35 percent and the newly enacted 21 percent corporate income tax rate. The ASU No. 2018-02 is effective for all entities for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years with early adoption permitted, including adoption in any interim period, for (i) public business entities for reporting periods for which financial statements have not yet been issued and (ii) all other entities for reporting periods for which financial statements have not yet been made available for issuance. The changes are required to be applied retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Cuts and Jobs Act of 2017 is recognized. Management early adopted this ASU as of December 31, 2017 , which resulted in the reclassification from accumulated other comprehensive loss to retained earnings totaling $1.1 million , reflected in the Consolidated Statements of Changes in Shareholders' Equity. In November 2017, the FASB issued ASU 2017-14, Income Statement-Reporting Comprehensive Income (Topic 220), Revenue Recognition (Topic 605), and Revenue from Contracts with Customers (Topic 606): Amendments to SEC Paragraphs Pursuant to Staff Accounting Bulletin No. 116 and SEC Release No. 33-10403. This ASU was issued to amend certain SEC paragraphs pursuant to the SEC Staff Accounting Bulletin No.116 and SEC Release No. 33-10403, which bring existing guidance into conformity with Topic 606, Revenue from Contract with Customers. The ASU was effective for annual periods beginning after December 15, 2017. Management has determined that this ASU does apply as of December 31, 2017 and has determined the impact to be immaterial. The standard will be adopted on January 1, 2018. In May 2017, the FASB issued ASU 2017-09, Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting. FASB issued this Update to address the diversity in practice as well as the cost and complexity when applying the guidance in Topic 718, Compensation - Stock Compensation, to a change to the terms or conditions of a share-based payment award. For public entities, this ASU is effective for annual reporting periods beginning after December 15, 2017. Management has evaluated this ASU and has determined that ASU 2017-09 does apply as of December 31, 2017 . In March 2017, the FASB issued Accounting Standards Update ASU 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost (Topic 715). This ASU was issued primarily to improve the presentation of net periodic pension cost and net periodic postretirement benefit cost. This ASU is effective for annual reporting periods beginning after December 15, 2017. Management has determined that this ASU does apply as of December 31, 2017 and has determined the impact to be immaterial. The standard will be adopted on January 1, 2018. In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350). This ASU was issued to simplify the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. For public entities, this ASU is effective for the fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted and application should be on a prospective basis. Management has evaluated this ASU and as of December 31, 2017 , the Company has adopted the ASU and determined the impact to be immaterial. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230). This ASU was issued to provide clarification and uniformity on the presentation and classification of certain cash receipts and cash payments in the statement of cash flows under Topic 230. Early adoption is permitted as of the fiscal years beginning after December 15, 2017, for public entities that file with the SEC. The Company adopted ASU 2016-15 effective January 1, 2017 and the adoption did not have a material impact on the Company’s consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The intent of this ASU is to replace the current GAAP method of calculating credit losses. Current GAAP uses a higher threshold at which likely losses can be calculated and recorded. The new process will require institutions to account for likely losses that originally would not have been part of the calculation. The calculation will incorporate future forecasting in addition to historical and current measures. For public entities that file with the SEC, this ASU is effective for the fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. This ASU must be applied prospectively to debt securities marked as other than temporarily impaired. A retrospective approach will be applied cumulatively to retained earnings. Early adoption is permitted as of the fiscal years beginning after December 15, 2018. Management has determined that ASU 2016-13 does apply, but has not determined the impact, if any, as of December 31, 2017 . In preparation for the adoption in 2019 of this ASU, management formed a steering committee to oversee the adoption of ASU 2016-13. The steering committee along with a project team has developed an approach for implementation and has selected a third party software service provider. The project team is in the testing phase of the third party software. In May 2016, the FASB issued ASU 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients. The intention of this ASU is to provide additional clarification on specific issues brought forth by the FASB and the International Accounting Standards Board Joint Transition Resource Group for Revenue Recognition in relation to Topic 606 and revenue recognition. The ASU was effective for annual periods beginning after December 15, 2017. Management has determined that ASU 2016-12 does apply as of December 31, 2017 . Management assembled a project team to address the changes pursuant to Topic 606. The work has been completed on the contracts and management believes there will be no material impact or significant changes in the timing of revenue recognition when considering the amended accounting guidance. The standard will be adopted on January 1, 2018 . In March 2016, the FASB issued ASU 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. This ASU was issued as part of the FASB Simplification Initiative which intends to reduce the complexity of GAAP while improving usefulness to users. The ASU was effective for annual periods beginning after December 15, 2016, and interim periods within those annual reporting periods with early adoption available. The Company adopted ASU 2016-09 effective January 1, 2017 and the adoption did not have a material impact on the Company’s consolidated financial statements. In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net). This ASU was issued to clarify how to recognize revenue depending on an entities position, in relation to another entity involved, on contracts with customers. The entity can either be a principal party or an agent, and must record revenue accordingly. The ASU was effective for annual periods beginning after December 15, 2017. Management has determined that ASU 2016-08 does apply as of December 31, 2017 . Management assembled a project team to address the changes pursuant to Topic 606. The work has been completed on the contracts and management believes there will be no material impact or significant changes in the timing of revenue recognition when considering the amended accounting guidance. The standard will be adopted on January 1, 2018 . In February 2016, FASB issued ASU 2016-02, Leases. This ASU requires lessees to put most leases on their balance sheet but recognize expenses on their income statements in a manner similar to current accounting. This ASU also eliminates current real estate-specific provisions for all companies. For lessors, this ASU modifies the classification criteria and the accounting for sales-type and direct financing leases. This ASU is effective for fiscal years beginning after December 15, 2018, including interim periods therein. Early adoption is permitted. Management believes that this ASU applies and has not determined the impact, if any, as of December 31, 2017 . Management has met to discuss the impact and will assemble a project team to assess steps required for adoption. The steps will include a review of third party lease software service providers. In January 2016, the FASB issued ASU 2016-01, Financial Instruments. This ASU significantly revises an entity’s accounting related to (1) the classification and measurement of investments in equity securities and (2) the presentation of certain fair value changes for financial liabilities measured at fair value. It also amends certain disclosure requirements associated with the fair value of financial instruments. This ASU is effective for fiscal years beginning after December 15, 2017, including interim periods therein. Management has determined that ASU 2016-01 does apply as of December 31, 2017 and management believes the impact to be immaterial. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date. This ASU was issued to defer the effective date of ASU 2014-09 for all entities by one year. In effect, public business entities, certain not-for-profit entities, and certain employee benefit plans should apply the guidance in ASU 2014-09 to annual reporting periods (including interim reporting periods within those period) beginning after December 15, 2017. Management has determined that ASU 2015-14 does apply as of December 31, 2017 . Management assembled a project team to address the changes pursuant to Topic 606. The work has been completed on the contracts and management believes there will be no material impact or significant changes in the timing of revenue recognition when considering the amended accounting guidance. The standard will be adopted on January 1, 2018 . In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). This ASU was issued to clarify the principles for recognizing revenue and to develop a common revenue standard for U.S. GAAP and IFRS that would: remove inconsistencies and weaknesses in revenue requirements, provide a more robust framework for addressing revenue issues, improve comparability of revenue recognition practices across entities industries, jurisdictions, and capital markets, provide more useful information to users of financial statements through improved disclosure requirements and simplify the preparation of financial statements by reducing the number of requirements to which an entity must refer. The main provisions in this ASU are 1) Identify the contract(s) with a customer, 2) Identify the performance obligations in the contract, 3) Determine the transaction price, 4) Allocate the transaction price to the performance obligations in the contract and 5) Recognize revenue when (or as) the entity satisfies a performance obligation. The ASU was effective for annual periods beginning after December 15, 2017. Management has determined that this ASU 2014-09 does apply as of December 31, 2017 . Management assembled a project team to address the changes pursuant to Topic 606. The work has been completed on the contracts and management believes there will be no material impact or significant changes in the timing of revenue recognition when considering the amended accounting guidance. The standard will be adopted on January 1, 2018 .

Cash and Short-Term Investments

Cash and Short-Term Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Short-term investments	Short-term investments are summarized as follows: At December 31, 2017 2016 (In Thousands) FRB interest bearing reserve $ 28,263 $ 19,952 FHLB overnight deposits 4,676 2,142 Federal funds sold 2,444 9,508 Total short-term investments $ 35,383 $ 31,602

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Schedule of securities available-for-sale securities	The following tables set forth investment securities available-for-sale and held-to-maturity at the dates indicated: At December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In Thousands) Investment securities available-for-sale: GSE debentures $ 151,483 $ 70 $ 1,629 $ 149,924 GSE CMOs 131,082 27 4,087 127,022 GSE MBSs 191,281 354 2,322 189,313 SBA commercial loan asset-backed securities 73 — 1 72 Corporate debt obligations 62,811 110 238 62,683 U.S. treasury bonds 8,785 7 62 8,730 Trust preferred securities 1,471 — 73 1,398 Marketable equity securities 978 13 9 982 Total investment securities available-for-sale $ 547,964 $ 581 $ 8,421 $ 540,124 Investment securities held-to-maturity: GSE debentures $ 41,612 $ — $ 811 $ 40,801 GSEs MBSs 13,923 — 218 13,705 Municipal obligations 53,695 159 337 53,517 Foreign government obligations 500 — — 500 Total investment securities held-to-maturity $ 109,730 $ 159 $ 1,366 $ 108,523 At December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value (In Thousands) Investment securities available-for-sale: GSE debentures $ 98,122 $ 188 $ 1,290 $ 97,020 GSE CMOs 161,483 37 3,480 158,040 GSE MBSs 214,946 794 2,825 212,915 SBA commercial loan asset-backed securities 107 — — 107 Corporate debt obligations 48,308 360 183 48,485 U.S. treasury bonds 4,801 — 64 4,737 Trust preferred securities 1,469 — 111 1,358 Marketable equity securities 966 15 9 972 Total investment securities available-for-sale $ 530,202 $ 1,394 $ 7,962 $ 523,634 Investment securities held-to-maturity: GSE debentures $ 14,735 $ — $ 634 $ 14,101 GSEs MBSs 17,666 — 187 17,479 Municipal obligations 54,219 5 1,020 53,204 Foreign government obligations 500 — 13 487 Total investment securities held-to-maturity $ 87,120 $ 5 $ 1,854 $ 85,271
Investment securities in a continuous unrealized loss position	Investment securities as of December 31, 2017 and 2016 that have been in a continuous unrealized loss position for less than twelve months or twelve months or longer are as follows: At December 31, 2017 Less than Twelve Months Twelve Months or Longer Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses (In Thousands) Investment securities available-for-sale: GSE debentures $ 120,409 $ 1,263 $ 12,481 $ 366 $ 132,890 $ 1,629 GSE CMOs 2,862 34 123,548 4,053 126,410 4,087 GSE MBSs 94,985 753 74,782 1,569 169,767 2,322 SBA commercial loan asset-backed securities 34 — 33 1 67 1 Corporate debt obligations 30,978 154 2,423 84 33,401 238 U.S. Treasury bonds 4,767 62 — — 4,767 62 Trust preferred securities — — 1,398 73 1,398 73 Marketable equity securities — — 503 9 503 9 Temporarily impaired investment securities available-for-sale 254,035 2,266 215,168 6,155 469,203 8,421 Investment securities held-to-maturity: GSE debentures 26,594 281 14,208 530 40,802 811 GSEs MBSs 1,996 15 11,674 203 13,670 218 Municipal obligations 30,542 235 7,408 102 37,950 337 Foreign government obligations — — 500 — 500 — Temporarily impaired investment securities held-to-maturity 59,132 531 33,790 835 92,922 1,366 Total temporarily impaired investment securities $ 313,167 $ 2,797 $ 248,958 $ 6,990 $ 562,125 $ 9,787 At December 31, 2016 Less than Twelve Months Twelve Months or Longer Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses (In Thousands) Investment securities available-for-sale: GSE debentures $ 67,216 $ 1,291 $ — $ — $ 67,216 $ 1,291 GSE CMOs 118,450 2,162 38,852 1,318 157,302 3,480 GSE MBSs 149,687 2,821 198 3 149,885 2,824 SBA commercial loan asset-backed securities — — 72 — 72 — Corporate debt obligations 7,953 183 — — 7,953 183 U.S. Treasury bonds 4,737 64 — — 4,737 64 Trust preferred securities — — 1,358 111 1,358 111 Marketable equity securities 503 9 — — 503 9 Temporarily impaired investment securities available-for-sale 348,546 6,530 40,480 1,432 389,026 7,962 Investment securities held-to-maturity: GSE debentures 14,101 634 — — 14,101 634 GSEs MBSs 17,289 187 — — 17,289 187 Municipal obligations 50,098 1,020 — — 50,098 1,020 Foreign government obligations 487 13 — — 487 13 Temporarily impaired investment securities held-to-maturity 81,975 1,854 — — 81,975 1,854 Total temporarily impaired investment securities $ 430,521 $ 8,384 $ 40,480 $ 1,432 $ 471,001 $ 9,816
Schedule of maturities of the investments in debt securities	The final stated maturities of the debt securities are as follows for the periods indicated: At December 31, 2017 2016 Amortized Cost Estimated Fair Value Weighted Average Rate Amortized Cost Estimated Fair Value Weighted Average Rate (Dollars in Thousands) Investment securities available-for-sale: Within 1 year $ 23,612 $ 23,652 2.27% $ 13 $ 13 0.17% After 1 year through 5 years 142,772 142,029 2.05% 81,524 81,833 2.14% After 5 years through 10 years 136,746 134,978 2.06% 128,956 127,952 2.03% Over 10 years 243,856 238,483 2.06% 318,743 312,864 2.03% $ 546,986 $ 539,142 2.07% $ 529,236 $ 522,662 2.04% Investment securities held-to-maturity: Within 1 year $ 918 $ 916 0.78% $ 190 $ 190 1.00% After 1 year through 5 years 58,335 57,939 1.74% 23,012 22,750 1.30% After 5 years through 10 years 36,589 35,998 1.79% 46,442 45,042 1.75% Over 10 years 13,888 13,670 1.98% 17,476 17,289 2.11% $ 109,730 $ 108,523 1.78% $ 87,120 $ 85,271 1.70%
Schedule of sales of investment securities	Sales of investment and restricted equity securities are summarized as follows: Year Ended December 31, 2017 (In Thousands) Sales of debt securities $ — Sales of marketable and restricted equity securities 11,393 Gross gains from sales 11,612 Gross losses from sales (219 ) Gain on sales of securities, net $ 11,393

Restricted Equity Securities (T

Restricted Equity Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Restricted Investments Note [Abstract]
Components of investments in the restricted equity securities of various entities	Investments in the restricted equity securities of various entities are as follows: At December 31, 2017 2016 (In Thousands) FHLBB stock $ 42,427 $ 47,284 FRB stock 16,842 16,752 Other restricted equity securities 100 475 $ 59,369 $ 64,511

Loans and Leases (Tables)

Loans and Leases (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Summary of loan and lease balances for the originated and acquired portfolios	The following tables present loan and lease balances and weighted average coupon rates for the originated and acquired loan and lease portfolios at the dates indicated: At December 31, 2017 Originated Acquired Total Balance Weighted Average Coupon Balance Weighted Average Coupon Balance Weighted Average Coupon (Dollars In Thousands) Commercial real estate loans: Commercial real estate $ 2,069,392 4.17 % $ 105,577 4.37 % $ 2,174,969 4.18 % Multi-family mortgage 735,921 4.09 % 24,749 4.48 % 760,670 4.10 % Construction 140,138 4.58 % — — % 140,138 4.58 % Total commercial real estate loans 2,945,451 4.17 % 130,326 4.39 % 3,075,777 4.18 % Commercial loans and leases: Commercial 696,825 4.35 % 8,179 5.77 % 705,004 4.37 % Equipment financing 861,974 7.28 % 4,514 5.92 % 866,488 7.27 % Condominium association 52,619 4.49 % — — % 52,619 4.49 % Total commercial loans and leases 1,611,418 5.92 % 12,693 5.82 % 1,624,111 5.92 % Consumer loans: Residential mortgage 604,897 3.81 % 55,168 4.28 % 660,065 3.85 % Home equity 314,189 4.16 % 41,765 4.62 % 355,954 4.21 % Other consumer 14,667 5.51 % 105 18.00 % 14,772 5.60 % Total consumer loans 933,753 3.95 % 97,038 4.44 % 1,030,791 4.00 % Total loans and leases $ 5,490,622 4.65 % $ 240,057 4.49 % $ 5,730,679 4.64 % At December 31, 2016 Originated Acquired Total Balance Weighted Average Coupon Balance Weighted Average Coupon Balance Weighted Average Coupon (Dollars In Thousands) Commercial real estate loans: Commercial real estate $ 1,907,254 3.95 % $ 143,128 4.24 % $ 2,050,382 3.97 % Multi-family mortgage 701,450 3.79 % 29,736 4.53 % 731,186 3.82 % Construction 136,785 3.79 % 214 3.67 % 136,999 3.79 % Total commercial real estate loans 2,745,489 3.90 % 173,078 4.29 % 2,918,567 3.92 % Commercial loans and leases: Commercial 621,285 4.11 % 14,141 5.44 % 635,426 4.14 % Equipment financing 793,702 7.06 % 6,158 5.86 % 799,860 7.05 % Condominium association 60,122 4.39 % — — % 60,122 4.39 % Total commercial loans and leases 1,475,109 5.71 % 20,299 5.57 % 1,495,408 5.71 % Consumer loans: Residential mortgage 555,430 3.67 % 68,919 3.98 % 624,349 3.70 % Home equity 289,361 3.50 % 52,880 4.26 % 342,241 3.62 % Other consumer 18,171 5.48 % 128 17.92 % 18,299 5.57 % Total consumer loans 862,962 3.65 % 121,927 4.12 % 984,889 3.71 % Total loans and leases $ 5,083,560 4.38 % $ 315,304 4.31 % $ 5,398,864 4.38 %
Schedule of activity in the accretable yield for acquired loan portfolio	The following table summarizes activity in the accretable yield for the acquired loan portfolio for the periods indicated: Year Ended December 31, 2017 2016 2015 (In Thousands) Balance at beginning of year $ 14,353 $ 20,796 $ 32,044 Accretion (7,801 ) (6,781 ) (10,467 ) Reclassification from/(to) nonaccretable difference as a result from changes in expected cash flows 3,970 338 (781 ) Balance at end of year $ 10,522 $ 14,353 $ 20,796
Summary of the change in the total amounts of loans and advances, all of which were performing, to directors, executive officers and their affiliates	The following table summarizes the change in the total amounts of loans and advances, to directors, executive officers and their affiliates for the periods indicated. All loans were performing as of December 31, 2017 . Year Ended December 31, 2017 2016 (In Thousands) Balance at beginning of year $ 43,458 $ 37,375 New loans granted during the year 13,554 8,352 Advances on lines of credit 473 26 Repayments (9,544 ) (2,295 ) Balance at end of year $ 47,941 $ 43,458

Allowance for Loan and Lease 38

Allowance for Loan and Lease Losses (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Schedule of changes in the allowance for loan and lease losses	The following tables present the changes in the allowance for loan and lease losses and the recorded investment in loans and leases by portfolio segment for the periods indicated: Year Ended December 31, 2017 Commercial Real Estate Commercial Consumer Total (In Thousands) Balance at December 31, 2016 $ 27,645 $ 20,906 $ 5,115 $ 53,666 Charge-offs (494 ) (14,914 ) (403 ) (15,811 ) Recoveries 476 1,158 319 1,953 (Credit) provision for loan and lease losses (515 ) 19,183 116 18,784 Balance at December 31, 2017 $ 27,112 $ 26,333 $ 5,147 $ 58,592 Year Ended December 31, 2016 Commercial Real Estate Commercial Consumer Total (In Thousands) Balance at December 31, 2015 $ 30,151 $ 22,018 $ 4,570 $ 56,739 Charge-offs (2,169 ) (10,516 ) (1,982 ) (14,667 ) Recoveries — 642 750 1,392 (Credit) provision for loan and lease losses (337 ) 8,762 1,777 10,202 Balance at December 31, 2016 $ 27,645 $ 20,906 $ 5,115 $ 53,666 Year Ended December 31, 2015 Commercial Real Estate Commercial Consumer Unallocated Total (In Thousands) Balance at December 31, 2014 $ 29,594 $ 15,957 $ 5,690 $ 2,418 $ 53,659 Charge-offs (550 ) (3,634 ) (2,370 ) — (6,554 ) Recoveries — 667 1,544 — 2,211 Provision (credit) for loan and lease losses 1,107 9,028 (294 ) (2,418 ) 7,423 Balance at December 31, 2015 $ 30,151 $ 22,018 $ 4,570 $ — $ 56,739
Provisions for credit losses	The provisions for credit losses are set forth below for the periods indicated: Originated Acquired Total Year Ended December 31, Year Ended December 31, Year Ended December 31, 2017 2016 2015 2017 2016 2015 2017 2016 2015 (In Thousands) Provision (credit) for loan and lease losses: Commercial real estate $ (343 ) $ (750 ) $ 1,459 $ (172 ) $ 413 $ (352 ) $ (515 ) $ (337 ) $ 1,107 Commercial 18,899 8,469 9,077 284 293 (49 ) 19,183 8,762 9,028 Consumer 273 1,263 (763 ) (157 ) 514 469 116 1,777 (294 ) Unallocated — — (2,418 ) — — — — — (2,418 ) Total provision for loan and lease losses 18,829 8,982 7,355 (45 ) 1,220 68 18,784 10,202 7,423 Unfunded credit commitments 204 151 28 — — — 204 151 28 Total provision (credit) for credit losses $ 19,033 $ 9,133 $ 7,383 $ (45 ) $ 1,220 $ 68 $ 18,988 $ 10,353 $ 7,451
Summary of the recorded investments by credit quality indicator, by loan class	The following tables present the recorded investment in loans in each class as of December 31, 2017 by credit quality indicator. At December 31, 2017 Commercial Real Estate Multi- Family Mortgage Construction Commercial Equipment Financing Condominium Association Other Consumer Total (In Thousands) Originated: Loan rating: Pass $ 2,054,376 $ 735,313 $ 139,278 $ 670,265 $ 850,006 $ 52,619 $ 14,628 $ 4,516,485 OAEM 8,889 — — 7,691 3,630 — — 20,210 Substandard 5,926 608 860 17,681 5,012 — 39 30,126 Doubtful 201 — — 1,188 3,326 — — 4,715 Total originated 2,069,392 735,921 140,138 696,825 861,974 52,619 14,667 4,571,536 Acquired: Loan rating: Pass 94,244 24,459 — 6,643 4,501 — 104 129,951 OAEM 9,839 — — 265 — — 1 10,105 Substandard 1,494 290 — 1,271 13 — — 3,068 Doubtful — — — — — — — — Total acquired 105,577 24,749 — 8,179 4,514 — 105 143,124 Total loans $ 2,174,969 $ 760,670 $ 140,138 $ 705,004 $ 866,488 $ 52,619 $ 14,772 $ 4,714,660 As of December 31, 2017 , there were no loans categorized as definite loss. At December 31, 2017 Residential Mortgage Home Equity ($ In Thousands) Originated: Loan-to-value ratio: Less than 50% $ 153,373 23.2 % $ 148,137 41.6 % 50% - 69% 265,328 40.2 % 75,099 21.1 % 70% - 79% 168,272 25.5 % 63,742 17.9 % 80% and over 16,547 2.5 % 27,122 7.6 % Data not available* 1,377 0.2 % 89 — % Total originated 604,897 91.6 % 314,189 88.2 % Acquired: Loan-to-value ratio: Less than 50% 16,521 2.5 % 25,312 7.1 % 50%—69% 19,182 2.9 % 13,883 3.9 % 70%—79% 10,507 1.6 % 943 0.3 % 80% and over 7,893 1.2 % 582 0.2 % Data not available* 1,065 0.2 % 1,045 0.3 % Total acquired 55,168 8.4 % 41,765 11.8 % Total loans $ 660,065 100.0 % $ 355,954 100.0 % _______________________________________________________________________________ * Represents in process general ledger accounts for which data are not available. The following tables present the recorded investment in loans in each class as of December 31, 2016 by credit quality indicator. At December 31, 2016 Commercial Real Estate Multi- Family Mortgage Construction Commercial Equipment Financing Condominium Association Other Consumer Total (In Thousands) Originated: Loan rating: Pass $ 1,899,162 $ 700,046 $ 136,607 $ 583,940 $ 786,050 $ 60,122 $ 12,018 $ 4,177,945 OAEM 1,538 — 178 8,675 824 — — 11,215 Substandard 6,288 1,404 — 28,595 4,848 — 12 41,147 Doubtful 266 — — 75 1,980 — — 2,321 Total originated 1,907,254 701,450 136,785 621,285 793,702 60,122 12,030 4,232,628 Acquired: Loan rating: Pass 131,850 29,153 214 10,312 6,158 — 128 177,815 OAEM 1,408 270 — 249 — — — 1,927 Substandard 9,768 313 — 3,017 — — — 13,098 Doubtful 102 — — 563 — — — 665 Total acquired 143,128 29,736 214 14,141 6,158 — 128 193,505 Total loans $ 2,050,382 $ 731,186 $ 136,999 $ 635,426 $ 799,860 $ 60,122 $ 12,158 $ 4,426,133 As of December 31, 2016 , there were no loans categorized as definite loss. At December 31, 2016 Residential Mortgage Home Equity ($ In Thousands) Originated: Loan-to-value ratio: Less than 50% $ 138,030 22.1 % $ 153,679 44.9 % 50%—69% 229,799 36.9 % 61,553 18.1 % 70%—79% 162,614 26.0 % 49,987 14.6 % 80% and over 21,859 3.5 % 23,317 6.8 % Data not available* 3,128 0.5 % 825 0.2 % Total originated 555,430 89.0 % 289,361 84.6 % Acquired: Loan-to-value ratio: Less than 50% 17,809 2.9 % 32,334 9.4 % 50%—69% 24,027 3.8 % 15,059 4.4 % 70%—79% 14,030 2.2 % 3,069 0.9 % 80% and over 10,069 1.6 % 1,016 0.3 % Data not available* 2,984 0.5 % 1,402 0.4 % Total acquired 68,919 11.0 % 52,880 15.4 % Total loans $ 624,349 100.0 % $ 342,241 100.0 % _______________________________________________________________________________ * Represents in process general ledger accounts for which data are not available.
Information regarding troubled debt restructuring loans	The following table sets forth information regarding troubled debt restructured loans and leases at the dates indicated: At December 31, 2017 At December 31, 2016 (In Thousands) Troubled debt restructurings: On accrual $ 16,241 $ 13,883 On nonaccrual 9,770 11,919 Total troubled debt restructurings $ 26,011 $ 25,802 The following table presents information regarding foreclosed residential real estate property for the periods indicated: At December 31, 2017 At December 31, 2016 (In Thousands) Foreclosed residential real estate property held by the creditor $ — $ 251 Recorded investment in mortgage loans collateralized by residential real estate property that are in the process of foreclosure 633 1,213
Information regarding the aging of past due loans, by loan class	The following tables present an age analysis of the recorded investment in total loans and leases as of December 31, 2017 and 2016 . At December 31, 2017 Past Due Loans and Leases Past Due Greater Than 90 Days and Accruing 31-60 Days 61-90 Days Greater Than 90 Days Total Current Total Loans and Leases Nonaccrual Loans and Leases (In Thousands) Originated: Commercial real estate loans: Commercial real estate $ 3,294 $ 391 $ 1,843 $ 5,528 $ 2,063,864 $ 2,069,392 $ — $ 3,182 Multi-family mortgage 6,141 2,590 — 8,731 727,190 735,921 — 608 Construction 6,537 330 860 7,727 132,411 140,138 — 860 Total commercial real estate loans 15,972 3,311 2,703 21,986 2,923,465 2,945,451 — 4,650 Commercial loans and leases: Commercial 1,344 597 7,724 9,665 687,160 696,825 — 10,365 Equipment financing 3,214 2,494 3,203 8,911 853,063 861,974 224 8,106 Condominium association 857 262 — 1,119 51,500 52,619 — — Total commercial loans and leases 5,415 3,353 10,927 19,695 1,591,723 1,611,418 224 18,471 Consumer loans: Residential mortgage 1,256 166 728 2,150 602,747 604,897 — 1,979 Home equity 643 19 32 694 313,495 314,189 1 132 Other consumer 238 20 28 286 14,381 14,667 — 43 Total consumer loans 2,137 205 788 3,130 930,623 933,753 1 2,154 Total originated loans and leases $ 23,524 $ 6,869 $ 14,418 $ 44,811 $ 5,445,811 $ 5,490,622 $ 225 $ 25,275 (Continued) At December 31, 2017 Past Due Loans and Leases Past Due Greater Than 90 Days and Accruing 31-60 Days 61-90 Days Greater Than 90 Days Total Current Total Loans and Leases Nonaccrual Loans and Leases (In Thousands) Acquired: Commercial real estate loans: Commercial real estate $ 1,008 $ — $ 656 $ 1,664 $ 103,913 $ 105,577 $ 586 $ 131 Multi-family mortgage — — 3 3 24,746 24,749 3 — Total commercial real estate loans 1,008 — 659 1,667 128,659 130,326 589 131 Commercial loans and leases: Commercial — 44 1,022 1,066 7,113 8,179 17 1,254 Equipment financing — — 13 13 4,501 4,514 13 — Total commercial loans and leases — 44 1,035 1,079 11,614 12,693 30 1,254 Consumer loans: Residential mortgage — 463 1,990 2,453 52,715 55,168 1,990 — Home equity 508 — 186 694 41,071 41,765 186 612 Other consumer — — — — 105 105 — — Total consumer loans 508 463 2,176 3,147 93,891 97,038 2,176 612 Total acquired loans and leases 1,516 507 3,870 5,893 234,164 240,057 2,795 1,997 Total loans and leases $ 25,040 $ 7,376 $ 18,288 $ 50,704 $ 5,679,975 $ 5,730,679 $ 3,020 $ 27,272 At December 31, 2016 Past Due Loans and Leases Past Due Greater Than 90 Days and Accruing 31-60 Days 61-90 Days Greater Than 90 Days Total Current Total Loans and Leases Nonaccrual Loans and Leases (In Thousands) Originated: Commercial real estate loans: Commercial real estate $ 1,525 $ 2,075 $ 429 $ 4,029 $ 1,903,225 $ 1,907,254 $ 2 $ 5,035 Multi-family mortgage 2,296 — 291 2,587 698,863 701,450 — 1,404 Construction 547 — — 547 136,238 136,785 — — Total commercial real estate loans 4,368 2,075 720 7,163 2,738,326 2,745,489 2 6,439 Commercial loans and leases: Commercial 5,396 815 10,014 16,225 605,060 621,285 — 20,587 Equipment financing 2,983 1,444 5,341 9,768 783,934 793,702 — 6,758 Condominium association 266 — — 266 59,856 60,122 — — Total commercial loans and leases 8,645 2,259 15,355 26,259 1,448,850 1,475,109 — 27,345 Consumer loans: Residential mortgage 3,745 2,294 163 6,202 549,228 555,430 — 2,455 Home equity 25 219 5 249 289,112 289,361 3 128 Other consumer 549 87 16 652 17,519 18,171 — 149 Total consumer loans 4,319 2,600 184 7,103 855,859 862,962 3 2,732 Total originated loans and leases $ 17,332 $ 6,934 $ 16,259 $ 40,525 $ 5,043,035 $ 5,083,560 $ 5 $ 36,516 (Continued) At December 31, 2016 Past Due Loans and Leases Past Due Greater Than 90 Days and Accruing 31-60 Days 61-90 Days Greater Than 90 Days Total Current Total Loans and Leases Nonaccrual Loans and Leases (In Thousands) Acquired: Commercial real estate loans: Commercial real estate $ 925 $ — $ 4,011 $ 4,936 $ 138,192 $ 143,128 $ 3,786 $ 305 Multi-family mortgage — — — — 29,736 29,736 — — Construction — — — — 214 214 — — Total commercial real estate loans 925 — 4,011 4,936 168,142 173,078 3,786 305 Commercial loans and leases: Commercial 306 — 2,651 2,957 11,184 14,141 264 2,387 Equipment financing — — — — 6,158 6,158 — — Total commercial loans and leases 306 — 2,651 2,957 17,342 20,299 264 2,387 Consumer loans: Residential mortgage — 318 2,865 3,183 65,736 68,919 2,820 46 Home equity 288 97 339 724 52,156 52,880 202 823 Other consumer — 1 — 1 127 128 — — Total consumer loans 288 416 3,204 3,908 118,019 121,927 3,022 869 Total acquired loans and leases 1,519 416 9,866 11,801 303,503 315,304 7,072 3,561 Total loans and leases $ 18,851 $ 7,350 $ 26,125 $ 52,326 $ 5,346,538 $ 5,398,864 $ 7,077 $ 40,077
Impaired loans and leases, by loan and leases class	The following tables include the recorded investment and unpaid principal balances of impaired loans and leases with the related allowance amount, if applicable, for the originated and acquired loan and lease portfolios at the dates indicated. Also presented are the average recorded investments in the impaired loans and leases and the related amount of interest recognized during the period that the impaired loans were impaired. At December 31, 2017 At December 31, 2016 Recorded (1) Unpaid Related Recorded Investment (2) Unpaid Related (In Thousands) Originated: With no related allowance recorded: Commercial real estate $ 9,978 $ 9,962 $ — $ 9,113 $ 9,104 $ — Commercial 24,906 25,040 — 39,269 39,210 — Consumer 3,508 3,500 — 4,823 4,815 — Total originated with no related allowance recorded 38,392 38,502 — 53,205 53,129 — With an allowance recorded: Commercial real estate 3,056 3,056 — 3,984 3,984 28 Commercial 8,912 8,862 3,105 605 605 97 Total originated with an allowance recorded 11,968 11,918 3,105 4,589 4,589 125 Total originated impaired loans and leases 50,360 50,420 3,105 57,794 57,718 125 Acquired: With no related allowance recorded: Commercial real estate 1,880 1,880 — 10,400 10,400 — Commercial 1,594 1,594 — 3,948 3,948 — Consumer 4,736 4,736 — 6,384 6,399 — Total acquired with no related allowance recorded 8,210 8,210 — 20,732 20,747 — With an allowance recorded: Consumer 115 115 22 253 253 27 Total acquired with an allowance recorded 115 115 22 253 253 27 Total acquired impaired loans and leases 8,325 8,325 22 20,985 21,000 27 Total impaired loans and leases $ 58,685 $ 58,745 $ 3,127 $ 78,779 $ 78,718 $ 152 ___________________________________________________________________________ (1) Includes originated and acquired nonaccrual loans of $24.9 million and $2.0 million , respectively as of December 31, 2017 . (2) Includes originated and acquired nonaccrual loans of $34.1 million and $3.6 million , respectively as of December 31, 2016 . Year Ended December 31, 2017 December 31, 2016 December 31, 2015 Average Interest Average Interest Average Interest (In Thousands) Originated: With no related allowance recorded: Commercial real estate $ 10,125 $ 72 $ 6,608 $ 152 $ 3,999 $ 86 Commercial 26,439 225 23,445 600 15,143 641 Consumer 3,565 14 4,126 76 4,267 65 Total originated with no related allowance recorded 40,129 311 34,179 828 23,409 792 With an allowance recorded: Commercial real estate 3,058 38 4,715 195 5,132 197 Commercial 13,604 — 9,915 6 5,650 10 Consumer — — 124 — 84 — Total originated with an allowance recorded 16,662 38 14,754 201 10,866 207 Total originated impaired loans and leases 56,791 349 48,933 1,029 34,275 999 Acquired: With no related allowance recorded: Commercial real estate 1,996 1 8,906 151 9,200 125 Commercial 1,610 5 4,255 75 4,428 65 Consumer 4,784 17 7,537 68 7,837 62 Total acquired with no related allowance recorded 8,390 23 20,698 294 21,465 252 With an allowance recorded: Commercial real estate — — 1,093 — 713 — Commercial — — 364 — 638 — Consumer 116 1 431 8 249 8 Total acquired with an allowance recorded 116 1 1,888 8 1,600 8 Total acquired impaired loans and leases 8,506 24 22,586 302 23,065 260 Total impaired loans and leases $ 65,297 $ 373 $ 71,519 $ 1,331 $ 57,340 $ 1,259
Schedule of the impaired and non-impaired loans and leases, by loan and leases class	The following tables present information regarding impaired and non-impaired loans and leases at the dates indicated: At December 31, 2017 Commercial Real Estate Commercial Consumer Total (In Thousands) Allowance for Loan and Lease Losses: Originated: Individually evaluated for impairment $ — $ 3,105 $ — $ 3,105 Collectively evaluated for impairment 26,366 23,078 5,003 54,447 Total originated loans and leases 26,366 26,183 5,003 57,552 Acquired: Individually evaluated for impairment — — 22 22 Collectively evaluated for impairment 145 13 17 175 Acquired with deteriorated credit quality 601 137 105 843 Total acquired loans and leases 746 150 144 1,040 Total allowance for loan and lease losses $ 27,112 $ 26,333 $ 5,147 $ 58,592 Loans and Leases: Originated: Individually evaluated for impairment $ 13,031 $ 29,386 $ 3,070 $ 45,487 Collectively evaluated for impairment 2,932,420 1,582,032 930,683 5,445,135 Total originated loans and leases 2,945,451 1,611,418 933,753 5,490,622 Acquired: Individually evaluated for impairment — 1,487 1,867 3,354 Collectively evaluated for impairment 34,244 6,399 55,921 96,564 Acquired with deteriorated credit quality 96,082 4,807 39,250 140,139 Total acquired loans and leases 130,326 12,693 97,038 240,057 Total loans and leases $ 3,075,777 $ 1,624,111 $ 1,030,791 $ 5,730,679 At December 31, 2016 Commercial Real Estate Commercial Consumer Total (In Thousands) Allowance for Loan and Lease Losses: Originated: Individually evaluated for impairment $ 28 $ 97 $ — $ 125 Collectively evaluated for impairment 26,830 20,682 4,776 52,288 Total originated loans and leases 26,858 20,779 4,776 52,413 Acquired: Individually evaluated for impairment — — 27 27 Collectively evaluated for impairment 221 13 34 268 Acquired with deteriorated credit quality 566 114 278 958 Total acquired loans and leases 787 127 339 1,253 Total allowance for loan and lease losses $ 27,645 $ 20,906 $ 5,115 $ 53,666 Loans and Leases: Originated: Individually evaluated for impairment $ 13,097 $ 37,637 $ 4,711 $ 55,445 Collectively evaluated for impairment 2,732,392 1,437,472 858,251 5,028,115 Total originated loans and leases 2,745,489 1,475,109 862,962 5,083,560 Acquired: Individually evaluated for impairment 690 3,047 2,028 5,765 Collectively evaluated for impairment 47,599 10,863 70,115 128,577 Acquired with deteriorated credit quality 124,789 6,389 49,784 180,962 Total acquired loans and leases 173,078 20,299 121,927 315,304 Total loans and leases $ 2,918,567 $ 1,495,408 $ 984,889 $ 5,398,864
Summary of loans restructured or defaulted	The recorded investment in troubled debt restructurings and the associated specific allowances for loan and lease losses, in the originated and acquired loan and lease portfolios, that were modified during the periods indicated, are as follows. At and for the Year Ended December 31, 2017 Recorded Investment Specific Allowance for Loan and Lease Losses Defaulted (1) Number of Loans/ Leases At Modification At End of Period Nonaccrual Loans and Leases Number of Loans/ Leases Recorded Investment (Dollars in Thousands) Originated: Commercial real estate 1 $ 189 $ 189 $ — $ — — $ — Commercial 10 7,861 3,911 191 2,189 2 1,361 Equipment financing 16 2,687 2,901 137 1,440 1 188 Total originated 27 10,737 7,001 328 3,629 3 1,549 ______________________________________________________________________ (1) Includes loans and leases that have been modified within the past twelve months and subsequently had payment defaults during the period indicated. There were no acquired loans and leases that met the definition of a troubled debt restructured during the twelve months ended December 31, 2017 . At and for the Year Ended December 31, 2016 Recorded Investment Specific Allowance for Loan and Lease Losses Defaulted (1) Number of Loans/ Leases At Modification At End of Period Nonaccrual Loans and Leases Number of Loans/ Leases Recorded Investment (Dollars in Thousands) Originated: Multi-family mortgage 2 $ 1,155 $ 1,114 $ — $ 1,114 — $ — Commercial 22 9,701 6,015 — 6,015 2 364 Equipment financing 3 797 524 — 524 2 341 Total originated 27 11,653 7,653 — 7,653 4 705 Acquired: Home equity 5 374 368 20 145 — — Total acquired 5 374 368 20 145 — — Total loans and leases 32 $ 12,027 $ 8,021 $ 20 $ 7,798 4 $ 705 ______________________________________________________________________ (1) Includes loans and leases that have been modified within the past twelve months and subsequently had payment defaults during the period indicated. At and for the Year Ended December 31, 2015 Recorded Investment Specific Allowance for Loan and Lease Losses Defaulted (1) Number of Loans/ Leases At Modification At End of Period Nonaccrual Loans and Leases Number of Loans/ Leases Recorded Investment (Dollars in Thousands) Originated: Commercial real estate — $ — $ — $ — $ — — $ — Commercial 9 5,757 5,497 119 258 1 237 Equipment financing 1 112 100 — — — — Residential mortgage 1 100 150 — 151 — — Home equity 3 353 298 — 99 1 28 Total originated 14 6,322 6,045 119 508 2 265 Acquired: Commercial 4 642 632 — — 1 11 Home equity 2 200 196 — — 1 24 Total acquired 6 842 828 — — 2 35 Total loans and leases 20 $ 7,164 $ 6,873 $ 119 $ 508 4 $ 300 ______________________________________________________________________ (1) Includes loans and leases that have been modified within the past twelve months and subsequently had payment defaults during the period indicated.
Schedule of troubled debt restructurings by type of modification	The following table sets forth the Company's end-of-period balances for troubled debt restructurings that were modified during the periods indicated, by type of modification. Year Ended December 31, 2017 2016 2015 (In Thousands) Loans with one modification: Extended maturity $ 2,810 $ 599 $ 2,215 Adjusted principal 19 249 — Interest only 174 1,493 1,335 Combination maturity, principal, interest rate 1,914 5,455 692 Total loans modified once $ 4,917 $ 7,796 $ 4,242 Loans with more than one modification: Extended maturity $ 1,910 $ 225 $ 2,598 Combination maturity, principal, interest rate 174 — 33 Total loans modified more than once $ 2,084 $ 225 $ 2,631

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Schedule of premises and equipment	Premises and equipment consist of the following: At December 31, Estimated Useful Life 2017 2016 (In Thousands) (In Years) Land $ 11,057 $ 7,562 NA Fine art 495 472 NA Computer equipment 9,728 9,004 3 Vehicles 126 221 3 to 5 Core processing system and software 19,791 19,433 3 to 7.5 Furniture, fixtures and equipment 14,226 13,439 5 to 25 Office building and improvements 88,283 84,835 10 to 40 Total 143,706 134,966 Accumulated depreciation and amortization 63,423 58,790 Total premises and equipment $ 80,283 $ 76,176

Goodwill and Other Intangible40

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of changes in the carrying value of goodwill	The changes in the carrying value of goodwill for the periods indicated were as follows: Year Ended December 31, 2017 2016 2015 (In Thousands) Balance at beginning of year $ 137,890 $ 137,890 $ 137,890 Additions — — — Adjustments to original goodwill — — — Balance at end of year $ 137,890 $ 137,890 $ 137,890
Schedule of composition of other intangible assets	The following is a summary of the Company's other intangible assets: At December 31, 2017 At December 31, 2016 Gross Accumulated Carrying Gross Accumulated Carrying (In Thousands) Other intangible assets: Core deposits $ 36,172 $ 31,217 $ 4,955 $ 36,172 $ 29,128 $ 7,044 Trade name 1,600 511 1,089 1,600 511 1,089 Trust relationship 1,568 1,568 — 1,568 1,568 — Other intangible 442 442 — 442 442 — Total other intangible assets $ 39,782 $ 33,738 $ 6,044 $ 39,782 $ 31,649 $ 8,133
Schedule of estimated aggregate future amortization expense for intangible assets	The estimated aggregate future amortization expense for other intangible assets for each of the next five years and thereafter is as follows: Year ended December 31: Amount (In Thousands) 2018 $ 1,669 2019 1,295 2020 944 2021 601 2022 299 Thereafter 147 Total $ 4,955

Other Assets (Tables)

Other Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of information regarding the Company's investments in affordable housing projects	Further information regarding the Company's investments in affordable housing projects follows: At December 31, 2017 2016 (In Thousands) Investments in affordable housing projects included in other assets $ 11,432 $ 11,565 Unfunded commitments related to affordable housing projects included in other liabilities 1,933 1,686 Investment in affordable housing tax credits 1,745 1,753 Investment in affordable housing tax benefits 653 598 For the year ended December 31, 2017 2016 2015 (In Thousands) Investment amortization included in provision for income taxes $ 1,844 $ 1,726 $ 1,654 Amount recognized as income tax benefit 623 598 656

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Summary of deposits	A summary of deposits follows: December 31, 2017 December 31, 2016 Amount Weighted Average Rate Amount Weighted Average Rate (Dollars in Thousands) Demand checking accounts $ 942,583 — % $ 900,474 — % NOW accounts 350,568 0.07 % 323,160 0.07 % Savings accounts 646,359 0.25 % 613,061 0.20 % Money market accounts 1,724,363 0.56 % 1,733,359 0.47 % Total core deposit accounts 3,663,873 0.31 % 3,570,054 0.27 % Certificate of deposit accounts maturing: Within six months 363,866 0.93 % 345,339 0.77 % After six months but within 1 year 342,500 1.09 % 233,470 0.83 % After 1 year but within 2 years 300,921 1.48 % 264,993 1.08 % After 2 years but within 3 years 90,805 1.87 % 84,673 1.56 % After 3 years but within 4 years 57,926 1.79 % 52,522 1.88 % After 4 years but within 5 years 50,380 2.02 % 59,910 1.78 % 5+ Years 1,072 1.03 % 115 1.66 % Total certificate of deposit accounts 1,207,470 1.27 % 1,041,022 1.04 % Total deposits $ 4,871,343 0.55 % $ 4,611,076 0.44 %
Schedule of interest expense on deposit balances	Interest expense on deposit balances is summarized as follows: Year Ended December 31, 2017 2016 2015 (In Thousands) Interest-bearing deposits: NOW accounts $ 225 $ 209 $ 179 Savings accounts 1,297 1,322 1,094 Money market accounts 8,863 7,549 6,935 Certificate of deposit accounts 12,903 10,990 9,272 Total interest-bearing deposits $ 23,288 $ 20,070 $ 17,480

Borrowed Funds (Tables)

Borrowed Funds (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of borrowed funds	Borrowed funds are comprised of the following: At December 31, 2017 2016 (In Thousands) Advances from the FHLBB $ 889,909 $ 910,774 Subordinated debentures and notes 83,271 83,105 Other borrowed funds 47,639 50,207 Total borrowed funds $ 1,020,819 $ 1,044,086
Schedule of interest expense on borrowed funds	Interest expense on borrowed funds for the periods indicated is as follows: Year Ended December 31, 2017 2016 2015 (In Thousands) Advances from the FHLBB $ 11,330 $ 10,760 $ 9,950 Subordinated debentures and notes 5,081 5,038 5,001 Other borrowed funds 170 116 114 Total interest expense on borrowed funds $ 16,581 $ 15,914 $ 15,065
Schedule of federal home loan bank advances	FHLBB advances mature as follows: At December 31, 2017 2016 Amount Callable Amount Weighted Average Rate Amount Callable Amount Weighted Average Rate (Dollars in Thousands) Within 1 year $ 514,314 $ 55,000 1.43 % $ 651,489 $ 75,705 1.22 % Over 1 year to 2 years 279,928 115,000 1.70 % 168,598 290,311 1.44 % Over 2 years to 3 years 16,026 — 0.47 % 14,354 — 0.09 % Over 3 years to 4 years 30,849 — 0.41 % 85 — 2.04 % Over 4 years to 5 years 33,217 — 0.30 % 1,110 — 3.07 % Over 5 years 15,575 — 3.95 % 75,138 — 1.08 % $ 889,909 $ 170,000 1.47 % $ 910,774 $ 366,016 1.24 %
Schedule of information concerning repurchase agreements during the period	Information concerning other borrowed funds is as follows for the periods indicated below: Year Ended December 31, 2017 2016 (Dollars In Thousands) Outstanding at end of year $ 47,639 $ 50,207 Average outstanding for the year 45,908 41,053 Maximum outstanding at any month-end 54,064 50,207 Weighted average rate at end of year 0.46 % 0.14 % Weighted average rate paid for the year 0.37 % 0.27 %
Summary of subordinated debentures	The following table summarizes the Company's subordinated debentures and notes at the dates indicated. Carrying Amount Issue Date Rate Maturity Date Next Call Date December 31, 2017 December 31, 2016 (Dollars in Thousands) June 26, 2003 Variable; 3-month LIBOR + 3.10% June 26, 2033 March 26, 2018 $ 4,778 $ 4,752 March 17, 2004 Variable; 3-month LIBOR + 2.79% March 17, 2034 March 19, 2018 4,668 4,628 September 15, 2014 6.0% Fixed-to-Variable; 3-month LIBOR + 3.315% September 15, 2029 September 15, 2024 73,825 73,725 Total $ 83,271 $ 83,105

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of financial instruments with off-balance sheet risk	Financial instruments with off-balance-sheet risk at the dates indicated follow: At December 31, 2017 2016 (In Thousands) Financial instruments whose contract amounts represent credit risk: Commitments to originate loans and leases: Commercial real estate $ 76,653 $ 27,750 Commercial 83,270 71,716 Residential mortgage 28,745 28,179 Unadvanced portion of loans and leases 571,668 580,416 Unused lines of credit: Home equity 407,552 340,682 Other consumer 34,191 13,157 Other commercial 323 208 Unused letters of credit: Financial standby letters of credit 12,422 11,720 Performance standby letters of credit 736 516 Commercial and similar letters of credit 184 785 Loan level derivatives: Receive fixed, pay variable 494,659 383,780 Pay fixed, receive variable 494,659 383,780 Risk participation-out agreements 36,627 16,961 Risk participation-in agreements 3,825 — Foreign exchange contracts: Buys foreign currency, sells U.S. currency 1,495 195 Sells foreign currency, buys U.S. currency 1,502 195
Schedule of future minimum rental payments under noncancellable operating leases	A summary of future minimum rental payments under such leases at the dates indicated follows: Year ended December 31, Minimum Rental Payments (In Thousands) 2018 $ 4,921 2019 4,053 2020 3,497 2021 2,988 2022 2,743 Thereafter 10,138 Total $ 28,340

Earnings per Share (EPS) (Table

Earnings per Share (EPS) (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Reconciliation of basic EPS and diluted EPS	The following table is a reconciliation of basic EPS and diluted EPS: For the year ended December 31, 2017 2016 2015 Basic Fully Diluted Basic Fully Diluted Basic Fully Diluted (Dollars in Thousands, Except Per Share Amounts) Numerator: Net income $ 50,518 $ 50,518 $ 52,362 $ 52,362 $ 49,782 $ 49,782 Denominator: Weighted average shares outstanding 74,459,508 74,459,508 70,261,954 70,261,954 70,098,561 70,098,561 Effect of dilutive securities — 351,900 — 182,129 — 137,307 Adjusted weighted average shares outstanding 74,459,508 74,811,408 70,261,954 70,444,083 70,098,561 70,235,868 EPS $ 0.68 $ 0.68 $ 0.74 $ 0.74 $ 0.71 $ 0.71

Comprehensive Income_(Loss) (Ta

Comprehensive Income/(Loss) (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of changes in accumulated other comprehensive (loss) income by component, net of tax	Changes in accumulated other comprehensive loss by component, net of tax, were as follows for the periods indicated: Year Ended December 31, 2017 Investment Securities Available-for-Sale Postretirement Benefits Accumulated Other Comprehensive Loss (In Thousands) Balance at December 31, 2016 $ (4,213 ) $ 395 $ (3,818 ) Other comprehensive loss (817 ) (252 ) (1,069 ) Balance at December 31, 2017 $ (5,030 ) $ 143 $ (4,887 ) Year Ended December 31, 2016 Investment Securities Available-for-Sale Postretirement Benefits Accumulated Other Comprehensive Loss (In Thousands) Balance at December 31, 2015 $ (2,827 ) $ 351 $ (2,476 ) Other comprehensive (loss) income (1,386 ) 44 (1,342 ) Balance at December 31, 2016 $ (4,213 ) $ 395 $ (3,818 ) Year Ended December 31, 2015 Investment Securities Available-for-Sale Postretirement Benefits Accumulated Other Comprehensive Loss (In Thousands) Balance at December 31, 2014 $ (1,733 ) $ 111 $ (1,622 ) Other comprehensive (loss) income (1,094 ) 240 (854 ) Balance at December 31, 2015 $ (2,827 ) $ 351 $ (2,476 )

Derivatives and Hedging Activ47

Derivatives and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of fair value and classification of derivative financial instruments on the consolidated balance sheets and the effect of the derivative financial instruments on the consolidated income statements	The following tables presents the Company's customer related derivative positions for the periods indicated below for those derivatives not designated as hedging. Notional Amount Maturing Number of Positions Less than 1 year Less than 2 years Less than 3 years Less than 4 years Thereafter Total Fair Value December 31, 2017 (Dollars In Thousands) Loan level derivatives Receive fixed, pay variable 66 $ 3,903 $ 2,036 $ 27,992 $ — $ 460,728 $ 494,659 $ 8,865 Pay fixed, receive variable 66 3,903 2,036 27,992 — 460,728 494,659 8,865 Risk participation-out agreements 8 — — 8,613 — 28,014 36,627 65 Risk participation-in agreements 1 — — — — 3,825 3,825 10 Foreign exchange contracts Buys foreign currency, sells U.S. currency 22 $ 1,495 $ — $ — $ — $ — $ 1,495 $ 65 Sells foreign currency, buys U.S. currency 44 1,502 — — — — 1,502 72 Notional Amount Maturing Number of Positions Less than 1 year Less than 2 years Less than 3 years Less than 4 years Thereafter Total Fair Value December 31, 2016 (Dollars In Thousands) Loan level derivatives Receive fixed, pay variable 54 $ — $ 4,025 $ 2,141 $ 29,501 $ 348,113 $ 383,780 $ 9,738 Pay fixed, receive variable 54 — 4,025 2,141 29,501 348,113 383,780 9,738 Risk participation-out agreements 5 — — — 9,078 7,883 16,961 20 Foreign exchange contracts Buys foreign currency, sells U.S. currency 3 $ 195 $ — $ — $ — $ — $ 195 $ — Sells foreign currency, buys U.S. currency 3 195 — — — — 195 — As of December 31, 2016 , the Company held no risk participation-in agreements and the fair value of the foreign exchange contracts was nominal. Refer also to Note 21, "Fair Value of Financial Instruments." Changes in the fair value are recognized directly in the Company's consolidated statements of income and are included in other non-interest income in the consolidated statements of income. The table below presents the gain (loss) recognized in income due to changes in the fair value for the year ended December 31, 2017 . There were no gains (losses) recognized in income due to changes in the fair value for the year ended December 31, 2016 . Year Ended December 31, 2017 (In Thousands) Gain recognized in income on: Loan level derivatives $ — Risk participation-out agreements 55 Foreign exchange contracts 7 Total $ 62
Schedule of offsetting derivatives and amounts subject to master netting agreements not offset in the audited consolidated balance sheet	The tables below present the offsetting of derivatives and amounts subject to master netting agreements not offset in the consolidated balance sheet at the dates indicated. At December 31, 2017 Gross Gross Amounts Statement of Financial Position Net Amounts Presented in the Statement of Financial Position Gross Amounts Not Offset in the Statement of Financial Position Net Amount Financial Instruments Pledged Cash Collateral Pledged (In Thousands) Asset derivatives Loan level derivatives $ 8,865 $ — $ 8,865 $ — $ — $ 8,865 Risk participation-out agreements 65 — 65 — — 65 Foreign exchange contracts 72 — 72 — — 72 Total $ 9,002 $ — $ 9,002 $ — $ — $ 9,002 Liability derivatives Loan level derivatives $ 8,865 $ — $ 8,865 $ 25,159 $ 1,510 $ — Risk participation-in agreements 10 — 10 — — — Foreign exchange contracts 65 — 65 — — — Total $ 8,940 $ — $ 8,940 $ 25,159 $ 1,510 $ — At December 31, 2016 Gross Gross Amounts Statement of Financial Position Net Amounts Presented in the Statement of Financial Position Gross Amounts Not Offset in the Statement of Financial Position Net Amount Financial Instruments Pledged Cash Collateral Pledged (In Thousands) Asset derivatives Loan level derivatives $ 9,738 $ — $ 9,738 $ — $ — $ 9,738 Risk participation-out agreements 20 — 20 — — 20 Total $ 9,758 $ — $ 9,758 $ — $ — $ 9,758 Liability derivatives Loan level derivatives $ 9,738 $ — $ 9,738 $ 33,744 $ 720 $ — Total $ 9,738 $ — $ 9,738 $ 33,744 $ 720 $ —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of income tax expense	Income tax expense is comprised of the following amounts: Year Ended December 31, 2017 2016 2015 (In Thousands) Current provision: Federal $ 27,825 $ 22,954 $ 23,340 State 5,013 5,116 4,774 Total current provision 32,838 28,070 28,114 Deferred provision: Federal 10,209 2,271 679 State 589 51 560 Total deferred provision 10,798 2,322 1,239 Total provision for income taxes $ 43,636 $ 30,392 $ 29,353
Schedule of reconciliation of income tax expense	Total provision for income taxes differed from the amounts computed by applying the statutory U.S. federal income tax rate 35.0% to income before tax expense as a result of the following: Year Ended December 31, 2017 2016 2015 (Dollars In Thousands) Expected income tax expense at statutory federal tax rate $ 34,039 $ 29,965 $ 28,603 State taxes, net of federal income tax benefit 3,641 3,358 3,467 Bank-owned life insurance (364 ) (368 ) (367 ) Tax-exempt interest income (873 ) (826 ) (622 ) Income attributable to noncontrolling interest in subsidiary (870 ) (1,163 ) (994 ) Merger and acquisition expense 138 — — Tax Reform Act Adjustment 8,965 — — Investments in affordable housing projects (653 ) (640 ) (526 ) Other, net (387 ) 66 (208 ) Total provision for income taxes $ 43,636 $ 30,392 $ 29,353 Effective income tax rate 44.9 % 35.5 % 35.9 %
Schedule of the tax effects of temporary differences that give rise to significant portions of the deferred tax assets and liabilities	The tax effects of temporary differences that give rise to significant portions of the deferred tax assets and liabilities at the dates indicated are as follows: At December 31, 2017 2016 (In Thousands) Deferred tax assets: Allowance for loan and lease losses $ 15,618 $ 21,655 Deferred compensation 1,032 5,659 Supplemental Executive Retirement Plans 2,805 4,127 Unrealized loss on investment securities available-for-sale 1,728 2,355 Net operating loss carryforwards 415 999 Postretirement benefits 400 465 Nonaccrual interest 551 621 Accrued expense 563 828 Restricted stock and stock option plans 621 573 Employee stock ownership plan 124 147 Other 67 61 Total gross deferred tax assets 23,924 37,490 Deferred tax liabilities: Identified intangible assets and goodwill 2,778 4,660 Deferred loan origination costs, net 2,918 3,370 Depreciation 1,866 2,193 Prepaid expense 109 1,045 Acquisition fair value adjustments 1,192 975 Total gross deferred tax liabilities 8,863 12,243 Net deferred tax asset $ 15,061 $ 25,247

Regulatory Capital Requiremen49

Regulatory Capital Requirements (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Schedule of the Company's and the bank's actual and required capital amounts and ratios	Actual Minimum Required for Capital Adequacy Purposes Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer Minimum Required to be Considered “Well-Capitalized” Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio Amount Ratio (Dollars in Thousands) At December 31, 2017: Brookline Bancorp, Inc. Common equity Tier 1 capital ratio (1) $ 669,238 12.02 % $ 250,547 4.50 % $ 389,739 7.00 % N/A N/A Tier 1 leverage capital ratio (2) 687,299 10.43 % 263,585 4.00 % 263,585 4.00 % N/A N/A Tier 1 risk-based capital ratio (3) 687,299 12.34 % 334,181 6.00 % 473,423 8.50 % N/A N/A Total risk-based capital ratio (4) 821,373 14.75 % 445,490 8.00 % 584,706 10.50 % N/A N/A Brookline Bank Common equity Tier 1 capital ratio (1) $ 414,282 11.56 % $ 161,269 4.50 % $ 250,863 7.00 % $ 232,944 6.50 % Tier 1 leverage capital ratio (2) 423,035 10.35 % 163,492 4.00 % 163,492 4.00 % 204,365 5.00 % Tier 1 risk-based capital ratio (3) 423,035 11.81 % 214,920 6.00 % 304,471 8.50 % 286,561 8.00 % Total risk-based capital ratio (4) 463,986 12.95 % 286,632 8.00 % 376,205 10.50 % 358,290 10.00 % BankRI Common equity Tier 1 capital ratio (1) $ 193,849 11.38 % $ 76,654 4.50 % $ 119,239 7.00 % $ 110,722 6.50 % Tier 1 leverage capital ratio (2) 193,849 9.16 % 84,650 4.00 % 84,650 4.00 % 105,813 5.00 % Tier 1 risk-based capital ratio (3) 193,849 11.38 % 102,205 6.00 % 144,791 8.50 % 136,273 8.00 % Total risk-based capital ratio (4) 210,025 12.33 % 136,269 8.00 % 178,853 10.50 % 170,337 10.00 % First Ipswich Common equity Tier 1 capital ratio (1) $ 37,502 13.38 % $ 12,613 4.50 % $ 19,620 7.00 % $ 18,218 6.50 % Tier 1 leverage capital ratio (2) 37,502 9.44 % 15,891 4.00 % 15,891 4.00 % 19,863 5.00 % Tier 1 risk-based capital ratio (3) 37,502 13.38 % 16,817 6.00 % 23,824 8.50 % 22,423 8.00 % Total risk-based capital ratio (4) 40,625 14.50 % 22,414 8.00 % 29,418 10.50 % 28,017 10.00 % _______________________________________________________________________________ (1) Common equity Tier 1 capital ratio is calculated by dividing common equity Tier 1 capital by risk-weighted assets. The ratio was established as part of the implementation of Basel III, effective January 1, 2015. (2) Tier 1 leverage capital ratio is calculated by dividing Tier 1 capital by average assets. (3) Tier 1 risk-based capital ratio is calculated by dividing Tier 1 capital by risk-weighted assets. (4) Total risk-based capital ratio is calculated by dividing total capital by risk-weighted assets. The following table presents actual and required capital ratios as of December 31, 2016 for the Company and the Banks under the regulatory capital rules then in effect. Actual Minimum Required for Capital Adequacy Purposes Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer Minimum Required to be Considered “Well-Capitalized” Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio Amount Ratio (Dollars in Thousands) At December 31, 2016: Brookline Bancorp, Inc. Common equity Tier 1 capital ratio (1) $ 559,644 10.48 % $ 240,305 4.50 % $ 373,808 7.00 % N/A N/A Tier 1 leverage capital ratio (2) 575,830 9.16 % 251,454 4.00 % 251,454 4.00 % N/A N/A Tier 1 risk-based capital ratio (3) 575,830 10.79 % 320,202 6.00 % 453,620 8.50 % N/A N/A Total risk-based capital ratio (4) 704,675 13.20 % 427,076 8.00 % 560,537 10.50 % N/A N/A Brookline Bank Common equity Tier 1 capital ratio (1) $ 384,759 11.31 % $ 153,087 4.50 % $ 238,136 7.00 % $ 221,126 6.50 % Tier 1 leverage capital ratio (2) 391,964 10.07 % 155,696 4.00 % 155,696 4.00 % 194,620 5.00 % Tier 1 risk-based capital ratio (3) 391,964 11.53 % 203,971 6.00 % 288,959 8.50 % 271,961 8.00 % Total risk-based capital ratio (4) 428,966 12.61 % 272,143 8.00 % 357,188 10.50 % 340,179 10.00 % BankRI Common equity Tier 1 capital ratio (1) $ 182,202 10.94 % $ 74,946 4.50 % $ 116,583 7.00 % $ 108,255 6.50 % Tier 1 leverage capital ratio (2) 182,202 8.97 % 81,249 4.00 % 81,249 4.00 % 101,562 5.00 % Tier 1 risk-based capital ratio (3) 182,202 10.94 % 99,928 6.00 % 141,565 8.50 % 133,237 8.00 % Total risk-based capital ratio (4) 197,702 11.87 % 133,245 8.00 % 174,884 10.50 % 166,556 10.00 % First Ipswich Common equity Tier 1 capital ratio (1) $ 33,433 12.61 % $ 11,931 4.50 % $ 18,559 7.00 % $ 17,234 6.50 % Tier 1 leverage capital ratio (2) 33,433 9.23 % 14,489 4.00 % 14,489 4.00 % 18,111 5.00 % Tier 1 risk-based capital ratio (3) 33,433 12.61 % 15,908 6.00 % 22,536 8.50 % 21,210 8.00 % Total risk-based capital ratio (4) 36,053 13.60 % 21,208 8.00 % 27,835 10.50 % 26,510 10.00 % _______________________________________________________________________________ (1) Common equity Tier 1 capital ratio is calculated by dividing common equity Tier 1 capital by risk-weighted assets. The ratio was established as part of the implementation of Basel III, effective January 1, 2015. (2) Tier 1 leverage capital ratio is calculated by dividing Tier 1 capital by average assets. (3) Tier 1 risk-based capital ratio is calculated by dividing Tier 1 capital by risk-weighted assets. (4) Total risk-based capital ratio is calculated by dividing total capital by risk-weighted assets.

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Reconciliation of Changes in Plan Assets and Benefit Obligation	The following table presents the change in plan assets and change in benefit obligation: Year Ended December 31, 2017 2016 2015 (In Thousands) Change in plan assets: Fair value of plan assets at beginning of year $ — $ — $ — Employer contributions 19 21 25 Benefits paid (19 ) (21 ) (25 ) Fair value of plan assets at end of year $ — $ — $ — Change in benefit obligation: Benefit obligation at beginning of year $ 1,135 $ 1,188 $ 1,562 Service cost 49 48 55 Interest cost 43 45 49 Estimated benefits paid (19 ) (21 ) (25 ) Actuarial loss (gain) 326 (125 ) (453 ) Benefit obligation at end of year $ 1,534 $ 1,135 $ 1,188
Schedule of the components of net periodic postretirement benefit cost and other amounts recognized in other comprehensive income	The following table presents the components of net periodic postretirement benefit cost and other amounts recognized in other comprehensive income: Year Ended December 31, 2017 2016 2015 (In Thousands) Net periodic benefit expense: Service cost $ 49 $ 48 $ 55 Interest cost 43 45 49 Prior service credit (21 ) (21 ) (21 ) Actuarial gain (47 ) (42 ) (20 ) Net periodic benefit expense $ 24 $ 30 $ 63 Changes in postretirement benefit obligation recognized in other comprehensive income: Net actuarial (loss) gain (401 ) $ 90 $ 374 Prior service credit (21 ) (21 ) (21 ) Total pre-tax changes in postretirement benefit obligation recognized in other comprehensive income $ (422 ) $ 69 $ 353
Schedule of effect of 1% change in assumed health care cost trend rates	A 1% change in assumed health care cost trend rates would have the following effects: Year Ended 1% Increase 1% Decrease (In Thousands) Effect on total service and interest cost components of net periodic postretirement benefit costs $ 23 $ (18 ) Effect on the accumulated postretirement benefit obligation 356 (277 )
Activity under recognition and retention plans	Activity under the recognition and retention plans was as follows: Restricted Stock Awards Outstanding Weighted Average Price per Share (Dollars in Thousands, Except Per Share Amounts) Recognition and Retention Plans: Outstanding at December 31, 2016 476,854 $ 10.90 Granted 186,782 14.65 Vested (193,267 ) 10.24 Forfeited / Canceled (15,086 ) 16.10 Outstanding at December 31, 2017 455,283 $ 12.64 Unrecognized compensation cost $ 3,022 Weighted average remaining recognition period (months) 30
Schedule of stock option activity	Activity under the option plans was as follows: Options Outstanding Weighted Average Exercise Price Per Share Aggregate Intrinsic Value Weighted Average Contractual Term (In Years) (Dollars in Thousands, Except Per Share Amounts) Employee Stock Options: Outstanding at December 31, 2016 197,345 $ 10.18 Granted — — Exercised (147,345 ) 10.53 Forfeited / Canceled — — Outstanding at December 31, 2017 50,000 $ 10.80 $ 245 2.8 Exercisable at December 31, 2017 50,000 $ 10.80 $ 245 2.8

Fair Value of Financial Instr51

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Fair value of assets and liabilities
Schedule of quantitative information about significant unobservable inputs (Level 3) for assets measured at fair value on a recurring basis	The table below presents quantitative information about significant unobservable inputs (Level 3) for assets measured at fair value on a recurring basis at the dates indicated. Fair Value Valuation Technique At December 31, 2017 At December 31, 2016 (Dollars in Thousands) Collateral-dependent impaired loans and leases $ 21,195 $ 27,282 Appraisal of collateral (1) Other real estate owned 3,235 618 Appraisal of collateral (1) _______________________________________________________________________________ (1) Fair value is generally determined through independent appraisals of the underlying collateral. The Company may also use another available source of collateral assessment to determine a reasonable estimate of the fair value of the collateral. Appraisals may be adjusted by management for qualitative factors such as economic factors and estimated liquidation expenses. The range of the unobservable inputs used may vary but is generally 0% - 10% on the discount for costs to sell and 0% - 15% on appraisal adjustments.
Summary of the carrying values and estimated fair values	The following table presents the carrying amount, estimated fair value, and placement in the fair value hierarchy of the Company's financial instruments at the dates indicated. This table excludes financial instruments for which the carrying amount approximates fair value. Financial assets for which the fair value approximates carrying value include cash and cash equivalents, restricted equity securities, and accrued interest receivable. Financial liabilities for which the fair value approximates carrying value include non-maturity deposits, short-term borrowings, and accrued interest payable. There were no transfers between levels during 2017 . Fair Value Measurements Carrying Value Estimated Fair Value Level 1 Inputs Level 2 Inputs Level 3 Inputs (In Thousands) At December 31, 2017 Financial assets: Investment securities held-to-maturity: GSE debentures $ 41,612 $ 40,801 $ — $ 40,801 $ — GSE MBSs 13,923 13,705 — 13,705 — Municipal obligations 53,695 53,517 — 53,517 — Foreign government obligations 500 500 — 500 Loans held-for-sale 2,628 2,628 — 2,628 — Loans and leases, net 5,672,087 5,594,543 — — 5,594,543 Restricted equity securities 59,369 59,369 — — 59,369 Financial liabilities: Certificates of deposit 1,207,470 1,198,201 — 1,198,201 — Borrowed funds 1,020,819 995,335 — 995,335 — At December 31, 2016 Financial assets: Investment securities held-to-maturity: GSE debentures $ 14,735 $ 14,101 $ — $ 14,101 $ — GSE MBSs 17,666 17,479 — 17,479 — Municipal obligations 54,219 53,204 — 53,204 — Foreign government obligations 500 487 — — 487 Loans held-for-sale 13,078 13,078 — 13,078 — Loans and leases, net 5,345,198 5,195,312 — — 5,195,312 Restricted equity securities 64,511 75,589 — — 75,589 Financial liabilities: Certificates of deposit 1,041,022 1,042,653 — 1,042,653 — Borrowed funds 1,044,086 1,030,753 — 1,030,753 —
Recurring basis
Fair value of assets and liabilities
Schedule of assets and liabilities measured at fair value on a recurring and non-recurring basis	The following table set forth the carrying value of assets and liabilities measured at fair value on a recurring basis at December 31, 2017 and 2016 : Carrying Value as of December 31, 2017 Level 1 Level 2 Level 3 Total (In Thousands) Assets: Investment securities available-for-sale: GSE debentures $ — $ 149,924 $ — $ 149,924 GSE CMOs — 127,022 — 127,022 GSE MBSs — 189,313 — 189,313 SBA commercial loan asset-backed securities — 72 — 72 Corporate debt obligations — 62,683 — 62,683 U.S. Treasury bonds — 8,730 — 8,730 Trust preferred securities — 1,398 — 1,398 Marketable equity securities 982 — — 982 Total investment securities available-for-sale $ 982 $ 539,142 $ — $ 540,124 Loan level derivatives $ — $ 8,865 $ — $ 8,865 Risk participation-out agreements — 65 — 65 Foreign exchange contracts — 72 — 72 Liabilities: Loan level derivatives $ — $ 8,865 $ — $ 8,865 Risk participation-in agreements — 10 — 10 Foreign exchange contracts — 65 — 65 Carrying Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (In Thousands) Assets: Investment securities available-for-sale: GSE debentures $ — $ 97,020 $ — $ 97,020 GSE CMOs — 158,040 — 158,040 GSE MBSs — 212,915 — 212,915 SBA commercial loan asset-backed securities — 107 — 107 Corporate debt obligations — 48,485 — 48,485 U.S. Treasury bonds — 4,737 — 4,737 Trust preferred securities — 1,358 — 1,358 Marketable equity securities 972 — — 972 Total investment securities available-for-sale $ 972 $ 522,662 $ — $ 523,634 Loan level derivatives $ — $ 9,738 $ — $ 9,738 Risk participation-out agreements — 20 — 20 Liabilities: Loan level derivatives $ — $ 9,738 $ — $ 9,738
Nonrecurring basis
Fair value of assets and liabilities
Schedule of assets and liabilities measured at fair value on a recurring and non-recurring basis	Assets and liabilities measured at fair value on a non-recurring basis as of December 31, 2017 and 2016 are summarized below: Carrying Value as of December 31, 2017 Level 1 Level 2 Level 3 Total (In Thousands) Assets measured at fair value on a non-recurring basis: Collateral-dependent impaired loans and leases $ — $ — $ 21,195 $ 21,195 OREO — — 3,235 3,235 Repossessed assets — 1,184 — 1,184 Total assets measured at fair value on a non-recurring basis $ — $ 1,184 $ 24,430 $ 25,614 Carrying Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (In Thousands) Assets measured at fair value on a non-recurring basis: Collateral-dependent impaired loans and leases $ — $ — $ 27,282 $ 27,282 OREO — — 618 618 Repossessed assets — 781 — 781 Total assets measured at fair value on a non-recurring basis $ — $ 781 $ 27,900 $ 28,681

Condensed Parent Company Fina52

Condensed Parent Company Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Balance Sheets	Balance Sheets At December 31, 2017 2016 (In Thousands) ASSETS Cash and due from banks $ 5,511 $ 32,220 Short-term investments 32 32 Total cash and cash equivalents 5,543 32,252 ESOP loan to Brookline Bank 1,252 1,502 Intercompany loan to Brookline Bank 80,000 — Restricted equity securities 100 100 Premises and equipment, net 6,032 6,946 Investment in subsidiaries, at equity 753,056 701,943 Goodwill 35,267 35,267 Other assets 6,627 8,259 Total assets $ 887,877 $ 786,269 LIABILITIES AND STOCKHOLDERS' EQUITY Borrowed funds $ 83,271 $ 83,105 Deferred tax liability 608 243 Accrued expenses and other liabilities 168 7,377 Total liabilities 84,047 90,725 Stockholders' equity: Common stock, $0.01 par value; 200,000,000 shares authorized; 81,695,695 shares issued and 75,744,445 shares issued, respectively 817 757 Additional paid-in capital 699,976 616,734 Retained earnings, partially restricted 161,217 136,671 Accumulated other comprehensive loss (5,950 ) (3,818 ) Treasury stock, at cost; 4,440,665 shares and 4,707,096 shares, respectively (51,454 ) (53,837 ) Unallocated common stock held by ESOP; 142,332 shares and 176,688 shares, respectively (776 ) (963 ) Total stockholders' equity 803,830 695,544 Total liabilities and stockholders' equity $ 887,877 $ 786,269
Statements of Income	Statements of Income Year Ended December 31, 2017 2016 2015 (In Thousands) Interest and dividend income: Dividend income from subsidiaries $ 7,317 $ 109 $ — Marketable and restricted equity securities — — 97 ESOP loan to Brookline Bank 120 141 162 Intercompany loan to Brookline Bank 532 — — Total interest and dividend income 7,969 250 259 Interest expense: Borrowed funds 5,123 5,080 5,063 Net interest income 2,846 (4,830 ) (4,804 ) Non-interest income: Other — 15 5 Total non-interest income — 15 5 Non-interest expense: Compensation and employee benefits 391 82 205 Occupancy 1,584 1,582 22 Equipment and data processing (1) (1,011 ) (1,190 ) 687 Directors' fees 453 700 688 Franchise taxes 180 180 113 Insurance 528 490 490 Professional services 470 245 185 Advertising and marketing 4 — — Merger and acquisition expense 411 — — Other (2) (1,224 ) (1,300 ) (1,289 ) Total non-interest expense 1,786 789 1,101 Loss before income taxes 1,060 (5,604 ) (5,900 ) Credit for income taxes (1,944 ) (1,779 ) (1,854 ) Loss before equity in undistributed income of subsidiaries 3,004 (3,825 ) (4,046 ) Equity in undistributed income of subsidiaries 47,514 56,187 53,828 Net income $ 50,518 $ 52,362 $ 49,782 _______________________________________________________________________________ (1) The Parent Company received a net benefit in 2017 and 2016 from the intercompany allocation of expense that is eliminated in consolidation. (2) The Parent Company received a net benefit in 2017, 2016 and 2015 from the intercompany allocation of expense that is eliminated in consolidation.
Statements of Cash Flows	Statements of Cash Flows Year Ended December 31, 2017 2016 2015 (In Thousands) Cash flows from operating activities: Net income attributable to parent company $ 50,518 $ 52,362 $ 49,782 Adjustments to reconcile net income to net cash provided from operating activities: Equity in undistributed income of subsidiaries (47,514 ) (56,187 ) (53,828 ) Depreciation of premises and equipment 2,856 2,735 2,728 Amortization of debt issuance costs 100 101 100 Other operating activities, net (5,885 ) 30,895 2,479 Net cash provided from operating activities 75 29,906 1,261 Cash flows from investing activities: Repayment of ESOP loan by Brookline Bank 250 250 250 Issuance of intercompany loan to Brookline Bank (80,000 ) — — Purchase of premises and equipment (1,942 ) (641 ) (742 ) Net cash used for investing activities (81,692 ) (391 ) (492 ) Cash flows from financing activities: Proceeds from issuance of common stock 81,943 — — Payment of dividends on common stock (27,035 ) (25,366 ) (24,967 ) Net cash provided from (used for) financing activities 54,908 (25,366 ) (24,967 ) Net (decrease) increase in cash and cash equivalents (26,709 ) 4,149 (24,198 ) Cash and cash equivalents at beginning of year 32,252 28,103 52,301 Cash and cash equivalents at end of year $ 5,543 $ 32,252 $ 28,103

Quarterly Results of Operatio53

Quarterly Results of Operations (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of quarterly results of operations	2017 Quarters Fourth Third Second First (Dollars in Thousands Except Per Share Data) Interest and dividend income $ 68,337 $ 67,176 $ 65,186 $ 62,351 Interest expense 10,680 10,333 9,603 9,253 Net interest income 57,657 56,843 55,583 53,098 Provision for credit losses 1,802 2,911 873 13,402 Net interest income after provision for credit losses 55,855 53,932 54,710 39,696 Loan level derivative income, net 755 844 186 402 Gain on sales of investment securities, net — — — 11,393 Gain on sales of loans and leases held-for-sale 935 1,049 307 353 Other non-interest income 4,125 4,080 3,984 3,760 Amortization of identified intangible assets (519 ) (519 ) (519 ) (532 ) Other non-interest expense (34,633 ) (34,889 ) (34,276 ) (33,224 ) Income before provision for income taxes 26,518 24,497 24,392 21,848 Provision for income taxes 18,712 8,330 8,759 7,835 Net income before noncontrolling interest in subsidiary 7,806 16,167 15,633 14,013 Less net income attributable to noncontrolling interest in subsidiary 979 801 753 568 Net income attributable to Brookline Bancorp, Inc. $ 6,827 $ 15,366 $ 14,880 $ 13,445 Earnings per share: Basic $ 0.09 $ 0.20 $ 0.20 $ 0.19 Diluted 0.09 0.20 0.20 0.19 Average common shares outstanding: Basic 76,583,712 76,452,539 74,325,013 70,386,766 Diluted 76,868,307 76,961,948 74,810,088 70,844,096 Common stock price: High $ 16.35 $ 15.50 $ 15.95 $ 16.75 Low 14.50 13.75 13.75 14.50 Dividends per share $ 0.09 $ 0.09 $ 0.09 $ 0.09 2016 Quarters Fourth Third Second First (Dollars in Thousands Except Per Share Data) Interest and dividend income $ 60,983 $ 61,531 $ 59,236 $ 57,898 Interest expense 9,129 9,181 8,979 8,695 Net interest income 51,854 52,350 50,257 49,203 Provision for credit losses 3,215 2,215 2,545 2,378 Net interest income after provision for credit losses 48,639 50,135 47,712 46,825 Loan level derivative income, net 265 858 1,210 1,629 Gain on sales of loans and leases held-for-sale 1,270 588 345 905 Other non-interest income 3,895 3,883 3,820 3,935 Amortization of identified intangible assets (621 ) (623 ) (621 ) (635 ) Other non-interest expense (31,986 ) (32,765 ) (31,629 ) (31,418 ) Income before provision for income taxes 21,462 22,076 20,837 21,241 Provision for income taxes 7,524 7,804 7,465 7,599 Net income before noncontrolling interest in subsidiary 13,938 14,272 13,372 13,642 Less net income attributable to noncontrolling interest in subsidiary 659 655 718 830 Net income attributable to Brookline Bancorp, Inc. $ 13,279 $ 13,617 $ 12,654 $ 12,812 Earnings per share: Basic $ 0.19 $ 0.19 $ 0.18 $ 0.18 Diluted 0.19 0.19 0.18 0.18 Average common shares outstanding: Basic 70,362,702 70,299,722 70,196,950 70,186,921 Diluted 70,592,204 70,450,760 70,388,438 70,343,408 Common stock price: High $ 16.60 $ 12.19 $ 11.69 $ 11.21 Low 12.05 10.71 10.44 10.23 Dividends per share $ 0.09 $ 0.09 $ 0.09 $ 0.09

Basis of Presentation (Details)

Basis of Presentation (Details)	12 Months Ended
	Dec. 31, 2017USD ($)classbanksegment	Dec. 31, 2016USD ($)
Basis of Presentation
Number of full-service banking offices | bank	25
Percentage of insurance offered	100.00%
Impairment of restricted securities	$ 0	$ 0
Number of days past due, non-accrual status (in days)	90 days
Period after which a non-accrual loan is restructured (in months)	6 months
Total loans and leases	$ 5,730,679,000	5,398,864,000
BOLI, as percentage of capital plus reserves, maximum, individual carrier (as a percent)	10.00%
BOLI, as percentage of capital plus reserves, maximum, aggregate (as a percent)	25.00%
Number of reportable segments | segment	1
Minimum
Basis of Presentation
Term of operating lease	5 years
Maximum
Basis of Presentation
Term of operating lease	25 years
Taxi Medallion Portfolio
Basis of Presentation
Total loans and leases	$ 19,700,000	31,100,000
Commercial real estate
Basis of Presentation
Number of loan classes within specific portfolio | class	3
Commercial loans
Basis of Presentation
Number of loan classes within specific portfolio | class	3
Total loans and leases	$ 1,624,111,000	$ 1,495,408,000
Consumer Loan
Basis of Presentation
Number of loan classes within specific portfolio | class	3
Eastern Funding LLC
Basis of Presentation
Percentage of ownership in subsidiary	84.20%
BankRI
Basis of Presentation
Number of full-service banking offices | bank	20
First Ipswich
Basis of Presentation
Number of full-service banking offices | bank	6
Retained Earnings
Basis of Presentation
Reclassification due to the adoption of ASU No. 2018-02	$ 1,063,000

Acquisitions (Details)

Acquisitions (Details)	Sep. 20, 2017USD ($)branch$ / shares	Dec. 31, 2017USD ($)bank	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Acquisitions
Number of full-service banking offices | bank		25
Merger and acquisition expense		$ 411,000	$ 0	$ 0
First Commons Bank
Acquisitions
Share price (in usd per share) | $ / shares	$ 16.70
Total transaction value	$ 56,000,000
Share exchange ratio	1.171
Number of full-service banking offices | branch	2
Total consolidated assets		324,800,000
Value of loans acquired		263,000,000
Value of deposits assumed		282,800,000
Stockholders' equity of acquiree		35,700,000
Merger and acquisition expense		$ 411,000
First Commons Bank | Minimum
Acquisitions
Volume-weighted average stock price (in usd per share) | $ / shares	$ 13.19
First Commons Bank | Maximum
Acquisitions
Volume-weighted average stock price (in usd per share) | $ / shares	$ 15.33

Cash, Cash Equivalents and Sh56

Cash, Cash Equivalents and Short-Term Investments (Short-term Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Short-term investments
FRB interest bearing reserve	$ 28,263	$ 19,952
FHLB overnight deposits	4,676	2,142
Federal funds sold	2,444	9,508
Total short-term investments	$ 35,383	$ 31,602

Cash, Cash Equivalents and Sh57

Cash, Cash Equivalents and Short-Term Investments (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Average amount required to be held with Federal Reserve Bank	$ 5.9	$ 6.9
Aggregate reserves	$ 40	$ 30.9

Investment Securities (Summary

Investment Securities (Summary of Available-for-sale and Held-to-maturity Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment securities available-for-sale
Amortized Cost	$ 547,964	$ 530,202
Gross Unrealized Gains	581	1,394
Gross Unrealized Losses	8,421	7,962
Estimated Fair Value	540,124	523,634
Investment securities held-to-maturity
Amortized Cost	109,730	87,120
Gross Unrealized Gains	159	5
Gross Unrealized Losses	1,366	1,854
Estimated Fair Value	108,523	85,271
GSE debentures
Investment securities available-for-sale
Amortized Cost	151,483	98,122
Gross Unrealized Gains	70	188
Gross Unrealized Losses	1,629	1,290
Estimated Fair Value	149,924	97,020
Investment securities held-to-maturity
Amortized Cost	41,612	14,735
Gross Unrealized Gains	0	0
Gross Unrealized Losses	811	634
Estimated Fair Value	40,801	14,101
GSE CMOs
Investment securities available-for-sale
Amortized Cost	131,082	161,483
Gross Unrealized Gains	27	37
Gross Unrealized Losses	4,087	3,480
Estimated Fair Value	127,022	158,040
GSE MBSs
Investment securities available-for-sale
Amortized Cost	191,281	214,946
Gross Unrealized Gains	354	794
Gross Unrealized Losses	2,322	2,825
Estimated Fair Value	189,313	212,915
Investment securities held-to-maturity
Amortized Cost	13,923	17,666
Gross Unrealized Gains	0	0
Gross Unrealized Losses	218	187
Estimated Fair Value	13,705	17,479
SBA commercial loan asset-backed securities
Investment securities available-for-sale
Amortized Cost	73	107
Gross Unrealized Gains	0	0
Gross Unrealized Losses	1	0
Estimated Fair Value	72	107
Corporate debt obligations
Investment securities available-for-sale
Amortized Cost	62,811	48,308
Gross Unrealized Gains	110	360
Gross Unrealized Losses	238	183
Estimated Fair Value	62,683	48,485
U.S. treasury bonds
Investment securities available-for-sale
Amortized Cost	8,785	4,801
Gross Unrealized Gains	7	0
Gross Unrealized Losses	62	64
Estimated Fair Value	8,730	4,737
Trust preferred securities
Investment securities available-for-sale
Amortized Cost	1,471	1,469
Gross Unrealized Gains	0	0
Gross Unrealized Losses	73	111
Estimated Fair Value	1,398	1,358
Marketable equity securities
Investment securities available-for-sale
Amortized Cost	978	966
Gross Unrealized Gains	13	15
Gross Unrealized Losses	9	9
Estimated Fair Value	982	972
Municipal obligations
Investment securities held-to-maturity
Amortized Cost	53,695	54,219
Gross Unrealized Gains	159	5
Gross Unrealized Losses	337	1,020
Estimated Fair Value	53,517	53,204
Foreign government obligations
Investment securities held-to-maturity
Amortized Cost	500	500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	13
Estimated Fair Value	$ 500	$ 487

Investment Securities (Other-Th

Investment Securities (Other-Than-Temporary Impairment) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investment securities available-for-sale
Less than twelve months, estimated fair value		$ 348,546
Less than twelve months, unrealized losses		6,530
Twelve months or longer, estimated fair value		40,480
Twelve months or longer, unrealized losses		1,432
Estimated Fair Value	$ 469,200	389,026
Total, unrealized losses		7,962
Investment securities held-to-maturity
Total, estimated fair value	92,900	82,000
GSE debentures
Investment securities available-for-sale
Less than twelve months, estimated fair value	120,409	67,216
Less than twelve months, unrealized losses	1,263	1,291
Twelve months or longer, estimated fair value	12,481	0
Twelve months or longer, unrealized losses	366	0
Estimated Fair Value	132,890	67,216
Total, unrealized losses	1,629	1,291
Investment securities held-to-maturity
Less than twelve months, estimated fair value	26,594	14,101
Less than twelve months, unrealized losses	281	634
Twelve months or longer, estimated fair value	14,208	0
Twelve months or longer, unrealized losses	530	0
Total, estimated fair value	40,802	14,101
Total, unrealized losses	811	634
GSE CMOs
Investment securities available-for-sale
Less than twelve months, estimated fair value	2,862	118,450
Less than twelve months, unrealized losses	34	2,162
Twelve months or longer, estimated fair value	123,548	38,852
Twelve months or longer, unrealized losses	4,053	1,318
Estimated Fair Value	126,410	157,302
Total, unrealized losses	4,087	3,480
GSE MBSs
Investment securities available-for-sale
Less than twelve months, estimated fair value	94,985	149,687
Less than twelve months, unrealized losses	753	2,821
Twelve months or longer, estimated fair value	74,782	198
Twelve months or longer, unrealized losses	1,569	3
Estimated Fair Value	169,767	149,885
Total, unrealized losses	2,322	2,824
Investment securities held-to-maturity
Less than twelve months, estimated fair value	1,996	17,289
Less than twelve months, unrealized losses	15	187
Twelve months or longer, estimated fair value	11,674	0
Twelve months or longer, unrealized losses	203	0
Total, estimated fair value	13,670	17,289
Total, unrealized losses	218	187
SBA commercial loan asset-backed securities
Investment securities available-for-sale
Less than twelve months, estimated fair value	34	0
Less than twelve months, unrealized losses	0	0
Twelve months or longer, estimated fair value	33	72
Twelve months or longer, unrealized losses	1	0
Estimated Fair Value	67	72
Total, unrealized losses	1	0
Corporate debt obligations
Investment securities available-for-sale
Less than twelve months, estimated fair value	30,978	7,953
Less than twelve months, unrealized losses	154	183
Twelve months or longer, estimated fair value	2,423	0
Twelve months or longer, unrealized losses	84	0
Estimated Fair Value	33,401	7,953
Total, unrealized losses	238	183
U.S. treasury bonds
Investment securities available-for-sale
Less than twelve months, estimated fair value	4,767	4,737
Less than twelve months, unrealized losses	62	64
Twelve months or longer, estimated fair value	0	0
Twelve months or longer, unrealized losses	0	0
Estimated Fair Value	4,767	4,737
Total, unrealized losses	62	64
Trust preferred securities
Investment securities available-for-sale
Less than twelve months, estimated fair value	0	0
Less than twelve months, unrealized losses	0	0
Twelve months or longer, estimated fair value	1,398	1,358
Twelve months or longer, unrealized losses	73	111
Estimated Fair Value	1,398	1,358
Total, unrealized losses	73	111
Marketable equity securities
Investment securities available-for-sale
Less than twelve months, estimated fair value	0	503
Less than twelve months, unrealized losses	0	9
Twelve months or longer, estimated fair value	503	0
Twelve months or longer, unrealized losses	9	0
Estimated Fair Value	503	503
Total, unrealized losses	9	9
Municipal obligations
Investment securities held-to-maturity
Less than twelve months, estimated fair value	30,542	50,098
Less than twelve months, unrealized losses	235	1,020
Twelve months or longer, estimated fair value	7,408	0
Twelve months or longer, unrealized losses	102	0
Total, estimated fair value	37,950	50,098
Total, unrealized losses	337	1,020
Foreign government obligations
Investment securities held-to-maturity
Less than twelve months, estimated fair value	0	487
Less than twelve months, unrealized losses	0	13
Twelve months or longer, estimated fair value	500	0
Twelve months or longer, unrealized losses	0	0
Total, estimated fair value	500	487
Total, unrealized losses	0	13
Debt Securities
Investment securities available-for-sale
Less than twelve months, estimated fair value	254,035
Less than twelve months, unrealized losses	2,266
Twelve months or longer, estimated fair value	215,168
Twelve months or longer, unrealized losses	6,155
Estimated Fair Value	469,203
Total, unrealized losses	8,421
Investment securities held-to-maturity
Less than twelve months, estimated fair value	59,132	81,975
Less than twelve months, unrealized losses	531	1,854
Twelve months or longer, estimated fair value	33,790	0
Twelve months or longer, unrealized losses	835	0
Total, estimated fair value	92,922	81,975
Total, unrealized losses	1,366	1,854
Available-for-sale Securities and Held-to-maturity Securities [Abstract]
Less Than Twelve Months, Estimated Fair Value	313,167	430,521
Less Than Twelve Months, Unrealized Losses	2,797	8,384
Twelve Months or Longer, Estimated Fair Value	248,958	40,480
Twelve Months or Longer, Unrealized Losses	6,990	1,432
Total, Estimated Fair Value	562,125	471,001
Total, Unrealized Losses	$ 9,787	$ 9,816

Investment Securities (Portfoli

Investment Securities (Portfolio Maturities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available for Sale, Amortized Cost
Within 1 year	$ 23,612	$ 13
After 1 year through 5 years	142,772	81,524
After 5 years through 10 years	136,746	128,956
Over 10 years	243,856	318,743
Total	546,986	529,236
Available for Sale, Estimated Fair Value
Within 1 year	23,652	13
After 1 year through 5 years	142,029	81,833
After 5 years through 10 years	134,978	127,952
Over 10 years	238,483	312,864
Total	$ 539,142	$ 522,662
Available for Sale, Weighted Average Rate
Within 1 year (as a percent)	2.27%	0.17%
After 1 year through 5 years (as a percent)	2.05%	2.14%
After 5 years through 10 years (as a percent)	2.06%	2.03%
Over 10 years (as a percent)	2.06%	2.03%
Total (as a percent)	2.07%	2.04%
Held-to-Maturity, Amortized Cost
Within 1 year	$ 918	$ 190
After 1 year through 5 years	58,335	23,012
After 5 years through 10 years	36,589	46,442
Over 10 years	13,888	17,476
Total	109,730	87,120
Held-to-Maturity, Estimated Fair Value
Within 1 year	916	190
After 1 year through 5 years	57,939	22,750
After 5 years through 10 years	35,998	45,042
Over 10 years	13,670	17,289
Total	$ 108,523	$ 85,271
Held-to-Maturity, Weighted Average Rate
Within 1 year (as a percent)	0.78%	1.00%
After 1 year through 5 years (as a percent)	1.74%	1.30%
After 5 years through 10 years (as a percent)	1.79%	1.75%
Over 10 years (as a percent)	1.98%	2.11%
Total (as a percent)	1.78%	1.70%

Investment Securities (Security

Investment Securities (Security Sales) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Schedule of Available-for-sale Securities [Line Items]
Gross gains from sales	$ 11,612
Gross losses from sales	(219)
Gain on sales of securities, net	11,393
Sales of debt securities
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales	0
Sales of marketable and restricted equity securities
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales	$ 11,393

Investment Securities (Narrativ

Investment Securities (Narrative) (Details)	1 Months Ended	9 Months Ended	12 Months Ended
	Jul. 30, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)securityshares	Dec. 31, 2016USD ($)security	Dec. 31, 2015USD ($)	Jun. 30, 2017shares	Feb. 03, 2017$ / sharesshares
Investment [Line Items]
Estimated Fair Value			$ 540,124,000	$ 523,634,000
Net unrealized gain (loss)			(7,800,000)	(6,600,000)
Total, estimated fair value			$ 469,200,000	$ 389,026,000
Percentage of securities in unrealized loss positions, available-for-sale securities			86.90%	74.30%
Gross Unrealized Losses			$ 8,421,000	$ 7,962,000
Investment securities held to maturity, fair value			108,523,000	85,271,000
Net unrealized gain (loss), held-to-maturity securities			(1,200,000)	(1,800,000)
Gross unrealized losses, fair value, held-to-maturity securities			$ 92,900,000	$ 82,000,000
Percentage of securities in unrealized loss positions, held-to-maturity securities			85.60%	96.10%
Gross Unrealized Losses			$ 1,366,000	$ 1,854,000
Available for sale securities pledged as collateral			431,200,000	429,100,000
Purchases of securities available-for-sale			90,971,000	115,403,000	$ 63,615,000
Purchases of investment securities held-to-maturity			26,873,000	36,167,000	$ 102,847,000
Investment securities held-to-maturity (fair value of $108,523 and $85,271, respectively)			109,730,000	87,120,000
Estimated fair value of debt securities have right to call or prepay the obligations			58,800,000	27,900,000
Estimated fair value of debt securities have right to call or prepay the obligations, scheduled maturities of after one year through five years			32,700,000	3,000,000
Estimated fair value of debt securities have right to call or prepay the obligations, scheduled maturities after five years through ten years			25,200,000	23,500,000
Estimated fair value of debt securities have right to call or prepay the obligations, scheduled maturities of which is after 10 years			900,000	1,400,000
Gain on sales of securities, net			$ 11,393,000
Community Bank Systems, Inc.
Investment [Line Items]
Gain on sales of securities, net		$ 11,400,000
Community Bank Systems, Inc. | Brookline Bank
Investment [Line Items]
Cash received per share at exchange (in dollars per share) | $ / shares							$ 319.04
Number of acquirer shares received per acquiree shares held at exchange (in shares) | shares							14.876
Daily authorized amount of shares that can be sold (in shares) | shares							5,071
Northeast Retirement Services | Brookline Bank
Investment [Line Items]
Number of shares held as investment | shares			9,721				9,721
Savings Bank Life Insurance
Investment [Line Items]
Proceeds from investments	$ 265,500
Savings Bank Life Insurance | Common Class A
Investment [Line Items]
Number of shares held as investment | shares	1					1
Share price (in usd per share) | $ / shares	$ 500
Savings Bank Life Insurance | Common Class B
Investment [Line Items]
Number of shares held as investment | shares	2,070					2,070
Share price (in usd per share) | $ / shares	$ 128
US Government Sponsored Enterprises Debt Securities Excluding Specified Securities
Investment [Line Items]
Estimated Fair Value			$ 23,700,000	26,200,000
GSE debentures
Investment [Line Items]
Estimated Fair Value			149,924,000	97,020,000
Net unrealized gain (loss)			(1,600,000)	(1,100,000)
Gross Unrealized Losses			1,629,000	1,290,000
Investment securities held to maturity, fair value			40,801,000	14,101,000
Net unrealized gain (loss), held-to-maturity securities			(800,000)	(600,000)
Gross unrealized losses, fair value, held-to-maturity securities			40,800,000	14,100,000
Gross Unrealized Losses			$ 811,000	$ 634,000
Number of securities | security			48	29
Number of securities in unrealized loss positions | security			43	21
Purchases of securities available-for-sale			$ 54,200,000	$ 65,700,000
Number of securities | security			14	5
Purchases of investment securities held-to-maturity			$ 26,900,000	$ 17,700,000
Investment securities held-to-maturity (fair value of $108,523 and $85,271, respectively)			41,612,000	14,735,000
GSE CMOs
Investment [Line Items]
Estimated Fair Value			127,000,000	158,000,000
Net unrealized gain (loss)			$ (4,100,000)	$ (3,400,000)
Number of securities | security			62	62
Number of securities in unrealized loss positions | security			47
Purchases of securities available-for-sale			$ 0	$ 3,100,000
GSE mortgage-related securities
Investment [Line Items]
Estimated Fair Value			189,300,000	212,900,000
Net unrealized gain (loss)			$ (2,000,000)	$ (2,000,000)
Number of securities | security			194	195
Number of securities in unrealized loss positions | security			82	60
Purchases of securities available-for-sale			$ 18,300,000	$ 36,600,000
SBA commercial loan asset-backed securities
Investment [Line Items]
Estimated Fair Value			72,000	107,000
Gross Unrealized Losses			$ 1,000	$ 0
Number of securities | security			5	6
Number of securities in unrealized loss positions | security			4	4
Corporate debt obligations
Investment [Line Items]
Estimated Fair Value			$ 62,683,000	$ 48,485,000
Net unrealized gain (loss)			100,000	200,000
Gross Unrealized Losses			$ 238,000	$ 183,000
Number of securities | security			19	16
Number of securities in unrealized loss positions | security			9	3
Purchases of securities available-for-sale			$ 14,500,000	$ 5,100,000
U.S. Treasury bonds
Investment [Line Items]
Estimated Fair Value			8,700,000	4,700,000
Net unrealized gain (loss)			$ 100,000	$ (100,000)
Number of securities | security			2	1
Purchases of securities available-for-sale			$ 4,000,000	$ 4,800,000
Trust preferred securities
Investment [Line Items]
Estimated Fair Value			1,398,000	1,358,000
Net unrealized gain (loss)			(100,000)	(100,000)
Gross Unrealized Losses			$ 73,000	$ 111,000
Number of securities | security			2	2
Marketable equity securities
Investment [Line Items]
Estimated Fair Value			$ 982,000	$ 972,000
Gross Unrealized Losses			$ 9,000	$ 9,000
Number of securities | security			2	2
Number of securities in unrealized loss positions | security			1	1
GSE MBSs
Investment [Line Items]
Estimated Fair Value			$ 189,313,000	$ 212,915,000
Gross Unrealized Losses			2,322,000	2,825,000
Investment securities held to maturity, fair value			13,705,000	17,479,000
Net unrealized gain (loss), held-to-maturity securities			(200,000)	(200,000)
Gross unrealized losses, fair value, held-to-maturity securities			13,700,000	17,500,000
Gross Unrealized Losses			$ 218,000	$ 187,000
Number of securities | security			11	11
Purchases of investment securities held-to-maturity			$ 0	$ 2,300,000
Number of securities in an unrealized loss position | security			8	8
Investment securities held-to-maturity (fair value of $108,523 and $85,271, respectively)			$ 13,923,000	$ 17,666,000
Municipal obligations
Investment [Line Items]
Investment securities held to maturity, fair value			53,517,000	53,204,000
Gross unrealized losses, fair value, held-to-maturity securities			53,500,000	53,200,000
Gross Unrealized Losses			337,000	$ 1,020,000
Purchases of securities available-for-sale			$ 0
Number of securities | security			100	100
Purchases of investment securities held-to-maturity				$ 15,600,000
Number of securities in an unrealized loss position | security			69	93
Investment securities held-to-maturity (fair value of $108,523 and $85,271, respectively)			$ 53,695,000	$ 54,219,000
Foreign government obligations
Investment [Line Items]
Investment securities held to maturity, fair value			500,000	487,000
Gross unrealized losses, fair value, held-to-maturity securities			500,000	500,000
Gross Unrealized Losses			$ 0	$ 13,000
Number of securities | security			1	1
Investment securities held-to-maturity (fair value of $108,523 and $85,271, respectively)			$ 500,000	$ 500,000

Restricted Equity Securities (I

Restricted Equity Securities (Investments in Restricted Equity Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Restricted equity securities
Restricted equity securities	$ 59,369	$ 64,511
FHLBB stock
Restricted equity securities
Restricted equity securities	42,427	47,284
FRB stock
Restricted equity securities
Restricted equity securities	16,842	16,752
Other restricted equity securities
Restricted equity securities
Restricted equity securities	$ 100	$ 475

Restricted Equity Securities (N

Restricted Equity Securities (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended	12 Months Ended
	Jul. 30, 2017	Dec. 31, 2017	Mar. 31, 2017	Sep. 30, 2017	Dec. 31, 2017	Jun. 30, 2017	Feb. 03, 2017
Investment [Line Items]
Gain on sales of securities, net					$ 11,393,000
FHLBB stock
Investment [Line Items]
Dividend rate (as a percent)		4.33%	3.94%		3.63%
Northeast Retirement Services | Brookline Bank
Investment [Line Items]
Number of shares held as investment		9,721			9,721		9,721
Shares held as investment at cost		$ 122,000			$ 122,000
Community Bank Systems, Inc.
Investment [Line Items]
Gain on sales of securities, net				$ 11,400,000
Community Bank Systems, Inc. | Brookline Bank
Investment [Line Items]
Cash received per share at exchange (in dollars per share)							$ 319.04
Number of acquirer shares received per acquiree shares held at exchange (in shares)							14.876
Daily authorized amount of shares that can be sold (in shares)							5,071
Savings Bank Life Insurance
Investment [Line Items]
Proceeds from investments	$ 265,500
Savings Bank Life Insurance | Common Class A
Investment [Line Items]
Number of shares held as investment	1					1
Share price (in usd per share)	$ 500
Savings Bank Life Insurance | Common Class B
Investment [Line Items]
Number of shares held as investment	2,070					2,070
Share price (in usd per share)	$ 128

Loans and Leases (Summary of Lo

Loans and Leases (Summary of Loan and Lease Balances and Weighted Average Coupon Rates) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 5,490,622	$ 5,083,560
Originated, Weighted Average Coupon (as a percent)	4.65%	4.38%
Acquired loans	$ 240,057	$ 315,304
Acquired, Weighted Average Coupon (as a percent)	4.49%	4.31%
Total loans and leases	$ 5,730,679	$ 5,398,864
Total, Weighted Average Coupon (as a percent)	4.64%	4.38%
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 2,174,969	$ 2,050,382
Multi-family mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	760,670	731,186
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	140,138	136,999
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	705,004	635,426
Equipment financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	866,488	799,860
Condominium association
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	52,619	60,122
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	660,065	624,349
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	355,954	342,241
Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	14,772	12,158
Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 2,945,451	$ 2,745,489
Originated, Weighted Average Coupon (as a percent)	4.17%	3.90%
Acquired loans	$ 130,326	$ 173,078
Acquired, Weighted Average Coupon (as a percent)	4.39%	4.29%
Total loans and leases	$ 3,075,777	$ 2,918,567
Total, Weighted Average Coupon (as a percent)	4.18%	3.92%
Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 2,069,392	$ 1,907,254
Originated, Weighted Average Coupon (as a percent)	4.17%	3.95%
Acquired loans	$ 105,577	$ 143,128
Acquired, Weighted Average Coupon (as a percent)	4.37%	4.24%
Total loans and leases	$ 2,174,969	$ 2,050,382
Total, Weighted Average Coupon (as a percent)	4.18%	3.97%
Commercial real estate loans | Multi-family mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 735,921	$ 701,450
Originated, Weighted Average Coupon (as a percent)	4.09%	3.79%
Acquired loans	$ 24,749	$ 29,736
Acquired, Weighted Average Coupon (as a percent)	4.48%	4.53%
Total loans and leases	$ 760,670	$ 731,186
Total, Weighted Average Coupon (as a percent)	4.10%	3.82%
Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 140,138	$ 136,785
Originated, Weighted Average Coupon (as a percent)	4.58%	3.79%
Acquired loans	$ 0	$ 214
Acquired, Weighted Average Coupon (as a percent)	0.00%	3.67%
Total loans and leases	$ 140,138	$ 136,999
Total, Weighted Average Coupon (as a percent)	4.58%	3.79%
Commercial loans and leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 1,611,418	$ 1,475,109
Originated, Weighted Average Coupon (as a percent)	5.92%	5.71%
Acquired loans	$ 12,693	$ 20,299
Acquired, Weighted Average Coupon (as a percent)	5.82%	5.57%
Total loans and leases	$ 1,624,111	$ 1,495,408
Total, Weighted Average Coupon (as a percent)	5.92%	5.71%
Commercial loans and leases | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 696,825	$ 621,285
Originated, Weighted Average Coupon (as a percent)	4.35%	4.11%
Acquired loans	$ 8,179	$ 14,141
Acquired, Weighted Average Coupon (as a percent)	5.77%	5.44%
Total loans and leases	$ 705,004	$ 635,426
Total, Weighted Average Coupon (as a percent)	4.37%	4.14%
Commercial loans and leases | Equipment financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 861,974	$ 793,702
Originated, Weighted Average Coupon (as a percent)	7.28%	7.06%
Acquired loans	$ 4,514	$ 6,158
Acquired, Weighted Average Coupon (as a percent)	5.92%	5.86%
Total loans and leases	$ 866,488	$ 799,860
Total, Weighted Average Coupon (as a percent)	7.27%	7.05%
Commercial loans and leases | Condominium association
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 52,619	$ 60,122
Originated, Weighted Average Coupon (as a percent)	4.49%	4.39%
Acquired loans	$ 0	$ 0
Acquired, Weighted Average Coupon (as a percent)	0.00%	0.00%
Total loans and leases	$ 52,619	$ 60,122
Total, Weighted Average Coupon (as a percent)	4.49%	4.39%
Consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 933,753	$ 862,962
Originated, Weighted Average Coupon (as a percent)	3.95%	3.65%
Acquired loans	$ 97,038	$ 121,927
Acquired, Weighted Average Coupon (as a percent)	4.44%	4.12%
Total loans and leases	$ 1,030,791	$ 984,889
Total, Weighted Average Coupon (as a percent)	4.00%	3.71%
Consumer loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 604,897	$ 555,430
Originated, Weighted Average Coupon (as a percent)	3.81%	3.67%
Acquired loans	$ 55,168	$ 68,919
Acquired, Weighted Average Coupon (as a percent)	4.28%	3.98%
Total loans and leases	$ 660,065	$ 624,349
Total, Weighted Average Coupon (as a percent)	3.85%	3.70%
Consumer loans | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 314,189	$ 289,361
Originated, Weighted Average Coupon (as a percent)	4.16%	3.50%
Acquired loans	$ 41,765	$ 52,880
Acquired, Weighted Average Coupon (as a percent)	4.62%	4.26%
Total loans and leases	$ 355,954	$ 342,241
Total, Weighted Average Coupon (as a percent)	4.21%	3.62%
Consumer loans | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Originated loans	$ 14,667	$ 18,171
Originated, Weighted Average Coupon (as a percent)	5.51%	5.48%
Acquired loans	$ 105	$ 128
Acquired, Weighted Average Coupon (as a percent)	18.00%	17.92%
Total loans and leases	$ 14,772	$ 18,299
Total, Weighted Average Coupon (as a percent)	5.60%	5.57%

Loans and Leases (Accretable Yi

Loans and Leases (Accretable Yield for the Acquired Loan Portfolio) (Details) - Acquired - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summarized activity in accretable yield for the acquired loan portfolio
Balance at beginning of year	$ 14,353	$ 20,796	$ 32,044
Accretion	(7,801)	(6,781)	(10,467)
Reclassification from/(to) nonaccretable difference as a result from changes in expected cash flows	3,970	338	(781)
Balance at end of year	$ 10,522	$ 14,353	$ 20,796

Loans and Leases (Loans and Adv

Loans and Leases (Loans and Advances to Directors, Executive Officers and Their Affiliates) (Details) - Directors, executive officers and their affiliates - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Change in the total amounts of loans and advances, all of which were performing
Balance at beginning of year	$ 43,458	$ 37,375
New loans granted during the year	13,554	8,352
Advances on lines of credit	473	26
Repayments	(9,544)	(2,295)
Balance at end of year	$ 47,941	$ 43,458

Loans and Leases (Narrative) (D

Loans and Leases (Narrative) (Details) - USD ($)	3 Months Ended									12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unamortized deferred loan origination fees and costs	$ 15,500,000				$ 14,200,000					$ 15,500,000	$ 14,200,000
Percentage of loans to aggregate outstanding amount in the greater New York/New Jersey Metropolitan area and northeastern states										28.00%	29.60%
Percentage of loans to aggregate outstanding amount in Other areas of the United States										72.00%	70.40%
Proceeds from sales of loans and leases held-for-sale, net										$ 32,073,000	$ 55,636,000	$ 64,398,000
Gain on sales of loans and leases held-for-sale	935,000	$ 1,049,000	$ 307,000	$ 353,000	1,270,000	$ 588,000	$ 345,000	$ 905,000		2,644,000	3,256,000	2,208,000
Loans and leases pledged as collateral	2,300,000,000				2,100,000,000					2,300,000,000	2,100,000,000
Directors, executive officers and their affiliates
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded commitments on extensions of credit	$ 15,700,000				$ 8,700,000					15,700,000	8,700,000
Acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reclassification from/(to) nonaccretable difference as a result from changes in expected cash flows										$ 3,970,000	$ 338,000	$ (781,000)
Indirect automobile loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of loan portfolio sold (over)									90.00%
Proceeds from sales of loans and leases held-for-sale, net									$ 255,200,000
Gain on sales of loans and leases held-for-sale									$ (11,800)

Allowance for Loan and Lease 69

Allowance for Loan and Lease Losses (Summary of Changes in the Allowance for Loan and Lease Losses and Recorded Investments by Portfolio Segment) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in allowance for loan losses
Balance at the beginning of the period				$ 53,666				$ 56,739	$ 53,666	$ 56,739	$ 53,659
Charge-offs									(15,811)	(14,667)	(6,554)
Recoveries									1,953	1,392	2,211
(Credit) provision for loan and lease losses									18,784	10,202	7,423
Balance at the end of the period	$ 58,592				$ 53,666				58,592	53,666	56,739
Provisions for credit losses
Total provision for loan and lease losses									18,784	10,202	7,423
Unfunded credit commitments									204	151	28
Total provision (credit) for credit losses	1,802	$ 2,911	$ 873	13,402	3,215	$ 2,215	$ 2,545	2,378	18,988	10,353	7,451
Originated
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									18,829	8,982	7,355
Provisions for credit losses
Total provision for loan and lease losses									18,829	8,982	7,355
Unfunded credit commitments									204	151	28
Total provision (credit) for credit losses									19,033	9,133	7,383
Acquired
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									(45)	1,220	68
Provisions for credit losses
Total provision for loan and lease losses									(45)	1,220	68
Unfunded credit commitments									0	0	0
Total provision (credit) for credit losses									(45)	1,220	68
Commercial Real Estate
Changes in allowance for loan losses
Balance at the beginning of the period				27,645				30,151	27,645	30,151	29,594
Charge-offs									(494)	(2,169)	(550)
Recoveries									476	0	0
(Credit) provision for loan and lease losses									(515)	(337)	1,107
Balance at the end of the period	27,112				27,645				27,112	27,645	30,151
Provisions for credit losses
Total provision for loan and lease losses									(515)	(337)	1,107
Commercial Real Estate | Originated
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									(343)	(750)	1,459
Provisions for credit losses
Total provision for loan and lease losses									(343)	(750)	1,459
Commercial Real Estate | Acquired
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									(172)	413	(352)
Provisions for credit losses
Total provision for loan and lease losses									(172)	413	(352)
Commercial
Changes in allowance for loan losses
Balance at the beginning of the period				20,906				22,018	20,906	22,018	15,957
Charge-offs									(14,914)	(10,516)	(3,634)
Recoveries									1,158	642	667
(Credit) provision for loan and lease losses									19,183	8,762	9,028
Balance at the end of the period	26,333				20,906				26,333	20,906	22,018
Provisions for credit losses
Total provision for loan and lease losses									19,183	8,762	9,028
Commercial | Originated
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									18,899	8,469	9,077
Provisions for credit losses
Total provision for loan and lease losses									18,899	8,469	9,077
Commercial | Acquired
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									284	293	(49)
Provisions for credit losses
Total provision for loan and lease losses									284	293	(49)
Consumer
Changes in allowance for loan losses
Balance at the beginning of the period				$ 5,115				4,570	5,115	4,570	5,690
Charge-offs									(403)	(1,982)	(2,370)
Recoveries									319	750	1,544
(Credit) provision for loan and lease losses									116	1,777	(294)
Balance at the end of the period	$ 5,147				$ 5,115				5,147	5,115	4,570
Provisions for credit losses
Total provision for loan and lease losses									116	1,777	(294)
Consumer | Originated
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									273	1,263	(763)
Provisions for credit losses
Total provision for loan and lease losses									273	1,263	(763)
Consumer | Acquired
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									(157)	514	469
Provisions for credit losses
Total provision for loan and lease losses									(157)	514	469
Unallocated
Changes in allowance for loan losses
Balance at the beginning of the period								$ 0		0	2,418
Charge-offs											0
Recoveries											0
(Credit) provision for loan and lease losses									0	0	(2,418)
Balance at the end of the period											0
Provisions for credit losses
Total provision for loan and lease losses									0	0	(2,418)
Unallocated | Originated
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									0	0	(2,418)
Provisions for credit losses
Total provision for loan and lease losses									0	0	(2,418)
Unallocated | Acquired
Changes in allowance for loan losses
(Credit) provision for loan and lease losses									0	0	0
Provisions for credit losses
Total provision for loan and lease losses									$ 0	$ 0	$ 0

Allowance for Loan and Lease 70

Allowance for Loan and Lease Losses (Credit Quality Information) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Credit Quality Information
Recorded investment	$ 5,730,679	$ 5,398,864
Originated
Credit Quality Information
Recorded investment	5,490,622	5,083,560
Acquired
Credit Quality Information
Recorded investment	240,057	315,304
Commercial real estate
Credit Quality Information
Recorded investment	2,174,969	2,050,382
Commercial real estate | Originated
Credit Quality Information
Recorded investment	2,069,392	1,907,254
Commercial real estate | Acquired
Credit Quality Information
Recorded investment	105,577	143,128
Commercial real estate | Pass | Originated
Credit Quality Information
Recorded investment	2,054,376	1,899,162
Commercial real estate | Pass | Acquired
Credit Quality Information
Recorded investment	94,244	131,850
Commercial real estate | OAEM | Originated
Credit Quality Information
Recorded investment	8,889	1,538
Commercial real estate | OAEM | Acquired
Credit Quality Information
Recorded investment	9,839	1,408
Commercial real estate | Substandard | Originated
Credit Quality Information
Recorded investment	5,926	6,288
Commercial real estate | Substandard | Acquired
Credit Quality Information
Recorded investment	1,494	9,768
Commercial real estate | Doubtful | Originated
Credit Quality Information
Recorded investment	201	266
Commercial real estate | Doubtful | Acquired
Credit Quality Information
Recorded investment	0	102
Multi-family mortgage
Credit Quality Information
Recorded investment	760,670	731,186
Multi-family mortgage | Originated
Credit Quality Information
Recorded investment	735,921	701,450
Multi-family mortgage | Acquired
Credit Quality Information
Recorded investment	24,749	29,736
Multi-family mortgage | Pass | Originated
Credit Quality Information
Recorded investment	735,313	700,046
Multi-family mortgage | Pass | Acquired
Credit Quality Information
Recorded investment	24,459	29,153
Multi-family mortgage | OAEM | Originated
Credit Quality Information
Recorded investment	0	0
Multi-family mortgage | OAEM | Acquired
Credit Quality Information
Recorded investment	0	270
Multi-family mortgage | Substandard | Originated
Credit Quality Information
Recorded investment	608	1,404
Multi-family mortgage | Substandard | Acquired
Credit Quality Information
Recorded investment	290	313
Multi-family mortgage | Doubtful | Originated
Credit Quality Information
Recorded investment	0	0
Multi-family mortgage | Doubtful | Acquired
Credit Quality Information
Recorded investment	0	0
Construction
Credit Quality Information
Recorded investment	140,138	136,999
Construction | Originated
Credit Quality Information
Recorded investment	140,138	136,785
Construction | Acquired
Credit Quality Information
Recorded investment	0	214
Construction | Pass | Originated
Credit Quality Information
Recorded investment	139,278	136,607
Construction | Pass | Acquired
Credit Quality Information
Recorded investment	0	214
Construction | OAEM | Originated
Credit Quality Information
Recorded investment	0	178
Construction | OAEM | Acquired
Credit Quality Information
Recorded investment	0	0
Construction | Substandard | Originated
Credit Quality Information
Recorded investment	860	0
Construction | Substandard | Acquired
Credit Quality Information
Recorded investment	0	0
Construction | Doubtful | Originated
Credit Quality Information
Recorded investment	0	0
Construction | Doubtful | Acquired
Credit Quality Information
Recorded investment	0	0
Commercial
Credit Quality Information
Recorded investment	705,004	635,426
Commercial | Originated
Credit Quality Information
Recorded investment	696,825	621,285
Commercial | Acquired
Credit Quality Information
Recorded investment	8,179	14,141
Commercial | Pass | Originated
Credit Quality Information
Recorded investment	670,265	583,940
Commercial | Pass | Acquired
Credit Quality Information
Recorded investment	6,643	10,312
Commercial | OAEM | Originated
Credit Quality Information
Recorded investment	7,691	8,675
Commercial | OAEM | Acquired
Credit Quality Information
Recorded investment	265	249
Commercial | Substandard | Originated
Credit Quality Information
Recorded investment	17,681	28,595
Commercial | Substandard | Acquired
Credit Quality Information
Recorded investment	1,271	3,017
Commercial | Doubtful | Originated
Credit Quality Information
Recorded investment	1,188	75
Commercial | Doubtful | Acquired
Credit Quality Information
Recorded investment	0	563
Equipment financing
Credit Quality Information
Recorded investment	866,488	799,860
Equipment financing | Originated
Credit Quality Information
Recorded investment	861,974	793,702
Equipment financing | Acquired
Credit Quality Information
Recorded investment	4,514	6,158
Equipment financing | Pass | Originated
Credit Quality Information
Recorded investment	850,006	786,050
Equipment financing | Pass | Acquired
Credit Quality Information
Recorded investment	4,501	6,158
Equipment financing | OAEM | Originated
Credit Quality Information
Recorded investment	3,630	824
Equipment financing | OAEM | Acquired
Credit Quality Information
Recorded investment	0	0
Equipment financing | Substandard | Originated
Credit Quality Information
Recorded investment	5,012	4,848
Equipment financing | Substandard | Acquired
Credit Quality Information
Recorded investment	13	0
Equipment financing | Doubtful | Originated
Credit Quality Information
Recorded investment	3,326	1,980
Equipment financing | Doubtful | Acquired
Credit Quality Information
Recorded investment	0	0
Condominium association
Credit Quality Information
Recorded investment	52,619	60,122
Condominium association | Originated
Credit Quality Information
Recorded investment	52,619	60,122
Condominium association | Acquired
Credit Quality Information
Recorded investment	0	0
Condominium association | Pass | Originated
Credit Quality Information
Recorded investment	52,619	60,122
Condominium association | Pass | Acquired
Credit Quality Information
Recorded investment	0	0
Condominium association | OAEM | Originated
Credit Quality Information
Recorded investment	0	0
Condominium association | OAEM | Acquired
Credit Quality Information
Recorded investment	0	0
Condominium association | Substandard | Originated
Credit Quality Information
Recorded investment	0	0
Condominium association | Substandard | Acquired
Credit Quality Information
Recorded investment	0	0
Condominium association | Doubtful | Originated
Credit Quality Information
Recorded investment	0	0
Condominium association | Doubtful | Acquired
Credit Quality Information
Recorded investment	0	0
Other consumer
Credit Quality Information
Recorded investment	14,772	12,158
Other consumer | Originated
Credit Quality Information
Recorded investment	14,667	12,030
Other consumer | Acquired
Credit Quality Information
Recorded investment	105	128
Other consumer | Pass | Originated
Credit Quality Information
Recorded investment	14,628	12,018
Other consumer | Pass | Acquired
Credit Quality Information
Recorded investment	104	128
Other consumer | OAEM | Originated
Credit Quality Information
Recorded investment	0	0
Other consumer | OAEM | Acquired
Credit Quality Information
Recorded investment	1	0
Other consumer | Substandard | Originated
Credit Quality Information
Recorded investment	39	12
Other consumer | Substandard | Acquired
Credit Quality Information
Recorded investment	0	0
Other consumer | Doubtful | Originated
Credit Quality Information
Recorded investment	0	0
Other consumer | Doubtful | Acquired
Credit Quality Information
Recorded investment	0	0
Total
Credit Quality Information
Recorded investment		4,426,133
Total | Originated
Credit Quality Information
Recorded investment	4,571,536	4,232,628
Total | Acquired
Credit Quality Information
Recorded investment	143,124	193,505
Total | Pass
Credit Quality Information
Recorded investment	4,714,660
Total | Pass | Originated
Credit Quality Information
Recorded investment	4,516,485	4,177,945
Total | Pass | Acquired
Credit Quality Information
Recorded investment	129,951	177,815
Total | OAEM | Originated
Credit Quality Information
Recorded investment	20,210	11,215
Total | OAEM | Acquired
Credit Quality Information
Recorded investment	10,105	1,927
Total | Substandard | Originated
Credit Quality Information
Recorded investment	30,126	41,147
Total | Substandard | Acquired
Credit Quality Information
Recorded investment	3,068	13,098
Total | Doubtful | Originated
Credit Quality Information
Recorded investment	4,715	2,321
Total | Doubtful | Acquired
Credit Quality Information
Recorded investment	0	665
Residential mortgage
Credit Quality Information
Recorded investment	$ 660,065	$ 624,349
Percentage of loans to aggregate outstanding amount	100.00%	100.00%
Residential mortgage | Originated
Credit Quality Information
Recorded investment	$ 604,897	$ 555,430
Percentage of loans to aggregate outstanding amount	91.60%	89.00%
Residential mortgage | Acquired
Credit Quality Information
Recorded investment	$ 55,168	$ 68,919
Percentage of loans to aggregate outstanding amount	8.40%	11.00%
Residential mortgage | Loan-to-value ratio, less than 50% | Originated
Credit Quality Information
Recorded investment	$ 153,373	$ 138,030
Percentage of loans to aggregate outstanding amount	23.20%	22.10%
Residential mortgage | Loan-to-value ratio, less than 50% | Acquired
Credit Quality Information
Recorded investment	$ 16,521	$ 17,809
Percentage of loans to aggregate outstanding amount	2.50%	2.90%
Residential mortgage | Loan-to-value ratio, 50% - 69% | Originated
Credit Quality Information
Recorded investment	$ 265,328	$ 229,799
Percentage of loans to aggregate outstanding amount	40.20%	36.90%
Residential mortgage | Loan-to-value ratio, 50% - 69% | Acquired
Credit Quality Information
Recorded investment	$ 19,182	$ 24,027
Percentage of loans to aggregate outstanding amount	2.90%	3.80%
Residential mortgage | Loan-to-value ratio, 70% - 79% | Originated
Credit Quality Information
Recorded investment	$ 168,272	$ 162,614
Percentage of loans to aggregate outstanding amount	25.50%	26.00%
Residential mortgage | Loan-to-value ratio, 70% - 79% | Acquired
Credit Quality Information
Recorded investment	$ 10,507	$ 14,030
Percentage of loans to aggregate outstanding amount	1.60%	2.20%
Residential mortgage | Loan-to-value ratio, 80% and greater than | Originated
Credit Quality Information
Recorded investment	$ 16,547	$ 21,859
Percentage of loans to aggregate outstanding amount	2.50%	3.50%
Residential mortgage | Loan-to-value ratio, 80% and greater than | Acquired
Credit Quality Information
Recorded investment	$ 7,893	$ 10,069
Percentage of loans to aggregate outstanding amount	1.20%	1.60%
Residential mortgage | Data not available | Originated
Credit Quality Information
Recorded investment	$ 1,377	$ 3,128
Percentage of loans to aggregate outstanding amount	0.20%	0.50%
Residential mortgage | Data not available | Acquired
Credit Quality Information
Recorded investment	$ 1,065	$ 2,984
Percentage of loans to aggregate outstanding amount	0.20%	0.50%
Home equity
Credit Quality Information
Recorded investment	$ 355,954	$ 342,241
Percentage of loans to aggregate outstanding amount	100.00%	100.00%
Home equity | Originated
Credit Quality Information
Recorded investment	$ 314,189	$ 289,361
Percentage of loans to aggregate outstanding amount	88.20%	84.60%
Home equity | Acquired
Credit Quality Information
Recorded investment	$ 41,765	$ 52,880
Percentage of loans to aggregate outstanding amount	11.80%	15.40%
Home equity | Loan-to-value ratio, less than 50% | Originated
Credit Quality Information
Recorded investment	$ 148,137	$ 153,679
Percentage of loans to aggregate outstanding amount	41.60%	44.90%
Home equity | Loan-to-value ratio, less than 50% | Acquired
Credit Quality Information
Recorded investment	$ 25,312	$ 32,334
Percentage of loans to aggregate outstanding amount	7.10%	9.40%
Home equity | Loan-to-value ratio, 50% - 69% | Originated
Credit Quality Information
Recorded investment	$ 75,099	$ 61,553
Percentage of loans to aggregate outstanding amount	21.10%	18.10%
Home equity | Loan-to-value ratio, 50% - 69% | Acquired
Credit Quality Information
Recorded investment	$ 13,883	$ 15,059
Percentage of loans to aggregate outstanding amount	3.90%	4.40%
Home equity | Loan-to-value ratio, 70% - 79% | Originated
Credit Quality Information
Recorded investment	$ 63,742	$ 49,987
Percentage of loans to aggregate outstanding amount	17.90%	14.60%
Home equity | Loan-to-value ratio, 70% - 79% | Acquired
Credit Quality Information
Recorded investment	$ 943	$ 3,069
Percentage of loans to aggregate outstanding amount	0.30%	0.90%
Home equity | Loan-to-value ratio, 80% and greater than | Originated
Credit Quality Information
Recorded investment	$ 27,122	$ 23,317
Percentage of loans to aggregate outstanding amount	7.60%	6.80%
Home equity | Loan-to-value ratio, 80% and greater than | Acquired
Credit Quality Information
Recorded investment	$ 582	$ 1,016
Percentage of loans to aggregate outstanding amount	0.20%	0.30%
Home equity | Data not available | Originated
Credit Quality Information
Recorded investment	$ 89	$ 825
Percentage of loans to aggregate outstanding amount	0.00%	0.20%
Home equity | Data not available | Acquired
Credit Quality Information
Recorded investment	$ 1,045	$ 1,402
Percentage of loans to aggregate outstanding amount	0.30%	0.40%

Allowance for Loan and Lease 71

Allowance for Loan and Lease Losses (Foreclosed Residential Real Estate Property) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Foreclosed residential real estate property held by the creditor	$ 0	$ 251
Recorded investment in mortgage loans collateralized by residential real estate property that are in the process of foreclosure	$ 633	$ 1,213

Allowance for Loan and Lease 72

Allowance for Loan and Lease Losses (Past Due Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Age analysis of past due loans
Past Due	$ 50,704	$ 52,326
Current	5,679,975	5,346,538
Total Loans and Leases	5,730,679	5,398,864
Loans and Leases Past Due Greater Than 90 Days and Accruing	3,020	7,077
Nonaccrual Loans and Leases	27,272	40,077
Commercial real estate
Age analysis of past due loans
Total Loans and Leases	2,174,969	2,050,382
Multi-family mortgage
Age analysis of past due loans
Total Loans and Leases	760,670	731,186
Construction
Age analysis of past due loans
Total Loans and Leases	140,138	136,999
Commercial
Age analysis of past due loans
Total Loans and Leases	705,004	635,426
Equipment financing
Age analysis of past due loans
Total Loans and Leases	866,488	799,860
Condominium association
Age analysis of past due loans
Total Loans and Leases	52,619	60,122
Residential mortgage
Age analysis of past due loans
Total Loans and Leases	660,065	624,349
Home equity
Age analysis of past due loans
Total Loans and Leases	355,954	342,241
Other consumer
Age analysis of past due loans
Total Loans and Leases	14,772	12,158
Commercial real estate loans
Age analysis of past due loans
Total Loans and Leases	3,075,777	2,918,567
Commercial real estate loans | Commercial real estate
Age analysis of past due loans
Total Loans and Leases	2,174,969	2,050,382
Commercial real estate loans | Multi-family mortgage
Age analysis of past due loans
Total Loans and Leases	760,670	731,186
Commercial real estate loans | Construction
Age analysis of past due loans
Total Loans and Leases	140,138	136,999
Commercial loans and leases
Age analysis of past due loans
Total Loans and Leases	1,624,111	1,495,408
Commercial loans and leases | Commercial
Age analysis of past due loans
Total Loans and Leases	705,004	635,426
Commercial loans and leases | Equipment financing
Age analysis of past due loans
Total Loans and Leases	866,488	799,860
Commercial loans and leases | Condominium association
Age analysis of past due loans
Total Loans and Leases	52,619	60,122
Consumer loans
Age analysis of past due loans
Total Loans and Leases	1,030,791	984,889
Consumer loans | Residential mortgage
Age analysis of past due loans
Total Loans and Leases	660,065	624,349
Consumer loans | Home equity
Age analysis of past due loans
Total Loans and Leases	355,954	342,241
Consumer loans | Other consumer
Age analysis of past due loans
Total Loans and Leases	14,772	18,299
31-60 days past due
Age analysis of past due loans
Past Due	25,040	18,851
61-90 days past due
Age analysis of past due loans
Past Due	7,376	7,350
Greater than 90 days past due
Age analysis of past due loans
Past Due	18,288	26,125
Originated
Age analysis of past due loans
Past Due	44,811	40,525
Current	5,445,811	5,043,035
Total Loans and Leases	5,490,622	5,083,560
Loans and Leases Past Due Greater Than 90 Days and Accruing	225	5
Nonaccrual Loans and Leases	25,275	36,516
Originated | Commercial real estate
Age analysis of past due loans
Total Loans and Leases	2,069,392	1,907,254
Originated | Multi-family mortgage
Age analysis of past due loans
Total Loans and Leases	735,921	701,450
Originated | Construction
Age analysis of past due loans
Total Loans and Leases	140,138	136,785
Originated | Commercial
Age analysis of past due loans
Total Loans and Leases	696,825	621,285
Originated | Equipment financing
Age analysis of past due loans
Total Loans and Leases	861,974	793,702
Originated | Condominium association
Age analysis of past due loans
Total Loans and Leases	52,619	60,122
Originated | Residential mortgage
Age analysis of past due loans
Total Loans and Leases	604,897	555,430
Originated | Home equity
Age analysis of past due loans
Total Loans and Leases	314,189	289,361
Originated | Other consumer
Age analysis of past due loans
Total Loans and Leases	14,667	12,030
Originated | Commercial real estate loans
Age analysis of past due loans
Past Due	21,986	7,163
Current	2,923,465	2,738,326
Total Loans and Leases	2,945,451	2,745,489
Loans and Leases Past Due Greater Than 90 Days and Accruing	0	2
Nonaccrual Loans and Leases	4,650	6,439
Originated | Commercial real estate loans | Commercial real estate
Age analysis of past due loans
Past Due	5,528	4,029
Current	2,063,864	1,903,225
Total Loans and Leases	2,069,392	1,907,254
Loans and Leases Past Due Greater Than 90 Days and Accruing	0	2
Nonaccrual Loans and Leases	3,182	5,035
Originated | Commercial real estate loans | Multi-family mortgage
Age analysis of past due loans
Past Due	8,731	2,587
Current	727,190	698,863
Total Loans and Leases	735,921	701,450
Loans and Leases Past Due Greater Than 90 Days and Accruing	0	0
Nonaccrual Loans and Leases	608	1,404
Originated | Commercial real estate loans | Construction
Age analysis of past due loans
Past Due	7,727	547
Current	132,411	136,238
Total Loans and Leases	140,138	136,785
Loans and Leases Past Due Greater Than 90 Days and Accruing	0	0
Nonaccrual Loans and Leases	860	0
Originated | Commercial loans and leases
Age analysis of past due loans
Past Due	19,695	26,259
Current	1,591,723	1,448,850
Total Loans and Leases	1,611,418	1,475,109
Loans and Leases Past Due Greater Than 90 Days and Accruing	224	0
Nonaccrual Loans and Leases	18,471	27,345
Originated | Commercial loans and leases | Commercial
Age analysis of past due loans
Past Due	9,665	16,225
Current	687,160	605,060
Total Loans and Leases	696,825	621,285
Loans and Leases Past Due Greater Than 90 Days and Accruing	0	0
Nonaccrual Loans and Leases	10,365	20,587
Originated | Commercial loans and leases | Equipment financing
Age analysis of past due loans
Past Due	8,911	9,768
Current	853,063	783,934
Total Loans and Leases	861,974	793,702
Loans and Leases Past Due Greater Than 90 Days and Accruing	224	0
Nonaccrual Loans and Leases	8,106	6,758
Originated | Commercial loans and leases | Condominium association
Age analysis of past due loans
Past Due	1,119	266
Current	51,500	59,856
Total Loans and Leases	52,619	60,122
Loans and Leases Past Due Greater Than 90 Days and Accruing	0	0
Nonaccrual Loans and Leases	0	0
Originated | Consumer loans
Age analysis of past due loans
Past Due	3,130	7,103
Current	930,623	855,859
Total Loans and Leases	933,753	862,962
Loans and Leases Past Due Greater Than 90 Days and Accruing	1	3
Nonaccrual Loans and Leases	2,154	2,732
Originated | Consumer loans | Residential mortgage
Age analysis of past due loans
Past Due	2,150	6,202
Current	602,747	549,228
Total Loans and Leases	604,897	555,430
Loans and Leases Past Due Greater Than 90 Days and Accruing	0	0
Nonaccrual Loans and Leases	1,979	2,455
Originated | Consumer loans | Home equity
Age analysis of past due loans
Past Due	694	249
Current	313,495	289,112
Total Loans and Leases	314,189	289,361
Loans and Leases Past Due Greater Than 90 Days and Accruing	1	3
Nonaccrual Loans and Leases	132	128
Originated | Consumer loans | Other consumer
Age analysis of past due loans
Past Due	286	652
Current	14,381	17,519
Total Loans and Leases	14,667	18,171
Loans and Leases Past Due Greater Than 90 Days and Accruing	0	0
Nonaccrual Loans and Leases	43	149
Originated | 31-60 days past due
Age analysis of past due loans
Past Due	23,524	17,332
Originated | 31-60 days past due | Commercial real estate loans
Age analysis of past due loans
Past Due	15,972	4,368
Originated | 31-60 days past due | Commercial real estate loans | Commercial real estate
Age analysis of past due loans
Past Due	3,294	1,525
Originated | 31-60 days past due | Commercial real estate loans | Multi-family mortgage
Age analysis of past due loans
Past Due	6,141	2,296
Originated | 31-60 days past due | Commercial real estate loans | Construction
Age analysis of past due loans
Past Due	6,537	547
Originated | 31-60 days past due | Commercial loans and leases
Age analysis of past due loans
Past Due	5,415	8,645
Originated | 31-60 days past due | Commercial loans and leases | Commercial
Age analysis of past due loans
Past Due	1,344	5,396
Originated | 31-60 days past due | Commercial loans and leases | Equipment financing
Age analysis of past due loans
Past Due	3,214	2,983
Originated | 31-60 days past due | Commercial loans and leases | Condominium association
Age analysis of past due loans
Past Due	857	266
Originated | 31-60 days past due | Consumer loans
Age analysis of past due loans
Past Due	2,137	4,319
Originated | 31-60 days past due | Consumer loans | Residential mortgage
Age analysis of past due loans
Past Due	1,256	3,745
Originated | 31-60 days past due | Consumer loans | Home equity
Age analysis of past due loans
Past Due	643	25
Originated | 31-60 days past due | Consumer loans | Other consumer
Age analysis of past due loans
Past Due	238	549
Originated | 61-90 days past due
Age analysis of past due loans
Past Due	6,869	6,934
Originated | 61-90 days past due | Commercial real estate loans
Age analysis of past due loans
Past Due	3,311	2,075
Originated | 61-90 days past due | Commercial real estate loans | Commercial real estate
Age analysis of past due loans
Past Due	391	2,075
Originated | 61-90 days past due | Commercial real estate loans | Multi-family mortgage
Age analysis of past due loans
Past Due	2,590	0
Originated | 61-90 days past due | Commercial real estate loans | Construction
Age analysis of past due loans
Past Due	330	0
Originated | 61-90 days past due | Commercial loans and leases
Age analysis of past due loans
Past Due	3,353	2,259
Originated | 61-90 days past due | Commercial loans and leases | Commercial
Age analysis of past due loans
Past Due	597	815
Originated | 61-90 days past due | Commercial loans and leases | Equipment financing
Age analysis of past due loans
Past Due	2,494	1,444
Originated | 61-90 days past due | Commercial loans and leases | Condominium association
Age analysis of past due loans
Past Due	262	0
Originated | 61-90 days past due | Consumer loans
Age analysis of past due loans
Past Due	205	2,600
Originated | 61-90 days past due | Consumer loans | Residential mortgage
Age analysis of past due loans
Past Due	166	2,294
Originated | 61-90 days past due | Consumer loans | Home equity
Age analysis of past due loans
Past Due	19	219
Originated | 61-90 days past due | Consumer loans | Other consumer
Age analysis of past due loans
Past Due	20	87
Originated | Greater than 90 days past due
Age analysis of past due loans
Past Due	14,418	16,259
Originated | Greater than 90 days past due | Commercial real estate loans
Age analysis of past due loans
Past Due	2,703	720
Originated | Greater than 90 days past due | Commercial real estate loans | Commercial real estate
Age analysis of past due loans
Past Due	1,843	429
Originated | Greater than 90 days past due | Commercial real estate loans | Multi-family mortgage
Age analysis of past due loans
Past Due	0	291
Originated | Greater than 90 days past due | Commercial real estate loans | Construction
Age analysis of past due loans
Past Due	860	0
Originated | Greater than 90 days past due | Commercial loans and leases
Age analysis of past due loans
Past Due	10,927	15,355
Originated | Greater than 90 days past due | Commercial loans and leases | Commercial
Age analysis of past due loans
Past Due	7,724	10,014
Originated | Greater than 90 days past due | Commercial loans and leases | Equipment financing
Age analysis of past due loans
Past Due	3,203	5,341
Originated | Greater than 90 days past due | Commercial loans and leases | Condominium association
Age analysis of past due loans
Past Due	0	0
Originated | Greater than 90 days past due | Consumer loans
Age analysis of past due loans
Past Due	788	184
Originated | Greater than 90 days past due | Consumer loans | Residential mortgage
Age analysis of past due loans
Past Due	728	163
Originated | Greater than 90 days past due | Consumer loans | Home equity
Age analysis of past due loans
Past Due	32	5
Originated | Greater than 90 days past due | Consumer loans | Other consumer
Age analysis of past due loans
Past Due	28	16
Acquired
Age analysis of past due loans
Past Due	5,893	11,801
Current	234,164	303,503
Total Loans and Leases	240,057	315,304
Loans and Leases Past Due Greater Than 90 Days and Accruing	2,795	7,072
Nonaccrual Loans and Leases	1,997	3,561
Acquired | Commercial real estate
Age analysis of past due loans
Total Loans and Leases	105,577	143,128
Acquired | Multi-family mortgage
Age analysis of past due loans
Total Loans and Leases	24,749	29,736
Acquired | Construction
Age analysis of past due loans
Total Loans and Leases	0	214
Acquired | Commercial
Age analysis of past due loans
Total Loans and Leases	8,179	14,141
Acquired | Equipment financing
Age analysis of past due loans
Total Loans and Leases	4,514	6,158
Acquired | Condominium association
Age analysis of past due loans
Total Loans and Leases	0	0
Acquired | Residential mortgage
Age analysis of past due loans
Total Loans and Leases	55,168	68,919
Acquired | Home equity
Age analysis of past due loans
Total Loans and Leases	41,765	52,880
Acquired | Other consumer
Age analysis of past due loans
Total Loans and Leases	105	128
Acquired | Commercial real estate loans
Age analysis of past due loans
Past Due	1,667	4,936
Current	128,659	168,142
Total Loans and Leases	130,326	173,078
Loans and Leases Past Due Greater Than 90 Days and Accruing	589	3,786
Nonaccrual Loans and Leases	131	305
Acquired | Commercial real estate loans | Commercial real estate
Age analysis of past due loans
Past Due	1,664	4,936
Current	103,913	138,192
Total Loans and Leases	105,577	143,128
Loans and Leases Past Due Greater Than 90 Days and Accruing	586	3,786
Nonaccrual Loans and Leases	131	305
Acquired | Commercial real estate loans | Multi-family mortgage
Age analysis of past due loans
Past Due	3	0
Current	24,746	29,736
Total Loans and Leases	24,749	29,736
Loans and Leases Past Due Greater Than 90 Days and Accruing	3	0
Nonaccrual Loans and Leases	0	0
Acquired | Commercial real estate loans | Construction
Age analysis of past due loans
Past Due		0
Current		214
Total Loans and Leases		214
Loans and Leases Past Due Greater Than 90 Days and Accruing		0
Nonaccrual Loans and Leases		0
Acquired | Commercial loans and leases
Age analysis of past due loans
Past Due	1,079	2,957
Current	11,614	17,342
Total Loans and Leases	12,693	20,299
Loans and Leases Past Due Greater Than 90 Days and Accruing	30	264
Nonaccrual Loans and Leases	1,254	2,387
Acquired | Commercial loans and leases | Commercial
Age analysis of past due loans
Past Due	1,066	2,957
Current	7,113	11,184
Total Loans and Leases	8,179	14,141
Loans and Leases Past Due Greater Than 90 Days and Accruing	17	264
Nonaccrual Loans and Leases	1,254	2,387
Acquired | Commercial loans and leases | Equipment financing
Age analysis of past due loans
Past Due	13	0
Current	4,501	6,158
Total Loans and Leases	4,514	6,158
Loans and Leases Past Due Greater Than 90 Days and Accruing	13	0
Nonaccrual Loans and Leases	0	0
Acquired | Consumer loans
Age analysis of past due loans
Past Due	3,147	3,908
Current	93,891	118,019
Total Loans and Leases	97,038	121,927
Loans and Leases Past Due Greater Than 90 Days and Accruing	2,176	3,022
Nonaccrual Loans and Leases	612	869
Acquired | Consumer loans | Residential mortgage
Age analysis of past due loans
Past Due	2,453	3,183
Current	52,715	65,736
Total Loans and Leases	55,168	68,919
Loans and Leases Past Due Greater Than 90 Days and Accruing	1,990	2,820
Nonaccrual Loans and Leases	0	46
Acquired | Consumer loans | Home equity
Age analysis of past due loans
Past Due	694	724
Current	41,071	52,156
Total Loans and Leases	41,765	52,880
Loans and Leases Past Due Greater Than 90 Days and Accruing	186	202
Nonaccrual Loans and Leases	612	823
Acquired | Consumer loans | Other consumer
Age analysis of past due loans
Past Due	0	1
Current	105	127
Total Loans and Leases	105	128
Loans and Leases Past Due Greater Than 90 Days and Accruing	0	0
Nonaccrual Loans and Leases	0	0
Acquired | 31-60 days past due
Age analysis of past due loans
Past Due	1,516	1,519
Acquired | 31-60 days past due | Commercial real estate loans
Age analysis of past due loans
Past Due	1,008	925
Acquired | 31-60 days past due | Commercial real estate loans | Commercial real estate
Age analysis of past due loans
Past Due	1,008	925
Acquired | 31-60 days past due | Commercial real estate loans | Multi-family mortgage
Age analysis of past due loans
Past Due	0	0
Acquired | 31-60 days past due | Commercial real estate loans | Construction
Age analysis of past due loans
Past Due		0
Acquired | 31-60 days past due | Commercial loans and leases
Age analysis of past due loans
Past Due	0	306
Acquired | 31-60 days past due | Commercial loans and leases | Commercial
Age analysis of past due loans
Past Due	0	306
Acquired | 31-60 days past due | Commercial loans and leases | Equipment financing
Age analysis of past due loans
Past Due	0	0
Acquired | 31-60 days past due | Consumer loans
Age analysis of past due loans
Past Due	508	288
Acquired | 31-60 days past due | Consumer loans | Residential mortgage
Age analysis of past due loans
Past Due	0	0
Acquired | 31-60 days past due | Consumer loans | Home equity
Age analysis of past due loans
Past Due	508	288
Acquired | 31-60 days past due | Consumer loans | Other consumer
Age analysis of past due loans
Past Due	0	0
Acquired | 61-90 days past due
Age analysis of past due loans
Past Due	507	416
Acquired | 61-90 days past due | Commercial real estate loans
Age analysis of past due loans
Past Due	0	0
Acquired | 61-90 days past due | Commercial real estate loans | Commercial real estate
Age analysis of past due loans
Past Due	0	0
Acquired | 61-90 days past due | Commercial real estate loans | Multi-family mortgage
Age analysis of past due loans
Past Due	0	0
Acquired | 61-90 days past due | Commercial real estate loans | Construction
Age analysis of past due loans
Past Due		0
Acquired | 61-90 days past due | Commercial loans and leases
Age analysis of past due loans
Past Due	44	0
Acquired | 61-90 days past due | Commercial loans and leases | Commercial
Age analysis of past due loans
Past Due	44	0
Acquired | 61-90 days past due | Commercial loans and leases | Equipment financing
Age analysis of past due loans
Past Due	0	0
Acquired | 61-90 days past due | Consumer loans
Age analysis of past due loans
Past Due	463	416
Acquired | 61-90 days past due | Consumer loans | Residential mortgage
Age analysis of past due loans
Past Due	463	318
Acquired | 61-90 days past due | Consumer loans | Home equity
Age analysis of past due loans
Past Due	0	97
Acquired | 61-90 days past due | Consumer loans | Other consumer
Age analysis of past due loans
Past Due	0	1
Acquired | Greater than 90 days past due
Age analysis of past due loans
Past Due	3,870	9,866
Acquired | Greater than 90 days past due | Commercial real estate loans
Age analysis of past due loans
Past Due	659	4,011
Acquired | Greater than 90 days past due | Commercial real estate loans | Commercial real estate
Age analysis of past due loans
Past Due	656	4,011
Acquired | Greater than 90 days past due | Commercial real estate loans | Multi-family mortgage
Age analysis of past due loans
Past Due	3	0
Acquired | Greater than 90 days past due | Commercial real estate loans | Construction
Age analysis of past due loans
Past Due		0
Acquired | Greater than 90 days past due | Commercial loans and leases
Age analysis of past due loans
Past Due	1,035	2,651
Acquired | Greater than 90 days past due | Commercial loans and leases | Commercial
Age analysis of past due loans
Past Due	1,022	2,651
Acquired | Greater than 90 days past due | Commercial loans and leases | Equipment financing
Age analysis of past due loans
Past Due	13	0
Acquired | Greater than 90 days past due | Consumer loans
Age analysis of past due loans
Past Due	2,176	3,204
Acquired | Greater than 90 days past due | Consumer loans | Residential mortgage
Age analysis of past due loans
Past Due	1,990	2,865
Acquired | Greater than 90 days past due | Consumer loans | Home equity
Age analysis of past due loans
Past Due	186	339
Acquired | Greater than 90 days past due | Consumer loans | Other consumer
Age analysis of past due loans
Past Due	$ 0	$ 0

Allowance for Loan and Lease 73

Allowance for Loan and Lease Losses (Recorded Investment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired Loans and Leases
Recorded investment	$ 58,685	$ 78,779
Unpaid principal balance	58,745	78,718
Related allowance	3,127	152
Average recorded investment	65,297	71,519	$ 57,340
Interest income recognized, Total	373	1,331	1,259
Recorded investment in loans and leases by portfolio segment
Total, Allowance	58,592	53,666
Total Loans and Leases	5,730,679	5,398,864
Commercial real estate loans
Recorded investment in loans and leases by portfolio segment
Total, Allowance	27,112	27,645
Total Loans and Leases	3,075,777	2,918,567
Commercial
Recorded investment in loans and leases by portfolio segment
Total, Allowance	26,333	20,906
Total Loans and Leases	1,624,111	1,495,408
Consumer loans
Recorded investment in loans and leases by portfolio segment
Total, Allowance	5,147	5,115
Total Loans and Leases	1,030,791	984,889
Originated
Impaired Loans and Leases
Recorded investment, loans with no related allowance recorded	38,392	53,205
Recorded investment, loans with related allowance recorded	11,968	4,589
Recorded investment	50,360	57,794
Unpaid principal balance with no related allowance recorded	38,502	53,129
Unpaid principal balance with related allowance recorded	11,918	4,589
Unpaid principal balance	50,420	57,718
Related allowance	3,105	125
Recorded investment, nonaccrual loans	24,900	34,100
Average recorded investment with no related allowance recorded	40,129	34,179	23,409
Average recorded investment with related allowance recorded	16,662	14,754	10,866
Average recorded investment	56,791	48,933	34,275
Interest income recognized with no related allowance recorded	311	828	792
Interest income recognized with related allowance recorded	38	201	207
Interest income recognized, Total	349	1,029	999
Recorded investment in loans and leases by portfolio segment
Individually evaluated for impairment, allowance	3,105	125
Collectively evaluated for impairment, allowance	54,447	52,288
Total, Allowance	57,552	52,413
Individually evaluated for impairment, Loans and Leases	45,487	55,445
Collectively evaluated for impairment, Loans and Leases	5,445,135	5,028,115
Total Loans and Leases	5,490,622	5,083,560
Originated | Commercial real estate loans
Impaired Loans and Leases
Recorded investment, loans with no related allowance recorded	9,978	9,113
Recorded investment, loans with related allowance recorded	3,056	3,984
Unpaid principal balance with no related allowance recorded	9,962	9,104
Unpaid principal balance with related allowance recorded	3,056	3,984
Related allowance	0	28
Average recorded investment with no related allowance recorded	10,125	6,608	3,999
Average recorded investment with related allowance recorded	3,058	4,715	5,132
Interest income recognized with no related allowance recorded	72	152	86
Interest income recognized with related allowance recorded	38	195	197
Recorded investment in loans and leases by portfolio segment
Individually evaluated for impairment, allowance	0	28
Collectively evaluated for impairment, allowance	26,366	26,830
Total, Allowance	26,366	26,858
Individually evaluated for impairment, Loans and Leases	13,031	13,097
Collectively evaluated for impairment, Loans and Leases	2,932,420	2,732,392
Total Loans and Leases	2,945,451	2,745,489
Originated | Commercial
Impaired Loans and Leases
Recorded investment, loans with no related allowance recorded	24,906	39,269
Recorded investment, loans with related allowance recorded	8,912	605
Unpaid principal balance with no related allowance recorded	25,040	39,210
Unpaid principal balance with related allowance recorded	8,862	605
Related allowance	3,105	97
Average recorded investment with no related allowance recorded	26,439	23,445	15,143
Average recorded investment with related allowance recorded	13,604	9,915	5,650
Interest income recognized with no related allowance recorded	225	600	641
Interest income recognized with related allowance recorded	0	6	10
Recorded investment in loans and leases by portfolio segment
Individually evaluated for impairment, allowance	3,105	97
Collectively evaluated for impairment, allowance	23,078	20,682
Total, Allowance	26,183	20,779
Individually evaluated for impairment, Loans and Leases	29,386	37,637
Collectively evaluated for impairment, Loans and Leases	1,582,032	1,437,472
Total Loans and Leases	1,611,418	1,475,109
Originated | Consumer loans
Impaired Loans and Leases
Recorded investment, loans with no related allowance recorded	3,508	4,823
Unpaid principal balance with no related allowance recorded	3,500	4,815
Average recorded investment with no related allowance recorded	3,565	4,126	4,267
Average recorded investment with related allowance recorded	0	124	84
Interest income recognized with no related allowance recorded	14	76	65
Interest income recognized with related allowance recorded	0	0	0
Recorded investment in loans and leases by portfolio segment
Individually evaluated for impairment, allowance	0	0
Collectively evaluated for impairment, allowance	5,003	4,776
Total, Allowance	5,003	4,776
Individually evaluated for impairment, Loans and Leases	3,070	4,711
Collectively evaluated for impairment, Loans and Leases	930,683	858,251
Total Loans and Leases	933,753	862,962
Acquired
Impaired Loans and Leases
Recorded investment, loans with no related allowance recorded	8,210	20,732
Recorded investment, loans with related allowance recorded	115	253
Recorded investment	8,325	20,985
Unpaid principal balance with no related allowance recorded	8,210	20,747
Unpaid principal balance with related allowance recorded	115	253
Unpaid principal balance	8,325	21,000
Related allowance	22	27
Recorded investment, nonaccrual loans	2,000	3,600
Average recorded investment with no related allowance recorded	8,390	20,698	21,465
Average recorded investment with related allowance recorded	116	1,888	1,600
Average recorded investment	8,506	22,586	23,065
Interest income recognized with no related allowance recorded	23	294	252
Interest income recognized with related allowance recorded	1	8	8
Interest income recognized, Total	24	302	260
Recorded investment in loans and leases by portfolio segment
Individually evaluated for impairment, allowance	22	27
Collectively evaluated for impairment, allowance	175	268
Total, Allowance	1,040	1,253
Individually evaluated for impairment, Loans and Leases	3,354	5,765
Collectively evaluated for impairment, Loans and Leases	96,564	128,577
Total Loans and Leases	240,057	315,304
Acquired | Acquired with deteriorated credit quality
Recorded investment in loans and leases by portfolio segment
Total, Allowance	843	958
Total Loans and Leases	140,139	180,962
Acquired | Commercial real estate loans
Impaired Loans and Leases
Recorded investment, loans with no related allowance recorded	1,880	10,400
Unpaid principal balance with no related allowance recorded	1,880	10,400
Average recorded investment with no related allowance recorded	1,996	8,906	9,200
Average recorded investment with related allowance recorded	0	1,093	713
Interest income recognized with no related allowance recorded	1	151	125
Interest income recognized with related allowance recorded	0	0	0
Recorded investment in loans and leases by portfolio segment
Individually evaluated for impairment, allowance	0	0
Collectively evaluated for impairment, allowance	145	221
Total, Allowance	746	787
Individually evaluated for impairment, Loans and Leases	0	690
Collectively evaluated for impairment, Loans and Leases	34,244	47,599
Total Loans and Leases	130,326	173,078
Acquired | Commercial real estate loans | Acquired with deteriorated credit quality
Recorded investment in loans and leases by portfolio segment
Total, Allowance	601	566
Total Loans and Leases	96,082	124,789
Acquired | Commercial
Impaired Loans and Leases
Recorded investment, loans with no related allowance recorded	1,594	3,948
Unpaid principal balance with no related allowance recorded	1,594	3,948
Average recorded investment with no related allowance recorded	1,610	4,255	4,428
Average recorded investment with related allowance recorded	0	364	638
Interest income recognized with no related allowance recorded	5	75	65
Interest income recognized with related allowance recorded	0	0	0
Recorded investment in loans and leases by portfolio segment
Individually evaluated for impairment, allowance	0	0
Collectively evaluated for impairment, allowance	13	13
Total, Allowance	150	127
Individually evaluated for impairment, Loans and Leases	1,487	3,047
Collectively evaluated for impairment, Loans and Leases	6,399	10,863
Total Loans and Leases	12,693	20,299
Acquired | Commercial | Acquired with deteriorated credit quality
Recorded investment in loans and leases by portfolio segment
Total, Allowance	137	114
Total Loans and Leases	4,807	6,389
Acquired | Consumer loans
Impaired Loans and Leases
Recorded investment, loans with no related allowance recorded	4,736	6,384
Recorded investment, loans with related allowance recorded	115	253
Unpaid principal balance with no related allowance recorded	4,736	6,399
Unpaid principal balance with related allowance recorded	115	253
Related allowance	22	27
Average recorded investment with no related allowance recorded	4,784	7,537	7,837
Average recorded investment with related allowance recorded	116	431	249
Interest income recognized with no related allowance recorded	17	68	62
Interest income recognized with related allowance recorded	1	8	$ 8
Recorded investment in loans and leases by portfolio segment
Individually evaluated for impairment, allowance	22	27
Collectively evaluated for impairment, allowance	17	34
Total, Allowance	144	339
Individually evaluated for impairment, Loans and Leases	1,867	2,028
Collectively evaluated for impairment, Loans and Leases	55,921	70,115
Total Loans and Leases	97,038	121,927
Acquired | Consumer loans | Acquired with deteriorated credit quality
Recorded investment in loans and leases by portfolio segment
Total, Allowance	105	278
Total Loans and Leases	$ 39,250	$ 49,784

Allowance for Loan and Lease 74

Allowance for Loan and Lease Losses (Troubled Debt Restructurings) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)loan	Dec. 31, 2015USD ($)loan
Receivables [Abstract]
On accrual	$ 16,241	$ 13,883
On nonaccrual	9,770	11,919
Total troubled debt restructurings	26,011	$ 25,802
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan		32	20
Recorded Investment, At Modification		$ 12,027	$ 7,164
Recorded Investment, At end of period	7,000	8,021	6,873
Specific Allowance for Loan and Lease Losses		20	119
Nonaccrual Loans and Leases		$ 7,798	$ 508
Defaulted, number of loans/leases | loan		4	4
Defaulted, recorded investment		$ 705	$ 300
Loans with one modification	4,917	7,796	4,242
Loans with more than one modification	2,084	225	2,631
Extended maturity
Financing Receivable, Modifications [Line Items]
Loans with one modification	2,810	599	2,215
Loans with more than one modification	1,910	225	2,598
Adjusted principal
Financing Receivable, Modifications [Line Items]
Loans with one modification	19	249	0
Interest only
Financing Receivable, Modifications [Line Items]
Loans with one modification	174	1,493	1,335
Combination maturity, principal, interest rate
Financing Receivable, Modifications [Line Items]
Loans with one modification	1,914	5,455	692
Loans with more than one modification	$ 174	$ 0	$ 33
Originated
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan	27	27	14
Recorded Investment, At Modification	$ 10,737	$ 11,653	$ 6,322
Recorded Investment, At end of period	7,001	7,653	6,045
Specific Allowance for Loan and Lease Losses	328	0	119
Nonaccrual Loans and Leases	$ 3,629	$ 7,653	$ 508
Defaulted, number of loans/leases | loan	3	4	2
Defaulted, recorded investment	$ 1,549	$ 705	$ 265
Originated | Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan	1		0
Recorded Investment, At Modification	$ 189		$ 0
Recorded Investment, At end of period	189		0
Specific Allowance for Loan and Lease Losses	0		0
Nonaccrual Loans and Leases	$ 0		$ 0
Defaulted, number of loans/leases | loan	0		0
Defaulted, recorded investment	$ 0		$ 0
Originated | Multi-family mortgage
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan		2
Recorded Investment, At Modification		$ 1,155
Recorded Investment, At end of period		1,114
Specific Allowance for Loan and Lease Losses		0
Nonaccrual Loans and Leases		$ 1,114
Defaulted, number of loans/leases | loan		0
Defaulted, recorded investment		$ 0
Originated | Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan	10	22	9
Recorded Investment, At Modification	$ 7,861	$ 9,701	$ 5,757
Recorded Investment, At end of period	3,911	6,015	5,497
Specific Allowance for Loan and Lease Losses	191	0	119
Nonaccrual Loans and Leases	$ 2,189	$ 6,015	$ 258
Defaulted, number of loans/leases | loan	2	2	1
Defaulted, recorded investment	$ 1,361	$ 364	$ 237
Originated | Equipment financing
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan	16	3	1
Recorded Investment, At Modification	$ 2,687	$ 797	$ 112
Recorded Investment, At end of period	2,901	524	100
Specific Allowance for Loan and Lease Losses	137	0	0
Nonaccrual Loans and Leases	$ 1,440	$ 524	$ 0
Defaulted, number of loans/leases | loan	1	2	0
Defaulted, recorded investment	$ 188	$ 341	$ 0
Originated | Residential mortgage
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan			1
Recorded Investment, At Modification			$ 100
Recorded Investment, At end of period			150
Specific Allowance for Loan and Lease Losses			0
Nonaccrual Loans and Leases			$ 151
Defaulted, number of loans/leases | loan			0
Defaulted, recorded investment			$ 0
Originated | Home equity
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan			3
Recorded Investment, At Modification			$ 353
Recorded Investment, At end of period			298
Specific Allowance for Loan and Lease Losses			0
Nonaccrual Loans and Leases			$ 99
Defaulted, number of loans/leases | loan			1
Defaulted, recorded investment			$ 28
Acquired
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan		5	6
Recorded Investment, At Modification		$ 374	$ 842
Recorded Investment, At end of period		368	828
Specific Allowance for Loan and Lease Losses		20	0
Nonaccrual Loans and Leases		$ 145	$ 0
Defaulted, number of loans/leases | loan		0	2
Defaulted, recorded investment		$ 0	$ 35
Acquired | Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan			4
Recorded Investment, At Modification			$ 642
Recorded Investment, At end of period			632
Specific Allowance for Loan and Lease Losses			0
Nonaccrual Loans and Leases			$ 0
Defaulted, number of loans/leases | loan			1
Defaulted, recorded investment			$ 11
Acquired | Home equity
Financing Receivable, Modifications [Line Items]
Number of Loans/ Leases | loan		5	2
Recorded Investment, At Modification		$ 374	$ 200
Recorded Investment, At end of period		368	196
Specific Allowance for Loan and Lease Losses		20	0
Nonaccrual Loans and Leases		$ 145	$ 0
Defaulted, number of loans/leases | loan		0	1
Defaulted, recorded investment		$ 0	$ 24

Allowance for Loan and Lease 75

Allowance for Loan and Lease Losses (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017USD ($)class	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Unfunded credit commitments liability included in other liabilities	$ 1,700,000	$ 1,500,000
Unfunded credit commitments liability charge-off	0	0	$ 0
Total loans and leases	5,730,679,000	5,398,864,000
Related allowance	3,127,000	152,000
Specific allowance for loan and lease losses	3,100,000	200,000
General allowance for loan and lease losses	55,500,000	53,500,000
Increase (decrease) in total debt restructured loans and leases	200,000
Total troubled debt restructurings	26,011,000	25,802,000
Nonaccrual Loans and Leases	27,272,000	40,077,000
Increase in general portion of the allowance for loan and lease losses	2,000,000
Increase (decrease) in specific portion of the allowance for loan and lease losses	$ 3,000,000
Number of days past due, non-accrual status (in days)	90 days
Financial impact of modification of performing and nonperforming loans	$ 4,800,000	4,300,000	$ 200,000
Commitments to lend funds to debtors owing receivables whose terms had been modified in troubled debt restructurings	0
Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	240,057,000	315,304,000
Related allowance	22,000	27,000
Nonaccrual Loans and Leases	1,997,000	3,561,000
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	2,174,969,000	2,050,382,000
Commercial real estate | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	105,577,000	143,128,000
Multi-family mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	760,670,000	731,186,000
Multi-family mortgage | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	24,749,000	29,736,000
Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	140,138,000	136,999,000
Construction | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	0	214,000
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	705,004,000	635,426,000
Commercial | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	8,179,000	14,141,000
Equipment financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	866,488,000	799,860,000
Equipment financing | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	4,514,000	6,158,000
Condominium association
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	52,619,000	60,122,000
Condominium association | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	0	0
Residential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	660,065,000	624,349,000
Residential mortgage | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	55,168,000	68,919,000
Home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	355,954,000	342,241,000
Home equity | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	41,765,000	52,880,000
Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	14,772,000	12,158,000
Other consumer | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	105,000	128,000
Taxi Medallion Portfolio
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	19,700,000	31,100,000
Related allowance	3,800,000	1,300,000
Specific allowance for loan and lease losses	2,700,000	100,000
General allowance for loan and lease losses	1,100,000	1,200,000
Increase (decrease) in total debt restructured loans and leases	(2,400,000)
Total troubled debt restructurings	3,700,000	6,100,000
Nonaccrual Loans and Leases	$ 7,800,000	13,400,000
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of loan classes within specific portfolio | class	3
Commercial loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of loan classes within specific portfolio | class	3
Total loans and leases	$ 1,624,111,000	1,495,408,000
Commercial loans | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	12,693,000	20,299,000
Nonaccrual Loans and Leases	1,254,000	2,387,000
Commercial loans | Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 705,004,000	635,426,000
Percentage of loans to aggregate outstanding amount	12.30%
Commercial loans | Commercial | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 8,179,000	14,141,000
Nonaccrual Loans and Leases	1,254,000	2,387,000
Commercial loans | Equipment financing
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 866,488,000	799,860,000
Percentage of loans to aggregate outstanding amount	15.10%
Commercial loans | Equipment financing | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 4,514,000	6,158,000
Nonaccrual Loans and Leases	0	0
Commercial loans | Condominium association
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 52,619,000	60,122,000
Percentage of loans to aggregate outstanding amount	0.90%
Consumer Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of loan classes within specific portfolio | class	3
Commercial real estate loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of loan classes within specific portfolio | class	3
Total loans and leases	$ 3,075,777,000	2,918,567,000
Commercial real estate loans | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	130,326,000	173,078,000
Nonaccrual Loans and Leases	131,000	305,000
Commercial real estate loans | Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 2,174,969,000	2,050,382,000
Percentage of loans to aggregate outstanding amount	38.00%
Commercial real estate loans | Commercial real estate | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 105,577,000	143,128,000
Nonaccrual Loans and Leases	131,000	305,000
Commercial real estate loans | Multi-family mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 760,670,000	731,186,000
Percentage of loans to aggregate outstanding amount	13.30%
Commercial real estate loans | Multi-family mortgage | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 24,749,000	29,736,000
Nonaccrual Loans and Leases	0	0
Commercial real estate loans | Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 140,138,000	136,999,000
Percentage of loans to aggregate outstanding amount	2.40%
Commercial real estate loans | Construction | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases		214,000
Nonaccrual Loans and Leases		0
Consumer loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of loan classes within specific portfolio | class	3
Total loans and leases	$ 1,030,791,000	984,889,000
Loans not made, loan to value ratio, minimum (as a percent)	80.00%
Number of days past due, non-accrual status (in days)	90 days
Consumer loans | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 97,038,000	121,927,000
Related allowance	22,000	27,000
Nonaccrual Loans and Leases	612,000	869,000
Consumer loans | Residential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 660,065,000	624,349,000
Percentage of loans to aggregate outstanding amount	11.50%
Consumer loans | Residential mortgage | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 55,168,000	68,919,000
Nonaccrual Loans and Leases	0	46,000
Consumer loans | Home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 355,954,000	342,241,000
Percentage of loans to aggregate outstanding amount	6.20%
Consumer loans | Home equity | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 41,765,000	52,880,000
Nonaccrual Loans and Leases	612,000	823,000
Consumer loans | Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 14,772,000	18,299,000
Percentage of loans to aggregate outstanding amount	0.30%
Consumer loans | Other consumer | Acquired
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans and leases	$ 105,000	128,000
Nonaccrual Loans and Leases	$ 0	$ 0

Premises and Equipment (Summary

Premises and Equipment (Summary of Premises and Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Premises and Equipment
Premises and Equipment, gross amount	$ 143,706	$ 134,966
Accumulated depreciation and amortization	63,423	58,790
Total premises and equipment	80,283	76,176
Land
Premises and Equipment
Premises and Equipment, gross amount	11,057	7,562
Fine art
Premises and Equipment
Premises and Equipment, gross amount	495	472
Computer equipment
Premises and Equipment
Premises and Equipment, gross amount	$ 9,728	$ 9,004
Estimated useful life	3 years	3 years
Vehicles
Premises and Equipment
Premises and Equipment, gross amount	$ 126	$ 221
Core processing system and software
Premises and Equipment
Premises and Equipment, gross amount	19,791	19,433
Furniture, fixtures and equipment
Premises and Equipment
Premises and Equipment, gross amount	14,226	13,439
Office building and improvements
Premises and Equipment
Premises and Equipment, gross amount	$ 88,283	$ 84,835
Minimum | Vehicles
Premises and Equipment
Estimated useful life	3 years	3 years
Minimum | Core processing system and software
Premises and Equipment
Estimated useful life	3 years	3 years
Minimum | Furniture, fixtures and equipment
Premises and Equipment
Estimated useful life	5 years	5 years
Minimum | Office building and improvements
Premises and Equipment
Estimated useful life	10 years	10 years
Maximum | Vehicles
Premises and Equipment
Estimated useful life	5 years	5 years
Maximum | Core processing system and software
Premises and Equipment
Estimated useful life	7 years 6 months	7 years 6 months
Maximum | Furniture, fixtures and equipment
Premises and Equipment
Estimated useful life	25 years	25 years
Maximum | Office building and improvements
Premises and Equipment
Estimated useful life	40 years	40 years

Premises and Equipment (Narrati

Premises and Equipment (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 7.4	$ 7.2	$ 7.2

Goodwill and Other Intangible78

Goodwill and Other Intangible Assets (Rollforward of Goodwill) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Balance at beginning of year	$ 137,890	$ 137,890	$ 137,890
Additions	0	0	0
Adjustments to original goodwill	0	0	0
Balance at end of year	$ 137,890	$ 137,890	$ 137,890

Goodwill and Other Intangible79

Goodwill and Other Intangible Assets (Summary of Intangible Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other intangibe assets:
Gross amount	$ 39,782	$ 39,782
Accumulated amortization	33,738	31,649
Carrying Amount	6,044	8,133
Core deposits
Other intangibe assets:
Gross amount	36,172	36,172
Accumulated amortization	31,217	29,128
Carrying Amount	4,955	7,044
Trade name
Other intangibe assets:
Gross amount	1,600	1,600
Accumulated amortization	511	511
Carrying Amount	1,089	1,089
Trust relationship
Other intangibe assets:
Gross amount	1,568	1,568
Accumulated amortization	1,568	1,568
Carrying Amount	0	0
Other intangible
Other intangibe assets:
Gross amount	442	442
Accumulated amortization	442	442
Carrying Amount	$ 0	$ 0

Goodwill and Other Intangible80

Goodwill and Other Intangible Assets (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013
Indefinite-lived Intangible Assets [Line Items]
Impairment losses	$ 0	$ 0	$ 0
Trade name
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived intangible assets				$ 1,100,000
Core deposits
Indefinite-lived Intangible Assets [Line Items]
Weighted-average amortization period	7 years 9 months 18 days

Goodwill and Other Intangible81

Goodwill and Other Intangible Assets (Future Amortization Expense) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2,018	$ 1,669
2,019	1,295
2,020	944
2,021	601
2,022	299
Thereafter	147
Total	$ 4,955

Other Assets (Narrative) (Detai

Other Assets (Narrative) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)project	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)policyproject		Dec. 31, 2016USD ($)policy		Dec. 31, 2015USD ($)policy		Jan. 01, 2015USD ($)
Acquisitions
Number of policies owned | policy									9		9		9
Net income attributable to Brookline Bancorp, Inc.	$ 6,827	$ 15,366	$ 14,880	$ 13,445	$ 13,279	$ 13,617	$ 12,654	$ 12,812	$ 50,518	[1]	$ 52,362	[1]	$ 49,782	[1]
Accounting Standards Update 2014-01
Acquisitions
Net income attributable to Brookline Bancorp, Inc.													500
Retained earnings															$ 1,100
Affordable housing project
Acquisitions
Number of investments | project	12								12
Maximum percentage of outstanding equity interest that can be invested by the entity in any single project									50.00%
Other non-interest income
Acquisitions
Tax exempt BOLI income									$ 1,000		$ 1,100		$ 1,000
BankRI
Acquisitions
Number of policies owned | policy									7		7
Net cash surrender value	$ 38,900				37,900				$ 38,900		$ 37,900
First Ipswich
Acquisitions
Number of policies owned | policy									2		2
Net cash surrender value	$ 800				$ 800				$ 800		$ 800
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjNlMjQ5ZGFhMTk1YTQ2MWY5YTYxNGE1ZjY5NGNkOWQyfFRleHRTZWxlY3Rpb246MUQ1NTE1RjYxMjZDOTNCRTNEMEZGRTY3MTNDNDMyNkYM}

Other Assets (Additional Inform

Other Assets (Additional Information on Investments in Affordable Housing Projects) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments in Affordable Housing Projects [Abstract]
Investments in affordable housing projects included in other assets	[1]	$ 91,609	$ 88,086
Unfunded commitments related to affordable housing projects included in other liabilities		1,700	1,500
Investment amortization included in provision for income taxes		1,844	1,726	$ 1,654
Amount recognized as income tax benefit		623	598	$ 656
Affordable housing project
Investments in Affordable Housing Projects [Abstract]
Investments in affordable housing projects included in other assets		11,432	11,565
Unfunded commitments related to affordable housing projects included in other liabilities		1,933	1,686
Investment in affordable housing tax credits		1,745	1,753
Investment in affordable housing tax benefits		$ 653	$ 598
[1]	Previously reported amounts prior to January 1, 2015 have been restated to reflect a retrospective change in accounting principle for investments in qualified affordable housing projects, in accordance with ASU 2014-01. Refer to Note 10, "Other Assets".

Deposits (Summary of Deposits)

Deposits (Summary of Deposits) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Banking and Thrift [Abstract]
Demand checking accounts	$ 942,583	$ 900,474
NOW accounts	350,568	323,160
Savings accounts	646,359	613,061
Money market accounts	1,724,363	1,733,359
Total core deposit accounts	3,663,873	3,570,054
Certificate of deposit accounts maturing:
Within six months	363,866	345,339
After six months but within 1 year	342,500	233,470
After 1 year but within 2 years	300,921	264,993
After 2 years but within 3 years	90,805	84,673
After 3 years but within 4 years	57,926	52,522
After 4 years but within 5 years	50,380	59,910
After 5 Years	1,072	115
Total certificate of deposit accounts	1,207,470	1,041,022
Total deposits	$ 4,871,343	$ 4,611,076
Weighted Average Rate of deposit accounts
Demand checking accounts (as a percent)	0.00%	0.00%
NOW accounts (as a percent)	0.07%	0.07%
Savings accounts (as a percent)	0.25%	0.20%
Money market savings accounts (as a percent)	0.56%	0.47%
Total transaction deposit accounts (as a percent)	0.31%	0.27%
Weighted Average Rate of certificate of deposit accounts maturing:
Within six months (as a percent)	0.93%	0.77%
After six months but within 1 year (as a percent)	1.09%	0.83%
After 1 year but within 2 years (as a percent)	1.48%	1.08%
After 2 years but within 3 years (as a percent)	1.87%	1.56%
After 3 years but within 4 years (as a percent)	1.79%	1.88%
After 4 years but within 5 years (as a percent)	2.02%	1.78%
After 5 years (as a percent)	1.03%	1.66%
Total certificate of deposit accounts (as a percent)	1.27%	1.04%
Total of weighted average rate of deposits (as a percent)	0.55%	0.44%

Deposits (Interest Expense) (De

Deposits (Interest Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest-bearing deposits:
NOW accounts	$ 225	$ 209	$ 179
Savings accounts	1,297	1,322	1,094
Money market accounts	8,863	7,549	6,935
Certificate of deposit accounts	12,903	10,990	9,272
Total interest-bearing deposits	$ 23,288	$ 20,070	$ 17,480

Deposits (Narrative) (Details)

Deposits (Narrative) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Banking and Thrift [Abstract]
Threshold for disclosure of time deposit issued amounts	$ 250,000	$ 250,000
Time Deposits, $100,000 or More	265,800,000	196,700,000
Related party deposits	41,400,000	39,500,000
Deposits pledged as collateral	$ 165,500,000	$ 160,900,000

Borrowed Funds (Components and

Borrowed Funds (Components and Interest Expenses of Borrowed Funds) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total borrowed funds	$ 1,020,819	$ 1,044,086
Total interest expense on borrowed funds	16,581	15,914	$ 15,065
Advances from the FHLBB
Debt Instrument [Line Items]
Total borrowed funds	889,909	910,774
Total interest expense on borrowed funds	11,330	10,760	9,950
Subordinated debentures and notes
Debt Instrument [Line Items]
Total borrowed funds	83,271	83,105
Total interest expense on borrowed funds	5,081	5,038	5,001
Other borrowed funds
Debt Instrument [Line Items]
Total borrowed funds	47,639	50,207
Total interest expense on borrowed funds	$ 170	$ 116	$ 114

Borrowed Funds (Narrative) (Det

Borrowed Funds (Narrative) (Details) - USD ($)	Sep. 15, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Securities available-for-sale and loans pledged as collateral		$ 1,900,000,000	$ 1,800,000,000
Total available borrowing capacity from Federal Home Loan Bank		1,700,000,000
Qualifying collateral available for Federal Home Loan Bank borrowings		2,500,000,000
Outstanding at end of year		1,020,819,000	1,044,086,000
Accretion adjustment		(2,042,000)	(2,158,000)	$ (1,841,000)
Repurchase agreements
Debt Instrument [Line Items]
Decrease in agreement amount		12,600,000
Outstanding at end of year		37,600,000	50,200,000
Committed line of credit | Line of credit
Debt Instrument [Line Items]
Borrowing capacity		12,000,000
Uncommitted lines of credit | Line of credit
Debt Instrument [Line Items]
Borrowing capacity		203,000,000
Outstanding balance		10,000,000
Subordinated debenture maturing September 15, 2029
Debt Instrument [Line Items]
Outstanding at end of year		$ 73,825,000	73,725,000
Subordinated debenture maturing September 15, 2029 | Interest rate period 1
Debt Instrument [Line Items]
Fixed interest rate		6.00%
Subordinated debenture maturing September 15, 2029 | Interest rate period 2 | LIBOR
Debt Instrument [Line Items]
Variable interest rate spread (as a percent)		3.315%
Subordinated debenture maturing September 15, 2029 | Subordinated debentures and notes
Debt Instrument [Line Items]
Principal amount	$ 75,000,000
Accretion adjustment		$ 600,000	600,000
Capitalized financing costs		$ 1,200,000	$ 1,300,000
Subordinated debenture maturing September 15, 2029 | Subordinated debentures and notes | Interest rate period 1
Debt Instrument [Line Items]
Fixed interest rate	6.00%
Subordinated debenture maturing September 15, 2029 | Subordinated debentures and notes | Interest rate period 2 | LIBOR
Debt Instrument [Line Items]
Variable interest rate spread (as a percent)	3.315%

Borrowed Funds (FHLBB Advances)

Borrowed Funds (FHLBB Advances) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amount
Within 1 year	$ 514,314	$ 651,489
Over 1 year to 2 years	279,928	168,598
Over 2 years to 3 years	16,026	14,354
Over 3 years to 4 years	30,849	85
Over 4 years to 5 years	33,217	1,110
Over 5 years	15,575	75,138
Total	889,909	910,774
Callable Amount
Within 1 year	55,000	75,705
Over 1 year to 2 years	115,000	290,311
Over 2 years to 3 years	0	0
Over 3 years to 4 years	0	0
Over 4 years to 5 years	0	0
Over 5 years	0	0
Total	$ 170,000	$ 366,016
Weighted Average Rate
Within 1 year (as a percent)	1.43%	1.22%
Over 1 year to 2 years (as a percent)	1.70%	1.44%
Over 2 years to 3 years (as a percent)	0.47%	0.09%
Over 3 years to 4 years (as a percent)	0.41%	2.04%
Over 4 years to 5 years (as a percent)	0.30%	3.07%
Over 5 years (as a percent)	3.95%	1.08%
Weighted average interest rate of total advances from the FHLB (as a percent)	1.47%	1.24%

Borrowed Funds (Other Borrowed

Borrowed Funds (Other Borrowed Funds) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Outstanding at end of year	$ 1,020,819	$ 1,044,086
Other borrowed funds
Debt Instrument [Line Items]
Outstanding at end of year	47,639	50,207
Average outstanding for the year	45,908	41,053
Maximum outstanding at any month-end	$ 54,064	$ 50,207
Weighted average rate at end of year	0.46%	0.14%
Weighted average rate paid for the year	0.37%	0.27%

Borrowed Funds (Summary of Subo

Borrowed Funds (Summary of Subordinated Debentures) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total borrowed funds	$ 1,020,819	$ 1,044,086
Subordinated debenture maturing June 26, 2033
Debt Instrument [Line Items]
Total borrowed funds	4,778	4,752
Subordinated debenture maturing March 17, 2034
Debt Instrument [Line Items]
Total borrowed funds	4,668	4,628
Subordinated debenture maturing September 15, 2029
Debt Instrument [Line Items]
Total borrowed funds	73,825	73,725
Subordinated Debentures Maturing June 26, 2033, March 17, 2034 and September 15, 2029
Debt Instrument [Line Items]
Total borrowed funds	$ 83,271	$ 83,105
LIBOR | Subordinated debenture maturing June 26, 2033
Debt Instrument [Line Items]
Variable interest rate spread (as a percent)	3.10%
LIBOR | Subordinated debenture maturing March 17, 2034
Debt Instrument [Line Items]
Variable interest rate spread (as a percent)	2.79%

Commitments and Contingencies92

Commitments and Contingencies (Financial Instruments with Off-Balance Sheet Risk) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Loan commitments
Unadvanced portion of loans and leases	$ 571,668	$ 580,416
Unused lines of credit:
Home equity	407,552	340,682
Other consumer	34,191	13,157
Other commercial	323	208
Unused letters of credit:
Financial standby letters of credit	12,422	11,720
Performance standby letters of credit	736	516
Commercial and similar letters of credit	184	785
Commercial real estate
Loan commitments
Commitments to originate loans and leases	76,653	27,750
Commercial
Loan commitments
Commitments to originate loans and leases	83,270	71,716
Residential mortgage
Loan commitments
Commitments to originate loans and leases	28,745	28,179
Receive fixed, pay variable
Unused letters of credit:
Derivatives	494,659	383,780
Pay fixed, receive variable
Unused letters of credit:
Derivatives	494,659	383,780
Risk participation-out agreements
Unused letters of credit:
Derivatives	36,627	16,961
Risk participation-in agreements
Unused letters of credit:
Derivatives	3,825	0
Derivatives not designed as hedging instruments | Receive fixed, pay variable
Unused letters of credit:
Derivatives	494,659	383,780
Derivatives not designed as hedging instruments | Pay fixed, receive variable
Unused letters of credit:
Derivatives	494,659	383,780
Derivatives not designed as hedging instruments | Risk participation-out agreements
Unused letters of credit:
Derivatives	36,627	16,961
Derivatives not designed as hedging instruments | Risk participation-in agreements
Unused letters of credit:
Derivatives	3,825
Derivatives not designed as hedging instruments | Foreign exchange contracts | Buys foreign currency, sells U.S. currency
Unused letters of credit:
Derivatives	1,495	195
Derivatives not designed as hedging instruments | Foreign exchange contracts | Sells foreign currency, buys U.S. currency
Unused letters of credit:
Derivatives	$ 1,502	$ 195

Commitments and Contingencies93

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leased Assets [Line Items]
Unfunded credit commitments liability	$ 1,700	$ 1,500
Fair value of interest rate swap assets	9,000	9,700
Fair value of interest rate swap liabilities	8,900	9,700
Total rental expense	5,500	5,300	$ 5,500
Lease acceleration related to relocation			200
Proceeds from sales of loans and leases held-for-sale, net	32,073	55,636	64,398
Rental income	$ 400	$ 400	400
Indirect automobile loans
Operating Leased Assets [Line Items]
Proceeds from sales of loans and leases held-for-sale, net			$ 255,200
Minimum
Operating Leased Assets [Line Items]
Term of operating lease	5 years
Maximum
Operating Leased Assets [Line Items]
Term of operating lease	25 years

Commitments and Contingencies94

Commitments and Contingencies (Future Minimum Rental Payments) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Summary of future minimum rental payments under noncancellable operating leases year ending December 31
2,018	$ 4,921
2,019	4,053
2,020	3,497
2,021	2,988
2,022	2,743
Thereafter	10,138
Total	$ 28,340

Earnings per Share (EPS) (Detai

Earnings per Share (EPS) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income (in usd)									$ 50,518	$ 52,362	$ 49,782
Weighted average shares outstanding	76,583,712	76,452,539	74,325,013	70,386,766	70,362,702	70,299,722	70,196,950	70,186,921	74,459,508	70,261,954	70,098,561
Effect of dilutive securities									351,900	182,129	137,307
Adjusted weighted average shares outstanding	76,868,307	76,961,948	74,810,088	70,844,096	70,592,204	70,450,760	70,388,438	70,343,408	74,811,408	70,444,083	70,235,868
Basic EPS (in dollars per share)	$ 0.09	$ 0.20	$ 0.20	$ 0.19	$ 0.19	$ 0.19	$ 0.18	$ 0.18	$ 0.68	$ 0.74	$ 0.71
Diluted EPS (in dollars per share)	$ 0.09	$ 0.20	$ 0.20	$ 0.19	$ 0.19	$ 0.19	$ 0.18	$ 0.18	$ 0.68	$ 0.74	$ 0.71

Comprehensive Income_(Loss) (Ch

Comprehensive Income/(Loss) (Changes in AOCI) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in accumulated other comprehensive (loss) income by component, net of tax
Balance at the beginning of the period	[1]	$ 695,544
Other comprehensive loss		(1,069)	$ (1,342)	$ (854)
Balance at the end of the period	[1]	803,830	695,544
Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive (loss) income by component, net of tax
Balance at the beginning of the period		(3,818)	(2,476)	(1,622)
Balance at the end of the period		(4,887)	(3,818)	(2,476)
Investment Securities Available-for-Sale
Changes in accumulated other comprehensive (loss) income by component, net of tax
Balance at the beginning of the period		(4,213)	(2,827)	(1,733)
Other comprehensive loss		(817)	(1,386)	(1,094)
Balance at the end of the period		(5,030)	(4,213)	(2,827)
Postretirement Benefits
Changes in accumulated other comprehensive (loss) income by component, net of tax
Balance at the beginning of the period		395	351	111
Other comprehensive loss		(252)	44	240
Balance at the end of the period		$ 143	$ 395	$ 351
[1]	Previously reported amounts prior to January 1, 2015 have been restated to reflect a retrospective change in accounting principle for investments in qualified affordable housing projects, in accordance with ASU 2014-01. Refer to Note 10, "Other Assets".

Derivatives and Hedging Activ97

Derivatives and Hedging Activities (Summary of Derivative Positions) (Details)	12 Months Ended
	Dec. 31, 2017USD ($)derivative	Dec. 31, 2016USD ($)derivative
Loss Recognized in Income on Derivatives
Gain (loss) recognized in income	$ 62,000
Estimated net credit risk exposure	0
Collateral posted	26,700,000	$ 34,500,000
Receive fixed, pay variable
Derivatives and Hedging Activities
Total	$ 494,659,000	$ 383,780,000
Receive fixed, pay variable | Derivatives not designed as hedging instruments
Derivatives and Hedging Activities
Number of Positions | derivative	66,000	54,000
Notional Amount Maturing, Less than 1 year	$ 3,903,000	$ 0
Notional Amount Maturing, Less than 2 years	2,036,000	4,025,000
Notional Amount Maturing, Less than 3 years	27,992,000	2,141,000
Notional Amount Maturing, Less than 4 years	0	29,501,000
Notional Amount Maturing, Thereafter	460,728,000	348,113,000
Total	494,659,000	383,780,000
Fair Value	8,865,000	9,738,000
Pay fixed, receive variable
Derivatives and Hedging Activities
Total	$ 494,659,000	$ 383,780,000
Pay fixed, receive variable | Derivatives not designed as hedging instruments
Derivatives and Hedging Activities
Number of Positions | derivative	66,000	54,000
Notional Amount Maturing, Less than 1 year	$ 3,903,000	$ 0
Notional Amount Maturing, Less than 2 years	2,036,000	4,025,000
Notional Amount Maturing, Less than 3 years	27,992,000	2,141,000
Notional Amount Maturing, Less than 4 years	0	29,501,000
Notional Amount Maturing, Thereafter	460,728,000	348,113,000
Total	494,659,000	383,780,000
Fair Value	8,865,000	9,738,000
Risk participation-out agreements
Derivatives and Hedging Activities
Total	36,627,000	$ 16,961,000
Loss Recognized in Income on Derivatives
Gain (loss) recognized in income	$ 55,000
Risk participation-out agreements | Derivatives not designed as hedging instruments
Derivatives and Hedging Activities
Number of Positions | derivative	8,000	5,000
Notional Amount Maturing, Less than 1 year	$ 0	$ 0
Notional Amount Maturing, Less than 2 years	0	0
Notional Amount Maturing, Less than 3 years	8,613,000	0
Notional Amount Maturing, Less than 4 years	0	9,078,000
Notional Amount Maturing, Thereafter	28,014,000	7,883,000
Total	36,627,000	16,961,000
Fair Value	65,000	20,000
Risk participation-in agreements
Derivatives and Hedging Activities
Total	$ 3,825,000	$ 0
Risk participation-in agreements | Derivatives not designed as hedging instruments
Derivatives and Hedging Activities
Number of Positions | derivative	1,000
Notional Amount Maturing, Less than 1 year	$ 0
Notional Amount Maturing, Less than 2 years	0
Notional Amount Maturing, Less than 3 years	0
Notional Amount Maturing, Less than 4 years	0
Notional Amount Maturing, Thereafter	3,825,000
Total	3,825,000
Fair Value	10,000
Foreign exchange contracts
Loss Recognized in Income on Derivatives
Gain (loss) recognized in income	7,000
Loan level derivatives
Loss Recognized in Income on Derivatives
Gain (loss) recognized in income	$ 0
Buys foreign currency, sells U.S. currency | Foreign exchange contracts | Derivatives not designed as hedging instruments
Derivatives and Hedging Activities
Number of Positions | derivative	22,000	3,000
Notional Amount Maturing, Less than 1 year	$ 1,495,000	$ 195,000
Notional Amount Maturing, Less than 2 years	0	0
Notional Amount Maturing, Less than 3 years	0	0
Notional Amount Maturing, Less than 4 years	0	0
Notional Amount Maturing, Thereafter	0	0
Total	1,495,000	195,000
Fair Value	$ 65,000	$ 0
Sells foreign currency, buys U.S. currency | Foreign exchange contracts | Derivatives not designed as hedging instruments
Derivatives and Hedging Activities
Number of Positions | derivative	44,000	3,000
Notional Amount Maturing, Less than 1 year	$ 1,502,000	$ 195,000
Notional Amount Maturing, Less than 2 years	0	0
Notional Amount Maturing, Less than 3 years	0	0
Notional Amount Maturing, Less than 4 years	0	0
Notional Amount Maturing, Thereafter	0	0
Total	1,502,000	195,000
Fair Value	$ 72,000	$ 0

Derivatives and Hedging Activ98

Derivatives and Hedging Activities (Amounts Subject to Master Netting Agreement) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Asset derivatives
Gross Amounts Recognized, Assets	$ 9,002	$ 9,758
Net Amounts Presented in the Statement of Financial Position	9,002	9,758
Net Amount	9,002	9,758
Liability derivatives
Gross Amounts Recognized, Liabilities	8,940	9,738
Net Amounts Presented in the Statement of Financial Position	8,940	9,738
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments Pledged	25,159	33,744
Cash Collateral Pledged	1,510	720
Net Amount	0	0
Loan level derivatives
Asset derivatives
Gross Amounts Recognized, Assets	8,865	9,738
Net Amounts Presented in the Statement of Financial Position	8,865	9,738
Net Amount	8,865	9,738
Liability derivatives
Gross Amounts Recognized, Liabilities	8,865	9,738
Net Amounts Presented in the Statement of Financial Position	8,865	9,738
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments Pledged	25,159	33,744
Cash Collateral Pledged	1,510	720
Net Amount	0	0
Risk participation-out agreements
Asset derivatives
Gross Amounts Recognized, Assets	65	20
Net Amounts Presented in the Statement of Financial Position	65	20
Net Amount	65	$ 20
Liability derivatives
Gross Amounts Recognized, Liabilities	10
Net Amounts Presented in the Statement of Financial Position	10
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments Pledged	0
Cash Collateral Pledged	0
Net Amount	0
Foreign exchange contracts
Asset derivatives
Gross Amounts Recognized, Assets	72
Net Amounts Presented in the Statement of Financial Position	72
Net Amount	72
Liability derivatives
Gross Amounts Recognized, Liabilities	65
Net Amounts Presented in the Statement of Financial Position	65
Gross Amounts Not Offset in the Statement of Financial Position
Financial Instruments Pledged	0
Cash Collateral Pledged	0
Net Amount	$ 0

Income Taxes (Components of Inc

Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current provision:
Federal									$ 27,825	$ 22,954	$ 23,340
State									5,013	5,116	4,774
Total current provision									32,838	28,070	28,114
Deferred provision:
Federal									10,209	2,271	679
State									589	51	560
Total deferred provision									10,798	2,322	1,239
Total provision for income taxes	$ 18,712	$ 8,330	$ 8,759	$ 7,835	$ 7,524	$ 7,804	$ 7,465	$ 7,599	$ 43,636	$ 30,392	$ 29,353

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory U.S federal income tax rate (as a percent)	35.00%	35.00%	35.00%
Effective income tax rate (as a percent)	44.90%	35.50%	35.90%
Merger and acquisition expense	$ 138	$ 0	$ 0
Net operating loss carryforwards for U.S. federal income tax purposes	400
Net operating loss carryforwards and credit subject to annual limitation	900
Reserve for loan losses	$ 1,800
Percentage of the amount the used reserve for loan losses would be subject to taxation, if, the reserve is used for purposes other than to absorb the losses for which it was established	150.00%
Amount of liability that would result if 100% of the reserve were recaptured on which no provision has been made	$ 500
Reserve for loan losses recaptured (as a percent)	100.00%
Net deferred tax asset	$ 15,061	25,247
Valuation Allowance [Line Items]
Tax Reform Act Adjustment	8,965	$ 0	$ 0
Deferred tax assets, net
Valuation Allowance [Line Items]
Tax Reform Act Adjustment	8,600
Affordable housing project
Valuation Allowance [Line Items]
Tax Reform Act Adjustment	$ 300

Income Taxes (Reconciliation of

Income Taxes (Reconciliation of Effective Income Tax Expense) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory U.S federal income tax rate (as a percent)									35.00%	35.00%	35.00%
Reconciliation of income tax expense
Expected income tax expense at statutory federal tax rate									$ 34,039	$ 29,965	$ 28,603
State taxes, net of federal income tax benefit									3,641	3,358	3,467
Bank-owned life insurance									(364)	(368)	(367)
Tax-exempt interest income									(873)	(826)	(622)
Income attributable to noncontrolling interest in subsidiary									(870)	(1,163)	(994)
Merger and acquisition expense									138	0	0
Tax Reform Act Adjustment									8,965	0	0
Investments in affordable housing projects									(653)	(640)	(526)
Other, net									(387)	66	(208)
Total provision for income taxes	$ 18,712	$ 8,330	$ 8,759	$ 7,835	$ 7,524	$ 7,804	$ 7,465	$ 7,599	$ 43,636	$ 30,392	$ 29,353
Effective income tax rate (as a percent)									44.90%	35.50%	35.90%

Income Taxes (Components of Def

Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Allowance for loan and lease losses	$ 15,618	$ 21,655
Deferred compensation	1,032	5,659
Supplemental Executive Retirement Plans	2,805	4,127
Unrealized loss on investment securities available-for-sale	1,728	2,355
Net operating loss carryforwards	415	999
Postretirement benefits	400	465
Nonaccrual interest	551	621
Accrued expense	563	828
Restricted stock and stock option plans	621	573
Employee stock ownership plan	124	147
Other	67	61
Total gross deferred tax assets	23,924	37,490
Deferred tax liabilities:
Identified intangible assets and goodwill	2,778	4,660
Deferred loan origination costs, net	2,918	3,370
Depreciation	1,866	2,193
Prepaid expense	109	1,045
Acquisition fair value adjustments	1,192	975
Total gross deferred tax liabilities	8,863	12,243
Net deferred tax asset	$ 15,061	$ 25,247

Stockholders' Equity (Narrative

Stockholders' Equity (Narrative) (Details) - USD ($)	May 02, 2017	Apr. 27, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 04, 2016
Subsidiary, Sale of Stock [Line Items]
Common stock, par value (in dollars per share)			$ 0.01	$ 0.01
Proceeds from issuance of common stock			$ 81,943,000	$ 0	$ 0
Authorized serial preferred stock			50,000,000
Serial preferred stock, par value (in dollars per share)			$ 0.01
Preferred stock issued			0
Number of shares repurchased			0	0	0
Stock repurchase program, authorized amount						$ 10,000,000
Liquidation account, total			$ 15,100,000	$ 15,200,000	$ 16,600,000
Public stock offering
Subsidiary, Sale of Stock [Line Items]
Shares in offering (in shares)		5,175,000
Common stock, par value (in dollars per share)		$ 0.01
Sale of stock price (in usd per share)		$ 14.50
Underwriters option
Subsidiary, Sale of Stock [Line Items]
Shares in offering (in shares)	5,951,250	776,250
Sale of stock price (in usd per share)	$ 14.50

Regulatory Capital Requireme104

Regulatory Capital Requirements (Narrative) (Details)	Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total (as a percent)	10.00%	10.00%
Tier 1 (as a percent)	8.00%	8.00%
Tier 1 leverage capital ratio (as a percent)	5.00%	5.00%
Brookline Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital ratio, Minimum Required to Be Considered Well-Capitalized, Ratio (as a percent)	6.50%	6.50%

Regulatory Capital Requireme105

Regulatory Capital Requirements (Summary of Regulatory Capital Requirements) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Bank actual capital amount
Common equity Tier 1 capital ratio, Actual, Amount	$ 669,238	$ 559,644
Tier 1 leverage capital	687,299	575,830
Risk-based capital:
Tier 1	687,299	575,830
Total risk-based capital	$ 821,373	$ 704,675
Bank actual capital ratio
Common equity Tier 1 capital ratio, Actual, Ratio (as a percent)	12.02%	10.48%
Tier 1 leverage capital ratio (as a percent)	10.43%	9.16%
Risk-based capital:
Tier 1 (as a percent)	12.34%	10.79%
Total (as a percent)	14.75%	13.20%
Minimum capital adequacy amount
Common equity Tier 1 capital ratio, Minimum Required for Capital Adequacy Purposes, Amount	$ 250,547	$ 240,305
Tier 1 leverage capital	263,585	251,454
Risk-based capital:
Tier 1	334,181	320,202
Total	$ 445,490	$ 427,076
Minimum capital adequacy ratio
Common equity Tier 1 capital ratio, Minimum Required for Capital Adequacy Purposes, Ratio (as a percent)	4.50%	4.50%
Tier 1 leverage capital ratio (as a percent)	4.00%	4.00%
Risk-based capital:
Tier 1 (as a percent)	6.00%	6.00%
Total (as a percent)	8.00%	8.00%
Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer
Common equity Tier 1 capital ratio	$ 389,739
Tier 1 leverage capital ratio	263,585
Risk-based capital:
Tier 1 risk-based capital ratio	473,423
Total risk-based capital ratio	$ 584,706
Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer
Common equity Tier 1 capital ratio (as a percent)	7.00%
Tier 1 leverage capital ratio (as a percent)	4.00%
Risk-based capital:
Tier 1 (as a percent)	8.50%
Total (as a percent)	10.50%
Classified as well capitalized ratio
Tier 1 leverage capital ratio (as a percent)	5.00%	5.00%
Risk-based capital:
Tier 1 (as a percent)	8.00%	8.00%
Total (as a percent)	10.00%	10.00%
Brookline Bank
Bank actual capital amount
Common equity Tier 1 capital ratio, Actual, Amount	$ 414,282	$ 384,759
Tier 1 leverage capital	423,035	391,964
Risk-based capital:
Tier 1	423,035	391,964
Total risk-based capital	$ 463,986	$ 428,966
Bank actual capital ratio
Common equity Tier 1 capital ratio, Actual, Ratio (as a percent)	11.56%	11.31%
Tier 1 leverage capital ratio (as a percent)	10.35%	10.07%
Risk-based capital:
Tier 1 (as a percent)	11.81%	11.53%
Total (as a percent)	12.95%	12.61%
Minimum capital adequacy amount
Common equity Tier 1 capital ratio, Minimum Required for Capital Adequacy Purposes, Amount	$ 161,269	$ 153,087
Tier 1 leverage capital	163,492	155,696
Risk-based capital:
Tier 1	214,920	203,971
Total	$ 286,632	$ 272,143
Minimum capital adequacy ratio
Common equity Tier 1 capital ratio, Minimum Required for Capital Adequacy Purposes, Ratio (as a percent)	4.50%	4.50%
Tier 1 leverage capital ratio (as a percent)	4.00%	4.00%
Risk-based capital:
Tier 1 (as a percent)	6.00%	6.00%
Total (as a percent)	8.00%	8.00%
Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer
Common equity Tier 1 capital ratio	$ 250,863
Tier 1 leverage capital ratio	163,492
Risk-based capital:
Tier 1 risk-based capital ratio	304,471
Total risk-based capital ratio	$ 376,205
Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer
Common equity Tier 1 capital ratio (as a percent)	7.00%
Tier 1 leverage capital ratio (as a percent)	4.00%
Risk-based capital:
Tier 1 (as a percent)	8.50%
Total (as a percent)	10.50%
Classified as well capitalized
Common equity Tier 1 capital ratio, Minimum Required to Be Considered Well-Capitalized, Amount	$ 232,944	$ 221,126
Tier 1 leverage capital	204,365	194,620
Risk-based capital:
Tier 1	286,561	271,961
Total	$ 358,290	$ 340,179
Classified as well capitalized ratio
Common equity Tier 1 capital ratio, Minimum Required to Be Considered Well-Capitalized, Ratio (as a percent)	6.50%	6.50%
BankRI
Bank actual capital amount
Common equity Tier 1 capital ratio, Actual, Amount	$ 193,849	$ 182,202
Tier 1 leverage capital	193,849	182,202
Risk-based capital:
Tier 1	193,849	182,202
Total risk-based capital	$ 210,025	$ 197,702
Bank actual capital ratio
Common equity Tier 1 capital ratio, Actual, Ratio (as a percent)	11.38%	10.94%
Tier 1 leverage capital ratio (as a percent)	9.16%	8.97%
Risk-based capital:
Tier 1 (as a percent)	11.38%	10.94%
Total (as a percent)	12.33%	11.87%
Minimum capital adequacy amount
Common equity Tier 1 capital ratio, Minimum Required for Capital Adequacy Purposes, Amount	$ 76,654	$ 74,946
Tier 1 leverage capital	84,650	81,249
Risk-based capital:
Tier 1	102,205	99,928
Total	$ 136,269	$ 133,245
Minimum capital adequacy ratio
Common equity Tier 1 capital ratio, Minimum Required for Capital Adequacy Purposes, Ratio (as a percent)	4.50%	4.50%
Tier 1 leverage capital ratio (as a percent)	4.00%	4.00%
Risk-based capital:
Tier 1 (as a percent)	6.00%	6.00%
Total (as a percent)	8.00%	8.00%
Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer
Common equity Tier 1 capital ratio	$ 119,239
Tier 1 leverage capital ratio	84,650
Risk-based capital:
Tier 1 risk-based capital ratio	144,791
Total risk-based capital ratio	$ 178,853
Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer
Common equity Tier 1 capital ratio (as a percent)	7.00%
Tier 1 leverage capital ratio (as a percent)	4.00%
Risk-based capital:
Tier 1 (as a percent)	8.50%
Total (as a percent)	10.50%
Classified as well capitalized
Common equity Tier 1 capital ratio, Minimum Required to Be Considered Well-Capitalized, Amount	$ 110,722	$ 108,255
Tier 1 leverage capital	105,813	101,562
Risk-based capital:
Tier 1	136,273	133,237
Total	$ 170,337	$ 166,556
Classified as well capitalized ratio
Common equity Tier 1 capital ratio, Minimum Required to Be Considered Well-Capitalized, Ratio (as a percent)	6.50%	6.50%
Tier 1 leverage capital ratio (as a percent)	5.00%	5.00%
Risk-based capital:
Tier 1 (as a percent)	8.00%	8.00%
Total (as a percent)	10.00%	10.00%
First Ipswich
Bank actual capital amount
Common equity Tier 1 capital ratio, Actual, Amount	$ 37,502	$ 33,433
Tier 1 leverage capital	37,502	33,433
Risk-based capital:
Tier 1	37,502	33,433
Total risk-based capital	$ 40,625	$ 36,053
Bank actual capital ratio
Common equity Tier 1 capital ratio, Actual, Ratio (as a percent)	13.38%	12.61%
Tier 1 leverage capital ratio (as a percent)	9.44%	9.23%
Risk-based capital:
Tier 1 (as a percent)	13.38%	12.61%
Total (as a percent)	14.50%	13.60%
Minimum capital adequacy amount
Common equity Tier 1 capital ratio, Minimum Required for Capital Adequacy Purposes, Amount	$ 12,613	$ 11,931
Tier 1 leverage capital	15,891	14,489
Risk-based capital:
Tier 1	16,817	15,908
Total	$ 22,414	$ 21,208
Minimum capital adequacy ratio
Common equity Tier 1 capital ratio, Minimum Required for Capital Adequacy Purposes, Ratio (as a percent)	4.50%	4.50%
Tier 1 leverage capital ratio (as a percent)	4.00%	4.00%
Risk-based capital:
Tier 1 (as a percent)	6.00%	6.00%
Total (as a percent)	8.00%	8.00%
Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer
Common equity Tier 1 capital ratio	$ 19,620
Tier 1 leverage capital ratio	15,891
Risk-based capital:
Tier 1 risk-based capital ratio	23,824
Total risk-based capital ratio	$ 29,418
Minimum Required for Fully Phased in Capital Adequacy Purposes plus Capital Conservation Buffer
Common equity Tier 1 capital ratio (as a percent)	7.00%
Tier 1 leverage capital ratio (as a percent)	4.00%
Risk-based capital:
Tier 1 (as a percent)	8.50%
Total (as a percent)	10.50%
Classified as well capitalized
Common equity Tier 1 capital ratio, Minimum Required to Be Considered Well-Capitalized, Amount	$ 18,218	$ 17,234
Tier 1 leverage capital	19,863	18,111
Risk-based capital:
Tier 1	22,423	21,210
Total	$ 28,017	$ 26,510
Classified as well capitalized ratio
Common equity Tier 1 capital ratio, Minimum Required to Be Considered Well-Capitalized, Ratio (as a percent)	6.50%	6.50%
Tier 1 leverage capital ratio (as a percent)	5.00%	5.00%
Risk-based capital:
Tier 1 (as a percent)	8.00%	8.00%
Total (as a percent)	10.00%	10.00%

Employee Benefit Plans (Rollfor

Employee Benefit Plans (Rollforward of Plan Assets and Benefit Obligation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in plan assets:
Fair value of plan assets at beginning of year	$ 0	$ 0	$ 0
Employer contributions	19	21	25
Benefits paid	(19)	(21)	(25)
Fair value of plan assets at end of year	0	0	0
Change in benefit obligation:
Benefit obligation at beginning of year	1,135	1,188	1,562
Service cost	49	48	55
Interest cost	43	45	49
Estimated benefits paid	(19)	(21)	(25)
Actuarial loss (gain)	326	(125)	(453)
Benefit obligation at end of year	$ 1,534	$ 1,135	$ 1,188

Employee Benefit Plans (Compone

Employee Benefit Plans (Components of Net Periodic Postretirement Benefit Costs and Other Amounts Recognized in OCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net periodic benefit expense:
Service cost	$ 49	$ 48	$ 55
Interest cost	43	45	49
Changes in postretirement benefit obligation recognized in other comprehensive income:
Total pre-tax changes in postretirement benefit obligation recognized in other comprehensive income	422	(69)	(353)
Health Insurance Postretirement Benefit
Net periodic benefit expense:
Service cost	49	48	55
Interest cost	43	45	49
Prior service credit	(21)	(21)	(21)
Actuarial gain	(47)	(42)	(20)
Net periodic benefit expense	24	30	63
Changes in postretirement benefit obligation recognized in other comprehensive income:
Net actuarial (loss) gain	(401)	90	374
Prior service credit	(21)	(21)	(21)
Total pre-tax changes in postretirement benefit obligation recognized in other comprehensive income	$ (422)	$ 69	$ 353

Employee Benefit Plans (Effects

Employee Benefit Plans (Effects of Changes in Assumed Healthcare Cost Trends) (Details) - Health Insurance Postretirement Benefit $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Effect of 1% change in assumed health care cost trend rates
Effect of 1% increase on total service and interest cost components of net periodic postretirement benefit costs	$ 23
Effect of 1% decrease on total service and interest cost components of net periodic postretirement benefit costs	(18)
Effect of 1% increase on the accumulated postretirement benefit obligation	356
Effect of 1% decrease on the accumulated postretirement benefit obligation	$ (277)

Employee Benefit Plans (Activit

Employee Benefit Plans (Activity in Recognition and Retention Plans) (Details) - Restricted stock $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Restricted Stock Awards Outstanding
Outstanding at beginning of year (in shares) | shares	476,854
Granted (in shares) | shares	186,782
Vested (in shares) | shares	(193,267)
Forfeited / Canceled (in shares) | shares	(15,086)
Outstanding at end of year (in shares) | shares	455,283
Weighted Average Grant Price per Share
Outstanding at beginning of year (in dollars per share) | $ / shares	$ 10.90
Granted (in dollars per share) | $ / shares	14.65
Vested (in dollars per share) | $ / shares	10.24
Forfeited / Canceled (in dollars per share) | $ / shares	16.10
Outstanding at end of year (in dollars per share) | $ / shares	$ 12.64
Unrecognized compensation cost | $	$ 3,022
Weighted average remaining recognition period	30 months

Employee Benefit Plans (Acti110

Employee Benefit Plans (Activity in Option Plans) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock option activity
Outstanding at the beginning of the period (in shares)	197,345
Granted (in shares)	0	0	0
Exercised (in shares)	(147,345)
Forfeited/Canceled (in shares)	0
Outstanding at the end of the period (in shares)	50,000	197,345
Exercisable at the end of the period (in shares)	50,000
Stock Option Activity, Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 10.18
Granted (in dollars per share)	0
Exercised (in dollars per share)	10.53
Forfeited/Canceled (in dollars per share)	0
Outstanding at the end of the period (in dollars per share)	10.80	$ 10.18
Exercisable at the end of the period (in dollars per share)	$ 10.80
Stock Option Activity, Aggregate Intrinsic Value
Outstanding at the end of the period	$ 245
Exercisable at the end of the period	$ 245
Stock Option Activity, Weighted Average Contractual Term
Outstanding at the end of the period (in years)	2 years 9 months 18 days
Exercisable at the end of the period (in years)	2 years 9 months 18 days

Employee Benefit Plans (Narrati

Employee Benefit Plans (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017USD ($)participantfinancial_institutionyrplanshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated prior service credit that will be amortized from accumulated other comprehensive income into net periodic benefit cost	$ 100,000
Number of 401(k) plans administered | plan	1
Minimum employee age required to participate in the plan (in years) | yr	21
Expense for the company plan contributions	$ 2,600,000	$ 2,800,000	$ 2,300,000
Accrued liabilities with deferred compensation plan	$ 100,000	$ 200,000	200,000
Unallocated shares | shares	142,332	176,688
Unallocated shares, aggregate cost	$ 776,000	$ 963,000
ESOP shares committed to be released	$ 501,000	$ 395,000	$ 395,000
Number of share-based compensation plans | plan	3
Granted (in shares) | shares	0	0	0
401(k) plan 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Company contribution as percentage of compensation of eligible employees	5.00%
Health Insurance Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate used to determine the actuarial present value of projected postretirement benefit obligations (as a percent)	3.62%	4.15%	4.35%
Aggregate benefits payable included in accrued expenses and other liabilities	$ 1,500,000	$ 1,100,000	$ 1,200,000
Assumed health care trend rates used in 2016 through 2020, high end of range (as a percent)	6.50%
Assumed health care trend rates used in 2016 through 2020, low end of range (as a percent)	5.50%
Assumed health care trend rate after 2020 (as a percent)	4.90%
Expenses for benefits payable recognized under agreement	$ 24,000	30,000	63,000
Supplemental retirement plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Aggregate benefits payable included in accrued expenses and other liabilities	$ 12,000,000	11,600,000
Number of participants | participant	13
Expenses for benefits payable recognized under agreement	$ 800,000	$ 800,000
Discount rate used to determine the actuarial present value (as a percent)	4.00%	4.00%
Below age 65 | Health Insurance Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual health care trend that will be used to measure the accumulated postretirement benefit obligation (as a percent)	(14.70%)
Actual health care trend used to measure the accumulated postretirement benefit obligation (as a percent)		7.50%
Over age 65 | Health Insurance Postretirement Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual health care trend that will be used to measure the accumulated postretirement benefit obligation (as a percent)	33.90%
Actual health care trend used to measure the accumulated postretirement benefit obligation (as a percent)		8.30%
Employee Stock Ownership Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
ESOP loan to purchase shares of entity's common stock | shares	546,986
Number of years during which quarterly installments are payable	30 years
Percentage of interest payable per annum on loan obtained by the ESOP	8.50%
Outstanding balance of loan	$ 1,300,000	$ 1,500,000
Unallocated shares | shares	142,332	176,688
Unallocated shares, aggregate cost	$ 700,000	$ 900,000
Unallocated shares, market value	2,300,000	2,900,000
ESOP shares committed to be released	$ 500,000	$ 400,000	$ 400,000
Number of shares committed to be released to eligible employees | shares	34,356	36,372	38,316
2003 RRP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of authorized shares | shares	1,250,000
2011 Restricted Stock Award Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of authorized shares | shares	500,000
Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of authorized shares | shares	1,750,000
Share-based compensation expense	$ 2,300,000	$ 1,800,000	$ 1,400,000
Tax benefits from vested awards	$ 700,000	300,000	300,000
Equity Incentive Plan 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of authorized shares | shares	1,750,000
Performance-based shares
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of financial institutions comprising peer group | financial_institution	17
Restricted stock
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Dividends paid on unvested shares recognized as compensation expense	$ 100,000	100,000	100,000
Stock Options
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Share-based compensation expense	$ 0	0	0
Exercisable period upon happening of a specific event, low end of range (in months)	3 months
Exercisable period upon happening of a specific event, high end of range (in years)	5 years
Dividend equivalent rights	$ 0	$ 0	$ 0
Vesting equally over three years | Time-based shares
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of shares in tranche	50.00%
Award vesting period	3 years
Vesting percentage	33.00%
Vesting after achievement of performance targets | Performance-based shares
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of shares in tranche	50.00%
Award vesting period	3 years

Fair Value of Financial Inst112

Fair Value of Financial Instruments (Assets and Liabilities Recorded at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Investment securities available-for-sale	$ 540,124	$ 523,634
Derivatives	9,002	9,758
Liabilities:
Derivatives	8,940	9,738
Recurring basis
Assets:
Derivatives		9,738
Liabilities:
Derivatives	8,865	9,738
Recurring basis | Investment securities available for sale
Assets:
Investment securities available-for-sale	540,124	523,634
Recurring basis | GSE debentures
Assets:
Investment securities available-for-sale	149,924	97,020
Recurring basis | GSE CMOs
Assets:
Investment securities available-for-sale	127,022	158,040
Recurring basis | GSE MBSs
Assets:
Investment securities available-for-sale	189,313	212,915
Recurring basis | SBA commercial loan asset-backed securities
Assets:
Investment securities available-for-sale	72	107
Recurring basis | Corporate debt obligations
Assets:
Investment securities available-for-sale	62,683	48,485
Recurring basis | U.S. treasury bonds
Assets:
Investment securities available-for-sale	8,730	4,737
Recurring basis | Trust preferred securities
Assets:
Investment securities available-for-sale	1,398	1,358
Recurring basis | Marketable equity securities
Assets:
Investment securities available-for-sale	982	972
Recurring basis | Level 1
Assets:
Derivatives		0
Liabilities:
Derivatives	0	0
Recurring basis | Level 1 | Investment securities available for sale
Assets:
Investment securities available-for-sale	982	972
Recurring basis | Level 1 | GSE debentures
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 1 | GSE CMOs
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 1 | GSE MBSs
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 1 | SBA commercial loan asset-backed securities
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 1 | Corporate debt obligations
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 1 | U.S. treasury bonds
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 1 | Trust preferred securities
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 1 | Marketable equity securities
Assets:
Investment securities available-for-sale	982	972
Recurring basis | Level 2
Assets:
Derivatives		9,738
Liabilities:
Derivatives	8,865	9,738
Recurring basis | Level 2 | Investment securities available for sale
Assets:
Investment securities available-for-sale	539,142	522,662
Recurring basis | Level 2 | GSE debentures
Assets:
Investment securities available-for-sale	149,924	97,020
Recurring basis | Level 2 | GSE CMOs
Assets:
Investment securities available-for-sale	127,022	158,040
Recurring basis | Level 2 | GSE MBSs
Assets:
Investment securities available-for-sale	189,313	212,915
Recurring basis | Level 2 | SBA commercial loan asset-backed securities
Assets:
Investment securities available-for-sale	72	107
Recurring basis | Level 2 | Corporate debt obligations
Assets:
Investment securities available-for-sale	62,683	48,485
Recurring basis | Level 2 | U.S. treasury bonds
Assets:
Investment securities available-for-sale	8,730	4,737
Recurring basis | Level 2 | Trust preferred securities
Assets:
Investment securities available-for-sale	1,398	1,358
Recurring basis | Level 2 | Marketable equity securities
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 3
Assets:
Derivatives		0
Liabilities:
Derivatives	0	0
Recurring basis | Level 3 | Investment securities available for sale
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 3 | GSE debentures
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 3 | GSE CMOs
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 3 | GSE MBSs
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 3 | SBA commercial loan asset-backed securities
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 3 | Corporate debt obligations
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 3 | U.S. treasury bonds
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 3 | Trust preferred securities
Assets:
Investment securities available-for-sale	0	0
Recurring basis | Level 3 | Marketable equity securities
Assets:
Investment securities available-for-sale	0	0
Loan level derivatives
Assets:
Derivatives	8,865	9,738
Liabilities:
Derivatives	8,865	9,738
Loan level derivatives | Recurring basis
Assets:
Derivatives	8,865
Loan level derivatives | Recurring basis | Level 1
Assets:
Derivatives	0
Loan level derivatives | Recurring basis | Level 2
Assets:
Derivatives	8,865
Loan level derivatives | Recurring basis | Level 3
Assets:
Derivatives	0
Risk participation-out agreements
Assets:
Derivatives	65	20
Liabilities:
Derivatives	10
Risk participation-out agreements | Recurring basis
Assets:
Derivatives	65	20
Risk participation-out agreements | Recurring basis | Level 1
Assets:
Derivatives	0	0
Risk participation-out agreements | Recurring basis | Level 2
Assets:
Derivatives	65	20
Risk participation-out agreements | Recurring basis | Level 3
Assets:
Derivatives	0	$ 0
Foreign exchange contracts
Assets:
Derivatives	72
Liabilities:
Derivatives	65
Foreign exchange contracts | Recurring basis
Assets:
Derivatives	72
Liabilities:
Derivatives	65
Foreign exchange contracts | Recurring basis | Level 1
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Foreign exchange contracts | Recurring basis | Level 2
Assets:
Derivatives	72
Liabilities:
Derivatives	65
Foreign exchange contracts | Recurring basis | Level 3
Assets:
Derivatives	0
Liabilities:
Derivatives	0
Risk participation-in agreements | Recurring basis
Liabilities:
Derivatives	10
Risk participation-in agreements | Recurring basis | Level 1
Liabilities:
Derivatives	0
Risk participation-in agreements | Recurring basis | Level 2
Liabilities:
Derivatives	10
Risk participation-in agreements | Recurring basis | Level 3
Liabilities:
Derivatives	$ 0

Fair Value of Financial Inst113

Fair Value of Financial Instruments (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Changes in generic pricing of securities period one, considered for analyzing changes in prices obtained from pricing service (in years)	15 years
Changes in generic pricing of securities period two, considered for analyzing changes in prices obtained from pricing service (in years)	30 years

Fair Value of Financial Inst114

Fair Value of Financial Instruments (Assets and Liabilities Recorded at Fair Value on a Non-Recurring Basis) (Details) - Nonrecurring basis - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	$ 25,614	$ 28,681
Level 1
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	0	0
Level 2
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	1,184	781
Level 3
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	24,430	27,900
Collateral-dependent impaired loans and leases
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	21,195	27,282
Collateral-dependent impaired loans and leases | Level 1
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	0	0
Collateral-dependent impaired loans and leases | Level 2
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	0	0
Collateral-dependent impaired loans and leases | Level 3
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	21,195	27,282
OREO
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	3,235	618
OREO | Level 1
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	0	0
OREO | Level 2
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	0	0
OREO | Level 3
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	3,235	618
Repossessed assets
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	1,184	781
Repossessed assets | Level 1
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	0	0
Repossessed assets | Level 2
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	1,184	781
Repossessed assets | Level 3
Fair value of assets and liabilities
Total assets measured at fair value on a non-recurring basis	$ 0	$ 0

Fair Value of Financial Inst115

Fair Value of Financial Instruments (Repossessed Assets) (Details) - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Recurring basis | Collateral-dependent impaired loans and leases | Appraisal of collateral
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value of assets	$ 21,195	$ 27,282
Recurring basis | Other real estate owned | Appraisal of collateral
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value of assets	$ 3,235	$ 618
Minimum | Discount for Costs to Sell
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value inputs, basis spread (as a percent)	0.00%
Minimum | Appraisal Adjustments
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value inputs, basis spread (as a percent)	0.00%
Maximum | Discount for Costs to Sell
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value inputs, basis spread (as a percent)	10.00%
Maximum | Appraisal Adjustments
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value inputs, basis spread (as a percent)	15.00%

Fair Value of Financial Inst116

Fair Value of Financial Instruments (Summary of Estimated Fair Values of Financial Instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financial assets:
Investment securities held-to-maturity:	$ 108,523	$ 85,271
Loans and leases, net	5,672,087	5,345,198
Restricted equity securities	59,369	64,511
Financial liabilities:
Certificates of deposit	1,207,470	1,041,022
Borrowed funds	47,639	50,207
Level 1
Financial assets:
Loans held-for-sale	0	0
Loans and leases, net	0	0
Restricted equity securities	0	0
Financial liabilities:
Certificates of deposit	0	0
Borrowed funds	0	0
Level 2
Financial assets:
Loans held-for-sale	2,628	13,078
Loans and leases, net	0	0
Restricted equity securities	0	0
Financial liabilities:
Certificates of deposit	1,198,201	1,042,653
Borrowed funds	995,335	1,030,753
Level 3
Financial assets:
Loans held-for-sale	0	0
Loans and leases, net	5,594,543	5,195,312
Restricted equity securities	59,369	75,589
Financial liabilities:
Certificates of deposit	0	0
Borrowed funds	0	0
Carrying Value
Financial assets:
Loans held-for-sale	2,628	13,078
Loans and leases, net	5,672,087	5,345,198
Restricted equity securities	59,369	64,511
Financial liabilities:
Certificates of deposit	1,207,470	1,041,022
Borrowed funds	1,020,819	1,044,086
Estimated Fair Value
Financial assets:
Loans held-for-sale	2,628	13,078
Loans and leases, net	5,594,543	5,195,312
Restricted equity securities	59,369	75,589
Financial liabilities:
Certificates of deposit	1,198,201	1,042,653
Borrowed funds	995,335	1,030,753
GSE debentures
Financial assets:
Investment securities held-to-maturity:	40,801	14,101
GSE debentures | Level 1
Financial assets:
Investment securities held-to-maturity:	0	0
GSE debentures | Level 2
Financial assets:
Investment securities held-to-maturity:	40,801	14,101
GSE debentures | Level 3
Financial assets:
Investment securities held-to-maturity:	0	0
GSE debentures | Carrying Value
Financial assets:
Investment securities held-to-maturity:	41,612	14,735
GSE debentures | Estimated Fair Value
Financial assets:
Investment securities held-to-maturity:	40,801	14,101
GSE MBSs
Financial assets:
Investment securities held-to-maturity:	13,705	17,479
GSE MBSs | Level 1
Financial assets:
Investment securities held-to-maturity:	0	0
GSE MBSs | Level 2
Financial assets:
Investment securities held-to-maturity:	13,705	17,479
GSE MBSs | Level 3
Financial assets:
Investment securities held-to-maturity:	0	0
GSE MBSs | Carrying Value
Financial assets:
Investment securities held-to-maturity:	13,923	17,666
GSE MBSs | Estimated Fair Value
Financial assets:
Investment securities held-to-maturity:	13,705	17,479
Municipal obligations
Financial assets:
Investment securities held-to-maturity:	53,517	53,204
Municipal obligations | Level 1
Financial assets:
Investment securities held-to-maturity:	0	0
Municipal obligations | Level 2
Financial assets:
Investment securities held-to-maturity:	53,517	53,204
Municipal obligations | Level 3
Financial assets:
Investment securities held-to-maturity:	0	0
Municipal obligations | Carrying Value
Financial assets:
Investment securities held-to-maturity:	53,695	54,219
Municipal obligations | Estimated Fair Value
Financial assets:
Investment securities held-to-maturity:	53,517	53,204
Foreign government obligations
Financial assets:
Investment securities held-to-maturity:	500	487
Foreign government obligations | Level 1
Financial assets:
Investment securities held-to-maturity:	0	0
Foreign government obligations | Level 2
Financial assets:
Investment securities held-to-maturity:		0
Foreign government obligations | Level 3
Financial assets:
Investment securities held-to-maturity:	500	487
Foreign government obligations | Carrying Value
Financial assets:
Investment securities held-to-maturity:	500	500
Foreign government obligations | Estimated Fair Value
Financial assets:
Investment securities held-to-maturity:	$ 500	$ 487

Condensed Parent Company Fin117

Condensed Parent Company Financial Statements (Condensed Balance Sheets) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Cash and due from banks		$ 25,622	$ 36,055
Short-term investments		35,383	31,602
Total cash and cash equivalents		61,005	67,657	$ 75,489	$ 62,723
Restricted equity securities		59,369	64,511
Premises and equipment, net		80,283	76,176
Goodwill		137,890	137,890	137,890	137,890
Other assets	[1]	91,609	88,086
Total assets		6,780,249	6,438,129
LIABILITIES AND STOCKHOLDERS' EQUITY
Borrowed funds		1,020,819	1,044,086
Accrued expenses and other liabilities		67,818	72,573
Total liabilities		5,967,666	5,735,380
Stockholders' equity
Common stock, $0.01 par value; 200,000,000 shares authorized; 81,695,695 shares issued and 75,744,445 shares issued, respectively		817	757
Additional paid-in capital		699,976	616,734
Retained earnings, partially restricted	[1]	161,217	136,671
Accumulated other comprehensive loss		(5,950)	(3,818)
Treasury stock, at cost; 4,440,665 shares and 4,707,096 shares, respectively		(51,454)	(53,837)
Unallocated common stock held by Employee Stock Ownership Plan (ESOP); 142,332 shares and 176,688 shares, respectively		(776)	(963)
Total Brookline Bancorp, Inc. stockholders' equity	[1]	803,830	695,544
Total liabilities and stockholders' equity	[1]	6,780,249	6,438,129
Parent Company
ASSETS
Cash and due from banks		5,511	32,220
Short-term investments		32	32
Total cash and cash equivalents		5,543	32,252	$ 28,103	$ 52,301
ESOP loan to Brookline Bank		1,252	1,502
Intercompany loan to Brookline Bank		80,000	0
Restricted equity securities		100	100
Premises and equipment, net		6,032	6,946
Investment in subsidiaries, at equity		753,056	701,943
Goodwill		35,267	35,267
Other assets		6,627	8,259
Total assets		887,877	786,269
LIABILITIES AND STOCKHOLDERS' EQUITY
Borrowed funds		83,271	83,105
Deferred tax liability		608	243
Accrued expenses and other liabilities		168	7,377
Total liabilities		84,047	90,725
Stockholders' equity
Common stock, $0.01 par value; 200,000,000 shares authorized; 81,695,695 shares issued and 75,744,445 shares issued, respectively		817	757
Additional paid-in capital		699,976	616,734
Retained earnings, partially restricted		161,217	136,671
Accumulated other comprehensive loss		(5,950)	(3,818)
Treasury stock, at cost; 4,440,665 shares and 4,707,096 shares, respectively		(51,454)	(53,837)
Unallocated common stock held by Employee Stock Ownership Plan (ESOP); 142,332 shares and 176,688 shares, respectively		(776)	(963)
Total Brookline Bancorp, Inc. stockholders' equity		803,830	695,544
Total liabilities and stockholders' equity		$ 887,877	$ 786,269
[1]	Previously reported amounts prior to January 1, 2015 have been restated to reflect a retrospective change in accounting principle for investments in qualified affordable housing projects, in accordance with ASU 2014-01. Refer to Note 10, "Other Assets".

Condensed Parent Company Fin118

Condensed Parent Company Financial Statements (Condensed Balance Sheets (Parenthetical)) (Details) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	81,695,695	75,744,445
Treasury stock, shares	4,440,665	4,707,096
Unallocated common stock held by ESOP, shares	142,332	176,688
Parent Company
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	75,744,445	75,744,445
Treasury stock, shares	4,707,096	4,861,554
Unallocated common stock held by ESOP, shares	176,688	213,066

Condensed Parent Company Fin119

Condensed Parent Company Financial Statements (Condensed Income Statements) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Interest and dividend income:
Marketable and restricted equity securities									$ 3,062		$ 2,975		$ 2,762
Total interest and dividend income	$ 68,337	$ 67,176	$ 65,186	$ 62,351	$ 60,983	$ 61,531	$ 59,236	$ 57,898	263,050		239,648		226,910
Interest expense:
Net interest income	57,657	56,843	55,583	53,098	51,854	52,350	50,257	49,203	223,181		203,664		194,365
Non-interest income:
Other									4,789		4,683		4,124
Total non-interest income									32,173		22,667		20,184
Non-interest expense:
Compensation and employee benefits									82,413		77,836		71,272
Occupancy									14,546		13,882		13,926
Equipment and data processing									16,854		15,496		14,837
Professional services									4,315		3,852		4,192
Advertising and marketing									3,369		3,381		3,352
Merger and acquisition expense									411		0		0
Other	34,633	34,889	34,276	33,224	31,986	32,765	31,629	31,418	11,788		10,083		11,377
Total non-interest expense									139,111		130,362		125,377
Credit for income taxes	18,712	8,330	8,759	7,835	7,524	7,804	7,465	7,599	43,636		30,392		29,353
Net income attributable to Brookline Bancorp, Inc.	$ 6,827	$ 15,366	$ 14,880	$ 13,445	$ 13,279	$ 13,617	$ 12,654	$ 12,812	50,518	[1]	52,362	[1]	49,782	[1]
Parent Company
Interest and dividend income:
Dividend income from subsidiaries									7,317		109		0
Marketable and restricted equity securities									0		0		97
ESOP loan to Brookline Bank									120		141		162
Intercompany loan to Brookline Bank									532		0		0
Total interest and dividend income									7,969		250		259
Interest expense:
Borrowed funds									5,123		5,080		5,063
Net interest income									2,846		(4,830)		(4,804)
Non-interest income:
Other									0		15		5
Total non-interest income									0		15		5
Non-interest expense:
Compensation and employee benefits									391		82		205
Occupancy									1,584		1,582		22
Equipment and data processing									(1,011)		(1,190)		687
Directors' fees									453		700		688
Franchise taxes									180		180		113
Insurance									528		490		490
Professional services									470		245		185
Advertising and marketing									4		0		0
Merger and acquisition expense									411		0		0
Other									(1,224)		(1,300)		(1,289)
Total non-interest expense									1,786		789		1,101
Loss before income taxes									1,060		(5,604)		(5,900)
Credit for income taxes									(1,944)		(1,779)		(1,854)
Loss before equity in undistributed income of subsidiaries									3,004		(3,825)		(4,046)
Equity in undistributed income of subsidiaries									47,514		56,187		53,828
Net income attributable to Brookline Bancorp, Inc.									$ 50,518		$ 52,362		$ 49,782
[1]	{F|ahBzfndlYmZpbGluZ3MtaHJkcmoLEgZYTUxEb2MiXlhCUkxEb2NHZW5JbmZvOjNlMjQ5ZGFhMTk1YTQ2MWY5YTYxNGE1ZjY5NGNkOWQyfFRleHRTZWxlY3Rpb246MUQ1NTE1RjYxMjZDOTNCRTNEMEZGRTY3MTNDNDMyNkYM}

Condensed Parent Company Fin120

Condensed Parent Company Financial Statements (Condensed Cash Flows) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Net income attributable to Brookline Bancorp, Inc.		$ 6,827	$ 15,366	$ 14,880	$ 13,445	$ 13,279	$ 13,617	$ 12,654	$ 12,812	$ 50,518	[1]	$ 52,362	[1]	$ 49,782	[1]
Adjustments to reconcile net income to net cash provided from operating activities:
Depreciation of premises and equipment										7,232		7,080		7,074
Amortization of debt issuance costs										100		101		100
Net cash provided from operating activities	[1]									84,947		77,930		64,604
Cash flows from investing activities:
Purchase of premises and equipment										(11,557)		(5,262)		(4,775)
Net cash used for investing activities										(383,974)		(427,795)		(231,820)
Cash flows from financing activities:
Proceeds from issuance of common stock										81,943		0		0
Payment of dividends on common stock										(27,035)		(25,366)		(24,967)
Net cash provided from (used for) financing activities										292,375		342,033		179,982
Net (decrease) increase in cash and cash equivalents										(6,652)		(7,832)		12,766
Cash and cash equivalents at beginning of year					67,657				75,489	67,657		75,489		62,723
Cash and cash equivalents at end of year		61,005				67,657				61,005		67,657		75,489
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Net income attributable to Brookline Bancorp, Inc.										50,518		52,362		49,782
Adjustments to reconcile net income to net cash provided from operating activities:
Equity in undistributed income of subsidiaries										(47,514)		(56,187)		(53,828)
Depreciation of premises and equipment										2,856		2,735		2,728
Amortization of debt issuance costs										100		101		100
Other operating activities, net										(5,885)		30,895		2,479
Net cash provided from operating activities										75		29,906		1,261
Cash flows from investing activities:
Repayment of ESOP loan by Brookline Bank										250		250		250
Issuance of intercompany loan to Brookline Bank										(80,000)		0		0
Purchase of premises and equipment										(1,942)		(641)		(742)
Net cash used for investing activities										(81,692)		(391)		(492)
Cash flows from financing activities:
Proceeds from issuance of common stock										81,943		0		0
Payment of dividends on common stock										(27,035)		(25,366)		(24,967)
Net cash provided from (used for) financing activities										54,908		(25,366)		(24,967)
Net (decrease) increase in cash and cash equivalents										(26,709)		4,149		(24,198)
Cash and cash equivalents at beginning of year					$ 32,252				$ 28,103	32,252		28,103		52,301
Cash and cash equivalents at end of year		$ 5,543				$ 32,252				$ 5,543		$ 32,252		$ 28,103
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Quarterly Results of Operati121

Quarterly Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Interest and dividend income	$ 68,337	$ 67,176	$ 65,186	$ 62,351	$ 60,983	$ 61,531	$ 59,236	$ 57,898	$ 263,050		$ 239,648		$ 226,910
Interest expense	10,680	10,333	9,603	9,253	9,129	9,181	8,979	8,695	39,869		35,984		32,545
Net interest income	57,657	56,843	55,583	53,098	51,854	52,350	50,257	49,203	223,181		203,664		194,365
Provision for credit losses	1,802	2,911	873	13,402	3,215	2,215	2,545	2,378	18,988		10,353		7,451
Net interest income after provision for credit losses	55,855	53,932	54,710	39,696	48,639	50,135	47,712	46,825	204,193		193,311		186,914
Loan level derivative income, net	755	844	186	402	265	858	1,210	1,629	2,187		3,962		3,397
Gain on sales of investment securities, net	0	0	0	11,393					11,393		0		0
Gain on sales of loans and leases held-for-sale	935	1,049	307	353	1,270	588	345	905	2,644		3,256		2,208
Other non-interest income	4,125	4,080	3,984	3,760	3,895	3,883	3,820	3,935
Amortization of identified intangible assets	(519)	(519)	(519)	(532)	(621)	(623)	(621)	(635)	(2,089)		(2,500)		(2,911)
Other non-interest expense	(34,633)	(34,889)	(34,276)	(33,224)	(31,986)	(32,765)	(31,629)	(31,418)	(11,788)		(10,083)		(11,377)
Income before provision for income taxes	26,518	24,497	24,392	21,848	21,462	22,076	20,837	21,241	97,255		85,616		81,721
Provision for income taxes	18,712	8,330	8,759	7,835	7,524	7,804	7,465	7,599	43,636		30,392		29,353
Net income before noncontrolling interest in subsidiary	7,806	16,167	15,633	14,013	13,938	14,272	13,372	13,642	53,619	[1]	55,224	[1]	52,368	[1]
Less net income attributable to noncontrolling interest in subsidiary	979	801	753	568	659	655	718	830	3,101		2,862		2,586
Net income attributable to Brookline Bancorp, Inc.	$ 6,827	$ 15,366	$ 14,880	$ 13,445	$ 13,279	$ 13,617	$ 12,654	$ 12,812	$ 50,518	[2]	$ 52,362	[2]	$ 49,782	[2]
Earnings per share:
Basic (in dollars per share)	$ 0.09	$ 0.20	$ 0.20	$ 0.19	$ 0.19	$ 0.19	$ 0.18	$ 0.18	$ 0.68		$ 0.74		$ 0.71
Diluted (in dollars per share)	$ 0.09	$ 0.20	$ 0.20	$ 0.19	$ 0.19	$ 0.19	$ 0.18	$ 0.18	$ 0.68		$ 0.74		$ 0.71
Average common shares outstanding:
Basic (in shares)	76,583,712	76,452,539	74,325,013	70,386,766	70,362,702	70,299,722	70,196,950	70,186,921	74,459,508		70,261,954		70,098,561
Diluted (in shares)	76,868,307	76,961,948	74,810,088	70,844,096	70,592,204	70,450,760	70,388,438	70,343,408	74,811,408		70,444,083		70,235,868
Common stock price:
High (in dollars per share)	$ 16.35	$ 15.50	$ 15.95	$ 16.75	$ 16.60	$ 12.19	$ 11.69	$ 11.21
Low (in dollars per share)	14.50	13.75	13.75	14.50	12.05	10.71	10.44	10.23
Dividends paid:
Dividends per share (in dollars per share)	$ 0.090	$ 0.090	$ 0.090	$ 0.090	$ 0.090	$ 0.09	$ 0.09	$ 0.090
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Subsequent Events (Narrative) (

Subsequent Events (Narrative) (Details) - First Commons Bank - Subsequent Event	Jan. 17, 2018
Subsequent Event [Line Items]
Percentage voted in favor of merger	89.00%
Percentage of voters abstaining	11.00%