Cambridge Bancorp (CATC) 10-Q 9 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Nov. 06, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Trading Symbol	CATC
Entity Registrant Name	CAMBRIDGE BANCORP
Entity Central Index Key	711,772
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		4,082,188

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 13,668	$ 54,050
Investment securities
Available for sale, at fair value (amortized cost $215,007 and $329,726, respectively)	212,449	325,641
Held to maturity, at amortized cost (fair value $222,251 and $83,755, respectively)	219,870	82,502
Total investment securities	432,319	408,143
Loans held for sale, at lower of cost or fair value	560	6,506
Loans
Residential mortgage	537,425	534,404
Commercial mortgage	631,752	616,140
Home equity	76,007	75,051
Commercial & Industrial	65,861	59,706
Consumer	44,863	34,853
Total loans	1,355,908	1,320,154
Less: allowance for loan losses	(15,620)	(15,261)
Net loans	1,340,288	1,304,893
Stock in FHLB of Boston, at cost	4,938	4,098
Bank owned life insurance	30,947	30,499
Banking premises and equipment, net	9,502	10,451
Deferred income taxes, net	13,392	13,693
Accrued interest receivable	4,899	4,627
Other assets	13,718	12,039
Total assets	1,864,231	1,848,999
Deposits
Demand	465,970	472,923
Interest bearing checking	387,343	430,706
Money market	64,232	72,057
Savings	600,475	539,190
Certificates of deposit	158,898	171,162
Total deposits	1,676,918	1,686,038
Short-term borrowings	11,500
Long-term borrowings	3,621	3,746
Other liabilities	26,141	24,544
Total liabilities	1,718,180	1,714,328
Shareholders’ Equity
Common stock, par value $1.00; Authorized 10,000,000 shares; Outstanding: 4,082,188 shares and 4,036,879 shares, respectively	4,082	4,037
Additional paid-in capital	35,435	33,253
Retained earnings	115,048	107,262
Accumulated other comprehensive loss	(8,514)	(9,881)
Total shareholders’ equity	146,051	134,671
Total liabilities and shareholders’ equity	$ 1,864,231	$ 1,848,999

CONSOLIDATED BALANCE SHEETS (U3

CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Available for sale securities, amortized cost	$ 215,007	$ 329,726
Held-to-maturity securities, fair value	$ 222,251	$ 83,755
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares, outstanding	4,082,188	4,036,879

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest and dividend income
Interest on taxable loans	$ 13,038	$ 12,322	$ 37,966	$ 35,796
Interest on tax-exempt loans	121	116	391	293
Interest on taxable investment securities	1,712	1,115	4,762	3,979
Interest on tax-exempt investment securities	641	688	1,966	2,071
Dividends on FHLB of Boston stock	107	52	192	132
Interest on overnight investments	54	22	170	94
Total interest and dividend income	15,673	14,315	45,447	42,365
Interest expense
Interest on deposits	809	769	2,183	2,526
Interest on borrowed funds	225	26	434	66
Total interest expense	1,034	795	2,617	2,592
Net interest and dividend income	14,639	13,520	42,830	39,773
Provision for loan losses	310	113	360	338
Net interest and dividend income after provision for loan losses	14,329	13,407	42,470	39,435
Noninterest income
Wealth management revenue	6,131	5,481	17,077	15,026
Deposit account fees	768	766	2,387	2,134
ATM/Debit card income	334	285	879	852
Bank owned life insurance income	139	149	448	474
Gain (loss) on disposition of investment securities		3	(3)	438
Gain on loans held for sale	39	305	324	591
Loan related derivative income	284	392	647	1,191
Other income	282	234	890	677
Total noninterest income	7,977	7,615	22,649	21,383
Noninterest expense
Salaries and employee benefits	9,066	8,620	27,211	25,431
Occupancy and equipment	2,358	2,278	6,936	7,029
Data processing	1,111	1,279	3,830	3,744
Professional services	954	654	2,650	1,857
Marketing	355	463	1,098	1,388
FDIC Insurance	154	176	466	628
Other expenses	604	693	2,089	2,078
Total noninterest expense	14,602	14,163	44,280	42,155
Income before income taxes	7,704	6,859	20,839	18,663
Income tax expense	2,694	2,284	6,987	6,190
Net income	$ 5,010	$ 4,575	$ 13,852	$ 12,473
Share data
Weighted average number of shares outstanding, basic	4,037,026	3,996,687	4,027,378	3,982,696
Weighted average number of shares outstanding, diluted	4,070,332	4,043,651	4,062,743	4,029,281
Basic earnings per share	$ 1.23	$ 1.13	$ 3.40	$ 3.09
Diluted earnings per share	$ 1.22	$ 1.13	$ 3.37	$ 3.09

Unaudited Consolidated Statemen

Unaudited Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 5,010	$ 4,575	$ 13,852	$ 12,473
Unrealized gains (losses) on available for sale securities
Unrealized holding gains (losses) arising during period	286	(402)	968	2,991
Less: reclassification adjustment for (gains) losses included in net income		(2)	1	(281)
Total unrealized gains (losses) on securities	286	(404)	969	2,710
Defined benefit retirement plans
Change in unfunded retirement liability	133	117	398	351
Other comprehensive income (loss)	419	(287)	1,367	3,061
Comprehensive income	$ 5,429	$ 4,288	$ 15,219	$ 15,534

UNAUDITED CONSOLIDATED STATEME6

UNAUDITED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2015	$ 125,063	$ 4,000	$ 30,427	$ 99,064	$ (8,428)
Net income	12,473			12,473
Other comprehensive income	3,061				3,061
Share based compensation	670	13	657
Exercise of stock options	1,184	36	1,148
Shares issued to ESOP and Directors	778	16	762
Dividends declared	(5,570)			(5,570)
Shares repurchased	(1,431)	(30)	(238)	(1,163)
Ending balance at Sep. 30, 2016	136,228	4,035	32,756	104,804	(5,367)
Beginning balance at Dec. 31, 2016	134,671	4,037	33,253	107,262	(9,881)
Net income	13,852			13,852
Other comprehensive income	1,367				1,367
Share based compensation	772	15	757
Exercise of stock options	765	25	740
Shares issued to ESOP and Directors	757	12	745
Dividends declared	(5,663)			(5,663)
Shares repurchased	(470)	(7)	(60)	(403)
Ending balance at Sep. 30, 2017	$ 146,051	$ 4,082	$ 35,435	$ 115,048	$ (8,514)

UNAUDITED CONSOLIDATED STATEME7

UNAUDITED CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS EQUITY (Parenthetical) - $ / shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Retained Earnings
Dividends declared, per share	$ 1.39	$ 1.38

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 13,852	$ 12,473
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	360	338
Amortization of deferred charges and fees, net	720	1,232
Depreciation and amortization	1,470	1,554
Bank owned life insurance income	(448)	(474)
Loss/(gain) on disposition of investment securities	3	(438)
Compensation expense from stock option and restricted stock grants	772	670
Change in accrued interest receivable	(272)	47
Change in deferred income taxes	301	1,107
Change in unrealized (gain)/loss of securities available for sale, net of taxes	(557)	(1,575)
Change in unfunded pension liability	398	351
Change in other assets	(1,679)	(2,905)
Change in other liabilities	1,597	4,172
Change in loans held for sale	5,946	(3,268)
Other, net	(1)	38
Net cash provided by operating activities	22,462	13,322
CASH FLOWS FROM INVESTING ACTIVITIES
Origination of loans	(257,931)	(234,039)
Proceeds from principal payments of loans	222,187	113,837
Proceeds from calls/maturities of securities available for sale	41,982	140,336
Proceeds from sales of securities available for sale and held to maturity	77,369	18,070
Purchase of securities available for sale	(5,091)	(129,733)
Proceeds from calls/maturities of securities held to maturity	27,100	8,521
Purchase of securities held to maturity	(164,684)	(10,719)
(Purchase) sale of FHLB of Boston stock	(840)	1,451
Purchase of banking premises and equipment	(521)	(1,091)
Net cash used by investing activities	(60,429)	(93,367)
CASH FLOWS FROM FINANCING ACTIVITIES
Change in demand, interest bearing, money market and savings accounts	3,144	64,519
Change in certificates of deposit	(12,323)	2,460
Change in short-term borrowings	11,500	12,600
Repayment of long-term borrowings	(125)	(123)
Cash dividends paid on common stock	(5,663)	(5,570)
Repurchase of common stock	(470)	(1,432)
Proceeds from issuance of common stock	1,522	1,962
Net cash provided by financing activities	(2,415)	74,416
Net decrease in cash and cash equivalents	(40,382)	(5,629)
Cash and cash equivalents at beginning of period	54,050	24,645
Cash and cash equivalents at end of period	13,668	19,016
Cash paid during the period for:
Interest	2,626	2,612
Income taxes	$ 7,305	$ 6,550

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	1. BASIS OF PRESENTATION The unaudited consolidated financial statements include the accounts of Cambridge Bancorp (the “Company”) and its wholly owned subsidiary, Cambridge Trust Company (the “Bank”), and the Bank’s wholly owned subsidiaries, Cambridge Trust Company of New Hampshire Inc., CTC Security Corporation, and CTC Security Corporation III. References to the Company herein relate to the consolidated group of companies. All significant intercompany accounts and transactions have been eliminated in preparation of the consolidated financial statements. The Company is a state-chartered, federally registered bank holding company headquartered in Cambridge, Massachusetts and was incorporated in 1983. The Company is the sole shareholder of the Bank, a Massachusetts trust company chartered in 1890, which is a private bank. The Company’s lines of business consisting of wealth management services, commercial banking, and consumer banking are managed as a single strategic unit. The unaudited consolidated financial statements reflect all adjustments (consisting of normal recurring adjustments) and disclosures necessary to present fairly the Company’s financial position, as of September 30, 2017 and December 31, 2016, respectively, and the results of operations and cash flows for the interim periods presented in accordance with U.S. generally accepted accounting principles (“GAAP”). Interim results are not necessarily reflective of the results of the entire year.

Use of Estimates

Use of Estimates	9 Months Ended
	Sep. 30, 2017
Use Of Estimates [Abstract]
Use of Estimates	2. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates. The allowance for loan losses, the fair values of financial instruments, and the valuation of deferred tax assets are particularly subject to change.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2017
Subsequent Events [Abstract]
Subsequent Events	3. Subsequent Events Changes to retirement plans . On October 23, 2017, the Company announced the decision to freeze the accrual of benefits effective December 31, 2017, within the defined benefit pension plan. Management has reviewed events occurring through November 8, 2017, the date the unaudited consolidated financial statements were available to be issued, and determined that no other subsequent events occurred requiring adjustment to or disclosure in these financial statements.

Recently Issued and Adopted Acc

Recently Issued and Adopted Accounting Guidance	9 Months Ended
	Sep. 30, 2017
New Accounting Pronouncements And Changes In Accounting Principles [Abstract]
Recently Issued and Adopted Accounting Guidance	4. Recently Issued and Adopted Accounting Guidance Accounting Standard Update No. Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities h is s e e s ta da r a a l l o c p a i e b t a l i e i e g a c c o n t i n a r i s a n a e ac t i v i t i es d c c o s a c m l e x i t a p l y i h d g a c c o n t i n T s ta d a r r q i r e c p a n i e c h a n h r c o n i t i a r s n t a t i o o t f c t h d g a c c o n ti b y • e li m i n a ti t q u i r e t s e a r a t l m a s r a p e g i e ff e c ti v n s s a n • re q i r i c m t p e s n a h l m n e a c o n i n a a e c e a a i n c m s t a e l i e d e i The standard also permits hedge accounting for strategies for which hedge accounting is not permitted today and includes new alternatives for measuring the hedged item for fair value hedges of interest rate risk. Furthermore, the standard eases the requirements for effectiveness testing, hedge documentation, applying the critical terms match method, and introduces new alternatives that will permit companies to reduce the risk of material error corrections if they misapply the shortcut method. The new accounting standard is effective on January 1, 2019 for the Company, and early adoption is permitted. The new standard requires a modified retrospective transition method in which the Company will recognize the cumulative effect of the change on the opening balance of each affected component of equity in the statement of financial position as of the date of adoption. While the Company continues to assess all potential impacts of the standard, we currently expect adoption to have an immaterial impact on our consolidated financial statements. Accounting Standards Update No. 2017-08 - Premium Amortization on Purchased Callable Debt Securities Accounting Standards Update No. 2017-07 - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost Accounting Standards Update No. 2016-18 - Restricted Cash Accounting Standards Update No. 2016-15 - Classification of Certain Cash Receipts and Cash Payments . Accounting Standards Update No. 2016-13 - Financial Instruments - Measurement of Credit Losses on Financial Instruments Accounting Standards Update No. 2016-09 - Improvements to Employee Share-Based Payment Accounting Accounting Standards Update No. 2016-02 - Leases Accounting Standards Update No. 2016-01 - Recognition and Measurement of Financial Assets and Financial Liabilities • Requires equity investments (with certain exceptions) to be measured at fair value with changes in fair value recognized in net income. • Requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. • Requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset (that is, securities or loans and receivables) on the statement of condition or the accompanying notes to the financial statements. • Clarifies that an entity must assess valuation allowances on a deferred tax asset related to available for sale debt securities in combination with its other deferred tax assets. • Eliminates the requirement for public entities to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the statement of condition. This guidance becomes effective for the Company for the interim and annual periods beginning on January 1, 2018, and early adoption is only permitted for certain provisions. The amendments, in general, are required to be applied by means of a cumulative-effect adjustment on the statement of condition as of the beginning of the period of adoption. The adoption of this guidance is not expected to have a material impact on our consolidated balance sheets, statements of income, and cash flows. Accounting Standards Update No. 2014-09 - Revenue from Contracts with Customers

Cash and Due from Banks

Cash and Due from Banks	9 Months Ended
	Sep. 30, 2017
Cash And Due From Banks [Abstract]
Cash and due from Banks	5. Cash and Due from Banks At September 30, 2017 and December 31, 2016, cash and due from banks totaled $13.7 million and $54.1 million, respectively. Of this amount, $12.9 million and $11.2 million, respectively, were maintained to satisfy the reserve requirements of the Federal Reserve Bank of Boston (“FRB Boston”). Additionally, at September 30, 2017 and December 31, 2016, the Company pledged $500,000 and $500,000, respectively, to the New Hampshire Banking Department relating to Cambridge Trust Company of New Hampshire, Inc.’s operations in that state.

Investment Securities

Investment Securities	9 Months Ended
	Sep. 30, 2017
Investments Debt And Equity Securities [Abstract]
Investment Securities	6. Investment Securities Investment securities have been classified in the unaudited consolidated balance sheets according to management’s intent. The carrying amounts of securities and their approximate fair values were as follows: September 30, 2017 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (dollars in thousands) Available for sale securities U.S. GSE obligations $ 90,024 $ — $ (844 ) $ 89,180 $ 140,026 $ 23 $ (1,340 ) $ 138,709 Mortgage-backed securities 119,272 299 (1,950 ) 117,621 183,974 479 (3,154 ) 181,299 Corporate debt securities 5,039 24 (18 ) 5,045 5,054 13 (38 ) 5,029 Mutual funds 672 — (69 ) 603 672 — (68 ) 604 Total available for sale securities $ 215,007 $ 323 $ (2,881 ) $ 212,449 $ 329,726 $ 515 $ (4,600 ) $ 325,641 Held to maturity securities U.S. GSE obligations $ 29,998 $ 2 $ (41 ) $ 29,959 $ — $ — $ — $ — Mortgage-backed securities 107,762 128 (245 ) 107,645 696 23 — 719 Corporate debt securities 1,997 29 — 2,026 — — — — Municipal securities 80,113 2,673 (165 ) 82,621 81,806 1,894 (664 ) 83,036 Total held to maturity securities $ 219,870 $ 2,832 $ (451 ) $ 222,251 $ 82,502 $ 1,917 $ (664 ) $ 83,755 Total $ 434,877 $ 3,155 $ (3,332 ) $ 434,700 $ 412,228 $ 2,432 $ (5,264 ) $ 409,396 All of the Company’s mortgage-backed securities have been issued by, or are collateralized by securities issued by, either Government National Mortgage Association (Ginnie Mae), Federal National Mortgage Association (Fannie Mae), or Federal Home Loan Mortgage Corporation (Freddie Mac). The following tables show the Company’s securities with gross unrealized losses aggregated by investment category and length of time that individual securities have been in a continuous loss position: September 30, 2017 Less than 12 months 12 months or longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses (dollars in thousands) Temporarily Impaired Securities Available for sale securities U.S. GSE obligations $ 59,652 $ (372 ) $ 29,528 $ (472 ) $ 89,180 $ (844 ) Mortgage-backed securities 82,766 (1,208 ) 31,122 (742 ) 113,888 (1,950 ) Corporate debt securities 4,021 (18 ) — — 4,021 (18 ) Mutual funds — — 603 (69 ) 603 (69 ) Total available for sale securities $ 146,439 $ (1,598 ) $ 61,253 $ (1,283 ) $ 207,692 $ (2,881 ) Held to maturity securities U.S. GSE obligations $ 24,957 $ (41 ) $ — $ — $ 24,957 $ (41 ) Mortgage-backed securities 74,790 (245 ) 3 — 74,793 (245 ) Corporate debt securities — — — — — — Municipal securities 6,795 (72 ) 2,485 (93 ) 9,280 (165 ) Total held to maturity securities $ 106,542 $ (358 ) $ 2,488 $ (93 ) $ 109,030 $ (451 ) Total temporarily impaired securities $ 252,981 $ (1,956 ) $ 63,741 $ (1,376 ) $ 316,722 $ (3,332 ) December 31, 2016 Less than 12 months 12 months or longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses (dollars in thousands) Temporarily Impaired Securities Available for sale securities U.S. GSE obligations $ 118,686 $ (1,340 ) $ — $ — $ 118,686 $ (1,340 ) Mortgage-backed securities 149,859 (2,795 ) 14,422 (359 ) 164,281 (3,154 ) Corporate debt securities 4,016 (38 ) — — 4,016 (38 ) Mutual funds — — 604 (68 ) 604 (68 ) Total available for sale securities $ 272,561 $ (4,173 ) $ 15,026 $ (427 ) $ 287,587 $ (4,600 ) Held to maturity securities Mortgage-backed securities $ 1 $ — $ 3 $ — $ 4 $ — Municipal securities 18,626 (664 ) — — 18,626 (664 ) Total held to maturity securities $ 18,627 $ (664 ) $ 3 $ — $ 18,630 $ (664 ) Total temporarily impaired securities $ 291,188 $ (4,837 ) $ 15,029 $ (427 ) $ 306,217 $ (5,264 ) Management evaluates securities for other-than-temporary impairment on at least a quarterly basis, and more frequently, when economic or market conditions warrant such evaluation. Consideration is given to: (1) the length of time and the extent to which the fair value has been less than cost; (2) the financial condition and near-term prospects of the issuer; and (3) the intent and ability of the Company to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value. As of September 30, 2017, 104 debt securities and one equity security had gross unrealized losses, with an aggregate depreciation of 1.04% from the Company’s amortized cost basis. The largest unrealized loss percentage of any single security was 10.21%, or $69,000 of its amortized cost. The largest unrealized dollar loss of any single security was $150,000, or 3.01% of its amortized cost. As of December 31, 2016, 132 debt securities and one equity security had gross unrealized losses, with an aggregate depreciation of 1.69% from the Company’s amortized cost basis. The largest unrealized loss percentage of any single security was 10.16%, or $51,000 of its amortized cost. The largest unrealized dollar loss of any single security was $189,000, or 3.79% of its amortized cost. The Company believes that the nature and duration of impairment on its debt security positions are primarily a function of interest rate movements and changes in investment spreads, and does not consider full repayment of principal on the reported debt obligations to be at risk. Since nearly all of these securities are rated “investment grade” and (a) the Company does not intend to sell these securities before recovery and (b) that it is more likely than not that the Company will not be required to sell these securities before recovery, the Company does not consider these securities to be other-than-temporarily impaired as of September 30, 2017 and December 31, 2016. The amortized cost and fair value of debt securities, aggregated by the earlier of guaranteed call date or contractual maturity, are shown below. Maturities of mortgage-backed securities do not take into consideration scheduled amortization or prepayments. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Within One Year After One, But Within Five Years After Five, But Within Ten Years After Ten Years Total Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value At September 30, 2017 (dollars in thousands) Available for sale securities U.S. GSE obligations $ 5,000 $ 4,987 $ 85,024 $ 84,193 $ — $ — $ — $ — $ 90,024 $ 89,180 Mortgage-backed securities 154 157 148 155 19,607 19,464 99,363 97,845 119,272 117,621 Corporate debt securities — — 4,039 4,021 1,000 1,024 — — 5,039 5,045 Total available for sale Securities $ 5,154 $ 5,144 $ 89,211 $ 88,369 $ 20,607 $ 20,488 $ 99,363 $ 97,845 $ 214,335 $ 211,846 Held to maturity securities U.S. GSE obligations $ — $ — $ 29,998 $ 29,959 $ — $ — $ — $ — $ 29,998 $ 29,959 Mortgage-backed securities 24 25 330 339 23,447 23,391 83,961 83,890 107,762 107,645 Corporate debt securities — — 1,997 2,026 — — — — 1,997 2,026 Municipal securities 3,960 3,985 13,714 14,086 33,389 34,789 29,050 29,761 80,113 82,621 Total held to maturity Securities $ 3,984 $ 4,010 $ 46,039 $ 46,410 $ 56,836 $ 58,180 $ 113,011 $ 113,651 $ 219,870 $ 222,251 Total $ 9,138 $ 9,154 $ 135,250 $ 134,779 $ 77,443 $ 78,668 $ 212,374 $ 211,496 $ 434,205 $ 434,097 The following table sets forth information regarding sales of investment securities and the resulting gains (losses) from such sales: Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 (dollars in thousands) Amortized cost of securities sold $ — $ 250 $ 77,372 $ 17,632 Gain/(loss) realized on securities sold — 3 (3 ) 438 Net proceeds from securities sold $ — $ 253 $ 77,369 $ 18,070

Loans and the Allowance for Loa

Loans and the Allowance for Loan Losses	9 Months Ended
	Sep. 30, 2017
Receivables [Abstract]
Loans and the Allowance for Loan Losses	7. LOANS AND THE ALLOWANCE FOR LOAN LOSSES The Company’s lending activities are conducted principally in Eastern Massachusetts. The Company grants single-family and multi-family residential loans, commercial and industrial, commercial real estate, construction loans, and a variety of consumer loans. Most loans granted by the Company are secured by real estate collateral. The Company’s commercial business loans are primarily made based on the cash flow of the borrower and secondarily on the underlying collateral provided by the borrower. In the event of a default, the liquidation of the underlying real estate collateral is typically viewed as the primary source of repayment. The borrowers’ cash flow may be difficult to predict, and collateral securing these loans may fluctuate in value. The repayment of commercial business loans depends primarily on the cash flow and credit worthiness of the borrower and secondarily on the underlying collateral provided by the borrower. Although commercial business loans are often collateralized by equipment, inventory, accounts receivable, or other business assets, the liquidation of collateral in the event of default is often an insufficient source of repayment. Repayment of the Company’s residential loans are generally dependent on the health of the employment market in the borrowers’ geographic areas and that of the general economy with liquidation of the underlying real estate collateral being typically viewed as the primary source of repayment in the event of borrower default. Loans outstanding are detailed by category as follows: September 30, 2017 December 31, 2016 (dollars in thousands) Residential mortgage Mortgages - fixed rate $ 300,071 $ 305,403 Mortgages - adjustable rate 236,323 228,028 Deferred costs net of unearned fees 1,031 973 Total residential mortgages 537,425 534,404 Commercial mortgage Mortgages - nonowner occupied 560,254 513,578 Mortgages - owner occupied 36,287 43,932 Construction 35,031 58,406 Deferred costs net of unearned fees 180 224 Total commercial mortgages 631,752 616,140 Home equity Home equity - lines of credit 72,083 70,883 Home equity - term loans 3,670 3,925 Deferred costs net of unearned fees 254 243 Total home equity 76,007 75,051 Commercial & industrial Commercial & industrial 65,818 59,638 Deferred costs net of unearned fees 43 68 Total commercial & industrial 65,861 59,706 Consumer Secured 43,695 33,386 Unsecured 1,151 1,451 Deferred costs net of unearned fees 17 16 Total consumer 44,863 34,853 Total loans $ 1,355,908 $ 1,320,154 Directors and officers of the Company and their associates are customers of, and have other transactions with, the Company in the normal course of business. All loans and commitments included in such transactions were made on substantially the same terms, including interest rates and collateral, as those prevailing at the time for comparable transactions with other persons and do not involve more than normal risk of collection or present other unfavorable features. At September 30, 2017 and December 31, 2016, total loans outstanding to such directors and officers were $632,000 and $690,000, respectively. During the nine months ended September 30, 2017, $97,000 of additions and $155,000 of repayments were made to these loans. There were $355,000 of additions and $406,000 of repayments during the year ended December 31, 2016. At September 30, 2017 and December 31, 2016, all of the loans to directors and officers were performing according to their original terms. The following tables set forth information regarding non-performing loans disaggregated by loan category: September 30, 2017 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Total (dollars in thousands) Non-performing loans: Non-accrual loans $ 1,031 $ 216 $ 3 $ 21 $ — $ 1,271 Loans past due >90 days, but still accruing — — — — — — Troubled debt restructurings 123 — — 308 — 431 Total $ 1,154 $ 216 $ 3 $ 329 $ — $ 1,702 December 31, 2016 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Total (dollars in thousands) Non-performing loans: Non-accrual loans $ 998 $ — $ — $ 24 $ 1 $ 1,023 Loans past due >90 days, but still accruing — 232 — — — 232 Troubled debt restructurings 132 — — 289 — 421 Total $ 1,130 $ 232 $ — $ 313 $ 1 $ 1,676 Troubled Debt Restructurings. Loans are considered restructured in a troubled debt restructuring (“TDR”) when the Company has granted concessions to a borrower due to the borrower’s financial condition that it otherwise would not have considered. These concessions may include modifications of the terms of the debt, such as; deferral of payments, extension of maturity, reduction of principal balance, reduction of the stated interest rate other than normal market rate adjustments, or a combination of these concessions. Debt may be bifurcated with separate terms for each tranche of the restructured debt. Restructuring a loan in lieu of aggressively enforcing the collection of the loan may benefit the Company by increasing the ultimate probability of collection. Restructured loans are classified as accruing or non-accruing based on management’s assessment of the collectability of the loan. Loans which are already on non-accrual status at the time of the restructuring generally remain on non-accrual status for approximately six months or longer before management considers such loans for return to accruing status. Accruing restructured loans are placed into non-accrual status if and when the borrower fails to comply with the restructured terms and management deems it unlikely that the borrower will return to a status of compliance in the near term. TDRs are classified as impaired loans. The Company identifies loss allocations for impaired loans on an individual loan basis. There were no new TDRs during the three months ended September 30, 2017. During the nine months ended September 30, 2017, the Company modified one loan as a TDR with a pre-modification carrying value (which consists of the unpaid principal balance, net of charge-offs, and unamortized deferred loan origination fees and costs, at the time of the restructuring) of $65,000 and a post-modification carrying value of $48,000. At September 30, 2017, five loans were determined to be TDRs with a total carrying value of $431,000. There were no TDR defaults during the three months and nine months ended September 30, 2017. During the three months and nine months ended September 30, 2016, the Company modified one loan with a pre- and post-modification carrying value of $247,000. There were no TDR defaults during the three months and nine months ended September 30, 2016. The allowance for loan losses includes a specific reserve for these TDRs of approximately $259,000 and $117,000 as of September 30, 2017 and December 31, 2016, respectively. As of September 30, 2017, there were no significant commitments to lend additional funds to borrowers whose loans were restructured. Loans by Credit Quality Indicator. The following tables contain period-end balances of loans receivable disaggregated by credit quality indicator: September 30, 2017 Residential Mortgages Home Equity Consumer (dollars in thousands) Credit risk profile based on payment activity: Performing $ 536,271 $ 76,004 $ 44,863 Non-performing 1,154 3 — Total $ 537,425 $ 76,007 $ 44,863 Commercial Mortgages Commercial & Industrial Credit risk profile by internally assigned grade: 1-6 (Pass) $ 620,847 $ 62,332 7 (Special Mention) 10,688 2,776 8 (Substandard) 217 753 9 (Doubtful) — — 10 (Loss) — — Total $ 631,752 $ 65,861 December 31, 2016 Residential Mortgages Home Equity Consumer (dollars in thousands) Credit risk profile based on payment activity: Performing $ 533,273 $ 75,051 $ 34,852 Non-performing 1,131 — 1 Total $ 534,404 $ 75,051 $ 34,853 Commercial Mortgages Commercial & Industrial Credit risk profile by internally assigned grade: 1-6 (Pass) $ 612,636 $ 56,310 7 (Special Mention) 2,861 1,431 8 (Substandard) 643 1,965 9 (Doubtful) — — 10 (Loss) — — Total $ 616,140 $ 59,706 With respect to residential real estate mortgages, home equity, and consumer loans, the Bank utilizes the following categories as indicators of credit quality: • Performing – These loans are accruing and are considered having low to moderate risk. • Non-performing – These loans either have been placed on non-accrual, or are past due more than 90 days but are still accruing, and may contain greater than average risk. With respect to commercial real estate mortgages and commercial loans, the Bank utilizes a 10 grade internal loan rating system as an indicator of credit quality. The grades are as follows: • Loans rated 1-6 (Pass) – These loans are considered “pass” rated with low to moderate risk. • Loans rated 7 (Special Mention) – These loans have potential weaknesses warranting close attention, which, if left uncorrected, may result in deterioration of the credit at some future date. • Loans rated 8 (Substandard) – These loans have well-defined weaknesses that jeopardize the orderly liquidation of the debt under the original loan terms. Loss potential exists but is not identifiable in any one customer. • Loans rated 9 (Doubtful) – These loans have pronounced weaknesses that make full collection highly questionable and improbable. • Loans rated 10 (Loss) – These loans are considered uncollectible and continuance as a bankable asset is not warranted. Delinquencies. The past due status of a loan is determined in accordance with its contractual repayment terms. All loan types are reported past due when one scheduled payment is due and unpaid for 30 days or more. Loan delinquencies can be attributed to many factors, such as but not limited to a continuing weakness in, or deteriorating economic conditions in, the region in which the collateral is located, the loss of a tenant or lower lease rates for commercial borrowers, or the loss of income for consumers and the resulting liquidity impacts on the borrowers. The following tables contain period-end balances of loans receivable disaggregated by past due status: September 30, 2017 30-59 Days Past Due 60-89 Days Past Due 90 Days or Greater Total Past Due Current Loans Total (dollars in thousands) Residential Mortgages $ 3,889 $ 371 $ 65 $ 4,325 $ 533,100 $ 537,425 Commercial Mortgages 1,979 — — 1,979 629,773 631,752 Home Equity — — 3 3 76,004 76,007 Commercial & Industrial 15 22 — 37 65,824 65,861 Consumer loans 37 1 — 38 44,825 44,863 Total $ 5,920 $ 394 $ 68 $ 6,382 $ 1,349,526 $ 1,355,908 December 31, 2016 30-59 Days Past Due 60-89 Days Past Due 90 Days or Greater Total Past Due Current Loans Total (dollars in thousands) Residential Mortgages $ 698 $ 179 $ 602 $ 1,479 $ 532,925 $ 534,404 Commercial Mortgages — 250 232 482 615,658 616,140 Home Equity 4 — — 4 75,047 75,051 Commercial & Industrial 173 — 1 174 59,532 59,706 Consumer loans 6 5 — 11 34,842 34,853 Total $ 881 $ 434 $ 835 $ 2,150 $ 1,318,004 $ 1,320,154 Allowance for Loan Losses. The Company maintains an allowance for loan losses in an amount determined by management on the basis of the character of the loans, loan performance, financial condition of borrowers, the value of collateral securing loans, and other relevant factors. We provide for loan losses based upon the consistent application of our documented allowance for loan loss methodology. All loan losses are charged to the allowance for loan losses and all recoveries are credited to it. Additions to the allowance for loan losses are provided by charges to income based on various factors which, in our judgment, deserve current recognition in estimating probable losses. We regularly review the loan portfolio, including a review of our classified assets, and make provisions for loan losses in order to maintain the allowance for loan losses in accordance with GAAP. The allowance for loan losses consists primarily of two components: 1. Specific allowances established for impaired loans (as defined by GAAP). The amount of impairment provided for as a specific allowance is measured based on the deficiency, if any, between the present value of expected future cash flows discounted at the loan’s effective interest rate at the time of impairment or, as a practical expedient, at the loan’s observable market price, or the fair value of the collateral if the loan is collateral-dependent, and the carrying value of the loan; and 2. General allowances established for loan losses on a portfolio basis for loans that do not meet the definition of impaired loans. The portfolio is grouped into homogenous pools by similar risk characteristics, primarily by loan type and regulatory classification. We apply an estimated incurred loss rate to each loan group. The loss rates applied are based upon our historical loss experience over a designated look back period adjusted, as appropriate, for the quantitative, qualitative, and environmental factors discussed below. This evaluation is inherently subjective, as it requires material estimates that may be susceptible to significant revisions based upon changes in economic and real estate market conditions. Actual loan losses may be significantly more than the allowance for loan losses we have established, which could have a material negative effect on our financial results. The adjustments to historical loss experience are based on our evaluation of several quantitative, qualitative, and environmental factors, including: • the loss emergence period, which represents the average amount of time between when loss events occur for specific loan types and when such problem loans are identified and the related loss amounts are confirmed through charge-offs; • changes in any concentration of credit (including, but not limited to, concentrations by geography, industry, or collateral type); • changes in the number and amount of non-accrual loans and past due loans; • changes in national, state, and local economic trends; • changes in the types of loans in the loan portfolio; • changes in the experience and ability of personnel; • changes in lending strategies; and • changes in lending policies and procedures. In addition, we may establish an unallocated allowance to provide for probable losses that have been incurred as of the reporting date but are not reflected in the allocated allowance. We evaluate the allowance for loan losses based upon the combined total of the specific and general components. Generally, when the loan portfolio increases, absent other factors, the allowance for loan loss methodology results in a higher dollar amount of estimated probable losses than would be the case without the increase. Generally, when the loan portfolio decreases, absent other factors, the allowance for loan losses methodology results in a lower dollar amount of estimated probable losses than would be the case without the decrease. Periodically, management conducts an analysis to estimate the loss emergence period for various loan categories based on samples of historical charge-offs. Model output by loan category is reviewed to evaluate the reasonableness of the reserve levels in comparison to the estimated loss emergence period applied to historical loss experience. We evaluate the loan portfolio on a quarterly basis and the allowance is adjusted accordingly. While we use the best information available to make evaluations, future adjustments to the allowance may be necessary if conditions differ substantially from the information used in making the evaluations. In addition, various regulatory agencies, as an integral part of their examination process, will periodically review the allowance for loan losses. Such agencies may require us to recognize additions to the allowance based on their analysis of information available to them at the time of their examination. The following tables contain changes in the allowance for loan losses disaggregated by loan category at September 30, 2017: For the Three Months Ended September 30, 2017 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Unallocated Impaired Total (dollars in thousands) Allowance for loan losses: Balance at June 30, 2017 $ 4,783 $ 8,449 $ 632 $ 758 $ 324 $ — $ 357 $ 15,303 Charge-offs — — — — (1 ) — — (1 ) Recoveries — — — 6 2 — — 8 Provision 303 (126 ) (4 ) 94 43 — — 310 Balance at September 30, 2017 $ 5,086 $ 8,323 $ 628 $ 858 $ 368 $ — $ 357 $ 15,620 For the Nine Months Ended September 30, 2017 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Unallocated Impaired Total (dollars in thousands) Allowance for loan losses: Balance at December 31, 2016 $ 4,898 $ 8,451 $ 651 $ 807 $ 264 $ — $ 190 $ 15,261 Charge-offs — — — (1 ) (14 ) — — (15 ) Recoveries — — — 8 6 — — 14 Provision 188 (128 ) (23 ) 44 112 — 167 360 Balance at September 30, 2017 $ 5,086 $ 8,323 $ 628 $ 858 $ 368 $ — $ 357 $ 15,620 The following tables contain changes in the allowance for loan losses disaggregated by loan category at September 30, 2016: For the Three Months Ended September 30, 2016 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Unallocated Impaired Total (dollars in thousands) Allowance for loan losses: Balance at June 30, 2016 $ 4,773 $ 8,562 $ 753 $ 766 $ 376 $ 7 $ 174 $ 15,411 Charge-offs — — — — (3 ) — — (3 ) Recoveries — 1 — 1 14 — — 16 Provision (242 ) 380 (40 ) (23 ) 4 29 5 113 Balance at September 30, 2016 $ 4,531 $ 8,943 $ 713 $ 744 $ 391 $ 36 $ 179 $ 15,537 For the Nine Months Ended September 30, 2016 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Unallocated Impaired Total (dollars in thousands) Allowance for loan losses: Balance at December 31, 2015 $ 5,244 $ 8,094 $ 699 $ 615 $ 354 $ 11 $ 174 $ 15,191 Charge-offs — — — (13 ) (17 ) — — (30 ) Recoveries 13 7 1 11 6 — — 38 Provision (726 ) 842 13 131 48 25 5 338 Balance at September 30, 2016 $ 4,531 $ 8,943 $ 713 $ 744 $ 391 $ 36 $ 179 $ 15,537 The following tables contain period-end balances of the allowance for loan losses and related loans receivable disaggregated by impairment method: September 30, 2017 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Total (dollars in thousands) Allowance for loan losses Individually evaluated for impairment $ 98 $ — $ — $ 259 $ — $ 357 Collectively evaluated for impairment 5,086 8,323 628 858 368 15,263 Total $ 5,184 $ 8,323 $ 628 $ 1,117 $ 368 $ 15,620 Loans receivable Individually evaluated for impairment $ 1,056 $ 217 $ 98 $ 307 $ — $ 1,678 Collectively evaluated for impairment 536,369 631,535 75,909 65,554 44,863 1,354,230 Total $ 537,425 $ 631,752 $ 76,007 $ 65,861 $ 44,863 $ 1,355,908 December 31, 2016 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Total (dollars in thousands) Allowance for loan losses Individually evaluated for impairment $ 69 $ — $ 7 $ 114 $ — $ 190 Collectively evaluated for impairment 4,898 8,452 650 807 264 15,071 Total $ 4,967 $ 8,452 $ 657 $ 921 $ 264 $ 15,261 Loans receivable Individually evaluated for impairment $ 1,027 $ — $ 102 $ 289 $ — $ 1,418 Collectively evaluated for impairment 533,377 616,140 74,949 59,417 34,853 1,318,736 Total $ 534,404 $ 616,140 $ 75,051 $ 59,706 $ 34,853 $ 1,320,154 The following tables present information pertaining to impaired loans: For the Three Months Ended September 30, 2017 Carrying Value Average Carrying Value Unpaid Principal Balance Related Allowance Interest Income Recognized (dollars in thousands) With no required reserve recorded: Commercial and industrial $ 38 $ 40 $ 38 $ — $ 1 Commercial real estate 217 221 229 — — Residential real estate 991 997 1,187 — — Home equity 98 99 128 — — Total 1,344 1,357 1,582 — 1 With required reserve recorded: Commercial and industrial 269 273 281 259 — Commercial real estate — — — — — Residential real estate 65 65 65 98 — Home equity — — — — — Total 334 338 346 357 - Total: Commercial and industrial 307 313 319 259 1 Commercial real estate 217 221 229 — — Residential real estate 1,056 1,062 1,252 98 — Home equity 98 99 128 — — Total $ 1,678 $ 1,695 $ 1,928 $ 357 $ 1 For the Nine Months Ended September 30, 2017 Carrying Value Average Carrying Value Unpaid Principal Balance Related Allowance Interest Income Recognized (dollars in thousands) With no required reserve recorded: Commercial and industrial $ 38 $ 38 $ 38 $ — $ 2 Commercial real estate 217 227 229 — 3 Residential real estate 991 1,012 1,187 — — Home equity 98 102 128 — — Total 1,344 1,379 1,582 — 5 With required reserve recorded: Commercial and industrial 269 279 281 259 — Commercial real estate — — — — — Residential real estate 65 66 65 98 1 Home equity — — — — — Total 334 345 346 357 1 Total: Commercial and industrial 307 317 319 259 2 Commercial real estate 217 227 229 — 3 Residential real estate 1,056 1,078 1,252 98 1 Home equity 98 102 128 — — Total $ 1,678 $ 1,724 $ 1,928 $ 357 $ 6 For the Three Months Ended September 30, 2016 Carrying Value Average Carrying Value Unpaid Principal Balance Related Allowance Interest Income Recognized (dollars in thousands) With no required reserve recorded: Commercial and industrial $ — $ — $ — $ — $ — Commercial real estate 293 293 390 — — Residential real estate 714 716 883 — 1 Home equity 78 78 101 — — Consumer 1 1 1 — — Total 1,086 1,088 1,375 — 1 With required reserve recorded: Commercial and industrial 458 459 462 179 — Commercial real estate — — — — — Residential real estate — — — — — Home equity — — — — — Total 458 459 462 179 — Total: Commercial and industrial 458 459 462 179 — Commercial real estate 293 293 390 — — Residential real estate 714 716 883 — 1 Home equity 78 78 101 — — Consumer 1 1 1 — — Total $ 1,544 $ 1,547 $ 1,837 $ 179 $ 1 For the Nine Months Ended September 30, 2016 Carrying Value Average Carrying Value Unpaid Principal Balance Related Allowance Interest Income Recognized (dollars in thousands) With no required reserve recorded: Commercial and industrial $ — $ — $ — $ — $ — Commercial real estate 293 295 390 — — Residential real estate 714 729 883 — 3 Home equity 78 80 101 — — Consumer 1 1 1 — — Total 1,086 1,105 1,375 — 3 With required reserve recorded: Commercial and industrial 458 461 462 179 — Commercial real estate — — — — — Residential real estate — — — — — Home equity — — — — — Total 458 461 462 179 — Total: Commercial and industrial 458 461 462 179 — Commercial real estate 293 295 390 — — Residential real estate 714 729 883 — 3 Home equity 78 80 101 — — Consumer 1 1 1 — — Total $ 1,544 $ 1,566 $ 1,837 $ 179 $ 3

Federal Home Loan Bank of Bosto

Federal Home Loan Bank of Boston Stock	9 Months Ended
	Sep. 30, 2017
Federal Home Loan Bank of Boston
Federal Home Loan Bank Stock [Line Items]
Federal Home Loan Bank of Boston Stock	8. Federal Home Loan Bank of Boston Stock As a voluntary member of the Federal Home Loan Bank (“FHLB”) of Boston, the Bank is required to invest in stock of the FHLB of Boston in an amount based upon its outstanding advances from the FHLB of Boston. At September 30, 2017 and December 31, 2016, the Bank’s investment in FHLB of Boston stock totaled $4.9 million and $4.1 million, respectively. No market exists for shares of this stock. The Bank’s cost for FHLB of Boston stock is equal to its par value. Upon redemption of the stock, which is at the discretion of the FHLB of Boston, the Bank would receive an amount equal to the par value of the stock. At its discretion, the FHLB of Boston may also declare dividends on its stock. The Bank’s investment in FHLB of Boston stock is reviewed for impairment at each reporting date based on the ultimate recoverability of the cost basis of the stock. As of September 30, 2017 and December 31, 2016, no impairment has been recognized.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	9 Months Ended
	Sep. 30, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	9. Goodwill and Other Intangible Assets Goodwill . At September 30, 2017 and December 31, 2016, the carrying value of goodwill, which is included in other assets, totaled $412,000 and $412,000, respectively. Goodwill is tested for impairment, based on its fair value, at least annually. As of September 30, 2017 and December 31, 2016, no goodwill impairment has been recognized. Mortgage servicing rights . Certain residential mortgage loans are periodically sold by the Company to the secondary market. Loans held for sale totaled $560,000 and $6.5 million at September 30, 2017 and December 31, 2016, respectively. Generally, these loans are sold without recourse. The Company sells loans and either releases or retains the servicing rights. For loans sold with servicing rights retained, we provide the servicing for the loans on a per-loan fee basis. Mortgage loans sold and servicing rights retained during the nine months ended September 30, 2017 and September 30, 2016 were $11.5 million and $25.9 million, respectively, with net gains recognized in gain on loans held for sale of $172,000 and $607,000, respectively. The fair value of our mortgage servicing rights (“MSR”) portfolio was $1.1 million and $1.0 million at September 30, 2017 and December 31, 2016, respectively. The fair value of mortgage servicing rights is estimated based on the present value of expected cash flows, incorporating assumptions for discount rate, prepayment speed, and servicing cost. An analysis of mortgage servicing rights, which are included in other assets, follows: Mortgage Servicing Rights Valuation Allowance Total (dollars in thousands) Balance at December 31, 2015 $ 499 $ (8 ) $ 491 Mortgage servicing rights capitalized 274 — 274 Amortization charged against servicing income (153 ) — (153 ) Change in impairment reserve — (22 ) (22 ) Balance at September 30, 2016 $ 620 $ (30 ) $ 590 Balance at December 31, 2016 $ 842 $ (30 ) $ 812 Mortgage servicing rights capitalized 128 — 128 Amortization charged against servicing income (112 ) — (112 ) Change in impairment reserve — — — Balance at September 30, 2017 $ 858 $ (30 ) $ 828 The weighted-average amortization period for mortgage servicing rights portfolio was 7.3 years and 8.0 years at September 30, 2017 and September 30, 2016, respectively.

Deposits

Deposits	9 Months Ended
	Sep. 30, 2017
Deposits [Abstract]
Deposit	10. DEPOSITS Deposits are summarized as follows: September 30, 2017 December 31, 2016 (dollars in thousands) Demand deposits (non-interest bearing) $ 465,970 $ 472,923 Interest bearing checking 387,343 430,706 Money market 64,232 72,057 Savings 600,475 539,190 Retail certificates of deposit under $100,000 39,920 42,471 Retail certificates of deposit $100,000 or greater 68,808 72,355 Wholesale certificates of deposit 50,170 56,336 Total deposits $ 1,676,918 $ 1,686,038 Certificates of deposit had the following schedule of maturities: September 30, 2017 December 31, 2016 (dollars in thousands) Less than 3 months remaining $ 26,750 $ 32,268 3 to 5 months remaining 28,608 17,558 6 to 11 months remaining 43,111 36,240 12 to 23 months remaining 32,940 44,467 24 to 47 months remaining 19,885 29,826 48 months or more remaining 7,604 10,803 Total certificates of deposit $ 158,898 $ 171,162 Interest expense on retail certificates of deposit $100,000 or greater was $112,000 and $125,000 for the three months ended September 30, 2017 and September 30, 2016, respectively. Interest expense on retail certificates of deposit $100,000 or greater was $335,000 and $347,000 for the nine months ended September 30, 2017 and September 30, 2016, respectively. The aggregate amount of certificates of deposit in denominations that meet or exceed the Federal Deposit Insurance Corporation (the “FDIC”) insurance limit of $250,000 at September 30, 2017 and December 31, 2016 was $43.9 million and $46.0 million, respectively. Related Party Deposits Deposit accounts of directors, executive officers and their respective affiliates totaled $8.3 million and $7.2 million as of September 30, 2017 and December 31, 2016, respectively.

Borrowings

Borrowings	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Borrowings	11. Borrowings Information relating to short-term borrowings is presented below: For the Nine Months Ended September 30, 2017 For the Year Ended December 31, 2016 (dollars in thousands) FHLB of Boston short-term advances Ending balance $ 11,500 $ — Average daily balance 42,293 3,668 Highest month-end balance 110,000 21,000 Weighted average interest rate 1.20 % 0.54 % Information relating to long-term borrowings is presented below: September 30, 2017 December 31, 2016 Amount Rate Amount Rate (dollars in thousands) FHLB of Boston long-term advances Due 09/01/2020; amortizing $ 3,621 1.94 % $ 3,746 1.94 % All short- and long-term borrowings with the FHLB of Boston are secured by the Bank’s stock in the FHLB of Boston and a blanket lien on “qualified collateral” defined principally as 90% of the market value of certain U.S. Government and GSE obligations and 75% of the carrying value of certain residential mortgage loans. Based upon collateral pledged, the Bank’s unused borrowing capacity with the FHLB of Boston at September 30, 2017 and December 31, 2016 was approximately $292.8 million and $306.8 million, respectively. The Bank also has a line of credit with the FRB Boston. At September 30, 2017, the Bank had pledged commercial real estate and commercial & industrial loans with aggregate principal balances of approximately $301.6 million as collateral for this line of credit. Based upon the collateral pledged, the Bank’s unused borrowing capacity with the FRB Boston at September 30, 2017 was $165.1 million and $159.6 million as of December 31, 2016.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes The components of income tax expense were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 (dollars in thousands) Current Federal $ 2,651 $ 2,295 $ 5,966 $ 5,592 State 690 624 1,552 1,310 Total current expense 3,341 2,919 7,518 6,902 Deferred Federal (504 ) (495 ) (414 ) (555 ) State (143 ) (140 ) (117 ) (157 ) Total deferred (647 ) (635 ) (531 ) (712 ) Total income tax expense $ 2,694 $ 2,284 $ 6,987 $ 6,190 The following is a reconciliation of the total income tax provision, calculated at statutory federal income tax rates, to the income tax expense in the consolidated statements of income: Three Months Ended September 30, Nine Months Ended September 30, 2017 Rate 2016 Rate 2017 Rate 2016 Rate (dollars in thousands) (dollars in thousands) Provision at statutory rates $ 2,697 35.00 % $ 2,401 35.00 % $ 7,294 35.00 % $ 6,532 35.00 % Increase/(decrease) resulting from: State tax, net of federal tax benefit 356 4.62 314 4.58 933 4.48 749 4.01 Tax-exempt income (265 ) (3.44 ) (281 ) (4.10 ) (822 ) (3.94 ) (827 ) (4.43 ) ESOP dividends (71 ) (0.92 ) (53 ) (0.77 ) (164 ) (0.79 ) (158 ) (0.85 ) Bank owned life insurance (49 ) (0.64 ) (52 ) (0.76 ) (157 ) (0.75 ) (166 ) (0.89 ) Benefit from stock compensation — — — — (188 ) (0.90 ) — — Other 26 0.35 (45 ) (0.65 ) 91 0.43 60 0.33 Total income tax expense $ 2,694 34.97 % $ 2,284 33.30 % $ 6,987 33.53 % $ 6,190 33.17 % The effective tax rate for the three months ended September 30, 2017 and September 30, 2016 was 34.97% and 33.30%, respectively. The effective tax rate for the nine months ended September 30, 2017 and September 30, 2016 was 33.53% and 33.17%, respectively. At September 30, 2017 and December 31, 2016, the Company had no unrecognized tax benefits or any uncertain tax positions. The Company does not expect the total amount of unrecognized tax benefits to significantly increase in the next 12 months. We did not record any interest or penalties for the three months and nine months ended September 30, 2017 and September 30, 2016. The Company’s federal income tax returns are open and subject to examination from the 2014 tax return year and forward. The Company’s state income tax returns are generally open from the 2014 and later tax return years based on individual state statute of limitations. On January 1, 2017, we adopted Accounting Standards Update No. 2016-09 - “Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”). ASU 2016-09 requires that excess tax benefits or tax deficiencies be recognized as income tax benefit or expense in earnings in the period that they occur. For the three months and nine months ended September 30, 2017, the Company recognized a tax benefit of $0 and $219,000, respectively, resulting from share-based compensation.

Pension and Retirement Plans

Pension and Retirement Plans	9 Months Ended
	Sep. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Pension and Retirement Plans	13. Pension and Retirement Plans The Company has a noncontributory, defined benefit pension plan (“Pension Plan”) covering substantially all employees hired before May 2, 2011. Employees in positions requiring at least 1,000 hours of service per year were eligible to participate upon the attainment of age 21 and the completion of one year of service. Benefits are based primarily on years of service and the employee’s average monthly pay during the five highest consecutive plan years of the employee’s final ten years. The Company also provides supplemental retirement benefits to certain executive officers of the Company under the terms of Supplemental Executive Retirement Agreements (“Supplemental Retirement Plan”). The Supplemental Retirement Plan became effective on October 1, 1989. Benefits to be paid under the plan are contractually agreed upon and detailed in individual agreements with the executives. The Company also offers postretirement health care benefits for current and future retirees of the Bank. Certain employees receive a fixed monthly benefit at age 65 toward the purchase of postretirement medical coverage. The benefit received is based on the employee’s years of active service. The Company uses a December 31 measurement date each year to determine the benefit obligations for these plans. The components of net periodic benefit cost was as follows: Three Months Ended September 30, Pension Plan Supplemental Retirement Plan Retirement Healthcare Plan 2017 2016 2017 2016 2017 2016 (dollars in thousands) Net periodic benefit cost Service cost $ 338 $ 399 $ 67 $ 57 $ 4 $ 7 Interest cost 412 452 91 75 5 8 Expected return on assets (618 ) (725 ) — - — — Amortization of prior service credit (1 ) (1 ) — 13 — (2 ) Amortization of net actuarial loss 179 228 — - (2 ) (3 ) Net periodic benefit cost $ 310 $ 353 $ 158 $ 145 $ 7 $ 10 Nine Months Ended September 30, Pension Plan Supplemental Retirement Plan Retirement Healthcare Plan 2017 2016 2017 2016 2017 2016 (dollars in thousands) Net periodic benefit cost Service cost $ 1,162 $ 1,162 $ 200 $ 209 $ 12 $ 19 Interest cost 1,413 1,319 273 271 15 25 Expected return on assets (2,122 ) (2,113 ) — — — — Amortization of prior service credit (3 ) (3 ) — 47 — (5 ) Amortization of net actuarial loss 614 664 — — (6 ) (9 ) Net periodic benefit cost $ 1,064 $ 1,029 $ 473 $ 527 $ 21 $ 30 The Company does not intend to contribute to the Pension Plan in 2017. Employee Profit Sharing Plan The Company maintains a Profit Sharing Plan (“PSP”) that provides for deferral of federal and state income taxes on employee contributions allowed under Section 401(k) of federal law. The Company matches employee contributions up to 100% of the first 3% of each participant’s salary. Each year, the Company may also make a discretionary contribution to the PSP. Employees are eligible to participate in the 401(k) feature of the PSP on the first business day of the quarter following their initial date of service and attainment of age 21. Employees are eligible to participate in discretionary contribution feature of the PSP on January 1 and July 1 of each year provided they have attained the age of 21 and the completion of 12 months of service consisting of at least 1,000 hours. Employee Stock Ownership Plan The Company has an Employee Stock Ownership Plan (“ESOP”) for its eligible employees. Employees are eligible to participate upon the attainment of age 21 and the completion of 12 months of service consisting of at least 1,000 hours. Historically, the ESOP would purchase from the Company shares presently authorized but unissued at a price determined by an independent appraiser and certified by a committee of the trustees of the ESOP. Purchases of the Company’s stock by the ESOP are funded by employer contributions to the plan and proceeds from dividends paid to the plan participants. Total expenses related to the PSP and ESOP for the three months ended September 30, 2017 and September 30, 2016 amounted to approximately $238,000 and $238,000, respectively. Total expenses related to the PSP and ESOP for the nine months ended September 30, 2017 and September 30, 2016 amounted to $713,000 and $713,000, respectively.

Stock Based Compensation

Stock Based Compensation	9 Months Ended
	Sep. 30, 2017
Share Based Compensation [Abstract]
Stock Based Compensation	14. STOCK BASED COMPENSATION The following table presents the pre-tax expense associated with non-vested restricted stock awards and non-vested performance based restricted stock units (share-based compensation) and the related tax benefits recognized: Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 (dollars in thousands) Stock based compensation expense $ 253 $ 251 $ 805 $ 688 Related tax benefits $ 103 $ 103 $ 329 $ 281

Financial Instruments with Off-

Financial Instruments with Off-Balance-Sheet Risk	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Financial Instruments with Off-Balance-Sheet Risk	15. Financial Instruments with Off-Balance-Sheet Risk To meet the financing needs of its customers, the Company is a party to financial instruments with off-balance-sheet risk in the normal course of business. These financial instruments are primarily comprised of commitments to extend credit, commitments to sell residential real estate mortgage loans, risk participation agreements, and standby letters of credit. Those instruments involve, to varying degrees, elements of credit and interest rate risk in excess of the amounts recognized in the consolidated balance sheets. The Company’s exposure to credit loss in the event of nonperformance by the other party to the financial instrument for loan commitments and standby letters of credit is represented by the contractual amount of those instruments assuming that the amounts are fully advanced and that collateral or other security is of no value. The Company uses the same credit policies in making commitments and conditional obligations as it does for on-balance-sheet instruments. Off-balance-sheet financial instruments with contractual amounts that present credit risk include the following: September 30, 2017 December 31, 2016 (dollars in thousands) Financial instruments whose contractual amount represents credit risk: Commitments to extend credit: Unused portion of existing lines of credit $ 282,008 $ 256,767 Origination of new loans 65,313 26,024 Standby letters of credit 8,298 7,763 Financial instruments whose notional amount exceeds the amount of credit risk: Commitments to sell residential mortgage loans 1,623 9,622 Customer related derivative contracts: Interest rate swaps with customers 83,155 68,372 Mirror swaps with counterparties 83,155 68,372 Risk participation agreements with counterparties 28,467 16,378

Shareholders_ Equity

Shareholders’ Equity	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Shareholders’ Equity	16. Shareholders’ Equity Capital guidelines issued by the Federal Reserve Bank (the “FRB”) and by the FDIC require that the Company and the Bank maintain minimum capital levels for capital adequacy purposes. These regulations also require banks and their holding companies to maintain higher capital levels to be considered “well-capitalized.” 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 and the regulatory framework for prompt corrective action, there are specific capital guidelines that involve quantitative measures of assets, liabilities, and certain off-balance-sheet items as calculated under regulatory accounting practices. The risk-based capital rules are designed to make regulatory capital more sensitive to differences in risk profiles among bank and bank holding companies to account for off-balance-sheet exposure and to minimize disincentives for holding liquid assets. On July 2, 2013, the FRB approved the final rules implementing the Basel Committee on Banking Supervision’s capital guidelines for U.S. banks (“Basel III Capital Rules”). On July 9, 2013, the FDIC also approved, as an interim final rule, the regulatory capital requirements for U.S. banks, following the actions of the FRB. On April 8, 2014, the FDIC adopted as final its interim final rule, which is identical in substance to the final rules issued by the FRB in July 2013. Under the final rules, minimum requirements increased for both the quantity and quality of capital held by the Bank. The rules include a new common equity Tier 1 capital risk-weighted assets minimum ratio of 4.5%, raise the minimum ratio of Tier 1 capital to risk-weighted assets from 4.0% to 6.0%, require a minimum ratio of Total capital to risk-weighted assets of 8.0%, and require a minimum Tier 1 leverage ratio of 4.0%. The Basel III Capital Rules became effective for the Company and the Bank on January 1, 2015 (subject to a phase-in period for the capital conservation buffer discussed below). Quantitative measures established by the Basel III Capital Rules to ensure capital adequacy require the maintenance of minimum amounts and ratios (set forth in the table below) of Common Equity Tier 1 capital, Tier 1 capital, Total capital (as defined in the regulations) to risk-weighted assets (as defined), and of Tier 1 capital to adjusted quarterly average assets (as defined). When fully phased in on January 1, 2019, the Basel III Capital Rules will require the Company and the Bank to maintain (i) a minimum ratio of Common Equity Tier 1 capital to risk-weighted assets of at least 4.5%, plus a 2.5% “capital conservation buffer” (which is added to the 4.5% Common Equity Tier 1 capital ratio as that buffer is phased in, effectively resulting in a minimum ratio of Common Equity Tier 1 capital to risk-weighted assets of at least 7.0% upon full implementation), (ii) a minimum ratio of Tier 1 capital to risk-weighted assets of at least 6.0%, plus the capital conservation buffer (which is added to the 6.0% Tier 1 capital ratio as that buffer is phased in, effectively resulting in a minimum Tier 1 capital ratio of 8.5% upon full implementation), (iii) a minimum ratio of Total capital (that is, Tier 1 plus Tier 2) to risk-weighted assets of at least 8.0%, plus the capital conservation buffer (which is added to the 8.0% total capital ratio as that buffer is phased in, effectively resulting in a minimum total capital ratio of 10.5% upon full implementation), and (iv) a minimum leverage ratio of 4.0% calculated as the ratio of Tier 1 capital to average quarterly assets. The implementation of the capital conservation buffer began on January 1, 2016 at the 0.625% level and will be phased in over a four-year period (increasing by that amount on each subsequent January 1, until it reaches 2.5% on January 1, 2019). The capital conservation buffer is designed to absorb losses during periods of economic stress and, as detailed above, effectively increases the minimum required risk-weighted capital ratios. Banking institutions with a ratio of Common Equity Tier 1 capital to risk-weighted assets below the effective minimum (4.5% plus the capital conservation buffer) will face constraints on dividends, equity repurchases, and compensation based on the amount of the shortfall. Management believes that as of September 30, 2017 and December 31, 2016, the Company and the Bank met all applicable minimum capital requirements and were considered “well-capitalized” by both the FRB and the FDIC. Actual Minimum Capital Required For Capital Adequacy Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio Amount Ratio Amount Ratio (dollars in thousands) At September 30, 2017 Cambridge Bancorp: Total capital (to risk-weighted assets) $ 169,487 13.7% $ 99,005 8.0% $ 114,474 9.25% $ 129,944 10.5% N/A N/A Tier I capital (to risk-weighted assets) 154,015 12.4% 74,253 6.0% 89,723 7.25% 105,192 8.5% N/A N/A Common equity tier I capital (to risk-weighted assets) 154,015 12.4% 55,690 4.5% 71,160 5.75% 86,629 7.0% N/A N/A Tier I capital (to average assets) 154,015 8.1% 75,897 4.0% 75,897 4.00% 75,897 4.0% N/A N/A Cambridge Trust Company: Total capital (to risk-weighted assets) $ 165,751 13.4% $ 99,005 8.0% $ 114,474 9.25% $ 129,944 10.5% $ 123,756 10.0% Tier I capital (to risk-weighted assets) 150,279 12.1% 74,253 6.0% 89,723 7.25% 105,192 8.5% 99,005 8.0% Common equity tier I capital (to risk-weighted assets) 150,279 12.1% 55,690 4.5% 71,160 5.75% 86,629 7.0% 80,441 6.5% Tier I capital (to average assets) 150,279 7.9% 75,897 4.0% 75,897 4.00% 75,897 4.0% 94,871 5.0% At December 31, 2016 Cambridge Bancorp: Total capital (to risk-weighted assets) $ 159,141 13.1% $ 96,873 8.0% $ 104,441 8.625% $ 127,145 10.5% N/A N/A Tier I capital (to risk-weighted assets) 144,003 11.9% 72,654 6.0% 80,223 6.625% 102,927 8.5% N/A N/A Common equity tier I capital (to risk-weighted assets) 144,003 11.9% 54,491 4.5% 62,059 5.125% 84,763 7.0% N/A N/A Tier I capital (to average assets) 144,003 7.9% 72,488 4.0% 72,488 4.000% 72,488 4.0% N/A N/A Cambridge Trust Company: Total capital (to risk-weighted assets) $ 156,928 13.0% $ 96,873 8.0% $ 104,441 8.625% $ 127,145 10.5% $ 121,091 10.0% Tier I capital (to risk-weighted assets) 141,790 11.7% 72,654 6.0% 80,223 6.625% 102,927 8.5% 96,873 8.0% Common equity tier I capital (to risk-weighted assets) 141,790 11.7% 54,491 4.5% 62,059 5.125% 84,763 7.0% 78,709 6.5% Tier I capital (to average assets) 141,790 7.8% 72,488 4.0% 72,488 4.000% 72,488 4.0% 90,610 5.0%

Other Comprehensive Income

Other Comprehensive Income	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Other Comprehensive Income	17. Other Comprehensive Income Comprehensive income is defined as all changes to equity except investments by and distributions to shareholders. Net income is a component of comprehensive income, with all other components referred to in the aggregate as ‘other comprehensive income.’ The Company’s other comprehensive income consists of unrealized gains or losses on securities classified as available for sale and the component of the unfunded retirement liability computed in accordance with the requirements of ASC 715, “Compensation – Retirement Benefits.” Three Months Ended September 30, 2017 Three Months Ended September 30, 2016 Before Tax Amount Tax (Expense) or Benefit Net-of-tax Amount Before Tax Amount Tax (Expense) or Benefit Net-of-tax Amount (dollars in thousands) Unrealized gains (losses) on available for sale securities Unrealized holding gains (losses) arising during period $ 452 $ (166 ) $ 286 $ (539 ) $ 137 $ (402 ) Reclassification adjustment for losses (gains) recognized in net income — — — (3 ) 1 (2 ) Defined benefit retirement plans Change in unfunded retirement liability 225 (92 ) 133 198 (81 ) 117 Total Other Comprehensive Income $ 677 $ (258 ) $ 419 $ (344 ) $ 57 $ (287 ) Nine Months Ended September 30, 2017 Nine Months Ended September 30, 2016 Before Tax Amount Tax (Expense) or Benefit Net-of-tax Amount Before Tax Amount Tax (Expense) or Benefit Net-of-tax Amount (dollars in thousands) Unrealized gains (losses) on available for sale securities Unrealized holding gains (losses) arising during period $ 1,524 $ (556 ) $ 968 $ 4,724 $ (1,733 ) $ 2,991 Reclassification adjustment for losses (gains) recognized in net income 3 (2 ) 1 (438 ) 157 (281 ) Defined benefit retirement plans Change in unfunded retirement liability 673 (275 ) 398 593 (242 ) 351 Total Other Comprehensive Income $ 2,200 $ (833 ) $ 1,367 $ 4,879 $ (1,818 ) $ 3,061 Reclassifications out of Accumulated Other Comprehensive Income (“AOCI”) are presented below: Three Months Ended September 30, Details about Accumulated Other Comprehensive Income Components 2017 2016 Affected Line Item in the Statement where Net Income is Presented (dollars in thousands) Unrealized gains and losses on available for sale securities $ — $ 3 Gain on disposition of investment securities Tax benefit or (expense) — (1 ) Provision for income taxes Net of tax $ — $ 2 Net income Nine Months Ended September 30, Details about Accumulated Other Comprehensive Income Components 2017 2016 Affected Line Item in the Statement where Net Income is Presented (dollars in thousands) Unrealized gains and losses on available for sale securities $ (3 ) $ 438 (Loss) gain on disposition of investment securities Tax benefit or (expense) 2 (157 ) Provision for income taxes Net of tax $ (1 ) $ 281 Net income

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Earnings Per Share	18. Earnings per Share The following represents a reconciliation between basic and diluted earnings per share: Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 (dollars in thousands, except per share data) Earnings per common share - basic: Numerator: Net income $ 5,010 $ 4,575 $ 13,852 $ 12,473 Less dividends and undistributed earnings allocated to participating securities (53 ) (53 ) (148 ) (154 ) Net income applicable to common shareholders $ 4,957 $ 4,522 $ 13,704 $ 12,319 Denominator: Weighted average common shares outstanding 4,037 3,997 4,027 3,983 Earnings per common share - basic $ 1.23 $ 1.13 $ 3.40 $ 3.09 Earnings per common share - diluted: Numerator: Net income $ 5,010 $ 4,575 $ 13,852 $ 12,473 Less dividends and undistributed earnings allocated to participating securities (53 ) — (148 ) — Net income applicable to common shareholders $ 4,957 $ 4,575 $ 13,704 $ 12,473 Denominator: Weighted average common shares outstanding 4,037 3,997 4,027 3,983 Dilutive effect of common stock equivalents 33 47 36 46 Weighted average diluted common shares outstanding 4,070 4,044 4,063 4,029 Earnings per common share - diluted $ 1.22 $ 1.13 $ 3.37 $ 3.09

Derivative Financial Instrument

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2017
Derivative Instruments Not Designated As Hedging Instruments [Abstract]
Derivative Financial Instruments	19. Derivative Financial Instruments The Company enters into interest rate derivatives to accommodate the business requirements of its customers. Derivatives are recognized as either assets or liabilities and reported in other assets or other liabilities on the balance sheet and are measured at fair value. The accounting for changes in the fair value of derivatives depends on the intended use of the derivative and resulting designation. Interest Rate Swaps The Company has entered into interest rate swap contracts to help commercial loan borrowers manage their interest rate risk. The interest rate swap contracts with commercial loan borrowers allow them to convert floating-rate loan payments to fixed-rate loan payments. When the Bank enters into an interest rate swap contract with a commercial loan borrower, it simultaneously enters into a “mirror” swap contract with a third party. The third party exchanges the client’s fixed‑rate loan payments for floating-rate loan payments. As of September 30, 2017 and December 31, 2016, the Bank had interest rate swap contracts with commercial loan borrowers with notional amounts of $83.2 million and $68.4 million, respectively, and equal amounts of “mirror” swap contracts with third-party financial institutions. These derivatives are not designated as hedges and therefore, changes in fair value are recognized in earnings. Because these derivatives have mirror-image contractual terms, the changes in fair value substantially offset each other through earnings. Fees earned in connection with the execution of derivatives related to this program are recognized in earnings through loan related derivative income. The credit risk associated with swap transactions is the risk of default by the counterparty. To minimize this risk, the Company enters into interest rate agreements only with highly rated counterparties that management believes to be creditworthy. The notional amounts of these agreements do not represent amounts exchanged by the parties and, thus, are not a measure of the potential loss exposure. Risk Participation Agreements The Company has entered into risk participation agreements (“RPAs”) with other banks participating in commercial loan arrangements. Participating banks guarantee the performance on borrower-related interest rate swap contracts. RPAs are derivative financial instruments and are recorded at fair value and reported in other assets or other liabilities. These derivatives are not designated as hedges, and therefore, changes in fair value are recognized in earnings with a corresponding offset within other liabilities. 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. As of September 30, 2017, the notional amounts of the risk participation-in agreements and risk participation-out agreements were $28.5 million and $0, respectively. The following table presents the fair values of derivative instruments in the Company’s unaudited consolidated balance sheets: Fair Value Fair Value Balance Sheet Location September 30, 2017 December 31, 2016 Balance Sheet Location September 30, 2017 December 31, 2016 (dollars in thousands) (dollars in thousands) Derivatives not Designated as Hedging Instruments Loan related derivative contracts Interest rate swaps with customers Other Assets $ 1,839 $ 1,632 Other Liabilities $ — $ — Mirror swaps with counterparties Other Assets — — Other Liabilities 1,839 1,632 Risk participation agreements Other Assets — — Other Liabilities 43 12 Total $ 1,839 $ 1,632 $ 1,882 $ 1,644 For the three months ended September 30, 2017 and September 30, 2016, the Company recorded $284,000 and $392,000, respectively, of loan related derivative income. For the nine months ended September 30, 2017 and September 30, 2016, the Company recorded $647,000 and $1.2 million, respectively, of loan related derivative income.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	20. Fair Value Measurements The Company follows ASC 820, “Fair Value Measurements and Disclosures,” • Level 1 – Quoted prices for identical assets or liabilities in active markets. • Level 2 – Quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar assets or liabilities in inactive markets; and model-derived valuations in which all significant inputs and significant value drivers are observable in active markets. • Level 3 – Valuations derived from techniques in which one or more significant inputs or significant value drivers are unobservable in the markets and which reflect the Company’s market assumptions. The Company uses fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures. Securities available for sale and derivative instruments and hedges are recorded at fair value on a recurring basis. Additionally, from time to time, the Company may be required to record at fair value other assets on a nonrecurring basis, such as collateral dependent impaired loans. The following is a summary of the carrying values and estimated fair values of the Company’s significant financial instruments as of the dates indicated: September 30, 2017 December 31, 2016 Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value (dollars in thousands) Financial assets Cash and cash equivalents $ 13,668 $ 13,668 $ 54,050 $ 54,050 Securities - available for sale 212,449 212,449 325,641 325,641 Securities - held to maturity 219,870 222,251 82,502 83,755 Loans, net 1,340,288 1,319,757 1,304,893 1,286,497 Loans held for sale 560 560 6,506 6,506 FHLB Boston stock 4,938 4,938 4,098 4,098 Accrued interest receivable 4,899 4,899 4,627 4,627 Loan level interest rate swaps 1,839 1,839 1,632 1,632 Financial liabilities Deposits 1,676,918 1,602,764 1,686,038 1,684,065 Short-term borrowings 11,500 11,500 — — Long-term borrowings 3,621 3,634 3,746 3,745 Loan level interest rate swaps 1,839 1,839 1,632 1,632 Risk participation agreements 43 43 12 12 The following tables summarize certain assets reported at fair value on a recurring basis: Fair Value as of September 30, 2017 Level 1 Level 2 Level 3 Total (dollars in thousands) Measured on a recurring basis Securities available for sale U.S. GSE obligations $ — $ 89,180 $ — $ 89,180 Mortgage-backed securities — 117,621 — 117,621 Corporate debt securities — 5,045 — 5,045 Mutual funds 603 — — 603 Other assets Interest rate swaps with customers — 1,839 — 1,839 Other liabilities Mirror swaps with counterparties — 1,839 — 1,839 Risk participation agreements — 43 — 43 Fair Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (dollars in thousands) Measured on a recurring basis Securities available for sale U.S. GSE obligations $ — $ 138,709 $ — $ 138,709 Mortgage-backed securities — 181,299 — 181,299 Corporate debt securities — 5,029 — 5,029 Mutual funds 604 — — 604 Other assets Interest rate swaps with customers — 1,632 — 1,632 Other liabilities Mirror swaps with counterparties — 1,632 — 1,632 Risk participation agreements — 12 — 12 The following tables present the carrying value of assets measured at fair value on a non-recurring basis: September 30, 2017 Level 1 Level 2 Level 3 Total (dollars in thousands) Items recorded at fair value on a nonrecurring basis Assets Collateral dependent impaired loans $ — $ — $ 10 $ 10 Loans held for sale — — 560 560 Total $ — $ — $ 570 $ 570 December 31, 2016 Level 1 Level 2 Level 3 Total (dollars in thousands) Items recorded at fair value on a nonrecurring basis Assets Collateral dependent impaired loans $ — $ — $ 654 $ 654 Loans held for sale — — 6,506 6,506 Total $ — $ — $ 7,160 $ 7,160 Collateral dependent impaired loans . Collateral dependent loans are carried at the lower of cost or fair value of the collateral less estimated costs to sell which approximates fair value. The Company uses the appraisal value of the collateral and applies a discount rate of between 0% to 15% depending on the nature, quality and type of collateral securing the loan. Loans held for sale . The Company uses a pricing service to calculate the fair value of loans held for sale. At September 30, 2017, the fair value of loans held for sale equals the carrying value (unpaid principle and unamortized loans fees). There were no transfers between levels for the three and nine months ended September 30, 2017 and three and nine months ended September 30, 2016. The following is a description of the principal valuation methodologies used by the Company to estimate the fair values of its financial instruments: Investment Securities For investment securities, fair values are primarily based upon valuations obtained from a national pricing service which uses matrix pricing with inputs that are observable in the market or can be derived from, or corroborated by, observable market data. When available, quoted prices in active markets for identical securities are utilized. Loans Held for Sale For loans held for sale, fair values are estimated using projected future cash flows, discounted at rates based upon either trades of similar loans or mortgage-backed securities, or at current rates at which similar loans would be made to borrowers with similar credit ratings and for similar remaining maturities. Loans For most categories of loans, fair values are estimated using projected future cash flows, discounted at rates based upon either trades of similar loans or mortgage-backed securities, or at current rates at which similar loans would be made to borrowers with similar credit ratings and for similar remaining maturities. Loans that are deemed to be impaired in accordance with ASC 310, “Receivables,” FHLB of Boston Stock The fair value of FHLB of Boston stock equals its carrying value since such stock is only redeemable at its par value. Deposits The fair value of non-maturity deposit accounts is the amount payable on demand at the reporting date. This amount does not take into account the value of the Bank’s long-term relationships with core depositors. The fair value of fixed-maturity certificates of deposit is estimated using a replacement cost of funds approach and is based upon rates currently offered for deposits of similar remaining maturities. Long-Term Borrowings For long-term borrowings, fair values are estimated using future cash flows, discounted at rates based upon current costs for debt securities with similar terms and remaining maturities. Other Financial Assets and Liabilities Cash and cash equivalents, accrued interest receivable, and short-term borrowings have fair values which approximate their respective carrying values because these instruments are payable on demand or have short-term maturities and present relatively low credit risk and interest rate risk. Derivative Instruments and Hedges The valuation of these instruments is determined using widely accepted valuation techniques including discounted cash flow analysis on the expected cash flows of each derivative. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate curves and implied volatilities. The Bank incorporates credit valuation adjustments to appropriately reflect nonperformance risk in the fair value measurements. In adjusting the fair value of its derivative contracts for the effect of nonperformance risk, the Bank has considered the impact of netting and any applicable credit enhancements, such as collateral postings. Off-Balance-Sheet Financial Instruments In the course of originating loans and extending credit, the Bank will charge fees in exchange for its commitment. While these commitment fees have value, the Bank has not estimated their value due to the short-term nature of the underlying commitments and their immateriality. Values Not Determined In accordance with ASC 820, the Company has not estimated fair values for non-financial assets such as banking premises and equipment, goodwill, the intangible value of the Bank’s portfolio of loans serviced for itself and the intangible value inherent in the Bank’s deposit relationships (i.e., core deposits), among others. Accordingly, the aggregate fair value amounts presented do not represent the underlying value of the Company.

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates. The allowance for loan losses, the fair values of financial instruments, and the valuation of deferred tax assets are particularly subject to change.
Recently Issued and Adopted Accounting Guidance	Recently Issued and Adopted Accounting Guidance Accounting Standard Update No. Derivatives and Hedging: Targeted Improvements to Accounting for Hedging Activities h is s e e s ta da r a a l l o c p a i e b t a l i e i e g a c c o n t i n a r i s a n a e ac t i v i t i es d c c o s a c m l e x i t a p l y i h d g a c c o n t i n T s ta d a r r q i r e c p a n i e c h a n h r c o n i t i a r s n t a t i o o t f c t h d g a c c o n ti b y • e li m i n a ti t q u i r e t s e a r a t l m a s r a p e g i e ff e c ti v n s s a n • re q i r i c m t p e s n a h l m n e a c o n i n a a e c e a a i n c m s t a e l i e d e i The standard also permits hedge accounting for strategies for which hedge accounting is not permitted today and includes new alternatives for measuring the hedged item for fair value hedges of interest rate risk. Furthermore, the standard eases the requirements for effectiveness testing, hedge documentation, applying the critical terms match method, and introduces new alternatives that will permit companies to reduce the risk of material error corrections if they misapply the shortcut method. The new accounting standard is effective on January 1, 2019 for the Company, and early adoption is permitted. The new standard requires a modified retrospective transition method in which the Company will recognize the cumulative effect of the change on the opening balance of each affected component of equity in the statement of financial position as of the date of adoption. While the Company continues to assess all potential impacts of the standard, we currently expect adoption to have an immaterial impact on our consolidated financial statements. Accounting Standards Update No. 2017-08 - Premium Amortization on Purchased Callable Debt Securities Accounting Standards Update No. 2017-07 - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost Accounting Standards Update No. 2016-18 - Restricted Cash Accounting Standards Update No. 2016-15 - Classification of Certain Cash Receipts and Cash Payments . Accounting Standards Update No. 2016-13 - Financial Instruments - Measurement of Credit Losses on Financial Instruments Accounting Standards Update No. 2016-09 - Improvements to Employee Share-Based Payment Accounting Accounting Standards Update No. 2016-02 - Leases Accounting Standards Update No. 2016-01 - Recognition and Measurement of Financial Assets and Financial Liabilities • Requires equity investments (with certain exceptions) to be measured at fair value with changes in fair value recognized in net income. • Requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. • Requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset (that is, securities or loans and receivables) on the statement of condition or the accompanying notes to the financial statements. • Clarifies that an entity must assess valuation allowances on a deferred tax asset related to available for sale debt securities in combination with its other deferred tax assets. • Eliminates the requirement for public entities to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the statement of condition. This guidance becomes effective for the Company for the interim and annual periods beginning on January 1, 2018, and early adoption is only permitted for certain provisions. The amendments, in general, are required to be applied by means of a cumulative-effect adjustment on the statement of condition as of the beginning of the period of adoption. The adoption of this guidance is not expected to have a material impact on our consolidated balance sheets, statements of income, and cash flows. Accounting Standards Update No. 2014-09 - Revenue from Contracts with Customers

Investment Securities (Tables)

Investment Securities (Tables)	9 Months Ended
	Sep. 30, 2017
Investments Debt And Equity Securities [Abstract]
Summary of Carrying Amounts of Securities and Their Approximate Fair Values	Investment securities have been classified in the unaudited consolidated balance sheets according to management’s intent. The carrying amounts of securities and their approximate fair values were as follows: September 30, 2017 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (dollars in thousands) Available for sale securities U.S. GSE obligations $ 90,024 $ — $ (844 ) $ 89,180 $ 140,026 $ 23 $ (1,340 ) $ 138,709 Mortgage-backed securities 119,272 299 (1,950 ) 117,621 183,974 479 (3,154 ) 181,299 Corporate debt securities 5,039 24 (18 ) 5,045 5,054 13 (38 ) 5,029 Mutual funds 672 — (69 ) 603 672 — (68 ) 604 Total available for sale securities $ 215,007 $ 323 $ (2,881 ) $ 212,449 $ 329,726 $ 515 $ (4,600 ) $ 325,641 Held to maturity securities U.S. GSE obligations $ 29,998 $ 2 $ (41 ) $ 29,959 $ — $ — $ — $ — Mortgage-backed securities 107,762 128 (245 ) 107,645 696 23 — 719 Corporate debt securities 1,997 29 — 2,026 — — — — Municipal securities 80,113 2,673 (165 ) 82,621 81,806 1,894 (664 ) 83,036 Total held to maturity securities $ 219,870 $ 2,832 $ (451 ) $ 222,251 $ 82,502 $ 1,917 $ (664 ) $ 83,755 Total $ 434,877 $ 3,155 $ (3,332 ) $ 434,700 $ 412,228 $ 2,432 $ (5,264 ) $ 409,396
Gross Unrealized Losses of Aggregated by Investment Category and Length of Time that Individual Securities have been in Continuous Loss Position	The following tables show the Company’s securities with gross unrealized losses aggregated by investment category and length of time that individual securities have been in a continuous loss position: September 30, 2017 Less than 12 months 12 months or longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses (dollars in thousands) Temporarily Impaired Securities Available for sale securities U.S. GSE obligations $ 59,652 $ (372 ) $ 29,528 $ (472 ) $ 89,180 $ (844 ) Mortgage-backed securities 82,766 (1,208 ) 31,122 (742 ) 113,888 (1,950 ) Corporate debt securities 4,021 (18 ) — — 4,021 (18 ) Mutual funds — — 603 (69 ) 603 (69 ) Total available for sale securities $ 146,439 $ (1,598 ) $ 61,253 $ (1,283 ) $ 207,692 $ (2,881 ) Held to maturity securities U.S. GSE obligations $ 24,957 $ (41 ) $ — $ — $ 24,957 $ (41 ) Mortgage-backed securities 74,790 (245 ) 3 — 74,793 (245 ) Corporate debt securities — — — — — — Municipal securities 6,795 (72 ) 2,485 (93 ) 9,280 (165 ) Total held to maturity securities $ 106,542 $ (358 ) $ 2,488 $ (93 ) $ 109,030 $ (451 ) Total temporarily impaired securities $ 252,981 $ (1,956 ) $ 63,741 $ (1,376 ) $ 316,722 $ (3,332 ) December 31, 2016 Less than 12 months 12 months or longer Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses (dollars in thousands) Temporarily Impaired Securities Available for sale securities U.S. GSE obligations $ 118,686 $ (1,340 ) $ — $ — $ 118,686 $ (1,340 ) Mortgage-backed securities 149,859 (2,795 ) 14,422 (359 ) 164,281 (3,154 ) Corporate debt securities 4,016 (38 ) — — 4,016 (38 ) Mutual funds — — 604 (68 ) 604 (68 ) Total available for sale securities $ 272,561 $ (4,173 ) $ 15,026 $ (427 ) $ 287,587 $ (4,600 ) Held to maturity securities Mortgage-backed securities $ 1 $ — $ 3 $ — $ 4 $ — Municipal securities 18,626 (664 ) — — 18,626 (664 ) Total held to maturity securities $ 18,627 $ (664 ) $ 3 $ — $ 18,630 $ (664 ) Total temporarily impaired securities $ 291,188 $ (4,837 ) $ 15,029 $ (427 ) $ 306,217 $ (5,264 )
Schedule of Amortized Cost and Fair Value of Debt Securities, Aggregated By Earlier of Guaranteed Call Date or Contractual Maturity	The amortized cost and fair value of debt securities, aggregated by the earlier of guaranteed call date or contractual maturity, are shown below. Maturities of mortgage-backed securities do not take into consideration scheduled amortization or prepayments. Actual maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Within One Year After One, But Within Five Years After Five, But Within Ten Years After Ten Years Total Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value At September 30, 2017 (dollars in thousands) Available for sale securities U.S. GSE obligations $ 5,000 $ 4,987 $ 85,024 $ 84,193 $ — $ — $ — $ — $ 90,024 $ 89,180 Mortgage-backed securities 154 157 148 155 19,607 19,464 99,363 97,845 119,272 117,621 Corporate debt securities — — 4,039 4,021 1,000 1,024 — — 5,039 5,045 Total available for sale Securities $ 5,154 $ 5,144 $ 89,211 $ 88,369 $ 20,607 $ 20,488 $ 99,363 $ 97,845 $ 214,335 $ 211,846 Held to maturity securities U.S. GSE obligations $ — $ — $ 29,998 $ 29,959 $ — $ — $ — $ — $ 29,998 $ 29,959 Mortgage-backed securities 24 25 330 339 23,447 23,391 83,961 83,890 107,762 107,645 Corporate debt securities — — 1,997 2,026 — — — — 1,997 2,026 Municipal securities 3,960 3,985 13,714 14,086 33,389 34,789 29,050 29,761 80,113 82,621 Total held to maturity Securities $ 3,984 $ 4,010 $ 46,039 $ 46,410 $ 56,836 $ 58,180 $ 113,011 $ 113,651 $ 219,870 $ 222,251 Total $ 9,138 $ 9,154 $ 135,250 $ 134,779 $ 77,443 $ 78,668 $ 212,374 $ 211,496 $ 434,205 $ 434,097
Summary of Gains (Losses) from Sale of Investment Securities	The following table sets forth information regarding sales of investment securities and the resulting gains (losses) from such sales: Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 (dollars in thousands) Amortized cost of securities sold $ — $ 250 $ 77,372 $ 17,632 Gain/(loss) realized on securities sold — 3 (3 ) 438 Net proceeds from securities sold $ — $ 253 $ 77,369 $ 18,070

Loans and the Allowance for L31

Loans and the Allowance for Loan Losses (Tables)	9 Months Ended
	Sep. 30, 2017
Receivables [Abstract]
Loans Outstanding by Category	Loans outstanding are detailed by category as follows: September 30, 2017 December 31, 2016 (dollars in thousands) Residential mortgage Mortgages - fixed rate $ 300,071 $ 305,403 Mortgages - adjustable rate 236,323 228,028 Deferred costs net of unearned fees 1,031 973 Total residential mortgages 537,425 534,404 Commercial mortgage Mortgages - nonowner occupied 560,254 513,578 Mortgages - owner occupied 36,287 43,932 Construction 35,031 58,406 Deferred costs net of unearned fees 180 224 Total commercial mortgages 631,752 616,140 Home equity Home equity - lines of credit 72,083 70,883 Home equity - term loans 3,670 3,925 Deferred costs net of unearned fees 254 243 Total home equity 76,007 75,051 Commercial & industrial Commercial & industrial 65,818 59,638 Deferred costs net of unearned fees 43 68 Total commercial & industrial 65,861 59,706 Consumer Secured 43,695 33,386 Unsecured 1,151 1,451 Deferred costs net of unearned fees 17 16 Total consumer 44,863 34,853 Total loans $ 1,355,908 $ 1,320,154
Non-performing Loans Disaggregated by Loan Category	The following tables set forth information regarding non-performing loans disaggregated by loan category: September 30, 2017 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Total (dollars in thousands) Non-performing loans: Non-accrual loans $ 1,031 $ 216 $ 3 $ 21 $ — $ 1,271 Loans past due >90 days, but still accruing — — — — — — Troubled debt restructurings 123 — — 308 — 431 Total $ 1,154 $ 216 $ 3 $ 329 $ — $ 1,702 December 31, 2016 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Total (dollars in thousands) Non-performing loans: Non-accrual loans $ 998 $ — $ — $ 24 $ 1 $ 1,023 Loans past due >90 days, but still accruing — 232 — — — 232 Troubled debt restructurings 132 — — 289 — 421 Total $ 1,130 $ 232 $ — $ 313 $ 1 $ 1,676
Loans Receivable Disaggregated by Credit Quality Indicator	The following tables contain period-end balances of loans receivable disaggregated by credit quality indicator: September 30, 2017 Residential Mortgages Home Equity Consumer (dollars in thousands) Credit risk profile based on payment activity: Performing $ 536,271 $ 76,004 $ 44,863 Non-performing 1,154 3 — Total $ 537,425 $ 76,007 $ 44,863 Commercial Mortgages Commercial & Industrial Credit risk profile by internally assigned grade: 1-6 (Pass) $ 620,847 $ 62,332 7 (Special Mention) 10,688 2,776 8 (Substandard) 217 753 9 (Doubtful) — — 10 (Loss) — — Total $ 631,752 $ 65,861 December 31, 2016 Residential Mortgages Home Equity Consumer (dollars in thousands) Credit risk profile based on payment activity: Performing $ 533,273 $ 75,051 $ 34,852 Non-performing 1,131 — 1 Total $ 534,404 $ 75,051 $ 34,853 Commercial Mortgages Commercial & Industrial Credit risk profile by internally assigned grade: 1-6 (Pass) $ 612,636 $ 56,310 7 (Special Mention) 2,861 1,431 8 (Substandard) 643 1,965 9 (Doubtful) — — 10 (Loss) — — Total $ 616,140 $ 59,706
Schedule of Loans Receivable Disaggregated by Past Due Status	The following tables contain period-end balances of loans receivable disaggregated by past due status: September 30, 2017 30-59 Days Past Due 60-89 Days Past Due 90 Days or Greater Total Past Due Current Loans Total (dollars in thousands) Residential Mortgages $ 3,889 $ 371 $ 65 $ 4,325 $ 533,100 $ 537,425 Commercial Mortgages 1,979 — — 1,979 629,773 631,752 Home Equity — — 3 3 76,004 76,007 Commercial & Industrial 15 22 — 37 65,824 65,861 Consumer loans 37 1 — 38 44,825 44,863 Total $ 5,920 $ 394 $ 68 $ 6,382 $ 1,349,526 $ 1,355,908 December 31, 2016 30-59 Days Past Due 60-89 Days Past Due 90 Days or Greater Total Past Due Current Loans Total (dollars in thousands) Residential Mortgages $ 698 $ 179 $ 602 $ 1,479 $ 532,925 $ 534,404 Commercial Mortgages — 250 232 482 615,658 616,140 Home Equity 4 — — 4 75,047 75,051 Commercial & Industrial 173 — 1 174 59,532 59,706 Consumer loans 6 5 — 11 34,842 34,853 Total $ 881 $ 434 $ 835 $ 2,150 $ 1,318,004 $ 1,320,154
Summary of Changes in Allowance for Loan Losses Disaggregated by Loan Category	The following tables contain changes in the allowance for loan losses disaggregated by loan category at September 30, 2017: For the Three Months Ended September 30, 2017 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Unallocated Impaired Total (dollars in thousands) Allowance for loan losses: Balance at June 30, 2017 $ 4,783 $ 8,449 $ 632 $ 758 $ 324 $ — $ 357 $ 15,303 Charge-offs — — — — (1 ) — — (1 ) Recoveries — — — 6 2 — — 8 Provision 303 (126 ) (4 ) 94 43 — — 310 Balance at September 30, 2017 $ 5,086 $ 8,323 $ 628 $ 858 $ 368 $ — $ 357 $ 15,620 For the Nine Months Ended September 30, 2017 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Unallocated Impaired Total (dollars in thousands) Allowance for loan losses: Balance at December 31, 2016 $ 4,898 $ 8,451 $ 651 $ 807 $ 264 $ — $ 190 $ 15,261 Charge-offs — — — (1 ) (14 ) — — (15 ) Recoveries — — — 8 6 — — 14 Provision 188 (128 ) (23 ) 44 112 — 167 360 Balance at September 30, 2017 $ 5,086 $ 8,323 $ 628 $ 858 $ 368 $ — $ 357 $ 15,620 The following tables contain changes in the allowance for loan losses disaggregated by loan category at September 30, 2016: For the Three Months Ended September 30, 2016 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Unallocated Impaired Total (dollars in thousands) Allowance for loan losses: Balance at June 30, 2016 $ 4,773 $ 8,562 $ 753 $ 766 $ 376 $ 7 $ 174 $ 15,411 Charge-offs — — — — (3 ) — — (3 ) Recoveries — 1 — 1 14 — — 16 Provision (242 ) 380 (40 ) (23 ) 4 29 5 113 Balance at September 30, 2016 $ 4,531 $ 8,943 $ 713 $ 744 $ 391 $ 36 $ 179 $ 15,537 For the Nine Months Ended September 30, 2016 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Unallocated Impaired Total (dollars in thousands) Allowance for loan losses: Balance at December 31, 2015 $ 5,244 $ 8,094 $ 699 $ 615 $ 354 $ 11 $ 174 $ 15,191 Charge-offs — — — (13 ) (17 ) — — (30 ) Recoveries 13 7 1 11 6 — — 38 Provision (726 ) 842 13 131 48 25 5 338 Balance at September 30, 2016 $ 4,531 $ 8,943 $ 713 $ 744 $ 391 $ 36 $ 179 $ 15,537
Summary of Allowance for Loan Losses and Related Loans Receivable Disaggregated by Impairment Method	The following tables contain period-end balances of the allowance for loan losses and related loans receivable disaggregated by impairment method: September 30, 2017 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Total (dollars in thousands) Allowance for loan losses Individually evaluated for impairment $ 98 $ — $ — $ 259 $ — $ 357 Collectively evaluated for impairment 5,086 8,323 628 858 368 15,263 Total $ 5,184 $ 8,323 $ 628 $ 1,117 $ 368 $ 15,620 Loans receivable Individually evaluated for impairment $ 1,056 $ 217 $ 98 $ 307 $ — $ 1,678 Collectively evaluated for impairment 536,369 631,535 75,909 65,554 44,863 1,354,230 Total $ 537,425 $ 631,752 $ 76,007 $ 65,861 $ 44,863 $ 1,355,908 December 31, 2016 Residential Mortgages Commercial Mortgages Home Equity Commercial & Industrial Consumer Total (dollars in thousands) Allowance for loan losses Individually evaluated for impairment $ 69 $ — $ 7 $ 114 $ — $ 190 Collectively evaluated for impairment 4,898 8,452 650 807 264 15,071 Total $ 4,967 $ 8,452 $ 657 $ 921 $ 264 $ 15,261 Loans receivable Individually evaluated for impairment $ 1,027 $ — $ 102 $ 289 $ — $ 1,418 Collectively evaluated for impairment 533,377 616,140 74,949 59,417 34,853 1,318,736 Total $ 534,404 $ 616,140 $ 75,051 $ 59,706 $ 34,853 $ 1,320,154
Information Pertaining to Impaired Loans	The following tables present information pertaining to impaired loans: For the Three Months Ended September 30, 2017 Carrying Value Average Carrying Value Unpaid Principal Balance Related Allowance Interest Income Recognized (dollars in thousands) With no required reserve recorded: Commercial and industrial $ 38 $ 40 $ 38 $ — $ 1 Commercial real estate 217 221 229 — — Residential real estate 991 997 1,187 — — Home equity 98 99 128 — — Total 1,344 1,357 1,582 — 1 With required reserve recorded: Commercial and industrial 269 273 281 259 — Commercial real estate — — — — — Residential real estate 65 65 65 98 — Home equity — — — — — Total 334 338 346 357 - Total: Commercial and industrial 307 313 319 259 1 Commercial real estate 217 221 229 — — Residential real estate 1,056 1,062 1,252 98 — Home equity 98 99 128 — — Total $ 1,678 $ 1,695 $ 1,928 $ 357 $ 1 For the Nine Months Ended September 30, 2017 Carrying Value Average Carrying Value Unpaid Principal Balance Related Allowance Interest Income Recognized (dollars in thousands) With no required reserve recorded: Commercial and industrial $ 38 $ 38 $ 38 $ — $ 2 Commercial real estate 217 227 229 — 3 Residential real estate 991 1,012 1,187 — — Home equity 98 102 128 — — Total 1,344 1,379 1,582 — 5 With required reserve recorded: Commercial and industrial 269 279 281 259 — Commercial real estate — — — — — Residential real estate 65 66 65 98 1 Home equity — — — — — Total 334 345 346 357 1 Total: Commercial and industrial 307 317 319 259 2 Commercial real estate 217 227 229 — 3 Residential real estate 1,056 1,078 1,252 98 1 Home equity 98 102 128 — — Total $ 1,678 $ 1,724 $ 1,928 $ 357 $ 6 For the Three Months Ended September 30, 2016 Carrying Value Average Carrying Value Unpaid Principal Balance Related Allowance Interest Income Recognized (dollars in thousands) With no required reserve recorded: Commercial and industrial $ — $ — $ — $ — $ — Commercial real estate 293 293 390 — — Residential real estate 714 716 883 — 1 Home equity 78 78 101 — — Consumer 1 1 1 — — Total 1,086 1,088 1,375 — 1 With required reserve recorded: Commercial and industrial 458 459 462 179 — Commercial real estate — — — — — Residential real estate — — — — — Home equity — — — — — Total 458 459 462 179 — Total: Commercial and industrial 458 459 462 179 — Commercial real estate 293 293 390 — — Residential real estate 714 716 883 — 1 Home equity 78 78 101 — — Consumer 1 1 1 — — Total $ 1,544 $ 1,547 $ 1,837 $ 179 $ 1 For the Nine Months Ended September 30, 2016 Carrying Value Average Carrying Value Unpaid Principal Balance Related Allowance Interest Income Recognized (dollars in thousands) With no required reserve recorded: Commercial and industrial $ — $ — $ — $ — $ — Commercial real estate 293 295 390 — — Residential real estate 714 729 883 — 3 Home equity 78 80 101 — — Consumer 1 1 1 — — Total 1,086 1,105 1,375 — 3 With required reserve recorded: Commercial and industrial 458 461 462 179 — Commercial real estate — — — — — Residential real estate — — — — — Home equity — — — — — Total 458 461 462 179 — Total: Commercial and industrial 458 461 462 179 — Commercial real estate 293 295 390 — — Residential real estate 714 729 883 — 3 Home equity 78 80 101 — — Consumer 1 1 1 — — Total $ 1,544 $ 1,566 $ 1,837 $ 179 $ 3

Goodwill and Other Intangible32

Goodwill and Other Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Schedule of Mortgage Servicing Rights	An analysis of mortgage servicing rights, which are included in other assets, follows: Mortgage Servicing Rights Valuation Allowance Total (dollars in thousands) Balance at December 31, 2015 $ 499 $ (8 ) $ 491 Mortgage servicing rights capitalized 274 — 274 Amortization charged against servicing income (153 ) — (153 ) Change in impairment reserve — (22 ) (22 ) Balance at September 30, 2016 $ 620 $ (30 ) $ 590 Balance at December 31, 2016 $ 842 $ (30 ) $ 812 Mortgage servicing rights capitalized 128 — 128 Amortization charged against servicing income (112 ) — (112 ) Change in impairment reserve — — — Balance at September 30, 2017 $ 858 $ (30 ) $ 828

Deposits (Tables)

Deposits (Tables)	9 Months Ended
	Sep. 30, 2017
Deposits [Abstract]
Summary of Deposits	Deposits are summarized as follows: September 30, 2017 December 31, 2016 (dollars in thousands) Demand deposits (non-interest bearing) $ 465,970 $ 472,923 Interest bearing checking 387,343 430,706 Money market 64,232 72,057 Savings 600,475 539,190 Retail certificates of deposit under $100,000 39,920 42,471 Retail certificates of deposit $100,000 or greater 68,808 72,355 Wholesale certificates of deposit 50,170 56,336 Total deposits $ 1,676,918 $ 1,686,038
Scheduled Maturities of Certificates of Deposits	Certificates of deposit had the following schedule of maturities: September 30, 2017 December 31, 2016 (dollars in thousands) Less than 3 months remaining $ 26,750 $ 32,268 3 to 5 months remaining 28,608 17,558 6 to 11 months remaining 43,111 36,240 12 to 23 months remaining 32,940 44,467 24 to 47 months remaining 19,885 29,826 48 months or more remaining 7,604 10,803 Total certificates of deposit $ 158,898 $ 171,162

Borrowings (Tables)

Borrowings (Tables)	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Schedule of Information Relating to Short-term Borrowings	Information relating to short-term borrowings is presented below: For the Nine Months Ended September 30, 2017 For the Year Ended December 31, 2016 (dollars in thousands) FHLB of Boston short-term advances Ending balance $ 11,500 $ — Average daily balance 42,293 3,668 Highest month-end balance 110,000 21,000 Weighted average interest rate 1.20 % 0.54 %
Schedule of Information Relating to Long-term Borrowings	Information relating to long-term borrowings is presented below: September 30, 2017 December 31, 2016 Amount Rate Amount Rate (dollars in thousands) FHLB of Boston long-term advances Due 09/01/2020; amortizing $ 3,621 1.94 % $ 3,746 1.94 %

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Components of Income Tax Expense	The components of income tax expense were as follows: Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 (dollars in thousands) Current Federal $ 2,651 $ 2,295 $ 5,966 $ 5,592 State 690 624 1,552 1,310 Total current expense 3,341 2,919 7,518 6,902 Deferred Federal (504 ) (495 ) (414 ) (555 ) State (143 ) (140 ) (117 ) (157 ) Total deferred (647 ) (635 ) (531 ) (712 ) Total income tax expense $ 2,694 $ 2,284 $ 6,987 $ 6,190
Reconciliation of Total Income Tax Provision, Calculated at Statutory Federal Income Tax Rates, to Income Tax Expense in consolidated Statements of Income	The following is a reconciliation of the total income tax provision, calculated at statutory federal income tax rates, to the income tax expense in the consolidated statements of income: Three Months Ended September 30, Nine Months Ended September 30, 2017 Rate 2016 Rate 2017 Rate 2016 Rate (dollars in thousands) (dollars in thousands) Provision at statutory rates $ 2,697 35.00 % $ 2,401 35.00 % $ 7,294 35.00 % $ 6,532 35.00 % Increase/(decrease) resulting from: State tax, net of federal tax benefit 356 4.62 314 4.58 933 4.48 749 4.01 Tax-exempt income (265 ) (3.44 ) (281 ) (4.10 ) (822 ) (3.94 ) (827 ) (4.43 ) ESOP dividends (71 ) (0.92 ) (53 ) (0.77 ) (164 ) (0.79 ) (158 ) (0.85 ) Bank owned life insurance (49 ) (0.64 ) (52 ) (0.76 ) (157 ) (0.75 ) (166 ) (0.89 ) Benefit from stock compensation — — — — (188 ) (0.90 ) — — Other 26 0.35 (45 ) (0.65 ) 91 0.43 60 0.33 Total income tax expense $ 2,694 34.97 % $ 2,284 33.30 % $ 6,987 33.53 % $ 6,190 33.17 %

Pension and Retirement Plans (T

Pension and Retirement Plans (Tables)	9 Months Ended
	Sep. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Components of Net Periodic Benefit Cost	The components of net periodic benefit cost was as follows: Three Months Ended September 30, Pension Plan Supplemental Retirement Plan Retirement Healthcare Plan 2017 2016 2017 2016 2017 2016 (dollars in thousands) Net periodic benefit cost Service cost $ 338 $ 399 $ 67 $ 57 $ 4 $ 7 Interest cost 412 452 91 75 5 8 Expected return on assets (618 ) (725 ) — - — — Amortization of prior service credit (1 ) (1 ) — 13 — (2 ) Amortization of net actuarial loss 179 228 — - (2 ) (3 ) Net periodic benefit cost $ 310 $ 353 $ 158 $ 145 $ 7 $ 10 Nine Months Ended September 30, Pension Plan Supplemental Retirement Plan Retirement Healthcare Plan 2017 2016 2017 2016 2017 2016 (dollars in thousands) Net periodic benefit cost Service cost $ 1,162 $ 1,162 $ 200 $ 209 $ 12 $ 19 Interest cost 1,413 1,319 273 271 15 25 Expected return on assets (2,122 ) (2,113 ) — — — — Amortization of prior service credit (3 ) (3 ) — 47 — (5 ) Amortization of net actuarial loss 614 664 — — (6 ) (9 ) Net periodic benefit cost $ 1,064 $ 1,029 $ 473 $ 527 $ 21 $ 30

Stock Based Compensation (Table

Stock Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2017
Share Based Compensation [Abstract]
Schedule of Pre-tax Expense Associated with Non-Vested Restricted Stock Awards and Non-Vested Performance Based Restricted Stock Units and Related Tax Benefits	The following table presents the pre-tax expense associated with non-vested restricted stock awards and non-vested performance based restricted stock units (share-based compensation) and the related tax benefits recognized: Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 (dollars in thousands) Stock based compensation expense $ 253 $ 251 $ 805 $ 688 Related tax benefits $ 103 $ 103 $ 329 $ 281

Financial Instruments with Of38

Financial Instruments with Off-Balance-Sheet Risk (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Summary of Off-Balance-Sheet Financial Instruments with Contractual Amounts Include Present Credit Risk	Off-balance-sheet financial instruments with contractual amounts that present credit risk include the following: September 30, 2017 December 31, 2016 (dollars in thousands) Financial instruments whose contractual amount represents credit risk: Commitments to extend credit: Unused portion of existing lines of credit $ 282,008 $ 256,767 Origination of new loans 65,313 26,024 Standby letters of credit 8,298 7,763 Financial instruments whose notional amount exceeds the amount of credit risk: Commitments to sell residential mortgage loans 1,623 9,622 Customer related derivative contracts: Interest rate swaps with customers 83,155 68,372 Mirror swaps with counterparties 83,155 68,372 Risk participation agreements with counterparties 28,467 16,378

Shareholders_ Equity (Tables)

Shareholders’ Equity (Tables)	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Schedule of Minimum Capital Requirements Considered Well Capitalized by FRB and FDIC	Management believes that as of September 30, 2017 and December 31, 2016, the Company and the Bank met all applicable minimum capital requirements and were considered “well-capitalized” by both the FRB and the FDIC. Actual Minimum Capital Required For Capital Adequacy Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions Amount Ratio Amount Ratio Amount Ratio Amount Ratio Amount Ratio (dollars in thousands) At September 30, 2017 Cambridge Bancorp: Total capital (to risk-weighted assets) $ 169,487 13.7% $ 99,005 8.0% $ 114,474 9.25% $ 129,944 10.5% N/A N/A Tier I capital (to risk-weighted assets) 154,015 12.4% 74,253 6.0% 89,723 7.25% 105,192 8.5% N/A N/A Common equity tier I capital (to risk-weighted assets) 154,015 12.4% 55,690 4.5% 71,160 5.75% 86,629 7.0% N/A N/A Tier I capital (to average assets) 154,015 8.1% 75,897 4.0% 75,897 4.00% 75,897 4.0% N/A N/A Cambridge Trust Company: Total capital (to risk-weighted assets) $ 165,751 13.4% $ 99,005 8.0% $ 114,474 9.25% $ 129,944 10.5% $ 123,756 10.0% Tier I capital (to risk-weighted assets) 150,279 12.1% 74,253 6.0% 89,723 7.25% 105,192 8.5% 99,005 8.0% Common equity tier I capital (to risk-weighted assets) 150,279 12.1% 55,690 4.5% 71,160 5.75% 86,629 7.0% 80,441 6.5% Tier I capital (to average assets) 150,279 7.9% 75,897 4.0% 75,897 4.00% 75,897 4.0% 94,871 5.0% At December 31, 2016 Cambridge Bancorp: Total capital (to risk-weighted assets) $ 159,141 13.1% $ 96,873 8.0% $ 104,441 8.625% $ 127,145 10.5% N/A N/A Tier I capital (to risk-weighted assets) 144,003 11.9% 72,654 6.0% 80,223 6.625% 102,927 8.5% N/A N/A Common equity tier I capital (to risk-weighted assets) 144,003 11.9% 54,491 4.5% 62,059 5.125% 84,763 7.0% N/A N/A Tier I capital (to average assets) 144,003 7.9% 72,488 4.0% 72,488 4.000% 72,488 4.0% N/A N/A Cambridge Trust Company: Total capital (to risk-weighted assets) $ 156,928 13.0% $ 96,873 8.0% $ 104,441 8.625% $ 127,145 10.5% $ 121,091 10.0% Tier I capital (to risk-weighted assets) 141,790 11.7% 72,654 6.0% 80,223 6.625% 102,927 8.5% 96,873 8.0% Common equity tier I capital (to risk-weighted assets) 141,790 11.7% 54,491 4.5% 62,059 5.125% 84,763 7.0% 78,709 6.5% Tier I capital (to average assets) 141,790 7.8% 72,488 4.0% 72,488 4.000% 72,488 4.0% 90,610 5.0%

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Summary of Other Comprehensive Income	The Company’s other comprehensive income consists of unrealized gains or losses on securities classified as available for sale and the component of the unfunded retirement liability computed in accordance with the requirements of ASC 715, “Compensation – Retirement Benefits.” Three Months Ended September 30, 2017 Three Months Ended September 30, 2016 Before Tax Amount Tax (Expense) or Benefit Net-of-tax Amount Before Tax Amount Tax (Expense) or Benefit Net-of-tax Amount (dollars in thousands) Unrealized gains (losses) on available for sale securities Unrealized holding gains (losses) arising during period $ 452 $ (166 ) $ 286 $ (539 ) $ 137 $ (402 ) Reclassification adjustment for losses (gains) recognized in net income — — — (3 ) 1 (2 ) Defined benefit retirement plans Change in unfunded retirement liability 225 (92 ) 133 198 (81 ) 117 Total Other Comprehensive Income $ 677 $ (258 ) $ 419 $ (344 ) $ 57 $ (287 ) Nine Months Ended September 30, 2017 Nine Months Ended September 30, 2016 Before Tax Amount Tax (Expense) or Benefit Net-of-tax Amount Before Tax Amount Tax (Expense) or Benefit Net-of-tax Amount (dollars in thousands) Unrealized gains (losses) on available for sale securities Unrealized holding gains (losses) arising during period $ 1,524 $ (556 ) $ 968 $ 4,724 $ (1,733 ) $ 2,991 Reclassification adjustment for losses (gains) recognized in net income 3 (2 ) 1 (438 ) 157 (281 ) Defined benefit retirement plans Change in unfunded retirement liability 673 (275 ) 398 593 (242 ) 351 Total Other Comprehensive Income $ 2,200 $ (833 ) $ 1,367 $ 4,879 $ (1,818 ) $ 3,061
Summary of Reclassifications out of Accumulated Other Comprehensive Income (“AOCI”)	Reclassifications out of Accumulated Other Comprehensive Income (“AOCI”) are presented below: Three Months Ended September 30, Details about Accumulated Other Comprehensive Income Components 2017 2016 Affected Line Item in the Statement where Net Income is Presented (dollars in thousands) Unrealized gains and losses on available for sale securities $ — $ 3 Gain on disposition of investment securities Tax benefit or (expense) — (1 ) Provision for income taxes Net of tax $ — $ 2 Net income Nine Months Ended September 30, Details about Accumulated Other Comprehensive Income Components 2017 2016 Affected Line Item in the Statement where Net Income is Presented (dollars in thousands) Unrealized gains and losses on available for sale securities $ (3 ) $ 438 (Loss) gain on disposition of investment securities Tax benefit or (expense) 2 (157 ) Provision for income taxes Net of tax $ (1 ) $ 281 Net income

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Summary of Reconciliation Between Basic and Diluted Earnings Per Share	The following represents a reconciliation between basic and diluted earnings per share: Three Months Ended September 30, Nine Months Ended September 30, 2017 2016 2017 2016 (dollars in thousands, except per share data) Earnings per common share - basic: Numerator: Net income $ 5,010 $ 4,575 $ 13,852 $ 12,473 Less dividends and undistributed earnings allocated to participating securities (53 ) (53 ) (148 ) (154 ) Net income applicable to common shareholders $ 4,957 $ 4,522 $ 13,704 $ 12,319 Denominator: Weighted average common shares outstanding 4,037 3,997 4,027 3,983 Earnings per common share - basic $ 1.23 $ 1.13 $ 3.40 $ 3.09 Earnings per common share - diluted: Numerator: Net income $ 5,010 $ 4,575 $ 13,852 $ 12,473 Less dividends and undistributed earnings allocated to participating securities (53 ) — (148 ) — Net income applicable to common shareholders $ 4,957 $ 4,575 $ 13,704 $ 12,473 Denominator: Weighted average common shares outstanding 4,037 3,997 4,027 3,983 Dilutive effect of common stock equivalents 33 47 36 46 Weighted average diluted common shares outstanding 4,070 4,044 4,063 4,029 Earnings per common share - diluted $ 1.22 $ 1.13 $ 3.37 $ 3.09

Derivative Financial Instrume42

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2017
Derivative Instruments Not Designated As Hedging Instruments [Abstract]
Summary of Fair Values of Derivative Instruments in the Company's Unaudited Consolidated Balance Sheets	The following table presents the fair values of derivative instruments in the Company’s unaudited consolidated balance sheets: Fair Value Fair Value Balance Sheet Location September 30, 2017 December 31, 2016 Balance Sheet Location September 30, 2017 December 31, 2016 (dollars in thousands) (dollars in thousands) Derivatives not Designated as Hedging Instruments Loan related derivative contracts Interest rate swaps with customers Other Assets $ 1,839 $ 1,632 Other Liabilities $ — $ — Mirror swaps with counterparties Other Assets — — Other Liabilities 1,839 1,632 Risk participation agreements Other Assets — — Other Liabilities 43 12 Total $ 1,839 $ 1,632 $ 1,882 $ 1,644

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Summary of Carrying Values and Estimated Fair Values of Financial Instruments	The following is a summary of the carrying values and estimated fair values of the Company’s significant financial instruments as of the dates indicated: September 30, 2017 December 31, 2016 Carrying Value Estimated Fair Value Carrying Value Estimated Fair Value (dollars in thousands) Financial assets Cash and cash equivalents $ 13,668 $ 13,668 $ 54,050 $ 54,050 Securities - available for sale 212,449 212,449 325,641 325,641 Securities - held to maturity 219,870 222,251 82,502 83,755 Loans, net 1,340,288 1,319,757 1,304,893 1,286,497 Loans held for sale 560 560 6,506 6,506 FHLB Boston stock 4,938 4,938 4,098 4,098 Accrued interest receivable 4,899 4,899 4,627 4,627 Loan level interest rate swaps 1,839 1,839 1,632 1,632 Financial liabilities Deposits 1,676,918 1,602,764 1,686,038 1,684,065 Short-term borrowings 11,500 11,500 — — Long-term borrowings 3,621 3,634 3,746 3,745 Loan level interest rate swaps 1,839 1,839 1,632 1,632 Risk participation agreements 43 43 12 12
Summary of Certain Assets Reported at Fair Value on a Recurring Basis	The following tables summarize certain assets reported at fair value on a recurring basis: Fair Value as of September 30, 2017 Level 1 Level 2 Level 3 Total (dollars in thousands) Measured on a recurring basis Securities available for sale U.S. GSE obligations $ — $ 89,180 $ — $ 89,180 Mortgage-backed securities — 117,621 — 117,621 Corporate debt securities — 5,045 — 5,045 Mutual funds 603 — — 603 Other assets Interest rate swaps with customers — 1,839 — 1,839 Other liabilities Mirror swaps with counterparties — 1,839 — 1,839 Risk participation agreements — 43 — 43 Fair Value as of December 31, 2016 Level 1 Level 2 Level 3 Total (dollars in thousands) Measured on a recurring basis Securities available for sale U.S. GSE obligations $ — $ 138,709 $ — $ 138,709 Mortgage-backed securities — 181,299 — 181,299 Corporate debt securities — 5,029 — 5,029 Mutual funds 604 — — 604 Other assets Interest rate swaps with customers — 1,632 — 1,632 Other liabilities Mirror swaps with counterparties — 1,632 — 1,632 Risk participation agreements — 12 — 12
Schedule of Carrying Value of Assets Measured at Fair Value on a Non-Recurring Basis	The following tables present the carrying value of assets measured at fair value on a non-recurring basis: September 30, 2017 Level 1 Level 2 Level 3 Total (dollars in thousands) Items recorded at fair value on a nonrecurring basis Assets Collateral dependent impaired loans $ — $ — $ 10 $ 10 Loans held for sale — — 560 560 Total $ — $ — $ 570 $ 570 December 31, 2016 Level 1 Level 2 Level 3 Total (dollars in thousands) Items recorded at fair value on a nonrecurring basis Assets Collateral dependent impaired loans $ — $ — $ 654 $ 654 Loans held for sale — — 6,506 6,506 Total $ — $ — $ 7,160 $ 7,160

Recently Issued and Adopted A44

Recently Issued and Adopted Accounting Guidance - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Income tax expense	$ 2,694,000	$ 2,284,000	$ 6,987,000	$ 6,190,000
Accounting Standards Update 2016-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Income tax expense			$ 219,000

Cash and Due from Banks - Addit

Cash and Due from Banks - Additional Information (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Cash And Due From Banks [Line Items]
Cash and due from banks	$ 13,700,000	$ 54,100,000
New Hampshire
Cash And Due From Banks [Line Items]
Pledged amount to federal banking department	500,000	500,000
FRB Boston
Cash And Due From Banks [Line Items]
Reserve balance of cash and due from banks	$ 12,900,000	$ 11,200,000

Investment Securities - Summary

Investment Securities - Summary of Carrying Amounts of Securities and Their Approximate Fair Values (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Available for sale securities, Amortized Cost	$ 215,007	$ 329,726
Available for sale securities, Gross Unrealized Gains	323	515
Available for sale securities, Gross Unrealized Losses	(2,881)	(4,600)
Available for sale securities, Fair Value	212,449	325,641
Held to maturity securities, Amortized Cost	219,870	82,502
Held to maturity securities, Gross Unrealized Gains	2,832	1,917
Held to maturity securities, Gross Unrealized Losses	(451)	(664)
Held to maturity securities, Fair Value	222,251	83,755
Total, Amortized Cost	434,877	412,228
Total, Gross Unrealized Gains	3,155	2,432
Total, Gross Unrealized Losses	(3,332)	(5,264)
Total, Fair Value	434,700	409,396
U.S. GSE Obligations
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Available for sale securities, Amortized Cost	90,024	140,026
Available for sale securities, Gross Unrealized Gains		23
Available for sale securities, Gross Unrealized Losses	(844)	(1,340)
Available for sale securities, Fair Value	89,180	138,709
Held to maturity securities, Amortized Cost	29,998
Held to maturity securities, Gross Unrealized Gains	2
Held to maturity securities, Gross Unrealized Losses	(41)
Held to maturity securities, Fair Value	29,959
Corporate Debt Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Available for sale securities, Amortized Cost	5,039	5,054
Available for sale securities, Gross Unrealized Gains	24	13
Available for sale securities, Gross Unrealized Losses	(18)	(38)
Available for sale securities, Fair Value	5,045	5,029
Held to maturity securities, Amortized Cost	1,997
Held to maturity securities, Gross Unrealized Gains	29
Held to maturity securities, Fair Value	2,026
Mortgage Backed Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Available for sale securities, Amortized Cost	119,272	183,974
Available for sale securities, Gross Unrealized Gains	299	479
Available for sale securities, Gross Unrealized Losses	(1,950)	(3,154)
Available for sale securities, Fair Value	117,621	181,299
Held to maturity securities, Amortized Cost	107,762	696
Held to maturity securities, Gross Unrealized Gains	128	23
Held to maturity securities, Gross Unrealized Losses	(245)
Held to maturity securities, Fair Value	107,645	719
Mutual Funds
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Available for sale securities, Amortized Cost	672	672
Available for sale securities, Gross Unrealized Losses	(69)	(68)
Available for sale securities, Fair Value	603	604
Municipal Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Held to maturity securities, Amortized Cost	80,113	81,806
Held to maturity securities, Gross Unrealized Gains	2,673	1,894
Held to maturity securities, Gross Unrealized Losses	(165)	(664)
Held to maturity securities, Fair Value	$ 82,621	$ 83,036

Investment Securities - Gross U

Investment Securities - Gross Unrealized Losses of Aggregated by Investment Category and Length of Time that Individual Securities have been in Continuous Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, Less than 12 months	$ 146,439	$ 272,561
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, Less than 12 months	(1,598)	(4,173)
Temporarily Impaired Securities, Available for sale securities, Fair Value, 12 months or longer	61,253	15,026
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, 12 months or longer	(1,283)	(427)
Temporarily Impaired Securities, Available for sale securities, Fair Value	207,692	287,587
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses	(2,881)	(4,600)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, Less than 12 months	106,542	18,627
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, Less than 12 months	(358)	(664)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, 12 months or longer	2,488	3
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, 12 months or longer	(93)
Temporarily Impaired Securities, Held to maturity securities, Fair Value	109,030	18,630
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses	(451)	(664)
Temporarily Impaired Securities, Fair Value, Less than 12 months	252,981	291,188
Temporarily Impaired Securities, Unrealized Losses, Less than 12 months	(1,956)	(4,837)
Temporarily Impaired Securities, Fair Value, 12 months or longer	63,741	15,029
Temporarily Impaired Securities, Unrealized Losses, 12 months or longer	(1,376)	(427)
Temporarily Impaired Securities, Fair Value	316,722	306,217
Temporarily Impaired Securities, Unrealized Losses	(3,332)	(5,264)
U.S. GSE Obligations
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, Less than 12 months	59,652	118,686
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, Less than 12 months	(372)	(1,340)
Temporarily Impaired Securities, Available for sale securities, Fair Value, 12 months or longer	29,528
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, 12 months or longer	(472)
Temporarily Impaired Securities, Available for sale securities, Fair Value	89,180	118,686
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses	(844)	(1,340)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, Less than 12 months	24,957
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, Less than 12 months	(41)
Temporarily Impaired Securities, Held to maturity securities, Fair Value	24,957
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses	(41)
Mortgage Backed Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, Less than 12 months	82,766	149,859
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, Less than 12 months	(1,208)	(2,795)
Temporarily Impaired Securities, Available for sale securities, Fair Value, 12 months or longer	31,122	14,422
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, 12 months or longer	(742)	(359)
Temporarily Impaired Securities, Available for sale securities, Fair Value	113,888	164,281
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses	(1,950)	(3,154)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, Less than 12 months	74,790	1
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, Less than 12 months	(245)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, 12 months or longer	3	3
Temporarily Impaired Securities, Held to maturity securities, Fair Value	74,793	4
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses	(245)
Corporate Debt Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, Less than 12 months	4,021	4,016
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, Less than 12 months	(18)	(38)
Temporarily Impaired Securities, Available for sale securities, Fair Value	4,021	4,016
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses	(18)	(38)
Mutual Funds
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Available for sale securities, Fair Value, 12 months or longer	603	604
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses, 12 months or longer	(69)	(68)
Temporarily Impaired Securities, Available for sale securities, Fair Value	603	604
Temporarily Impaired Securities, Available for sale securities, Unrealized Losses	(69)	(68)
Municipal Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Temporarily Impaired Securities, Held to maturity securities, Fair Value, Less than 12 months	6,795	18,626
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, Less than 12 months	(72)	(664)
Temporarily Impaired Securities, Held to maturity securities, Fair Value, 12 months or longer	2,485
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses, 12 months or longer	(93)
Temporarily Impaired Securities, Held to maturity securities, Fair Value	9,280	18,626
Temporarily Impaired Securities, Held to maturity securities, Unrealized Losses	$ (165)	$ (664)

Investment Securities - Additio

Investment Securities - Additional Information (Details)	Sep. 30, 2017USD ($)Security	Dec. 31, 2016USD ($)Security
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Number of debt securities with unrealized losses | Security	104	132
Number of equity securities with unrealized losses | Security	1	1
Aggregate depreciation percentage of gross unrealized losses from amortized cost	1.04%	1.69%
Maximum
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Percentage of unrealized loss on amortized cost	10.21%	10.16%
Unrealized loss of amortized cost basis | $	$ 69,000	$ 51,000
Unrealized dollar loss of amortized cost basis | $	$ 150,000	$ 189,000
Percentage of unrealized dollar loss on amortized cost	3.01%	3.79%

Investment Securities - Schedul

Investment Securities - Schedule of Amortized Cost and Fair Value of Debt Securities, Aggregated By Earlier of Guaranteed Call Date or Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Available for sale securities, Within One Year, Amortized Cost	$ 5,154
Available for sale securities, Within One Year, Fair Value	5,144
Available for sale securities, After One, But Within Five Years, Amortized Cost	89,211
Available for sale securities, After One, But Within Five Years, Fair Value	88,369
Available for sale securities, After Five, But Within Ten Years, Amortized Cost	20,607
Available for sale securities, After Five, But Within Ten Years, Fair Value	20,488
Available for sale securities, After Ten Years, Amortized Cost	99,363
Available for sale securities, After Ten Years, Fair Value	97,845
Available for sale securities, Total, Amortized Cost	214,335
Available for sale securities, Total, Fair Value	211,846
Held to maturity securities, Within One Year, Amortized Cost	3,984
Held to maturity securities, Within One Year, Fair Value	4,010
Held to maturity securities, After One, But Within Five Years, Amortized Cost	46,039
Held to maturity securities, After One, But Within Five Years, Fair Value	46,410
Held to maturity securities, After Five, But Within Ten Years, Amortized Cost	56,836
Held to maturity securities, After Five, But Within Ten Years, Fair Value	58,180
Held to maturity securities, After Ten Years, Amortized Cost	113,011
Held to maturity securities, After Ten Years, Fair Value	113,651
Held to maturity securities, Amortized Cost	219,870	$ 82,502
Held to maturity securities, Fair Value	222,251	83,755
Available for sale securities and Held to maturity securities, Within One Year, Amortized Cost	9,138
Available for sale securities and Held to maturity securities, Within One Year, Fair Value	9,154
Available for sale securities and Held to maturity securities, After One, But Within Five Years, Amortized Cost	135,250
Available for sale securities and Held to maturity securities, After One, But Within Five Years, Fair Value	134,779
Available for sale securities and Held to maturity securities, After Five, But Within Ten Years, Amortized Cost	77,443
Available for sale securities and Held to maturity securities, After Five, But Within Ten Years, Fair Value	78,668
Available for sale securities and Held to maturity securities, After Ten Years, Amortized Cost	212,374
Available for sale securities and Held to maturity securities, After Ten Years, Fair Value	211,496
Available for sale securities and Held to maturity securities, Total, Amortized Cost	434,205
Available for sale securities and Held to maturity securities, Total, Fair Value	434,097
U.S. GSE Obligations
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Available for sale securities, Within One Year, Amortized Cost	5,000
Available for sale securities, Within One Year, Fair Value	4,987
Available for sale securities, After One, But Within Five Years, Amortized Cost	85,024
Available for sale securities, After One, But Within Five Years, Fair Value	84,193
Available for sale securities, Total, Amortized Cost	90,024
Available for sale securities, Total, Fair Value	89,180
Held to maturity securities, After One, But Within Five Years, Amortized Cost	29,998
Held to maturity securities, After One, But Within Five Years, Fair Value	29,959
Held to maturity securities, Amortized Cost	29,998
Held to maturity securities, Fair Value	29,959
Mortgage Backed Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Available for sale securities, Within One Year, Amortized Cost	154
Available for sale securities, Within One Year, Fair Value	157
Available for sale securities, After One, But Within Five Years, Amortized Cost	148
Available for sale securities, After One, But Within Five Years, Fair Value	155
Available for sale securities, After Five, But Within Ten Years, Amortized Cost	19,607
Available for sale securities, After Five, But Within Ten Years, Fair Value	19,464
Available for sale securities, After Ten Years, Amortized Cost	99,363
Available for sale securities, After Ten Years, Fair Value	97,845
Available for sale securities, Total, Amortized Cost	119,272
Available for sale securities, Total, Fair Value	117,621
Held to maturity securities, Within One Year, Amortized Cost	24
Held to maturity securities, Within One Year, Fair Value	25
Held to maturity securities, After One, But Within Five Years, Amortized Cost	330
Held to maturity securities, After One, But Within Five Years, Fair Value	339
Held to maturity securities, After Five, But Within Ten Years, Amortized Cost	23,447
Held to maturity securities, After Five, But Within Ten Years, Fair Value	23,391
Held to maturity securities, After Ten Years, Amortized Cost	83,961
Held to maturity securities, After Ten Years, Fair Value	83,890
Held to maturity securities, Amortized Cost	107,762
Held to maturity securities, Fair Value	107,645
Corporate Debt Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Available for sale securities, After One, But Within Five Years, Amortized Cost	4,039
Available for sale securities, After One, But Within Five Years, Fair Value	4,021
Available for sale securities, After Five, But Within Ten Years, Amortized Cost	1,000
Available for sale securities, After Five, But Within Ten Years, Fair Value	1,024
Available for sale securities, Total, Amortized Cost	5,039
Available for sale securities, Total, Fair Value	5,045
Held to maturity securities, After One, But Within Five Years, Amortized Cost	1,997
Held to maturity securities, After One, But Within Five Years, Fair Value	2,026
Held to maturity securities, Amortized Cost	1,997
Held to maturity securities, Fair Value	2,026
Municipal Securities
Schedule of Available for Sale Securities and Held to Maturity Securities [Line Items]
Held to maturity securities, Within One Year, Amortized Cost	3,960
Held to maturity securities, Within One Year, Fair Value	3,985
Held to maturity securities, After One, But Within Five Years, Amortized Cost	13,714
Held to maturity securities, After One, But Within Five Years, Fair Value	14,086
Held to maturity securities, After Five, But Within Ten Years, Amortized Cost	33,389
Held to maturity securities, After Five, But Within Ten Years, Fair Value	34,789
Held to maturity securities, After Ten Years, Amortized Cost	29,050
Held to maturity securities, After Ten Years, Fair Value	29,761
Held to maturity securities, Amortized Cost	80,113	81,806
Held to maturity securities, Fair Value	$ 82,621	$ 83,036

Investment Securities - Summa50

Investment Securities - Summary of Gains (Losses) from Sale of Investment Securities (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Investments Debt And Equity Securities [Abstract]
Amortized cost of securities sold	$ 250	$ 77,372	$ 17,632
Gain (loss) on disposition of investment securities	3	(3)	438
Net proceeds from securities sold	$ 253	$ 77,369	$ 18,070

Loans and the Allowance for L51

Loans and the Allowance for Loan Losses - Loans Outstanding by Category (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Loans And Leases Receivable Disclosure [Line Items]
Total loans	$ 1,355,908	$ 1,320,154
Residential Mortgage
Loans And Leases Receivable Disclosure [Line Items]
Deferred costs net of unearned fees	1,031	973
Total loans	537,425	534,404
Residential Mortgage | Mortgages - Fixed Rate
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	300,071	305,403
Residential Mortgage | Mortgages - Adjustable Rate
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	236,323	228,028
Commercial Mortgage
Loans And Leases Receivable Disclosure [Line Items]
Deferred costs net of unearned fees	180	224
Total loans	631,752	616,140
Commercial Mortgage | Construction
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	35,031	58,406
Commercial Mortgage | Mortgages - Nonowner Occupied
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	560,254	513,578
Commercial Mortgage | Mortgages - Owner Occupied
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	36,287	43,932
Home Equity
Loans And Leases Receivable Disclosure [Line Items]
Deferred costs net of unearned fees	254	243
Total loans	76,007	75,051
Home Equity | Home Equity - Lines of Credit
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	72,083	70,883
Home Equity | Home Equity - Term Loans
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	3,670	3,925
Commercial & Industrial
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	65,818	59,638
Deferred costs net of unearned fees	43	68
Total loans	65,861	59,706
Consumer
Loans And Leases Receivable Disclosure [Line Items]
Deferred costs net of unearned fees	17	16
Total loans	44,863	34,853
Consumer | Secured
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	43,695	33,386
Consumer | Unsecured
Loans And Leases Receivable Disclosure [Line Items]
Loans outstanding by category gross	$ 1,151	$ 1,451

Loans and the Allowance for L52

Loans and the Allowance for Loan Losses - Additional Information (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017USD ($)TDR	Sep. 30, 2016USD ($)TDRLoan	Sep. 30, 2017USD ($)TDRLoan	Sep. 30, 2016USD ($)TDRLoan	Dec. 31, 2016USD ($)
Receivables [Abstract]
Loans outstanding to directors and officers	$ 632,000		$ 632,000		$ 690,000
Loans to directors and officers, additions			97,000		355,000
Loans to directors and officers, repayments			$ 155,000		406,000
Number of loans modified as troubled debt restructuring	0	1	1	1
Pre-modification carrying value		$ 247,000	$ 65,000	$ 247,000
Post-modification carrying value		$ 247,000	$ 48,000	$ 247,000
Number of loans determined to be troubled debt restructurings | Loan			5
Troubled debt restructuring carrying value	$ 431,000		$ 431,000
Number of TDRs defaulted during the period | TDR	0	0	0	0
Specific reserve for troubled debt restructurings	$ 259,000		$ 259,000		$ 117,000

Loans and the Allowance for L53

Loans and the Allowance for Loan Losses - Non-performing Loans Disaggregated by Loan Category (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment Past Due [Line Items]
Troubled debt restructurings	$ 431,000
Non-Performing Loans
Financing Receivable Recorded Investment Past Due [Line Items]
Non-accrual loans	1,271,000	$ 1,023,000
Loans past due >90 days, but still accruing		232,000
Troubled debt restructurings	431,000	421,000
Total	1,702,000	1,676,000
Non-Performing Loans | Residential Mortgage
Financing Receivable Recorded Investment Past Due [Line Items]
Non-accrual loans	1,031,000	998,000
Troubled debt restructurings	123,000	132,000
Total	1,154,000	1,130,000
Non-Performing Loans | Commercial Mortgage
Financing Receivable Recorded Investment Past Due [Line Items]
Non-accrual loans	216,000
Loans past due >90 days, but still accruing		232,000
Total	216,000	232,000
Non-Performing Loans | Home Equity
Financing Receivable Recorded Investment Past Due [Line Items]
Non-accrual loans	3,000
Total	3,000
Non-Performing Loans | Commercial & Industrial
Financing Receivable Recorded Investment Past Due [Line Items]
Non-accrual loans	21,000	24,000
Troubled debt restructurings	308,000	289,000
Total	$ 329,000	313,000
Non-Performing Loans | Consumer
Financing Receivable Recorded Investment Past Due [Line Items]
Non-accrual loans		1,000
Total		$ 1,000

Loans and the Allowance for L54

Loans and the Allowance for Loan Losses - Loans Receivable Disaggregated by Credit Quality Indicator (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment [Line Items]
Loans receivable	$ 1,355,908	$ 1,320,154
Residential Mortgage
Financing Receivable Recorded Investment [Line Items]
Loans receivable	537,425	534,404
Home Equity
Financing Receivable Recorded Investment [Line Items]
Loans receivable	76,007	75,051
Consumer
Financing Receivable Recorded Investment [Line Items]
Loans receivable	44,863	34,853
Commercial Mortgage
Financing Receivable Recorded Investment [Line Items]
Loans receivable	631,752	616,140
Commercial Mortgage | 1-6 (Pass)
Financing Receivable Recorded Investment [Line Items]
Loans receivable	620,847	612,636
Commercial Mortgage | 7 (Special Mention)
Financing Receivable Recorded Investment [Line Items]
Loans receivable	10,688	2,861
Commercial Mortgage | 8 (Substandard)
Financing Receivable Recorded Investment [Line Items]
Loans receivable	217	643
Commercial & Industrial
Financing Receivable Recorded Investment [Line Items]
Loans receivable	65,861	59,706
Commercial & Industrial | 1-6 (Pass)
Financing Receivable Recorded Investment [Line Items]
Loans receivable	62,332	56,310
Commercial & Industrial | 7 (Special Mention)
Financing Receivable Recorded Investment [Line Items]
Loans receivable	2,776	1,431
Commercial & Industrial | 8 (Substandard)
Financing Receivable Recorded Investment [Line Items]
Loans receivable	753	1,965
Performing | Residential Mortgage
Financing Receivable Recorded Investment [Line Items]
Loans receivable	536,271	533,273
Performing | Home Equity
Financing Receivable Recorded Investment [Line Items]
Loans receivable	76,004	75,051
Performing | Consumer
Financing Receivable Recorded Investment [Line Items]
Loans receivable	44,863	34,852
Non-performing | Residential Mortgage
Financing Receivable Recorded Investment [Line Items]
Loans receivable	1,154	1,131
Non-performing | Home Equity
Financing Receivable Recorded Investment [Line Items]
Loans receivable	$ 3
Non-performing | Consumer
Financing Receivable Recorded Investment [Line Items]
Loans receivable		$ 1

Loans and the Allowance for L55

Loans and the Allowance for Loan Losses - Schedule of Loans Receivable Disaggregated by Past Due Status (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	$ 6,382	$ 2,150
Current Loans	1,349,526	1,318,004
Total	1,355,908	1,320,154
30-59 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	5,920	881
60-89 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	394	434
90 Days or Greater
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	68	835
Residential Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	4,325	1,479
Current Loans	533,100	532,925
Total	537,425	534,404
Residential Mortgage | 30-59 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	3,889	698
Residential Mortgage | 60-89 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	371	179
Residential Mortgage | 90 Days or Greater
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	65	602
Commercial Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	1,979	482
Current Loans	629,773	615,658
Total	631,752	616,140
Commercial Mortgage | 30-59 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	1,979
Commercial Mortgage | 60-89 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due		250
Commercial Mortgage | 90 Days or Greater
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due		232
Commercial & Industrial
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	37	174
Current Loans	65,824	59,532
Total	65,861	59,706
Commercial & Industrial | 30-59 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	15	173
Commercial & Industrial | 60-89 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	22
Commercial & Industrial | 90 Days or Greater
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due		1
Consumer loans
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	38	11
Current Loans	44,825	34,842
Total	44,863	34,853
Consumer loans | 30-59 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	37	6
Consumer loans | 60-89 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	1	5
Home Equity
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	3	4
Current Loans	76,004	75,047
Total	76,007	75,051
Home Equity | 30-59 Days Past Due
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due		$ 4
Home Equity | 90 Days or Greater
Financing Receivable Allowance For Credit Losses [Line Items]
Total Past Due	$ 3

Loans and the Allowance for L56

Loans and the Allowance for Loan Losses - Summary of Changes in Allowance for Loan Losses Disaggregated by Loan Category (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, Beginning balance	$ 15,303	$ 15,411	$ 15,261	$ 15,191
Charge-offs	(1)	(3)	(15)	(30)
Recoveries	8	16	14	38
Provision	310	113	360	338
Allowance for loan losses, Ending balance	15,620	15,537	15,620	15,537
Residential Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, Beginning balance	4,783	4,773	4,898	5,244
Recoveries				13
Provision	303	(242)	188	(726)
Allowance for loan losses, Ending balance	5,086	4,531	5,086	4,531
Commercial Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, Beginning balance	8,449	8,562	8,451	8,094
Recoveries		1		7
Provision	(126)	380	(128)	842
Allowance for loan losses, Ending balance	8,323	8,943	8,323	8,943
Home Equity
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, Beginning balance	632	753	651	699
Recoveries				1
Provision	(4)	(40)	(23)	13
Allowance for loan losses, Ending balance	628	713	628	713
Commercial & Industrial
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, Beginning balance	758	766	807	615
Charge-offs			(1)	(13)
Recoveries	6	1	8	11
Provision	94	(23)	44	131
Allowance for loan losses, Ending balance	858	744	858	744
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, Beginning balance	324	376	264	354
Charge-offs	(1)	(3)	(14)	(17)
Recoveries	2	14	6	6
Provision	43	4	112	48
Allowance for loan losses, Ending balance	368	391	368	391
Unallocated
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, Beginning balance		7		11
Provision		29		25
Allowance for loan losses, Ending balance		36		36
Impaired
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses, Beginning balance	357	174	190	174
Provision		5	167	5
Allowance for loan losses, Ending balance	$ 357	$ 179	$ 357	$ 179

Loans and the Allowance for L57

Loans and the Allowance for Loan Losses - Summary of Allowance for Loan Losses and Related Loans Receivable Disaggregated by Impairment Method (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
Individually evaluated for impairment	$ 357	$ 190
Collectively evaluated for impairment	15,263	15,071
Allowance for loan losses	15,620	15,261
Individually evaluated for impairment	1,678	1,418
Collectively evaluated for impairment	1,354,230	1,318,736
Loans receivable	1,355,908	1,320,154
Residential Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Individually evaluated for impairment	98	69
Collectively evaluated for impairment	5,086	4,898
Allowance for loan losses	5,184	4,967
Individually evaluated for impairment	1,056	1,027
Collectively evaluated for impairment	536,369	533,377
Loans receivable	537,425	534,404
Commercial Mortgage
Financing Receivable Allowance For Credit Losses [Line Items]
Collectively evaluated for impairment	8,323	8,452
Allowance for loan losses	8,323	8,452
Individually evaluated for impairment	217
Collectively evaluated for impairment	631,535	616,140
Loans receivable	631,752	616,140
Home Equity
Financing Receivable Allowance For Credit Losses [Line Items]
Individually evaluated for impairment		7
Collectively evaluated for impairment	628	650
Allowance for loan losses	628	657
Individually evaluated for impairment	98	102
Collectively evaluated for impairment	75,909	74,949
Loans receivable	76,007	75,051
Commercial & Industrial
Financing Receivable Allowance For Credit Losses [Line Items]
Individually evaluated for impairment	259	114
Collectively evaluated for impairment	858	807
Allowance for loan losses	1,117	921
Individually evaluated for impairment	307	289
Collectively evaluated for impairment	65,554	59,417
Loans receivable	65,861	59,706
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Collectively evaluated for impairment	368	264
Allowance for loan losses	368	264
Collectively evaluated for impairment	44,863	34,853
Loans receivable	$ 44,863	$ 34,853

Loans and the Allowance for L58

Loans and the Allowance for Loan Losses - Information Pertaining to Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable Allowance For Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 1,344	$ 1,086	$ 1,344	$ 1,086
With no required reserve recorded, Average Carrying Value	1,357	1,088	1,379	1,105
With no required reserve recorded, Unpaid Principal Balance	1,582	1,375	1,582	1,375
With no required reserve recorded, Interest Income Recognized	1	1	5	3
With required reserve recorded, Carrying Value	334	458	334	458
With required reserve recorded, Average Carrying Value	338	459	345	461
With required reserve recorded, Unpaid Principal Balance	346	462	346	462
With required reserve recorded, Related Allowance	357	179	357	179
With required reserve recorded, Interest Income Recognized			1
Carrying Value	1,678	1,544	1,678	1,544
Average Carrying Value	1,695	1,547	1,724	1,566
Unpaid Principal Balance	1,928	1,837	1,928	1,837
Related Allowance	357	179	357	179
Interest Income Recognized	1	1	6	3
Commercial and Industrial
Financing Receivable Allowance For Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	38		38
With no required reserve recorded, Average Carrying Value	40		38
With no required reserve recorded, Unpaid Principal Balance	38		38
With no required reserve recorded, Interest Income Recognized	1		2
With required reserve recorded, Carrying Value	269	458	269	458
With required reserve recorded, Average Carrying Value	273	459	279	461
With required reserve recorded, Unpaid Principal Balance	281	462	281	462
With required reserve recorded, Related Allowance	259	179	259	179
Carrying Value	307	458	307	458
Average Carrying Value	313	459	317	461
Unpaid Principal Balance	319	462	319	462
Related Allowance	259	179	259	179
Interest Income Recognized	1		2
Commercial Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	217	293	217	293
With no required reserve recorded, Average Carrying Value	221	293	227	295
With no required reserve recorded, Unpaid Principal Balance	229	390	229	390
With no required reserve recorded, Interest Income Recognized			3
Carrying Value	217	293	217	293
Average Carrying Value	221	293	227	295
Unpaid Principal Balance	229	390	229	390
Interest Income Recognized			3
Residential Real Estate
Financing Receivable Allowance For Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	991	714	991	714
With no required reserve recorded, Average Carrying Value	997	716	1,012	729
With no required reserve recorded, Unpaid Principal Balance	1,187	883	1,187	883
With no required reserve recorded, Interest Income Recognized		1		3
With required reserve recorded, Carrying Value	65		65
With required reserve recorded, Average Carrying Value	65		66
With required reserve recorded, Unpaid Principal Balance	65		65
With required reserve recorded, Related Allowance	98		98
With required reserve recorded, Interest Income Recognized			1
Carrying Value	1,056	714	1,056	714
Average Carrying Value	1,062	716	1,078	729
Unpaid Principal Balance	1,252	883	1,252	883
Related Allowance	98		98
Interest Income Recognized		1	1	3
Home Equity
Financing Receivable Allowance For Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	98	78	98	78
With no required reserve recorded, Average Carrying Value	99	78	102	80
With no required reserve recorded, Unpaid Principal Balance	128	101	128	101
Carrying Value	98	78	98	78
Average Carrying Value	99	78	102	80
Unpaid Principal Balance	$ 128	101	$ 128	101
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
With no required reserve recorded, Carrying Value		1		1
With no required reserve recorded, Average Carrying Value		1		1
With no required reserve recorded, Unpaid Principal Balance		1		1
Carrying Value		1		1
Average Carrying Value		1		1
Unpaid Principal Balance		$ 1		$ 1

Federal Home Loan Bank of Bos59

Federal Home Loan Bank of Boston Stock - Additional Information (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Federal Home Loan Bank Stock [Line Items]
Investment in FHLB	$ 4,938,000	$ 4,098,000
Federal Home Loan Bank of Boston
Federal Home Loan Bank Stock [Line Items]
Investment in FHLB	4,900,000	4,100,000
Impairment on investment of federal home loan bank stock	$ 0	$ 0

Goodwill and Other Intangible60

Goodwill and Other Intangible Assets - Additional Information (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Finite Lived Intangible Assets [Line Items]
Carrying value of goodwill	$ 412,000		$ 412,000
Impairment of goodwill recognized	0		0
Mortgage Servicing Rights
Finite Lived Intangible Assets [Line Items]
Loans held for sale	560,000		6,500,000
Amount of mortgage loans sold and servicing rights retained	11,500,000	$ 25,900,000
Net gains recognized in gain on loans held for sale	172,000	$ 607,000
Fair value of mortgage servicing rights portfolio	$ 1,100,000		$ 1,000,000
Weighted average amortization period	7 years 3 months 19 days	8 years

Goodwill and Other Intangible61

Goodwill and Other Intangible Assets - Schedule of Mortgage Servicing Rights (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Servicing Assets At Amortized Value [Line Items]
Beginning Balance	$ 812	$ 491
Mortgage servicing rights capitalized	128	274
Amortization charged against servicing income	(112)	(153)
Change in impairment reserve		(22)
Ending Balance	828	590
Mortgage Servicing Rights
Servicing Assets At Amortized Value [Line Items]
Beginning Balance	842	499
Mortgage servicing rights capitalized	128	274
Amortization charged against servicing income	(112)	(153)
Ending Balance	858	620
Valuation Allowance
Servicing Assets At Amortized Value [Line Items]
Beginning Balance	(30)	(8)
Change in impairment reserve		(22)
Ending Balance	$ (30)	$ (30)

Deposits - Summary of Deposits

Deposits - Summary of Deposits (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Deposits [Abstract]
Demand deposits (non-interest bearing)	$ 465,970	$ 472,923
Interest bearing checking	387,343	430,706
Money market	64,232	72,057
Savings	600,475	539,190
Retail certificates of deposit under $100,000	39,920	42,471
Retail certificates of deposit $100,000 or greater	68,808	72,355
Wholesale certificates of deposit	50,170	56,336
Total deposits	$ 1,676,918	$ 1,686,038

Deposits - Schedule of Maturiti

Deposits - Schedule of Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Deposits [Abstract]
Less than 3 months remaining	$ 26,750	$ 32,268
3 to 5 months remaining	28,608	17,558
6 to 11 months remaining	43,111	36,240
12 to 23 months remaining	32,940	44,467
24 to 47 months remaining	19,885	29,826
48 months or more remaining	7,604	10,803
Total certificates of deposit	$ 158,898	$ 171,162

Deposits - Additional Informati

Deposits - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Deposits [Abstract]
Interest expense on retail certificates of deposit $100,000 or greater	$ 112,000	$ 125,000	$ 335,000	$ 347,000
Certificates of deposit, at or above FDIC insurance limit of 250,000	43,900,000		43,900,000		$ 46,000,000
Deposit accounts of directors, executive officers and their respective affiliates	$ 8,300,000		$ 8,300,000		$ 7,200,000

Borrowings - Schedule of Inform

Borrowings - Schedule of Information Relating to Short-term Borrowings (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Advances From Federal Home Loan Banks [Abstract]
Ending balance	$ 11,500,000
Average daily balance	42,293,000	$ 3,668,000
Highest month-end balance	$ 110,000,000	$ 21,000,000
Weighted average interest rate	1.20%	0.54%

Borrowings - Schedule of Info66

Borrowings - Schedule of Information Relating to Long-term Borrowings (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Federal Home Loan Banks [Abstract]
FHLB of Boston long-term advances due amortizing, amount	$ 3,621	$ 3,746
FHLB of Boston long-term advances due amortizing, interest rate	1.94%	1.94%

Borrowings - Schedule of Info67

Borrowings - Schedule of Information Relating to Long-term Borrowings (Parenthetical) (Details)	9 Months Ended
	Sep. 30, 2017
Federal Home Loan Banks [Abstract]
FHLB of long-term advances due date	Sep. 1, 2020

Borrowings - Additional Informa

Borrowings - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Percentage of market value, secured blanket lien on qualified collateral	90.00%
Percentage of carrying value, secured blanket lien on qualified collateral	75.00%
Unused borrowing capacity based upon collateral pledged	$ 292.8	$ 306.8
Commercial Real Estate And Commercial And Industrial Loans | Line of Credit
Debt Instrument [Line Items]
Collateral pledged amount	301.6
FRB Boston | Commercial Real Estate And Commercial And Industrial Loans
Debt Instrument [Line Items]
Line of credit unused borrowing capacity	$ 165.1	$ 159.6

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Current
Federal	$ 2,651	$ 2,295	$ 5,966	$ 5,592
State	690	624	1,552	1,310
Total current expense	3,341	2,919	7,518	6,902
Deferred
Federal	(504)	(495)	(414)	(555)
State	(143)	(140)	(117)	(157)
Total deferred	(647)	(635)	(531)	(712)
Total income tax expense	$ 2,694	$ 2,284	$ 6,987	$ 6,190

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Total Income Tax Provision, Calculated at Statutory Federal Income Tax Rates, to Income Tax Expense in Consolidated Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Provision at statutory rates	$ 2,697	$ 2,401	$ 7,294	$ 6,532
Increase/(decrease) resulting from: (Amount)
State tax, net of federal tax benefit	356	314	933	749
Tax-exempt income	(265)	(281)	(822)	(827)
ESOP dividends	(71)	(53)	(164)	(158)
Bank owned life insurance	(49)	(52)	(157)	(166)
Benefit from stock compensation			(188)
Other	26	(45)	91	60
Total income tax expense	$ 2,694	$ 2,284	$ 6,987	$ 6,190
Provision at statutory rates, Rate	35.00%	35.00%	35.00%	35.00%
Increase/(decrease) resulting from: (Rate)
State tax, net of federal tax benefit, Rate	4.62%	4.58%	4.48%	4.01%
Tax-exempt income, Rate	(3.44%)	(4.10%)	(3.94%)	(4.43%)
ESOP dividends, Rate	(0.92%)	(0.77%)	(0.79%)	(0.85%)
Bank owned life insurance, Rate	(0.64%)	(0.76%)	(0.75%)	(0.89%)
Benefit from stock compensation, Rate			(0.90%)
Other, Rate	0.35%	(0.65%)	0.43%	0.33%
Total income tax expense, Rate	34.97%	33.30%	33.53%	33.17%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Taxes [Line Items]
Effective tax rate	34.97%	33.30%	33.53%	33.17%
Unrecognized tax benefits	$ 0		$ 0		$ 0
Interest and penalties related to unrecognized tax benefits	0	$ 0	0	$ 0
Tax benefit resulting from share based compensation	103,000	$ 103,000	329,000	$ 281,000
Accounting Standards Update 2016-09
Income Taxes [Line Items]
Tax benefit resulting from share based compensation	$ 0		$ 219,000
Federal Income Tax | Earliest Tax Year
Income Taxes [Line Items]
Income tax returns year open and subject to examination			2,014
State Income Tax | Earliest Tax Year
Income Taxes [Line Items]
Income tax returns year open and subject to examination			2,014

Pension and Retirement Plans -

Pension and Retirement Plans - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, description			The Company has a noncontributory, defined benefit pension plan (“Pension Plan”) covering substantially all employees hired before May 2, 2011. Employees in positions requiring at least 1,000 hours of service per year were eligible to participate upon the attainment of age 21 and the completion of one year of service. Benefits are based primarily on years of service and the employee’s average monthly pay during the five highest consecutive plan years of the employee’s final ten years. The Company also provides supplemental retirement benefits to certain executive officers of the Company under the terms of Supplemental Executive Retirement Agreements (“Supplemental Retirement Plan”).
Minimum number of hours of service per year required for eligibility			1000 hours
Employee eligibility age under the plan			21 years
Minimum number of years of service required for eligibility			1 year
Supplemental Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Employee eligibility age under the plan			65 years
Supplemental retirement plan, effective date			Oct. 1, 1989
Profit Sharing Plan | 401(k)
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, maximum employee contribution, percent			100.00%
Defined contribution plan, employer matching contribution, percent			3.00%
Defined contribution plan, employee eligibility age			21 years
Profit Sharing Plan | Discretionary Contribution
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employee eligibility age			21 years
Defined contribution plan, minimum service period required for eligibility			12 months
Defined contribution plan, minimum number of hours of service per year required for eligibility			1000 hours
Employee Stock Ownership Plan (ESOP)
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employee eligibility age			21 years
Defined contribution plan, minimum service period required for eligibility			12 months
Defined contribution plan, minimum number of hours of service per year required for eligibility			1000 hours
PSP and ESOP
Defined Benefit Plan Disclosure [Line Items]
Contribution expense related to Plans	$ 238,000	$ 238,000	$ 713,000	$ 713,000

Pension and Retirement Plans 73

Pension and Retirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plan
Net periodic benefit cost
Service cost	$ 338	$ 399	$ 1,162	$ 1,162
Interest cost	412	452	1,413	1,319
Expected return on assets	(618)	(725)	(2,122)	(2,113)
Amortization of prior service credit	(1)	(1)	(3)	(3)
Amortization of net actuarial loss	179	228	614	664
Net periodic benefit cost	310	353	1,064	1,029
Supplemental Retirement Plan
Net periodic benefit cost
Service cost	67	57	200	209
Interest cost	91	75	273	271
Amortization of prior service credit		13		47
Net periodic benefit cost	158	145	473	527
Retirement Healthcare Plan
Net periodic benefit cost
Service cost	4	7	12	19
Interest cost	5	8	15	25
Amortization of prior service credit		(2)		(5)
Amortization of net actuarial loss	(2)	(3)	(6)	(9)
Net periodic benefit cost	$ 7	$ 10	$ 21	$ 30

Stock Based Compensation - Sche

Stock Based Compensation - Schedule of Pre-tax Expense Associated with Non-Vested Restricted Stock Awards and Non-Vested Performance Based Restricted Stock Units and Related Tax Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share Based Compensation [Abstract]
Stock based compensation expense	$ 253	$ 251	$ 805	$ 688
Related tax benefits	$ 103	$ 103	$ 329	$ 281

Financial Instruments with Of75

Financial Instruments with Off-Balance-Sheet Risk - Summary of Off-Balance-Sheet Financial Instruments with Contractual Amounts Include Present Credit Risk (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Interest Rate Swap with Customers
Financial instruments whose notional amount exceeds the amount of credit risk:
Financial instrument notional amount exceeds credit risk	$ 83,155	$ 68,372
Mirror Swaps with Counterparties
Financial instruments whose notional amount exceeds the amount of credit risk:
Financial instrument notional amount exceeds credit risk	83,155	68,372
Standby Letters of Credit
Financial instruments whose contractual amount represents credit risk:
Financial instruments with off-balance-sheet risk	8,298	7,763
Unused Portion of Existing Lines of Credit
Financial instruments whose contractual amount represents credit risk:
Financial instruments with off-balance-sheet risk	282,008	256,767
Origination of New Loans
Financial instruments whose contractual amount represents credit risk:
Financial instruments with off-balance-sheet risk	65,313	26,024
Commitments to Sell Residential Mortgage Loans
Financial instruments whose notional amount exceeds the amount of credit risk:
Financial instrument notional amount exceeds credit risk	1,623	9,622
Risk Participation Agreements with Counterparties
Financial instruments whose notional amount exceeds the amount of credit risk:
Financial instrument notional amount exceeds credit risk	$ 28,467	$ 16,378

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information (Details)	Jan. 02, 2016	Jan. 01, 2019	Sep. 30, 2017	Dec. 31, 2016	Apr. 08, 2014	Jul. 09, 2013
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Common equity tier 1 risk based capital to risk weighted assets			12.40%	11.90%
Tier 1 risk based capital to risk weighted assets			12.40%	11.90%
Capital to risk weighted assets			13.70%	13.10%
Minimum leverage ratio of Tier 1 capital to average assets			8.10%	7.90%
Capital conservation buffer rate	0.625%
Capital conservation buffer phased in period	4 years
Scenario, Forecast
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Capital conservation buffer rate		2.50%
Minimum
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Common equity tier 1 risk based capital to risk weighted assets			4.50%		4.50%
Tier 1 risk based capital to risk weighted assets					6.00%	4.00%
Capital to risk weighted assets					8.00%
Minimum leverage ratio of Tier 1 capital to average assets					4.00%
Minimum | Scenario, Forecast
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Common equity tier 1 risk based capital to risk weighted assets		4.50%
Tier 1 risk based capital to risk weighted assets		6.00%
Capital to risk weighted assets		8.00%
Minimum leverage ratio of Tier 1 capital to average assets		4.00%
Effective minimum ratio of Common Equity Tier 1 capital to risk-weighted assets		7.00%
Effective minimum Tier 1 capital assets ratio		8.50%
Effective minimum capital to risk weighted asset ratio		10.50%

Shareholders' Equity - Minimum

Shareholders' Equity - Minimum Capital Requirements were Considered Well Capitalized by FRB and FDIC (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016	Apr. 08, 2014	Jul. 09, 2013
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 169,487,000	$ 159,141,000
Tier I capital (to risk-weighted assets), Actual, Amount	154,015,000	144,003,000
Common equity tier I capital (to risk-weighted assets), Actual, Amount	154,015,000	144,003,000
Tier I capital (to average assets), Actual, Amount	$ 154,015,000	$ 144,003,000
Total capital (to risk-weighted assets), Actual, Ratio	13.70%	13.10%
Tier I capital (to risk-weighted assets), Actual, Ratio	12.40%	11.90%
Common equity tier I capital (to risk-weighted assets), Actual, Ratio	12.40%	11.90%
Tier I capital (to average assets), Actual, Ratio	8.10%	7.90%
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Amount	$ 99,005,000	$ 96,873,000
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Amount	74,253,000	72,654,000
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Amount	55,690,000	54,491,000
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy, Amount	$ 75,897,000	$ 72,488,000
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Ratio	8.00%	8.00%
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Ratio	6.00%	6.00%
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Ratio	4.50%	4.50%
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy, Ratio	4.00%	4.00%
Minimum
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Actual, Ratio			8.00%
Tier I capital (to risk-weighted assets), Actual, Ratio			6.00%	4.00%
Common equity tier I capital (to risk-weighted assets), Actual, Ratio	4.50%		4.50%
Tier I capital (to average assets), Actual, Ratio			4.00%
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Amount	$ 114,474,000	$ 104,441,000
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Amount	89,723,000	80,223,000
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Amount	71,160,000	62,059,000
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Amount	$ 75,897,000	$ 72,488,000
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Ratio	9.25%	8.625%
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Ratio	7.25%	6.625%
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Ratio	5.75%	5.125%
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Ratio	4.00%	4.00%
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Amount	$ 129,944,000	$ 127,145,000
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Amount	105,192,000	102,927,000
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Amount	86,629,000	84,763,000
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Amount	$ 75,897,000	$ 72,488,000
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Ratio	10.50%	10.50%
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Ratio	8.50%	8.50%
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Ratio	7.00%	7.00%
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Ratio	4.00%	4.00%
Cambridge Trust Company
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Actual, Amount	$ 165,751,000	$ 156,928,000
Tier I capital (to risk-weighted assets), Actual, Amount	150,279,000	141,790,000
Common equity tier I capital (to risk-weighted assets), Actual, Amount	150,279,000	141,790,000
Tier I capital (to average assets), Actual, Amount	$ 150,279,000	$ 141,790,000
Total capital (to risk-weighted assets), Actual, Ratio	13.40%	13.00%
Tier I capital (to risk-weighted assets), Actual, Ratio	12.10%	11.70%
Common equity tier I capital (to risk-weighted assets), Actual, Ratio	12.10%	11.70%
Tier I capital (to average assets), Actual, Ratio	7.90%	7.80%
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Amount	$ 99,005,000	$ 96,873,000
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Amount	74,253,000	72,654,000
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Amount	55,690,000	54,491,000
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy, Amount	$ 75,897,000	$ 72,488,000
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Ratio	8.00%	8.00%
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Ratio	6.00%	6.00%
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy, Ratio	4.50%	4.50%
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy, Ratio	4.00%	4.00%
Cambridge Trust Company | Minimum
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Amount	$ 114,474,000	$ 104,441,000
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Amount	89,723,000	80,223,000
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Amount	71,160,000	62,059,000
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Amount	$ 75,897,000	$ 72,488,000
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Ratio	9.25%	8.625%
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Ratio	7.25%	6.625%
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Ratio	5.75%	5.125%
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Phase-In Schedule, Ratio	4.00%	4.00%
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Amount	$ 129,944,000	$ 127,145,000
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Amount	105,192,000	102,927,000
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Amount	86,629,000	84,763,000
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Amount	$ 75,897,000	$ 72,488,000
Total capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Ratio	10.50%	10.50%
Tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Ratio	8.50%	8.50%
Common equity tier I capital (to risk-weighted assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Ratio	7.00%	7.00%
Tier I capital (to average assets), Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Basel III Fully Phased In, Ratio	4.00%	4.00%
Total capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Amount	$ 123,756,000	$ 121,091,000
Tier I capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Amount	99,005,000	96,873,000
Common equity tier I capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Amount	80,441,000	78,709,000
Tier I capital (to average assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Amount	$ 94,871,000	$ 90,610,000
Total capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%
Tier I capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%
Common equity tier I capital (to risk-weighted assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Tier I capital (to average assets), Minimum To Be Well-Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%

Other Comprehensive Income - Su

Other Comprehensive Income - Summary of Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Unrealized gains (losses) on available for sale securities, before tax amount
Unrealized holding gains (losses) arising during period, before tax amount	$ 452	$ (539)	$ 1,524	$ 4,724
Reclassification adjustment for losses (gains) recognized in net income, before tax amount		(3)	3	(438)
Defined benefit retirement plans, before tax amount
Change in unfunded retirement liability, before tax amount	225	198	673	593
Total Other Comprehensive Income, before tax amount	677	(344)	2,200	4,879
Unrealized gains (losses) on available for sale securities, tax (expense) or benefit
Unrealized holding gains (losses) arising during period, tax (expense) or benefit	(166)	137	(556)	(1,733)
Reclassification adjustment for losses (gains) recognized in net income, tax (expense) or benefit		1	(2)	157
Defined benefit retirement plans, tax (expense) or benefit
Change in unfunded retirement liability, tax (expense) or benefit	(92)	(81)	(275)	(242)
Total Other Comprehensive Income, tax (expense) or benefit	(258)	57	(833)	(1,818)
Unrealized gains (losses) on available for sale securities
Unrealized holding gains (losses) arising during period, net-of-tax amount	286	(402)	968	2,991
Reclassification adjustment for losses (gains) recognized in net income, net-of-tax amount		(2)	1	(281)
Defined benefit retirement plans
Change in unfunded retirement liability	133	117	398	351
Other comprehensive income (loss)	$ 419	$ (287)	$ 1,367	$ 3,061

Other Comprehensive Income - 79

Other Comprehensive Income - Summary of Reclassifications out of Accumulated Other Comprehensive Income ("AOCI") (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
(Loss) gain on disposition of investment securities		$ 3	$ (3)	$ 438
Provision for income taxes	$ (2,694)	(2,284)	(6,987)	(6,190)
Net income	$ 5,010	4,575	13,852	12,473
Reclassifications out of Accumulated Other Comprehensive Income | Unrealized Gains and Losses on Available for Sale Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
(Loss) gain on disposition of investment securities		3	(3)	438
Provision for income taxes		(1)	2	(157)
Net income		$ 2	$ (1)	$ 281

Earnings Per Share - Summary of

Earnings Per Share - Summary of Reconciliation Between Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income	$ 5,010	$ 4,575	$ 13,852	$ 12,473
Less dividends and undistributed earnings allocated to participating securities	(53)	(53)	(148)	(154)
Net income applicable to common shareholders	$ 4,957	$ 4,522	$ 13,704	$ 12,319
Denominator:
Weighted average number of shares outstanding, basic	4,037,026	3,996,687	4,027,378	3,982,696
Earnings per common share - basic	$ 1.23	$ 1.13	$ 3.40	$ 3.09
Numerator:
Net income	$ 5,010	$ 4,575	$ 13,852	$ 12,473
Less dividends and undistributed earnings allocated to participating securities	(53)		(148)
Net income applicable to common shareholders	$ 4,957	$ 4,575	$ 13,704	$ 12,473
Denominator:
Weighted average number of shares outstanding, basic	4,037,026	3,996,687	4,027,378	3,982,696
Dilutive effect of common stock equivalents	$ 33	$ 47	$ 36	$ 46
Weighted average number of shares outstanding, diluted	4,070,332	4,043,651	4,062,743	4,029,281
Diluted earnings per share	$ 1.22	$ 1.13	$ 3.37	$ 3.09

Derivative Financial Instrume81

Derivative Financial Instruments - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Loan related derivative income	$ 284,000	$ 392,000	$ 647,000	$ 1,191,000
Interest Rate Swap Contracts | Commercial Loan Borrowers
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative, notional amount	83,200,000		83,200,000		$ 68,400,000
Mirror Swap Contracts | Third-Party Financial Institutions
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative, notional amount	83,200,000		83,200,000		$ 68,400,000
Risk Participation-In Agreements
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative, notional amount	28,500,000		28,500,000
Risk Participation-Out Agreements
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative, notional amount	$ 0		$ 0

Derivative Financial Instrume82

Derivative Financial Instruments - Summary of Fair Values of Derivative Instruments in the Company's Unaudited Consolidated Balance Sheets (Details) - Loan Related Derivative Contracts - Derivatives Not Designated as Hedging Instruments - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative assets	$ 1,839	$ 1,632
Derivative liabilities	1,882	1,644
Interest Rate Swap Contracts
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative assets	1,839	1,632
Mirror Swaps with Counterparties
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative liabilities	1,839	1,632
Risk Participation Agreements
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Derivative liabilities	$ 43	$ 12

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Carrying Values and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financial assets
Securities - available for sale	$ 212,449	$ 325,641
Securities - held to maturity	222,251	83,755
Investment in FHLB	4,938	4,098
Recurring Basis | Carrying Value
Financial assets
Cash and cash equivalents	13,668	54,050
Securities - available for sale	212,449	325,641
Securities - held to maturity	219,870	82,502
Loans, net	1,340,288	1,304,893
Loans held for sale	560	6,506
Investment in FHLB	4,938	4,098
Accrued interest receivable	4,899	4,627
Loan level interest rate swaps	1,839	1,632
Financial liabilities
Deposits	1,676,918	1,686,038
Short-term borrowings	11,500
Long-term borrowings	3,621	3,746
Loan level interest rate swaps	1,839	1,632
Risk participation agreements	43	12
Recurring Basis | Estimated Fair Value
Financial assets
Cash and cash equivalents	13,668	54,050
Securities - available for sale	212,449	325,641
Securities - held to maturity	222,251	83,755
Loans, net	1,319,757	1,286,497
Loans held for sale	560	6,506
Investment in FHLB	4,938	4,098
Accrued interest receivable	4,899	4,627
Loan level interest rate swaps	1,839	1,632
Financial liabilities
Deposits	1,602,764	1,684,065
Short-term borrowings	11,500
Long-term borrowings	3,634	3,745
Loan level interest rate swaps	1,839	1,632
Risk participation agreements	$ 43	$ 12

Fair Value Measurements - Sum84

Fair Value Measurements - Summary of Certain Assets Reported at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	$ 212,449	$ 325,641
U.S. GSE Obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	89,180	138,709
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	5,045	5,029
Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	603	604
Recurring Basis | U.S. GSE Obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	89,180	138,709
Recurring Basis | Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	117,621	181,299
Recurring Basis | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	5,045	5,029
Recurring Basis | Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	603	604
Recurring Basis | Interest Rate Swap Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other assets	1,839	1,632
Recurring Basis | Mirror Swaps with Counterparties
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other liabilities	1,839	1,632
Recurring Basis | Risk Participation Agreements
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other liabilities	43	12
Recurring Basis | Level 1 | Mutual Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	603	604
Recurring Basis | Level 2 | U.S. GSE Obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	89,180	138,709
Recurring Basis | Level 2 | Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	117,621	181,299
Recurring Basis | Level 2 | Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available for sale	5,045	5,029
Recurring Basis | Level 2 | Interest Rate Swap Contracts
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other assets	1,839	1,632
Recurring Basis | Level 2 | Mirror Swaps with Counterparties
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other liabilities	1,839	1,632
Recurring Basis | Level 2 | Risk Participation Agreements
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other liabilities	$ 43	$ 12

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Carrying Value of Assets Measured at Fair Value on a Non-Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value, non-recurring basis	$ 570	$ 7,160
Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value, non-recurring basis	570	7,160
Collateral Dependent Impaired Loans
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value, non-recurring basis	10	654
Collateral Dependent Impaired Loans | Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value, non-recurring basis	10	654
Loans Held For Sale
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value, non-recurring basis	560	6,506
Loans Held For Sale | Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value, non-recurring basis	$ 560	$ 6,506

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Transfers between levels	$ 0	$ 0	$ 0	$ 0
Collateral Dependent Impaired Loans | Maximum
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Discount on appraisals of collateral			15.00%