BSB Bancorp 10-K 16 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 09, 2018	Jun. 30, 2017
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	BLMT
Entity Registrant Name	BSB BANCORP, INC.
Entity Central Index Key	1,522,420
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		9,749,842
Entity Public Float			$ 229,885,274

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and due from banks	$ 1,771	$ 2,211
Interest-bearing deposits in other banks	109,117	56,665
Cash and cash equivalents	110,888	58,876
Interest-bearing time deposits with other banks	2,440	234
Investments in available-for-sale securities	16,921	22,048
Investments in held-to-maturity securities (fair value of $158,385 as of December 31, 2017 and $129,465 as of December 31, 2016)	160,090	130,197
Federal Home Loan Bank stock, at cost	32,382	25,071
Loans, net of allowance for loan losses of $16,312 as of December 31, 2017 and $13,585 as of December 31, 2016	2,296,958	1,866,035
Premises and equipment, net	2,254	2,355
Accrued interest receivable	6,344	4,635
Deferred tax asset, net	5,794	8,321
Income taxes receivable	53	423
Bank-owned life insurance	36,967	35,842
Other assets	5,474	4,667
Total assets	2,676,565	2,158,704
Deposits:
Noninterest-bearing	221,462	208,082
Interest-bearing	1,529,789	1,261,340
Total deposits	1,751,251	1,469,422
Federal Home Loan Bank advances	723,150	508,850
Securities sold under agreements to repurchase	3,268	1,985
Accrued interest payable	1,594	1,023
Deferred compensation liability	7,919	7,043
Other liabilities	11,354	9,460
Total liabilities	2,498,536	1,997,783
Stockholders' equity:
Common stock; $0.01 par value, 100,000,000 shares authorized; 9,707,665 and 9,110,077 shares issued and outstanding at December 31, 2017 and 2016, respectively	97	91
Additional paid-in capital	94,590	92,013
Retained earnings	86,884	72,498
Accumulated other comprehensive income	89	103
Unearned compensation - ESOP	(3,631)	(3,784)
Total stockholders' equity	178,029	160,921
Total liabilities and stockholders' equity	$ 2,676,565	$ 2,158,704

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments in held-to-maturity securities, fair value	$ 158,385	$ 129,465
Loans, allowance for loan losses	$ 16,312	$ 13,585
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	9,707,665	9,110,077
Common stock, shares outstanding	9,707,665	9,110,077

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest and dividend income:
Interest and fees on loans	$ 72,011	$ 57,513	$ 44,890
Interest on debt securities:
Taxable	3,356	3,163	3,064
Dividends	1,193	760	373
Other interest income	583	185	79
Total interest and dividend income	77,143	61,621	48,406
Interest expense:
Interest on deposits	12,900	9,434	7,768
Interest on Federal Home Loan Bank advances	8,150	4,788	2,394
Interest on securities sold under agreements to repurchase	4	4	4
Interest on other borrowed funds		5	28
Total interest expense	21,054	14,231	10,194
Net interest and dividend income	56,089	47,390	38,212
Provision for loan losses	2,762	2,385	2,317
Net interest and dividend income after provision for loan losses	53,327	45,005	35,895
Noninterest income:
Customer service fees	785	903	894
Income from bank-owned life insurance	1,120	1,050	893
Net gain on sales of securities	38
Net gain on sales of loans	936	271	395
Loan servicing fee income	398	350	614
Other income	350	176	369
Total noninterest income	3,627	2,750	3,165
Noninterest expense:
Salaries and employee benefits	19,587	17,819	17,610
Director compensation	1,355	971	912
Occupancy expense	964	991	1,074
Equipment expense	422	452	533
Deposit insurance	1,733	1,285	969
Data processing	2,793	3,120	3,108
Professional fees	1,044	964	749
Marketing	912	872	926
Other expense	1,876	1,875	1,943
Total noninterest expense	30,686	28,349	27,824
Income before income tax expense	26,268	19,406	11,236
Income tax expense	11,882	7,425	4,322
Net income	14,386	11,981	6,914
Net income available to common stockholders	$ 14,278	$ 11,791	$ 6,747
Earnings per share
Basic	$ 1.63	$ 1.38	$ 0.80
Diluted	$ 1.55	$ 1.33	$ 0.78

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income	$ 14,386	$ 11,981	$ 6,914
Other comprehensive (loss) income, net of tax:
Net change in fair value of securities available for sale	(31)	149	(78)
Net change in other comprehensive income for defined-benefit postretirement plan	17	70	(16)
Total other comprehensive (loss) income	(14)	219	(94)
Total comprehensive income	$ 14,372	$ 12,200	$ 6,820

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive (Loss) Income	Unearned Compensation - ESOP
Balance (in shares) at Dec. 31, 2014		9,067,792
Balance at Dec. 31, 2014	$ 137,010	$ 91	$ 87,428	$ 53,603	$ (22)	$ (4,090)
Net income	6,914			6,914
Other comprehensive income (loss)	(94)				(94)
Release of ESOP stock	321		168			153
Stock based compensation-restricted stock awards	869		869
Stock based compensation-stock options	791		791
Tax benefit from stock compensation	215		215
Stock option exercises, net of shares surrendered	228		228
Stock option exercises, net of shares surrendered (in shares)		21,113
Restricted stock awards issued (in shares)		(2,266)
Restricted stock awards issued, net of awards surrendered	(51)		(51)
Balance (in shares) at Dec. 31, 2015		9,086,639
Balance at Dec. 31, 2015	146,203	$ 91	89,648	60,517	(116)	(3,937)
Net income	11,981			11,981
Other comprehensive income (loss)	219				219
Release of ESOP stock	360		207			153
Stock based compensation-restricted stock awards	869		869
Stock based compensation-stock options	780		780
Tax benefit from stock compensation	329		329
Stock option exercises, net of shares surrendered	298		298
Stock option exercises, net of shares surrendered (in shares)		27,964
Restricted stock awards issued (in shares)		(4,526)
Restricted stock awards issued, net of awards surrendered	$ (118)		(118)
Balance (in shares) at Dec. 31, 2016	9,110,077	9,110,077
Balance at Dec. 31, 2016	$ 160,921	$ 91	92,013	72,498	103	(3,784)
Net income	14,386			14,386
Other comprehensive income (loss)	(14)				(14)
Release of ESOP stock	444		291			153
Stock based compensation-restricted stock awards	1,835		1,835
Stock based compensation-stock options	724		724
Stock option exercises, net of shares surrendered	$ 56	$ 1	55
Stock option exercises, net of shares surrendered (in shares)	213,962	120,749
Restricted stock awards issued (in shares)		476,839
Restricted stock awards issued, net of awards surrendered	$ (323)	$ 5	(328)
Balance (in shares) at Dec. 31, 2017	9,707,665	9,707,665
Balance at Dec. 31, 2017	$ 178,029	$ 97	$ 94,590	$ 86,884	$ 89	$ (3,631)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 14,386	$ 11,981	$ 6,914
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of securities, net	843	833	732
Gain on sales of securities	(38)
Gain on sales of loans, net	(936)	(271)	(395)
Loans originated for sale	(5,439)	(10,134)	(13,678)
Proceeds from sales of loans	71,473	11,649	22,943
Provision for loan losses	2,762	2,385	2,317
Change in unamortized mortgage premium	(2,388)	(1,928)	(1,796)
Change in net deferred loan costs	196	1,041	405
ESOP expense	444	360	321
Depreciation and amortization expense	595	621	726
Impairment of fixed assets	18	16	6
Deferred income tax expense (benefit)	2,535	(1,741)	(1,021)
Increase in bank-owned life insurance	(1,120)	(1,050)	(893)
Loss on sale of other real estate owned			10
Stock based compensation expense	2,559	1,649	1,660
Excess tax benefit from stock-based compensation		(329)	(215)
Net change in:
Accrued interest receivable	(1,709)	(854)	(804)
Other assets	(807)	400	(1,027)
Income taxes receivable	370	(423)	321
Income taxes payable		145	398
Accrued interest payable	571	30	32
Deferred compensation liability	876	609	683
Other liabilities	574	(2,216)	446
Net cash provided by operating activities	85,765	12,773	18,085
Cash flows from investing activities:
Maturities of interest-bearing time deposits with other banks	234	131
Purchases of interest-bearing time deposits with other banks	(2,440)	(234)
Proceeds from sales of available-for-sale securities	5,038	0	0
Proceeds from maturities, payments, and calls of held-to-maturity securities	28,362	25,976	21,459
Purchases of held-to-maturity securities	(59,022)	(19,812)	(40,708)
Redemption of Federal Home Loan Bank stock	3,767	3,014
Purchases of Federal Home Loan Bank stock	(11,078)	(9,776)	(4,597)
Recoveries of loans previously charged off	24	61	261
Loan originations and principal collections, net	(57,732)	16,997	(79,445)
Purchases of loans	(438,883)	(350,653)	(288,928)
Capital expenditures	(512)	(335)	(323)
Capital expenditures on other real estate owned			(7)
Premiums paid on bank-owned life insurance	(5)	(5,005)	(5,006)
Proceeds from sales of other real estate owned			1,510
Net cash (used in) investing activities	(532,247)	(339,636)	(395,784)
Cash flows from financing activities:
Net increase in demand deposits, interest-bearing checking and savings accounts	112,716	122,737	252,735
Net increase in time deposits	169,113	77,166	32,222
Proceeds from Federal Home Loan Bank advances	125,000	211,250	84,000
Principal payments on Federal Home Loan Bank advances	(85,000)	(7,000)	(14,100)
Net change in short-term Federal Home Loan Bank advances	174,300	(69,400)	19,000
Net increase (decrease) in securities sold under agreements to repurchase	1,283	(1,710)	2,303
Repayment of principal on other borrowed funds			(47)
Proceeds from exercise of stock options, net of cash paid	56	298	228
Restricted stock awards issued, net of awards surrendered	(323)	(118)	(51)
Net increase in mortgagors' escrow accounts	1,349	926	688
Excess tax benefit from stock-based compensation		329	215
Net cash provided by financing activities	498,494	334,478	377,193
Net increase (decrease) in cash and cash equivalents	52,012	7,615	(506)
Cash and cash equivalents at beginning of period	58,876	51,261	51,767
Cash and cash equivalents at end of period	110,888	58,876	51,261
Supplemental disclosures:
Interest paid	20,483	14,201	10,162
Income taxes paid	8,977	9,446	4,624
Transfer of loans receivable to loans held for sale	$ 63,913		10,116
Transfer of loans to other real estate owned			$ 1,513
Derecognition of loans and related recourse obligation in other borrowings		$ 1,020

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2017
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	NOTE 1 – SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Operations BSB Bancorp, Inc. (the “Company”) was incorporated in Maryland in June, 2011 to become the holding company of Belmont Savings Bank (the “Bank”), a state-chartered Massachusetts savings bank. The Company is supervised by the Board of Governors of the Federal Reserve System (“FRB”), while the Bank is subject to the regulations of, and periodic examination by, the Federal Deposit Insurance Corporation (“FDIC”) and the Massachusetts Division of Banks (the “Division”). The Bank’s deposits are insured by the Bank Insurance Fund of the FDIC up to $250,000 per account. For balances in excess of the FDIC deposit insurance limits, coverage is provided by the Massachusetts Depositors Insurance Fund, Inc. (“Mass DIF”). In connection with the Company’s conversion from a mutual holding company to stock holding company form of organization (the “conversion”), on October 4, 2011 we completed our initial public offering of common stock, selling 8,993,000 shares of common stock at $10.00 per share for approximately $89.9 million in gross proceeds, including 458,643 shares sold to the Bank’s employee stock ownership plan. In addition, in connection with the conversion, we issued 179,860 shares of our common stock and contributed $200,000 in cash to the Belmont Savings Bank Foundation. Belmont Savings Bank is a state chartered savings bank which was incorporated in 1885 and is headquartered in Belmont, Massachusetts. The Bank is engaged principally in the business of attracting deposits from the general public and investing those deposits in residential and commercial real estate loans, consumer loans, including indirect auto loans, commercial loans and construction loans, as well as investment securities. Basis of Presentation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, Belmont Savings Bank and BSB Funding Corporation and the Bank’s wholly owned subsidiary, BSB Investment Corporation. All significant intercompany balances and transactions have been eliminated in consolidation. The Company’s consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles and general practices within the financial services industry. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant changes in the near-term relate to the determination of the allowance for loan losses, valuation and potential other-than-temporary impairment (“OTTI”) of investment securities and the valuation of deferred tax assets. Reclassification Certain previously reported amounts have been reclassified to conform to the current year’s presentation. Significant Group Concentrations of Credit Risk Most of the Company’s business activity is with customers located within the Commonwealth of Massachusetts. There are no concentrations of credit to borrowers that have similar economic characteristics. The majority of the Company’s loan portfolio is comprised of loans collateralized by real estate located in the Commonwealth of Massachusetts. Cash and Cash Equivalents For purposes of the consolidated statements of cash flows, cash and cash equivalents include cash, balances due from banks and interest-bearing deposits in other banks. Securities Debt securities that management has the positive intent and ability to hold to maturity are classified as “held-to-maturity” held-to-maturity “available-for-sale” Purchase premiums and discounts are recognized in interest income using the interest method over the terms of the securities, adjusted for the effect of actual prepayments in the case of mortgage-backed securities. Gains and losses on the sale of securities are recorded on the trade date and are determined using the specific identification method. Each reporting period, the Company evaluates all securities classified as available-for-sale held-to-maturity, OTTI is required to be recognized if (1) the Company intends to sell the security; (2) it is “more likely than not” that the Company will be required to sell the security before recovery of its amortized cost basis; or (3) for debt securities, the present value of expected cash flows is not sufficient to recover the entire amortized cost basis. Marketable equity securities are evaluated for OTTI based on the severity and duration of the impairment and, if deemed to be other than temporary, the declines in fair value are reflected in earnings as realized losses. For impaired debt securities that the Company intends to sell, or more likely than not will be required to sell, the full amount of the depreciation is recognized as OTTI through earnings. For all other impaired debt securities, credit-related OTTI is recognized through earnings and non-credit Federal Home Loan Bank Stock As a member of the Federal Home Loan Bank of Boston (FHLB), the Company is required to invest in stock of the FHLB. Based on redemption provisions, the stock has no quoted market value and is carried at cost. Management evaluates the Company’s investment in the FHLB of Boston stock for other-than-temporary impairment at least on a quarterly basis and more frequently when economic or market conditions warrant such evaluation. Based on its most recent analysis of the FHLB of Boston as of December 31, 2017, management deems its investment in FHLB of Boston stock to not be other-than-temporarily impaired. Loans Held For Sale Loans purchased or transferred from held for investment, (if intent or ability to hold existing loans changes), and loans originated and intended for sale in the secondary market are carried at the lower of cost or estimated fair value, in the aggregate. Net unrealized losses, if any, are recognized through a valuation allowance by charges to income. Direct loan origination costs and fees are deferred upon origination and are recognized on the date of sale. Loans Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off Interest income is accrued on the unpaid principal balance. Loan origination fees, net of certain direct origination costs, are deferred and recognized over the expected term as an adjustment of the related loan yield using the interest method. The accrual of interest on all loans is discontinued at the time the loan is 90 days past due unless the credit is well-secured and in process of collection. Past due status is based on contractual terms of the loan. In all cases, loans are placed on nonaccrual if collection of principal or interest is considered doubtful. All interest accrued but not collected for loans that are placed on nonaccrual is reversed against interest income. The interest on these loans is accounted for on the cash-basis or cost-recovery method, until qualifying for return to accrual. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured. Cash receipts of interest income on impaired loans are credited to principal to the extent necessary to eliminate doubt as to the collectability of the net carrying amount of the loan. Some or all of the cash receipts of interest income on impaired loans is recognized as interest income if the remaining net carrying amount of the loan is deemed to be fully collectible. When recognition of interest income on an impaired loan on a cash basis is appropriate, the amount of income that is recognized is limited to that which would have been accrued on the net carrying amount of the loan at the contractual interest rate. Any cash interest payments received in excess of the limit and not applied to reduce the net carrying amount of the loan are recorded as recoveries of charge-offs until the charge-offs are fully recovered. Allowance for Loan Losses The allowance for loan losses is established as losses are estimated to have occurred through a provision for loan losses charged to earnings. Loan losses are charged against the allowance when management believes the uncollectibility of a loan balance is confirmed. Subsequent recoveries, if any, are credited to the allowance. The allowance for loan losses is evaluated on a regular basis by management. This evaluation is inherently subjective as it requires estimates that are susceptible to significant revision as more information becomes available. The allowance consists of general, allocated and unallocated components, as further described below. General Component: The general component of the allowance for loan losses is based on historical loss experience adjusted for qualitative factors stratified by the following loan segments: residential real estate, home equity lines of credit, commercial real estate, construction, commercial, indirect auto and other consumer. Management uses a rolling average of historical losses based on a time frame appropriate to capture relevant loss data for each loan segment. This historical loss factor is adjusted for the following qualitative factors: levels/trends in delinquencies; trends in volume and terms of loans; effects of changes in risk selection and underwriting standards and other changes in lending policies, procedures and practices; experience/ability/depth of lending management and staff; and national and local economic trends and conditions. There were no changes in the Company’s policies or methodology pertaining to the general component of the allowance for loan losses during 2017 or 2016. The qualitative factors are determined based on the various risk characteristics of each loan segment. Risk characteristics relevant to each portfolio segment are as follows: Residential real estate loans and home equity lines of credit – The Company generally does not originate or purchase loans with a loan-to-value Commercial real estate loans – Loans in this segment are primarily income-producing properties throughout New England. The underlying cash flows generated by the properties are adversely impacted by a downturn in the economy as evidenced by increased vacancy rates, which in turn, will have an effect on the credit quality in this segment. Management generally obtains rent rolls annually and continually monitors the cash flows of these borrowers. Construction loans – Loans in this segment primarily include speculative real estate development loans for which payment is derived from sale and/or lease up of the property. Credit risk is affected by cost overruns, time to sell at an adequate price, and market conditions. Commercial loans – Loans in this segment are made to businesses and are generally secured by real estate and assets of the business. Repayment is expected from the cash flows of the business. A weakened economy, and resultant decreased consumer and business spending, will have an effect on the credit quality in this segment. Indirect auto loans – Loans in this segment are secured installment loans that are originated through a network of select regional automobile dealerships. The Company’s interest in the vehicle is secured with a recorded lien on the state title of each automobile. Collections are sensitive to changes in borrower financial circumstances, and the collateral can depreciate or be damaged in the event of repossession. Repayment is primarily dependent on the credit worthiness and the cash flow of the individual borrower and secondarily, liquidation of collateral. Consumer loans – Loans in this segment include secured and unsecured consumer loans including passbook loans, consumer lines of credit, overdraft protection and consumer unsecured loans. Repayment is dependent on the credit quality and the cash flow of the individual borrower. Allocated Component: The allocated component relates to loans that are classified as impaired. A loan is considered impaired when, based on current information and events, it is probable that the Company will be unable to collect the scheduled payments of principal or interest when due according to the contractual terms of the loan agreement. Factors considered by management in determining impairment include payment status, collateral value, and the probability of collecting scheduled principal and interest payments when due. Loans that experience insignificant payment delays and payment shortfalls generally are not classified as impaired. Management determines the significance of payment delays and payment shortfalls on a case-by-case The Company periodically may agree to modify the contractual terms of loans. When a loan is modified and a concession is made to a borrower experiencing financial difficulty, the modification is considered a troubled debt restructuring (“TDR”). All TDRs are classified as impaired and therefore are subject to a specific review for impairment. Impaired loans are measured based on 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. Generally, impairment on TDRs is measured using the discounted cash flow method by discounting expected cash flows by the loan’s contractual rate of interest in effect prior to the loan’s modification. Loans that have been classified as TDRs and which subsequently default are reviewed to determine if the loan should be deemed collateral dependent. In such an instance, any shortfall between the value of the collateral and the book value of the loan is determined by measuring the recorded investment in the loan against the fair value of the collateral less costs to sell. Generally, all other impaired loans are collateral dependent and impairment is measured through the collateral method. All loans on non-accrual Unallocated Component: An unallocated component is maintained to cover uncertainties that could affect management’s estimate of probable losses. The unallocated component of the allowance reflects the margin of imprecision inherent in the underlying assumptions used in the methodologies for estimating allocated and general reserves in the portfolio. In the ordinary course of business, the Bank enters into commitments to extend credit, commercial letters of credit and standby letters of credit. Such financial instruments are recorded in the financial statements when they are funded or become payable. The credit risk associated with these commitments is evaluated in a manner similar to the allowance for loan losses. The reserve for off-balance off-balance non-interest Premises and Equipment Land is carried at cost. Buildings and equipment are stated at cost, less accumulated depreciation, computed on the straight-line method over the estimated useful lives of the assets. It is general practice to charge the cost of maintenance and repairs to earnings when incurred; major expenditures for betterments are capitalized and depreciated over the shorter of the lease term for leasehold improvements or their estimated useful lives. The cost and related accumulated depreciation of assets sold, or otherwise disposed of, are removed from the related accounts and any gain or loss is included in earnings. Bank-owned Life Insurance Bank-owned life insurance policies are reflected on the consolidated balance sheets at cash surrender value. Changes in the net cash surrender value of the policies, as well as insurance proceeds received, are reflected in non-interest A life insurance policy with any individual carrier is limited to 15% of tier one capital and the total cash surrender value of life insurance policies is limited to 25% of tier one capital. Transfers and Servicing of Financial Assets Transfers of an entire financial asset, a group of entire financial assets, or a participating interest in an entire financial asset are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when (1) the assets have been isolated from the Company, (2) the transferee obtains the right to pledge or exchange the transferred assets, and (3) the Company does not maintain effective control over the transferred assets. During the normal course of business, the Company may transfer whole loans or a portion of a financial asset, such as a participation loan or the government guaranteed portion of a loan. In order to be eligible for sales treatment, the transfer of the portion of the loan must meet the criteria of a participating interest. If it does not meet the criteria of a participating interest, the transfer will be accounted for as a secured borrowing. In order to meet the criteria for a participating interest, all cash flows from the loan must be divided proportionately, the rights of each loan holder must have the same priority, the loan holders must have no recourse to the transferor other than standard representations and warranties and no loan holder has the right to pledge or exchange the entire loan. The Company services mortgage and indirect auto loans for others. Loan servicing fee income is reported in the consolidated statements of operations as fees are earned for servicing loans. The fees are based on a contractual percentage of the outstanding principal and are recorded as income when earned. Late fees and ancillary fees related to loan servicing are not material. Mortgage servicing rights (“MSR”) are initially recorded as an asset and measured at fair value when loans are sold to third parties with servicing rights retained. MSR assets are amortized in proportion to, and over the period of, estimated net servicing revenues. The carrying value of these assets is periodically reviewed for impairment using the lower of amortized cost or fair value methodology. The fair value of the servicing rights is determined by estimating the present value of future net cash flows, taking into consideration market loan prepayment speeds, discount rates, servicing costs and other economic factors. For purposes of measuring impairment, the underlying loans are stratified into relatively homogeneous pools based on predominant risk characteristics which include product type (i.e., fixed or adjustable) and interest rate bands. If the aggregate carrying value of the capitalized mortgage servicing rights for a stratum exceeds its fair value, MSR impairment is recognized in earnings through a valuation allowance for the difference. As the loans are repaid and net servicing revenue is earned, the MSR asset is amortized as an offset to loan servicing income. Servicing revenues are expected to exceed this amortization expense. However, if actual prepayment experience or defaults exceed what was originally anticipated, net servicing revenues may be less than expected and mortgage servicing rights may be impaired. No servicing assets or liabilities related to auto loans were recorded, as the contractual servicing fees are adequate to compensate the Company for its servicing responsibilities. Other Real Estate Owned and Other Foreclosed Assets Assets acquired through, or in lieu of, loan foreclosure are held for sale and are initially recorded at fair value, less estimated costs to sell, at the date of foreclosure or when control is established, establishing a new cost basis. Subsequent to foreclosure, valuations are periodically performed by management and the assets are carried at the lower of carrying amount or fair value less cost to sell. Revenue and expenses from operations, changes in the valuation allowance and any direct writedowns are included in other noninterest expense. The Company classifies commercial loans as in-substance in-substance Advertising Costs Advertising costs are expensed as incurred and recorded within marketing expense. Belmont Savings Bank Supplemental Executive Retirement Plan The compensation cost of an employee’s retirement benefit is recognized on the projected unit credit method over the employee’s approximate service period. The aggregate cost method is utilized for funding purposes. The Company accounts for its supplemental executive retirement plan using an actuarial model that allocates benefit costs over the service period of employees in the plan. The Company accounts for the over-funded or under-funded status of the plan as an asset or liability in its consolidated balance sheets and recognizes changes in the funded status in the year in which the changes occur through other comprehensive income or loss. Other Supplemental Executive Retirement Plans The compensation cost of an employe’s retirement benefit is accrued over the estimated period of the employee’s service. At each measurement date, the aggregate amount accrued equals the then present value of the benefits expected to be provided to the employee in exchange for the employee’s service to that date. Employee Stock Ownership Plan Compensation expense for the Employee Stock Ownership Plan (“ESOP”) is recorded at an amount equal to the shares allocated by the ESOP multiplied by the average fair value of the shares during the period. The Company recognizes compensation expense ratably over the year based upon the Company’s estimate of the number of shares expected to be allocated by the ESOP. Unearned compensation applicable to the ESOP is reflected as a reduction of stockholders’ equity in the consolidated balance sheets. The difference between the average fair value and the cost of the shares allocated by the ESOP is recorded as an adjustment to additional paid-in Stock Based Compensation The Company recognizes stock-based compensation based on the grant-date fair value of the award adjusted for expected forfeitures. The Company values share-based stock option awards granted using the Black-Scholes option-pricing model. The Company recognizes compensation expense for its awards on a straight-line basis over the requisite service period for the entire award (straight-line attribution method), ensuring that the amount of compensation cost recognized at any date at least equals the portion of the grant-date fair value of the award that is vested at that time. Income Taxes Deferred income tax assets and liabilities are determined using the liability (or balance sheet) method. Under this method, the net deferred tax asset or liability is determined based on the tax effects of the temporary differences between the book and tax bases of the various balance sheet assets and liabilities and gives current recognition to changes in tax rates and laws. A valuation allowance is established against deferred tax assets when, based upon all available evidence, both positive and negative, it is determined that it is more likely than not that some or all of the deferred tax assets will not be realized. Fair Value Hierarchy The Company measures the fair values of its financial instruments in accordance with accounting guidance that requires an entity to base fair value on exit price, and maximize the use of observable inputs and minimize the use of unobservable inputs to determine the exit price. Under applicable accounting guidance, the Company categorizes its financial instruments, based on the priority of inputs to the valuation technique, into a three-level hierarchy, as described below. Level 1 - Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 - Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 - Level 3 inputs are unobservable inputs for the asset or liability. Transfers between levels are recognized at the end of a reporting period, if applicable. Earnings per Share (“EPS”) Basic earnings per share is calculated using the two-class two-class Under this method, all earnings distributed and undistributed, are allocated to participating securities and common shares based on their respective rights to receive dividends. Unvested share-based payment awards that contain nonforfeitable rights to dividends are considered participating securities (i.e. unvested restricted stock), not subject to performance based measures. Basic earnings per share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding. Diluted earnings per share have been calculated in a manner similar to that of basic earnings per share except that the weighted average number of common shares outstanding is increased to include the number of additional common shares that would have been outstanding if all potentially dilutive common shares (such as those resulting from the exercise of stock options or the attainment of performance measures) were issued during the period, computed using the treasury stock method. Comprehensive Income Accounting principles generally require that recognized revenue, expenses, gains and losses be included in net income. Although certain changes in assets and liabilities are reported as a separate component of the stockholders’ equity section of the consolidated balance sheets, such items, along with net income, are components of comprehensive income. Other comprehensive income includes unrealized gains and losses on securities available for sale and changes in the funded status of the Belmont Savings Bank Supplemental Executive Retirement Plan. Recent Accounting Pronouncements In May 2014, the FASB issued amendments to Accounting Standards Codification (“ASC”) section 606 “Revenue from Contracts with Customers” through issuance of ASU 2014-09, 2015-14, 2015-14 2014-09 2014-09, non-interest 2014-09 non-interest In May 2015, the FASB issued ASU 2015-07, In January 2016, the FASB issued ASU 2016-01, 825-10): ASU 2016-01, available-for-sale In February 2016, the FASB issued ASU 2016-02, “Leases In March 2016, the FASB issued ASU 2016-09, Share-Based 2016-09 In June 2016, the FASB issued ASU 2016-13, off-balance In August 2016, the FASB issued ASU 2016-15, In November 2016, the FASB issued ASU 2016-18, beginning-of-period end-of-period In February 2017, the FASB issued ASU 2017-05, 610-20): 610-20, 2014-09. In March 2017, the FASB issued ASU 2017-07, In March 2017, the FASB issued ASU 2017-08, 310-20): In July 2017, the FASB issued ASU 2017-11, No. 2017-11, In August 2017, the FASB issued ASU 2017-12, In February 2018, the FASB issued ASU 2018-02,

RESTRICTIONS ON CASH AND AMOUNT

RESTRICTIONS ON CASH AND AMOUNTS DUE FROM BANKS	12 Months Ended
	Dec. 31, 2017
RESTRICTIONS ON CASH AND AMOUNTS DUE FROM BANKS	NOTE 2 – RESTRICTIONS ON CASH AND AMOUNTS DUE FROM BANKS Cash and cash equivalents as of December 31, 2017 and 2016 includes $25,218,000 and $23,450,000, respectively, which is subject to withdrawals and usage restrictions to satisfy the reserve requirements of the Federal Reserve Bank of Boston.

SECURITIES

SECURITIES	12 Months Ended
	Dec. 31, 2017
SECURITIES	NOTE 3 – SECURITIES Debt securities have been classified in the consolidated balance sheets according to management’s intent. The following table presents a summary of the amortized cost, gross unrealized holding gains and losses and fair value of securities available for sale and securities held to maturity for the periods indicated. Gross unrealized holding gains and losses on available-for-sale December 31, 2017 December 31, 2016 Amortized Gross Gross Amortized Gross Gross Cost Unrealized Unrealized Fair Cost Unrealized Unrealized Fair Basis Gains Losses Value Basis Gains Losses Value Available for sale securities: Corporate debt securities $ 16,975 $ 24 $ (78 ) $ 16,921 $ 22,051 $ 147 $ (150 ) $ 22,048 $ 16,975 $ 24 $ (78 ) $ 16,921 $ 22,051 $ 147 $ (150 ) $ 22,048 Held to maturity securities: U.S. government sponsored mortgage-backed securities $ 142,383 $ 145 $ (2,089 ) $ 140,439 $ 112,543 $ 306 $ (1,289 ) $ 111,560 Corporate debt securities 17,707 239 — 17,946 17,654 251 — 17,905 $ 160,090 $ 384 $ (2,089 ) $ 158,385 $ 130,197 $ 557 $ (1,289 ) $ 129,465 The amortized cost and estimated fair value of debt securities by contractual maturity at December 31, 2017 is as follows. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Available-for-Sale Held-to-Maturity Amortized Fair Amortized Fair Cost Basis Value Cost Basis Value Due within one year $ 12,753 $ 12,777 $ 7,003 $ 7,019 Due after one year through five years 4,222 4,144 12,747 12,918 Due after five years through ten years — — 32,640 32,143 Due after ten years — — 107,700 106,305 $ 16,975 $ 16,921 $ 160,090 $ 158,385 At December 31, 2017 and 2016, securities with a carrying value of $5,582,000 and $4,721,000, respectively, were pledged to secure securities sold under agreements to repurchase. Securities with a carrying value of $47,666,000 and $37,561,000 were pledged to secure borrowings with the Federal Home Loan Bank of Boston at December 31, 2017 and 2016, respectively, and securities with a carrying value of $15,780,000 and $15,739,000 were pledged to an available line of credit with the Federal Reserve Bank of Boston at December 31, 2017 and 2016, respectively. During the year ended December 31, 2017 proceeds from the sale of securities available for sale amounted to $5,038,000, resulting in realized gains of $38,000. There were no sales of securities available for sale during the years ending December 31, 2016 and 2015. In addition to the securities listed above, the Company holds investments in a Rabbi Trust that are used to fund the executive and director non-qualified These investments are available to satisfy the claims of general creditors of the Company in the event of bankruptcy and are consolidated in our consolidated balance sheets in other assets and consisted primarily of cash and cash equivalents and mutual funds, and are classified as trading securities and recorded at fair value. The fair value of these investments at December 31, 2017 and December 31, 2016 was $2.8 million and $2.6 million, respectively. For the years ended December 31, 2017 and 2016, the net gain on these investments still held at the reporting date was $159,000 and $36,000, respectively. Refer to Note 15 – Employee Benefit Plans, for more information on the non-qualified Information pertaining to securities with gross unrealized losses at December 31, 2017 and 2016, aggregated by investment category and length of time that individual securities have been in a continuous loss position, follows: Less than 12 Months 12 Months and Over # of Fair Unrealized Fair Unrealized Holdings Value Losses Value Losses December 31, 2017: Available-for-sale Corporate debt securities 1 $ — $ — $ 4,144 $ (78 ) Held-to-maturity U.S. government sponsored mortgage-backed securities 81 64,056 (718 ) 62,798 (1,371 ) Total temporarily impaired securities 82 $ 64,056 $ (718 ) $ 66,942 $ (1,449 ) December 31, 2016: Available-for-sale Corporate debt securities 1 $ 4,130 $ (150 ) $ — $ — Held-to-maturity U.S. government sponsored mortgage-backed securities 57 77,474 (1,097 ) 6,518 (192 ) Total temporarily impaired securities 58 $ 81,604 $ (1,247 ) $ 6,518 $ (192 ) Management evaluates securities for other-than-temporary impairment at least on a quarterly basis, and more frequently when economic or market concerns warrant such evaluation. When there are securities in an unrealized loss position, 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. At December 31, 2017, 82 debt securities had unrealized losses with aggregate depreciation of 1.63% from the Company’s amortized cost basis. The Company’s unrealized losses on investments in corporate bonds and mortgage-backed securities are primarily caused by changes in market interest rates. The contractual terms of these investments do not permit the companies to settle the security at a price less than the par value of the investment. The Company currently does not believe it is probable that it will be unable to collect all amounts due according to the contractual terms of the investments. Therefore, it is expected that the securities would not be settled at a price less than the par value of the investment. Because the Company does not intend to sell the investments and it is more likely than not that the Company will not be required to sell the investments before recovery of their amortized cost basis, it does not consider these investments to be other-than-temporarily impaired at December 31, 2017.

LOANS, ALLOWANCE FOR LOAN LOSSE

LOANS, ALLOWANCE FOR LOAN LOSSES AND CREDIT QUALITY	12 Months Ended
	Dec. 31, 2017
LOANS, ALLOWANCE FOR LOAN LOSSES AND CREDIT QUALITY	NOTE 4 – LOANS, ALLOWANCE FOR LOAN LOSSES AND CREDIT QUALITY A summary of the balances of loans follows: December 31, 2017 2016 Mortgage loans on real estate: Residential one-to-four $ 1,333,058 $ 997,336 Commercial real estate 642,072 491,838 Home equity lines of credit 178,624 167,465 Construction 53,045 89,003 Total real estate loans 2,206,799 1,745,642 Other loans: Commercial 63,722 63,404 Indirect auto 30,227 60,240 Consumer 435 439 94,384 124,083 Total loans 2,301,183 1,869,725 Net deferred loan costs 3,426 3,622 Net unamortized mortgage premiums 8,661 6,273 Allowance for loan losses (16,312 ) (13,585 ) Total loans, net $ 2,296,958 $ 1,866,035 The following tables present the activity in the allowance for loan losses for the years ended December 31, 2017, 2016 and 2015 and the balances of the allowance for loan losses and recorded investment in loans by portfolio class based on impairment method at December 31, 2017 and 2016. The recorded investment in loans in any of the following tables does not include accrued and unpaid interest or any deferred loan fees or costs, as amounts are not significant. Year Ended December 31, 2017 Beginning Provision Charge-offs Recoveries Ending Balance Residential one-to-four $ 4,828 $ 1,572 $ — $ — $ 6,400 Commercial real estate 4,885 1,698 — — 6,583 Construction 1,219 (455 ) — — 764 Commercial 728 30 — — 758 Home equity lines of credit 1,037 (90 ) — — 947 Indirect auto 362 (109 ) (45 ) 22 230 Consumer 9 12 (14 ) 2 9 Unallocated 517 104 — — 621 Total $ 13,585 $ 2,762 $ (59 ) $ 24 $ 16,312 Year Ended December 31, 2016 Beginning Provision Charge-offs Recoveries Ending Balance Residential one-to-four $ 3,574 $ 1,254 $ — $ — $ 4,828 Commercial real estate 4,478 407 — — 4,885 Construction 801 418 — — 1,219 Commercial 613 115 — — 728 Home equity lines of credit 928 109 — — 1,037 Indirect auto 623 (232 ) (85 ) 56 362 Consumer 10 10 (16 ) 5 9 Unallocated 213 304 — — 517 Total $ 11,240 $ 2,385 $ (101 ) $ 61 $ 13,585 Year Ended December 31, 2015 Beginning Provision Charge-offs Recoveries Ending Balance Residential one-to-four $ 2,364 $ 1,274 $ (64 ) $ — $ 3,574 Commercial real estate 4,043 435 — — 4,478 Construction 228 573 — — 801 Commercial 458 131 — 24 613 Home equity lines of credit 828 (99 ) — 199 928 Indirect auto 778 (48 ) (139 ) 32 623 Consumer 11 9 (16 ) 6 10 Unallocated 171 42 — — 213 Total $ 8,881 $ 2,317 $ (219 ) $ 261 $ 11,240 Year Ended December 31, 2017 Individually evaluated for impairment Collectively evaluated for impairment Total Loan Balance Allowance Loan Balance Allowance Loan Balance Allowance Residential one-to-four $ 2,688 $ 147 $ 1,330,370 $ 6,253 $ 1,333,058 $ 6,400 Commercial real estate 2,877 — 639,195 6,583 642,072 6,583 Construction — — 53,045 764 53,045 764 Commercial — — 63,722 758 63,722 758 Home equity lines of credit — — 178,624 947 178,624 947 Indirect auto 4 — 30,223 230 30,227 230 Consumer — — 435 9 435 9 Unallocated — — — 621 — 621 Total $ 5,569 $ 147 $ 2,295,614 $ 16,165 $ 2,301,183 $ 16,312 Year Ended December 31, 2016 Individually evaluated for impairment Collectively evaluated for impairment Total Loan Balance Allowance Loan Balance Allowance Loan Balance Allowance Residential one-to-four $ 2,896 $ 154 $ 994,440 $ 4,674 $ 997,336 $ 4,828 Commercial real estate 3,364 — 488,474 4,885 491,838 4,885 Construction — — 89,003 1,219 89,003 1,219 Commercial — — 63,404 728 63,404 728 Home equity lines of credit 200 — 167,265 1,037 167,465 1,037 Indirect auto 15 — 60,225 362 60,240 362 Consumer — — 439 9 439 9 Unallocated — — — 517 — 517 Total $ 6,475 $ 154 $ 1,863,250 $ 13,431 $ 1,869,725 $ 13,585 Information about loans that meet the definition of an impaired loan in ASC 310-10-35 Impaired loans with a related allowance for credit losses at December 31, 2017 Unpaid Related Recorded Principal Allowance For Investment Balance Credit Losses Residential one-to-four $ 725 $ 725 $ 147 Totals $ 725 $ 725 $ 147 Impaired loans with no related allowance for credit losses at December 31, 2017 Unpaid Related Recorded Principal Allowance For Investment Balance Credit Losses Residential one-to-four $ 1,963 $ 2,052 $ — Commercial real estate 2,877 2,877 — Indirect auto 4 4 — Totals $ 4,844 $ 4,933 $ — Impaired loans with a related allowance for credit losses at December 31, 2016 Unpaid Related Recorded Principal Allowance For Investment Balance Credit Losses Residential one-to-four $ 740 $ 740 $ 154 Totals $ 740 $ 740 $ 154 Impaired loans with no related allowance for credit losses at December 31, 2016 Unpaid Related Recorded Principal Allowance For Investment Balance Credit Losses Residential one-to-four $ 2,156 $ 2,278 $ — Commercial real estate 3,364 3,364 — Home equity lines of credit 200 200 — Indirect auto 15 15 — Totals $ 5,735 $ 5,857 $ — The following tables set forth information regarding interest income recognized on impaired loans, by portfolio, for the periods indicated. Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Average Interest Average Interest Average Interest Recorded Income Recorded Income Recorded Income With an allowance recorded Investment Recognized Investment Recognized Investment Recognized Residential one-to-four $ 897 $ 32 $ 1,273 $ 33 $ 1,265 $ 33 Commercial real estate — — 3,124 136 3,230 123 Totals $ 897 $ 32 $ 4,397 $ 169 $ 4,495 $ 156 Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Average Interest Average Interest Average Interest Recorded Income Recorded Income Recorded Income Without an allowance recorded Investment Recognized Investment Recognized Investment Recognized Residential one-to-four $ 1,986 $ 94 $ 2,977 $ 78 $ 4,296 $ 95 Commercial real estate 3,159 140 784 34 744 30 Home equity lines of credit 106 13 200 8 286 8 Indirect auto 6 — 12 — 8 — Totals $ 5,257 $ 247 $ 3,973 $ 120 $ 5,334 $ 133 At December 31, 2017, there were no additional funds committed to be advanced in connection with loans to borrowers with impaired loans. The following is a summary of past due and non-accrual December 31, 2017 30–59 Days 60–89 Days 90 Days Total 90 days Loans on Non-accrual Real estate loans: Residential one-to-four $ 711 $ — $ 260 $ 971 $ — $ 1,372 Home equity lines of credit 716 — — 716 — — Other loans: Indirect auto 347 30 4 381 — 4 $ 1,774 $ 30 $ 264 $ 2,068 $ — $ 1,376 December 31, 2016 30–59 Days 60–89 Days 90 Days Total 90 days or Loans on Non-accrual Real estate loans: Residential one-to-four $ — $ — $ 497 $ 497 $ — $ 1,804 Home equity lines of credit 57 486 — 543 — — Other loans: Indirect auto 460 106 15 581 — 15 $ 517 $ 592 $ 512 $ 1,621 $ — $ 1,819 Credit Quality Information The Company utilizes a nine grade internal loan rating system for commercial, commercial real estate and construction loans, and a five grade internal loan rating system for certain residential real estate, home equity and consumer loans that are rated if the loans become delinquent. Loans rated 1, 2, 2.5, 3 and 3.5: Loans in these categories are considered “pass” rated loans with low to average risk. Loans rated 4: Loans in this category are considered “special mention.” These loans are starting to show signs of potential weakness and are being closely monitored by management. Loans rated 5: Loans in this category are considered “substandard.” Generally, a loan is considered substandard if it is inadequately protected by the current net worth and paying capacity of the obligors and/or the collateral pledged. There is a distinct possibility that the Company will sustain some loss if the weakness is not corrected. Loans rated 6: Loans in this category are considered “doubtful.” Loans classified as doubtful have all the weaknesses inherent in those classified substandard with the added characteristic that the weaknesses make collection or liquidation in full, on the basis of currently existing facts, highly questionable and improbable. Loans rated 7: Loans in this category are considered uncollectible (“loss”) and of such little value that their continuance as loans is not warranted. On an annual basis, or more often if needed, the Company formally reviews the ratings on all commercial, commercial real estate, and construction loans. On an annual basis, the Company engages an independent third party to review a significant portion of loans within these segments and to assess the credit risk management practices of its commercial lending department. Management uses the results of these reviews as part of its annual review process and overall credit risk administration. On a quarterly basis, the Company formally reviews the ratings on all residential real estate and home equity loans if they have become delinquent. Criteria used to determine ratings consist of loan-to-value The following table presents the Company’s loans by risk rating at December 31, 2017 and 2016. There were no loans rated as 6 (“doubtful”) or 7 (“loss”) at the dates indicated. December 31, 2017 Loans rated 1-3.5 Loans rated 4 Loans rated 5 Loans not rated (A) Total Residential one-to-four $ — $ 344 $ 2,060 $ 1,330,654 $ 1,333,058 Commercial real estate 638,254 — 3,818 — 642,072 Construction 53,045 — — — 53,045 Commercial 63,682 40 — — 63,722 Home equity lines of credit — — 772 177,852 178,624 Indirect auto — — — 30,227 30,227 Consumer — — — 435 435 Total $ 754,981 $ 384 $ 6,650 $ 1,539,168 $ 2,301,183 December 31, 2016 Loans rated 1-3.5 Loans rated 4 Loans rated 5 Loans not rated (A) Total Residential one-to-four $ — $ 351 $ 2,509 $ 994,476 $ 997,336 Commercial real estate 471,491 16,032 4,315 — 491,838 Construction 89,003 — — — 89,003 Commercial 63,404 — — — 63,404 Home equity lines of credit — — 799 166,666 167,465 Indirect auto — — — 60,240 60,240 Consumer — — — 439 439 Total $ 623,898 $ 16,383 $ 7,623 $ 1,221,821 $ 1,869,725 (A) Residential one-to-four The Company periodically modifies loans to extend the term or make other concessions to help a borrower stay current on their loan and to avoid foreclosure. The Company generally does not forgive principal or interest on loans or modify the interest rates on loans to those not otherwise available in the market. During the year ended December 31, 2017, no loans were modified and determined to be TDRs and one existing TDR was modified again to extend the maturity. During the year ended December 31, 2016, four loans were modified and determined to be TDRs (three of which had previously been restructured and determined to be TDRs). The following table shows the Company’s total TDRs and other pertinent information as of the dates indicated: December 31, 2017 December 31, 2016 TDRs on Accrual Status $ 4,194 $ 4,656 TDRs on Non-accrual 645 1,442 Total TDRs $ 4,839 $ 6,098 Amount of specific allocation included in the allowance for loan losses associated with TDRs $ 147 $ 154 Additional commitments to lend to a borrower who has been a party to a TDR $ — $ — The following table shows the TDR modifications which occurred during the the years ended December 31, 2017 and 2016 and the outstanding recorded investment subsequent to the modifications occurring: Year Ended Pre-modification Post-modification # of outstanding outstanding Contracts recorded investment recorded investment (a) Real estate loans: Commercial real estate 1 $ 273 $ 273 1 $ 273 $ 273 Year Ended Pre-modification Post-modification # of outstanding outstanding Contracts recorded investment recorded investment (a) Real estate loans: Residential one-to-four 1 $ 621 $ 699 Commercial real estate 3 3,394 3,394 4 $ 4,015 $ 4,093 (a) The post-modification balances represent the balance of the loan on the date of modifications. These amounts may show an increase when modifications include a capitalization of interest or taxes. The following table shows the Company’s post-modification balance of TDRs listed by type of modification during the years indicated: For the years ended December 31, 2017 December 31, 2016 Capitalization of interest, taxes and extended maturity $ — $ 699 Extended maturity 273 3,394 Total $ 273 $ 4,093 For purposes of this table the Company generally considers a loan to have defaulted when it reaches 90 days past due. The following table shows the loans that have been modified during the past twelve months which have subsequently defaulted during the periods indicated: For the years ended December 31, 2017 2016 2015 Number Recorded Number Recorded Number Recorded of Contracts Investment of Contracts Investment of Contracts Investment TDRs that subsequently defaulted Residential one-to-four — $ — 1 $ 497 — $ — Totals — $ — 1 $ 497 — $ — Foreclosure Proceedings Consumer mortgage loans collateralized by residential real estate property that are in the process of foreclosure totaled $0 and $497,000 as of December 31, 2017 and December 31, 2016, respectively. The Company did not have any foreclosed residential real estate property held as of December 31, 2017 or December 31, 2016. Pledged Loans At December 31, 2017 and 2016, $1.4 billion and $1.1 billion in loans, respectively, were pledged to secure FHLB advances.

TRANSFERS AND SERVICING

TRANSFERS AND SERVICING	12 Months Ended
	Dec. 31, 2017
TRANSFERS AND SERVICING	NOTE 5 – TRANSFERS AND SERVICING Certain residential mortgage loans are periodically sold by the Company to the secondary market. Generally, these loans are sold without recourse or other credit enhancements. The Company sells loans and both releases and retains the servicing rights. For loans sold with servicing rights retained, the Company provides the servicing for the loans on a per-loan non-interest non-interest On March 16, 2006, seventeen loans with an aggregate principal balance of $10.5 million were sold to another financial institution. The agreement related to this sale contained provisions requiring the Company to repurchase any loan that became 90 days past due during the initial 120 months. The Company would repurchase the past due loan for 100 percent of the unpaid principal plus interest to repurchase date. During the twelve months ended December 31, 2016, the recourse provision expired and both the loans and recourse obligation were derecognized from the consolidated balance sheet. As of December 31, 2017 and 2016, the Company’s recorded balance of these loans sold with recourse amounted to $0. The Company did not incur any losses related to these loans. Changes in mortgage servicing rights, which are included in other assets, were as follows: Years Ended December 31, 2017 2016 2015 Balance at beginning of period $ 403 $ 479 $ 476 Capitalization 508 85 99 Amortization (130 ) (101 ) (93 ) Valuation allowance adjustment 74 (60 ) (3 ) Balance at end of period $ 855 $ 403 $ 479 As of December 31, 2017 and 2016, the fair value of mortgage servicing rights approximated carrying value.

PREMISES AND EQUIPMENT

PREMISES AND EQUIPMENT	12 Months Ended
	Dec. 31, 2017
PREMISES AND EQUIPMENT	NOTE 6 – PREMISES AND EQUIPMENT A summary of the cost and accumulated depreciation of premises and equipment follows: December 31, 2017 2016 Land $ 161 $ 161 Buildings 3,516 3,424 Leasehold improvements 1,414 1,399 Furniture and equipment 4,350 3,979 9,441 8,963 Accumulated depreciation (7,187 ) (6,608 ) $ 2,254 $ 2,355 Depreciation and amortization expense for the years ended December 31, 2017, 2016 and 2015 amounted to $595,000, $621,000 and $726,000, respectively. During the years ended December 31, 2017, 2016 and 2015, the Company determined that certain assets had no future economic benefit to the Company and recorded impairment charges of $18,000, $16,000, and $6,000, respectively, within equipment expense on the consolidated statements of operations. During the year ended December 31, 2016, assets with a cost of $3.5 million that were fully depreciated and no longer in use were disposed of. No gain or loss was recognized as a result of this disposal.

DEPOSITS

DEPOSITS	12 Months Ended
	Dec. 31, 2017
DEPOSITS	NOTE 7 – DEPOSITS The aggregate amount of time deposits in denominations that meet or exceed the FDIC insurance limit of $250,000 at December 31, 2017 and 2016 was $128.7 million and $74.4 million, respectively. At December 31, 2017, the scheduled maturities of time deposits are as follows: 2018 $ 226,910 2019 94,797 2020 129,044 2021 42,587 2022 11,376 $ 504,714 Included in time deposits are brokered deposits of $247.2 million at December 31, 2017 and $156.4 million at December 31, 2016. The amounts of overdraft deposits that were reclassified to loans at December 31, 2017 and 2016 were $48,000 and $36,000, respectively. Related Party Deposits Deposit accounts of directors, executive officers and their affiliates totaled $8.5 million and $11.0 million at December 31, 2017 and 2016, respectively. Secured Deposits The Bank has an Irrevocable Letter of Credit Reimbursement Agreement with the FHLB, whereby upon the Bank’s request, an irrevocable letter of credit is issued to secure public unit deposit accounts. These letters of credit are secured by a blanket security agreement on qualified collateral, principally mortgage loans, home equity lines of credit, commercial loans and U.S. government sponsored mortgage-backed securities in an aggregate amount equal to outstanding letters of credit. The amount of funds available to the Bank through the FHLB is reduced by any letters of credit outstanding. At December 31, 2017 and 2016, there were $5.0 million and $0 letters of credit outstanding.

SHORT-TERM BORROWINGS

SHORT-TERM BORROWINGS	12 Months Ended
	Dec. 31, 2017
SHORT-TERM BORROWINGS	NOTE 8 – SHORT-TERM BORROWINGS Federal Home Loan Bank Advances Fixed rate FHLB advances with an original maturity of less than one year, amounted to $305.9 million and $131.6 million at December 31, 2017 and 2016, respectively, at a weighted average rate of 1.52% and 0.79%, respectively. The Bank also has an available line of credit with the FHLB in the amount of $5.6 million at December 31, 2017 and 2016 at an interest rate that adjusts daily. All borrowings from the FHLB are secured by a blanket security agreement on qualified collateral, principally mortgage loans, home equity lines of credit, commercial loans and U.S. government sponsored mortgage-backed securities in an aggregate amount equal to outstanding advances. The Bank’s unused remaining available borrowing capacity at the FHLB was approximately $279.2 million and $289.7 million at December 31, 2017 and 2016, respectively. At December 31, 2017 and 2016, the Bank had sufficient collateral at the FHLB to support its obligations and was in compliance with the FHLB’s collateral pledging program. Securities Sold Under Agreements to Repurchase Securities sold under agreements to repurchase amounted to $3.3 million and $2.0 million at December 31, 2017 and 2016, respectively, mature on a daily basis and are secured by U.S. government sponsored mortgage-backed securities. The weighted average interest rate on these agreements was 0.15% at December 31, 2017 and 2016. The obligations to repurchase the securities sold are reflected as a liability in the consolidated balance sheets. The dollar amounts of the securities underlying the agreements remain in the asset accounts. The repurchase agreements stipulate that the securities are not delivered to the customer and instead are held in segregated safekeeping accounts maintained by the Company’s safekeeping agent.

LONG-TERM BORROWINGS

LONG-TERM BORROWINGS	12 Months Ended
	Dec. 31, 2017
LONG-TERM BORROWINGS	NOTE 9 – LONG-TERM BORROWINGS Long-term debt at December 31, 2017 and 2016 consists of the following fixed rate FHLB advances: Amount Weighted Average Rate 2017 2016 2017 2016 Fixed rate advances maturing: 2017 $ — $ 35,000 — % 1.14 % 2018 47,000 47,000 1.63 % 1.63 % 2019 225,250 225,250 1.49 % 1.49 % 2020 35,000 20,000 1.76 % 1.75 % 2021 15,000 — 2.03 % — % 2022 95,000 — 2.17 % — % 2031 — 50,000 — % 0.39 % $ 417,250 $ 377,250 1.70 % 1.34 % Included in the advances above at December 31, 2016 was a long-term advance in the amount of $50.0 million with an interest rate of 0.39% which was callable by the FHLB on September 12, 2017. The advance was called on September 12, 2017.

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2017
INCOME TAXES	NOTE 10 – INCOME TAXES Allocation of federal and state income taxes between current and deferred portions is as follows: Years Ended December 31, 2017 2016 2015 Current tax provision: Federal $ 7,386 $ 7,212 $ 4,223 State 1,961 1,954 1,120 9,347 9,166 5,343 Deferred tax expense (benefit): Federal (71 ) (1,391 ) (799 ) State (20 ) (350 ) (222 ) Effect of change in statutory federal tax rate 2,626 — — 2,535 (1,741 ) (1,021 ) Total provision for income taxes $ 11,882 $ 7,425 $ 4,322 The reasons for the differences between the statutory federal income tax rate and the effective tax rates are summarized as follows: Years Ended December 31, 2017 2016 2015 Statutory federal tax rate 35.0 % 35.0 % 34.0 % Increase (decrease) resulting from: State taxes, net of federal tax benefit 4.8 5.4 5.3 Bank-owned life insurance (1.5 ) (1.9 ) (2.7 ) Tax exempt income (0.6 ) (0.8 ) (0.3 ) Change in statutory federal tax rate 10.0 — — Share based compensation (3.5 ) 1.2 1.9 Other, net 1.0 (0.6 ) 0.3 Effective tax rates 45.2 % 38.3 % 38.5 % The components of the net deferred tax asset are as follows: December 31, 2017 2016 Deferred tax assets: Employee benefit and deferred compensation plans $ 2,375 $ 3,827 Allowance for loan losses 4,596 5,577 Accrued rent 8 10 Interest on non-performing 34 50 Stock options 356 547 Unrealized loss on securities available for sale 15 1 ESOP 92 116 Gross deferred tax assets 7,476 10,128 Deferred tax liabilities: Mortgage servicing rights (240 ) (164 ) Deferred loan origination costs (860 ) (1,104 ) Restricted stock awards (280 ) (140 ) Depreciation (201 ) (305 ) Unrecognized retirement benefit (58 ) (72 ) Other (43 ) (22 ) Gross deferred tax liabilities (1,682 ) (1,807 ) Net deferred tax asset $ 5,794 $ 8,321 The Company does not have any uncertain tax positions at December 31, 2017 or 2016 which require accrual or disclosure. The Company records interest and penalties as part of income tax expense. No interest or penalties were recorded for the years ended December 31, 2017, 2016 and 2015. The Company’s income tax returns are subject to review and examination by federal and state taxing authorities. The Company is currently open to audit under the applicable statutes of limitations by the Internal Revenue Service for the years ended December 31, 2014 through 2017. The years open to examination by state taxing authorities vary by jurisdiction; no years prior to 2014 are open. In prior years, the Company was allowed a special tax-basis bad debt deduction under certain provisions of the Internal Revenue Code. As a result, retained earnings of the Company as of December 31, 2017 and 2016 includes approximately $3.6 million for which federal and state income taxes have not been provided. If the Company no longer qualifies as a bank as defined in certain provisions of the Internal Revenue Code, this amount will be subject to recapture in taxable income ratably over four (4) years, subject to a combined federal and state tax rate of approximately 28%. The Tax Cuts and Jobs Act. one-time

OFF-BALANCE SHEET ARRANGEMENTS

OFF-BALANCE SHEET ARRANGEMENTS	12 Months Ended
	Dec. 31, 2017
OFF-BALANCE SHEET ARRANGEMENTS	NOTE 11 – OFF-BALANCE Credit-Related Financial Instruments The Company is a party to credit related financial instruments with off-balance The Company’s exposure to credit loss is represented by the contractual amount of these commitments. The Company follows the same credit policies in making commitments as it does for on-balance At December 31, 2017 and 2016, the following financial instruments were outstanding whose contract amounts represent credit risk: Contract Amount 2017 2016 Commitments to grant loans $ 23,702 $ 44,677 Unfunded commitments under lines of credit 325,768 259,124 Unadvanced portion of construction loans 11,486 36,555 Standby letters of credit 561 658 Commitments to purchase loans 65,692 62,036 Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the contract. Commitments generally have fixed expiration dates or other termination clauses and may require payment of a fee. The commitments for home equity and commercial lines of credit may expire without being drawn upon. Therefore, the total commitment amounts do not necessarily represent future cash requirements. The amount of collateral obtained, if it is deemed necessary by the Company, is based on management’s credit evaluation of the customer. Unfunded commitments under revolving credit lines and overdraft protection agreements are commitments for possible future extensions of credit to existing customers. These lines-of-credit Standby letters-of-credit letters-of-credit The credit risk involved in issuing letters-of-credit Commitments to purchase loans are conditional commitments issued by the Company to purchase loans through select correspondent mortgage companies who originate and sell loans as part of their operations. Typically the commitment to purchase is valid as long as there is no violation of any condition established in the correspondent contract. Commitments generally have fixed expiration dates or other termination clauses and generally do not require payment of a fee.

COMMITMENTS AND CONTINGENT LIAB

COMMITMENTS AND CONTINGENT LIABILITIES	12 Months Ended
	Dec. 31, 2017
COMMITMENTS AND CONTINGENT LIABILITIES	NOTE 12 – COMMITMENTS AND CONTINGENT LIABILITIES Pursuant to the terms of noncancelable lease agreements in effect at December 31, 2017, pertaining to banking premises and equipment, future minimum rent commitments under various operating leases are as follows: 2018 $ 361 2019 359 2020 266 2021 122 2022 122 Thereafter 122 $ 1,352 Certain leases contain provisions for escalation of minimum lease payments contingent upon increases in real estate taxes and percentage increases in the consumer price index. Also, certain leases contain options to extend for periods from one to ten years. The cost of such rentals is not included above. Total rent expense for the years ended December 31, 2017, 2016 and 2015 amounted to $363,000, $384,000 and $398,000, respectively.

LEGAL CONTINGENCIES

LEGAL CONTINGENCIES	12 Months Ended
	Dec. 31, 2017
LEGAL CONTINGENCIES	NOTE 13 – LEGAL CONTINGENCIES In the normal course of business, there are various outstanding legal proceedings. In the opinion of management, after consulting with legal counsel, the consolidated financial position and results of operations of the Company are not expected to be affected materially by the outcome of such proceedings.

MINIMUM REGULATORY CAPITAL REQU

MINIMUM REGULATORY CAPITAL REQUIREMENTS	12 Months Ended
	Dec. 31, 2017
MINIMUM REGULATORY CAPITAL REQUIREMENTS	NOTE 14 – MINIMUM REGULATORY CAPITAL REQUIREMENTS The Company’s primary source of cash is dividends from the Bank. The Bank is subject to certain restrictions on the amount of dividends that it may declare without prior regulatory approval. In addition, the dividends declared cannot be in excess of the amount which would cause the Bank to fall below the minimum required for capital adequacy purposes. The Company (on a consolidated basis) and the Bank are subject to various regulatory capital requirements administered by the federal banking agencies. 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 and Bank’s financial statements. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, the Company and the Bank must meet specific capital guidelines that involve quantitative measures of their assets, liabilities and certain off-balance On July 2, 2013, the Federal Reserve Bank (“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 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, as of December 31, 2017 and 2016, that the Company and the Bank meet all capital adequacy requirements to which they are subject. As of December 31, 2017, the most recent notification from the FDIC categorized the Bank as well capitalized under the regulatory framework for prompt corrective action. To be categorized as well capitalized, an institution must maintain minimum total risk-based, Tier 1 risk-based, Common Equity Tier 1 risk-based and Tier 1 leverage ratios as set forth in the following tables. There are no conditions or events since the notification that management believes have changed the Bank’s category. The following table presents actual and required capital ratios as of December 31, 2017 and December 31, 2016 for the Company and the Bank under the Basel III Capital Rules. The minimum required capital amounts presented include the minimum required capital levels as of December 31, 2017 and December 31, 2016 based on the phase-in phased-in. Actual Minimum Capital Minimum Capital Required Basel III Phase-In Schedule Minimum Capital Required Minimum To Be Well Amount Ratio Amount Ratio Amount Ratio Amount Ratio Amount Ratio As of December 31, 2017: Total Capital (to Risk Weighted Assets) Consolidated $ 194,287 11.30 % $ 137,498 8.00 % $ 158,982 9.25 % $ 180,466 10.50 % N/A N/A Belmont Savings Bank 189,311 11.01 % 137,497 8.00 % 158,981 9.25 % 180,465 10.50 % $ 171,871 10.00 % Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 177,939 10.35 % $ 103,123 6.00 % $ 124,607 7.25 % $ 146,092 8.50 % N/A N/A Belmont Savings Bank 172,963 10.06 % 103,123 6.00 % 124,607 7.25 % 146,091 8.50 % $ 137,497 8.00 % Common Equity Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 177,939 10.35 % $ 77,343 4.50 % $ 98,827 5.75 % $ 120,311 7.00 % N/A N/A Belmont Savings Bank 172,963 10.06 % 77,342 4.50 % 98,826 5.75 % 120,310 7.00 % $ 111,716 6.50 % Tier 1 Capital (to Average Assets) Consolidated $ 177,939 6.97 % $ 102,148 4.00 % $ 102,148 4.00 % $ 102,148 4.00 % N/A N/A Belmont Savings Bank 172,963 6.77 % 102,147 4.00 % 102,147 4.00 % 102,147 4.00 % $ 127,683 5.00 % Actual Minimum Capital Minimum Capital Required Basel III Phase-In Schedule Minimum Capital Required Minimum To Be Well Amount Ratio Amount Ratio Amount Ratio Amount Ratio Amount Ratio As of December 31, 2016: Total Capital (to Risk Weighted Assets) Consolidated $ 174,465 11.72 % $ 119,116 8.00 % $ 128,422 8.625 % $ 156,340 10.50 % N/A N/A Belmont Savings Bank 169,499 11.38 % 119,114 8.00 % 128,420 8.625 % 156,337 10.50 % $ 148,893 10.00 % Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 160,817 10.80 % $ 89,337 6.00 % $ 98,643 6.625 % $ 126,561 8.50 % N/A N/A Belmont Savings Bank 155,851 10.47 % 89,336 6.00 % 98,641 6.625 % 126,559 8.50 % $ 119,114 8.00 % Common Equity Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 160,817 10.80 % $ 67,003 4.50 % $ 76,309 5.125 % $ 104,227 7.00 % N/A N/A Belmont Savings Bank 155,851 10.47 % 67,002 4.50 % 76,308 5.125 % 104,225 7.00 % $ 96,780 6.50 % Tier 1 Capital (to Average Assets) Consolidated $ 160,817 7.63 % $ 84,253 4.00 % $ 84,253 4.00 % $ 84,253 4.00 % N/A N/A Belmont Savings Bank 155,851 7.40 % 84,251 4.00 % 84,251 4.00 % 84,251 4.00 % $ 105,314 5.00 % Stock Repurchase Plans.

EMPLOYEE BENEFIT PLANS

EMPLOYEE BENEFIT PLANS	12 Months Ended
	Dec. 31, 2017
EMPLOYEE BENEFIT PLANS	NOTE 15 – EMPLOYEE BENEFIT PLANS Belmont Savings Bank Supplemental Executive Retirement Plan Effective October 1, 2010, the Company established the Belmont Savings Bank Supplemental Executive Retirement Plan (the “Plan”). The purpose of the Plan is to remain competitive with our peers in our compensation arrangements and to help us retain certain executive officers of the Company. At December 31, 2017 and 2016, there were four participants in the Plan. Participants are fully vested after the completion of between five and ten years of service. The plan is unfunded. Information pertaining to the activity in the plan is as follows: Years Ended December 31, 2017 2016 Change in benefit obligation: Benefit obligation at beginning of year $ 1,521 $ 1,316 Service cost 253 261 Interest cost 66 57 Actuarial gain (42 ) (113 ) Benefit obligation at end of year 1,798 1,521 Funded status at end of year $ (1,798 ) $ (1,521 ) Accrued pension benefit $ (2,003 ) $ (1,696 ) Accumulated benefit obligation $ 1,175 $ 985 The assumptions used to determine the benefit obligation are as follows: December 31, 2017 2016 Discount rate 3.80 % 4.35 % Rate of compensation increase 3.00 % 3.00 % The components of net periodic pension cost are as follows: December 31, 2017 2016 Service cost $ 253 $ 261 Interest cost 66 57 Amortization of gain (19 ) — Amortization of prior service cost 6 6 Net periodic cost $ 306 $ 324 Other changes in benefit obligations recognized in other comprehensive loss are as follows: December 31, 2017 2016 Amortization of prior service cost $ (6 ) $ (6 ) Amortization of unrecognized gain 19 — Net actuarial gain (42 ) (112 ) Total recognized in other comprehensive loss $ (29 ) $ (118 ) The assumptions used to determine net periodic pension cost are as follows: December 31, 2017 2016 Discount rate 4.35 % 4.30 % Rate of compensation increase 3.00 % 3.00 % Amounts recognized in accumulated other comprehensive income, before tax effects, consist of the following: December 31, 2017 2016 Unrecognized prior service cost $ 40 $ 46 Unrecognized net gain (245 ) (222 ) $ (205 ) $ (176 ) The estimated prior service cost that will be amortized from accumulated other comprehensive income into net periodic pension expense during the year ending December 31, 2018 is $6,000. The estimated unrecognized net gain that will be accreted from accumulated other comprehensive income into net periodic pension expense during the year ending December 31, 2018 is $18,500. The Company does not expect to contribute to the Plan in 2018. Estimated future benefit payments, which reflect expected future service, as appropriate, are as follows: Year Ending December 31, Amount 2018 $ — 2019 57 2020 191 2021 267 2022 267 Years 2023-2027 1,565 Other Supplemental Retirement Plans The Company has supplemental retirement plans for certain eligible executive officers that do not participate in the Belmont Savings Bank Supplemental Executive Retirement Plan which provide for a lump sum benefit upon termination of employment at or after age 55 and completing 10 or more years of service (certain reduced benefits are available prior to attaining age 55 or fewer than 10 years of service), subject to certain limitations as set forth in the agreements. The present value of these future payments is being accrued over the service period. The estimated liability at December 31, 2017 and 2016 relating to these plans was $2.6 million and $2.3 million, respectively. The discount rate used to determine the Company’s obligation was 3.8% and 4.35% during the years ended December 31, 2017 and 2016, respectively. The projected rate of salary increase was 3% during the years ended December 31, 2017 and 2016. Total supplemental retirement plan expense amounted to $331,000, $233,000 and $254,000 for the years ended December 31, 2017, 2016 and 2015, respectively. The Company has a supplemental retirement plan for eligible directors that provides for monthly benefits based upon years of service to the Company, subject to certain limitations as set forth in the agreements. The present value of these future payments is being accrued over the estimated period of service. The estimated liability at December 31, 2017 and 2016 relating to this plan was $697,000 and $661,000, respectively. The discount rate used to determine the Company’s obligation was 3.8% and 4.35% during the years ended December 31, 2017 and 2016, respectively. Total supplemental retirement plan expense amounted to $64,000, $55,000 and $17,000 for the years ended December 31, 2017, 2016 and 2015, respectively. Incentive Compensation Plan The Incentive Compensation Plan is a discretionary annual cash-based incentive plan that is an integral part of the participant’s total compensation package and supports the continued growth and profitability of the Bank. Each year participants are awarded for the achievement of certain performance objectives on a company-wide and individual basis. Compensation expense recognized was $2.3 million, $2.0 million and $2.0 million for the years ended December 31, 2017, 2016 and 2015, respectively. Defined Contribution Plan The Bank sponsors a 401(k) plan covering substantially all employees meeting certain eligibility requirements. Under the provisions of the plan, employees are able to contribute up to an annual limit of the lesser of 75% of eligible compensation or the maximum allowed by the Internal Revenue Service. The Company’s contributions for the years ended December 31, 2017, 2016 and 2015 totaled $891,000, $839,000 and $842,000, respectively. Deferred Compensation Plan The Company has a deferred compensation plan by which selected employees and directors of the Company are entitled to elect, prior to the beginning of each year, to defer the receipt of an amount of their compensation for the forthcoming year to an individual deferred compensation account established by the Bank. Compensation that is deferred is held in a Rabbi Trust, or grantor trust. The Rabbi Trust is maintained by the Bank primarily for purposes of providing a vehicle for deferred compensation for certain Directors and employees of the Company. The plan is administered by a third party and permits participants to select from a number of investment options for the investment of their account balances. Each participant is always 100% vested in his or her deferred compensation account balance. As of December 31, 2017 and 2016, the recorded liability relating to the Rabbi Trust was $2.8 million and $2.6 million, respectively. Employee Stock Ownership Plan The Company maintains an Employee Stock Ownership Plan (“ESOP”) to provide eligible employees the opportunity to own Company stock. This plan is a tax-qualified The Company contributed funds to a subsidiary to enable it to grant a loan to the ESOP for the purchase of 458,643 shares of the Company’s common stock at a price of $10.00 per share. The loan obtained by the ESOP from the Company’s Subsidiary to purchase Company common stock is payable annually over 30 years at a rate per annum equal to the Prime Rate on the first business day of each calendar year, or 3.75% for 2017. Loan payments are principally funded by cash contributions from the Bank. The loan is secured by the shares purchased, which are held in a suspense account for allocation among participants as the loan is repaid. Cash dividends paid on allocated shares are distributed to participants and cash dividends paid on unallocated shares are used to repay the outstanding debt of the ESOP. Shares used as collateral to secure the loan are released and available for allocation to eligible employees as the principal and interest on the loan is paid. At December 31, 2017, the remaining principal balance on the ESOP debt is payable as follows: Years Ending December 31, Amount 2018 $ 96 2019 100 2020 104 2021 110 2022 115 Thereafter 3,444 $ 3,969 Shares held by the ESOP include the following: December 31, 2017 2016 Unallocated 363,091 378,379 Allocated 84,813 72,598 447,904 450,977 The fair value of unallocated shares was approximately $10.6 million at December 31, 2017 and $11.0 million at December 31, 2016. Total compensation expense recognized in connection with the ESOP for the years ended December 31, 2017, 2016 and 2015 was $444,000, $360,000 and $321,000, respectively. Severance Agreements The Company has entered into employment agreements and change in control agreements with certain executive officers which would provide the executive officers with severance payments based on salary, and the continuation of other benefits, upon a change in control as defined in the agreements.

STOCK BASED COMPENSATION

STOCK BASED COMPENSATION	12 Months Ended
	Dec. 31, 2017
STOCK BASED COMPENSATION	NOTE 16 – STOCK BASED COMPENSATION On November 14, 2012, the stockholders of BSB Bancorp, Inc. approved the BSB Bancorp, Inc. 2012 Equity Incentive Plan. The table below presents the amount of cumulatively granted stock options and restricted stock awards, net of forfeitures, through December 31, 2017 under the BSB Bancorp, Inc. 2012 Equity Incentive Plan. On February 8, 2017, the stockholders of the Company approved the BSB Bancorp, Inc. 2017 Equity Incentive Plan. The BSB Bancorp, Inc. 2017 Equity Incentive Plan authorized the issuance or delivery to participants of up to 487,200 shares of BSB Bancorp, Inc. common stock pursuant to grants of restricted stock awards and/or restricted stock unit awards. On March 15, 2017, 487,200 restricted stock awards were granted under the Plan at $27.10, the grant date fair value per share, with a ten year vesting period and an estimated 2.64% forfeiture rate. The awards are not deemed to be participating securities. Upon the approval of this new plan, the Company canceled the existing 2012 Equity Incentive Plan and no further awards will be granted out of that plan. The following table presents the amount of cumulatively granted restricted stock awards, net of forfeitures, through December 31, 2017 under the BSB Bancorp, Inc. 2017 Equity Incentive Plan: Authorized Authorized Cumulative Granted Net of Forfeitures Outstanding Stock Restricted Authorized Stock Restricted 2012 Equity Incentive Plan 917,286 366,914 1,284,200 889,092 363,570 1,252,662 2017 Equity Incentive Plan — 487,200 487,200 — 483,302 483,302 The following table presents the pre-tax For the year ended December 31, 2017 2016 2015 Stock based compensation expense Stock options $ 724 $ 780 $ 791 Restricted stock awards 1,835 869 869 Total stock based award expense $ 2,559 $ 1,649 $ 1,660 Related tax benefits recognized in earnings $ 874 $ 492 $ 481 The following table presents relevant information relating to the Company’s stock options for the periods indicated: For the year ended December 31, 2017 2016 2015 Weighted average grant date fair value of options granted $ — $ 4.63 $ 3.90 Intrinsic value of stock options exercised 3,299 368 226 Cash paid to settle equity instruments granted under stock based compensation arrangements — — — Total compensation cost related to non-vested As of December 31, 2017 Amount Weighted Stock options $ 136 2.36 Restricted stock 10,574 9.19 Total $ 10,710 The Company granted the awards presented in the table below. The fair value of the stock options granted was estimated on the date of the grant using the Black-Scholes option pricing model with the following assumptions used: • Expected volatility is based on the standard deviation of the historical volatility of the daily adjusted closing price of the Company’s shares. • Expected term represents the period of time that the option is expected to be outstanding. The Company determined the expected life using the “Simplified Method.” • Expected dividend yield is determined based on management’s expectations regarding issuing dividends in the foreseeable future. • The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant for a period equivalent to the expected life of the option. • The stock-based compensation expense recognized in earnings is based on the amount of awards ultimately expected to vest, therefore a forfeiture assumption is estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Date of grant 3/1/2016 2/25/2015 2/11/2015 Options granted 27,500 5,414 7,828 Exercise price $ 22.31 $ 18.83 $ 18.78 Vesting period (1) 5 years 5 years 5 years Expiration date 3/1/2026 2/25/2025 2/11/2025 Expected volatility 16.13 % 15.51 % 15.52 % Expected term 6.5 years 6.5 years 6.5 years Expected dividend yield 0 % 0 % 0 % Risk free interest rate 1.54 % 1.70 % 1.76 % Fair value $ 4.63 $ 3.89 $ 3.91 (1)- Vesting is ratably and the period begins on the date of grant. The option exercise price is derived from trading value on the date of grant. A summary of the status of the Company’s Stock Option and Restricted Stock Awards for the year ended December 31, 2017 is presented in the tables below: Outstanding Stock option Weighted average Weighted average Aggregate Balance at January 1, 2017 804,484 $ 12.68 Granted — — Exercised (213,962 ) 12.17 Forfeited — — Balance at December 31, 2017 590,522 $ 12.86 5.17 $ 9,676 Exercisable 543,763 $ 12.31 5.00 $ 9,209 Non-vested Weighted average Balance at January 1, 2017 73,429 $ 12.22 Granted 487,200 27.10 Vested (71,829 ) 12.10 Forfeited (3,898 ) 27.10 Balance at December 31, 2017 484,902 $ 27.07 For the years ended December 31, 2017, 2016 and 2015, the fair value of shares vested during the year amounted to $2.2 million, $1.9 million and $1.6 million, respectively.

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2017
EARNINGS PER SHARE	NOTE 17 – EARNINGS PER SHARE Earnings per share consisted of the following components for the years ended December 31, 2017, 2016 and 2015: December 31, December 31, December 31, Net income $ 14,386 $ 11,981 $ 6,914 Undistributed earnings attributable to participating securities (108 ) (190 ) (167 ) Net income available to common stockholders $ 14,278 $ 11,791 $ 6,747 Weighted average shares outstanding, basic 8,754,393 8,571,861 8,465,177 Effect of dilutive shares 429,400 286,030 217,813 Weighted average shares outstanding, assuming dilution 9,183,793 8,857,891 8,682,990 Basic EPS $ 1.63 $ 1.38 $ 0.80 Effect of dilutive shares (0.08 ) (0.05 ) (0.02 ) Diluted EPS $ 1.55 $ 1.33 $ 0.78 For 2017, 2016 and 2015, average options to purchase 0, 22,992, and 17,159 shares of common stock were outstanding, respectively, but not included in the computation of EPS because they were antidilutive under the treasury stock method.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	12 Months Ended
	Dec. 31, 2017
RELATED PARTY TRANSACTIONS	NOTE 18 – RELATED PARTY TRANSACTIONS In the ordinary course of business, the Bank has granted loans to principal officers and directors and their affiliates. As of December 31, 2017 and 2016, related party loans were not significant.

RESTRICTIONS ON DIVIDENDS, LOAN

RESTRICTIONS ON DIVIDENDS, LOANS AND ADVANCES	12 Months Ended
	Dec. 31, 2017
RESTRICTIONS ON DIVIDENDS, LOANS AND ADVANCES	NOTE 19 – RESTRICTIONS ON DIVIDENDS, LOANS AND ADVANCES Federal and state banking regulations place certain restrictions on dividends paid and loans or advances made by the Bank to the Company. The total amount for dividends which may be paid in any calendar year cannot exceed the Bank’s net income for the current year, plus the Bank’s net income retained for the two previous years, without regulatory approval. Loans or advances are limited to 10 percent of the Bank’s capital stock and surplus on a secured basis. In addition, dividends paid by the Bank to the Company would be prohibited if the effect thereof would cause the Bank’s capital to be reduced below applicable minimum capital requirements.

FAIR VALUES OF ASSETS AND LIABI

FAIR VALUES OF ASSETS AND LIABILITIES	12 Months Ended
	Dec. 31, 2017
FAIR VALUES OF ASSETS AND LIABILITIES	NOTE 20 – FAIR VALUES OF ASSETS AND LIABILITIES Determination of Fair Value The fair value of an asset or liability is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including during periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may be reduced for many instruments. This condition could cause an instrument to be reclassified from one level to another. Fair value is best determined based upon quoted market prices. However, in many instances, there are no quoted market prices for the Company’s various assets and liabilities. In cases where quoted market prices are not available, fair values are based on estimates using present value of cash flows or other valuation techniques. Those techniques are significantly affected by the assumptions used, including the discount rate and estimates of future cash flows. Accordingly, the fair value estimates may not be realized in an immediate settlement of the instrument. The Company groups its assets and liabilities measured at fair value in three levels, based on the markets in which the assets and liabilities are traded and the observability and reliability of the assumptions used to determine fair value. Level 1 - Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 - Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 - Level 3 inputs are unobservable inputs for the asset or liability. For assets and liabilities, fair value is based upon the lowest level of observable input that is significant to the fair value measurement. In general, fair value is based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon models that primarily use, as inputs, observable market based parameters. The Company’s valuation methodologies may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. While management believes the Company’s valuation methodologies are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. Furthermore, the reported fair value amounts have not been comprehensively revalued since the presentation dates, and therefore, estimates of fair value after the balance sheet date may differ significantly from the amounts presented herein. A more detailed description of the valuation methodologies used for assets and liabilities measured at fair value is set forth below. A description of the valuation methodologies used for instruments measured at fair value, as well as the general classification of such instruments pursuant to the valuation hierarchy, is set forth below. These valuation methodologies were applied to all of the Company’s financial assets and financial liabilities carried at fair value for December 31, 2017 and 2016. There were no significant transfers between levels of the fair value hierarchy during the years ended December 31, 2017 and 2016. Financial Assets and Financial Liabilities: Financial assets and financial liabilities measured at fair value on a recurring basis include the following: Securities Available for Sale Investments held in the Rabbi Trust non-qualified The following table summarizes financial assets measured at fair value on a recurring basis as of December 31, 2017 and 2016, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value: Level 1 Level 2 Level 3 Total At December 31, 2017 Securities available for sale Corporate debt securities $ — $ 16,921 $ — $ 16,921 Trading securities Rabbi Trust 2,808 — — 2,808 Totals $ 2,808 $ 16,921 $ — $ 19,729 Level 1 Level 2 Level 3 Total At December 31, 2016 Securities available for sale Corporate debt securities $ — $ 22,048 $ — $ 22,048 Trading securities Rabbi Trust 2,606 — — 2,606 Totals $ 2,606 $ 22,048 $ — $ 24,654 Certain financial assets and financial liabilities are measured at fair value on a non-recurring non-recurring non-recurring non-recurring There were no impaired loans that were remeasured and reported at fair value through either a charge off or a specific valuation allowance based upon the fair value of the underlying collateral or and loans held for sale at December 31, 2017 and 2016. Non-Financial Non-Financial non-financial non-financial Non-financial non-recurring charge-off non-interest Non-financial non-financial re-measured December 31, 2017 Level 1 Level 2 Level 3 Mortgage servicing rights $ — $ — $ 855 Totals $ — $ — $ 855 December 31, 2016 Level 1 Level 2 Level 3 Mortgage servicing rights $ — $ — $ 403 Totals $ — $ — $ 403 There were no foreclosed assets at December 31, 2017 or 2016. ASC Topic 825, “Financial Instruments,” requires disclosure of the fair value of financial assets and financial liabilities, including those financial assets and financial liabilities that are not measured and reported at fair value on a recurring basis or non-recurring non-recurring Securities held-to-maturity Loans - For variable-rate loans that reprice frequently and with no significant change in credit risk, fair values are based on carrying values. The fair values for other loans are estimated using discounted cash flow analyses, using interest rates currently being offered for loans with similar terms to borrowers of similar credit quality. Deposits - The fair values disclosed for demand deposits (e.g., interest and non-interest Federal Home Loan Bank advances - The fair values of the Company’s Federal Home Loan Bank advances are estimated using discounted cash flow analyses based on the current incremental borrowing rates in the market for similar types of borrowing arrangements. Summary of Fair Values of Financial Instruments not Carried at Fair Value The estimated fair values, and related carrying or notional amounts, of the Company’s financial instruments are as follows: December 31, 2017 Carrying Fair Amount Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 110,888 $ 110,888 $ 110,888 $ — $ — Interest-bearing time deposits with other banks 2,440 2,440 — 2,440 — Held-to-maturity 160,090 158,385 — 158,385 — Federal Home Loan Bank stock 32,382 32,382 — 32,382 — Bank owned life insurance 36,967 36,967 — 36,967 Loans, net 2,296,958 2,251,971 — — 2,251,971 Accrued interest receivable 6,344 6,344 6,344 — — Financial liabilities: Deposits 1,751,251 1,748,995 1,246,537 502,458 — Federal Home Loan Bank advances 723,150 719,430 — 719,430 — Securities sold under agreements to repurchase 3,268 3,268 — 3,268 — Accrued interest payable 1,594 1,594 1,594 — — Mortgagors’ escrow accounts 4,690 4,690 — 4,690 — December 31, 2016 Carrying Fair Amount Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 58,876 $ 58,876 $ 58,876 $ — $ — Interest-bearing time deposits with other banks 234 233 — 233 — Held-to-maturity 130,197 129,465 — 129,465 — Federal Home Loan Bank stock 25,071 25,071 — 25,071 — Bank owned life insurance 35,842 35,842 — 35,842 Loans, net 1,866,035 1,837,068 — — 1,837,068 Accrued interest receivable 4,635 4,635 4,635 — — Financial liabilities: Deposits 1,469,422 1,469,906 1,133,821 336,085 — Federal Home Loan Bank advances 508,850 507,773 — 507,773 — Securities sold under agreements to repurchase 1,985 1,985 — 1,985 — Accrued interest payable 1,023 1,023 1,023 — — Mortgagors’ escrow accounts 3,341 3,341 — 3,341 —

OTHER COMPREHENSIVE (LOSS) INCO

OTHER COMPREHENSIVE (LOSS) INCOME	12 Months Ended
	Dec. 31, 2017
OTHER COMPREHENSIVE (LOSS) INCOME	NOTE 21 – OTHER COMPREHENSIVE (LOSS) INCOME The following table presents a reconciliation of the changes in the components of other comprehensive (loss) income for the dates indicated, including the amount of income tax benefit (expense) allocated to each component of other comprehensive (loss) income: Year Ended December 31, 2017 Pre Tax Tax Benefit After Tax Amount (Expense) Amount Securities available-for-sale: Change in fair value of securities available for sale $ (13 ) $ 5 $ (8 ) Reclassification adjustment for net gains included in net income 1 (38 ) 15 (23 ) Net change in fair value of securities available for sale (51 ) 20 (31 ) Defined benefit post-retirement benefit plans: Change in the actuarial gain/loss 42 (17 ) 25 Reclassification adjustment included in net income 2 (13 ) 5 (8 ) Net change defined-benefit post-retirement benefit plans 29 (12 ) 17 Total other comprehensive loss $ (22 ) $ 8 $ (14 ) Year Ended December 31, 2016 Pre Tax Tax After Tax Amount Expense Amount Securities available-for-sale: Change in fair value of securities available for sale $ 247 $ (98 ) $ 149 Net change in fair value of securities available for sale 247 (98 ) 149 Defined benefit post-retirement benefit plans: Change in the actuarial gain/loss 112 (46 ) 66 Reclassification adjustment included in net income 2 6 (2 ) 4 Net change defined-benefit post-retirement benefit plans 118 (48 ) 70 Total other comprehensive income $ 365 $ (146 ) $ 219 Year Ended December 31, 2015 Pre Tax Tax Benefit After Tax Amount (Expense) Amount Securities available-for-sale: Change in fair value of securities available for sale $ (130 ) $ 52 $ (78 ) Net change in fair value of securities available for sale (130 ) 52 (78 ) Defined benefit post-retirement benefit plans: Change in the actuarial gain/loss (33 ) 13 (20 ) Reclassification adjustment included in net income 2 6 (2 ) 4 Net change defined-benefit post-retirement benefit plans (27 ) 11 (16 ) Total other comprehensive loss $ (157 ) $ 63 $ (94 ) 1- Reclassification adjustments are comprised of realized security gains. The gains have been reclassified out of accumulated other comprehensive income and have affected certain lines in the consolidated statements of operations as follows; the pre-tax 2- Reclassification adjustments are comprised of amortization of prior service cost and unrecognized gain and have been reclassified out of accumulated other comprehensive income (loss). The amounts affected certain lines in the consolidated statements of operations as follows: amortization of prior service cost and unrecognized gain is included in salaries and employee benefits expense. The tax expense amount is included in income tax expense and the after tax amount is included in net income. The components of accumulated other comprehensive income, included in stockholders’ equity, are as follows: December 31, 2017 December 31, 2016 Net unrealized holding loss on available-for-sale $ (32 ) $ (1 ) Unrecognized benefit pertaining to defined benefit plan, net of tax 121 104 Accumulated other comprehensive income $ 89 $ 103 Accumulated other comprehensive income at December 31, 2017 included $19,000 related to stranded amounts resulting from the re-measurement 2018-02,

CONDENSED FINANCIAL STATEMENTS

CONDENSED FINANCIAL STATEMENTS OF PARENT COMPANY	12 Months Ended
	Dec. 31, 2017
CONDENSED FINANCIAL STATEMENTS OF PARENT COMPANY	NOTE 22 – CONDENSED FINANCIAL STATEMENTS OF PARENT COMPANY The following condensed financial statements are for the Parent Company only and should be read in conjunction with the consolidated financial statements of the Company. Condensed Balance Sheets December 31, 2017 2016 Assets Cash and cash equivalents held at Belmont Savings Bank $ 919 $ 519 Investment in Belmont Savings Bank 173,054 155,955 Investment in BSB Funding Corp. 4,065 4,436 Other assets 45 62 Total assets $ 178,083 $ 160,972 Liabilities and Stockholders’ Equity Accrued expenses $ 38 $ 37 Other liabilities 16 14 Total liabilities 54 51 Stockholders’ equity 178,029 160,921 Total liabilities and stockholders’ equity $ 178,083 $ 160,972 Condensed Statements of Operations Years Ended December 31, 2017 2016 2015 Interest and dividend income: Interest on cash equivalents $ — $ — $ 1 Dividends from subsidiaries — — — Total interest and dividend income — — 1 Interest expense — — — Net interest and dividend income — — 1 Non-interest — — — Non-interest 230 219 242 Loss before income taxes and equity in undistributed earnings of subsidiaries (230 ) (219 ) (241 ) Income tax benefit (94 ) (89 ) (96 ) Loss before equity in income of subsidiaries (136 ) (130 ) (145 ) Equity in undistributed earnings of Belmont Savings Bank 14,432 12,025 6,976 Equity in undistributed earnings of BSB Funding Corp 90 86 83 Net income $ 14,386 $ 11,981 $ 6,914 Condensed Statements of Cash Flows Years Ended December 31, 2017 2016 2015 Cash flows from operating activities: Net income $ 14,386 $ 11,981 $ 6,914 Adjustments to reconcile net income to net cash (used in) provided by operating activities: Equity in undistributed earnings of Belmont Savings Bank (14,432 ) (12,025 ) (6,976 ) Equity in undistributed earnings of BSB Funding Corp. (90 ) (86 ) (83 ) Deferred income tax expense — — 190 Other, net 26 (27 ) 720 Net cash (used in) provided by operating activities (110 ) (157 ) 765 Cash flows from investing activities: Return of capital from BSB Funding Corp. 460 — 600 Investment in Belmont Savings Bank — — (3,800 ) Net cash provided by (used in) investing activities 460 — (3,200 ) Cash flows from financing activities: Proceeds from exercise of stock options, net of cash paid 50 298 228 Restricted stock awards issued, net of awards surrendered — (118 ) (51 ) Net cash provided by financing activities 50 180 177 Net increase (decrease) in cash and cash equivalents 400 23 (2,258 ) Cash and cash equivalents at beginning of period 519 496 2,754 Cash and cash equivalents at end of period $ 919 $ 519 $ 496

QUARTERLY DATA (UNAUDITED)

QUARTERLY DATA (UNAUDITED)	12 Months Ended
	Dec. 31, 2017
QUARTERLY DATA (UNAUDITED)	NOTE 23 – QUARTERLY DATA (UNAUDITED) Quarterly results of operations are as follows: Years Ended December 31, 2017 2016 Fourth Third Second First Fourth Third Second First Quarter Quarter Quarter Quarter Quarter Quarter Quarter Quarter Interest and dividend income $ 21,114 $ 19,758 $ 18,764 $ 17,506 $ 16,291 $ 15,726 $ 15,164 $ 14,439 Interest expense 6,414 5,579 4,816 4,245 3,918 3,699 3,457 3,158 Net interest income 14,700 14,179 13,948 13,261 12,373 12,027 11,707 11,281 Provision for loan losses 691 535 707 829 601 443 741 599 Net interest income, after provision for loan losses 14,009 13,644 13,241 12,432 11,772 11,584 10,966 10,682 Non-interest 1,117 885 995 630 703 680 705 660 Non-interest 7,636 7,929 7,645 7,476 7,045 7,066 6,984 7,252 Income before taxes 7,490 6,600 6,591 5,586 5,430 5,198 4,687 4,090 Income tax expense 5,382 2,001 2,579 1,920 2,120 2,018 1,735 1,551 Net income $ 2,108 $ 4,599 $ 4,012 $ 3,666 $ 3,310 $ 3,180 $ 2,952 $ 2,539 Earnings per common share Basic $ 0.24 $ 0.52 $ 0.45 $ 0.42 $ 0.38 $ 0.36 $ 0.34 $ 0.29 Diluted $ 0.23 $ 0.50 $ 0.43 $ 0.40 $ 0.37 $ 0.35 $ 0.33 $ 0.28

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	12 Months Ended
	Dec. 31, 2017
SUBSEQUENT EVENTS	NOTE 24 – SUBSEQUENT EVENTS The Company has evaluated subsequent events for potential recognition and/or disclosure through the date these consolidated financial statements were issued.

SUMMARY OF SIGNIFICANT ACCOUN32

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2017
Nature of Operations	Nature of Operations BSB Bancorp, Inc. (the “Company”) was incorporated in Maryland in June, 2011 to become the holding company of Belmont Savings Bank (the “Bank”), a state-chartered Massachusetts savings bank. The Company is supervised by the Board of Governors of the Federal Reserve System (“FRB”), while the Bank is subject to the regulations of, and periodic examination by, the Federal Deposit Insurance Corporation (“FDIC”) and the Massachusetts Division of Banks (the “Division”). The Bank’s deposits are insured by the Bank Insurance Fund of the FDIC up to $250,000 per account. For balances in excess of the FDIC deposit insurance limits, coverage is provided by the Massachusetts Depositors Insurance Fund, Inc. (“Mass DIF”). In connection with the Company’s conversion from a mutual holding company to stock holding company form of organization (the “conversion”), on October 4, 2011 we completed our initial public offering of common stock, selling 8,993,000 shares of common stock at $10.00 per share for approximately $89.9 million in gross proceeds, including 458,643 shares sold to the Bank’s employee stock ownership plan. In addition, in connection with the conversion, we issued 179,860 shares of our common stock and contributed $200,000 in cash to the Belmont Savings Bank Foundation. Belmont Savings Bank is a state chartered savings bank which was incorporated in 1885 and is headquartered in Belmont, Massachusetts. The Bank is engaged principally in the business of attracting deposits from the general public and investing those deposits in residential and commercial real estate loans, consumer loans, including indirect auto loans, commercial loans and construction loans, as well as investment securities.
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, Belmont Savings Bank and BSB Funding Corporation and the Bank’s wholly owned subsidiary, BSB Investment Corporation. All significant intercompany balances and transactions have been eliminated in consolidation. The Company’s consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles and general practices within the financial services industry.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant changes in the near-term relate to the determination of the allowance for loan losses, valuation and potential other-than-temporary impairment (“OTTI”) of investment securities and the valuation of deferred tax assets.
Reclassification	Reclassification Certain previously reported amounts have been reclassified to conform to the current year’s presentation.
Significant Group Concentrations of Credit Risk	Significant Group Concentrations of Credit Risk Most of the Company’s business activity is with customers located within the Commonwealth of Massachusetts. There are no concentrations of credit to borrowers that have similar economic characteristics. The majority of the Company’s loan portfolio is comprised of loans collateralized by real estate located in the Commonwealth of Massachusetts.
Cash and Cash Equivalents	Cash and Cash Equivalents For purposes of the consolidated statements of cash flows, cash and cash equivalents include cash, balances due from banks and interest-bearing deposits in other banks.
Securities	Securities Debt securities that management has the positive intent and ability to hold to maturity are classified as “held-to-maturity” held-to-maturity “available-for-sale” Purchase premiums and discounts are recognized in interest income using the interest method over the terms of the securities, adjusted for the effect of actual prepayments in the case of mortgage-backed securities. Gains and losses on the sale of securities are recorded on the trade date and are determined using the specific identification method. Each reporting period, the Company evaluates all securities classified as available-for-sale held-to-maturity, OTTI is required to be recognized if (1) the Company intends to sell the security; (2) it is “more likely than not” that the Company will be required to sell the security before recovery of its amortized cost basis; or (3) for debt securities, the present value of expected cash flows is not sufficient to recover the entire amortized cost basis. Marketable equity securities are evaluated for OTTI based on the severity and duration of the impairment and, if deemed to be other than temporary, the declines in fair value are reflected in earnings as realized losses. For impaired debt securities that the Company intends to sell, or more likely than not will be required to sell, the full amount of the depreciation is recognized as OTTI through earnings. For all other impaired debt securities, credit-related OTTI is recognized through earnings and non-credit
Federal Home Loan Bank Stock	Federal Home Loan Bank Stock As a member of the Federal Home Loan Bank of Boston (FHLB), the Company is required to invest in stock of the FHLB. Based on redemption provisions, the stock has no quoted market value and is carried at cost. Management evaluates the Company’s investment in the FHLB of Boston stock for other-than-temporary impairment at least on a quarterly basis and more frequently when economic or market conditions warrant such evaluation. Based on its most recent analysis of the FHLB of Boston as of December 31, 2017, management deems its investment in FHLB of Boston stock to not be other-than-temporarily impaired.
Loans Held For Sale	Loans Held For Sale Loans purchased or transferred from held for investment, (if intent or ability to hold existing loans changes), and loans originated and intended for sale in the secondary market are carried at the lower of cost or estimated fair value, in the aggregate. Net unrealized losses, if any, are recognized through a valuation allowance by charges to income. Direct loan origination costs and fees are deferred upon origination and are recognized on the date of sale.
Loans	Loans Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off Interest income is accrued on the unpaid principal balance. Loan origination fees, net of certain direct origination costs, are deferred and recognized over the expected term as an adjustment of the related loan yield using the interest method. The accrual of interest on all loans is discontinued at the time the loan is 90 days past due unless the credit is well-secured and in process of collection. Past due status is based on contractual terms of the loan. In all cases, loans are placed on nonaccrual if collection of principal or interest is considered doubtful. All interest accrued but not collected for loans that are placed on nonaccrual is reversed against interest income. The interest on these loans is accounted for on the cash-basis or cost-recovery method, until qualifying for return to accrual. Loans are returned to accrual status when all the principal and interest amounts contractually due are brought current and future payments are reasonably assured. Cash receipts of interest income on impaired loans are credited to principal to the extent necessary to eliminate doubt as to the collectability of the net carrying amount of the loan. Some or all of the cash receipts of interest income on impaired loans is recognized as interest income if the remaining net carrying amount of the loan is deemed to be fully collectible. When recognition of interest income on an impaired loan on a cash basis is appropriate, the amount of income that is recognized is limited to that which would have been accrued on the net carrying amount of the loan at the contractual interest rate. Any cash interest payments received in excess of the limit and not applied to reduce the net carrying amount of the loan are recorded as recoveries of charge-offs until the charge-offs are fully recovered.
Allowance for Loan Losses	Allowance for Loan Losses The allowance for loan losses is established as losses are estimated to have occurred through a provision for loan losses charged to earnings. Loan losses are charged against the allowance when management believes the uncollectibility of a loan balance is confirmed. Subsequent recoveries, if any, are credited to the allowance. The allowance for loan losses is evaluated on a regular basis by management. This evaluation is inherently subjective as it requires estimates that are susceptible to significant revision as more information becomes available. The allowance consists of general, allocated and unallocated components, as further described below. General Component: The general component of the allowance for loan losses is based on historical loss experience adjusted for qualitative factors stratified by the following loan segments: residential real estate, home equity lines of credit, commercial real estate, construction, commercial, indirect auto and other consumer. Management uses a rolling average of historical losses based on a time frame appropriate to capture relevant loss data for each loan segment. This historical loss factor is adjusted for the following qualitative factors: levels/trends in delinquencies; trends in volume and terms of loans; effects of changes in risk selection and underwriting standards and other changes in lending policies, procedures and practices; experience/ability/depth of lending management and staff; and national and local economic trends and conditions. There were no changes in the Company’s policies or methodology pertaining to the general component of the allowance for loan losses during 2017 or 2016. The qualitative factors are determined based on the various risk characteristics of each loan segment. Risk characteristics relevant to each portfolio segment are as follows: Residential real estate loans and home equity lines of credit – The Company generally does not originate or purchase loans with a loan-to-value Commercial real estate loans – Loans in this segment are primarily income-producing properties throughout New England. The underlying cash flows generated by the properties are adversely impacted by a downturn in the economy as evidenced by increased vacancy rates, which in turn, will have an effect on the credit quality in this segment. Management generally obtains rent rolls annually and continually monitors the cash flows of these borrowers. Construction loans – Loans in this segment primarily include speculative real estate development loans for which payment is derived from sale and/or lease up of the property. Credit risk is affected by cost overruns, time to sell at an adequate price, and market conditions. Commercial loans – Loans in this segment are made to businesses and are generally secured by real estate and assets of the business. Repayment is expected from the cash flows of the business. A weakened economy, and resultant decreased consumer and business spending, will have an effect on the credit quality in this segment. Indirect auto loans – Loans in this segment are secured installment loans that are originated through a network of select regional automobile dealerships. The Company’s interest in the vehicle is secured with a recorded lien on the state title of each automobile. Collections are sensitive to changes in borrower financial circumstances, and the collateral can depreciate or be damaged in the event of repossession. Repayment is primarily dependent on the credit worthiness and the cash flow of the individual borrower and secondarily, liquidation of collateral. Consumer loans – Loans in this segment include secured and unsecured consumer loans including passbook loans, consumer lines of credit, overdraft protection and consumer unsecured loans. Repayment is dependent on the credit quality and the cash flow of the individual borrower. Allocated Component: The allocated component relates to loans that are classified as impaired. A loan is considered impaired when, based on current information and events, it is probable that the Company will be unable to collect the scheduled payments of principal or interest when due according to the contractual terms of the loan agreement. Factors considered by management in determining impairment include payment status, collateral value, and the probability of collecting scheduled principal and interest payments when due. Loans that experience insignificant payment delays and payment shortfalls generally are not classified as impaired. Management determines the significance of payment delays and payment shortfalls on a case-by-case The Company periodically may agree to modify the contractual terms of loans. When a loan is modified and a concession is made to a borrower experiencing financial difficulty, the modification is considered a troubled debt restructuring (“TDR”). All TDRs are classified as impaired and therefore are subject to a specific review for impairment. Impaired loans are measured based on 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. Generally, impairment on TDRs is measured using the discounted cash flow method by discounting expected cash flows by the loan’s contractual rate of interest in effect prior to the loan’s modification. Loans that have been classified as TDRs and which subsequently default are reviewed to determine if the loan should be deemed collateral dependent. In such an instance, any shortfall between the value of the collateral and the book value of the loan is determined by measuring the recorded investment in the loan against the fair value of the collateral less costs to sell. Generally, all other impaired loans are collateral dependent and impairment is measured through the collateral method. All loans on non-accrual Unallocated Component: An unallocated component is maintained to cover uncertainties that could affect management’s estimate of probable losses. The unallocated component of the allowance reflects the margin of imprecision inherent in the underlying assumptions used in the methodologies for estimating allocated and general reserves in the portfolio. In the ordinary course of business, the Bank enters into commitments to extend credit, commercial letters of credit and standby letters of credit. Such financial instruments are recorded in the financial statements when they are funded or become payable. The credit risk associated with these commitments is evaluated in a manner similar to the allowance for loan losses. The reserve for off-balance off-balance non-interest
Premises and Equipment	Premises and Equipment Land is carried at cost. Buildings and equipment are stated at cost, less accumulated depreciation, computed on the straight-line method over the estimated useful lives of the assets. It is general practice to charge the cost of maintenance and repairs to earnings when incurred; major expenditures for betterments are capitalized and depreciated over the shorter of the lease term for leasehold improvements or their estimated useful lives. The cost and related accumulated depreciation of assets sold, or otherwise disposed of, are removed from the related accounts and any gain or loss is included in earnings.
Bank-owned Life Insurance	Bank-owned Life Insurance Bank-owned life insurance policies are reflected on the consolidated balance sheets at cash surrender value. Changes in the net cash surrender value of the policies, as well as insurance proceeds received, are reflected in non-interest A life insurance policy with any individual carrier is limited to 15% of tier one capital and the total cash surrender value of life insurance policies is limited to 25% of tier one capital.
Transfers and Servicing of Financial Assets	Transfers and Servicing of Financial Assets Transfers of an entire financial asset, a group of entire financial assets, or a participating interest in an entire financial asset are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when (1) the assets have been isolated from the Company, (2) the transferee obtains the right to pledge or exchange the transferred assets, and (3) the Company does not maintain effective control over the transferred assets. During the normal course of business, the Company may transfer whole loans or a portion of a financial asset, such as a participation loan or the government guaranteed portion of a loan. In order to be eligible for sales treatment, the transfer of the portion of the loan must meet the criteria of a participating interest. If it does not meet the criteria of a participating interest, the transfer will be accounted for as a secured borrowing. In order to meet the criteria for a participating interest, all cash flows from the loan must be divided proportionately, the rights of each loan holder must have the same priority, the loan holders must have no recourse to the transferor other than standard representations and warranties and no loan holder has the right to pledge or exchange the entire loan. The Company services mortgage and indirect auto loans for others. Loan servicing fee income is reported in the consolidated statements of operations as fees are earned for servicing loans. The fees are based on a contractual percentage of the outstanding principal and are recorded as income when earned. Late fees and ancillary fees related to loan servicing are not material. Mortgage servicing rights (“MSR”) are initially recorded as an asset and measured at fair value when loans are sold to third parties with servicing rights retained. MSR assets are amortized in proportion to, and over the period of, estimated net servicing revenues. The carrying value of these assets is periodically reviewed for impairment using the lower of amortized cost or fair value methodology. The fair value of the servicing rights is determined by estimating the present value of future net cash flows, taking into consideration market loan prepayment speeds, discount rates, servicing costs and other economic factors. For purposes of measuring impairment, the underlying loans are stratified into relatively homogeneous pools based on predominant risk characteristics which include product type (i.e., fixed or adjustable) and interest rate bands. If the aggregate carrying value of the capitalized mortgage servicing rights for a stratum exceeds its fair value, MSR impairment is recognized in earnings through a valuation allowance for the difference. As the loans are repaid and net servicing revenue is earned, the MSR asset is amortized as an offset to loan servicing income. Servicing revenues are expected to exceed this amortization expense. However, if actual prepayment experience or defaults exceed what was originally anticipated, net servicing revenues may be less than expected and mortgage servicing rights may be impaired. No servicing assets or liabilities related to auto loans were recorded, as the contractual servicing fees are adequate to compensate the Company for its servicing responsibilities.
Other Real Estate Owned and Other Foreclosed Assets	Other Real Estate Owned and Other Foreclosed Assets Assets acquired through, or in lieu of, loan foreclosure are held for sale and are initially recorded at fair value, less estimated costs to sell, at the date of foreclosure or when control is established, establishing a new cost basis. Subsequent to foreclosure, valuations are periodically performed by management and the assets are carried at the lower of carrying amount or fair value less cost to sell. Revenue and expenses from operations, changes in the valuation allowance and any direct writedowns are included in other noninterest expense. The Company classifies commercial loans as in-substance in-substance
Advertising Costs	Advertising Costs Advertising costs are expensed as incurred and recorded within marketing expense.
Belmont Savings Bank and Other Supplemental Executive Retirement Plan	Belmont Savings Bank Supplemental Executive Retirement Plan The compensation cost of an employee’s retirement benefit is recognized on the projected unit credit method over the employee’s approximate service period. The aggregate cost method is utilized for funding purposes. The Company accounts for its supplemental executive retirement plan using an actuarial model that allocates benefit costs over the service period of employees in the plan. The Company accounts for the over-funded or under-funded status of the plan as an asset or liability in its consolidated balance sheets and recognizes changes in the funded status in the year in which the changes occur through other comprehensive income or loss. Other Supplemental Executive Retirement Plans The compensation cost of an employe’s retirement benefit is accrued over the estimated period of the employee’s service. At each measurement date, the aggregate amount accrued equals the then present value of the benefits expected to be provided to the employee in exchange for the employee’s service to that date.
Employee Stock Ownership Plan	Employee Stock Ownership Plan Compensation expense for the Employee Stock Ownership Plan (“ESOP”) is recorded at an amount equal to the shares allocated by the ESOP multiplied by the average fair value of the shares during the period. The Company recognizes compensation expense ratably over the year based upon the Company’s estimate of the number of shares expected to be allocated by the ESOP. Unearned compensation applicable to the ESOP is reflected as a reduction of stockholders’ equity in the consolidated balance sheets. The difference between the average fair value and the cost of the shares allocated by the ESOP is recorded as an adjustment to additional paid-in
Stock Based Compensation	Stock Based Compensation The Company recognizes stock-based compensation based on the grant-date fair value of the award adjusted for expected forfeitures. The Company values share-based stock option awards granted using the Black-Scholes option-pricing model. The Company recognizes compensation expense for its awards on a straight-line basis over the requisite service period for the entire award (straight-line attribution method), ensuring that the amount of compensation cost recognized at any date at least equals the portion of the grant-date fair value of the award that is vested at that time.
Income Taxes	Income Taxes Deferred income tax assets and liabilities are determined using the liability (or balance sheet) method. Under this method, the net deferred tax asset or liability is determined based on the tax effects of the temporary differences between the book and tax bases of the various balance sheet assets and liabilities and gives current recognition to changes in tax rates and laws. A valuation allowance is established against deferred tax assets when, based upon all available evidence, both positive and negative, it is determined that it is more likely than not that some or all of the deferred tax assets will not be realized.
Fair Value Hierarchy	Fair Value Hierarchy The Company measures the fair values of its financial instruments in accordance with accounting guidance that requires an entity to base fair value on exit price, and maximize the use of observable inputs and minimize the use of unobservable inputs to determine the exit price. Under applicable accounting guidance, the Company categorizes its financial instruments, based on the priority of inputs to the valuation technique, into a three-level hierarchy, as described below. Level 1 - Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 - Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 - Level 3 inputs are unobservable inputs for the asset or liability. Transfers between levels are recognized at the end of a reporting period, if applicable.
Earnings per Share (EPS)	Earnings per Share (“EPS”) Basic earnings per share is calculated using the two-class two-class Under this method, all earnings distributed and undistributed, are allocated to participating securities and common shares based on their respective rights to receive dividends. Unvested share-based payment awards that contain nonforfeitable rights to dividends are considered participating securities (i.e. unvested restricted stock), not subject to performance based measures. Basic earnings per share is calculated by dividing net income available to common shareholders by the weighted average number of common shares outstanding. Diluted earnings per share have been calculated in a manner similar to that of basic earnings per share except that the weighted average number of common shares outstanding is increased to include the number of additional common shares that would have been outstanding if all potentially dilutive common shares (such as those resulting from the exercise of stock options or the attainment of performance measures) were issued during the period, computed using the treasury stock method.
Comprehensive Income	Comprehensive Income Accounting principles generally require that recognized revenue, expenses, gains and losses be included in net income. Although certain changes in assets and liabilities are reported as a separate component of the stockholders’ equity section of the consolidated balance sheets, such items, along with net income, are components of comprehensive income. Other comprehensive income includes unrealized gains and losses on securities available for sale and changes in the funded status of the Belmont Savings Bank Supplemental Executive Retirement Plan.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the FASB issued amendments to Accounting Standards Codification (“ASC”) section 606 “Revenue from Contracts with Customers” through issuance of ASU 2014-09, 2015-14, 2015-14 2014-09 2014-09, non-interest 2014-09 non-interest In May 2015, the FASB issued ASU 2015-07, In January 2016, the FASB issued ASU 2016-01, 825-10): ASU 2016-01, available-for-sale In February 2016, the FASB issued ASU 2016-02, “Leases In March 2016, the FASB issued ASU 2016-09, Share-Based 2016-09 In June 2016, the FASB issued ASU 2016-13, off-balance In August 2016, the FASB issued ASU 2016-15, In November 2016, the FASB issued ASU 2016-18, beginning-of-period end-of-period In February 2017, the FASB issued ASU 2017-05, 610-20): 610-20, 2014-09. In March 2017, the FASB issued ASU 2017-07, In March 2017, the FASB issued ASU 2017-08, 310-20): In July 2017, the FASB issued ASU 2017-11, No. 2017-11, In August 2017, the FASB issued ASU 2017-12, In February 2018, the FASB issued ASU 2018-02,

SECURITIES (Tables)

SECURITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Amortized Cost Basis and Fair Value of Available for Sale and Held-to-Maturity Securities	The following table presents a summary of the amortized cost, gross unrealized holding gains and losses and fair value of securities available for sale and securities held to maturity for the periods indicated. Gross unrealized holding gains and losses on available-for-sale December 31, 2017 December 31, 2016 Amortized Gross Gross Amortized Gross Gross Cost Unrealized Unrealized Fair Cost Unrealized Unrealized Fair Basis Gains Losses Value Basis Gains Losses Value Available for sale securities: Corporate debt securities $ 16,975 $ 24 $ (78 ) $ 16,921 $ 22,051 $ 147 $ (150 ) $ 22,048 $ 16,975 $ 24 $ (78 ) $ 16,921 $ 22,051 $ 147 $ (150 ) $ 22,048 Held to maturity securities: U.S. government sponsored mortgage-backed securities $ 142,383 $ 145 $ (2,089 ) $ 140,439 $ 112,543 $ 306 $ (1,289 ) $ 111,560 Corporate debt securities 17,707 239 — 17,946 17,654 251 — 17,905 $ 160,090 $ 384 $ (2,089 ) $ 158,385 $ 130,197 $ 557 $ (1,289 ) $ 129,465
Amortized Cost Basis and Estimated Fair Value of Debt Securities by Contractual Maturity	The amortized cost and estimated fair value of debt securities by contractual maturity at December 31, 2017 is as follows. Expected maturities will differ from contractual maturities because issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Available-for-Sale Held-to-Maturity Amortized Fair Amortized Fair Cost Basis Value Cost Basis Value Due within one year $ 12,753 $ 12,777 $ 7,003 $ 7,019 Due after one year through five years 4,222 4,144 12,747 12,918 Due after five years through ten years — — 32,640 32,143 Due after ten years — — 107,700 106,305 $ 16,975 $ 16,921 $ 160,090 $ 158,385
Securities with Gross Unrealized Losses Aggregated by Investment Category and Length of Time	Information pertaining to securities with gross unrealized losses at December 31, 2017 and 2016, aggregated by investment category and length of time that individual securities have been in a continuous loss position, follows: Less than 12 Months 12 Months and Over # of Fair Unrealized Fair Unrealized Holdings Value Losses Value Losses December 31, 2017: Available-for-sale Corporate debt securities 1 $ — $ — $ 4,144 $ (78 ) Held-to-maturity U.S. government sponsored mortgage-backed securities 81 64,056 (718 ) 62,798 (1,371 ) Total temporarily impaired securities 82 $ 64,056 $ (718 ) $ 66,942 $ (1,449 ) December 31, 2016: Available-for-sale Corporate debt securities 1 $ 4,130 $ (150 ) $ — $ — Held-to-maturity U.S. government sponsored mortgage-backed securities 57 77,474 (1,097 ) 6,518 (192 ) Total temporarily impaired securities 58 $ 81,604 $ (1,247 ) $ 6,518 $ (192 )

LOANS, ALLOWANCE FOR LOAN LOS34

LOANS, ALLOWANCE FOR LOAN LOSSES AND CREDIT QUALITY (Tables)	12 Months Ended
	Dec. 31, 2017
Summary of Loans	A summary of the balances of loans follows: December 31, 2017 2016 Mortgage loans on real estate: Residential one-to-four $ 1,333,058 $ 997,336 Commercial real estate 642,072 491,838 Home equity lines of credit 178,624 167,465 Construction 53,045 89,003 Total real estate loans 2,206,799 1,745,642 Other loans: Commercial 63,722 63,404 Indirect auto 30,227 60,240 Consumer 435 439 94,384 124,083 Total loans 2,301,183 1,869,725 Net deferred loan costs 3,426 3,622 Net unamortized mortgage premiums 8,661 6,273 Allowance for loan losses (16,312 ) (13,585 ) Total loans, net $ 2,296,958 $ 1,866,035
Activity in Allowance for Loan Losses by Portfolio Class and Balances of Allowance for Loan Losses and Recorded Investment in Loans by Portfolio Class	The following tables present the activity in the allowance for loan losses for the years ended December 31, 2017, 2016 and 2015 and the balances of the allowance for loan losses and recorded investment in loans by portfolio class based on impairment method at December 31, 2017 and 2016. The recorded investment in loans in any of the following tables does not include accrued and unpaid interest or any deferred loan fees or costs, as amounts are not significant. Year Ended December 31, 2017 Beginning Provision Charge-offs Recoveries Ending Balance Residential one-to-four $ 4,828 $ 1,572 $ — $ — $ 6,400 Commercial real estate 4,885 1,698 — — 6,583 Construction 1,219 (455 ) — — 764 Commercial 728 30 — — 758 Home equity lines of credit 1,037 (90 ) — — 947 Indirect auto 362 (109 ) (45 ) 22 230 Consumer 9 12 (14 ) 2 9 Unallocated 517 104 — — 621 Total $ 13,585 $ 2,762 $ (59 ) $ 24 $ 16,312 Year Ended December 31, 2016 Beginning Provision Charge-offs Recoveries Ending Balance Residential one-to-four $ 3,574 $ 1,254 $ — $ — $ 4,828 Commercial real estate 4,478 407 — — 4,885 Construction 801 418 — — 1,219 Commercial 613 115 — — 728 Home equity lines of credit 928 109 — — 1,037 Indirect auto 623 (232 ) (85 ) 56 362 Consumer 10 10 (16 ) 5 9 Unallocated 213 304 — — 517 Total $ 11,240 $ 2,385 $ (101 ) $ 61 $ 13,585 Year Ended December 31, 2015 Beginning Provision Charge-offs Recoveries Ending Balance Residential one-to-four $ 2,364 $ 1,274 $ (64 ) $ — $ 3,574 Commercial real estate 4,043 435 — — 4,478 Construction 228 573 — — 801 Commercial 458 131 — 24 613 Home equity lines of credit 828 (99 ) — 199 928 Indirect auto 778 (48 ) (139 ) 32 623 Consumer 11 9 (16 ) 6 10 Unallocated 171 42 — — 213 Total $ 8,881 $ 2,317 $ (219 ) $ 261 $ 11,240 Year Ended December 31, 2017 Individually evaluated for impairment Collectively evaluated for impairment Total Loan Balance Allowance Loan Balance Allowance Loan Balance Allowance Residential one-to-four $ 2,688 $ 147 $ 1,330,370 $ 6,253 $ 1,333,058 $ 6,400 Commercial real estate 2,877 — 639,195 6,583 642,072 6,583 Construction — — 53,045 764 53,045 764 Commercial — — 63,722 758 63,722 758 Home equity lines of credit — — 178,624 947 178,624 947 Indirect auto 4 — 30,223 230 30,227 230 Consumer — — 435 9 435 9 Unallocated — — — 621 — 621 Total $ 5,569 $ 147 $ 2,295,614 $ 16,165 $ 2,301,183 $ 16,312 Year Ended December 31, 2016 Individually evaluated for impairment Collectively evaluated for impairment Total Loan Balance Allowance Loan Balance Allowance Loan Balance Allowance Residential one-to-four $ 2,896 $ 154 $ 994,440 $ 4,674 $ 997,336 $ 4,828 Commercial real estate 3,364 — 488,474 4,885 491,838 4,885 Construction — — 89,003 1,219 89,003 1,219 Commercial — — 63,404 728 63,404 728 Home equity lines of credit 200 — 167,265 1,037 167,465 1,037 Indirect auto 15 — 60,225 362 60,240 362 Consumer — — 439 9 439 9 Unallocated — — — 517 — 517 Total $ 6,475 $ 154 $ 1,863,250 $ 13,431 $ 1,869,725 $ 13,585
Information about Loans that Meet Definition of Impaired Loan	Information about loans that meet the definition of an impaired loan in ASC 310-10-35 Impaired loans with a related allowance for credit losses at December 31, 2017 Unpaid Related Recorded Principal Allowance For Investment Balance Credit Losses Residential one-to-four $ 725 $ 725 $ 147 Totals $ 725 $ 725 $ 147 Impaired loans with no related allowance for credit losses at December 31, 2017 Unpaid Related Recorded Principal Allowance For Investment Balance Credit Losses Residential one-to-four $ 1,963 $ 2,052 $ — Commercial real estate 2,877 2,877 — Indirect auto 4 4 — Totals $ 4,844 $ 4,933 $ — Impaired loans with a related allowance for credit losses at December 31, 2016 Unpaid Related Recorded Principal Allowance For Investment Balance Credit Losses Residential one-to-four $ 740 $ 740 $ 154 Totals $ 740 $ 740 $ 154 Impaired loans with no related allowance for credit losses at December 31, 2016 Unpaid Related Recorded Principal Allowance For Investment Balance Credit Losses Residential one-to-four $ 2,156 $ 2,278 $ — Commercial real estate 3,364 3,364 — Home equity lines of credit 200 200 — Indirect auto 15 15 — Totals $ 5,735 $ 5,857 $ —
Information regarding Interest Income Recognized on Impaired Loans	The following tables set forth information regarding interest income recognized on impaired loans, by portfolio, for the periods indicated. Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Average Interest Average Interest Average Interest Recorded Income Recorded Income Recorded Income With an allowance recorded Investment Recognized Investment Recognized Investment Recognized Residential one-to-four $ 897 $ 32 $ 1,273 $ 33 $ 1,265 $ 33 Commercial real estate — — 3,124 136 3,230 123 Totals $ 897 $ 32 $ 4,397 $ 169 $ 4,495 $ 156 Year Ended December 31, 2017 Year Ended December 31, 2016 Year Ended December 31, 2015 Average Interest Average Interest Average Interest Recorded Income Recorded Income Recorded Income Without an allowance recorded Investment Recognized Investment Recognized Investment Recognized Residential one-to-four $ 1,986 $ 94 $ 2,977 $ 78 $ 4,296 $ 95 Commercial real estate 3,159 140 784 34 744 30 Home equity lines of credit 106 13 200 8 286 8 Indirect auto 6 — 12 — 8 — Totals $ 5,257 $ 247 $ 3,973 $ 120 $ 5,334 $ 133
Summary of Past Due and Non-Accrual Loans	The following is a summary of past due and non-accrual December 31, 2017 30–59 Days 60–89 Days 90 Days Total 90 days Loans on Non-accrual Real estate loans: Residential one-to-four $ 711 $ — $ 260 $ 971 $ — $ 1,372 Home equity lines of credit 716 — — 716 — — Other loans: Indirect auto 347 30 4 381 — 4 $ 1,774 $ 30 $ 264 $ 2,068 $ — $ 1,376 December 31, 2016 30–59 Days 60–89 Days 90 Days Total 90 days or Loans on Non-accrual Real estate loans: Residential one-to-four $ — $ — $ 497 $ 497 $ — $ 1,804 Home equity lines of credit 57 486 — 543 — — Other loans: Indirect auto 460 106 15 581 — 15 $ 517 $ 592 $ 512 $ 1,621 $ — $ 1,819
Company's Loans by Risk Rating	The following table presents the Company’s loans by risk rating at December 31, 2017 and 2016. There were no loans rated as 6 (“doubtful”) or 7 (“loss”) at the dates indicated. December 31, 2017 Loans rated 1-3.5 Loans rated 4 Loans rated 5 Loans not rated (A) Total Residential one-to-four $ — $ 344 $ 2,060 $ 1,330,654 $ 1,333,058 Commercial real estate 638,254 — 3,818 — 642,072 Construction 53,045 — — — 53,045 Commercial 63,682 40 — — 63,722 Home equity lines of credit — — 772 177,852 178,624 Indirect auto — — — 30,227 30,227 Consumer — — — 435 435 Total $ 754,981 $ 384 $ 6,650 $ 1,539,168 $ 2,301,183 December 31, 2016 Loans rated 1-3.5 Loans rated 4 Loans rated 5 Loans not rated (A) Total Residential one-to-four $ — $ 351 $ 2,509 $ 994,476 $ 997,336 Commercial real estate 471,491 16,032 4,315 — 491,838 Construction 89,003 — — — 89,003 Commercial 63,404 — — — 63,404 Home equity lines of credit — — 799 166,666 167,465 Indirect auto — — — 60,240 60,240 Consumer — — — 439 439 Total $ 623,898 $ 16,383 $ 7,623 $ 1,221,821 $ 1,869,725 (A) Residential one-to-four
Trouble Debt Restructuring Accrual Status	The following table shows the Company’s total TDRs and other pertinent information as of the dates indicated: December 31, 2017 December 31, 2016 TDRs on Accrual Status $ 4,194 $ 4,656 TDRs on Non-accrual 645 1,442 Total TDRs $ 4,839 $ 6,098 Amount of specific allocation included in the allowance for loan losses associated with TDRs $ 147 $ 154 Additional commitments to lend to a borrower who has been a party to a TDR $ — $ —
Troubled Debt Restructurings on Financing Receivables	The following table shows the TDR modifications which occurred during the the years ended December 31, 2017 and 2016 and the outstanding recorded investment subsequent to the modifications occurring: Year Ended Pre-modification Post-modification # of outstanding outstanding Contracts recorded investment recorded investment (a) Real estate loans: Commercial real estate 1 $ 273 $ 273 1 $ 273 $ 273 Year Ended Pre-modification Post-modification # of outstanding outstanding Contracts recorded investment recorded investment (a) Real estate loans: Residential one-to-four 1 $ 621 $ 699 Commercial real estate 3 3,394 3,394 4 $ 4,015 $ 4,093 (a) The post-modification balances represent the balance of the loan on the date of modifications. These amounts may show an increase when modifications include a capitalization of interest or taxes.
Post Modification of Troubled Debt Restructuring Balance	The following table shows the Company’s post-modification balance of TDRs listed by type of modification during the years indicated: For the years ended December 31, 2017 December 31, 2016 Capitalization of interest, taxes and extended maturity $ — $ 699 Extended maturity 273 3,394 Total $ 273 $ 4,093
Modified and subsequently defaulted
Post Modification of Troubled Debt Restructuring Balance	The following table shows the loans that have been modified during the past twelve months which have subsequently defaulted during the periods indicated: For the years ended December 31, 2017 2016 2015 Number Recorded Number Recorded Number Recorded of Contracts Investment of Contracts Investment of Contracts Investment TDRs that subsequently defaulted Residential one-to-four — $ — 1 $ 497 — $ — Totals — $ — 1 $ 497 — $ —

TRANSFERS AND SERVICING (Tables

TRANSFERS AND SERVICING (Tables)	12 Months Ended
	Dec. 31, 2017
Changes in Mortgage Servicing Rights	Changes in mortgage servicing rights, which are included in other assets, were as follows: Years Ended December 31, 2017 2016 2015 Balance at beginning of period $ 403 $ 479 $ 476 Capitalization 508 85 99 Amortization (130 ) (101 ) (93 ) Valuation allowance adjustment 74 (60 ) (3 ) Balance at end of period $ 855 $ 403 $ 479

PREMISES AND EQUIPMENT (Tables)

PREMISES AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2017
Summary of Cost and Accumulated Depreciation of Premises and Equipment	A summary of the cost and accumulated depreciation of premises and equipment follows: December 31, 2017 2016 Land $ 161 $ 161 Buildings 3,516 3,424 Leasehold improvements 1,414 1,399 Furniture and equipment 4,350 3,979 9,441 8,963 Accumulated depreciation (7,187 ) (6,608 ) $ 2,254 $ 2,355

DEPOSITS (Tables)

DEPOSITS (Tables)	12 Months Ended
	Dec. 31, 2017
Scheduled Maturities of Time Deposits	At December 31, 2017, the scheduled maturities of time deposits are as follows: 2018 $ 226,910 2019 94,797 2020 129,044 2021 42,587 2022 11,376 $ 504,714

LONG-TERM BORROWINGS (Tables)

LONG-TERM BORROWINGS (Tables)	12 Months Ended
	Dec. 31, 2017
Federal Home Loan Bank Advances
Schedule of Maturities of Long-Term Debt	Long-term debt at December 31, 2017 and 2016 consists of the following fixed rate FHLB advances: Amount Weighted Average Rate 2017 2016 2017 2016 Fixed rate advances maturing: 2017 $ — $ 35,000 — % 1.14 % 2018 47,000 47,000 1.63 % 1.63 % 2019 225,250 225,250 1.49 % 1.49 % 2020 35,000 20,000 1.76 % 1.75 % 2021 15,000 — 2.03 % — % 2022 95,000 — 2.17 % — % 2031 — 50,000 — % 0.39 % $ 417,250 $ 377,250 1.70 % 1.34 %

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2017
Allocation of Federal and State Income Taxes between Current and Deferred Portions	Allocation of federal and state income taxes between current and deferred portions is as follows: Years Ended December 31, 2017 2016 2015 Current tax provision: Federal $ 7,386 $ 7,212 $ 4,223 State 1,961 1,954 1,120 9,347 9,166 5,343 Deferred tax expense (benefit): Federal (71 ) (1,391 ) (799 ) State (20 ) (350 ) (222 ) Effect of change in statutory federal tax rate 2,626 — — 2,535 (1,741 ) (1,021 ) Total provision for income taxes $ 11,882 $ 7,425 $ 4,322
Summary of Reasons for Differences between Statutory Income Tax Rate and Effective Tax Rate	The reasons for the differences between the statutory federal income tax rate and the effective tax rates are summarized as follows: Years Ended December 31, 2017 2016 2015 Statutory federal tax rate 35.0 % 35.0 % 34.0 % Increase (decrease) resulting from: State taxes, net of federal tax benefit 4.8 5.4 5.3 Bank-owned life insurance (1.5 ) (1.9 ) (2.7 ) Tax exempt income (0.6 ) (0.8 ) (0.3 ) Change in statutory federal tax rate 10.0 — — Share based compensation (3.5 ) 1.2 1.9 Other, net 1.0 (0.6 ) 0.3 Effective tax rates 45.2 % 38.3 % 38.5 %
Components of Net Deferred Tax Assets	The components of the net deferred tax asset are as follows: December 31, 2017 2016 Deferred tax assets: Employee benefit and deferred compensation plans $ 2,375 $ 3,827 Allowance for loan losses 4,596 5,577 Accrued rent 8 10 Interest on non-performing 34 50 Stock options 356 547 Unrealized loss on securities available for sale 15 1 ESOP 92 116 Gross deferred tax assets 7,476 10,128 Deferred tax liabilities: Mortgage servicing rights (240 ) (164 ) Deferred loan origination costs (860 ) (1,104 ) Restricted stock awards (280 ) (140 ) Depreciation (201 ) (305 ) Unrecognized retirement benefit (58 ) (72 ) Other (43 ) (22 ) Gross deferred tax liabilities (1,682 ) (1,807 ) Net deferred tax asset $ 5,794 $ 8,321

OFF-BALANCE SHEET ARRANGEMENTS

OFF-BALANCE SHEET ARRANGEMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Financial Instruments Outstanding whose Contract Amounts Represent Credit Risk	At December 31, 2017 and 2016, the following financial instruments were outstanding whose contract amounts represent credit risk: Contract Amount 2017 2016 Commitments to grant loans $ 23,702 $ 44,677 Unfunded commitments under lines of credit 325,768 259,124 Unadvanced portion of construction loans 11,486 36,555 Standby letters of credit 561 658 Commitments to purchase loans 65,692 62,036

COMMITMENTS AND CONTINGENT LI41

COMMITMENTS AND CONTINGENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Future Minimum Rent Commitments under Operating Leases	Pursuant to the terms of noncancelable lease agreements in effect at December 31, 2017, pertaining to banking premises and equipment, future minimum rent commitments under various operating leases are as follows: 2018 $ 361 2019 359 2020 266 2021 122 2022 122 Thereafter 122 $ 1,352

MINIMUM REGULATORY CAPITAL RE42

MINIMUM REGULATORY CAPITAL REQUIREMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Actual Capital Amounts and Ratio	The following table presents actual and required capital ratios as of December 31, 2017 and December 31, 2016 for the Company and the Bank under the Basel III Capital Rules. The minimum required capital amounts presented include the minimum required capital levels as of December 31, 2017 and December 31, 2016 based on the phase-in phased-in. Actual Minimum Capital Minimum Capital Required Basel III Phase-In Schedule Minimum Capital Required Minimum To Be Well Amount Ratio Amount Ratio Amount Ratio Amount Ratio Amount Ratio As of December 31, 2017: Total Capital (to Risk Weighted Assets) Consolidated $ 194,287 11.30 % $ 137,498 8.00 % $ 158,982 9.25 % $ 180,466 10.50 % N/A N/A Belmont Savings Bank 189,311 11.01 % 137,497 8.00 % 158,981 9.25 % 180,465 10.50 % $ 171,871 10.00 % Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 177,939 10.35 % $ 103,123 6.00 % $ 124,607 7.25 % $ 146,092 8.50 % N/A N/A Belmont Savings Bank 172,963 10.06 % 103,123 6.00 % 124,607 7.25 % 146,091 8.50 % $ 137,497 8.00 % Common Equity Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 177,939 10.35 % $ 77,343 4.50 % $ 98,827 5.75 % $ 120,311 7.00 % N/A N/A Belmont Savings Bank 172,963 10.06 % 77,342 4.50 % 98,826 5.75 % 120,310 7.00 % $ 111,716 6.50 % Tier 1 Capital (to Average Assets) Consolidated $ 177,939 6.97 % $ 102,148 4.00 % $ 102,148 4.00 % $ 102,148 4.00 % N/A N/A Belmont Savings Bank 172,963 6.77 % 102,147 4.00 % 102,147 4.00 % 102,147 4.00 % $ 127,683 5.00 % Actual Minimum Capital Minimum Capital Required Basel III Phase-In Schedule Minimum Capital Required Minimum To Be Well Amount Ratio Amount Ratio Amount Ratio Amount Ratio Amount Ratio As of December 31, 2016: Total Capital (to Risk Weighted Assets) Consolidated $ 174,465 11.72 % $ 119,116 8.00 % $ 128,422 8.625 % $ 156,340 10.50 % N/A N/A Belmont Savings Bank 169,499 11.38 % 119,114 8.00 % 128,420 8.625 % 156,337 10.50 % $ 148,893 10.00 % Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 160,817 10.80 % $ 89,337 6.00 % $ 98,643 6.625 % $ 126,561 8.50 % N/A N/A Belmont Savings Bank 155,851 10.47 % 89,336 6.00 % 98,641 6.625 % 126,559 8.50 % $ 119,114 8.00 % Common Equity Tier 1 Capital (to Risk Weighted Assets) Consolidated $ 160,817 10.80 % $ 67,003 4.50 % $ 76,309 5.125 % $ 104,227 7.00 % N/A N/A Belmont Savings Bank 155,851 10.47 % 67,002 4.50 % 76,308 5.125 % 104,225 7.00 % $ 96,780 6.50 % Tier 1 Capital (to Average Assets) Consolidated $ 160,817 7.63 % $ 84,253 4.00 % $ 84,253 4.00 % $ 84,253 4.00 % N/A N/A Belmont Savings Bank 155,851 7.40 % 84,251 4.00 % 84,251 4.00 % 84,251 4.00 % $ 105,314 5.00 %

EMPLOYEE BENEFIT PLANS (Tables)

EMPLOYEE BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2017
Information Pertaining to Activity in Plan	Information pertaining to the activity in the plan is as follows: Years Ended December 31, 2017 2016 Change in benefit obligation: Benefit obligation at beginning of year $ 1,521 $ 1,316 Service cost 253 261 Interest cost 66 57 Actuarial gain (42 ) (113 ) Benefit obligation at end of year 1,798 1,521 Funded status at end of year $ (1,798 ) $ (1,521 ) Accrued pension benefit $ (2,003 ) $ (1,696 ) Accumulated benefit obligation $ 1,175 $ 985
Components of Net Periodic Pension Cost	The components of net periodic pension cost are as follows: December 31, 2017 2016 Service cost $ 253 $ 261 Interest cost 66 57 Amortization of gain (19 ) — Amortization of prior service cost 6 6 Net periodic cost $ 306 $ 324
Other Changes in Benefit Obligations Recognized in Other Comprehensive Loss	Other changes in benefit obligations recognized in other comprehensive loss are as follows: December 31, 2017 2016 Amortization of prior service cost $ (6 ) $ (6 ) Amortization of unrecognized gain 19 — Net actuarial gain (42 ) (112 ) Total recognized in other comprehensive loss $ (29 ) $ (118 )
Amounts Recognized in Accumulated Other Comprehensive Income, before Tax Effects	Amounts recognized in accumulated other comprehensive income, before tax effects, consist of the following: December 31, 2017 2016 Unrecognized prior service cost $ 40 $ 46 Unrecognized net gain (245 ) (222 ) $ (205 ) $ (176 )
Estimated Future Benefit Payments	Estimated future benefit payments, which reflect expected future service, as appropriate, are as follows: Year Ending December 31, Amount 2018 $ — 2019 57 2020 191 2021 267 2022 267 Years 2023-2027 1,565
Schedule of Employee Stock Ownership Plan (ESOP) Disclosures	At December 31, 2017, the remaining principal balance on the ESOP debt is payable as follows: Years Ending December 31, Amount 2018 $ 96 2019 100 2020 104 2021 110 2022 115 Thereafter 3,444 $ 3,969 Shares held by the ESOP include the following: December 31, 2017 2016 Unallocated 363,091 378,379 Allocated 84,813 72,598 447,904 450,977
Defined Benefit Obligations
Schedule of Assumptions Used	The assumptions used to determine the benefit obligation are as follows: December 31, 2017 2016 Discount rate 3.80 % 4.35 % Rate of compensation increase 3.00 % 3.00 %
Net Periodic Benefit Costs
Schedule of Assumptions Used	The assumptions used to determine net periodic pension cost are as follows: December 31, 2017 2016 Discount rate 4.35 % 4.30 % Rate of compensation increase 3.00 % 3.00 %

STOCK BASED COMPENSATION (Table

STOCK BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2017
Cumulatively Granted Restricted Stock Awards Net of Forfeitures	The following table presents the amount of cumulatively granted restricted stock awards, net of forfeitures, through December 31, 2017 under the BSB Bancorp, Inc. 2017 Equity Incentive Plan: Authorized Authorized Cumulative Granted Net of Forfeitures Outstanding Stock Restricted Authorized Stock Restricted 2012 Equity Incentive Plan 917,286 366,914 1,284,200 889,092 363,570 1,252,662 2017 Equity Incentive Plan — 487,200 487,200 — 483,302 483,302
Pre-Tax Expense Associated with Stock Option and Restricted Stock Awards and Related Tax Benefits Recognized	The following table presents the pre-tax For the year ended December 31, 2017 2016 2015 Stock based compensation expense Stock options $ 724 $ 780 $ 791 Restricted stock awards 1,835 869 869 Total stock based award expense $ 2,559 $ 1,649 $ 1,660 Related tax benefits recognized in earnings $ 874 $ 492 $ 481
Summary of Stock Option	The following table presents relevant information relating to the Company’s stock options for the periods indicated: For the year ended December 31, 2017 2016 2015 Weighted average grant date fair value of options granted $ — $ 4.63 $ 3.90 Intrinsic value of stock options exercised 3,299 368 226 Cash paid to settle equity instruments granted under stock based compensation arrangements — — —
Compensation Cost Related to Non-Vested Awards not Yet Recognized and Weighted Average Recognition Period	Total compensation cost related to non-vested As of December 31, 2017 Amount Weighted Stock options $ 136 2.36 Restricted stock 10,574 9.19 Total $ 10,710
Fair Value of Stock Options Granted Estimate on Date of Grant Using Black-Scholes Option-Pricing Model	Date of grant 3/1/2016 2/25/2015 2/11/2015 Options granted 27,500 5,414 7,828 Exercise price $ 22.31 $ 18.83 $ 18.78 Vesting period (1) 5 years 5 years 5 years Expiration date 3/1/2026 2/25/2025 2/11/2025 Expected volatility 16.13 % 15.51 % 15.52 % Expected term 6.5 years 6.5 years 6.5 years Expected dividend yield 0 % 0 % 0 % Risk free interest rate 1.54 % 1.70 % 1.76 % Fair value $ 4.63 $ 3.89 $ 3.91 (1)- Vesting is ratably and the period begins on the date of grant.
Summary of Stock Option and Restricted Stock Awards	A summary of the status of the Company’s Stock Option and Restricted Stock Awards for the year ended December 31, 2017 is presented in the tables below: Outstanding Stock option Weighted average Weighted average Aggregate Balance at January 1, 2017 804,484 $ 12.68 Granted — — Exercised (213,962 ) 12.17 Forfeited — — Balance at December 31, 2017 590,522 $ 12.86 5.17 $ 9,676 Exercisable 543,763 $ 12.31 5.00 $ 9,209 Non-vested Weighted average Balance at January 1, 2017 73,429 $ 12.22 Granted 487,200 27.10 Vested (71,829 ) 12.10 Forfeited (3,898 ) 27.10 Balance at December 31, 2017 484,902 $ 27.07

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2017
Components of Earning Per Share	Earnings per share consisted of the following components for the years ended December 31, 2017, 2016 and 2015: December 31, December 31, December 31, Net income $ 14,386 $ 11,981 $ 6,914 Undistributed earnings attributable to participating securities (108 ) (190 ) (167 ) Net income available to common stockholders $ 14,278 $ 11,791 $ 6,747 Weighted average shares outstanding, basic 8,754,393 8,571,861 8,465,177 Effect of dilutive shares 429,400 286,030 217,813 Weighted average shares outstanding, assuming dilution 9,183,793 8,857,891 8,682,990 Basic EPS $ 1.63 $ 1.38 $ 0.80 Effect of dilutive shares (0.08 ) (0.05 ) (0.02 ) Diluted EPS $ 1.55 $ 1.33 $ 0.78

FAIR VALUES OF ASSETS AND LIA46

FAIR VALUES OF ASSETS AND LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Summary of Financial Assets Measured at Fair Value on Recurring Basis	The following table summarizes financial assets measured at fair value on a recurring basis as of December 31, 2017 and 2016, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value: Level 1 Level 2 Level 3 Total At December 31, 2017 Securities available for sale Corporate debt securities $ — $ 16,921 $ — $ 16,921 Trading securities Rabbi Trust 2,808 — — 2,808 Totals $ 2,808 $ 16,921 $ — $ 19,729 Level 1 Level 2 Level 3 Total At December 31, 2016 Securities available for sale Corporate debt securities $ — $ 22,048 $ — $ 22,048 Trading securities Rabbi Trust 2,606 — — 2,606 Totals $ 2,606 $ 22,048 $ — $ 24,654
Schedule of Estimated Fair Values and Related Carrying or Notional Amounts of Financial Instruments	The estimated fair values, and related carrying or notional amounts, of the Company’s financial instruments are as follows: December 31, 2017 Carrying Fair Amount Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 110,888 $ 110,888 $ 110,888 $ — $ — Interest-bearing time deposits with other banks 2,440 2,440 — 2,440 — Held-to-maturity 160,090 158,385 — 158,385 — Federal Home Loan Bank stock 32,382 32,382 — 32,382 — Bank owned life insurance 36,967 36,967 — 36,967 Loans, net 2,296,958 2,251,971 — — 2,251,971 Accrued interest receivable 6,344 6,344 6,344 — — Financial liabilities: Deposits 1,751,251 1,748,995 1,246,537 502,458 — Federal Home Loan Bank advances 723,150 719,430 — 719,430 — Securities sold under agreements to repurchase 3,268 3,268 — 3,268 — Accrued interest payable 1,594 1,594 1,594 — — Mortgagors’ escrow accounts 4,690 4,690 — 4,690 — December 31, 2016 Carrying Fair Amount Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 58,876 $ 58,876 $ 58,876 $ — $ — Interest-bearing time deposits with other banks 234 233 — 233 — Held-to-maturity 130,197 129,465 — 129,465 — Federal Home Loan Bank stock 25,071 25,071 — 25,071 — Bank owned life insurance 35,842 35,842 — 35,842 Loans, net 1,866,035 1,837,068 — — 1,837,068 Accrued interest receivable 4,635 4,635 4,635 — — Financial liabilities: Deposits 1,469,422 1,469,906 1,133,821 336,085 — Federal Home Loan Bank advances 508,850 507,773 — 507,773 — Securities sold under agreements to repurchase 1,985 1,985 — 1,985 — Accrued interest payable 1,023 1,023 1,023 — — Mortgagors’ escrow accounts 3,341 3,341 — 3,341 —
Non-financial Assets
Non Financial Assets Remeasured and Reported at Lower of Cost or Fair Value	The following tables present the non-financial re-measured December 31, 2017 Level 1 Level 2 Level 3 Mortgage servicing rights $ — $ — $ 855 Totals $ — $ — $ 855 December 31, 2016 Level 1 Level 2 Level 3 Mortgage servicing rights $ — $ — $ 403 Totals $ — $ — $ 403

OTHER COMPREHENSIVE (LOSS) IN47

OTHER COMPREHENSIVE (LOSS) INCOME (Tables)	12 Months Ended
	Dec. 31, 2017
Schedules of Other Comprehensive (Loss) Income	The following table presents a reconciliation of the changes in the components of other comprehensive (loss) income for the dates indicated, including the amount of income tax benefit (expense) allocated to each component of other comprehensive (loss) income: Year Ended December 31, 2017 Pre Tax Tax Benefit After Tax Amount (Expense) Amount Securities available-for-sale: Change in fair value of securities available for sale $ (13 ) $ 5 $ (8 ) Reclassification adjustment for net gains included in net income 1 (38 ) 15 (23 ) Net change in fair value of securities available for sale (51 ) 20 (31 ) Defined benefit post-retirement benefit plans: Change in the actuarial gain/loss 42 (17 ) 25 Reclassification adjustment included in net income 2 (13 ) 5 (8 ) Net change defined-benefit post-retirement benefit plans 29 (12 ) 17 Total other comprehensive loss $ (22 ) $ 8 $ (14 ) Year Ended December 31, 2016 Pre Tax Tax After Tax Amount Expense Amount Securities available-for-sale: Change in fair value of securities available for sale $ 247 $ (98 ) $ 149 Net change in fair value of securities available for sale 247 (98 ) 149 Defined benefit post-retirement benefit plans: Change in the actuarial gain/loss 112 (46 ) 66 Reclassification adjustment included in net income 2 6 (2 ) 4 Net change defined-benefit post-retirement benefit plans 118 (48 ) 70 Total other comprehensive income $ 365 $ (146 ) $ 219 Year Ended December 31, 2015 Pre Tax Tax Benefit After Tax Amount (Expense) Amount Securities available-for-sale: Change in fair value of securities available for sale $ (130 ) $ 52 $ (78 ) Net change in fair value of securities available for sale (130 ) 52 (78 ) Defined benefit post-retirement benefit plans: Change in the actuarial gain/loss (33 ) 13 (20 ) Reclassification adjustment included in net income 2 6 (2 ) 4 Net change defined-benefit post-retirement benefit plans (27 ) 11 (16 ) Total other comprehensive loss $ (157 ) $ 63 $ (94 ) 1- Reclassification adjustments are comprised of realized security gains. The gains have been reclassified out of accumulated other comprehensive income and have affected certain lines in the consolidated statements of operations as follows; the pre-tax 2- Reclassification adjustments are comprised of amortization of prior service cost and unrecognized gain and have been reclassified out of accumulated other comprehensive income (loss). The amounts affected certain lines in the consolidated statements of operations as follows: amortization of prior service cost and unrecognized gain is included in salaries and employee benefits expense. The tax expense amount is included in income tax expense and the after tax amount is included in net income.
Components of Accumulated Other Comprehensive Income, included in Stockholders' Equity	The components of accumulated other comprehensive income, included in stockholders’ equity, are as follows: December 31, 2017 December 31, 2016 Net unrealized holding loss on available-for-sale $ (32 ) $ (1 ) Unrecognized benefit pertaining to defined benefit plan, net of tax 121 104 Accumulated other comprehensive income $ 89 $ 103

CONDENSED FINANCIAL STATEMENT48

CONDENSED FINANCIAL STATEMENTS OF PARENT COMPANY (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Balance Sheets	The following condensed financial statements are for the Parent Company only and should be read in conjunction with the consolidated financial statements of the Company. Condensed Balance Sheets December 31, 2017 2016 Assets Cash and cash equivalents held at Belmont Savings Bank $ 919 $ 519 Investment in Belmont Savings Bank 173,054 155,955 Investment in BSB Funding Corp. 4,065 4,436 Other assets 45 62 Total assets $ 178,083 $ 160,972 Liabilities and Stockholders’ Equity Accrued expenses $ 38 $ 37 Other liabilities 16 14 Total liabilities 54 51 Stockholders’ equity 178,029 160,921 Total liabilities and stockholders’ equity $ 178,083 $ 160,972
Condensed Statements of Operations	Condensed Statements of Operations Years Ended December 31, 2017 2016 2015 Interest and dividend income: Interest on cash equivalents $ — $ — $ 1 Dividends from subsidiaries — — — Total interest and dividend income — — 1 Interest expense — — — Net interest and dividend income — — 1 Non-interest — — — Non-interest 230 219 242 Loss before income taxes and equity in undistributed earnings of subsidiaries (230 ) (219 ) (241 ) Income tax benefit (94 ) (89 ) (96 ) Loss before equity in income of subsidiaries (136 ) (130 ) (145 ) Equity in undistributed earnings of Belmont Savings Bank 14,432 12,025 6,976 Equity in undistributed earnings of BSB Funding Corp 90 86 83 Net income $ 14,386 $ 11,981 $ 6,914
Condensed Statements of Cash Flows	Condensed Statements of Cash Flows Years Ended December 31, 2017 2016 2015 Cash flows from operating activities: Net income $ 14,386 $ 11,981 $ 6,914 Adjustments to reconcile net income to net cash (used in) provided by operating activities: Equity in undistributed earnings of Belmont Savings Bank (14,432 ) (12,025 ) (6,976 ) Equity in undistributed earnings of BSB Funding Corp. (90 ) (86 ) (83 ) Deferred income tax expense — — 190 Other, net 26 (27 ) 720 Net cash (used in) provided by operating activities (110 ) (157 ) 765 Cash flows from investing activities: Return of capital from BSB Funding Corp. 460 — 600 Investment in Belmont Savings Bank — — (3,800 ) Net cash provided by (used in) investing activities 460 — (3,200 ) Cash flows from financing activities: Proceeds from exercise of stock options, net of cash paid 50 298 228 Restricted stock awards issued, net of awards surrendered — (118 ) (51 ) Net cash provided by financing activities 50 180 177 Net increase (decrease) in cash and cash equivalents 400 23 (2,258 ) Cash and cash equivalents at beginning of period 519 496 2,754 Cash and cash equivalents at end of period $ 919 $ 519 $ 496

QUARTERLY DATA (UNAUDITED) (Tab

QUARTERLY DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Results of Operations	Quarterly results of operations are as follows: Years Ended December 31, 2017 2016 Fourth Third Second First Fourth Third Second First Quarter Quarter Quarter Quarter Quarter Quarter Quarter Quarter Interest and dividend income $ 21,114 $ 19,758 $ 18,764 $ 17,506 $ 16,291 $ 15,726 $ 15,164 $ 14,439 Interest expense 6,414 5,579 4,816 4,245 3,918 3,699 3,457 3,158 Net interest income 14,700 14,179 13,948 13,261 12,373 12,027 11,707 11,281 Provision for loan losses 691 535 707 829 601 443 741 599 Net interest income, after provision for loan losses 14,009 13,644 13,241 12,432 11,772 11,584 10,966 10,682 Non-interest 1,117 885 995 630 703 680 705 660 Non-interest 7,636 7,929 7,645 7,476 7,045 7,066 6,984 7,252 Income before taxes 7,490 6,600 6,591 5,586 5,430 5,198 4,687 4,090 Income tax expense 5,382 2,001 2,579 1,920 2,120 2,018 1,735 1,551 Net income $ 2,108 $ 4,599 $ 4,012 $ 3,666 $ 3,310 $ 3,180 $ 2,952 $ 2,539 Earnings per common share Basic $ 0.24 $ 0.52 $ 0.45 $ 0.42 $ 0.38 $ 0.36 $ 0.34 $ 0.29 Diluted $ 0.23 $ 0.50 $ 0.43 $ 0.40 $ 0.37 $ 0.35 $ 0.33 $ 0.28

Summary of Significant Accoun50

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2011
Significant Accounting Policies [Line Items]
Stock issued, shares				8,993,000
Stock issued, price per share				$ 10
Gross proceeds				$ 89,900,000
Shares sold to the Bank's employee stock ownership plan				458,643
Due days of accrual of interest on all loans	90 days
Originate loans with a loan-to-value	80.00%
Excess tax benefits from stock-based compensation		$ 329,000	$ 215,000
ASU 2016-09
Significant Accounting Policies [Line Items]
Excess tax benefits from stock-based compensation	$ 1,300,000
Maximum
Significant Accounting Policies [Line Items]
Insured amount for per account deposit by Bank Insurance Fund	$ 250,000
Life insurance policy with individual carrier as a percentage of tier one capital	15.00%
Total cash surrender value of life insurance policies as a percentage of tier one capital	25.00%
Reserve for Off-balance Sheet Activities
Significant Accounting Policies [Line Items]
Reserve for unfunded loan commitments	$ 36,000	$ 63,000
Belmont Savings Bank
Significant Accounting Policies [Line Items]
Stock issued, shares				179,860
Cash contribution to charity				$ 200,000

Restrictions on Cash and Amou51

Restrictions on Cash and Amounts due From Banks - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents subject to withdrawals and usage restrictions	$ 25,218,000	$ 23,450,000

Amortized Cost Basis of Availab

Amortized Cost Basis of Available for Sale and Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 16,975	$ 22,051
Available-for-sale Securities, Gross Unrealized Gains	24	147
Available-for-sale Securities, Gross Unrealized Losses	(78)	(150)
Available-for-sale Securities, Fair Value	16,921	22,048
Held-to-maturity securities, Amortized Cost Basis	160,090	130,197
Held-to-maturity securities, Gross Unrealized Gains	384	557
Held-to-maturity securities, Gross Unrealized Losses	(2,089)	(1,289)
Held-to-maturity securities, Fair Value	158,385	129,465
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	16,975	22,051
Available-for-sale Securities, Gross Unrealized Gains	24	147
Available-for-sale Securities, Gross Unrealized Losses	(78)	(150)
Available-for-sale Securities, Fair Value	16,921	22,048
Held-to-maturity securities, Amortized Cost Basis	17,707	17,654
Held-to-maturity securities, Gross Unrealized Gains	239	251
Held-to-maturity securities, Fair Value	17,946	17,905
U.S. government sponsored mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity securities, Amortized Cost Basis	142,383	112,543
Held-to-maturity securities, Gross Unrealized Gains	145	306
Held-to-maturity securities, Gross Unrealized Losses	(2,089)	(1,289)
Held-to-maturity securities, Fair Value	$ 140,439	$ 111,560

Amortized Cost Basis and Estima

Amortized Cost Basis and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Due within one year, Available-for-sale Securities, Amortized Cost Basis	$ 12,753
Due after one year through five years, Available-for-sale Securities, Amortized Cost Basis	4,222
Due after five years through ten years, Available-for-sale Securities, Amortized Cost Basis	0
Due after ten years, Available-for-sale Securities, Amortized Cost Basis	0
Available-for-sale Securities, Amortized Cost Basis	16,975	$ 22,051
Due within one year, Available-for-sale Securities, Fair Value	12,777
Due after one year through five years, Available-for-sale Securities, Fair Value	4,144
Due after five years through ten years, Available-for-sale Securities, Fair Value	0
Due after ten years, Available-for-sale Securities, Fair Value	0
Available-for-sale Securities, Fair Value	16,921	22,048
Due within one year, Held-to-Maturity, Amortized Cost Basis	7,003
Due after one year through five years, Held-to-Maturity, Amortized Cost Basis	12,747
Due after five years through ten years, Held-to-Maturity, Amortized Cost Basis	32,640
Due after ten years, Held-to-Maturity, Amortized Cost Basis	107,700
Held-to-maturity securities, Amortized Cost Basis	160,090	130,197
Due within one year, Held-to-Maturity, Fair Value	7,019
Due after one year through five years, Held-to-Maturity, Fair Value	12,918
Due after five years through ten years, Held-to-Maturity, Fair Value	32,143
Due after ten years, Held-to-Maturity, Fair Value	106,305
Held-to-Maturity, Fair Value	$ 158,385	$ 129,465

Securities - Additional Informa

Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017USD ($)Entity	Dec. 31, 2016USD ($)Entity	Dec. 31, 2015USD ($)
Investment Securities [Line Items]
Securities pledged to secure securities sold under agreements to repurchase	$ 5,582,000	$ 4,721,000
Securities pledged to secure borrowings with Federal Home Loan Bank	47,666,000	37,561,000
Securities pledged to secure available line of credit with Federal Home Loan Bank	15,780,000	15,739,000
Proceeds from sales of available-for-sale securities	5,038,000	$ 0	$ 0
Realized gains of investments	$ 38,000
Number of securities that had unrealized losses | Entity	82	58
Securities that had unrealized losses, aggregate depreciation percentage	1.63%
Rabbi Trust
Investment Securities [Line Items]
Trading securities, fair value	$ 2,808,000	$ 2,606,000
Trading securities, unrealized holding gain (loss)	$ 159,000	$ 36,000

Securities with Gross Unrealize

Securities with Gross Unrealized Losses Aggregated by Investment Category and Length of Time (Detail) $ in Thousands	Dec. 31, 2017USD ($)Entity	Dec. 31, 2016USD ($)Entity
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Number of Holdings | Entity	82	58
Less than 12 Months, Fair Value	$ 64,056	$ 81,604
Less than 12 Months, Unrealized Losses	(718)	(1,247)
12 Months or longer, Fair Value	66,942	6,518
12 Months or longer, Unrealized Losses	$ (1,449)	$ (192)
Corporate debt securities
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Number of Holdings | Entity	1	1
Available-for-sale, Less than 12 Months, Fair Value		$ 4,130
Available-for-sale, Less than 12 Months, Unrealized Losses		$ (150)
Available-for-sale, 12 Months or longer, Fair Value	$ 4,144
Available-for-sale, 12 Months or longer, Unrealized Losses	$ (78)
U.S. government sponsored mortgage-backed securities
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Number of Holdings | Entity	81	57
Held-to-maturity, Less than 12 Months, Fair Value	$ 64,056	$ 77,474
Held-to-maturity, Less than 12 Months, Unrealized Losses	(718)	(1,097)
Held-to-maturity, 12 Months or longer, Fair Value	62,798	6,518
Held-to-maturity, 12 Months or longer, Unrealized Losses	$ (1,371)	$ (192)

Summary of Loans (Detail)

Summary of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	$ 2,301,183	$ 1,869,725
Net deferred loan costs	3,426	3,622
Net unamortized mortgage premiums	8,661	6,273
Allowance for loan losses	(16,312)	(13,585)	$ (11,240)	$ (8,881)
Total loans, net	2,296,958	1,866,035
Mortgage Loan Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	2,206,799	1,745,642
Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	1,333,058	997,336
Allowance for loan losses	(6,400)	(4,828)	(3,574)	(2,364)
Mortgage Loan Portfolio Segment | Real Estate Loan | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	642,072	491,838
Allowance for loan losses	(6,583)	(4,885)	(4,478)	(4,043)
Mortgage Loan Portfolio Segment | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	178,624	167,465
Allowance for loan losses	(947)	(1,037)	(928)	(828)
Mortgage Loan Portfolio Segment | Construction loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	53,045	89,003
Allowance for loan losses	(764)	(1,219)	(801)	(228)
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	63,722	63,404
Allowance for loan losses	(758)	(728)	(613)	(458)
Consumer Portfolio Segment | Indirect auto loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	30,227	60,240
Allowance for loan losses	(230)	(362)	(623)	(778)
Consumer Portfolio Segment | Other Consumer Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	435	439
Allowance for loan losses	(9)	(9)	$ (10)	$ (11)
Commercial and Consumer Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans Balance	$ 94,384	$ 124,083

Allowance for Loan Losses by Po

Allowance for Loan Losses by Portfolio Class (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				$ 13,585				$ 11,240	$ 13,585	$ 11,240	$ 8,881
Provision (Benefit)	$ 691	$ 535	$ 707	829	$ 601	$ 443	$ 741	599	2,762	2,385	2,317
Charge-offs									(59)	(101)	(219)
Recoveries									24	61	261
Ending Balance	16,312				13,585				16,312	13,585	11,240
Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				4,828				3,574	4,828	3,574	2,364
Provision (Benefit)									1,572	1,254	1,274
Charge-offs											(64)
Ending Balance	6,400				4,828				6,400	4,828	3,574
Mortgage Loan Portfolio Segment | Real Estate Loan | Commercial real estate loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				4,885				4,478	4,885	4,478	4,043
Provision (Benefit)									1,698	407	435
Ending Balance	6,583				4,885				6,583	4,885	4,478
Mortgage Loan Portfolio Segment | Construction loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				1,219				801	1,219	801	228
Provision (Benefit)									(455)	418	573
Ending Balance	764				1,219				764	1,219	801
Mortgage Loan Portfolio Segment | Home equity lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				1,037				928	1,037	928	828
Provision (Benefit)									(90)	109	(99)
Recoveries											199
Ending Balance	947				1,037				947	1,037	928
Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				728				613	728	613	458
Provision (Benefit)									30	115	131
Recoveries											24
Ending Balance	758				728				758	728	613
Consumer Portfolio Segment | Indirect auto loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				362				623	362	623	778
Provision (Benefit)									(109)	(232)	(48)
Charge-offs									(45)	(85)	(139)
Recoveries									22	56	32
Ending Balance	230				362				230	362	623
Consumer Portfolio Segment | Other Consumer Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				9				10	9	10	11
Provision (Benefit)									12	10	9
Charge-offs									(14)	(16)	(16)
Recoveries									2	5	6
Ending Balance	9				9				9	9	10
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning Balance				$ 517				$ 213	517	213	171
Provision (Benefit)									104	304	42
Ending Balance	$ 621				$ 517				$ 621	$ 517	$ 213

Individually Impaired Loans by

Individually Impaired Loans by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment, Loan Balance	$ 5,569	$ 6,475
Individually evaluated for impairment, Loan allowance	147	154
Collectively evaluated for impairment, Loan Balance	2,295,614	1,863,250
Collectively evaluated for impairment, Loan allowance	16,165	13,431
Total Loan Balance	2,301,183	1,869,725
Total Loan, allowance	16,312	13,585	$ 11,240	$ 8,881
Mortgage Loan Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loan Balance	2,206,799	1,745,642
Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment, Loan Balance	2,688	2,896
Individually evaluated for impairment, Loan allowance	147	154
Collectively evaluated for impairment, Loan Balance	1,330,370	994,440
Collectively evaluated for impairment, Loan allowance	6,253	4,674
Total Loan Balance	1,333,058	997,336
Total Loan, allowance	6,400	4,828	3,574	2,364
Mortgage Loan Portfolio Segment | Real Estate Loan | Commercial real estate loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment, Loan Balance	2,877	3,364
Collectively evaluated for impairment, Loan Balance	639,195	488,474
Collectively evaluated for impairment, Loan allowance	6,583	4,885
Total Loan Balance	642,072	491,838
Total Loan, allowance	6,583	4,885	4,478	4,043
Mortgage Loan Portfolio Segment | Construction loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment, Loan Balance	53,045	89,003
Collectively evaluated for impairment, Loan allowance	764	1,219
Total Loan Balance	53,045	89,003
Total Loan, allowance	764	1,219	801	228
Mortgage Loan Portfolio Segment | Home equity lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment, Loan Balance		200
Collectively evaluated for impairment, Loan Balance	178,624	167,265
Collectively evaluated for impairment, Loan allowance	947	1,037
Total Loan Balance	178,624	167,465
Total Loan, allowance	947	1,037	928	828
Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment, Loan Balance	63,722	63,404
Collectively evaluated for impairment, Loan allowance	758	728
Total Loan Balance	63,722	63,404
Total Loan, allowance	758	728	613	458
Consumer Portfolio Segment | Indirect auto loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment, Loan Balance	4	15
Collectively evaluated for impairment, Loan Balance	30,223	60,225
Collectively evaluated for impairment, Loan allowance	230	362
Total Loan Balance	30,227	60,240
Total Loan, allowance	230	362	623	778
Consumer Portfolio Segment | Other Consumer Loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment, Loan Balance	435	439
Collectively evaluated for impairment, Loan allowance	9	9
Total Loan Balance	435	439
Total Loan, allowance	9	9	10	11
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment, Loan allowance	621	517
Total Loan, allowance	$ 621	$ 517	$ 213	$ 171

Impaired Loans (Detail)

Impaired Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired loans with a related allowance for credit losses, Recorded Investment	$ 725	$ 740
Impaired loans with a related allowance for credit losses at, Unpaid Principal Balance	725	740
Impaired loans with a related allowance for credit losses at, Specific Allowance	147	154
Impaired loans with no related allowance for credit losses, Recorded Investment	4,844	5,735
Impaired loans with no related allowance for credit losses, Unpaid Principal Balance	4,933	5,857
Impaired loans with no related allowance for credit losses at, Specific Allowance	0	0
Impaired loans with a related allowance for credit losses, Average recorded Investment	897	4,397	$ 4,495
Impaired loans with a related allowance for credit losses, Interest income recognized	32	169	156
Impaired loans with no related allowance for credit losses, Average recorded Investment	5,257	3,973	5,334
Impaired loans with no related allowance for credit losses, Interest income recognized	247	120	133
Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired loans with a related allowance for credit losses, Recorded Investment	725	740
Impaired loans with a related allowance for credit losses at, Unpaid Principal Balance	725	740
Impaired loans with a related allowance for credit losses at, Specific Allowance	147	154
Impaired loans with no related allowance for credit losses, Recorded Investment	1,963	2,156
Impaired loans with no related allowance for credit losses, Unpaid Principal Balance	2,052	2,278
Impaired loans with no related allowance for credit losses at, Specific Allowance	0	0
Impaired loans with a related allowance for credit losses, Average recorded Investment	897	1,273	1,265
Impaired loans with a related allowance for credit losses, Interest income recognized	32	33	33
Impaired loans with no related allowance for credit losses, Average recorded Investment	1,986	2,977	4,296
Impaired loans with no related allowance for credit losses, Interest income recognized	94	78	95
Mortgage Loan Portfolio Segment | Real Estate Loan | Commercial real estate loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired loans with no related allowance for credit losses, Recorded Investment	2,877	3,364
Impaired loans with no related allowance for credit losses, Unpaid Principal Balance	2,877	3,364
Impaired loans with no related allowance for credit losses at, Specific Allowance	0	0
Impaired loans with a related allowance for credit losses, Average recorded Investment		3,124	3,230
Impaired loans with a related allowance for credit losses, Interest income recognized		136	123
Impaired loans with no related allowance for credit losses, Average recorded Investment	3,159	784	744
Impaired loans with no related allowance for credit losses, Interest income recognized	140	34	30
Mortgage Loan Portfolio Segment | Home equity lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired loans with no related allowance for credit losses, Recorded Investment		200
Impaired loans with no related allowance for credit losses, Unpaid Principal Balance		200
Impaired loans with no related allowance for credit losses at, Specific Allowance		0
Impaired loans with no related allowance for credit losses, Average recorded Investment	106	200	286
Impaired loans with no related allowance for credit losses, Interest income recognized	13	8	8
Consumer Portfolio Segment | Indirect auto loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Impaired loans with no related allowance for credit losses, Recorded Investment	4	15
Impaired loans with no related allowance for credit losses, Unpaid Principal Balance	4	15
Impaired loans with no related allowance for credit losses at, Specific Allowance	0	0
Impaired loans with no related allowance for credit losses, Average recorded Investment	$ 6	$ 12	$ 8

Past Due and Non-Accrual Loans

Past Due and Non-Accrual Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	$ 2,068	$ 1,621
90 days or more and accruing	0	0
Loans on Non-accrual	1,376	1,819
Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	971	497
90 days or more and accruing	0	0
Loans on Non-accrual	1,372	1,804
Mortgage Loan Portfolio Segment | Home equity lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	716	543
90 days or more and accruing	0	0
Consumer Portfolio Segment | Indirect auto loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	381	581
90 days or more and accruing	0	0
Loans on Non-accrual	4	15
30-59 Days
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	1,774	517
30-59 Days | Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	711
30-59 Days | Mortgage Loan Portfolio Segment | Home equity lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	716	57
30-59 Days | Consumer Portfolio Segment | Indirect auto loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	347	460
60-89 Days
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	30	592
60-89 Days | Mortgage Loan Portfolio Segment | Home equity lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due		486
60-89 Days | Consumer Portfolio Segment | Indirect auto loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	30	106
Loans 90 Days Or More Past Due
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	264	512
Loans 90 Days Or More Past Due | Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	260	497
Loans 90 Days Or More Past Due | Consumer Portfolio Segment | Indirect auto loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Days Past Due	$ 4	$ 15

Loans Classified by Risk Rating

Loans Classified by Risk Rating (Detail) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		$ 2,301,183	$ 1,869,725
Mortgage Loan Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		2,206,799	1,745,642
Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		1,333,058	997,336
Mortgage Loan Portfolio Segment | Real Estate Loan | Commercial real estate loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		642,072	491,838
Mortgage Loan Portfolio Segment | Construction loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		53,045	89,003
Mortgage Loan Portfolio Segment | Home equity lines of credit
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		178,624	167,465
Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		63,722	63,404
Consumer Portfolio Segment | Indirect auto loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		30,227	60,240
Consumer Portfolio Segment | Other Consumer Loan
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		435	439
Loans rated 1-3.5
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		754,981	623,898
Loans rated 1-3.5 | Mortgage Loan Portfolio Segment | Real Estate Loan | Commercial real estate loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		638,254	471,491
Loans rated 1-3.5 | Mortgage Loan Portfolio Segment | Construction loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		53,045	89,003
Loans rated 1-3.5 | Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		63,682	63,404
Loans rated 4
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		384	16,383
Loans rated 4 | Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		344	351
Loans rated 4 | Mortgage Loan Portfolio Segment | Real Estate Loan | Commercial real estate loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance			16,032
Loans rated 4 | Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		40
Loans rated 5
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		6,650	7,623
Loans rated 5 | Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		2,060	2,509
Loans rated 5 | Mortgage Loan Portfolio Segment | Real Estate Loan | Commercial real estate loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		3,818	4,315
Loans rated 5 | Mortgage Loan Portfolio Segment | Home equity lines of credit
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance		772	799
Loans not rated
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance	[1]	1,539,168	1,221,821
Loans not rated | Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance	[1]	1,330,654	994,476
Loans not rated | Mortgage Loan Portfolio Segment | Home equity lines of credit
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance	[1]	177,852	166,666
Loans not rated | Consumer Portfolio Segment | Indirect auto loans
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance	[1]	30,227	60,240
Loans not rated | Consumer Portfolio Segment | Other Consumer Loan
Financing Receivable, Recorded Investment [Line Items]
Total Loans Balance	[1]	$ 435	$ 439
[1]	Residential one-to-four family, home equity lines of credit, indirect auto and consumer loans are not formally risk rated by the Company unless the loans become delinquent.

Loans, Allowance for Loan Los62

Loans, Allowance for Loan Losses and Credit Quality - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Contract	Dec. 31, 2016USD ($)Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged to secure FHLB advances	$ 1,400,000	$ 1,100,000
Financing Receivable Troubled Debt Restructurings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of financing receivables modified by troubled debt restructurings | Contract	0	4
Residential one-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Consumer mortgage loans in the process of foreclosure amount	$ 0	$ 497

Troubled Debt Restructuring Acc

Troubled Debt Restructuring Accrual Status (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total TDRs	$ 4,839	$ 6,098
Amount of specific allocation included in the allowance for loan losses associated with TDRs	147	154
Additional commitments to lend to a borrower who has been a party to a TDR	0	0
Accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total TDRs	4,194	4,656
Non-accrual Loans
Financing Receivable, Recorded Investment [Line Items]
Total TDRs	$ 645	$ 1,442

Troubled Debt Restructurings on

Troubled Debt Restructurings on Financing Receivables (Detail) $ in Thousands		12 Months Ended
		Dec. 31, 2017USD ($)Contract	Dec. 31, 2016USD ($)Contract
Financing Receivable, Modifications [Line Items]
Post-modification outstanding recorded investment		$ 273	$ 4,093
Mortgage Loan Portfolio Segment | Real Estate Loan
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract		1	4
Pre-modification outstanding recorded investment		$ 273	$ 4,015
Post-modification outstanding recorded investment	[1]	$ 273	$ 4,093
Mortgage Loan Portfolio Segment | Real Estate Loan | Commercial real estate loans
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract		1	3
Pre-modification outstanding recorded investment		$ 273	$ 3,394
Post-modification outstanding recorded investment	[1]	$ 273	$ 3,394
Mortgage Loan Portfolio Segment | Real Estate Loan | Residential one-to-four family
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract			1
Pre-modification outstanding recorded investment			$ 621
Post-modification outstanding recorded investment	[1]		$ 699
[1]	The post-modification balances represent the balance of the loan on the date of modifications. These amounts may show an increase when modifications include a capitalization of interest or taxes.

Post Modification of Troubled D

Post Modification of Troubled Debt Restructuring Balance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Post-modification outstanding recorded investment	$ 273	$ 4,093
Capitalization of interest, taxes and extended maturity
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Post-modification outstanding recorded investment		699
Extended Maturity
Troubled Debt Restructuring, Debtor, Subsequent Periods [Line Items]
Post-modification outstanding recorded investment	$ 273	$ 3,394

Summary of Loans Modified and S

Summary of Loans Modified and Subsequently Defaulted (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Contract	Dec. 31, 2016USD ($)Contract	Dec. 31, 2015Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	1	0
Recorded Investment | $	$ 0	$ 497
Residential one-to-four family
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	1	0
Recorded Investment | $	$ 0	$ 497

Transfers and Servicing - Addit

Transfers and Servicing - Additional Information (Detail)	Mar. 16, 2006USD ($)Loan	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Principal balance of loans sold to another financial institution	$ 10,500,000
Number of loans sold to another financial institution | Loan	17
Initial period for repurchase of loan		120 months
Repurchase Agreement		Loan that became 90 days past due
Indirect auto loans
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Proceed from sale of loans		$ 0	$ 0	$ 3,500,000
Gains from sale of loans				28,000
Loans previously sold and serviced		10,500,000	28,200,000
Residential Mortgage
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Proceed from sale of loans		70,500,000	11,400,000	19,100,000
Gains from sale of loans		936,000	271,000	$ 367,000
Loans previously sold and serviced		114,500,000	59,800,000
Transferred Loans
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Total principal balance of loans		$ 0	$ 0

Changes in Mortgage Servicing R

Changes in Mortgage Servicing Rights (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Servicing Asset at Amortized Cost [Line Items]
Balance at beginning of period	$ 403	$ 479	$ 476
Capitalization	508	85	99
Amortization	(130)	(101)	(93)
Valuation allowance adjustment	74	(60)	(3)
Balance at end of period	$ 855	$ 403	$ 479

Summary of Cost and Accumulated

Summary of Cost and Accumulated Depreciation of Premises and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Land	$ 161	$ 161
Buildings	3,516	3,424
Leasehold improvements	1,414	1,399
Furniture and equipment	4,350	3,979
Property, Plant and Equipment, Gross, Total	9,441	8,963
Accumulated depreciation	(7,187)	(6,608)
Premises and equipment, net	$ 2,254	$ 2,355

Premises and Equipment - Additi

Premises and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 595,000	$ 621,000	$ 726,000
Assets impairment charges	$ 18,000	16,000	$ 6,000
Assets cost		3,500,000
Gain loss on disposal of assets		$ 0

Deposits - Additional Informati

Deposits - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Time Deposits [Line Items]
Aggregate amount of time deposits	$ 128,700	$ 74,400
Brokered deposits included in time deposits	247,200	156,400
Overdraft deposits reclassified to loans	48	36
Letter of credit outstanding	5,000	0
Directors, Executive Officers and Affiliates
Time Deposits [Line Items]
Deposit accounts	$ 8,500	$ 11,000

Scheduled Maturities of Time De

Scheduled Maturities of Time Deposits (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Time Deposits [Line Items]
2,018	$ 226,910
2,019	94,797
2,020	129,044
2,021	42,587
2,022	11,376
Time Deposits Total	$ 504,714

Short-Term Borrowings - Additio

Short-Term Borrowings - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Federal Home Loan Bank advances, short-term	$ 305,900	$ 131,600
Federal Home Loan Bank advances weighted average interest rate, short term	1.52%	0.79%
Federal Home Loan Bank advances, available line of credit	$ 5,600	$ 5,600
Federal Home Loan Bank advances, unused remaining available borrowing capacity	279,200	289,700
Securities sold under agreements to repurchase	$ 3,268	$ 1,985
Securities sold under agreements to repurchase, weighted average interest rate	0.15%	0.15%

Long-Term Debt Consisting FHLB

Long-Term Debt Consisting FHLB Advances (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
2,017	$ 47,000	$ 35,000
2,018	225,250	47,000
2,019	35,000	225,250
2,020	15,000	20,000
2,021	95,000
2,022		0
2,031	0
2,031		50,000
Long-term Federal Home Loan Bank Advances, Total	$ 417,250	$ 377,250
2,017	1.63%	1.14%
2,018	1.49%	1.63%
2,019	1.76%	1.49%
2,020	2.03%	1.75%
2,021	2.17%
2,022		0.00%
2,031	0.00%
2,031		0.39%
Federal Home Loan Bank, Advances, Maturities Summary, Average Interest Rate	1.70%	1.34%

Long-Term Borrowings - Addition

Long-Term Borrowings - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017
Federal Home Loan Bank, Advances [Line Items]
Federal home loan bank, advances		$ 0
Federal home loan bank, advances, interest rate		0.00%
Federal Home Loan Bank, Advances, Callable Option
Federal Home Loan Bank, Advances [Line Items]
Federal home loan bank, advances	$ 50,000
Federal home loan bank, advances, interest rate	0.39%
Federal home loan bank, advances, callable date	Sep. 12, 2017

Allocation of Federal and State

Allocation of Federal and State Income Taxes Between Current and Deferred Portions (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components Of Income Tax Expense Benefit [Line Items]
Federal									$ 7,386	$ 7,212	$ 4,223
State									1,961	1,954	1,120
Total current tax provision									9,347	9,166	5,343
Federal									(71)	(1,391)	(799)
State									(20)	(350)	(222)
Effect of change in statutory federal tax rate									2,626
Total deferred tax benefit									2,535	(1,741)	(1,021)
Total provision for income taxes	$ 5,382	$ 2,001	$ 2,579	$ 1,920	$ 2,120	$ 2,018	$ 1,735	$ 1,551	$ 11,882	$ 7,425	$ 4,322

Summary of Reasons for differen

Summary of Reasons for differences Between Statutory Income Tax Rate and Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Effective Tax Rates [Line Items]
Statutory federal tax rate	35.00%	35.00%	34.00%
State taxes, net of federal tax benefit	4.80%	5.40%	5.30%
Bank-owned life insurance	(1.50%)	(1.90%)	(2.70%)
Tax exempt income	(0.60%)	(0.80%)	(0.30%)
Change in statutory federal tax rate	10.00%
Share based compensation	(3.50%)	1.20%	1.90%
Other, net	1.00%	(0.60%)	0.30%
Effective tax rates	45.20%	38.30%	38.50%

Components of Net Deferred Tax

Components of Net Deferred Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Deferred Tax Assets and Liabilities [Line Items]
Employee benefit and deferred compensation plans	$ 2,375	$ 3,827
Allowance for loan losses	4,596	5,577
Accrued rent	8	10
Interest on non-performing loans	34	50
Stock options	356	547
Unrealized loss on securities available for sale	15	1
ESOP	92	116
Gross deferred tax assets	7,476	10,128
Mortgage servicing rights	(240)	(164)
Deferred loan origination costs	(860)	(1,104)
Restricted stock awards	(280)	(140)
Depreciation	(201)	(305)
Unrecognized retirement benefit	(58)	(72)
Other	(43)	(22)
Gross deferred tax liabilities	(1,682)	(1,807)
Net deferred tax asset	$ 5,794	$ 8,321

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
Retained earnings which federal and state income taxes have not been provided		$ 3,600	$ 3,600
Period for recapture in taxable income if no longer qualifies as a bank		4 years
Federal and state tax rate applicable if no longer qualifies as a bank		28.00%
Statutory federal tax rate		35.00%	35.00%	34.00%
Charge recorded within income tax expense		$ 2,626
Scenario Plan
Income Tax [Line Items]
Statutory federal tax rate	21.00%

Financial Instruments Outstandi

Financial Instruments Outstanding whose Contract Amounts Represent Credit Risk (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Commitments to Grant Loans
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance-sheet risk	$ 23,702	$ 44,677
Unfunded Commitments under Line Of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance-sheet risk	325,768	259,124
Unfunded Commitments for Construction Loans
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance-sheet risk	11,486	36,555
Standby Letters of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance-sheet risk	561	658
Loan Purchase Commitments
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off-balance-sheet risk	$ 65,692	$ 62,036

Off-Balance Sheet Arrangement81

Off-Balance Sheet Arrangements - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Letters of credit issued expiration period	1 year

Future Minimum Rent Commitments

Future Minimum Rent Commitments under Operating Leases (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Leases Future Minimum Payments [Line Items]
2,018	$ 361
2,019	359
2,020	266
2,021	122
2,022	122
Thereafter	122
Total	$ 1,352

Commitments and Contingent Li83

Commitments and Contingent Liabilities - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Line Items]
Total rent expense	$ 363	$ 384	$ 398
Minimum
Commitments and Contingencies Disclosure [Line Items]
Operating lease, optional renewal period	1 year
Maximum
Commitments and Contingencies Disclosure [Line Items]
Operating lease, optional renewal period	10 years

Minimum Regulatory Capital Re84

Minimum Regulatory Capital Requirements - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer, phased period	4 years
Stock repurchase plan, number of shares repurchased	0	0	0
January 1, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer, risk-weighted assets ratio	0.625%
January 1, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer, risk-weighted assets ratio	2.50%
Two Thousand Nineteen | Scenario, Forecast
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 capital risk-weighted assets				4.50%
Minimum leverage ratio				4.00%
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Ratio				6.00%
Total Capital to Risk Weighted Assets, Minimum For Capital Adequacy Purposes Ratio				8.00%
Capital conservation buffer, risk-weighted assets ratio				2.50%
Maximum
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Active stock repurchase plan to repurchase	500,000	500,000
Basel III
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 capital risk-weighted assets	4.50%
Total capital to risk weighted assets	8.00%
Basel III | Minimum
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 capital to risk weighted assets	4.00%
Minimum leverage ratio	4.00%
Basel III | Maximum
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 capital to risk weighted assets	6.00%
Fully Phased In | Two Thousand Nineteen | Scenario, Forecast
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 capital risk-weighted assets				7.00%
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Ratio				8.50%
Total Capital to Risk Weighted Assets, Minimum For Capital Adequacy Purposes Ratio				10.50%

Actual Capital Amounts and Rati

Actual Capital Amounts and Ratios (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Consolidated
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets, Actual Amount	$ 194,287	$ 174,465
Total Capital to Risk Weighted Assets, Actual Ratio	11.30%	11.72%
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 137,498	$ 119,116
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	8.00%	8.00%
Tier 1 Capital to Risk Weighted Assets, Actual Amount	$ 177,939	$ 160,817
Tier 1 Capital to Risk Weighted Assets, Actual Ratio	10.35%	10.80%
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 103,123	$ 89,337
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	6.00%	6.00%
Common Equity Tier 1 Capital to Risk Weighted Assets, Actual Amount	$ 177,939	$ 160,817
Common Equity Tier 1 Capital to Risk Weighted Assets, Actual Ratio	10.35%	10.80%
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 77,343	$ 67,003
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Ratio	4.50%	4.50%
Belmont Savings Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets, Actual Amount	$ 189,311	$ 169,499
Total Capital to Risk Weighted Assets, Actual Ratio	11.01%	11.38%
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 137,497	$ 119,114
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	8.00%	8.00%
Total Capital to Risk Weighted Assets, Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 171,871	$ 148,893
Total Capital to Risk Weighted Assets, Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	10.00%	10.00%
Tier 1 Capital to Risk Weighted Assets, Actual Amount	$ 172,963	$ 155,851
Tier 1 Capital to Risk Weighted Assets, Actual Ratio	10.06%	10.47%
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 103,123	$ 89,336
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	6.00%	6.00%
Tier 1 Capital to Risk Weighted Assets, Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 137,497	$ 119,114
Tier 1 Capital to Risk Weighted Assets, Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	8.00%	8.00%
Common Equity Tier 1 Capital to Risk Weighted Assets, Actual Amount	$ 172,963	$ 155,851
Common Equity Tier 1 Capital to Risk Weighted Assets, Actual Ratio	10.06%	10.47%
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 77,342	$ 67,002
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Ratio	4.50%	4.50%
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 111,716	$ 96,780
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	6.50%	6.50%
Consolidated
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital to Average Assets, Actual Amount	$ 177,939	$ 160,817
Tier 1 Capital to Average Assets, Actual Ratio	6.97%	7.63%
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Amount	$ 102,148	$ 84,253
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	4.00%	4.00%
Belmont Savings Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital to Average Assets, Actual Amount	$ 172,963	$ 155,851
Tier 1 Capital to Average Assets, Actual Ratio	6.77%	7.40%
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Amount	$ 102,147	$ 84,251
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	4.00%	4.00%
Tier 1 Capital to Average Assets, Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 127,683	$ 105,314
Tier 1 Capital to Average Assets, Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	5.00%	5.00%
Basel III Phase-In Schedule | Consolidated
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 158,982	$ 128,422
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	9.25%	8.625%
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 124,607	$ 98,643
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	7.25%	6.625%
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 98,827	$ 76,309
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Ratio	5.75%	5.125%
Basel III Phase-In Schedule | Belmont Savings Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 158,981	$ 128,420
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	9.25%	8.625%
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 124,607	$ 98,641
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	7.25%	6.625%
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 98,826	$ 76,308
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Ratio	5.75%	5.125%
Basel III Phase-In Schedule | Consolidated
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Amount	$ 102,148	$ 84,253
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	4.00%	4.00%
Basel III Phase-In Schedule | Belmont Savings Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Amount	$ 102,147	$ 84,251
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	4.00%	4.00%
Basel III Fully Phased In | Consolidated
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 180,466	$ 156,340
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	10.50%	10.50%
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 146,092	$ 126,561
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	8.50%	8.50%
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 120,311	$ 104,227
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Ratio	7.00%	7.00%
Basel III Fully Phased In | Belmont Savings Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 180,465	$ 156,337
Total Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	10.50%	10.50%
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 146,091	$ 126,559
Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	8.50%	8.50%
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Amount	$ 120,310	$ 104,225
Common Equity Tier 1 Capital to Risk Weighted Assets, Minimum Capital Required For Capital Adequacy Ratio	7.00%	7.00%
Basel III Fully Phased In | Consolidated
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Amount	$ 102,148	$ 84,253
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	4.00%	4.00%
Basel III Fully Phased In | Belmont Savings Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Amount	$ 102,147	$ 84,251
Tier 1 Capital to Average Assets, Minimum Capital Required For Capital Adequacy Plus Capital Conservation Buffer Ratio	4.00%	4.00%

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2011	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate used to determine obligation	3.80%	4.35%
Net periodic cost	$ 306,000	$ 324,000
Projected rate of salary increase	3.00%	3.00%
Compensation expense recognized	$ 2,300,000	$ 2,000,000	$ 2,000,000
Percentage of eligible compensation of employee	75.00%
Contributions by the Company	$ 891,000	839,000	842,000
Percentage of deferred compensation vested	100.00%
ESOP, purchase shares				458,643
Common stock price per share	$ 10
Loan obtained by the ESOP, payable annually over	30 years
Loan Obtained By ESOP Rate Per Annum Equal To Prime Rate	3.75%
Fair value of unallocated shares	$ 10,600,000	11,000,000
Total compensation expense, Connection with ESOP	444,000	360,000	321,000
Deferred Compensation Plan | Rabbi Trust
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Recorded liability	$ 2,800,000	2,600,000
Scenario, Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated prior service benefit to be amortized from accumulated other comprehensive income					$ 6,000
Estimated unrecognized net gain to be amortized from accumulated other comprehensive income					$ 18,500
Executive Officers | Other Supplemental Retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefit upon termination of employment at or after age	55 years
Reduced benefits available prior to attaining age	55 years
Estimated liability	$ 2,600,000	$ 2,300,000
Discount rate used to determine obligation	3.80%	4.35%
Net periodic cost	$ 331,000	$ 233,000	254,000
Projected rate of salary increase	3.00%	3.00%
Executive Officers | Other Supplemental Retirement Plans | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of years of service to complete	10 years
Executive Officers | Other Supplemental Retirement Plans | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of years of service to complete	10 years
Executive Officers | Belmont Savings Bank Supplemental Executive Retirement Plan | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fully vested participants, years of service to complete	5 years
Executive Officers | Belmont Savings Bank Supplemental Executive Retirement Plan | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fully vested participants, years of service to complete	10 years
Directors
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated liability	$ 697,000	$ 661,000
Discount rate used to determine obligation	3.80%	4.35%
Directors | Other Supplemental Retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic cost	$ 64,000	$ 55,000	$ 17,000

Information Pertaining to Activ

Information Pertaining to Activity in Plan (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	$ 1,521	$ 1,316
Service cost	253	261
Interest cost	66	57
Actuarial gain	(42)	(113)
Benefit obligation at end of year	1,798	1,521
Funded status at end of year	(1,798)	(1,521)
Accrued pension benefit	(2,003)	(1,696)
Accumulated benefit obligation	$ 1,175	$ 985

Assumption used to Determine Be

Assumption used to Determine Benefit Obligation (Detail)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.80%	4.35%
Rate of compensation increase	3.00%	3.00%

Components of Net Periodic Pens

Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 253	$ 261
Interest cost	66	57
Amortization of gain	(19)
Amortization of prior service cost	6	6
Net periodic cost	$ 306	$ 324

Changes in Benefit Obligations

Changes in Benefit Obligations Recognized in Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost	$ (6)	$ (6)
Amortization of unrecognized gain	19
Net actuarial gain	(42)	(112)
Total recognized in other comprehensive loss	$ (29)	$ (118)

Assumptions Used to Determine N

Assumptions Used to Determine Net Periodic Pension Cost (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	4.35%	4.30%
Rate of compensation increase	3.00%	3.00%

Amounts Recognized in Accumulat

Amounts Recognized in Accumulated Other Comprehensive Income, before Tax Effects (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service cost	$ 40	$ 46
Unrecognized net gain	(245)	(222)
Total defined-benefit post-retirement benefit plans, Pre-Tax Amount	$ (205)	$ (176)

Estimated Future Benefit Paymen

Estimated Future Benefit Payments (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Defined Benefit Plan Disclosure [Line Items]
2,018	$ 0
2,019	57
2,020	191
2,021	267
2,022	267
Years 2023-2027	$ 1,565

Remaining Principal Balance on

Remaining Principal Balance on Employee Stock Ownership Plan Debt (Detail) - Employee Stock Ownership Plan $ in Thousands	Dec. 31, 2017USD ($)
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
2,018	$ 96
2,019	100
2,020	104
2,021	110
2,022	115
Thereafter	3,444
Total	$ 3,969

Shares Held by Employee Stock O

Shares Held by Employee Stock Ownership Plan ESOP (Detail) - shares	Dec. 31, 2017	Dec. 31, 2016
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
Unallocated	363,091	378,379
Allocated	84,813	72,598
Total	447,904	450,977

Stock Based Compensation - Addi

Stock Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Mar. 15, 2017	Feb. 08, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards granted			487,200
Restricted stock grant date price			$ 27.10
Fair value of shares vested			$ 2.2	$ 1.9	$ 1.6
2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Stock Awards		487,200	487,200
2017 Equity Incentive Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Stock Awards			487,200
Restricted stock awards granted	487,200
Restricted stock grant date price	$ 27.10
Vesting period of awards granted	10 years
Estimated forfeiture rate of awards granted	2.64%
2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Stock Awards			1,284,200
2012 Equity Incentive Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Stock Awards			366,914
Restricted stock awards granted	0

Cumulatively Granted Restricted

Cumulatively Granted Restricted Stock Awards Net of Forfeitures (Detail) - shares	Feb. 08, 2017	Dec. 31, 2017
2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Stock Awards		1,284,200
Cumulative Granted Net of Forfeitures		1,252,662
2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Stock Awards	487,200	487,200
Cumulative Granted Net of Forfeitures		483,302
Stock Options | 2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Stock Awards		917,286
Cumulative Granted Net of Forfeitures		889,092
Restricted Stock | 2012 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Stock Awards		366,914
Cumulative Granted Net of Forfeitures		363,570
Restricted Stock | 2017 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized Stock Awards		487,200
Cumulative Granted Net of Forfeitures		483,302

Pre-Tax Expense Associated with

Pre-Tax Expense Associated with Stock Option and Restricted Stock Awards and Related Tax Benefits Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock based compensation expense
Stock options	$ 724	$ 780	$ 791
Restricted stock awards	1,835	869	869
Total stock based award expense	2,559	1,649	1,660
Related tax benefits recognized in earnings	$ 874	$ 492	$ 481

Summary of Stock Option (Detail

Summary of Stock Option (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of options granted		$ 4.63	$ 3.90
Intrinsic value of stock options exercised	$ 3,299	$ 368	$ 226
Cash paid to settle equity instruments granted under stock based compensation arrangements	$ 0	$ 0	$ 0

Compensation Cost Related to No

Compensation Cost Related to Non-Vested Awards not Yet Recognized and Weighted Average Recognition Period (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total	$ 10,710
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, amount	$ 136
Restricted stock, weighted average period	2 years 4 months 9 days
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock, amount	$ 10,574
Restricted stock, weighted average period	9 years 2 months 8 days

Fair Value of Stock Options Gra

Fair Value of Stock Options Granted Estimate on Date of Grant Using Black-Scholes Option-Pricing Model (Detail)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted | shares	0
Date of grant 2016-03-01
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Date of grant	Mar. 1, 2016
Options granted | shares	27,500
Exercise price	$ 22.31
Vesting period	5 years	[1]
Expiration date	Mar. 1, 2026
Expected volatility	16.13%
Expected term	6 years 6 months
Expected dividend yield	0.00%
Risk free interest rate	1.54%
Fair value	$ 4.63
Date of grant 2015-02-25
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Date of grant	Feb. 25, 2015
Options granted | shares	5,414
Exercise price	$ 18.83
Vesting period	5 years	[1]
Expiration date	Feb. 25, 2025
Expected volatility	15.51%
Expected term	6 years 6 months
Expected dividend yield	0.00%
Risk free interest rate	1.70%
Fair value	$ 3.89
Date of grant 2015-02-11
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Date of grant	Feb. 11, 2015
Options granted | shares	7,828
Exercise price	$ 18.78
Vesting period	5 years	[1]
Expiration date	Feb. 11, 2025
Expected volatility	15.52%
Expected term	6 years 6 months
Expected dividend yield	0.00%
Risk free interest rate	1.76%
Fair value	$ 3.91
[1]	Vesting is ratably and the period begins on the date of grant.

Summary of Stock Option and Res

Summary of Stock Option and Restricted Stock Grants (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Stock option awards
Stock option awards, beginning balance | shares	804,484
Stock option awards, granted | shares	0
Stock option awards, exercised | shares	(213,962)
Stock option awards, forfeited | shares	0
Stock option awards, ending balance | shares	590,522
Stock option awards, Exercisable | shares	543,763
Weighted Average Exercise Price
Weighted average exercise price, Beginning Balance | $ / shares	$ 12.68
Weighted average exercise price, Granted | $ / shares	0
Weighted average exercise price, exercised | $ / shares	12.17
Weighted average exercise price, Forfeited | $ / shares	0
Weighted average exercise price, Ending balance | $ / shares	12.86
Weighted average exercise price, Exercisable | $ / shares	$ 12.31
Weighted average remaining contractual term
Weighted remaining contractual term, Ending balance	5 years 2 months 1 day
Weighted remaining contractual term, Exercisable	5 years
Aggregate intrinsic value
Aggregate intrinsic value, ending balance | $	$ 9,676
Aggregate intrinsic value, Exercisable | $	$ 9,209
Non-vested restricted stock awards
Non-vested restricted stock awards, Beginning balance | shares	73,429
Non-vested restricted stock awards, Granted | shares	487,200
Non-vested restricted stock awards, Vested | shares	(71,829)
Non-vested restricted stock awards, Forfeited | shares	(3,898)
Non-vested restricted stock awards, Ending balance | shares	484,902
Weighted Average Grant Price
Weighted Average Grant Price, Beginning balance | $ / shares	$ 12.22
Weighted Average Grant Price, Granted | $ / shares	27.10
Weighted Average Grant Price, Vested | $ / shares	12.10
Weighted Average Grant Price, Forfeited | $ / shares	27.10
Weighted Average Grant Price, Ending balance | $ / shares	$ 27.07

Earning Per Share (Detail)

Earning Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Computation of Earnings Per Share [Line Items]
Net income	$ 2,108	$ 4,599	$ 4,012	$ 3,666	$ 3,310	$ 3,180	$ 2,952	$ 2,539	$ 14,386	$ 11,981	$ 6,914
Undistributed earnings attributable to participating securities									(108)	(190)	(167)
Net income available to common stockholders									$ 14,278	$ 11,791	$ 6,747
Weighted average shares outstanding, basic									8,754,393	8,571,861	8,465,177
Effect of dilutive shares									429,400	286,030	217,813
Weighted average shares outstanding, assuming dilution									9,183,793	8,857,891	8,682,990
Basic EPS	$ 0.24	$ 0.52	$ 0.45	$ 0.42	$ 0.38	$ 0.36	$ 0.34	$ 0.29	$ 1.63	$ 1.38	$ 0.80
Effect of dilutive shares									(0.08)	(0.05)	(0.02)
Diluted EPS	$ 0.23	$ 0.50	$ 0.43	$ 0.40	$ 0.37	$ 0.35	$ 0.33	$ 0.28	$ 1.55	$ 1.33	$ 0.78

Earnings Per Share - Additional

Earnings Per Share - Additional information (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	22,992	17,159

Restrictions on Dividends Loans

Restrictions on Dividends Loans and Advances - Additional Information (Detail)	Dec. 31, 2017
Restrictions on Dividends, Loans and Advances [Line Items]
Loans or advances as a percentage of capital stock and surplus	10.00%

Summary of Financial Assets Mea

Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale	$ 16,921	$ 22,048
Rabbi Trust
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	2,808	2,606
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Totals	19,729	24,654
Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale	16,921	22,048
Fair Value, Measurements, Recurring | Rabbi Trust
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	2,808	2,606
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Totals	2,808	2,606
Fair Value, Measurements, Recurring | Level 1 | Rabbi Trust
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	2,808	2,606
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Totals	16,921	22,048
Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available-for-sale	$ 16,921	$ 22,048

Assets Remeasured and Reported

Assets Remeasured and Reported at Lower of Cost or Fair Value (Detail) - Level 3 - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis	$ 855	$ 403
Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis	$ 855	$ 403

Fair Values of Assets and Li108

Fair Values of Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents	$ 110,888	$ 58,876	$ 51,261	$ 51,767
Interest-bearing time deposits with other banks	2,440	234
Held-to-maturity securities	160,090	130,197
Federal Home Loan Bank stock	32,382	25,071
Bank owned life insurance	36,967	35,842
Loans, net	2,296,958	1,866,035
Accrued interest receivable	6,344	4,635
Liabilities
Deposits	1,751,251	1,469,422
Federal Home Loan Bank advances	723,150	508,850
Securities sold under agreements to repurchase	3,268	1,985
Accrued interest payable	1,594	1,023
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	110,888	58,876
Interest-bearing time deposits with other banks	2,440	233
Held-to-maturity securities	158,385	129,465
Federal Home Loan Bank stock	32,382	25,071
Bank owned life insurance	36,967	35,842
Loans, net	2,251,971	1,837,068
Accrued interest receivable	6,344	4,635
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits	1,748,995	1,469,906
Federal Home Loan Bank advances	719,430	507,773
Securities sold under agreements to repurchase	3,268	1,985
Accrued interest payable	1,594	1,023
Mortgagors' escrow accounts	4,690	3,341
Carrying Amount
ASSETS
Cash and cash equivalents	110,888	58,876
Interest-bearing time deposits with other banks	2,440	234
Held-to-maturity securities	160,090	130,197
Federal Home Loan Bank stock	32,382	25,071
Bank owned life insurance	36,967	35,842
Loans, net	2,296,958	1,866,035
Accrued interest receivable	6,344	4,635
Liabilities
Deposits	1,751,251	1,469,422
Federal Home Loan Bank advances	723,150	508,850
Securities sold under agreements to repurchase	3,268	1,985
Accrued interest payable	1,594	1,023
Mortgagors' escrow accounts	4,690	3,341
Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	110,888	58,876
Accrued interest receivable	6,344	4,635
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits	1,246,537	1,133,821
Accrued interest payable	1,594	1,023
Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Interest-bearing time deposits with other banks	2,440	233
Held-to-maturity securities	158,385	129,465
Federal Home Loan Bank stock	32,382	25,071
Bank owned life insurance	36,967	35,842
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Deposits	502,458	336,085
Federal Home Loan Bank advances	719,430	507,773
Securities sold under agreements to repurchase	3,268	1,985
Mortgagors' escrow accounts	4,690	3,341
Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Loans, net	$ 2,251,971	$ 1,837,068

Other Comprehensive (Loss) I109

Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Schedule of Other Comprehensive Income (Loss) [Line Items]
Net change defined-benefit post-retirement benefit plans, Pre-Tax Amount		$ 205		$ 176
Change in fair value of securities available for sale, After Tax Amount		(31)		149		$ (78)
Change in the net actuarial gain/loss, After Tax Amount		42		112
Net change defined-benefit post-retirement benefit plans, After Tax Amount		17		70		(16)
Total other comprehensive (loss) income		(14)		219		(94)
After Tax
Schedule of Other Comprehensive Income (Loss) [Line Items]
Change in fair value of securities available for sale, After Tax Amount		(8)		149		(78)
Reclassification adjustment included in net income, After Tax Amount	[1]	(23)
Net change in fair value of securities available for sale, After Tax Amount		(31)		149		(78)
Change in the net actuarial gain/loss, After Tax Amount		25		66		(20)
Reclassification adjustment included in net income, After Tax Amount	[2]	(8)		4		4
Net change defined-benefit post-retirement benefit plans, After Tax Amount		17		70		(16)
Total other comprehensive (loss) income		(14)		219		(94)
Tax Benefit (Expense)
Schedule of Other Comprehensive Income (Loss) [Line Items]
Change in fair value of securities available for sale, Tax (Expense) Benefit		(5)		(98)		52
Reclassification adjustment included in net income, Tax (Expense) Benefit	[1]	15
Net change in fair value of securities available for sale, Tax (Expense) Benefit		20		(98)		52
Change in the net actuarial gain/loss, Tax (Expense) Benefit		(17)		(46)		13
Reclassification adjustment included in net income, Tax (Expense) Benefit	[2]	5		(2)		(2)
Net change defined-benefit post-retirement benefit plans, Tax (Expense) Benefit		(12)		(48)		11
Total other comprehensive (loss) income, Tax (Expense) Benefit		8		(146)		63
Pre Tax
Schedule of Other Comprehensive Income (Loss) [Line Items]
Change in fair value of securities available for sale, Pre-Tax Amount		(13)		247		(130)
Reclassification adjustment included in net income, Pre-Tax Amount	[1]	(38)
Net change in fair value of securities available for sale, Pre-Tax Amount		(51)		247		(130)
Change in the net actuarial gain/loss, Pre-Tax Amount		42		112		(33)
Reclassification adjustment included in net income, Pre-Tax Amount		(13)	[2]	6	[2]	6
Net change defined-benefit post-retirement benefit plans, Pre-Tax Amount		29		118		(27)
Total other comprehensive (loss) income, Pre-Tax Amount		$ (22)		$ 365		$ (157)
[1]	Reclassification adjustments are comprised of realized security gains. The gains have been reclassified out of accumulated other comprehensive income and have affected certain lines in the consolidated statements of operations as follows; the pre-tax amount is included in net gain on sales of securities, the tax expense amount is included in income tax expense and the after tax amount is included in net income.
[2]	Reclassification adjustments are comprised of amortization of prior service cost and unrecognized gain and have been reclassified out of accumulated other comprehensive income (loss). The amounts affected certain lines in the consolidated statements of operations as follows: amortization of prior service cost and unrecognized gain is included in salaries and employee benefits expense. The tax expense amount is included in income tax expense and the after tax amount is included in net income.

Components of Accumulated Other

Components of Accumulated Other Comprehensive Income, included in Stockholders' Equity (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income [Line Items]
Net unrealized holding loss on available-for-sale securities, net of tax	$ (32)	$ (1)
Unrecognized benefit pertaining to defined benefit plan, net of tax	121	104
Accumulated other comprehensive income	$ 89	$ 103

Other Comprehensive (Loss) I111

Other Comprehensive (Loss) Income - Additional Information (Detail)	Dec. 31, 2017USD ($)
Other Comprehensive Income (Loss) [Line Items]
Tax cut and job act 2017 AOCI re-measurement of deferred tax assets and liabilities	$ 19,000

Condensed Balance Sheets of Par

Condensed Balance Sheets of Parent Company (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents held at Belmont Savings Bank	$ 110,888	$ 58,876	$ 51,261	$ 51,767
Investments in held-to-maturity securities	160,090	130,197
Other assets	5,474	4,667
Total assets	2,676,565	2,158,704
Liabilities and Stockholders' Equity
Other liabilities	11,354	9,460
Total liabilities	2,498,536	1,997,783
Stockholders' equity	178,029	160,921	146,203	137,010
Total liabilities and stockholders' equity	2,676,565	2,158,704
Parent Company
ASSETS
Cash and cash equivalents held at Belmont Savings Bank	919	519	$ 496	$ 2,754
Other assets	45	62
Total assets	178,083	160,972
Liabilities and Stockholders' Equity
Accrued expenses	38	37
Other liabilities	16	14
Total liabilities	54	51
Stockholders' equity	178,029	160,921
Total liabilities and stockholders' equity	178,083	160,972
Parent Company | Belmont Savings Bank
ASSETS
Investments in held-to-maturity securities	173,054	155,955
Parent Company | Belmont Savings Bank Funding Corporation
ASSETS
Investments in held-to-maturity securities	$ 4,065	$ 4,436

Condensed Statements of Operati

Condensed Statements of Operations of Parent Company (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest and dividend income:
Dividends from subsidiaries									$ 1,193	$ 760	$ 373
Total interest and dividend income	$ 21,114	$ 19,758	$ 18,764	$ 17,506	$ 16,291	$ 15,726	$ 15,164	$ 14,439	77,143	61,621	48,406
Interest expense	6,414	5,579	4,816	4,245	3,918	3,699	3,457	3,158	21,054	14,231	10,194
Net interest and dividend income	14,700	14,179	13,948	13,261	12,373	12,027	11,707	11,281	56,089	47,390	38,212
Non-interest income	1,117	885	995	630	703	680	705	660	3,627	2,750	3,165
Non-interest expense	7,636	7,929	7,645	7,476	7,045	7,066	6,984	7,252	30,686	28,349	27,824
Income tax benefit	5,382	2,001	2,579	1,920	2,120	2,018	1,735	1,551	11,882	7,425	4,322
Net income	$ 2,108	$ 4,599	$ 4,012	$ 3,666	$ 3,310	$ 3,180	$ 2,952	$ 2,539	14,386	11,981	6,914
Parent Company
Interest and dividend income:
Interest on cash equivalents											1
Dividends from subsidiaries									0	0	0
Total interest and dividend income											1
Interest expense									0	0	0
Net interest and dividend income											1
Non-interest income									0	0	0
Non-interest expense									230	219	242
Loss before income taxes and equity in undistributed earnings of subsidiaries									(230)	(219)	(241)
Income tax benefit									(94)	(89)	(96)
Loss before equity in income of subsidiaries									(136)	(130)	(145)
Net income									14,386	11,981	6,914
Parent Company | Belmont Savings Bank
Interest and dividend income:
Equity in undistributed income									14,432	12,025	6,976
Parent Company | Belmont Savings Bank Funding Corporation
Interest and dividend income:
Equity in undistributed income									$ 90	$ 86	$ 83

Condensed Statement of Cash Flo

Condensed Statement of Cash Flows of Parent Company (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 2,108	$ 4,599	$ 4,012	$ 3,666	$ 3,310	$ 3,180	$ 2,952	$ 2,539	$ 14,386	$ 11,981	$ 6,914
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Deferred income tax expense									2,535	(1,741)	(1,021)
Cash flows from investing activities:
Net cash (used in) investing activities									(532,247)	(339,636)	(395,784)
Cash flows from financing activities:
Proceeds from exercise of stock options, net of cash paid									56	298	228
Restricted stock awards issued, net of awards surrendered									(323)	(118)	(51)
Net increase (decrease) in cash and cash equivalents									52,012	7,615	(506)
Cash and cash equivalents at beginning of period				58,876				51,261	58,876	51,261	51,767
Cash and cash equivalents at end of period	110,888				58,876				110,888	58,876	51,261
Parent Company
Cash flows from operating activities:
Net income									14,386	11,981	6,914
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Deferred income tax expense											190
Other, net									26	(27)	720
Net cash (used in) provided by operating activities									(110)	(157)	765
Cash flows from investing activities:
Net cash (used in) investing activities									460		(3,200)
Cash flows from financing activities:
Proceeds from exercise of stock options, net of cash paid									50	298	228
Restricted stock awards issued, net of awards surrendered										(118)	(51)
Net cash provided by financing activities									50	180	177
Net increase (decrease) in cash and cash equivalents									400	23	(2,258)
Cash and cash equivalents at beginning of period				$ 519				$ 496	519	496	2,754
Cash and cash equivalents at end of period	$ 919				$ 519				919	519	496
Parent Company | Belmont Savings Bank
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Equity in undistributed earnings of Belmont Savings Bank									(14,432)	(12,025)	(6,976)
Cash flows from investing activities:
Investment in Belmont Savings Bank											(3,800)
Parent Company | Belmont Savings Bank Funding Corporation
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Equity in undistributed earnings of Belmont Savings Bank									(90)	$ (86)	(83)
Cash flows from investing activities:
Return of capital from BSB Funding Corp.									$ 460		$ 600

Quarterly Results of Operations

Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information [Line Items]
Interest and dividend income	$ 21,114	$ 19,758	$ 18,764	$ 17,506	$ 16,291	$ 15,726	$ 15,164	$ 14,439	$ 77,143	$ 61,621	$ 48,406
Interest expense	6,414	5,579	4,816	4,245	3,918	3,699	3,457	3,158	21,054	14,231	10,194
Net interest income	14,700	14,179	13,948	13,261	12,373	12,027	11,707	11,281	56,089	47,390	38,212
Provision for loan losses	691	535	707	829	601	443	741	599	2,762	2,385	2,317
Net interest income, after provision for loan losses	14,009	13,644	13,241	12,432	11,772	11,584	10,966	10,682	53,327	45,005	35,895
Non-interest income	1,117	885	995	630	703	680	705	660	3,627	2,750	3,165
Non-interest expense	7,636	7,929	7,645	7,476	7,045	7,066	6,984	7,252	30,686	28,349	27,824
Income before income tax expense	7,490	6,600	6,591	5,586	5,430	5,198	4,687	4,090	26,268	19,406	11,236
Income tax expense	5,382	2,001	2,579	1,920	2,120	2,018	1,735	1,551	11,882	7,425	4,322
Net income	$ 2,108	$ 4,599	$ 4,012	$ 3,666	$ 3,310	$ 3,180	$ 2,952	$ 2,539	$ 14,386	$ 11,981	$ 6,914
Earnings per common share
Basic	$ 0.24	$ 0.52	$ 0.45	$ 0.42	$ 0.38	$ 0.36	$ 0.34	$ 0.29	$ 1.63	$ 1.38	$ 0.80
Diluted	$ 0.23	$ 0.50	$ 0.43	$ 0.40	$ 0.37	$ 0.35	$ 0.33	$ 0.28	$ 1.55	$ 1.33	$ 0.78