Blue Hills Bancorp (BHBK) 10-K 8 Mar 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2016	Mar. 02, 2017	Jun. 30, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	Blue Hills Bancorp, Inc.
Entity Central Index Key	1,601,545
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		26,855,228
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 383,737,000

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets
Cash and due from banks	$ 14,752	$ 10,932
Short-term investments	15,744	22,366
Total cash and cash equivalents	30,496	33,298
Securities available for sale, at fair value	204,836	231,690
Securities held to maturity, at amortized cost	201,027	200,141
Federal Home Loan Bank stock, at cost	13,352	13,567
Loans held for sale	2,761	12,877
Loans, net of allowance for loan losses of $18,750 in 2016 and $17,102 in 2015	1,912,871	1,523,275
Premises and equipment, net	22,034	20,015
Accrued interest receivable	6,057	5,344
Goodwill	9,160	9,160
Core deposit intangible	1,400	2,625
Net deferred tax asset	10,146	10,665
Bank-owned life insurance	32,015	31,626
Other assets	23,537	20,060
Assets	2,469,692	2,114,343
Deposits:
Non-interest bearing	184,982	153,155
Interest bearing	1,623,705	1,280,694
Total deposits	1,808,687	1,433,849
Short-term borrowings	146,000	205,000
Long-term debt	105,000	55,000
Accrued expenses and other liabilities	23,098	21,665
Total liabilities	2,082,785	1,715,514
Commitments and contingencies (Notes 4 and 13)
Stockholders' Equity:
Preferred stock, zero par value, (50,000,000 shares authorized; none issued and outstanding)	0	0
Common stock, $0.01 par value; 100,000,000 shares authorized, 26,759,953 and 28,492,732 issued and outstanding at December 31, 2016 and 2015, respectively	259	276
Additional paid-in capital	249,317	269,078
Unearned compensation- ESOP	(20,496)	(21,255)
Retained earnings	161,896	155,918
Accumulated other comprehensive loss	(4,069)	(5,188)
Total stockholders' equity	386,907	398,829
Total liabilities and stockholders' equity	$ 2,469,692	$ 2,114,343

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Allowance for loan losses	$ 18,750	$ 17,102
Preferred stock, par value (dollars per share)	$ 0	$ 0
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	26,759,953	28,492,732
Common stock, shares outstanding	26,759,953	28,492,732

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest and dividend income:
Interest and fees on loans	$ 58,953	$ 45,342	$ 37,382
Interest on securities	8,895	8,828	7,859
Dividends	1,596	4,068	3,894
Other	94	63	140
Total interest and dividend income	69,538	58,301	49,275
Interest expense:
Interest on deposits	10,488	7,527	5,750
Interest on borrowings	2,088	1,217	1,148
Total interest expense	12,576	8,744	6,898
Net interest and dividend income	56,962	49,557	42,377
Provision for loan losses	4,885	4,090	3,381
Net interest and dividend income, after provision for loan losses	52,077	45,467	38,996
Noninterest income:
Net impairment losses recognized in earnings	0	0	(307)
Deposit account fees	1,327	1,314	1,313
Interchange and ATM fees	1,546	1,511	1,397
Mortgage banking	2,473	282	784
Loan level derivative fee income	2,371	2,120	660
Gains on sales and calls of securities, net	1,280	1,968	2,822
Gains on trading assets, net	0	0	25
Bank-owned life insurance income	1,048	1,031	1,006
Bank-owned life insurance death benefit gains	506	0	182
Pension curtailment gain	0	0	1,304
Miscellaneous	1,576	453	421
Total noninterest income	12,127	8,679	9,607
Noninterest expense:
Salaries and employee benefits	28,853	22,570	21,308
Occupancy and equipment	7,370	6,267	5,305
Data processing	3,460	3,510	2,989
Professional fees	2,638	2,689	3,551
Advertising	2,423	2,458	2,427
FDIC deposit insurance	1,125	999	1,266
Directors’ fees	1,458	644	486
Amortization of core deposit intangible	1,225	1,607	1,808
Charitable foundation contribution	0	0	7,000
Other general and administrative	3,194	3,338	3,268
Total noninterest expense	51,746	44,082	49,408
Income (loss) before income taxes	12,458	10,064	(805)
Provision (benefit) for income taxes	3,805	2,837	(622)
Net income (loss)	$ 8,653	$ 7,227	$ (183)
Earnings per common share:
Basic earnings per share (dollars per share)	$ 0.35	$ 0.28
Diluted earnings per share (dollars per share)	$ 0.35	$ 0.28
Weighted average shares outstanding:
Weighted average common shares (basic) (shares)	24,420,405	26,064,947
Weighted average common shares (diluted) (shares)	24,540,929	26,069,589

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)		$ 8,653	$ 7,227	$ (183)
Securities available for sale:
Change in unrealized holding gains (losses)		3,849	(8,332)	4,942
Reclassification adjustment for net gains realized in net income	[1]	(1,235)	(1,968)	(2,515)
Reclassification of unrealized gains on securities transferred to held to maturity		0	(666)	0
Net unrealized gains (losses)		2,614	(10,966)	2,427
Tax effect		(938)	3,818	(1,018)
Net-of-tax amount		1,676	(7,148)	1,409
Reclassification of unrealized gains on securities transferred from available-for-sale		0	666	0
Amortization of amounts previously recorded upon transfer to held-to-maturity from available-for-sale	[2]	(234)	(95)	0
Net change in unrealized gains		(234)	571	0
Tax effect		83	(197)	0
Net-of-tax amount		(151)	374	0
Defined benefit pension plan:
Losses arising during the period		(895)	(1,610)	(2,090)
Reclassification adjustments for losses (gains) recognized in net periodic benefit cost	[3]	271	110	(70)
Net losses		(624)	(1,500)	(2,160)
Tax effect		218	509	863
Net-of-tax amount		(406)	(991)	(1,297)
Other comprehensive income (loss)		1,119	(7,765)	112
Comprehensive income (loss)		$ 9,772	$ (538)	$ (71)
[1]	Amounts are included in gains on sales and calls of securities, net and net impairment losses, in noninterest income in the consolidated statements of operations. Income tax expense associated with the reclassification adjustment for the years ended December 31, 2016, 2015 and 2014 was approximately $431,000, $691,000 and $940,000, respectively. For the year ended December 31, 2016, included in net gains on sales and calls of securities, amounting to $1.3 million, in net income, was $45,000 related to a gain on a called security classified as held to maturity.
[2]	Amounts are included in interest income on securities in the consolidated statements of operations. Income tax expense associated with the amortization amount for the years ended December 31, 2016 and 2015 was $83,000 and $35,000, respectively.
[3]	Amounts are included in salaries and employee benefits, in noninterest expense in the consolidated statements of operations. Income tax expense (benefit) associated with the reclassification adjustment for the years ended December 31, 2016, 2015 and 2014 was $(97,000), $(37,000) and $24,000, respectively.

Consolidated Statements of Com6

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Reclassification adjustment for net gains realized in net income, tax	$ 431	$ 691	$ 940
Gains on sales and calls of securities, net	1,280	1,968	2,822
Gains on sales and calls of securities, net - securities reclassified as held-to-maturity	45
Other comprehensive (income) loss, amortization adjustment from AOCI, held-to-maturities, tax	83	35
Other comprehensive income (loss), reclassification adjustment and other postretirement benefit plans, for net gain (loss), tax expense (benefit)	$ (97)	$ (37)	$ 24

Consolidated Statements of Chan

Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	SBLF Preferred Stock	Common Stock	Additional paid-in capital	Unearned Compensation- ESOP	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	IPO	IPOCommon Stock	IPOAdditional paid-in capital	Private Placement	Private PlacementCommon Stock	Private PlacementAdditional paid-in capital
Beginning balance at Dec. 31, 2013	$ 171,534	$ 18,724	$ 0	$ 0	$ 0	$ 150,345	$ 2,465
Beginning balance (in shares) at Dec. 31, 2013			0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(71)					(183)	112
Preferred stock dividends declared	(439)					(439)
Issuance of common stock								$ 274,143	$ 278	$ 273,865	$ 6,943	$ 7	$ 6,936
Issuance of common stock (in shares)									27,772,500			694,313
Stock purchased by the ESOP	(22,773)				(22,773)
ESOP shares committed to be released	993			234	759
Redemption of SBLF preferred stock	(18,724)	(18,724)
Ending balance at Dec. 31, 2014	411,606	0	$ 285	281,035	(22,014)	149,723	2,577
Ending balance (in shares) at Dec. 31, 2014			28,466,813
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(538)					7,227	(7,765)
ESOP shares committed to be released	1,063			304	759
Common stock dividends declared	(1,032)					(1,032)
Repurchase of common stock	(13,121)		$ (10)	(13,111)
Repurchase of common stock (in shares)			(929,300)
Share redemption for tax withholdings on deferred compensation obligation and restricted stock vesting	(439)			(439)
Share redemption for tax withholdings on deferred compensation obligation and restricted stock vesting (in shares)			(27,956)
Restricted stock awards granted	0		$ 1	(1)
Restricted stock awards granted (in shares)			983,175
Stock based compensation expenses	1,124			1,124
Excess tax benefit from deferred compensation obligation and stock based compensation	166			166
Ending balance at Dec. 31, 2015	398,829	0	$ 276	269,078	(21,255)	155,918	(5,188)
Ending balance (in shares) at Dec. 31, 2015			28,492,732
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	9,772					8,653	1,119
ESOP shares committed to be released	1,130			371	759
Common stock dividends declared	(2,675)					(2,675)
Repurchase of common stock	(24,432)		$ (17)	(24,415)
Repurchase of common stock (in shares)			(1,708,340)
Share redemption for tax withholdings on deferred compensation obligation and restricted stock vesting	(730)			(730)
Share redemption for tax withholdings on deferred compensation obligation and restricted stock vesting (in shares)			(46,969)
Restricted stock awards granted (in shares)			31,450
Restricted stock awards forfeited (in shares)			(11,800)
Stock based compensation expenses	4,868
Excess tax benefit from deferred compensation obligation and stock based compensation	$ 105
Proceeds from exercise of options (in shares)	2,880		2,880
Proceeds from exercise of options	$ 40			40
Ending balance at Dec. 31, 2016	$ 386,907	$ 0	$ 259	$ 249,317	$ (20,496)	$ 161,896	$ (4,069)
Ending balance (in shares) at Dec. 31, 2016			26,759,953

Consolidated Statements of Cha8

Consolidated Statements of Changes in Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common stock dividends declared (dollars per share)	$ 0.11	$ 0.04
IPO | Common Stock
Issuance of common stock for initial public offering, net of expenses of $3,583			$ 3,583

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income (loss)	$ 8,653	$ 7,227	$ (183)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Provision for loan losses	4,885	4,090	3,381
Net amortization of securities	2,924	3,710	2,184
Gains on sales and calls of securities, net	(1,280)	(1,968)	(2,822)
Impairment losses on securities	0	0	307
Net change in loans held for sale	(1,106)	(374)	765
Loss (gains) on sales of portfolio loans, net	(319)	44	(440)
Net amortization of deferred loan origination costs and discounts	(374)	100	(336)
Depreciation and amortization of premises and equipment	2,011	1,824	1,475
Issuance of common stock to charitable foundation	0	0	6,943
Amortization of core deposit intangible	1,225	1,607	1,808
Bank-owned life insurance income, including death benefit gains	(1,554)	(1,031)	(1,188)
ESOP expense	1,130	1,063	993
Pension curtailment gain	0	0	(1,304)
Deferred income tax benefit	(118)	(302)	(3,557)
Stock based compensation expense	4,868	1,124	0
Excess tax benefit from deferred and stock based compensation	(105)	(166)	0
Net change in:
Trading assets	0	0	750
Accrued interest receivable	(713)	(911)	161
Other assets	(3,477)	(1,153)	(7,033)
Accrued expenses and other liabilities	914	(8,495)	14,220
Net cash provided by operating activities	17,564	6,389	16,124
Activity in securities available for sale:
Purchases	(76,512)	(153,222)	(367,511)
Sales	97,824	99,522	362,941
Maturities/calls	4,133	5,632	9,615
Principal paydowns	3,497	24,487	22,572
Activity in securities held to maturity:
Purchases	(59,939)	(23,361)	0
Maturities/calls	22,835	9,000	0
Principal paydowns	34,866	10,421	0
Loan originations and purchases, net of paydowns	(403,729)	(400,115)	(315,872)
Proceeds from portfolio loan sales	21,163	7,608	27,810
Net purchases of premises and equipment	(4,030)	(3,051)	(2,023)
Purchases of FHLBB stock	(5,487)	(3,296)	(936)
Redemption of FHLBB stock	5,702	1,431	0
Proceeds from bank-owned life insurance death benefits	1,165	0	424
Cash provided by business combination, net of purchase price	0	0	151,587
Net cash used in investing activities	(358,512)	(424,944)	(111,393)
Cash flows from financing activities:
Net change in deposits, excluding brokered	252,295	124,670	32,644
Net change in brokered deposits	122,543	96,463	(9,752)
Net change in short-term borrowings	(59,000)	165,000	(130,000)
Repayments of long-term debt	(20,000)	0	(10,000)
Proceeds from long-term debt	70,000	20,000	0
Net proceeds from issuance of common stock	0	0	274,143
Acquisition of common stock by ESOP	0	0	(22,773)
Redemption of SBLF preferred stock	0	0	(18,724)
Preferred stock dividends paid	0	0	(439)
Repurchase of common stock	(24,432)	(13,121)	0
Share redemption for tax withholdings on deferred compensation obligation	0	(439)	0
Share redemption for tax withholdings for restricted stock vesting	(730)	0	0
Proceeds from exercise of stock options	40	0	0
Excess tax benefit from deferred and stock based compensation	105	166	0
Common stock dividends paid	(2,675)	(1,032)	0
Net cash provided by financing activities	338,146	391,707	115,099
Net change in cash and cash equivalents	(2,802)	(26,848)	19,830
Cash and cash equivalents at beginning of year	33,298	60,146	40,316
Cash and cash equivalents at end of year	30,496	33,298	60,146
Supplementary information:
Interest paid	12,378	8,700	6,921
Income taxes paid, net of refunds	4,390	4,280	257
Securities transferred from available-for-sale to held-to-maturity	0	196,958	0
Fair value of non-cash assets acquired	0	0	123,733
Fair value of liabilities assumed	0	0	275,320
Portfolio loans transferred to loans held for sale designation	$ 0	$ 11,222	$ 14,591

Basis of Presentation and Conso

Basis of Presentation and Consolidation	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Consolidation	BASIS OF PRESENTATION AND CONSOLIDATION Conversion Blue Hills Bancorp, Inc. (the “Company”) is a Maryland corporation formed in February 2014 for the purpose of becoming the holding company for Blue Hills Bank (the “Bank”) concurrent with the conversion of Hyde Park Bancorp, MHC from the mutual holding company to the stock holding company form of organization on July 21, 2014. In connection with the conversion, the Bank became a wholly-owned subsidiary of the Company and the Company sold 27,772,500 shares of its common stock, at $10.00 per share, for gross offering proceeds of approximately $277.7 million , including the sale of 2,277,345 shares to the employee stock ownership plan (“ESOP”). The purchase of common stock by the ESOP was financed by a loan from Blue Hills Funding Corporation ("the Funding Corporation"), a subsidiary of the Company. Upon the completion of the conversion, Hyde Park Bancorp, MHC and the Bank’s former Massachusetts chartered mid-tier holding company, Hyde Park Bancorp, Inc., ceased to exist. In connection with the plan of conversion, the Company established the Blue Hills Bank Foundation (the “Foundation”). The Foundation was funded with $7.0 million , including 694,313 shares of the Company’s common stock and $57,000 in cash, which was recorded as an expense by the Company in July 2014. At the time of conversion, the Company substantially restricted retained earnings by establishing a liquidation account and the Bank established a parallel liquidation account. The liquidation accounts amounted to $61.0 million and $80.7 million at December 31, 2016 and 2015 , respectively, and are maintained for the benefit of eligible deposit account holders who continue to maintain their accounts at the Bank after the conversion. The liquidation accounts will be reduced annually to the extent that eligible account holders have reduced their qualifying deposits. Subsequent increases will not restore an eligible account holder’s interest in the liquidation accounts. In the event of a complete liquidation of the Bank, each account holder will be entitled to receive a distribution from the liquidation accounts as described in the Plan of Conversion. Neither the Company nor the Bank may declare or pay a cash dividend on its common stock if such dividend would cause its regulatory capital to be reduced below the amount required to maintain its respective liquidation account. Basis of Presentation The accompanying consolidated financial statements include the accounts of the Company, its wholly-owned subsidiaries, Blue Hills Funding Corporation and the Bank, the principal operating entity and its wholly-owned subsidiaries, B.H. Security Corporation and HP Security Corporation, which are Massachusetts security corporations, and 1196 Corporation, which holds stock in a company that administers pension and 401(k) plans for a number of savings banks. All significant intercompany balances and transactions have been eliminated in consolidation. Prior to the the establishment of the Foundation in 2014, the Company established Blue Hills Bank Charitable Foundation, (the "Charitable Foundation"), a not-for-profit organization, to provide charitable contributions within the Company’s surrounding communities. Neither the Foundation or Charitable Foundation are subsidiaries of the Company. Business The Company provides a variety of financial services to individuals and businesses online and through its offices in Boston, Brookline (closed in February of 2017), Cambridge, Concord, Dedham, Franklin, Hingham, Hyde Park, Lowell, Milton, Nantucket, Norwood, Plymouth, West Roxbury, Westwood, and Winchester Massachusetts. Its primary deposit products are checking, savings, money market and term certificate accounts and its primary lending products are residential mortgage loans, home equity loans, commercial real estate loans, commercial business loans and consumer loans. Use of estimates In preparing consolidated financial statements in conformity with accounting principles generally accepted in the United States of America, management is required 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 change in the near term relate to the determination of the allowance for loan losses and the realizability of deferred tax assets. Cash and cash equivalents For purposes of the consolidated statements of cash flows, cash and cash equivalents include cash on hand, balances due from banks, and short-term investments comprised of federal funds sold, money-market mutual funds, and interest-bearing deposits, all of which mature within ninety days. The Company normally maintains balances on deposit with other financial institutions in excess of the federally insured limit. Restrictions on cash and due from banks The Company is required to maintain average balances on hand or with the Federal Reserve Bank ( the “FRB”). At December 31, 2016 there was no reserve requirement. At December 31, 2015 the reserve requirement was $4.0 million . Fair value hierarchy 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 reliability of the assumptions used to determine fair value. Level 1 - Valuation is based on quoted prices in active markets for identical assets or liabilities. Valuations are obtained from readily available pricing sources for market transactions involving identical assets or liabilities. Level 2 - Valuation is based on observable inputs other than Level 1 prices, such as quoted prices for similar assets and liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets and liabilities. Level 3 - Valuation is based on unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Level 3 assets and liabilities include those whose value is determined using unobservable inputs to pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation. Securities Debt securities that management has the positive intent and ability to hold to maturity are classified as “held-to-maturity” and recorded at amortized cost. Securities not classified as held-to-maturity, including equity securities with readily determinable fair values, are classified as “available-for-sale” and recorded at fair value, with unrealized gains and losses excluded from earnings and reported in other comprehensive income. Purchase premiums and discounts are recognized in interest income using the interest method over the terms of the securities. Gains and losses on the sale of securities are recorded on the trade date and are determined using the specific identification method. At least quarterly, and more frequently when warranted by economic or market conditions, management evaluates all securities with a decline in fair value below the amortized cost of the investment to determine whether or not the impairment is deemed to be other-than-temporary ('OTTI"). 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. For all 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. Credit-related OTTI for all other impaired debt securities is recognized through earnings. Non-credit related OTTI for such debt securities is recognized in other comprehensive income, net of applicable taxes. 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. Federal Home Loan Bank stock The Company, as a member of the Federal Home Loan Bank of Boston (the "FHLBB") system, is required to maintain an investment in capital stock of the FHLBB. Based on the redemption provisions of the FHLBB, the stock has no quoted market value and is carried at cost. At its discretion, the FHLBB may declare dividends on the stock. The Company reviews its investment for impairment based on the ultimate recoverability of the cost basis in the FHLBB stock. As of December 31, 2016 , no impairment has been recognized. Loans held for sale 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. Loans The Company has historically granted mortgage and consumer loans to its customers and a substantial portion of the loan portfolio consists of mortgage loans in communities including and near the locations of its banking offices. The ability of the Company’s debtors to honor their contracts is dependent upon the real estate and general economic conditions in these areas. The Company’s loan portfolio includes 1-4 family residential real estate, home equity, commercial real estate, construction, commercial business, and consumer segments. Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off generally are reported at their outstanding unpaid principal balances adjusted for the allowance for loan losses, charge-offs, deferred origination fees and costs, and discounts on purchased loans. Interest income is accrued on the unpaid principal balance. Deferred loan origination fees/costs and discounts on purchased loans are recognized as an adjustment of the related loan yield using the interest method. It is the policy of the Company to discontinue the accrual of interest on loans past due in excess of 90 days, unless the loan is well-secured and in the process of collection, or when in the judgment of management, the ultimate collectability of the principal or interest becomes doubtful and to reverse all interest previously accrued against interest income. Past due status is based on contractual terms of the loan. The interest on non-accrual loans is accounted for on the cash-basis until qualifying for return to accrual. Loans are returned to accrual status when all the principal and interest amounts contractually due have been current for six consecutive months and future payments are reasonably assured. Allowance for loan losses The allowance for loan losses is based on the size and the composition of the loan portfolio, delinquency levels, loss experience, economic conditions and other factors related to the collectability of the loan portfolio. Prior to the second quarter of 2016, for portfolios for which the Company had insufficient prior loss experience, a national peer group losses of depository institutions with assets between one and five billion dollars for relevant portfolios dating back to 2008 were used. Commencing in the second quarter of 2016, the Company began to phase in its own loss history by loan type based upon the age and loss experience of the loan portfolio. While this change impacted the loss factors used for our residential real estate, home equity, commercial real estate, commercial business and consumer loan portfolios, there was no material impact to the amount of the allowance for loan losses. Loss experience is updated at least quarterly with consideration given to unique circumstances in the portfolio. Loan losses are charged against the allowance when management believes the uncollectability of a loan balance is confirmed. Subsequent recoveries, if any, are credited to the allowance. The allowance for loan losses is evaluated regularly by management and reflects consideration of all significant factors that affect the collectability of the loan portfolio. The evaluation is inherently subjective as it requires estimates that are susceptible to significant revision as more information becomes available. It is the intention of management to maintain an allowance that is prudently commensurate with the growth in the loan portfolio. 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 a combination of the Company's own history and an extrapolated historical loss experience based on FDIC data for depository institutions with assets of one billion to five billion dollars dating back to 2008, adjusted for qualitative and environmental factors including changes to lending policies and procedures, economic and business conditions, portfolio characteristics, staff experience, problem loan trends, collateral values, concentrations and the competitive, legal and regulatory environment. 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 - The Company does not generally originate loans with a loan-to-value ratio greater than 80 percent and does not generally grant loans that would be classified as subprime upon origination. When the Company does extend credit either on a first- or second-lien basis at a loan-to-value ratio greater than 80 percent , such loans are supported by either mortgage insurance or state guarantee programs. All loans in this segment are collateralized by owner-occupied, 1-4 family residential real estate and repayment is dependent on the credit quality of the individual borrower. The health of the national economy, including unemployment rates and housing prices, will have an effect on the credit quality of loans in this segment. Home equity - Loans in this segment are generally secured by first or second liens on residential real estate. Repayment is dependent on the credit quality of the individual borrower. The Company evaluates each loan application based on factors including the borrower’s credit score, income, length of employment, and other factors to establish the creditworthiness of the borrower. Commercial real estate - Loans in this segment include investment real estate and are generally secured by assignments of leases, real estate collateral and owner-occupied properties. In cases where there is a concentration of exposure to a single large tenant, underwriting standards include analysis of the tenant’s ability to support lease payments over the duration of the loan. The underlying cash flows generated by the properties may be adversely impacted by a downturn in the economy due to increased vacancy rates, which in turn, can have an effect on the credit quality in this segment. Payments on loans secured by income-producing properties often depend on the successful operation and management of the properties. Management continually monitors the cash flows of these loans. Construction - Loans in this segment primarily include real estate development loans for which payment is derived from permanent financing or sale of the property. Credit risk is affected by cost overruns, time to sell at an adequate price, and market conditions. Commercial business - Loans in this segment are generally secured by business assets, including accounts receivable, inventory, real estate and intangible assets. Strict underwriting standards include considerations of the borrower’s ability to support the debt service requirements from the underlying historical and projected cash flows of the business, collateral values, the borrower’s credit history and the ultimate collectability of the de bt. Economic conditions, real estate values, commodity prices, unemployment trends and other factors will affect the credit quality of loans in these segments. Consumer - Loans in this segment primarily include used classic and collector automobile loans. A significant portion of the used automobile loan portfolio is comprised of geographically diverse loans originated by and purchased from a third party, who also provides collection services. Allocated component The allocated component relates to loans that are on the watch list (partially charged-off loans, non-accruing loans and accruing adversely-rated loans) and considered impaired. Impairment is measured by either the present value of expected future cash flows discounted at the loan’s effective interest rate or the fair value of the collateral if the loan is collateral dependent. An allowance is established when the discounted cash flows (or collateral value) of the impaired loan is lower than the carrying value of that loan. 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. Management reviews all loan types for individual impairment. 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 basis, taking into consideration all of the circumstances surrounding the loan and the borrower, including the length of the delay, the reasons for the delay, the borrower’s prior payment record, and the amount of the shortfall in relation to the principal and interest owed. 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 initially classified as impaired and generally remain impaired for the remaining life of the loan. The impaired classification may be removed if the borrower demonstrates compliance with the modified terms and the restructuring agreement specifies an interest rate equal to that which would be provided to a borrower with similar credit at the time of restructuring. Unallocated component The Company previously maintained an unallocated component to cover uncertainties that could affect management’s estimate of probable losses. The unallocated component of the allowance reflected the margin of imprecision inherent in the underlying assumptions used in the methodologies for estimating allocated and general reserves in the portfolio. As a large portion of the Company's loan portfolios is now seasoned, the unallocated component of the allowance for loan losses was eliminated during the fourth quarter of 2016. Premises and equipment Land is carried at cost. Buildings, leasehold improvements and equipment are stated at cost, less accumulated depreciation and amortization, computed on the straight-line method over the estimated useful lives of the assets or the expected terms of the leases, if shorter. Expected terms include lease option periods to the extent that the exercise of such options is reasonably assured. Goodwill and identifiable intangible assets Goodwill is the price paid in excess of the fair value of net assets acquired and is not amortized. Goodwill at December 31, 2016 and 2015 relates to the acquisition of Nantucket Bank. Goodwill is evaluated for impairment at least annually, or more often if warranted, using a combined qualitative and quantitative impairment approach. The initial qualitative approach assesses whether the existence of events or circumstances led to a determination that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If, after assessing the totality of events and circumstances, the Company determines it is more likely than not that the fair value is less than carrying value, the two-step quantitative impairment test is performed. Step one of the quantitative impairment test compares book value to the fair value of the reporting unit. If test one is failed, a more detailed analysis is performed, which involves measuring the excess of the fair value of the reporting unit, as determined in step one, over the aggregate fair value of the individual assets, liabilities, and identifiable intangibles as if the reporting unit was being acquired in a business combination. Identifiable intangible assets subject to amortization consist of the core deposit intangible acquired in the acquisition of Nantucket Bank, which has an estimated life of approximately 5.5 years. Identifiable intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. The core deposit intangible is being amortized using the sum of the years' digits method over its estimated life. Information related to the core deposit intangible, including the estimated annual amortization expense, is summarized below: (In thousands) Balance at December 31, 2013 $ — Acquisition of Nantucket Bank 6,040 Amortization (1,808 ) Balance at December 31, 2014 $ 4,232 Amortization (1,607 ) Balance at December 31, 2015 2,625 Amortization (1,225 ) Balance at December 31, 2016 $ 1,400 Estimated amortization expense for the years ending December 31, 2017 $ 843 2018 461 2019 96 Total remaining $ 1,400 Bank-owned life insurance Bank-owned life insurance policies are reflected on the consolidated balance sheets at cash surrender value. Changes in cash surrender value are reflected in noninterest income in the consolidated statements of operations. Non-marketable investments The aggregate carrying amount of all cost and equity method investments included in other assets at December 31, 2016 and 2015 is $ 10.2 million and $ 8.7 million , respectively. The fair values of these investments are not readily available and are not evaluated for impairment unless there are identified events or changes in circumstances that may have a significant adverse effect on the fair value of the investments. At December 31, 2016 and 2015, the Company was contractually committed under these non-marketable investments to make additional capital contributions of $8.9 million and $8.4 million , respectively. Interest rate swap agreements For asset/liability management purposes, the Company periodically uses interest rate swap agreements to hedge various exposures or to modify interest rate characteristics of various balance sheet accounts. All interest rate swap agreements are recorded at fair value. Depending upon the intended use for the interest rate swap at inception, the Company designates the derivative as either an economic hedge of an asset or liability or a hedging instrument subject to the hedge accounting provisions. If the interest rate swap is not designated in a hedge relationship, gains or losses reflecting changes in fair value are recorded in earnings. Certain interest rate swap contracts are utilized to help commercial loan borrowers manage their interest rate risk. The interest rate swap contracts with commercial loan borrowers allow the borrowers to convert floating rate loan payments to fixed rate payments. When the Company enters into an interest rate swap contract with a commercial loan borrower, the Company concurrently enters into a matching interest rate swap with a correspondent bank counterparty in order to minimize interest rate risk to the Company. These interest rate derivative instruments are recorded on the consolidated balance sheets as either an asset or liability measured at fair value. These derivatives do not qualify for hedge accounting. As such, all changes in fair value of these derivative instruments are included in miscellaneous income. The Company pays and receives fees for entering into these contracts. The net fees are recognized in loan level derivative income when received. Derivative Loan Commitments Mortgage loan commitments are referred to as derivative loan commitments if the loan that will result from exercise of the commitment will be held for sale upon funding. Loan commitments that are derivatives are recognized at fair value on the consolidated balance sheet in other assets and other liabilities with changes in their fair values recorded in mortgage banking income. Forward Loan Sale Commitments To protect against the price risk inherent in derivative loan commitments, the Company enters into forward loan sale commitments to mitigate the risk of potential decreases in the values of loans that would result from the exercise of the derivative loan commitments. Forward loan sale commitments are recognized at fair value on the consolidated balance sheet in other assets or other liabilities with changes in their fair values recorded in mortgage banking income. The Company estimates the fair value of its forward loan sale commitments based on changes in the fair value of underlying mortgage loans. Transfers 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 (free of conditions that constrain it from taking advantage of that right) to pledge or exchange the transferred assets, and (3) the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity. During the normal course of business, the Company may transfer a portion of a financial asset, for example, a participation loan. In order to be eligible for sales treatment, the transfered 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 must 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. Retirement plan The Company accounts for its defined benefit pension plan using an actuarial model that allocates pension costs over the service period of employees in the plan. The Company accounts for the over-funded or under-funded status of its defined benefit plan as an asset or liability on its consolidated balance sheets and recognizes changes in the funded status that are not reflected in net periodic pension cost as other comprehensive income or loss. The Company amended its defined benefit pension plan in 2013 freezing the plan to new participants and subsequently amended the plan and froze it for all participants effective October 31, 2014. Earnings per common share Basic earnings per share represents income available to common stockholders divided by the weighted-average number of common shares outstanding during the period. Unallocated ESOP shares are not deemed outstanding for earnings per share calculations. Dividend rights on unvested options/awards are forfeitable; therefore unvested awards/options are not considered outstanding in the computation of basic earnings per share. Diluted earnings per share reflects additional common shares that would have been outstanding if dilutive potential common shares had been issued, as well as any adjustment to income that would result from the assumed issuance. Potential common shares that may be issued by the Company relate to outstanding stock options and restricted stock awards and are determined using the treasury stock method. Advertising costs Advertising costs are expensed as incurred. Stock-based Compensation Plans The Company measures and recognizes compensation cost relating to stock-based payment transactions based on the grant-date fair value of the equity instruments issued. Stock-based compensation is recognized over the period the employee is required to provide services for the award. The Company uses the Black-Scholes option-pricing model to determine the fair value of stock options granted. For an award with a performance and/or service condition that affects vesting, the performance and/or service condition is not considered in determining the award’s fair value on the grant date. Performance and service conditions considered in estimating the quantity of awards that will vest (i.e., the pre-vesting forfeiture assumption). Compensation cost reflects the number of awards that are expected to vest and is adjusted to reflect those awards that do ultimately vest. Employee Stock Ownership Plan Compensation expense for the ESOP is recorded at an amount equal to the shares allocated by the ESOP multiplied by the average fair market value of the shares during the 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 on the consolidated balance sheet. The difference between the average fair market value and the cost of the shares allocated by the ESOP is recorded as an adjustment to additional paid-in capital. Income taxes Deferred tax assets and liabilities are reflected at currently enacted income tax rates applicable to the period in which the deferred tax assets or liabilities are expected to be realized or settled. As changes in tax laws or rates are enacted, deferred tax assets and liabilities are adjusted accordingly through the provision for income taxes. The Company exercises significant judgment in evaluating the amount and timing of recognition of the resulting tax assets and liabilities. These judgments require the Company to make projections of future taxable income. These judgments and estimates, which are inherently subjective, are reviewed periodically as regulatory and business factors change. A valuation allowance related to deferred tax assets is established when, in the judgment of management, it is more likely than not that all or a portion of such deferred tax assets will not be realized. A tax position that meets the more likely than not recognition threshold is initially and subsequently measured as the largest amount of tax benefit that has a greater than 50% likelihood of being realized upon settlement with a taxing authority that has full knowledge of all relevant information. The determination of whether or not a tax position has met the more likely than not recognition threshold considers the facts, circumstances and information available at the reporting date and is subject to management’s judgment. There was no reserve for uncertain tax positions as of December 31, 2016 or 2015 . The Company records interest and penalties as part of income tax expense. Income tax benefits related to stock compensation in excess of grant date fair value less any proceeds on exercise are recognized as an increase to additional paid-in capital upon vesting or exercising and delivery of the stock. Any income tax effects related to stock compensation that are less than grant date fair value less any proceeds on exercise would be recognized as a reduction of additional paid-in capital to the extent of previously recognized income tax benefits and then through income tax expense for the remaining amount. 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 equity section of the balance sheet, such items, along with net income, are components of comprehensive income. Reclassification

Recent Accounting Standards Upd

Recent Accounting Standards Updates	12 Months Ended
	Dec. 31, 2016
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Standards Updates	RECENT ACCOUNTING STANDARDS UPDATES In January 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2016-01, Financial Instruments – Overall, (Subtopic 825-10) . The amendments in this Update address certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. Targeted improvements to generally accepted accounting principles include the requirement for equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income and the elimination of the requirement for public business entities to disclose the methods and significant assumptions used to estimate the fair value for financial instruments measured at amortized cost. For public business entities, the amendments in this Update are effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The impact of the change in equity investments will depend on market conditions but if applied in 2016, would have resulted in a gain of $592,000 (pre tax) being recognized in net income versus other comprehensive income. See the Consolidated Statement of Comprehensive Income (Loss). In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . This Update is intended to improve financial reporting about leasing transactions and the key provision impacting the Company is the requirement for a lessee to record a right-to-use asset and a liability representing the obligation to make lease payments for long-term operating leases. The Update will be effective for public business entities for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Management is currently evaluating the impact to the consolidated financial statements of adopting this Update. Future lease commitments as of December 31, 2016 were $24.8 million . In March 2016, the FASB issued ASU No. 2016-09 Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , to reduce the complexity of certain aspects of the accounting for employee share-based payment transactions. As a result of this ASU, changes applicable to all entities include: Minimum statutory withholding requirements – One of the previous requirements for an award to qualify for equity classification is that an entity cannot partially settle the award in cash in excess of the employer’s minimum statutory withholding requirements. The determination of employees’ minimum statutory withholding amount has been difficult for some entities. Under the ASU, the threshold to qualify for equity classification would permit withholding up to the maximum individual statutory tax rate in the applicable jurisdictions. Also, the ASU provides that cash paid by an employer when directly withholding shares for tax-withholding purposes would be classified as a financing activity on the statement of cash flows. Accounting for forfeitures – Under the new guidance, entities are permitted to make an accounting policy election for the impact of forfeitures on the recognition of expense for share based payment awards. Forfeitures can be estimated, as required today, or recognized when they occur. Estimates of forfeitures will still be required in certain circumstances, such as at the time of modification of an award or issuance of a replacement award in a business combination. If elected, the change to recognize forfeitures when they occur needs to be adopted using a modified retrospective approach, with a cumulative effect adjustment recorded to opening retained earnings. Accounting for income taxes – Currently, excess tax benefits are recognized in additional paid-in capital. Tax deficiencies are recognized either as an offset to accumulated excess tax benefits, if any, or in the income statement. Per the ASU, all excess tax benefits and tax deficiencies would be recognized as income tax expense or benefit in the income statement. An entity also would recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. Further, excess tax benefits would not be separated from other income tax cash flows and thus would be classified along with other cash flows as an operating activity. The ASU is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. Early adoption is permitted for any organization in any interim or annual period. The impact to the consolidated financial statements upon adopting this Update is not expected to be material. On June 16, 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , which removes the thresholds that companies apply to measure credit losses on financial instruments measured at amortized cost, such as loans, receivables, and held-to-maturity debt securities. Under current U.S. GAAP, companies generally recognize credit losses when it is probable that the loss has been incurred. The revised guidance will remove previously established recognition thresholds based on probability, and will require companies to recognize an allowance for credit losses for the difference between the amortized cost basis of a financial instrument and the net amount that the company expects to collect over the instrument’s contractual life. ASU 2016-13 also amends the credit loss measurement guidance for available-for-sale debt securities and will require that credit losses be recorded through an allowance for credit losses. The ASU is effective for public business entities fiscal years beginning after December 15, 2019 and for interim periods within those fiscal years. Management is currently evaluating the impact to the consolidated financial statements of adopting this Update. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory . The amendments in this Update require an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. For public business entities, the amendments are effective for annual reporting periods beginning after December 15, 2017, including interim reporting periods within those annual reporting periods. The impact to the consolidated financial statements upon adopting this Update is not expected to be material. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . The amendments in this Update require that in the statement of cash flows, amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts. For public business entities, the amendments are effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The impact to the consolidated financial statements upon adopting this Update is not expected to be material. In January 2017, the FASB issued ASU 2017-04 Goodwill Simplifications , which simplifies how all entities assess goodwill for impairment by eliminating Step 2 from the goodwill impairment test. As amended, the goodwill impairment test will consist of one step comparing the fair value of a reporting unit with its carrying amount. An entity should recognize a goodwill impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. For public business entities, the amendments are effective for its annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. The impact to the consolidated financial statements upon adopting this Update is not expected to be material.

Securities

Securities	12 Months Ended
	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Securities	SECURITIES The amortized cost and estimated fair value of securities available for sale and held to maturity, with gross unrealized gains and losses, follow: December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Securities Available for Sale: Debt securities: Mortgage- and other asset-backed securities: Privately issued commercial mortgage-backed securities $ 10,530 $ — $ (41 ) $ 10,489 Other asset-backed securities 9,174 6 (195 ) 8,985 Total mortgage- and other asset-backed securities 19,704 6 (236 ) 19,474 State and political 12,730 120 (157 ) 12,693 Financial services: Banks 20,263 57 (298 ) 20,022 Diversified financial entities 17,198 190 (198 ) 17,190 Insurance and REITs 18,304 150 (216 ) 18,238 Total financial services 55,765 397 (712 ) 55,450 Other corporate: Industrials 49,217 508 (761 ) 48,964 Utilities 24,895 292 (100 ) 25,087 Total other corporate 74,112 800 (861 ) 74,051 Total debt securities 162,311 1,323 (1,966 ) 161,668 Marketable equity securities: Mutual funds: Domestic community 3,216 25 (19 ) 3,222 Global asset allocation 42,396 48 (2,498 ) 39,946 Total marketable equity securities 45,612 73 (2,517 ) 43,168 Total securities available for sale $ 207,923 $ 1,396 $ (4,483 ) $ 204,836 Securities Held to Maturity: Debt securities: Government-sponsored enterprises $ 32,667 $ 4 $ (934 ) $ 31,737 Government-sponsored mortgage-backed and collateralized mortgage obligations 153,938 14 (1,806 ) 152,146 SBA asset-backed securities 14,422 — (212 ) 14,210 Total securities held to maturity $ 201,027 $ 18 $ (2,952 ) $ 198,093 December 31, 2015 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Securities Available for Sale: Debt securities: Mortgage- and other asset-backed securities: Privately issued commercial mortgage-backed securities $ 13,126 $ — $ (195 ) $ 12,931 Other asset-backed securities 11,395 — (142 ) 11,253 Total mortgage- and other asset-backed securities 24,521 — (337 ) 24,184 State and political 16,016 354 (55 ) 16,315 Financial services: Banks 18,813 138 (90 ) 18,861 Diversified financial entities 23,124 349 (173 ) 23,300 Insurance and REITs 16,883 1 (282 ) 16,602 Total financial services 58,820 488 (545 ) 58,763 Other corporate: Industrials 55,470 306 (1,244 ) 54,532 Utilities 31,952 7 (1,639 ) 30,320 Total other corporate 87,422 313 (2,883 ) 84,852 Total debt securities 186,779 1,155 (3,820 ) 184,114 Marketable equity securities: Mutual funds: Global equity 5,000 388 — 5,388 Domestic community 3,216 70 (13 ) 3,273 Global asset allocation 42,396 3 (3,484 ) 38,915 Total marketable equity securities 50,612 461 (3,497 ) 47,576 Total securities available for sale $ 237,391 $ 1,616 $ (7,317 ) $ 231,690 Securities Held to Maturity: Debt securities: U.S. Treasury $ 636 $ — $ (2 ) $ 634 Government-sponsored enterprises 28,256 94 (126 ) 28,224 Government-sponsored mortgage-backed and collateralized mortgage obligations 155,232 10 (832 ) 154,410 SBA asset-backed securities 16,017 — (59 ) 15,958 Total securities held to maturity $ 200,141 $ 104 $ (1,019 ) $ 199,226 During the third quarter of 2015, approximately $196.3 million of securities available-for-sale, with net unrealized gains of $666,000 , were reclassified to held-to-maturity designation. Held-to-maturity investments are investments that management has the positive intent and ability to hold to maturity. If a security is reclassified from available-for-sale to held-to-maturity, the fair value at the time of transfer becomes the security's new cost basis. The unrealized holding gain at the transfer date continues to be reported in accumulated other comprehensive income and is amortized over the security's remaining life as an adjustment of yield in a manner similar to a premium or discount. At December 31, 2016, there are $337,000 of net holding gains remaining in accumulated other comprehensive income. The amortized cost and estimated fair value of debt securities by contractual maturity at December 31, 2016 follow. Expected maturities will differ from contractual maturities because the issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Available for Sale Held to Maturity Amortized Cost Fair Value Amortized Cost Fair Value (In thousands) Within 1 year $ 3,021 $ 3,022 $ 5,006 $ 5,007 After 1 year through 5 years 56,673 56,850 9,687 9,439 After 5 years through 10 years 75,437 74,787 17,974 17,291 After 10 years 7,476 7,535 — — 142,607 142,194 32,667 31,737 Mortgage- and asset-backed securities and collateralized mortgage obligations amortizing monthly 19,704 19,474 168,360 166,356 Total debt securities $ 162,311 $ 161,668 $ 201,027 $ 198,093 For the years ended December 31, 2016 , 2015 and 2014 , proceeds from sales of securities available for sale amounted to $97.8 million , $99.5 million and $362.9 million , respectively. Gross realized gains amounted to $2.3 million , $2.0 million and $4.5 million , respectively, and gross realized losses amounted to $981,000 , $56,000 and $1.7 million , respectively. At December 31, 2016 and 2015 , government-sponsored enterprise obligations with an amortized cost of $27.3 million and $46.2 million , respectively, and a fair value of $27.0 million and $46.0 million , respectively, were pledged to secure borrowings. See Note 7. The Company continually reviews investment securities for the existence of OTTI, taking into consideration current market conditions, the extent and nature of changes in fair value, issuer rating changes and trends, the credit worthiness of the obligor of the security, volatility of earnings, current analysts’ evaluations, the Company’s intent to sell the security, or whether it is more likely than not that the Company will be required to sell the debt security before its anticipated recovery, as well as other qualitative factors. The term “other-than-temporary” is not intended to indicate that the decline is permanent, but indicates that the prospects for a near-term recovery of value is not necessarily favorable, or that there is a lack of evidence to support a realizable value equal to or greater than the carrying value of the investment. Information pertaining to securities with gross unrealized losses aggregated by investment category and length of time that individual securities have been in a continuous loss position, follows: December 31, 2016 Less Than Twelve Months More Than Twelve Months Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (In thousands) Securities Available for Sale: Debt securities: Mortgage- and other asset-backed securities: Privately issued commercial mortgage- backed securities $ (11 ) $ 3,163 $ (30 ) $ 7,326 Other asset-backed securities (43 ) 3,924 (152 ) 3,732 Total mortgage- and other asset-backed securities (54 ) 7,087 (182 ) 11,058 State and political (157 ) 5,301 — — Financial services: Banks (298 ) 14,553 — — Diversified financial entities (198 ) 9,369 — — Insurance and REITs (216 ) 6,900 — — Total financial services (712 ) 30,822 — — Other corporate: Industrials (655 ) 24,630 (106 ) 2,284 Utilities (99 ) 11,200 (1 ) 794 Total other corporate (754 ) 35,830 (107 ) 3,078 Total debt securities (1,677 ) 79,040 (289 ) 14,136 Marketable equity securities: Mutual funds: Domestic community — — (19 ) 448 Global asset allocation (424 ) 15,153 (2,074 ) 22,442 Total marketable equity securities (424 ) 15,153 (2,093 ) 22,890 Total temporarily impaired securities available for sale $ (2,101 ) $ 94,193 $ (2,382 ) $ 37,026 Securities Held to Maturity: Debt securities: Government-sponsored enterprises $ (934 ) $ 28,533 $ — $ — Government-sponsored mortgage-backed and collateralized mortgage obligations (1,763 ) 146,098 (43 ) 3,827 SBA asset-backed securities (104 ) 9,157 (108 ) 5,053 Total temporarily impaired securities held to maturity $ (2,801 ) $ 183,788 $ (151 ) $ 8,880 December 31, 2015 Less Than Twelve Months More Than Twelve Months Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (In thousands) Securities Available for Sale: Debt securities: Mortgage- and other asset-backed securities: Privately issued commercial mortgage- backed securities $ (84 ) $ 5,166 $ (111 ) $ 7,765 Other asset-backed securities (142 ) 11,253 — — Total mortgage- and other asset-backed securities (226 ) 16,419 (111 ) 7,765 State and political (55 ) 3,324 — — Financial services: Banks (90 ) 14,070 — — Diversified financial entities (173 ) 15,397 — — Insurance and REITs (282 ) 14,487 — — Total financial services (545 ) 43,954 — — Other corporate: Industrials (957 ) 43,848 (287 ) 395 Utilities (1,387 ) 25,353 (252 ) 1,618 Total other corporate (2,344 ) 69,201 (539 ) 2,013 Total debt securities (3,170 ) 132,898 (650 ) 9,778 Marketable equity securities: Mutual funds: Domestic community — — (13 ) 453 Global asset allocation (3,484 ) 36,609 — — Total marketable equity securities (3,484 ) 36,609 (13 ) 453 Total temporarily impaired securities available for sale $ (6,654 ) $ 169,507 $ (663 ) $ 10,231 Securities Held to Maturity: Debt securities: U.S. Treasury $ (2 ) $ 634 $ — $ — Government-sponsored enterprises (126 ) 14,084 — — Government-sponsored mortgage-backed and collateralized mortgage obligations (832 ) 144,820 — — SBA asset-backed securities (59 ) 15,958 — — Total temporarily impaired securities held to maturity $ (1,019 ) $ 175,496 $ — $ — At December 31, 2016 , several debt securities have unrealized losses with aggregate depreciation of 2% from the Company’s amortized cost basis. The unrealized losses were primarily caused by interest rate fluctuations. It is expected that none of these securities would be settled at a price less than the par value of the investment. Because the decline in market value is attributable to changes in interest rates and not to credit quality, and because the Company does not intend to sell the securities and it is more likely than not that the Company will not be required to sell the securities before recovery of their amortized cost bases, which may be maturity, the Company does not consider these securities to be other than temporarily impaired at December 31, 2016 . At December 31, 2016 , three mutual funds have aggregate unrealized losses of $2.5 million ; 6% of the Company’s cost basis. No issues have been identified that cause management to believe the declines in market value are other than temporary and the Company has the ability and intent to hold these investments until a recovery of fair value.

Loans and The Allowance for Loa

Loans and The Allowance for Loan Losses	12 Months Ended
	Dec. 31, 2016
Receivables [Abstract]
Loans and The Allowance for Loan Losses	LOANS AND THE ALLOWANCE FOR LOAN LOSSES A summary of the balances of loans follows: December 31, 2016 2015 (In thousands) Real estate: 1-4 family residential $ 851,154 $ 599,938 Home equity 78,719 77,399 Commercial real estate 687,289 561,203 Construction 76,351 79,773 1,693,513 1,318,313 Commercial business 206,234 182,677 Consumer 29,281 38,186 Total loans 1,929,028 1,539,176 Allowance for loan losses (18,750 ) (17,102 ) Discount and fair value adjustments on purchased loans (1,846 ) (1,959 ) Deferred loan costs and fees, net 4,439 3,160 Loans, net $ 1,912,871 $ 1,523,275 The Company has sold residential mortgage loans in the secondary mortgage market, some of which are sold with limited recourse. The Company has retained the servicing responsibility on a portion of the loans sold and receives fees for the services provided. The unpaid principal balances of mortgage loans serviced for others were $89.7 million and $39.8 million at December 31, 2016 and 2015 , respectively. The maximum contingent liability associated with loans sold with recourse is $3.8 million at December 31, 2016 . Neither mortgage loans serviced for others nor the contingent liability associated with sold loans is recorded on the consolidated balance sheets. There have been no contingency losses recognized on these loans to date. In 2016 and 2015 , the Company transferred a portion of its originated commercial real estate, commercial business and construction loans to participating lenders. The amounts transferred have been accounted for as sales and are therefore not included on the consolidated balance sheets. The Company and participating lenders share ratably in cash flows and any gains or losses that may result from a borrower’s lack of compliance with contractual terms of the loan. The Company continues to service the loans on behalf of the participating lenders and, as such, collects cash payments from the borrowers, remits payments (net of servicing fees) to participating lenders and disburses required escrow funds to relevant parties. At December 31, 2016 and 2015 , the Company was servicing loans for participants aggregating $56.0 million and $30.6 million , respectively. At December 31, 2016 and 2015 , 1-4 family residential loans in the amount of $759.9 million and $508.5 million , respectively, and commercial real estate loans in the amount of $293.1 million and $133.2 million , respectively, were pledged to secure borrowings. See Note 7. Activity in the allowance for loan losses for the years ended December 31, 2016 , 2015 and 2014 follows: 1-4 Family Residential Home Equity Commercial Real Estate Construction Commercial Business Consumer Unallocated Total (In thousands) 2016 Beginning balance $ 3,916 $ 636 $ 7,147 $ 1,364 $ 2,839 $ 772 $ 428 $ 17,102 Provision (credit) for loan losses 830 (99 ) 1,447 (11 ) 3,428 (282 ) (428 ) 4,885 Loans charged-off — — (321 ) — (3,098 ) (56 ) — (3,475 ) Recoveries 100 — 101 — 37 — — 238 Ending Balance $ 4,846 $ 537 $ 8,374 $ 1,353 $ 3,206 $ 434 $ — $ 18,750 2015 Beginning balance $ 3,222 $ 340 $ 3,551 $ 1,056 $ 3,410 $ 736 $ 658 $ 12,973 Provision (credit) for loan losses 612 296 3,596 308 (571 ) 79 (230 ) 4,090 Loans charged-off — — — — — (43 ) — (43 ) Recoveries 82 — — — — — — 82 Ending Balance $ 3,916 $ 636 $ 7,147 $ 1,364 $ 2,839 $ 772 $ 428 $ 17,102 2014 Beginning balance $ 2,835 $ 247 $ 2,608 $ 303 $ 2,416 $ 574 $ 688 $ 9,671 Provision (credit) for loan losses 405 93 943 753 994 223 (30 ) 3,381 Loans charged-off (18 ) — — — — (61 ) — (79 ) Recoveries — — — — — — — — Ending Balance $ 3,222 $ 340 $ 3,551 $ 1,056 $ 3,410 $ 736 $ 658 $ 12,973 Additional information pertaining to the allocation of the allowance for loan losses to loan segments at December 31, 2016 and 2015 , follows: 1-4 Family Home Commercial Construction Commercial Consumer Unallocated Total (In thousands) December 31, 2016 Allowance related to impaired loans $ 17 $ — $ — $ — $ — $ — $ — $ 17 Allowance related to non-impaired loans 4,829 537 8,374 1,353 3,206 434 — 18,733 Total allowance for loan losses $ 4,846 $ 537 $ 8,374 $ 1,353 $ 3,206 $ 434 $ — $ 18,750 Impaired loans $ 6,726 $ 1,153 $ 941 $ — $ 241 $ 170 $ — $ 9,231 Non-impaired loans 844,428 77,566 686,348 76,351 205,993 29,111 — 1,919,797 Total loans $ 851,154 $ 78,719 $ 687,289 $ 76,351 $ 206,234 $ 29,281 $ — $ 1,929,028 December 31, 2015 Allowance related to impaired loans $ — $ — $ 384 $ — $ 10 $ 10 $ — $ 404 Allowance related to non-impaired loans 3,916 636 6,763 1,364 2,829 762 428 16,698 Total allowance for loan losses $ 3,916 $ 636 $ 7,147 $ 1,364 $ 2,839 $ 772 $ 428 $ 17,102 Impaired loans $ 6,114 $ 270 $ 4,631 $ — $ 10 $ 145 $ — $ 11,170 Non-impaired loans 593,824 77,129 556,572 79,773 182,667 38,041 — 1,528,006 Total loans $ 599,938 $ 77,399 $ 561,203 $ 79,773 $ 182,677 $ 38,186 $ — $ 1,539,176 The following is a summary of past due and non-accrual loans, by loan segment, at December 31, 2016 and 2015 : 30-59 Days Past Due 60-89 Days Past Due Past Due 90 Days or More Total Past Due Loans on Non-accrual (In thousands) December 31, 2016 Real estate: 1-4 family residential $ 584 $ 373 $ 2,322 $ 3,279 $ 6,478 Home equity 452 496 775 1,723 1,153 Commercial real estate 1,393 — — 1,393 941 Commercial business 4,996 13 — 5,009 241 Consumer 175 5 7 187 170 Total $ 7,600 $ 887 $ 3,104 $ 11,591 $ 8,983 December 31, 2015 Real estate: 1-4 family residential $ 2,287 $ — $ 990 $ 3,277 $ 5,688 Home equity 1,031 19 176 1,226 270 Commercial real estate — 1,249 — 1,249 4,631 Commercial business 23 — — 23 10 Consumer 3 80 120 203 145 Total $ 3,344 $ 1,348 $ 1,286 $ 5,978 $ 10,744 There were no loans past due 90 days or more and still accruing at December 31, 2016 and 2015 . The following is a summary of information pertaining to impaired loans by loan segment at the dates indicated: Recorded Investment Unpaid Principal Balance Related Allowance December 31, 2016 (In thousands) Impaired loans without a valuation allowance: Real estate: 1-4 family residential $ 6,605 $ 7,023 $ — Home equity 1,153 1,225 — Commercial real estate 941 1,207 — Commercial business 241 3,279 — Consumer 170 183 — Total 9,110 12,917 — Impaired loans with a valuation allowance: 1-4 family residential 121 313 17 Total impaired loans $ 9,231 $ 13,230 $ 17 December 31, 2015 Impaired loans without a valuation allowance: Real estate: 1-4 family residential $ 6,114 $ 6,824 $ — Home equity 270 425 — Consumer 35 39 — Total 6,419 7,288 — Impaired loans with a valuation allowance: Commercial real estate 4,631 4,631 384 Commercial business 10 11 10 Consumer 110 110 10 Total 4,751 4,752 404 Total impaired loans $ 11,170 $ 12,040 $ 404 The following tables set forth information regarding average balances and interest income recognized (all on a cash basis) on impaired loans, by segment, for the years ended December 31, 2016 , 2015 and 2014 : Average Recorded Investment Interest Income Recognized 2016 (In thousands) Real estate: 1-4 family residential $ 6,451 $ 449 Home equity 555 29 Commercial real estate 3,192 206 Commercial business 672 55 Consumer 160 12 Total $ 11,030 $ 751 2015 Real estate: 1-4 family residential $ 4,869 $ 270 Home equity 575 14 Commercial real estate 926 161 Commercial business 2 1 Consumer 78 6 Total $ 6,450 $ 452 2014 Real estate: 1-4 family residential $ 4,076 $ 213 Home equity 476 17 Consumer 34 2 Total $ 4,586 $ 232 No additional funds are committed to be advanced in connection with impaired loans. There were no material troubled debt restructurings recorded during the years ended December 31, 2016, 2015 and 2014. Credit Quality Information The Company utilizes a ten-grade internal loan rating system for all loans as follows: Loans rated 1 - 6 are considered "acceptable" rated loans that are performing as agreed, and generally require only routine supervision. Loans rated 7 are considered “special mention.” These loans are starting to show signs of potential weakness and are being closely monitored by management. Loans rated 8 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. Generally, all loans 90 days delinquent are rated 8. Loans rated 9 are considered “doubtful.” Serious problems exist to the point where a partial loss of principal is likely. Weakness is so pronounced that on the basis of current information, conditions and values, collection in full is highly improbable. Loans rated 10 are considered "loss" and the credit extended to the customer is considered uncollectible or of such little value that it does not warrant consideration as an active asset. The Company assigns a 6 risk-rating to otherwise performing, satisfactorily collateralized consumer and residential loans where the Company becomes aware of deterioration in a FICO score or other indication of potential inability to service the debt. The Company assigns risk ratings of 7-10 to residential or consumer loans that have a well-defined weakness that may jeopardize the collection of the contractual principal and interest, are contractually past due 90 days or more or legal action has commenced against the borrower. All other residential mortgage and consumer loans have no risk rating. On an annual basis, or more often if needed, the Company formally reviews the ratings on all commercial and construction loans. At least annually, the Company engages an independent third party to review a significant portion of loans within these segments. Management uses the results of these reviews as part of its annual review process. Management primarily utilizes delinquency reports, the watch list and other loan reports to monitor credit quality of other loan segments. The following tables present the Company’s loans by risk rating at December 31, 2016 and 2015 : 1-4 Family Residential Home Equity Commercial Real Estate Construction Commercial Business Consumer Total Loans (In thousands) December 31, 2016 Loans rated 1 - 6 $ 1,054 $ 293 $ 671,872 $ 76,351 $ 188,706 $ 4 $ 938,280 Loans rated 7 3,514 967 9,720 — 17,510 146 31,857 Loans rated 8 2,442 258 5,697 — 18 37 8,452 Loans rated 9 645 — — — — — 645 Loans rated 10 — — — — — — — Loans not rated 843,499 77,201 — — — 29,094 949,794 $ 851,154 $ 78,719 $ 687,289 $ 76,351 $ 206,234 $ 29,281 $ 1,929,028 December 31, 2015 Loans rated 1 - 6 $ 1,950 $ 465 $ 548,360 $ 79,773 $ 181,792 $ 6 $ 812,346 Loans rated 7 4,461 321 7,765 — 874 — 13,421 Loans rated 8 1,592 144 5,078 — — 149 6,963 Loans rated 9 701 — — — 11 — 712 Loans rated 10 — — — — — — — Loans not rated 591,234 76,469 — — — 38,031 705,734 $ 599,938 $ 77,399 $ 561,203 $ 79,773 $ 182,677 $ 38,186 $ 1,539,176

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Premises and equipment	PREMISES AND EQUIPMENT A summary of the cost and accumulated depreciation and amortization of premises and equipment follows: December 31, Estimated Useful Lives 2016 2015 (In thousands) Land $ 4,087 $ 4,087 Buildings 10,322 10,322 5 to 40 years Leasehold improvements 9,334 7,727 5 to 10 years Furniture and fixtures 3,874 2,601 3 to 5 years Technology equipment 6,139 5,088 1 to 3 years Construction in progress 169 70 Premises and equipment, gross 33,925 29,895 Less accumulated depreciation and amortization (11,891 ) (9,880 ) Premises and equipment, net $ 22,034 $ 20,015 Depreciation and amortization expense for the years ended December 31, 2016 , 2015 and 2014 amounted to $2.0 million , $1.8 million and $1.5 million , respectively.

Deposits

Deposits	12 Months Ended
	Dec. 31, 2016
Banking and Thrift [Abstract]
Deposits	DEPOSITS A summary of deposit balances, by type, is as follows: December 31, 2016 2015 (In thousands) NOW and demand $ 331,508 $ 288,143 Regular savings 262,984 287,344 Money market 573,204 368,050 Brokered money market 53,357 41,807 Total non-certificate accounts 1,221,053 985,344 Term certificates of $250,000 or more 77,550 65,364 Term certificates less than $250,000 262,564 246,614 Brokered certificates of deposit 247,520 136,527 Total certificate accounts 587,634 448,505 Total deposits $ 1,808,687 $ 1,433,849 At December 31, 2016 , the scheduled maturities of certificate accounts, including brokered certificates of deposits, are as follows: Amount Weighted Average Rate (Dollars in thousands) 2017 372,461 0.67 % 2018 88,220 1.26 2019 68,928 1.69 2020 38,393 1.90 2021 19,632 1.76 $ 587,634 1.00 %

Borrowings

Borrowings	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Borrowings	BORROWINGS Federal Home Loan Bank of Boston advances FHLBB advances with an original maturity of less than one year amounted to $146.0 million and $205.0 million at December 31, 2016 and 2015 , respectively, with a weighted average rate of 0.76% and 0.41% , respectively. The Company also had, at both December 31, 2016 and 2015, a $7.7 million line of credit with the FHLBB with an interest rate that adjusts daily. No advances were outstanding on this line at December 31, 2016 or 2015 . All borrowings from the FHLBB are secured by a blanket security agreement on qualified collateral, principally residential and commercial mortgage loans, as well as certain U.S. government-sponsored enterprise securities. See Notes 3 and 4. Long-term debt consists of the following FHLBB advances: December 31, 2016 December 31, 2015 Amount Weighted Average Rate Amount Weighted Average Rate (Dollars in thousands) Fixed-rate advances maturing: 2016 $ — — % $ 10,000 2.29 % 2017 15,000 1.99 % 15,000 1.99 2018 20,000 2.12 20,000 2.23 2019 25,000 1.20 — — 2020 15,000 1.49 10,000 1.65 2021 * 30,000 0.28 — — $ 105,000 1.27 % $ 55,000 2.07 % * Includes advances callable in 2017. Other lines-of-credit At December 31, 2016 and 2015 , the Company had $42 million and $39 million , respectively, in available unsecured federal funds lines with correspondent banks, which could be drawn upon, as needed. There were no amounts outstanding at December 31, 2016 or 2015 .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES Allocation of federal and state income taxes between current and deferred portions is as follows: Years Ended December 31, 2016 2015 2014 (In thousands) Current tax provision: Federal $ 3,617 $ 2,933 $ 2,695 State 306 206 240 3,923 3,139 2,935 Deferred tax provision (benefit): Federal 55 7 (3,183 ) State 47 (148 ) (1,014 ) Federal and State 102 (141 ) (4,197 ) Change in valuation reserve (220 ) (161 ) 640 Deferred income tax benefit (118 ) (302 ) (3,557 ) Provision (benefit) for income taxes $ 3,805 $ 2,837 $ (622 ) The reasons for the differences between the statutory federal income tax provision and the actual tax provision (benefit) are summarized as follows: Years Ended December 31, 2016 2015 2014 (Dollars in thousands) Statutory federal tax provision (benefit) at 34% $ 4,236 $ 3,429 $ (274 ) Increase (decrease) resulting from: State taxes, net of federal tax benefit 233 39 (511 ) Dividends received deduction (41 ) (211 ) (201 ) Tax-exempt bank-owned life insurance (528 ) (351 ) (404 ) Tax-exempt interest (189 ) (222 ) (277 ) Change in valuation reserve (220 ) (161 ) 640 Nondeductible IPO costs — — 202 Equity incentives 339 52 — Amortization of low income housing partnership 219 — — Tax credits utilized (286 ) (45 ) — Accrual adjustment 207 13 — Statutory rate change for net deferred tax asset from 34% to 35% (289 ) — — Other, net 124 294 203 Tax provision (benefit) $ 3,805 $ 2,837 $ (622 ) Effective tax rates 30.5 % 28.2 % 77.3 % The components of the net deferred tax asset are as follows: December 31, 2016 2015 (In thousands) Deferred tax assets: Federal $ 11,700 $ 12,091 State 3,258 3,188 Deferred tax assets, gross 14,958 15,279 Valuation reserve (1,790 ) (1,966 ) Deferred tax assets, net 13,168 13,313 Deferred tax liabilities: Federal (2,427 ) (2,138 ) State (595 ) (510 ) Deferred tax liabilities (3,022 ) (2,648 ) Net deferred tax asset $ 10,146 $ 10,665 The tax effects of each item that give rise to deferred tax assets (liabilities) are as follows: December 31, 2016 2015 (In thousands) Deferred tax assets: Depreciation and amortization $ 747 $ 929 Employee benefit plans and share-based compensation plans 571 901 Allowance for loan losses 7,660 6,831 Contribution carryover 2,317 2,675 Net unrealized loss on securities held as, or transferred from, available for sale 893 1,748 Net unrealized losses on defined benefit pension plan 1,270 1,052 Deferred rent expense 123 28 Other 302 131 Valuation reserve (1,790 ) (1,966 ) Deferred tax liabilities: Deferred loan origination costs (1,947 ) (1,664 ) Net deferred tax asset $ 10,146 $ 10,665 A summary of the change in the net deferred tax asset (liability) is as follows: Years Ended December 31, 2016 2015 2014 (In thousands) Balance at beginning of year $ 10,665 $ 6,233 $ 2,831 Deferred tax benefit 118 302 3,557 Tax effect of changes in accumulated other comprehensive income (637 ) 4,130 (155 ) Balance at end of year $ 10,146 $ 10,665 $ 6,233 At December 31, 2016 and 2015, management maintained a valuation reserve in the amount of $1.8 million and $2.0 million , respectively, primarily related to state deferred tax assets, for which it was more likely than not that a tax benefit could not be realized due to positive evidence supporting future state profitability. Management reviews projections of state taxable income periodically to determine if circumstances have changed to warrant a reduction in the valuation reserve. A summary of the change in valuation reserve is as follows: For the Year Ended December 31, 2016 Federal State Total (In thousands) Balance at beginning of year $ (200 ) $ (1,766 ) $ (1,966 ) Change through the income statement 200 20 220 Change through other comprehensive income — (44 ) (44 ) Balance at end of year $ — $ (1,790 ) $ (1,790 ) At December 31, 2016, the Company allocated tax expense between the components of the consolidated statements of operations as required by the intraperiod allocation rules. The federal income tax reserve for loan losses at the Company’s base year amounted to $1.3 million. If any portion of the reserve is used for purposes other than to absorb loan losses, approximately 150% of the amount actually used (limited to the amount of the reserve) would be subject to taxation in the year in which used. As the Company intends to use the reserve to only absorb loan losses, a deferred income tax liability of $514,000 has not been provided. 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 and state taxing authorities for the years ended December 31, 2013 through 2016 . Management periodically evaluates the sustainability of tax positions taken. Whenever management estimates the probability of sustaining a tax position is at least more likely than not, the tax position is deemed warranted and is recognized at the largest amount of benefit that is greater than 50% likely of being realized upon settlement. Interest and penalties related to uncertain tax positions are recognized as income tax expense. In the year ended December 31, 2016, $22,000 of interest and penalties were paid. No interest or penalties were recorded for the years ended December 31, 2015 and 2014 .

Equity

Equity	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Equity	EQUITY Minimum regulatory capital requirements 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 the Bank’s consolidated 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 sheet items as calculated under regulatory accounting practices. The capital amounts and classification are also subject to qualitative judgments by the regulators about components, risk weightings, and other factors. Prompt corrective action provisions are not applicable to bank holding companies. Federal banking regulations include minimum capital ratios as displayed in the following table. Additionally, community banking institutions must maintain a capital conservation buffer of common equity Tier 1 capital in an amount greater than 2.5% of total risk-weighted assets to avoid being subject to limitations on capital distributions and discretionary bonuses. The capital conservation buffer is being phased in over three years , beginning on January 1, 2016, with an initial phase-in of 0.625% . Also, certain deductions from and adjustments to regulatory capital is being phased in over several years. Management believes that the Company will remain characterized as “well capitalized” throughout the phase-in periods. As of December 31, 2016 , the most recent notification from the Federal Deposit Insurance Corporation 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 ratios as set forth in the following table. There are no conditions or events since the notification that management believes have changed the Bank’s category. Management believes, as of December 31, 2016 and 2015 , that the Company and the Bank meet all capital adequacy requirements to which they are subject. The Company’s and the Bank’s actual capital amounts and ratios as of December 31, 2016 and 2015 are also presented in the following table. Actual Minimum Capital Requirement Minimum To Be Well Capitalized Amount Ratio Amount Ratio Amount Ratio (Dollars in thousands) Blue Hills Bancorp, Inc.: December 31, 2016 Total capital (to risk weighted assets) $ 395,325 20.5 % $ 154,471 8.0 % $ 193,089 10.0 % Tier 1 capital (to risk weighted assets) 376,575 19.5 115,854 6.0 154,471 8.0 Common equity Tier 1 (to risk weighted assets) 376,575 19.5 86,890 4.5 125,508 6.5 Tier 1 capital (to average assets) 376,575 16.0 94,166 4.0 117,708 5.0 December 31, 2015 Total capital (to risk weighted assets) 407,444 24.8 131,231 8.0 164,039 10.0 Tier 1 capital (to risk weighted assets) 390,342 23.8 98,423 6.0 131,231 8.0 Common equity Tier 1 (to risk weighted assets) 390,342 23.8 73,818 4.5 106,625 6.5 Tier 1 capital (to average assets) 390,342 19.6 79,658 4.0 99,573 5.0 Blue Hills Bank: December 31, 2016 Total capital (to risk weighted assets) 313,457 16.3 154,196 8.0 192,745 10.0 Tier 1 capital (to risk weighted assets) 294,707 15.3 115,647 6.0 154,196 8.0 Common equity Tier 1 (to risk weighted assets) 294,707 15.3 86,735 4.5 125,284 6.5 Tier 1 capital (to average assets) 294,707 12.5 94,099 4.0 117,623 5.0 December 31, 2015 Total capital (to risk weighted assets) 296,309 18.1 130,832 8.0 163,540 10.0 Tier 1 capital (to risk weighted assets) 279,207 17.1 98,124 6.0 130,832 8.0 Common equity Tier 1 (to risk weighted assets) 279,207 17.1 73,593 4.5 106,301 6.5 Tier 1 capital (to average assets) 279,207 14.0 79,867 4.0 99,608 5.0 Preferred stock On September 22, 2011, Hyde Park Bancorp, Inc. issued and sold 18,724 shares of senior non-cumulative perpetual preferred stock, Series A (“Series A Preferred”), with a liquidation value of $1,000 per share to the U.S. Treasury as part of the Small Business Lending Fund Program (“SBLF”) for an aggregate purchase price of $18.7 million . On July 11, 2014, the Company redeemed the $18.7 million of Series A Preferred Stock issued to the U.S. Treasury under the Small Business Lending Fund (“SBLF”) preferred stock program. The redemption was completed with a payment to the U.S. Treasury of $18.7 million plus accrued dividends. As part of the conversion (see Note 1), the Board of Directors of the Company authorized 50,000,000 shares, zero par value of Preferred Stock. As of December 31, 2016 , there were no shares issued or outstanding. 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 of 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. At December 31, 2016, the Bank's retained earnings available for the payment of dividends was $148.0 million . Accordingly, $154.2 million of the Company's equity in the net assets of the Bank was restricted at December 31, 2016. Funds available for loans or advances by the Bank to the Company amounted to $30.1 million . 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 capital requirements. The payment of dividends by the Company is subject to Maryland law. The Company can pay dividends on its common stock if, after giving effect to such distribution, (i) it would be able to pay its indebtedness as the indebtedness comes due in the usual course of business and (ii) its total assets exceed the sum of its liabilities and the amount needed, if Blue Hills Bancorp were to be dissolved at the time of the distribution, to satisfy the preferential rights upon dissolution of any holders of capital stock who have a preference in the event of dissolution; provided, however, that even if the Company's assets are less than the amount necessary to satisfy the requirement set forth in (ii) above, the Company may make a distribution from: (A) the Company's net earnings for the fiscal year in which the distribution is made; (B) the Company's net earnings for the preceding fiscal year; or (C) the sum of the Company's net earnings for the preceding eight fiscal quarters. The holders of common stock of the Company will be entitled to receive and share equally in dividends as may be declared by our Board of Directors out of funds legally available. If the Company issues shares of preferred stock, the holders thereof may have a priority over the holders of the common stock with respect to dividends.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS Pension plan The Company has historically provided basic and supplemental pension benefits for eligible employees through the Savings Banks Employees Retirement Association’s (“SBERA”) Pension Plan (the “Plan”). Each employee reaching the age of 21 and having completed at least 1000 hours of service in any one twelve -month period, beginning with such employee’s date of employment, was automatically enrolled in the Plan. The Company accounts for its defined benefit pension plan using an actuarial model that allocates pension costs over the service period of employees in the plan. The Company accounts for the over-funded or under-funded status of its defined benefit plan as an asset or liability on its consolidated balance sheets and recognizes changes in the funded status in the year in which the changes occur as other comprehensive income or loss. The Company amended its defined benefit pension plan in 2013 by freezing the plan to new participants and subsequently amended the plan and froze it for all participants effective October 31, 2014. Accumulated benefits for participants earned through the end of October 2014 will remain secured by the Plan assets. Information pertaining to the Plan is as follows: Years Ended December 31, 2016 2015 2014 (In thousands) Change in plan assets: Fair value of plan assets at beginning of year $ 8,814 $ 9,443 $ 9,535 Actual return (loss) on plan assets 847 (304 ) 391 Employer contribution 470 — — Benefits paid (320 ) (325 ) (483 ) Fair value of plan assets at end of year 9,811 8,814 9,443 Change in benefit obligation: Benefit obligation at beginning of year 10,772 10,135 9,287 Service cost — — 484 Interest cost 422 401 407 Actuarial loss 1,022 561 2,230 Benefits paid (320 ) (325 ) (483 ) Curtailment gain — — (1,790 ) Benefit obligation at end of year 11,896 10,772 10,135 Funded status and accrued liability at end of year $ (2,085 ) $ (1,958 ) $ (692 ) Accumulated benefit obligation at end of year $ 11,896 $ 10,772 $ 10,135 At December 31, 2016 and 2015 , the discount rate used to determine the benefit obligation was as follows: December 31, 2016 2015 Discount rate 3.86 % 4.01 % The components of net periodic pension benefit are as follows: Years Ended December 31, 2016 2015 2014 (In thousands) Service cost $ — $ — $ 484 Interest cost 422 401 407 Expected return on plan assets (720 ) (745 ) (735 ) Amortization of net actuarial loss (gain) 271 110 (70 ) Curtailment gain — — (1,304 ) Net periodic pension benefit $ (27 ) $ (234 ) $ (1,218 ) The assumptions used to determine net periodic pension benefit are as follows: Years Ended December 31, 2016 2015 2014 Discount rate 4.01 % 4.00 % 4.25 % Expected long-term rate of return on plan assets 8.00 % 8.00 % 8.00 % The Company has selected its assumption with respect to the expected long-term rate of return based on prevailing yields on high-quality, fixed-income investments increased by a premium for equity return expectations. SBERA offers a common and collective trust as the underlying investment structure for pension plans participating in SBERA. The target allocation mix for the common and collective trust portfolio calls for an equity-based investment range from 40% to 64% of total portfolio assets. The remainder of the portfolio is allocated to fixed income from 15% to 25% and other investments including global asset allocation and hedge funds from 25% to 41% . The Trustees of SBERA, through the Investment Committee, select investment managers for the common and collective trust portfolio. A professional investment advisory firm is retained by the Investment Committee to provide allocation analysis, performance measurement and to assist with manager searches. The overall investment objective is to diversify equity investments across a spectrum of investment types to limit risks from large market swings. The fair value of major categories of the Company’s pension plan assets are summarized below: Level 1 Level 2 Level 3 Total Fair Value (In thousands) December 31, 2016 Collective funds $ 681 $ — $ — $ 681 Equity securities 1,929 — — 1,929 Mutual funds 1,209 — — 1,209 Short-term investments 124 — — 124 Total investments measured in the fair value hierarchy 3,943 — — 3,943 Investments measured at net asset value (a) — — — 5,868 $ 3,943 $ — $ — $ 9,811 December 31, 2015 Collective funds $ 1,126 $ 4,266 $ — $ 5,392 Equity securities 1,566 — — 1,566 Mutual funds 1,046 — — 1,046 Hedge funds — — 660 660 Short-term investments 150 — — 150 $ 3,888 $ 4,266 $ 660 $ 8,814 (a) In accordance with FASB ASC 820, Fair Value Measurements , certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value hierarchy above was received from SBERA, the plan administrator. The Plan assets measured at fair value in Level 1 are based on quoted market prices in an active exchange market. Plan assets measured at fair value in Level 2 are based on pricing models that consider standard input factors such as observable market data, benchmark yields, interest rate volatilities, broker/dealer quotes, credit spreads and new issue data. Plan assets measured at fair value in Level 3 are based on unobservable inputs, which include the SBERA’s assumptions and the best information available under the circumstance. Estimated future benefit payments, assuming employees retire at age 65 and take normal distribution payments, are as follows: Amount Year Ending December 31, (In thousands) 2017 $ 785 2018 1,087 2019 614 2020 710 2021 930 2022-2026 3,223 The Company contributed $ 1.1 million to the Plan in January 2017. No further contributions are anticipated during 2017. 401(k) Plan The Company has a 401(k) Plan whereby each employee having completed at least three months of service beginning with their date of employment, automatically becomes a participant in the 401(k) Plan. Employees may contribute a portion of their compensation subject to certain limits based on Federal tax laws. Effective December 15, 2013, the Company enhanced its 401(k) Plan to include a 3% guaranteed non-elective contribution and a 2% elective contribution based on the financial performance of the Company. Effective January 1, 2015, the Company amended the 401(k) Plan to incorporate an overall 4% contribution that matches 100% of an employee’s first 3% of deferral and 50% of the next 2% deferral. In 2014, the Bank provided a 3% contribution. For the years ended December 31, 2016 , 2015 and 2014 expenses related to the plan were $784,000 , $610,000 , and $465,000 , respectively. Prior to 2014, the Company did not contribute to the 401(k) plan. Supplemental Executive Retirement Plans The Company entered into agreements with various executives and Board members which provided for a fixed dollar amount to be contributed each year to the participant’s supplemental executive retirement account. All benefits under these agreements became fully vested after five years of service, however during 2013 these agreements were terminated and all vesting was accelerated. No further awards have or will be granted under these agreements. The Supplemental Executive Retirement Plan was terminated in a manner that complies with Section 409A of the Internal Revenue Code, whereby benefits could not be distributed for 12 months following the plan’s termination but were required to be distributed in full no later than 24 months following the plan’s termination. To allow participants the opportunity to use their account balances within the plan to purchase Blue Hills Bancorp common stock in the stock offering prior to the date the account was distributed, the plan was amended prior to its termination. All participants elected to invest in employer stock and all participant balances were distributed in Blue Hills Bancorp common stock in December 2015. In connection with the distributions, 27,956 shares were redeemed by the Company for tax withholding. Short-term Incentive Compensation Plan All employees meeting specified service requirements are eligible to participate in the discretionary Short-term Incentive Compensation Plan. The purpose of the plan is to motivate and reward employees for achieving strategic objectives through a goals program. The Company recorded expenses of $2.5 million , $2.3 million , and $3.0 million for achievement of the 2016 , 2015 and 2014 goals, respectively. Employee Stock Ownership Plan The Company maintains the ESOP to provide eligible employees the opportunity to own Company stock. This plan is a tax-qualified retirement plan for the benefit of Company employees. In connection with the conversion (See Note 1), the Company contributed funds to the Funding Corporation to enable it to grant a loan to the ESOP for the purchase of 2,277,345 shares of the Company’s common stock at a price of $10.00 per share. Principal and interest is payable annually over 30 years at a rate per annum equal to the Prime Rate ( 3.75% at December 31, 2016 ). Loan payments are principally funded by cash contributions from the Company. The loan is secured by the shares purchased, which are held in a suspense account for allocation among participants as the loan is repaid. The balance of the ESOP loan at December 31, 2016 was $21.0 million . Contributions are allocated to eligible participants on the basis of compensation, subject to federal tax limits. The number of shares committed to be released per year is 75,912 through 2043. Shares held by the ESOP include the following: December 31, 2016 December 31, 2015 Allocated 149,613 75,912 Committed to be allocated 75,912 75,912 Unallocated 2,049,608 2,124,846 2,275,133 2,276,670 The fair value of unallocated shares was $38.4 million and $32.5 million at December 31, 2016 and 2015 , respectively. Total compensation expense recognized in connection with the ESOP amounted to $1.1 million for each of the years ended December 31, 2016 and 2015 , and $993,000 for the year ended December 31, 2014 .

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	STOCK BASED COMPENSATION Under the Blue Hills Bancorp, Inc. 2015 Equity Incentive Plan (the "Equity Plan"), the Company may grant options, restricted stock, restricted units or performance awards to its directors, officers and employees. Both incentive stock options and non-qualified stock options may be granted under the Equity Plan, with the total number of shares reserved for options equaling 2,846,681 . The exercise price of each option equals the market price of the Company’s stock on the date of grant and the maximum term of each option is ten years . The total number of shares reserved for restricted stock or restricted units equaling 1,138,673 . Options and awards vest ratably over five years . Expense related to options and restricted stock granted to employees is recognized in s alaries and employee benefits within noninterest expense and expense related to options and restricted stock granted to directors is recognized as directors' fees within noninterest expense. The Company has standard form agreements used for stock option and restricted stock awards and generally provide that: (1) any unvested options or unvested restricted stock vest upon a Change in Control; and, that (2) any stock options which vest pursuant to a Change in Control, which is an event described in Section 280G of the Internal Revenue Code of 1986, will be cashed out at the difference between the acquisition price and the exercise price of the stock option. Stock Options The fair value of each option grant is estimated on the date of the grant using the Black-Scholes option-pricing model with the following assumptions: • Volatility is based on peer group volatility because the Company does not have a sufficient trading history. • Expected life represents the period of time that the option is expected to be outstanding, taking into account the contractual term, and the vesting period. • Expected dividend yield is based on the Company's history and expectation of dividend payouts. • The risk-free 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 Company made the following awards of options to purchase shares of common stock in 2016 and 2015 : Date of grant February 29, 2016 October 7, 2015 Options granted 55,000 2,434,000 Vesting period (years) 5 5 Expiration date February 28, 2026 October 7, 2025 Expected volatility 28.47 % 28.85 % Expected life (years) 6.5 6.5 Expected dividend yield 0.58 % 0.54 % Risk free interest rate 1.38 % 1.55 % Fair value per option $ 4.02 $ 4.23 A summary of the status of the Company's stock option grants for the year ended December 31, 2016 is presented in the table below: Options Stock Option Awards Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value Balance at January 1, 2016 2,434,000 $ 14.07 — $ — Granted 55,000 13.80 — — Forfeited (36,450 ) 14.07 — — Exercised (2,880 ) 14.07 — — Balance at December 31, 2016 2,449,670 $ 14.06 8.77 $ 11,479,306 Outstanding and expected to vest at December 31, 2016 2,449,670 $ 14.06 8.77 $ 11,479,306 Exercisable at December 31, 2016 478,390 $ 14.07 3.78 $ 2,238,865 Unrecognized compensation cost at December 31, 2016 $7,827,000 Weighted average remaining recognition period (years) at December 31, 2016 3.78 For the years ended December 31, 2016 and 2015 , stock-based compensation expense applicable to the stock options was $2.1 million and $473,000 , respectively. The recognized tax benefit related to this expense was $502,000 and $112,000 , respectively. There was no stock-based compensation expense related to stock options for the year ended December 31, 2014. Restricted Stock Shares issued upon vesting may be either authorized but unissued shares or reacquired shares held by the Company. Any shares not issued because vesting requirements are not met will again be available for issuance under the plan. The fair market value of shares awarded, based on the market price at the date of grant, is recorded as unearned compensation and amortized over the applicable vesting period. There are 40,000 performance based awards outstanding as of December 31, 2016. The following table presents the activity in non-vested stock awards under the Equity Plan for the year ended December 31, 2016 : Outstanding Restricted Stock Awards Weighted Average Grant Price Non-vested stock awards at January 1, 2016 983,175 $ 14.07 Granted 31,450 13.83 Vested (186,755 ) 14.07 Forfeited (11,800 ) 14.07 Non-vested stock awards at December 31, 2016 816,070 $ 14.06 Unrecognized compensation cost, inclusive of directors' fees at December 31, 2016 $ 10,645,000 Weighted average remaining recognition period (years) at December 31, 2016 3.78 For the years ended December 31, 2016 and 2015 , stock-based compensation expense applicable to restricted stock awards was $2.8 million and $651,000 , respectively. The recognized tax benefit related to this expense was $987,000 and $228,000 , respectively. There was no expense related to restricted stock awards for the year ended December 31, 2014.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Earnings Per Share	EARNINGS PER SHARE Earnings per share consisted of the following components for the years ended December 31, 2016 and 2015. 2016 2015 (Dollars in thousands, except per share amounts) Net income applicable to common stock $ 8,653 $ 7,227 Average number of common shares outstanding 27,464,996 28,460,077 Less: Average unvested restricted stock awards (957,364 ) (231,652 ) Less: Average unallocated ESOP shares (2,087,227 ) (2,163,478 ) Average number of common shares outstanding used to calculate basic earnings per common share 24,420,405 26,064,947 Effect of dilutive unvested restricted stock awards 120,524 4,642 Average number of common shares outstanding used to calculate diluted earnings per common share 24,540,929 26,069,589 Earnings per common share: Basic $ 0.35 $ 0.28 Diluted $ 0.35 $ 0.28 Options for 2,486,000 and 2,434,000 shares were not included in the computation of diluted earnings per share because to do so would have been antidilutive for the years ended December 31, 2016 and 2015, respectively, as the weighted average exercise prices of the stock options exceeded the weighted average market price for the periods presented.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES In the normal course of business, there are outstanding commitments and contingencies which are not reflected in the accompanying consolidated financial statements. Loan commitments The Company is a party to financial instruments with off-balance sheet risk in the normal course of business to meet the financing needs of its customers. These financial instruments include commitments to extend credit, which involve elements of credit and interest rate risk in excess of the amount recognized in the accompanying consolidated balance sheets. The contract amount of these instruments reflects the extent of involvement the Company has in these particular classes of financial instruments. The Company’s exposure to credit loss is represented by the contractual amount of the instruments. The Company uses the same credit policies in making commitments as it does for on-balance sheet instruments. Financial instruments whose contract amounts represent credit risk consist of: December 31, 2016 2015 (In thousands) Commitments to originate loans $ 51,622 $ 69,554 Letters of credit 3,277 3,571 Unused lines-of-credit: Commercial 164,185 128,748 Home equity 55,344 44,968 Consumer 15,995 16,033 Undisbursed construction loans 96,169 80,336 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 and unadvanced funds on lines-of-credit generally have fixed expiration dates and may expire without being drawn upon. Therefore, the total commitment amount does not necessarily represent future cash requirements. The Company evaluates each customer’s creditworthiness on a case-by-case basis. These financial instruments are primarily secured by mortgage liens on real estate. Operating lease commitments Pursuant to the terms of noncancelable lease agreements in effect at December 31, 2016 , pertaining to premises, future minimum rent commitments are as follows: Year Ending December 31, Amount (In thousands) 2017 $ 2,530 2018 2,665 2019 2,479 2020 2,398 2021 2,288 Thereafter 12,408 $ 24,768 Rent expense for years ended December 31, 2016 , 2015 and 2014 amounted to $2.2 million , $1.6 million and $1.1 million , respectively. Certain leases contain renewal options for up to 30 years. The cost of such options is not included above. Other Commitments Effective January 1, 2014, the Bank entered into an agreement for the naming rights of a Boston waterfront music venue. The agreement spans a ten -year period, with an opt-out option at the end of year seven, where the Bank paid $390,000 during the first year with 5% annual increases in subsequent years. Total expenses related to the agreement were $430,000 , $410,000 and $390,000 for the years ended December 31, 2016, 2015 and 2014, respectively. Employment and change in control agreements The Company has entered into an employment agreement with its President and Chief Executive Officer that generally provides for a specified minimum annual compensation and the continuation of certain benefits currently received. Employment may be terminated for cause, as defined, or an aggregate cash severance payment that will be determined based on timing of any other future change in control. The agreement has an initial term of three years, with automatic one -year extensions on the anniversary date of the agreement. The Company has also entered into change in control agreements with certain members of management, including the Company’s Chief Financial Officer, the Company’s Executive Vice President, Commercial Lending, and the Company's Senior Vice President, Chief Risk Officer and others, which provide for the continuation of base salaries for specified periods of time in the event of involuntary termination without cause or termination for good reason in the event of a change in control. In March 2015, the Company revised the change in control agreement with its Chief Financial Officer to be a severance and change in control agreement so that it provided a benefit on an involuntary termination without cause (including resignation for good reason), whether or not the termination occurred in connection with or after a change in control. Contingencies The Company is involved in various litigation and other legal claims that arise in the normal course of business. On December 30, 2014, a former employee filed a complaint in U.S. Federal District Court of Massachusetts, claiming wrongful termination following a whistleblower claim. This complaint alleged violations of the Federal Deposit Insurance Act, the False Claims Act, and the Family and Medical Leave Act ("FMLA"). The former employee has since withdrawn his claim under the FMLA, but continues to seek alleged damages with interest of foregone compensation, including bonuses and employee benefits, compensatory and punitive damages, and attorney’s fees and litigation expenses in unspecified amounts. Blue Hills Bancorp, Inc. and Blue Hills Bank believe the allegations in this complaint to be completely without merit and are defending this action in the Federal District Court. In the opinion of management, these matters will have no material effect on the Company’s consolidated financial statements.

On Balance Sheet Derivative Ins

On Balance Sheet Derivative Instruments and Hedging Activities	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
On Balance Sheet Derivative Instruments and Hedging Activities	ON BALANCE SHEET DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES The Company is party to derivative financial instruments in the normal course of business to manage exposure to fluctuations in interest rates and to meet the needs of commercial customers. These financial instruments have been limited to loan level interest rate swap agreements, which are entered into with counterparties that meet established credit standards. These transactions involve both credit and market risk. The notional amounts are amounts on which calculations, payments, and the value of the derivatives are based. Notional amounts do not represent direct credit exposures. The fair value of the derivative instruments is reflected on the Company’s consolidated balance sheet as other assets or other liabilities as appropriate. Changes in the fair value of these agreements are recorded in miscellaneous income in the consolidated statements of operations. The Company did not have any fair value hedges or cash flow hedges at December 31, 2016 and 2015 . The table below presents information about derivative financial instruments not designated as hedging instruments at December 31, 2016 and 2015 . Derivative Gains Derivative Losses Notional Amount Fair Value Notional Amount Fair Value (In thousands) December 31, 2016 Economic hedges: Commercial loan level interest rate swap agreements $ 419,488 $ 9,016 $ 419,488 $ 8,932 Other contracts 15,865 8 33,045 56 Total derivatives $ 435,353 $ 9,024 $ 452,533 $ 8,988 December 31, 2015 Economic hedges: Commercial loan level interest rate swap agreements $ 282,546 $ 7,956 $ 282,546 $ 8,411 Other contracts 8,300 6 12,698 78 Total derivatives $ 290,846 $ 7,962 $ 295,244 $ 8,489 The Company is exposed to credit-related losses in the event of nonperformance by the counterparties to these agreements. The Company controls the credit risk of its financial contracts through credit approvals, limits and monitoring procedures, and does not expect any counterparties to fail their obligations. The Company has minimum collateral posting thresholds with certain of its counterparties. Other contracts represent risk participation agreements on commercial loan level interest rate swap agreements. The Company has entered into risk participation agreements with the correspondent institutions to share in any interest rate swap gains or losses incurred as a result of the commercial loan customers’ termination of a loan level interest rate swap agreement prior to maturity. The Company records these risk participation agreements at fair value. Mortgage Banking Derivatives The Company enters into commitments to fund residential mortgage loans at specified rates and times in the future, with the intention that loans will subsequently be sold in the secondary market. Mortgage loan commitments are referred to as derivative loan commitments if the loan that will result from exercise of the commitment will be held for sale upon funding. These commitments are recognized at fair value on the consolidated balance sheet in other assets and other liabilities with changes in their fair values recorded in mortgage banking income in the consolidated statement of operations. Outstanding loan commitments expose the Company to the risk that the price of the loans arising from exercise of the loan commitment might change from inception of the rate lock to funding of the loan due to changes in mortgage interest rates. If interest rates increase, the value of these loan commitments decreases. Conversely, if interest rates decrease, the value of these loan commitments increases. The notional amount of mortgage loan commitments as of December 31, 2016 was $6.8 million . The fair value of such commitments at December 31, 2016 included gains of $111,000 included in other assets, and losses of $3,000 included in other liabilities on the consolidated balance sheet. To protect against the price risk inherent in derivative loan commitments, the Company utilizes “best efforts” forward loan sale commitments to mitigate the risk of potential decreases in the values of loans that would result from the exercise of the derivative loan commitments. With a “best efforts” contract, the Company commits to deliver an individual mortgage loan of a specified principal amount and quality to an investor if the loan to the underlying borrower closes. Generally, the price the investor will pay the seller for an individual loan is specified prior to the loan being funded (e.g., on the same day the lender commits to lend funds to a potential borrower). The Company expects that these forward sale commitments will experience changes in fair value opposite to the change in fair value of derivative loan commitments. The notional amount of forward loan sale commitments at December 31, 2016 was $9.5 million . The fair value of such commitments December 31, 2016 included gains of $15,000 included in other assets and losses of $74,000 included in other liabilities on the consolidated balance sheet.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASURMENTS Determination of fair value The Company uses fair value measurements to record fair value adjustments to certain assets and liabilities and to determine fair value disclosures. Fair value 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. 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 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 assets and liabilities. The following methods and assumptions were used by the Company in estimating fair value disclosures for financial instruments: Cash and cash equivalents : The carrying amounts of cash and due from banks and short-term investments approximate fair value. Securities available for sale : All fair value measurements are obtained from a third-party pricing service and are not adjusted by management. The securities measured at fair value in Level 1 are based on quoted market prices in an active exchange market. These securities include U.S. Treasury obligations and marketable equity securities. All other securities are measured at fair value in Level 2 based on pricing models that consider standard input factors such as observable market data, benchmark yields, interest rate volatilities, broker/dealer quotes, credit spreads and new issue data. Federal Home Loan Bank stock : The carrying value of Federal Home Loan Bank stock approximates fair value based on the redemption provisions of the Federal Home Loan Bank. Loans held for sale : Fair values are based on commitments in effect from investors or prevailing market prices. Loans : Fair values are estimated using discounted cash flow analyses, using market interest rates currently being offered for loans with similar terms to borrowers of similar credit quality. Fair values for non-performing loans are estimated using discounted cash flow analyses or underlying collateral values, where applicable. Accrued interest receivable : The carrying amount of accrued interest receivable approximates fair value. Deposits : The fair values for non-certificate accounts are, by definition, equal to the amount payable on demand at the reporting date (i.e., their carrying amounts). Fair values for certificate accounts are estimated using a discounted cash flow calculation that applies market interest rates currently being offered on certificates to a schedule of aggregated expected monthly maturities on time deposits. Borrowings : The fair values of borrowings are estimated using discounted cash flow analyses based on the current incremental borrowing rates in the market for similar types of borrowing arrangements. Interest rate swap agreements and risk participation agreements : The fair values of interest rate swap agreements are based on a valuation model that uses primarily observable inputs, such as benchmark yield curves and interest rates and also include the value associated with counterparty credit risk. Forward loan sale commitments and derivative loan commitments : Fair values of forward loan sale commitments and derivative loan commitments are based on fair values of the underlying mortgage loans and, for derivative loan commitments, fair values also include the value of servicing, deferred origination fees/costs and the probability of such commitments being exercised. Significant judgment and estimation is required in determining these fair value measurements. Off-balance sheet instruments : Fair values for off-balance sheet lending commitments are based on fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements and the counterparties’ credit standing. The estimated fair value of off-balance sheet financial instruments at December 31, 2016 and 2015 , was immaterial since fees charged are not material. Assets and liabilities measured at fair value on a recurring basis Assets and liabilities measured at fair value on a recurring basis are summarized below: Level 1 Level 2 Level 3 Total Fair Value (In thousands) December 31, 2016 Assets Securities available for sale: Debt securities $ — $ 161,668 $ — $ 161,668 Marketable equity securities 43,168 — — 43,168 Derivative assets: Interest rate swap agreements — 9,024 — 9,024 Forward loan sale commitments — — 15 15 Mortgage loan commitments — — 111 111 Total assets $ 43,168 $ 170,692 $ 126 $ 213,986 Liabilities Derivative liabilities: Interest rate swap agreements $ — $ 8,988 $ — $ 8,988 Forward loan sale commitments — — 74 74 Mortgage loan commitments — — 3 3 Total liabilities $ — $ 8,988 $ 77 $ 9,065 December 31, 2015 Assets Securities available for sale: Debt securities $ — $ 184,114 $ — $ 184,114 Marketable equity securities 47,576 — — 47,576 Interest rate swap agreements — 7,962 — 7,962 Total assets $ 47,576 $ 192,076 $ — $ 239,652 Liabilities Interest rate swap agreements $ — $ 8,489 $ — $ 8,489 Assets measured at fair value on a non-recurring basis The Company may also be required, from time to time, to measure certain assets at fair value on a non-recurring basis in accordance with generally accepted accounting principles. These adjustments to fair value usually result from application of lower-of-cost-or-market accounting or write-downs of individual assets. There are no liabilities measured at fair value on a non-recurring basis. The following table summarizes the fair value hierarchy applicable to assets measured at fair value on a non-recurring basis: December 31, 2016 December 31, 2015 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 (In thousands) Impaired loans $ — $ — $ 136 $ — $ — $ 4,752 The following table summarizes the total losses on assets measured at fair value on a non-recurring basis for the years ended December 31, 2016, 2015 and 2014. Years Ended December 31, 2016 2015 2014 (In thousands) Impaired loans $ (2,911 ) $ (404 ) $ (18 ) Gains and losses applicable to impaired loans are based on the appraised value of the underlying collateral, discounted as necessary due to management’s estimates of changes in market conditions. The losses applicable to impaired loans are not recorded as a direct adjustment to current earnings or comprehensive income, but rather as a component in determining the overall adequacy of the allowance for loan losses. Adjustments to the estimated fair value of impaired loans may result in increases or decreases to the provision for loan losses. Summary of fair values of financial instruments The estimated fair values, and related carrying amounts, of the Company’s financial instruments are as follows. Certain financial instruments and all nonfinancial instruments are exempt from disclosure requirements. Accordingly, the aggregate fair value amounts presented herein do not represent the underlying fair value of the Company. Carrying Fair Value Level 1 Level 2 Level 3 Total (In thousands) December 31, 2016 Financial assets: Cash and cash equivalents $ 30,496 $ 30,496 $ — $ — $ 30,496 Securities available for sale 204,836 43,168 161,668 — 204,836 Securities held to maturity 201,027 — 198,093 — 198,093 Federal Home Loan Bank stock 13,352 — — 13,352 13,352 Loans and loans held for sale, net 1,915,632 — — 1,903,978 1,903,978 Accrued interest receivable 6,057 — — 6,057 6,057 Financial liabilities: Deposits 1,808,687 — — 1,808,629 1,808,629 Borrowings 251,000 — 250,648 — 250,648 On-balance sheet derivative financial instruments: Derivative assets: Interest rate swap agreements 9,024 — 9,024 — 9,024 Forward loan sale commitments 15 — — 15 15 Mortgage loan commitments 111 — — 111 111 Derivative liabilities: Interest rate swap agreements: 8,988 — 8,988 — 8,988 Forward loan sale commitments 74 — — 74 74 Mortgage loan commitments 3 — — 3 3 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total (In thousands) December 31, 2015 Financial assets: Cash and cash equivalents $ 33,298 $ 33,298 $ — $ — $ 33,298 Securities available for sale 231,690 47,576 184,114 — 231,690 Securities held to maturity 200,141 634 198,592 — 199,226 Federal Home Loan Bank stock 13,567 — — 13,567 13,567 Loans and loans held for sale, net 1,536,152 — — 1,538,809 1,538,809 Accrued interest receivable 5,344 — — 5,344 5,344 Financial liabilities: Deposits 1,433,849 — — 1,434,179 1,434,179 Borrowings 260,000 — 260,244 — 260,244 On-balance sheet derivative financial instruments: Derivative assets: Interest rate swap agreements 7,962 — 7,962 — 7,962 Derivative liabilities: Interest rate swap agreements: 8,489 — 8,489 — 8,489

Other Comprehensive Income

Other Comprehensive Income	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Other Comprehensive Income	OTHER COMPREHENSIVE INCOME Accounting principles generally require that recognized revenues, expenses, gains and losses be included in net income. Although certain changes in assets and liabilities are reported as a separate component of equity on the consolidated balance sheets, such items, along with net income, are components of comprehensive income. The components of accumulated other comprehensive loss, included in stockholders' equity, are as follows: December 31, 2016 2015 (In thousands) Securities available for sale: Net unrealized loss $ (3,087 ) $ (5,701 ) Tax effect 1,007 1,945 Net-of-tax amount (2,080 ) (3,756 ) Securities held to maturity: Net unrealized gain on transferred securities 337 571 Tax effect (114 ) (197 ) Net-of-tax amount 223 374 Defined benefit pension plan: Unrecognized net actuarial loss (3,482 ) (2,858 ) Tax effect 1,270 1,052 Net-of-tax amount (2,212 ) (1,806 ) $ (4,069 ) $ (5,188 ) Changes in accumulated other comprehensive income (loss) by component follows: Securities Available for Sale Securities Held to Maturity Defined Benefit Pension Plan Total Year Ended December 31, 2016 Beginning balance $ (3,756 ) $ 374 $ (1,806 ) $ (5,188 ) Other comprehensive income (loss) before reclassifications 3,849 — (895 ) 2,954 Realized gains reclassified (1,235 ) — — (1,235 ) Amortization of actuarial losses — — 271 271 Amortization of amounts previously recorded upon transfer to held-to-maturity from available-for-sale — (234 ) — (234 ) Tax effects (938 ) 83 218 (637 ) Net current-period other comprehensive income (loss) 1,676 (151 ) (406 ) 1,119 Ending balance $ (2,080 ) $ 223 $ (2,212 ) $ (4,069 ) Year ended December 31, 2015 Beginning balance $ 3,392 $ — $ (815 ) $ 2,577 Other comprehensive loss before reclassifications (8,332 ) — (1,610 ) (9,942 ) Realized gains reclassified (1,968 ) — — (1,968 ) Amortization of actuarial losses — — 110 110 Unrealized gains on securities reclassified as held to maturity (666 ) 666 — — Amortization of amounts previously recorded upon transfer to held-to-maturity from available-for-sale — (95 ) — (95 ) Tax effects 3,818 (197 ) 509 4,130 Net current-period other comprehensive income (loss) (7,148 ) 374 (991 ) (7,765 ) Ending balance $ (3,756 ) $ 374 $ (1,806 ) $ (5,188 ) Year Ended December 31, 2014 Beginning balance $ 1,983 $ — $ 482 $ 2,465 Other comprehensive income (loss) before reclassifications 4,942 — (2,090 ) 2,852 Realized gains reclassified (2,515 ) — — (2,515 ) Amortization of actuarial gains — — (70 ) (70 ) Tax effects (1,018 ) — 863 (155 ) Net current-period other comprehensive income (loss) 1,409 — (1,297 ) 112 Ending balance $ 3,392 $ — $ (815 ) $ 2,577 Actuarial gains of $358,000 , included in accumulated other comprehensive income at December 31, 2016, are expected to be recognized as a component of net periodic pension cost, included in salaries and employee benefits expense, during the year ending December 31, 2017.

Condensed Financial Statements

Condensed Financial Statements of Parent Company	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Financial Statements of Parent Company	CONDENSED FINANCIAL STATEMENTS OF PARENT COMPANY Financial information pertaining only to Blue Hills Bancorp, Inc. is as follows: December 31, BALANCE SHEETS 2016 2015 (In thousands) Assets Cash balances at Blue Hills Bank $ 66,326 $ 100,965 Total cash and cash equivalents 66,326 100,965 Investment in subsidiaries 328,201 311,357 Other assets 13,499 7,993 Total assets $ 408,026 $ 420,315 Liabilities and Stockholders' Equity Liability to ESOP $ 20,995 $ 21,459 Accrued expenses 124 27 Stockholders' equity 386,907 398,829 Total liabilities and stockholders' equity $ 408,026 $ 420,315 Years Ended December 31, 2016 2015 2014 STATEMENTS OF OPERATIONS (In thousands) Loss before income taxes and equity in undistributed net income of subsidiaries $ (2,478 ) $ (1,860 ) $ (9,432 ) Applicable income tax benefit (758 ) (1,112 ) (3,277 ) Loss before equity in income of subsidiaries (1,720 ) (748 ) (6,155 ) Equity in undistributed net income of subsidiaries 10,373 7,975 5,972 Net income (loss) $ 8,653 $ 7,227 $ (183 ) Years Ended December 31, 2016 2015 2014 STATEMENTS OF CASH FLOWS (In thousands) Cash flows from operating activities: Net income (loss) $ 8,653 $ 7,227 (183 ) Adjustments to reconcile net income to net cash provided by (used for) operating activities: Equity in undistributed net income of subsidiaries (10,373 ) (7,975 ) (5,972 ) Charitable Foundation contribution — — 6,943 Excess tax benefit from deferred and stock based compensation (105 ) (166 ) — Net change in other assets 11,625 (1,157 ) (1,731 ) Net change in other liabilities 97 (241 ) 267 Net cash provided by (used for) operating activities 9,897 (2,312 ) (676 ) Cash flows used for investing activities: Investment in Blue Hills Bank (16,844 ) (3,929 ) (161,820 ) Net cash used for investing activities (16,844 ) (3,929 ) (161,820 ) Cash flows provided by (used for) financing activities: Proceeds from the issuance of common stock — — 274,143 Redemption of SBLF preferred stock — — (18,724 ) Excess tax benefit from deferred and stock based compensation 105 166 — Repurchase of common stock (24,432 ) (13,121 ) — Share redemption for tax withholdings (730 ) (439 ) — Proceeds from exercise of stock options 40 — — Common and preferred stock dividends paid (2,675 ) (1,032 ) (439 ) Net cash provided by (used for) financing activities (27,692 ) (14,426 ) 254,980 Net change in cash and cash equivalents (34,639 ) (20,667 ) 92,484 Cash and cash equivalents at beginning of year 100,965 121,632 29,148 Cash and cash equivalents at end of year $ 66,326 $ 100,965 $ 121,632

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) First Quarter Second Quarter Third Quarter Fourth Quarter 2016 2015 2016 2015 2016 2015 2016 2015 (In thousands, except share data) Interest and dividend income $ 16,063 $ 12,682 $ 16,356 $ 13,130 $ 17,685 $ 15,418 $ 19,434 $ 17,071 Interest expense 2,862 2,017 3,040 2,015 3,190 2,213 3,484 2,499 Net interest and dividend income 13,201 10,665 13,316 11,115 14,495 13,205 15,950 14,572 Provision (credit) for loan losses (27 ) 279 1,113 544 2,872 1,318 927 1,949 Other noninterest income 1,621 866 2,147 2,210 3,834 1,456 3,509 2,179 Realized securities gains (losses), net (244 ) 1,318 664 267 298 238 298 145 Total noninterest income 1,377 2,184 2,811 2,477 4,132 1,694 3,807 2,324 Total noninterest expense 12,068 10,626 12,935 10,660 13,234 10,848 13,509 11,948 Provision for income taxes 870 638 721 689 891 923 1,323 587 Net income $ 1,667 $ 1,306 $ 1,358 $ 1,699 $ 1,630 $ 1,810 $ 3,998 $ 2,412 Basic earnings per share $ 0.07 $ 0.05 $ 0.06 $ 0.06 $ 0.07 $ 0.07 $ 0.17 $ 0.09 Diluted earnings per share $ 0.07 $ 0.05 $ 0.05 $ 0.06 $ 0.07 $ 0.07 $ 0.17 $ 0.09 Weighted average common shares (basic) 25,066,086 26,274,738 24,575,211 26,293,560 24,129,512 26,183,381 23,919,483 25,500,755 Weighted average common shares (diluted) 25,132,441 26,274,738 24,699,794 26,293,560 24,307,540 26,183,381 24,032,613 25,554,961

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS On December 5, 2016, Community Bank Systems, Inc. (“CBU”) announced an agreement to acquire Northeast Retirement Services, Inc. (“NRS”). After receiving necessary stockholder and regulatory approvals, CBU completed the acquisition of NRS on February 3, 2017. The Company, through its wholly owned subsidiary, 1196 Corporation ("1196 Corp."), owned 5,000 shares of NRS stock and for each share of NRS share,1196 Corp. received $319.04 in cash and 14.876 shares of CBU common stock. The Company recorded a gain of approximately $5.9 million in February 2017. Cash and stock valued at approximately $653,000 is being held in escrow for approximately one year on behalf of the Company, at which time any remaining escrow funds will be recorded as income by the Company. On February 17, 2017, the Company sold $42.4 million in global asset allocation equity mutual funds as a result of noted overall improvement in the equity markets. Specifically, the mutual funds had appreciated steadily from an unrealized loss position of $2.5 million at December 31, 2016 to an unrealized loss position of $1.1 million at the time of sale, with the net asset values at a one-year high. Accordingly, management decided to sell the mutual funds and realized the loss of $1.1 million .

Basis of Presentation and Con29

Basis of Presentation and Consolidation (Policies)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of the Company, its wholly-owned subsidiaries, Blue Hills Funding Corporation and the Bank, the principal operating entity and its wholly-owned subsidiaries, B.H. Security Corporation and HP Security Corporation, which are Massachusetts security corporations, and 1196 Corporation, which holds stock in a company that administers pension and 401(k) plans for a number of savings banks. All significant intercompany balances and transactions have been eliminated in consolidation. Prior to the the establishment of the Foundation in 2014, the Company established Blue Hills Bank Charitable Foundation, (the "Charitable Foundation"), a not-for-profit organization, to provide charitable contributions within the Company’s surrounding communities. Neither the Foundation or Charitable Foundation are subsidiaries of the Company.
Use of estimates	Use of estimates In preparing consolidated financial statements in conformity with accounting principles generally accepted in the United States of America, management is required 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 change in the near term relate to the determination of the allowance for loan losses and the realizability of deferred tax assets.
Cash and cash equivalents	Cash and cash equivalents For purposes of the consolidated statements of cash flows, cash and cash equivalents include cash on hand, balances due from banks, and short-term investments comprised of federal funds sold, money-market mutual funds, and interest-bearing deposits, all of which mature within ninety days. The Company normally maintains balances on deposit with other financial institutions in excess of the federally insured limit.
Restrictions on cash and due from banks	Restrictions on cash and due from banks The Company is required to maintain average balances on hand or with the Federal Reserve Bank ( the “FRB”).
Fair value hierarchy	Fair value hierarchy 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 reliability of the assumptions used to determine fair value. Level 1 - Valuation is based on quoted prices in active markets for identical assets or liabilities. Valuations are obtained from readily available pricing sources for market transactions involving identical assets or liabilities. Level 2 - Valuation is based on observable inputs other than Level 1 prices, such as quoted prices for similar assets and liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets and liabilities. Level 3 - Valuation is based on unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Level 3 assets and liabilities include those whose value is determined using unobservable inputs to pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant management judgment or estimation.
Securities	Securities Debt securities that management has the positive intent and ability to hold to maturity are classified as “held-to-maturity” and recorded at amortized cost. Securities not classified as held-to-maturity, including equity securities with readily determinable fair values, are classified as “available-for-sale” and recorded at fair value, with unrealized gains and losses excluded from earnings and reported in other comprehensive income. Purchase premiums and discounts are recognized in interest income using the interest method over the terms of the securities. Gains and losses on the sale of securities are recorded on the trade date and are determined using the specific identification method. At least quarterly, and more frequently when warranted by economic or market conditions, management evaluates all securities with a decline in fair value below the amortized cost of the investment to determine whether or not the impairment is deemed to be other-than-temporary ('OTTI"). 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. For all 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. Credit-related OTTI for all other impaired debt securities is recognized through earnings. Non-credit related OTTI for such debt securities is recognized in other comprehensive income, net of applicable taxes. 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.
Federal Home Loan Bank stock	Federal Home Loan Bank stock The Company, as a member of the Federal Home Loan Bank of Boston (the "FHLBB") system, is required to maintain an investment in capital stock of the FHLBB. Based on the redemption provisions of the FHLBB, the stock has no quoted market value and is carried at cost. At its discretion, the FHLBB may declare dividends on the stock. The Company reviews its investment for impairment based on the ultimate recoverability of the cost basis in the FHLBB stock.
Loans held for sale	Loans held for sale 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.
Loans	Loans The Company has historically granted mortgage and consumer loans to its customers and a substantial portion of the loan portfolio consists of mortgage loans in communities including and near the locations of its banking offices. The ability of the Company’s debtors to honor their contracts is dependent upon the real estate and general economic conditions in these areas. The Company’s loan portfolio includes 1-4 family residential real estate, home equity, commercial real estate, construction, commercial business, and consumer segments. Loans that management has the intent and ability to hold for the foreseeable future or until maturity or pay-off generally are reported at their outstanding unpaid principal balances adjusted for the allowance for loan losses, charge-offs, deferred origination fees and costs, and discounts on purchased loans. Interest income is accrued on the unpaid principal balance. Deferred loan origination fees/costs and discounts on purchased loans are recognized as an adjustment of the related loan yield using the interest method. It is the policy of the Company to discontinue the accrual of interest on loans past due in excess of 90 days, unless the loan is well-secured and in the process of collection, or when in the judgment of management, the ultimate collectability of the principal or interest becomes doubtful and to reverse all interest previously accrued against interest income. Past due status is based on contractual terms of the loan. The interest on non-accrual loans is accounted for on the cash-basis until qualifying for return to accrual. Loans are returned to accrual status when all the principal and interest amounts contractually due have been current for six consecutive months and future payments are reasonably assured.
Allowance for loan losses	Allowance for loan losses The allowance for loan losses is based on the size and the composition of the loan portfolio, delinquency levels, loss experience, economic conditions and other factors related to the collectability of the loan portfolio. Prior to the second quarter of 2016, for portfolios for which the Company had insufficient prior loss experience, a national peer group losses of depository institutions with assets between one and five billion dollars for relevant portfolios dating back to 2008 were used. Commencing in the second quarter of 2016, the Company began to phase in its own loss history by loan type based upon the age and loss experience of the loan portfolio. While this change impacted the loss factors used for our residential real estate, home equity, commercial real estate, commercial business and consumer loan portfolios, there was no material impact to the amount of the allowance for loan losses. Loss experience is updated at least quarterly with consideration given to unique circumstances in the portfolio. Loan losses are charged against the allowance when management believes the uncollectability of a loan balance is confirmed. Subsequent recoveries, if any, are credited to the allowance. The allowance for loan losses is evaluated regularly by management and reflects consideration of all significant factors that affect the collectability of the loan portfolio. The evaluation is inherently subjective as it requires estimates that are susceptible to significant revision as more information becomes available. It is the intention of management to maintain an allowance that is prudently commensurate with the growth in the loan portfolio. 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 a combination of the Company's own history and an extrapolated historical loss experience based on FDIC data for depository institutions with assets of one billion to five billion dollars dating back to 2008, adjusted for qualitative and environmental factors including changes to lending policies and procedures, economic and business conditions, portfolio characteristics, staff experience, problem loan trends, collateral values, concentrations and the competitive, legal and regulatory environment. 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 - The Company does not generally originate loans with a loan-to-value ratio greater than 80 percent and does not generally grant loans that would be classified as subprime upon origination. When the Company does extend credit either on a first- or second-lien basis at a loan-to-value ratio greater than 80 percent , such loans are supported by either mortgage insurance or state guarantee programs. All loans in this segment are collateralized by owner-occupied, 1-4 family residential real estate and repayment is dependent on the credit quality of the individual borrower. The health of the national economy, including unemployment rates and housing prices, will have an effect on the credit quality of loans in this segment. Home equity - Loans in this segment are generally secured by first or second liens on residential real estate. Repayment is dependent on the credit quality of the individual borrower. The Company evaluates each loan application based on factors including the borrower’s credit score, income, length of employment, and other factors to establish the creditworthiness of the borrower. Commercial real estate - Loans in this segment include investment real estate and are generally secured by assignments of leases, real estate collateral and owner-occupied properties. In cases where there is a concentration of exposure to a single large tenant, underwriting standards include analysis of the tenant’s ability to support lease payments over the duration of the loan. The underlying cash flows generated by the properties may be adversely impacted by a downturn in the economy due to increased vacancy rates, which in turn, can have an effect on the credit quality in this segment. Payments on loans secured by income-producing properties often depend on the successful operation and management of the properties. Management continually monitors the cash flows of these loans. Construction - Loans in this segment primarily include real estate development loans for which payment is derived from permanent financing or sale of the property. Credit risk is affected by cost overruns, time to sell at an adequate price, and market conditions. Commercial business - Loans in this segment are generally secured by business assets, including accounts receivable, inventory, real estate and intangible assets. Strict underwriting standards include considerations of the borrower’s ability to support the debt service requirements from the underlying historical and projected cash flows of the business, collateral values, the borrower’s credit history and the ultimate collectability of the de bt. Economic conditions, real estate values, commodity prices, unemployment trends and other factors will affect the credit quality of loans in these segments. Consumer - Loans in this segment primarily include used classic and collector automobile loans. A significant portion of the used automobile loan portfolio is comprised of geographically diverse loans originated by and purchased from a third party, who also provides collection services. Allocated component The allocated component relates to loans that are on the watch list (partially charged-off loans, non-accruing loans and accruing adversely-rated loans) and considered impaired. Impairment is measured by either the present value of expected future cash flows discounted at the loan’s effective interest rate or the fair value of the collateral if the loan is collateral dependent. An allowance is established when the discounted cash flows (or collateral value) of the impaired loan is lower than the carrying value of that loan. 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. Management reviews all loan types for individual impairment. 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 basis, taking into consideration all of the circumstances surrounding the loan and the borrower, including the length of the delay, the reasons for the delay, the borrower’s prior payment record, and the amount of the shortfall in relation to the principal and interest owed. 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 initially classified as impaired and generally remain impaired for the remaining life of the loan. The impaired classification may be removed if the borrower demonstrates compliance with the modified terms and the restructuring agreement specifies an interest rate equal to that which would be provided to a borrower with similar credit at the time of restructuring. Unallocated component
Premises and equipment	Premises and equipment Land is carried at cost. Buildings, leasehold improvements and equipment are stated at cost, less accumulated depreciation and amortization, computed on the straight-line method over the estimated useful lives of the assets or the expected terms of the leases, if shorter. Expected terms include lease option periods to the extent that the exercise of such options is reasonably assured.
Goodwill and identifiable intangible assets	Goodwill and identifiable intangible assets Goodwill is the price paid in excess of the fair value of net assets acquired and is not amortized. Goodwill at December 31, 2016 and 2015 relates to the acquisition of Nantucket Bank. Goodwill is evaluated for impairment at least annually, or more often if warranted, using a combined qualitative and quantitative impairment approach. The initial qualitative approach assesses whether the existence of events or circumstances led to a determination that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If, after assessing the totality of events and circumstances, the Company determines it is more likely than not that the fair value is less than carrying value, the two-step quantitative impairment test is performed. Step one of the quantitative impairment test compares book value to the fair value of the reporting unit. If test one is failed, a more detailed analysis is performed, which involves measuring the excess of the fair value of the reporting unit, as determined in step one, over the aggregate fair value of the individual assets, liabilities, and identifiable intangibles as if the reporting unit was being acquired in a business combination. Identifiable intangible assets subject to amortization consist of the core deposit intangible acquired in the acquisition of Nantucket Bank, which has an estimated life of approximately 5.5 years. Identifiable intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. The core deposit intangible is being amortized using the sum of the years' digits method over its estimated life.
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 cash surrender value are reflected in noninterest income in the consolidated statements of operations.
Non-marketable investments	Non-marketable investments The aggregate carrying amount of all cost and equity method investments included in other assets at December 31, 2016 and 2015 is $ 10.2 million and $ 8.7 million , respectively. The fair values of these investments are not readily available and are not evaluated for impairment unless there are identified events or changes in circumstances that may have a significant adverse effect on the fair value of the investments.
Interest rate swap agreements and Derivative Loan Commitments	Interest rate swap agreements For asset/liability management purposes, the Company periodically uses interest rate swap agreements to hedge various exposures or to modify interest rate characteristics of various balance sheet accounts. All interest rate swap agreements are recorded at fair value. Depending upon the intended use for the interest rate swap at inception, the Company designates the derivative as either an economic hedge of an asset or liability or a hedging instrument subject to the hedge accounting provisions. If the interest rate swap is not designated in a hedge relationship, gains or losses reflecting changes in fair value are recorded in earnings. Certain interest rate swap contracts are utilized to help commercial loan borrowers manage their interest rate risk. The interest rate swap contracts with commercial loan borrowers allow the borrowers to convert floating rate loan payments to fixed rate payments. When the Company enters into an interest rate swap contract with a commercial loan borrower, the Company concurrently enters into a matching interest rate swap with a correspondent bank counterparty in order to minimize interest rate risk to the Company. These interest rate derivative instruments are recorded on the consolidated balance sheets as either an asset or liability measured at fair value. These derivatives do not qualify for hedge accounting. As such, all changes in fair value of these derivative instruments are included in miscellaneous income. The Company pays and receives fees for entering into these contracts. The net fees are recognized in loan level derivative income when received. Derivative Loan Commitments Mortgage loan commitments are referred to as derivative loan commitments if the loan that will result from exercise of the commitment will be held for sale upon funding. Loan commitments that are derivatives are recognized at fair value on the consolidated balance sheet in other assets and other liabilities with changes in their fair values recorded in mortgage banking income. Forward Loan Sale Commitments To protect against the price risk inherent in derivative loan commitments, the Company enters into forward loan sale commitments to mitigate the risk of potential decreases in the values of loans that would result from the exercise of the derivative loan commitments. Forward loan sale commitments are recognized at fair value on the consolidated balance sheet in other assets or other liabilities with changes in their fair values recorded in mortgage banking income. The Company estimates the fair value of its forward loan sale commitments based on changes in the fair value of underlying mortgage loans.
Transfers of financial assets	Transfers 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 (free of conditions that constrain it from taking advantage of that right) to pledge or exchange the transferred assets, and (3) the Company does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity. During the normal course of business, the Company may transfer a portion of a financial asset, for example, a participation loan. In order to be eligible for sales treatment, the transfered 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 must 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.
Retirement plan	Retirement plan The Company accounts for its defined benefit pension plan using an actuarial model that allocates pension costs over the service period of employees in the plan. The Company accounts for the over-funded or under-funded status of its defined benefit plan as an asset or liability on its consolidated balance sheets and recognizes changes in the funded status that are not reflected in net periodic pension cost as other comprehensive income or loss. The Company amended its defined benefit pension plan in 2013 freezing the plan to new participants and subsequently amended the plan and froze it for all participants effective October 31, 2014.
Earnings per common share	Earnings per common share Basic earnings per share represents income available to common stockholders divided by the weighted-average number of common shares outstanding during the period. Unallocated ESOP shares are not deemed outstanding for earnings per share calculations. Dividend rights on unvested options/awards are forfeitable; therefore unvested awards/options are not considered outstanding in the computation of basic earnings per share. Diluted earnings per share reflects additional common shares that would have been outstanding if dilutive potential common shares had been issued, as well as any adjustment to income that would result from the assumed issuance. Potential common shares that may be issued by the Company relate to outstanding stock options and restricted stock awards and are determined using the treasury stock method.
Advertising costs	Advertising costs Advertising costs are expensed as incurred.
Stock-based Compensation Plans	Stock-based Compensation Plans The Company measures and recognizes compensation cost relating to stock-based payment transactions based on the grant-date fair value of the equity instruments issued. Stock-based compensation is recognized over the period the employee is required to provide services for the award. The Company uses the Black-Scholes option-pricing model to determine the fair value of stock options granted. For an award with a performance and/or service condition that affects vesting, the performance and/or service condition is not considered in determining the award’s fair value on the grant date. Performance and service conditions considered in estimating the quantity of awards that will vest (i.e., the pre-vesting forfeiture assumption). Compensation cost reflects the number of awards that are expected to vest and is adjusted to reflect those awards that do ultimately vest.
Employee Stock Ownership Plan	Employee Stock Ownership Plan Compensation expense for the ESOP is recorded at an amount equal to the shares allocated by the ESOP multiplied by the average fair market value of the shares during the 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 on the consolidated balance sheet. The difference between the average fair market value and the cost of the shares allocated by the ESOP is recorded as an adjustment to additional paid-in capital.
Income taxes	Income taxes Deferred tax assets and liabilities are reflected at currently enacted income tax rates applicable to the period in which the deferred tax assets or liabilities are expected to be realized or settled. As changes in tax laws or rates are enacted, deferred tax assets and liabilities are adjusted accordingly through the provision for income taxes. The Company exercises significant judgment in evaluating the amount and timing of recognition of the resulting tax assets and liabilities. These judgments require the Company to make projections of future taxable income. These judgments and estimates, which are inherently subjective, are reviewed periodically as regulatory and business factors change. A valuation allowance related to deferred tax assets is established when, in the judgment of management, it is more likely than not that all or a portion of such deferred tax assets will not be realized. A tax position that meets the more likely than not recognition threshold is initially and subsequently measured as the largest amount of tax benefit that has a greater than 50% likelihood of being realized upon settlement with a taxing authority that has full knowledge of all relevant information. The determination of whether or not a tax position has met the more likely than not recognition threshold considers the facts, circumstances and information available at the reporting date and is subject to management’s judgment. There was no reserve for uncertain tax positions as of December 31, 2016 or 2015 . The Company records interest and penalties as part of income tax expense. Income tax benefits related to stock compensation in excess of grant date fair value less any proceeds on exercise are recognized as an increase to additional paid-in capital upon vesting or exercising and delivery of the stock. Any income tax effects related to stock compensation that are less than grant date fair value less any proceeds on exercise would be recognized as a reduction of additional paid-in capital to the extent of previously recognized income tax benefits and then through income tax expense for the remaining amount.
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 equity section of the balance sheet, such items, along with net income, are components of comprehensive income.
Reclassification	Reclassification Certain amounts in the 2015 consolidated financial statements have been reclassified to conform to the 2016 presentation.
Recent Accounting Standards Updates	RECENT ACCOUNTING STANDARDS UPDATES In January 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2016-01, Financial Instruments – Overall, (Subtopic 825-10) . The amendments in this Update address certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. Targeted improvements to generally accepted accounting principles include the requirement for equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income and the elimination of the requirement for public business entities to disclose the methods and significant assumptions used to estimate the fair value for financial instruments measured at amortized cost. For public business entities, the amendments in this Update are effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The impact of the change in equity investments will depend on market conditions but if applied in 2016, would have resulted in a gain of $592,000 (pre tax) being recognized in net income versus other comprehensive income. See the Consolidated Statement of Comprehensive Income (Loss). In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . This Update is intended to improve financial reporting about leasing transactions and the key provision impacting the Company is the requirement for a lessee to record a right-to-use asset and a liability representing the obligation to make lease payments for long-term operating leases. The Update will be effective for public business entities for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Management is currently evaluating the impact to the consolidated financial statements of adopting this Update. Future lease commitments as of December 31, 2016 were $24.8 million . In March 2016, the FASB issued ASU No. 2016-09 Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , to reduce the complexity of certain aspects of the accounting for employee share-based payment transactions. As a result of this ASU, changes applicable to all entities include: Minimum statutory withholding requirements – One of the previous requirements for an award to qualify for equity classification is that an entity cannot partially settle the award in cash in excess of the employer’s minimum statutory withholding requirements. The determination of employees’ minimum statutory withholding amount has been difficult for some entities. Under the ASU, the threshold to qualify for equity classification would permit withholding up to the maximum individual statutory tax rate in the applicable jurisdictions. Also, the ASU provides that cash paid by an employer when directly withholding shares for tax-withholding purposes would be classified as a financing activity on the statement of cash flows. Accounting for forfeitures – Under the new guidance, entities are permitted to make an accounting policy election for the impact of forfeitures on the recognition of expense for share based payment awards. Forfeitures can be estimated, as required today, or recognized when they occur. Estimates of forfeitures will still be required in certain circumstances, such as at the time of modification of an award or issuance of a replacement award in a business combination. If elected, the change to recognize forfeitures when they occur needs to be adopted using a modified retrospective approach, with a cumulative effect adjustment recorded to opening retained earnings. Accounting for income taxes – Currently, excess tax benefits are recognized in additional paid-in capital. Tax deficiencies are recognized either as an offset to accumulated excess tax benefits, if any, or in the income statement. Per the ASU, all excess tax benefits and tax deficiencies would be recognized as income tax expense or benefit in the income statement. An entity also would recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. Further, excess tax benefits would not be separated from other income tax cash flows and thus would be classified along with other cash flows as an operating activity. The ASU is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. Early adoption is permitted for any organization in any interim or annual period. The impact to the consolidated financial statements upon adopting this Update is not expected to be material. On June 16, 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , which removes the thresholds that companies apply to measure credit losses on financial instruments measured at amortized cost, such as loans, receivables, and held-to-maturity debt securities. Under current U.S. GAAP, companies generally recognize credit losses when it is probable that the loss has been incurred. The revised guidance will remove previously established recognition thresholds based on probability, and will require companies to recognize an allowance for credit losses for the difference between the amortized cost basis of a financial instrument and the net amount that the company expects to collect over the instrument’s contractual life. ASU 2016-13 also amends the credit loss measurement guidance for available-for-sale debt securities and will require that credit losses be recorded through an allowance for credit losses. The ASU is effective for public business entities fiscal years beginning after December 15, 2019 and for interim periods within those fiscal years. Management is currently evaluating the impact to the consolidated financial statements of adopting this Update. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory . The amendments in this Update require an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. For public business entities, the amendments are effective for annual reporting periods beginning after December 15, 2017, including interim reporting periods within those annual reporting periods. The impact to the consolidated financial statements upon adopting this Update is not expected to be material. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . The amendments in this Update require that in the statement of cash flows, amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts. For public business entities, the amendments are effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The impact to the consolidated financial statements upon adopting this Update is not expected to be material. In January 2017, the FASB issued ASU 2017-04 Goodwill Simplifications , which simplifies how all entities assess goodwill for impairment by eliminating Step 2 from the goodwill impairment test. As amended, the goodwill impairment test will consist of one step comparing the fair value of a reporting unit with its carrying amount. An entity should recognize a goodwill impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. For public business entities, the amendments are effective for its annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. The impact to the consolidated financial statements upon adopting this Update is not expected to be material.

Basis of Presentation and Con30

Basis of Presentation and Consolidation (Tables)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Finite-Lived Intangible Assets	The core deposit intangible is being amortized using the sum of the years' digits method over its estimated life. Information related to the core deposit intangible, including the estimated annual amortization expense, is summarized below: (In thousands) Balance at December 31, 2013 $ — Acquisition of Nantucket Bank 6,040 Amortization (1,808 ) Balance at December 31, 2014 $ 4,232 Amortization (1,607 ) Balance at December 31, 2015 2,625 Amortization (1,225 ) Balance at December 31, 2016 $ 1,400
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Estimated amortization expense for the years ending December 31, 2017 $ 843 2018 461 2019 96 Total remaining $ 1,400

Securities (Tables)

Securities (Tables)	12 Months Ended
	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Schedule of Available-for-sale Securities Reconciliation	The amortized cost and estimated fair value of securities available for sale and held to maturity, with gross unrealized gains and losses, follow: December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Securities Available for Sale: Debt securities: Mortgage- and other asset-backed securities: Privately issued commercial mortgage-backed securities $ 10,530 $ — $ (41 ) $ 10,489 Other asset-backed securities 9,174 6 (195 ) 8,985 Total mortgage- and other asset-backed securities 19,704 6 (236 ) 19,474 State and political 12,730 120 (157 ) 12,693 Financial services: Banks 20,263 57 (298 ) 20,022 Diversified financial entities 17,198 190 (198 ) 17,190 Insurance and REITs 18,304 150 (216 ) 18,238 Total financial services 55,765 397 (712 ) 55,450 Other corporate: Industrials 49,217 508 (761 ) 48,964 Utilities 24,895 292 (100 ) 25,087 Total other corporate 74,112 800 (861 ) 74,051 Total debt securities 162,311 1,323 (1,966 ) 161,668 Marketable equity securities: Mutual funds: Domestic community 3,216 25 (19 ) 3,222 Global asset allocation 42,396 48 (2,498 ) 39,946 Total marketable equity securities 45,612 73 (2,517 ) 43,168 Total securities available for sale $ 207,923 $ 1,396 $ (4,483 ) $ 204,836 December 31, 2015 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (In thousands) Securities Available for Sale: Debt securities: Mortgage- and other asset-backed securities: Privately issued commercial mortgage-backed securities $ 13,126 $ — $ (195 ) $ 12,931 Other asset-backed securities 11,395 — (142 ) 11,253 Total mortgage- and other asset-backed securities 24,521 — (337 ) 24,184 State and political 16,016 354 (55 ) 16,315 Financial services: Banks 18,813 138 (90 ) 18,861 Diversified financial entities 23,124 349 (173 ) 23,300 Insurance and REITs 16,883 1 (282 ) 16,602 Total financial services 58,820 488 (545 ) 58,763 Other corporate: Industrials 55,470 306 (1,244 ) 54,532 Utilities 31,952 7 (1,639 ) 30,320 Total other corporate 87,422 313 (2,883 ) 84,852 Total debt securities 186,779 1,155 (3,820 ) 184,114 Marketable equity securities: Mutual funds: Global equity 5,000 388 — 5,388 Domestic community 3,216 70 (13 ) 3,273 Global asset allocation 42,396 3 (3,484 ) 38,915 Total marketable equity securities 50,612 461 (3,497 ) 47,576 Total securities available for sale $ 237,391 $ 1,616 $ (7,317 ) $ 231,690 Securities Held to Maturity: Debt securities: U.S. Treasury $ 636 $ — $ (2 ) $ 634 Government-sponsored enterprises 28,256 94 (126 ) 28,224 Government-sponsored mortgage-backed and collateralized mortgage obligations 155,232 10 (832 ) 154,410 SBA asset-backed securities 16,017 — (59 ) 15,958 Total securities held to maturity $ 200,141 $ 104 $ (1,019 ) $ 199,226
Schedule of Held-to-maturity Securities Reconciliation	Securities Held to Maturity: Debt securities: Government-sponsored enterprises $ 32,667 $ 4 $ (934 ) $ 31,737 Government-sponsored mortgage-backed and collateralized mortgage obligations 153,938 14 (1,806 ) 152,146 SBA asset-backed securities 14,422 — (212 ) 14,210 Total securities held to maturity $ 201,027 $ 18 $ (2,952 ) $ 198,093
Investments Classified by Contractual Maturity Date	The amortized cost and estimated fair value of debt securities by contractual maturity at December 31, 2016 follow. Expected maturities will differ from contractual maturities because the issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Available for Sale Held to Maturity Amortized Cost Fair Value Amortized Cost Fair Value (In thousands) Within 1 year $ 3,021 $ 3,022 $ 5,006 $ 5,007 After 1 year through 5 years 56,673 56,850 9,687 9,439 After 5 years through 10 years 75,437 74,787 17,974 17,291 After 10 years 7,476 7,535 — — 142,607 142,194 32,667 31,737 Mortgage- and asset-backed securities and collateralized mortgage obligations amortizing monthly 19,704 19,474 168,360 166,356 Total debt securities $ 162,311 $ 161,668 $ 201,027 $ 198,093
Available-for-sale Securities	Information pertaining to securities with gross unrealized losses aggregated by investment category and length of time that individual securities have been in a continuous loss position, follows: December 31, 2016 Less Than Twelve Months More Than Twelve Months Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (In thousands) Securities Available for Sale: Debt securities: Mortgage- and other asset-backed securities: Privately issued commercial mortgage- backed securities $ (11 ) $ 3,163 $ (30 ) $ 7,326 Other asset-backed securities (43 ) 3,924 (152 ) 3,732 Total mortgage- and other asset-backed securities (54 ) 7,087 (182 ) 11,058 State and political (157 ) 5,301 — — Financial services: Banks (298 ) 14,553 — — Diversified financial entities (198 ) 9,369 — — Insurance and REITs (216 ) 6,900 — — Total financial services (712 ) 30,822 — — Other corporate: Industrials (655 ) 24,630 (106 ) 2,284 Utilities (99 ) 11,200 (1 ) 794 Total other corporate (754 ) 35,830 (107 ) 3,078 Total debt securities (1,677 ) 79,040 (289 ) 14,136 Marketable equity securities: Mutual funds: Domestic community — — (19 ) 448 Global asset allocation (424 ) 15,153 (2,074 ) 22,442 Total marketable equity securities (424 ) 15,153 (2,093 ) 22,890 Total temporarily impaired securities available for sale $ (2,101 ) $ 94,193 $ (2,382 ) $ 37,026 December 31, 2015 Less Than Twelve Months More Than Twelve Months Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value (In thousands) Securities Available for Sale: Debt securities: Mortgage- and other asset-backed securities: Privately issued commercial mortgage- backed securities $ (84 ) $ 5,166 $ (111 ) $ 7,765 Other asset-backed securities (142 ) 11,253 — — Total mortgage- and other asset-backed securities (226 ) 16,419 (111 ) 7,765 State and political (55 ) 3,324 — — Financial services: Banks (90 ) 14,070 — — Diversified financial entities (173 ) 15,397 — — Insurance and REITs (282 ) 14,487 — — Total financial services (545 ) 43,954 — — Other corporate: Industrials (957 ) 43,848 (287 ) 395 Utilities (1,387 ) 25,353 (252 ) 1,618 Total other corporate (2,344 ) 69,201 (539 ) 2,013 Total debt securities (3,170 ) 132,898 (650 ) 9,778 Marketable equity securities: Mutual funds: Domestic community — — (13 ) 453 Global asset allocation (3,484 ) 36,609 — — Total marketable equity securities (3,484 ) 36,609 (13 ) 453 Total temporarily impaired securities available for sale $ (6,654 ) $ 169,507 $ (663 ) $ 10,231 Securities Held to Maturity: Debt securities: U.S. Treasury $ (2 ) $ 634 $ — $ — Government-sponsored enterprises (126 ) 14,084 — — Government-sponsored mortgage-backed and collateralized mortgage obligations (832 ) 144,820 — — SBA asset-backed securities (59 ) 15,958 — — Total temporarily impaired securities held to maturity $ (1,019 ) $ 175,496 $ — $ —
Held-to-maturity Securities	Securities Held to Maturity: Debt securities: Government-sponsored enterprises $ (934 ) $ 28,533 $ — $ — Government-sponsored mortgage-backed and collateralized mortgage obligations (1,763 ) 146,098 (43 ) 3,827 SBA asset-backed securities (104 ) 9,157 (108 ) 5,053 Total temporarily impaired securities held to maturity $ (2,801 ) $ 183,788 $ (151 ) $ 8,880

Loans and The Allowance for L32

Loans and The Allowance for Loan Losses (Tables)	12 Months Ended
	Dec. 31, 2016
Receivables [Abstract]
Schedule of Accounts, Notes, Loans and Financing Receivable	A summary of the balances of loans follows: December 31, 2016 2015 (In thousands) Real estate: 1-4 family residential $ 851,154 $ 599,938 Home equity 78,719 77,399 Commercial real estate 687,289 561,203 Construction 76,351 79,773 1,693,513 1,318,313 Commercial business 206,234 182,677 Consumer 29,281 38,186 Total loans 1,929,028 1,539,176 Allowance for loan losses (18,750 ) (17,102 ) Discount and fair value adjustments on purchased loans (1,846 ) (1,959 ) Deferred loan costs and fees, net 4,439 3,160 Loans, net $ 1,912,871 $ 1,523,275
Activity in Allowance for Loan Losses	Activity in the allowance for loan losses for the years ended December 31, 2016 , 2015 and 2014 follows: 1-4 Family Residential Home Equity Commercial Real Estate Construction Commercial Business Consumer Unallocated Total (In thousands) 2016 Beginning balance $ 3,916 $ 636 $ 7,147 $ 1,364 $ 2,839 $ 772 $ 428 $ 17,102 Provision (credit) for loan losses 830 (99 ) 1,447 (11 ) 3,428 (282 ) (428 ) 4,885 Loans charged-off — — (321 ) — (3,098 ) (56 ) — (3,475 ) Recoveries 100 — 101 — 37 — — 238 Ending Balance $ 4,846 $ 537 $ 8,374 $ 1,353 $ 3,206 $ 434 $ — $ 18,750 2015 Beginning balance $ 3,222 $ 340 $ 3,551 $ 1,056 $ 3,410 $ 736 $ 658 $ 12,973 Provision (credit) for loan losses 612 296 3,596 308 (571 ) 79 (230 ) 4,090 Loans charged-off — — — — — (43 ) — (43 ) Recoveries 82 — — — — — — 82 Ending Balance $ 3,916 $ 636 $ 7,147 $ 1,364 $ 2,839 $ 772 $ 428 $ 17,102 2014 Beginning balance $ 2,835 $ 247 $ 2,608 $ 303 $ 2,416 $ 574 $ 688 $ 9,671 Provision (credit) for loan losses 405 93 943 753 994 223 (30 ) 3,381 Loans charged-off (18 ) — — — — (61 ) — (79 ) Recoveries — — — — — — — — Ending Balance $ 3,222 $ 340 $ 3,551 $ 1,056 $ 3,410 $ 736 $ 658 $ 12,973
Allowance for Credit Losses on Financing Receivables	Additional information pertaining to the allocation of the allowance for loan losses to loan segments at December 31, 2016 and 2015 , follows: 1-4 Family Home Commercial Construction Commercial Consumer Unallocated Total (In thousands) December 31, 2016 Allowance related to impaired loans $ 17 $ — $ — $ — $ — $ — $ — $ 17 Allowance related to non-impaired loans 4,829 537 8,374 1,353 3,206 434 — 18,733 Total allowance for loan losses $ 4,846 $ 537 $ 8,374 $ 1,353 $ 3,206 $ 434 $ — $ 18,750 Impaired loans $ 6,726 $ 1,153 $ 941 $ — $ 241 $ 170 $ — $ 9,231 Non-impaired loans 844,428 77,566 686,348 76,351 205,993 29,111 — 1,919,797 Total loans $ 851,154 $ 78,719 $ 687,289 $ 76,351 $ 206,234 $ 29,281 $ — $ 1,929,028 December 31, 2015 Allowance related to impaired loans $ — $ — $ 384 $ — $ 10 $ 10 $ — $ 404 Allowance related to non-impaired loans 3,916 636 6,763 1,364 2,829 762 428 16,698 Total allowance for loan losses $ 3,916 $ 636 $ 7,147 $ 1,364 $ 2,839 $ 772 $ 428 $ 17,102 Impaired loans $ 6,114 $ 270 $ 4,631 $ — $ 10 $ 145 $ — $ 11,170 Non-impaired loans 593,824 77,129 556,572 79,773 182,667 38,041 — 1,528,006 Total loans $ 599,938 $ 77,399 $ 561,203 $ 79,773 $ 182,677 $ 38,186 $ — $ 1,539,176
Past Due Financing Receivables	The following is a summary of past due and non-accrual loans, by loan segment, at December 31, 2016 and 2015 : 30-59 Days Past Due 60-89 Days Past Due Past Due 90 Days or More Total Past Due Loans on Non-accrual (In thousands) December 31, 2016 Real estate: 1-4 family residential $ 584 $ 373 $ 2,322 $ 3,279 $ 6,478 Home equity 452 496 775 1,723 1,153 Commercial real estate 1,393 — — 1,393 941 Commercial business 4,996 13 — 5,009 241 Consumer 175 5 7 187 170 Total $ 7,600 $ 887 $ 3,104 $ 11,591 $ 8,983 December 31, 2015 Real estate: 1-4 family residential $ 2,287 $ — $ 990 $ 3,277 $ 5,688 Home equity 1,031 19 176 1,226 270 Commercial real estate — 1,249 — 1,249 4,631 Commercial business 23 — — 23 10 Consumer 3 80 120 203 145 Total $ 3,344 $ 1,348 $ 1,286 $ 5,978 $ 10,744
Impaired Financing Receivables	The following tables set forth information regarding average balances and interest income recognized (all on a cash basis) on impaired loans, by segment, for the years ended December 31, 2016 , 2015 and 2014 : Average Recorded Investment Interest Income Recognized 2016 (In thousands) Real estate: 1-4 family residential $ 6,451 $ 449 Home equity 555 29 Commercial real estate 3,192 206 Commercial business 672 55 Consumer 160 12 Total $ 11,030 $ 751 2015 Real estate: 1-4 family residential $ 4,869 $ 270 Home equity 575 14 Commercial real estate 926 161 Commercial business 2 1 Consumer 78 6 Total $ 6,450 $ 452 2014 Real estate: 1-4 family residential $ 4,076 $ 213 Home equity 476 17 Consumer 34 2 Total $ 4,586 $ 232 The following is a summary of information pertaining to impaired loans by loan segment at the dates indicated: Recorded Investment Unpaid Principal Balance Related Allowance December 31, 2016 (In thousands) Impaired loans without a valuation allowance: Real estate: 1-4 family residential $ 6,605 $ 7,023 $ — Home equity 1,153 1,225 — Commercial real estate 941 1,207 — Commercial business 241 3,279 — Consumer 170 183 — Total 9,110 12,917 — Impaired loans with a valuation allowance: 1-4 family residential 121 313 17 Total impaired loans $ 9,231 $ 13,230 $ 17 December 31, 2015 Impaired loans without a valuation allowance: Real estate: 1-4 family residential $ 6,114 $ 6,824 $ — Home equity 270 425 — Consumer 35 39 — Total 6,419 7,288 — Impaired loans with a valuation allowance: Commercial real estate 4,631 4,631 384 Commercial business 10 11 10 Consumer 110 110 10 Total 4,751 4,752 404 Total impaired loans $ 11,170 $ 12,040 $ 404
Financing Receivable Credit Quality Indicators	The following tables present the Company’s loans by risk rating at December 31, 2016 and 2015 : 1-4 Family Residential Home Equity Commercial Real Estate Construction Commercial Business Consumer Total Loans (In thousands) December 31, 2016 Loans rated 1 - 6 $ 1,054 $ 293 $ 671,872 $ 76,351 $ 188,706 $ 4 $ 938,280 Loans rated 7 3,514 967 9,720 — 17,510 146 31,857 Loans rated 8 2,442 258 5,697 — 18 37 8,452 Loans rated 9 645 — — — — — 645 Loans rated 10 — — — — — — — Loans not rated 843,499 77,201 — — — 29,094 949,794 $ 851,154 $ 78,719 $ 687,289 $ 76,351 $ 206,234 $ 29,281 $ 1,929,028 December 31, 2015 Loans rated 1 - 6 $ 1,950 $ 465 $ 548,360 $ 79,773 $ 181,792 $ 6 $ 812,346 Loans rated 7 4,461 321 7,765 — 874 — 13,421 Loans rated 8 1,592 144 5,078 — — 149 6,963 Loans rated 9 701 — — — 11 — 712 Loans rated 10 — — — — — — — Loans not rated 591,234 76,469 — — — 38,031 705,734 $ 599,938 $ 77,399 $ 561,203 $ 79,773 $ 182,677 $ 38,186 $ 1,539,176

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Premises and Equipment	A summary of the cost and accumulated depreciation and amortization of premises and equipment follows: December 31, Estimated Useful Lives 2016 2015 (In thousands) Land $ 4,087 $ 4,087 Buildings 10,322 10,322 5 to 40 years Leasehold improvements 9,334 7,727 5 to 10 years Furniture and fixtures 3,874 2,601 3 to 5 years Technology equipment 6,139 5,088 1 to 3 years Construction in progress 169 70 Premises and equipment, gross 33,925 29,895 Less accumulated depreciation and amortization (11,891 ) (9,880 ) Premises and equipment, net $ 22,034 $ 20,015

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2016
Banking and Thrift [Abstract]
Schedule of Deposit Balances	A summary of deposit balances, by type, is as follows: December 31, 2016 2015 (In thousands) NOW and demand $ 331,508 $ 288,143 Regular savings 262,984 287,344 Money market 573,204 368,050 Brokered money market 53,357 41,807 Total non-certificate accounts 1,221,053 985,344 Term certificates of $250,000 or more 77,550 65,364 Term certificates less than $250,000 262,564 246,614 Brokered certificates of deposit 247,520 136,527 Total certificate accounts 587,634 448,505 Total deposits $ 1,808,687 $ 1,433,849
Schedule of Contractual Maturities of Deposits and Weighted Average Rate	At December 31, 2016 , the scheduled maturities of certificate accounts, including brokered certificates of deposits, are as follows: Amount Weighted Average Rate (Dollars in thousands) 2017 372,461 0.67 % 2018 88,220 1.26 2019 68,928 1.69 2020 38,393 1.90 2021 19,632 1.76 $ 587,634 1.00 %

Borrowings (Tables)

Borrowings (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Schedule of Maturities of Long-term Debt	Long-term debt consists of the following FHLBB advances: December 31, 2016 December 31, 2015 Amount Weighted Average Rate Amount Weighted Average Rate (Dollars in thousands) Fixed-rate advances maturing: 2016 $ — — % $ 10,000 2.29 % 2017 15,000 1.99 % 15,000 1.99 2018 20,000 2.12 20,000 2.23 2019 25,000 1.20 — — 2020 15,000 1.49 10,000 1.65 2021 * 30,000 0.28 — — $ 105,000 1.27 % $ 55,000 2.07 % * Includes advances callable in 2017.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	Allocation of federal and state income taxes between current and deferred portions is as follows: Years Ended December 31, 2016 2015 2014 (In thousands) Current tax provision: Federal $ 3,617 $ 2,933 $ 2,695 State 306 206 240 3,923 3,139 2,935 Deferred tax provision (benefit): Federal 55 7 (3,183 ) State 47 (148 ) (1,014 ) Federal and State 102 (141 ) (4,197 ) Change in valuation reserve (220 ) (161 ) 640 Deferred income tax benefit (118 ) (302 ) (3,557 ) Provision (benefit) for income taxes $ 3,805 $ 2,837 $ (622 )
Schedule of Effective Income Tax Rate Reconciliation	The reasons for the differences between the statutory federal income tax provision and the actual tax provision (benefit) are summarized as follows: Years Ended December 31, 2016 2015 2014 (Dollars in thousands) Statutory federal tax provision (benefit) at 34% $ 4,236 $ 3,429 $ (274 ) Increase (decrease) resulting from: State taxes, net of federal tax benefit 233 39 (511 ) Dividends received deduction (41 ) (211 ) (201 ) Tax-exempt bank-owned life insurance (528 ) (351 ) (404 ) Tax-exempt interest (189 ) (222 ) (277 ) Change in valuation reserve (220 ) (161 ) 640 Nondeductible IPO costs — — 202 Equity incentives 339 52 — Amortization of low income housing partnership 219 — — Tax credits utilized (286 ) (45 ) — Accrual adjustment 207 13 — Statutory rate change for net deferred tax asset from 34% to 35% (289 ) — — Other, net 124 294 203 Tax provision (benefit) $ 3,805 $ 2,837 $ (622 ) Effective tax rates 30.5 % 28.2 % 77.3 %
Schedule of Deferred Tax Assets and Liabilities	he components of the net deferred tax asset are as follows: December 31, 2016 2015 (In thousands) Deferred tax assets: Federal $ 11,700 $ 12,091 State 3,258 3,188 Deferred tax assets, gross 14,958 15,279 Valuation reserve (1,790 ) (1,966 ) Deferred tax assets, net 13,168 13,313 Deferred tax liabilities: Federal (2,427 ) (2,138 ) State (595 ) (510 ) Deferred tax liabilities (3,022 ) (2,648 ) Net deferred tax asset $ 10,146 $ 10,665 The tax effects of each item that give rise to deferred tax assets (liabilities) are as follows: December 31, 2016 2015 (In thousands) Deferred tax assets: Depreciation and amortization $ 747 $ 929 Employee benefit plans and share-based compensation plans 571 901 Allowance for loan losses 7,660 6,831 Contribution carryover 2,317 2,675 Net unrealized loss on securities held as, or transferred from, available for sale 893 1,748 Net unrealized losses on defined benefit pension plan 1,270 1,052 Deferred rent expense 123 28 Other 302 131 Valuation reserve (1,790 ) (1,966 ) Deferred tax liabilities: Deferred loan origination costs (1,947 ) (1,664 ) Net deferred tax asset $ 10,146 $ 10,665 A summary of the change in the net deferred tax asset (liability) is as follows: Years Ended December 31, 2016 2015 2014 (In thousands) Balance at beginning of year $ 10,665 $ 6,233 $ 2,831 Deferred tax benefit 118 302 3,557 Tax effect of changes in accumulated other comprehensive income (637 ) 4,130 (155 ) Balance at end of year $ 10,146 $ 10,665 $ 6,233
Schedule of Changes in Deferred Tax Assets Valuation Allowance	A summary of the change in valuation reserve is as follows: For the Year Ended December 31, 2016 Federal State Total (In thousands) Balance at beginning of year $ (200 ) $ (1,766 ) $ (1,966 ) Change through the income statement 200 20 220 Change through other comprehensive income — (44 ) (44 ) Balance at end of year $ — $ (1,790 ) $ (1,790 )

Equity (Tables)

Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations	The Company’s and the Bank’s actual capital amounts and ratios as of December 31, 2016 and 2015 are also presented in the following table. Actual Minimum Capital Requirement Minimum To Be Well Capitalized Amount Ratio Amount Ratio Amount Ratio (Dollars in thousands) Blue Hills Bancorp, Inc.: December 31, 2016 Total capital (to risk weighted assets) $ 395,325 20.5 % $ 154,471 8.0 % $ 193,089 10.0 % Tier 1 capital (to risk weighted assets) 376,575 19.5 115,854 6.0 154,471 8.0 Common equity Tier 1 (to risk weighted assets) 376,575 19.5 86,890 4.5 125,508 6.5 Tier 1 capital (to average assets) 376,575 16.0 94,166 4.0 117,708 5.0 December 31, 2015 Total capital (to risk weighted assets) 407,444 24.8 131,231 8.0 164,039 10.0 Tier 1 capital (to risk weighted assets) 390,342 23.8 98,423 6.0 131,231 8.0 Common equity Tier 1 (to risk weighted assets) 390,342 23.8 73,818 4.5 106,625 6.5 Tier 1 capital (to average assets) 390,342 19.6 79,658 4.0 99,573 5.0 Blue Hills Bank: December 31, 2016 Total capital (to risk weighted assets) 313,457 16.3 154,196 8.0 192,745 10.0 Tier 1 capital (to risk weighted assets) 294,707 15.3 115,647 6.0 154,196 8.0 Common equity Tier 1 (to risk weighted assets) 294,707 15.3 86,735 4.5 125,284 6.5 Tier 1 capital (to average assets) 294,707 12.5 94,099 4.0 117,623 5.0 December 31, 2015 Total capital (to risk weighted assets) 296,309 18.1 130,832 8.0 163,540 10.0 Tier 1 capital (to risk weighted assets) 279,207 17.1 98,124 6.0 130,832 8.0 Common equity Tier 1 (to risk weighted assets) 279,207 17.1 73,593 4.5 106,301 6.5 Tier 1 capital (to average assets) 279,207 14.0 79,867 4.0 99,608 5.0

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Changes in Projected Benefit Obligations, Fair Value of Plan Assets, and Funded Status of Plan	Years Ended December 31, 2016 2015 2014 (In thousands) Change in plan assets: Fair value of plan assets at beginning of year $ 8,814 $ 9,443 $ 9,535 Actual return (loss) on plan assets 847 (304 ) 391 Employer contribution 470 — — Benefits paid (320 ) (325 ) (483 ) Fair value of plan assets at end of year 9,811 8,814 9,443 Change in benefit obligation: Benefit obligation at beginning of year 10,772 10,135 9,287 Service cost — — 484 Interest cost 422 401 407 Actuarial loss 1,022 561 2,230 Benefits paid (320 ) (325 ) (483 ) Curtailment gain — — (1,790 ) Benefit obligation at end of year 11,896 10,772 10,135 Funded status and accrued liability at end of year $ (2,085 ) $ (1,958 ) $ (692 ) Accumulated benefit obligation at end of year $ 11,896 $ 10,772 $ 10,135
Schedule of Assumptions Used	At December 31, 2016 and 2015 , the discount rate used to determine the benefit obligation was as follows: December 31, 2016 2015 Discount rate 3.86 % 4.01 % The assumptions used to determine net periodic pension benefit are as follows: Years Ended December 31, 2016 2015 2014 Discount rate 4.01 % 4.00 % 4.25 % Expected long-term rate of return on plan assets 8.00 % 8.00 % 8.00 %
Schedule of Net Benefit Costs	The components of net periodic pension benefit are as follows: Years Ended December 31, 2016 2015 2014 (In thousands) Service cost $ — $ — $ 484 Interest cost 422 401 407 Expected return on plan assets (720 ) (745 ) (735 ) Amortization of net actuarial loss (gain) 271 110 (70 ) Curtailment gain — — (1,304 ) Net periodic pension benefit $ (27 ) $ (234 ) $ (1,218 )
Schedule of Allocation of Plan Assets	The fair value of major categories of the Company’s pension plan assets are summarized below: Level 1 Level 2 Level 3 Total Fair Value (In thousands) December 31, 2016 Collective funds $ 681 $ — $ — $ 681 Equity securities 1,929 — — 1,929 Mutual funds 1,209 — — 1,209 Short-term investments 124 — — 124 Total investments measured in the fair value hierarchy 3,943 — — 3,943 Investments measured at net asset value (a) — — — 5,868 $ 3,943 $ — $ — $ 9,811 December 31, 2015 Collective funds $ 1,126 $ 4,266 $ — $ 5,392 Equity securities 1,566 — — 1,566 Mutual funds 1,046 — — 1,046 Hedge funds — — 660 660 Short-term investments 150 — — 150 $ 3,888 $ 4,266 $ 660 $ 8,814 (a) In accordance with FASB ASC 820, Fair Value Measurements , certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy.
Schedule of Expected Benefit Payments	Estimated future benefit payments, assuming employees retire at age 65 and take normal distribution payments, are as follows: Amount Year Ending December 31, (In thousands) 2017 $ 785 2018 1,087 2019 614 2020 710 2021 930 2022-2026 3,223
Employee Stock Ownership Plan (ESOP) Disclosures	Shares held by the ESOP include the following: December 31, 2016 December 31, 2015 Allocated 149,613 75,912 Committed to be allocated 75,912 75,912 Unallocated 2,049,608 2,124,846 2,275,133 2,276,670

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The Company made the following awards of options to purchase shares of common stock in 2016 and 2015 : Date of grant February 29, 2016 October 7, 2015 Options granted 55,000 2,434,000 Vesting period (years) 5 5 Expiration date February 28, 2026 October 7, 2025 Expected volatility 28.47 % 28.85 % Expected life (years) 6.5 6.5 Expected dividend yield 0.58 % 0.54 % Risk free interest rate 1.38 % 1.55 % Fair value per option $ 4.02 $ 4.23
Schedule of Share-based Compensation, Stock Options, Activity	A summary of the status of the Company's stock option grants for the year ended December 31, 2016 is presented in the table below: Options Stock Option Awards Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value Balance at January 1, 2016 2,434,000 $ 14.07 — $ — Granted 55,000 13.80 — — Forfeited (36,450 ) 14.07 — — Exercised (2,880 ) 14.07 — — Balance at December 31, 2016 2,449,670 $ 14.06 8.77 $ 11,479,306 Outstanding and expected to vest at December 31, 2016 2,449,670 $ 14.06 8.77 $ 11,479,306 Exercisable at December 31, 2016 478,390 $ 14.07 3.78 $ 2,238,865 Unrecognized compensation cost at December 31, 2016 $7,827,000 Weighted average remaining recognition period (years) at December 31, 2016 3.78
Schedule of Share-based Compensation, Restricted Stock Units Award Activity	The following table presents the activity in non-vested stock awards under the Equity Plan for the year ended December 31, 2016 : Outstanding Restricted Stock Awards Weighted Average Grant Price Non-vested stock awards at January 1, 2016 983,175 $ 14.07 Granted 31,450 13.83 Vested (186,755 ) 14.07 Forfeited (11,800 ) 14.07 Non-vested stock awards at December 31, 2016 816,070 $ 14.06 Unrecognized compensation cost, inclusive of directors' fees at December 31, 2016 $ 10,645,000 Weighted average remaining recognition period (years) at December 31, 2016 3.78

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	2016 2015 (Dollars in thousands, except per share amounts) Net income applicable to common stock $ 8,653 $ 7,227 Average number of common shares outstanding 27,464,996 28,460,077 Less: Average unvested restricted stock awards (957,364 ) (231,652 ) Less: Average unallocated ESOP shares (2,087,227 ) (2,163,478 ) Average number of common shares outstanding used to calculate basic earnings per common share 24,420,405 26,064,947 Effect of dilutive unvested restricted stock awards 120,524 4,642 Average number of common shares outstanding used to calculate diluted earnings per common share 24,540,929 26,069,589 Earnings per common share: Basic $ 0.35 $ 0.28 Diluted $ 0.35 $ 0.28

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Schedule of Fair Value, Off-balance Sheet Risks	Financial instruments whose contract amounts represent credit risk consist of: December 31, 2016 2015 (In thousands) Commitments to originate loans $ 51,622 $ 69,554 Letters of credit 3,277 3,571 Unused lines-of-credit: Commercial 164,185 128,748 Home equity 55,344 44,968 Consumer 15,995 16,033 Undisbursed construction loans 96,169 80,336
Schedule of Future Minimum Rental Payments for Operating Leases	Pursuant to the terms of noncancelable lease agreements in effect at December 31, 2016 , pertaining to premises, future minimum rent commitments are as follows: Year Ending December 31, Amount (In thousands) 2017 $ 2,530 2018 2,665 2019 2,479 2020 2,398 2021 2,288 Thereafter 12,408 $ 24,768

On Balance Sheet Derivative I42

On Balance Sheet Derivative Instruments and Hedging Activities (Tables)	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Interest Rate Derivatives	The table below presents information about derivative financial instruments not designated as hedging instruments at December 31, 2016 and 2015 . Derivative Gains Derivative Losses Notional Amount Fair Value Notional Amount Fair Value (In thousands) December 31, 2016 Economic hedges: Commercial loan level interest rate swap agreements $ 419,488 $ 9,016 $ 419,488 $ 8,932 Other contracts 15,865 8 33,045 56 Total derivatives $ 435,353 $ 9,024 $ 452,533 $ 8,988 December 31, 2015 Economic hedges: Commercial loan level interest rate swap agreements $ 282,546 $ 7,956 $ 282,546 $ 8,411 Other contracts 8,300 6 12,698 78 Total derivatives $ 290,846 $ 7,962 $ 295,244 $ 8,489

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	Assets and liabilities measured at fair value on a recurring basis are summarized below: Level 1 Level 2 Level 3 Total Fair Value (In thousands) December 31, 2016 Assets Securities available for sale: Debt securities $ — $ 161,668 $ — $ 161,668 Marketable equity securities 43,168 — — 43,168 Derivative assets: Interest rate swap agreements — 9,024 — 9,024 Forward loan sale commitments — — 15 15 Mortgage loan commitments — — 111 111 Total assets $ 43,168 $ 170,692 $ 126 $ 213,986 Liabilities Derivative liabilities: Interest rate swap agreements $ — $ 8,988 $ — $ 8,988 Forward loan sale commitments — — 74 74 Mortgage loan commitments — — 3 3 Total liabilities $ — $ 8,988 $ 77 $ 9,065 December 31, 2015 Assets Securities available for sale: Debt securities $ — $ 184,114 $ — $ 184,114 Marketable equity securities 47,576 — — 47,576 Interest rate swap agreements — 7,962 — 7,962 Total assets $ 47,576 $ 192,076 $ — $ 239,652 Liabilities Interest rate swap agreements $ — $ 8,489 $ — $ 8,489
Fair Value Measurements, Nonrecurring	The following table summarizes the fair value hierarchy applicable to assets measured at fair value on a non-recurring basis: December 31, 2016 December 31, 2015 Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 (In thousands) Impaired loans $ — $ — $ 136 $ — $ — $ 4,752 The following table summarizes the total losses on assets measured at fair value on a non-recurring basis for the years ended December 31, 2016, 2015 and 2014. Years Ended December 31, 2016 2015 2014 (In thousands) Impaired loans $ (2,911 ) $ (404 ) $ (18 )
Fair Value, by Balance Sheet Grouping	Carrying Fair Value Level 1 Level 2 Level 3 Total (In thousands) December 31, 2016 Financial assets: Cash and cash equivalents $ 30,496 $ 30,496 $ — $ — $ 30,496 Securities available for sale 204,836 43,168 161,668 — 204,836 Securities held to maturity 201,027 — 198,093 — 198,093 Federal Home Loan Bank stock 13,352 — — 13,352 13,352 Loans and loans held for sale, net 1,915,632 — — 1,903,978 1,903,978 Accrued interest receivable 6,057 — — 6,057 6,057 Financial liabilities: Deposits 1,808,687 — — 1,808,629 1,808,629 Borrowings 251,000 — 250,648 — 250,648 On-balance sheet derivative financial instruments: Derivative assets: Interest rate swap agreements 9,024 — 9,024 — 9,024 Forward loan sale commitments 15 — — 15 15 Mortgage loan commitments 111 — — 111 111 Derivative liabilities: Interest rate swap agreements: 8,988 — 8,988 — 8,988 Forward loan sale commitments 74 — — 74 74 Mortgage loan commitments 3 — — 3 3 Carrying Amount Fair Value Level 1 Level 2 Level 3 Total (In thousands) December 31, 2015 Financial assets: Cash and cash equivalents $ 33,298 $ 33,298 $ — $ — $ 33,298 Securities available for sale 231,690 47,576 184,114 — 231,690 Securities held to maturity 200,141 634 198,592 — 199,226 Federal Home Loan Bank stock 13,567 — — 13,567 13,567 Loans and loans held for sale, net 1,536,152 — — 1,538,809 1,538,809 Accrued interest receivable 5,344 — — 5,344 5,344 Financial liabilities: Deposits 1,433,849 — — 1,434,179 1,434,179 Borrowings 260,000 — 260,244 — 260,244 On-balance sheet derivative financial instruments: Derivative assets: Interest rate swap agreements 7,962 — 7,962 — 7,962 Derivative liabilities: Interest rate swap agreements: 8,489 — 8,489 — 8,489

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The components of accumulated other comprehensive loss, included in stockholders' equity, are as follows: December 31, 2016 2015 (In thousands) Securities available for sale: Net unrealized loss $ (3,087 ) $ (5,701 ) Tax effect 1,007 1,945 Net-of-tax amount (2,080 ) (3,756 ) Securities held to maturity: Net unrealized gain on transferred securities 337 571 Tax effect (114 ) (197 ) Net-of-tax amount 223 374 Defined benefit pension plan: Unrecognized net actuarial loss (3,482 ) (2,858 ) Tax effect 1,270 1,052 Net-of-tax amount (2,212 ) (1,806 ) $ (4,069 ) $ (5,188 ) Changes in accumulated other comprehensive income (loss) by component follows: Securities Available for Sale Securities Held to Maturity Defined Benefit Pension Plan Total Year Ended December 31, 2016 Beginning balance $ (3,756 ) $ 374 $ (1,806 ) $ (5,188 ) Other comprehensive income (loss) before reclassifications 3,849 — (895 ) 2,954 Realized gains reclassified (1,235 ) — — (1,235 ) Amortization of actuarial losses — — 271 271 Amortization of amounts previously recorded upon transfer to held-to-maturity from available-for-sale — (234 ) — (234 ) Tax effects (938 ) 83 218 (637 ) Net current-period other comprehensive income (loss) 1,676 (151 ) (406 ) 1,119 Ending balance $ (2,080 ) $ 223 $ (2,212 ) $ (4,069 ) Year ended December 31, 2015 Beginning balance $ 3,392 $ — $ (815 ) $ 2,577 Other comprehensive loss before reclassifications (8,332 ) — (1,610 ) (9,942 ) Realized gains reclassified (1,968 ) — — (1,968 ) Amortization of actuarial losses — — 110 110 Unrealized gains on securities reclassified as held to maturity (666 ) 666 — — Amortization of amounts previously recorded upon transfer to held-to-maturity from available-for-sale — (95 ) — (95 ) Tax effects 3,818 (197 ) 509 4,130 Net current-period other comprehensive income (loss) (7,148 ) 374 (991 ) (7,765 ) Ending balance $ (3,756 ) $ 374 $ (1,806 ) $ (5,188 ) Year Ended December 31, 2014 Beginning balance $ 1,983 $ — $ 482 $ 2,465 Other comprehensive income (loss) before reclassifications 4,942 — (2,090 ) 2,852 Realized gains reclassified (2,515 ) — — (2,515 ) Amortization of actuarial gains — — (70 ) (70 ) Tax effects (1,018 ) — 863 (155 ) Net current-period other comprehensive income (loss) 1,409 — (1,297 ) 112 Ending balance $ 3,392 $ — $ (815 ) $ 2,577

Condensed Financial Statement45

Condensed Financial Statements of Parent Company (Tables)	12 Months Ended
	Dec. 31, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Balance Sheet	Financial information pertaining only to Blue Hills Bancorp, Inc. is as follows: December 31, BALANCE SHEETS 2016 2015 (In thousands) Assets Cash balances at Blue Hills Bank $ 66,326 $ 100,965 Total cash and cash equivalents 66,326 100,965 Investment in subsidiaries 328,201 311,357 Other assets 13,499 7,993 Total assets $ 408,026 $ 420,315 Liabilities and Stockholders' Equity Liability to ESOP $ 20,995 $ 21,459 Accrued expenses 124 27 Stockholders' equity 386,907 398,829 Total liabilities and stockholders' equity $ 408,026 $ 420,315
Condensed Statements of Operations	Years Ended December 31, 2016 2015 2014 STATEMENTS OF OPERATIONS (In thousands) Loss before income taxes and equity in undistributed net income of subsidiaries $ (2,478 ) $ (1,860 ) $ (9,432 ) Applicable income tax benefit (758 ) (1,112 ) (3,277 ) Loss before equity in income of subsidiaries (1,720 ) (748 ) (6,155 ) Equity in undistributed net income of subsidiaries 10,373 7,975 5,972 Net income (loss) $ 8,653 $ 7,227 $ (183 )
Condensed Cash Flow Statement	Years Ended December 31, 2016 2015 2014 STATEMENTS OF CASH FLOWS (In thousands) Cash flows from operating activities: Net income (loss) $ 8,653 $ 7,227 (183 ) Adjustments to reconcile net income to net cash provided by (used for) operating activities: Equity in undistributed net income of subsidiaries (10,373 ) (7,975 ) (5,972 ) Charitable Foundation contribution — — 6,943 Excess tax benefit from deferred and stock based compensation (105 ) (166 ) — Net change in other assets 11,625 (1,157 ) (1,731 ) Net change in other liabilities 97 (241 ) 267 Net cash provided by (used for) operating activities 9,897 (2,312 ) (676 ) Cash flows used for investing activities: Investment in Blue Hills Bank (16,844 ) (3,929 ) (161,820 ) Net cash used for investing activities (16,844 ) (3,929 ) (161,820 ) Cash flows provided by (used for) financing activities: Proceeds from the issuance of common stock — — 274,143 Redemption of SBLF preferred stock — — (18,724 ) Excess tax benefit from deferred and stock based compensation 105 166 — Repurchase of common stock (24,432 ) (13,121 ) — Share redemption for tax withholdings (730 ) (439 ) — Proceeds from exercise of stock options 40 — — Common and preferred stock dividends paid (2,675 ) (1,032 ) (439 ) Net cash provided by (used for) financing activities (27,692 ) (14,426 ) 254,980 Net change in cash and cash equivalents (34,639 ) (20,667 ) 92,484 Cash and cash equivalents at beginning of year 100,965 121,632 29,148 Cash and cash equivalents at end of year $ 66,326 $ 100,965 $ 121,632

Selected Quarterly Financial 46

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	First Quarter Second Quarter Third Quarter Fourth Quarter 2016 2015 2016 2015 2016 2015 2016 2015 (In thousands, except share data) Interest and dividend income $ 16,063 $ 12,682 $ 16,356 $ 13,130 $ 17,685 $ 15,418 $ 19,434 $ 17,071 Interest expense 2,862 2,017 3,040 2,015 3,190 2,213 3,484 2,499 Net interest and dividend income 13,201 10,665 13,316 11,115 14,495 13,205 15,950 14,572 Provision (credit) for loan losses (27 ) 279 1,113 544 2,872 1,318 927 1,949 Other noninterest income 1,621 866 2,147 2,210 3,834 1,456 3,509 2,179 Realized securities gains (losses), net (244 ) 1,318 664 267 298 238 298 145 Total noninterest income 1,377 2,184 2,811 2,477 4,132 1,694 3,807 2,324 Total noninterest expense 12,068 10,626 12,935 10,660 13,234 10,848 13,509 11,948 Provision for income taxes 870 638 721 689 891 923 1,323 587 Net income $ 1,667 $ 1,306 $ 1,358 $ 1,699 $ 1,630 $ 1,810 $ 3,998 $ 2,412 Basic earnings per share $ 0.07 $ 0.05 $ 0.06 $ 0.06 $ 0.07 $ 0.07 $ 0.17 $ 0.09 Diluted earnings per share $ 0.07 $ 0.05 $ 0.05 $ 0.06 $ 0.07 $ 0.07 $ 0.17 $ 0.09 Weighted average common shares (basic) 25,066,086 26,274,738 24,575,211 26,293,560 24,129,512 26,183,381 23,919,483 25,500,755 Weighted average common shares (diluted) 25,132,441 26,274,738 24,699,794 26,293,560 24,307,540 26,183,381 24,032,613 25,554,961

Basis of Presentation and Con47

Basis of Presentation and Consolidation - Additional Information (Details) - USD ($)	Jul. 21, 2014	Jul. 31, 2014	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Subsidiary or Equity Method Investee [Line Items]
Issuance of common stock (in shares)	27,772,500
Shares issued (in dollars per share)	$ 10			$ 10
Net proceeds from issuance of common stock	$ 277,700,000			$ 0	$ 0	$ 274,143,000
Employee stock ownership plan, shares	2,277,345			2,277,345
Liquidation account amount				$ 61,000,000	80,700,000
Restricted cash and cash equivalents				$ 0	4,000,000
Core deposit intangible useful life				5 years 6 months
Contractual commitments for additional capital contributions				$ 8,900,000	8,400,000
1-4 Family Residential
Subsidiary or Equity Method Investee [Line Items]
Origination covenants, maximum loan-to-value ratio (greater than)			80.00%	80.00%
Other Assets
Subsidiary or Equity Method Investee [Line Items]
Non-marketable investments				$ 10,200,000	$ 8,700,000
Blue Hills Bank Foundation
Subsidiary or Equity Method Investee [Line Items]
Issuance of common stock (in shares)	694,313
Capital contribution to affiliate	$ 7,000,000
Cash payment to affiliate		$ 57,000
Federal Home Loan Bank of Boston
Subsidiary or Equity Method Investee [Line Items]
Impairments of investments				$ 0

Basis of Presentation and Con48

Basis of Presentation and Consolidation - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-lived Intangible Assets [Roll Forward]
Beginning balance	$ 2,625	$ 4,232	$ 0
Acquisition of Nantucket Bank			6,040
Amortization	(1,225)	(1,607)	(1,808)
Ending balance	$ 1,400	$ 2,625	$ 4,232

Basis of Presentation and Con49

Basis of Presentation and Consolidation - Estimated Amortization Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
2,017	$ 843
2,018	461
2,019	96
Total remaining	$ 1,400	$ 2,625	$ 4,232	$ 0

Recent Accounting Standards U50

Recent Accounting Standards Updates - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income (loss) before income taxes	$ 12,458	$ 10,064	$ (805)
Total future minimum payments due	24,768
New Accounting Pronouncement, Early Adoption, Effect | ASU 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income (loss) before income taxes	$ 592

Securities - Available-for-sale

Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Debt securities:
Amortized Cost	$ 162,311	$ 186,779
Gross Unrealized Gains	1,323	1,155
Gross Unrealized Losses	(1,966)	(3,820)
Fair Value	161,668	184,114
Marketable equity securities:
Amortized Cost	45,612	50,612
Gross Unrealized Gains	73	461
Gross Unrealized Losses	(2,517)	(3,497)
Fair Value	43,168	47,576
Available-for-sale securities:
Amortized Cost	207,923	237,391
Gross Unrealized Gains	1,396	1,616
Gross Unrealized Losses	(4,483)	(7,317)
Fair Value	204,836	231,690
Privately issued commercial mortgage- backed securities
Debt securities:
Amortized Cost	10,530	13,126
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(41)	(195)
Fair Value	10,489	12,931
Other asset-backed securities
Debt securities:
Amortized Cost	9,174	11,395
Gross Unrealized Gains	6	0
Gross Unrealized Losses	(195)	(142)
Fair Value	8,985	11,253
Total mortgage- and other asset-backed securities
Debt securities:
Amortized Cost	19,704	24,521
Gross Unrealized Gains	6	0
Gross Unrealized Losses	(236)	(337)
Fair Value	19,474	24,184
State and political
Debt securities:
Amortized Cost	12,730	16,016
Gross Unrealized Gains	120	354
Gross Unrealized Losses	(157)	(55)
Fair Value	12,693	16,315
Global
Marketable equity securities:
Amortized Cost		5,000
Gross Unrealized Gains		388
Gross Unrealized Losses		0
Fair Value		5,388
Domestic community
Marketable equity securities:
Amortized Cost	3,216	3,216
Gross Unrealized Gains	25	70
Gross Unrealized Losses	(19)	(13)
Fair Value	3,222	3,273
Global asset allocation
Marketable equity securities:
Amortized Cost	42,396	42,396
Gross Unrealized Gains	48	3
Gross Unrealized Losses	(2,498)	(3,484)
Fair Value	39,946	38,915
Financial Services | Corporate debt securities
Debt securities:
Amortized Cost	55,765	58,820
Gross Unrealized Gains	397	488
Gross Unrealized Losses	(712)	(545)
Fair Value	55,450	58,763
Banks | Corporate debt securities
Debt securities:
Amortized Cost	20,263	18,813
Gross Unrealized Gains	57	138
Gross Unrealized Losses	(298)	(90)
Fair Value	20,022	18,861
Diversified financial entities | Corporate debt securities
Debt securities:
Amortized Cost	17,198	23,124
Gross Unrealized Gains	190	349
Gross Unrealized Losses	(198)	(173)
Fair Value	17,190	23,300
Insurance and REITs | Corporate debt securities
Debt securities:
Amortized Cost	18,304	16,883
Gross Unrealized Gains	150	1
Gross Unrealized Losses	(216)	(282)
Fair Value	18,238	16,602
Other Corporate | Corporate debt securities
Debt securities:
Amortized Cost	74,112	87,422
Gross Unrealized Gains	800	313
Gross Unrealized Losses	(861)	(2,883)
Fair Value	74,051	84,852
Industrials | Corporate debt securities
Debt securities:
Amortized Cost	49,217	55,470
Gross Unrealized Gains	508	306
Gross Unrealized Losses	(761)	(1,244)
Fair Value	48,964	54,532
Utilities | Corporate debt securities
Debt securities:
Amortized Cost	24,895	31,952
Gross Unrealized Gains	292	7
Gross Unrealized Losses	(100)	(1,639)
Fair Value	$ 25,087	$ 30,320

Securities - Held-to-maturity S

Securities - Held-to-maturity Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 201,027	$ 200,141
Gross Unrealized Gains	18	104
Gross Unrealized Losses	(2,952)	(1,019)
Fair Value	198,093	199,226
U.S. Treasury
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		636
Gross Unrealized Gains		0
Gross Unrealized Losses		(2)
Fair Value		634
Government-sponsored enterprises
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	32,667	28,256
Gross Unrealized Gains	4	94
Gross Unrealized Losses	(934)	(126)
Fair Value	31,737	28,224
Government-sponsored mortgage-backed and collateralized mortgage obligations
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	153,938	155,232
Gross Unrealized Gains	14	10
Gross Unrealized Losses	(1,806)	(832)
Fair Value	152,146	154,410
SBA asset-backed securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	14,422	16,017
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(212)	(59)
Fair Value	$ 14,210	$ 15,958

Securities - Schedule of Contra

Securities - Schedule of Contractual Maturities of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities, Amortized Cost Basis [Abstract]
Within 1 year, Available-for-sale, Amortized Cost	$ 3,021
After 1 year through 5 years, Available-for-sale, Amortized Cost	56,673
After 5 years through 10 years, Available-for-sale, Amortized Cost	75,437
After 10 years, Available-for-sale, Amortized Cost	7,476
Single Maturity Date, Available-for-sale, Amortized Cost	142,607
Mortgage- and asset-backed securities and collateralized mortgage obligations amortizing monthly, Available-for-sale, Amortized Cost	19,704
Amortized Cost	162,311	$ 186,779
Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]
Within 1 year, Available-for-sale, Fair Value	3,022
After 1 year through 5 years, Available-for-sale, Fair Value	56,850
After 5 years through 10 years, Available-for-sale, Fair Value	74,787
After 10 years, Available-for-sale, Fair Value	7,535
Single Maturity Date, Available-for-sale, Fair Value	142,194
Mortgage- and asset-backed securities and collateralized mortgage obligations amortizing monthly , Available-for-sale, Fair Value	19,474
Total debt securities, Available-for-sale, Fair Value	161,668	184,114
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Within 1 year, Held-to-maturity, Amortized Cost	5,006
After 1 year through 5 years, Held-to-maturity, Amortized Cost	9,687
After 5 years through 10 years, Held-to-maturity, Amortized Cost	17,974
After 10 years, Held-to-maturity, Amortized Cost	0
Single Maturity Date, Held-to-maturity, Amortized Cost	32,667
Mortgage- and asset-backed securities and collateralized mortgage obligations amortizing monthly, Held-to-maturity, Amortized Cost	168,360
Amortized Cost	201,027	200,141
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value [Abstract]
Within 1 year, Held-to-maturity, Fair Value	5,007
After 1 year through 5 years, Held-to-maturity, Fair Value	9,439
After 5 years through 10 years, Held-to-maturity, Fair Value	17,291
After 10 years, Held-to-maturity, Fair Value	0
Single Maturity Date, Held-to-maturity, Fair Value	31,737
Mortgage- and asset-backed securities and collateralized mortgage obligations amortizing monthly, Held-to-maturity, Fair Value	166,356
Total debt securities, Held-to-maturity, Fair Value	$ 198,093	$ 199,226

Securities - Available-for-sa54

Securities - Available-for-sale Securities Unrealized Loss (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	$ (2,101)	$ (6,654)
Gross Unrealized Losses - More than twelve months	(2,382)	(663)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	94,193	169,507
Fair Value - More than twelve months	37,026	10,231
Total debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(1,677)	(3,170)
Gross Unrealized Losses - More than twelve months	(289)	(650)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	79,040	132,898
Fair Value - More than twelve months	14,136	9,778
Privately issued commercial mortgage- backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(11)	(84)
Gross Unrealized Losses - More than twelve months	(30)	(111)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	3,163	5,166
Fair Value - More than twelve months	7,326	7,765
Other asset-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(43)	(142)
Gross Unrealized Losses - More than twelve months	(152)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	3,924	11,253
Fair Value - More than twelve months	3,732	0
Total other mortgage- and asset-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(54)	(226)
Gross Unrealized Losses - More than twelve months	(182)	(111)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	7,087	16,419
Fair Value - More than twelve months	11,058	7,765
State and political
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(157)	(55)
Gross Unrealized Losses - More than twelve months	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	5,301	3,324
Fair Value - More than twelve months	0	0
Total marketable equity securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(424)	(3,484)
Gross Unrealized Losses - More than twelve months	(2,093)	(13)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	15,153	36,609
Fair Value - More than twelve months	22,890	453
Domestic community
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	0	0
Gross Unrealized Losses - More than twelve months	(19)	(13)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	0	0
Fair Value - More than twelve months	448	453
Global asset allocation
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(424)	(3,484)
Gross Unrealized Losses - More than twelve months	(2,074)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	15,153	36,609
Fair Value - More than twelve months	22,442	0
Financial Services | Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(712)	(545)
Gross Unrealized Losses - More than twelve months	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	30,822	43,954
Fair Value - More than twelve months	0	0
Banks | Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(298)	(90)
Gross Unrealized Losses - More than twelve months	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	14,553	14,070
Fair Value - More than twelve months	0	0
Diversified financial entities | Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(198)	(173)
Gross Unrealized Losses - More than twelve months	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	9,369	15,397
Fair Value - More than twelve months	0	0
Insurance and REITs | Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(216)	(282)
Gross Unrealized Losses - More than twelve months	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	6,900	14,487
Fair Value - More than twelve months	0	0
Other Corporate | Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(754)	(2,344)
Gross Unrealized Losses - More than twelve months	(107)	(539)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	35,830	69,201
Fair Value - More than twelve months	3,078	2,013
Industrials | Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(655)	(957)
Gross Unrealized Losses - More than twelve months	(106)	(287)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	24,630	43,848
Fair Value - More than twelve months	2,284	395
Utilities | Corporate debt securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(99)	(1,387)
Gross Unrealized Losses - More than twelve months	(1)	(252)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	11,200	25,353
Fair Value - More than twelve months	$ 794	$ 1,618

Securities - Held-to-maturity55

Securities - Held-to-maturity Securities Unrealized Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	$ (2,801)	$ (1,019)
Gross Unrealized Losses - More than twelve months	(151)	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	183,788	175,496
Fair Value - More than twelve months	8,880	0
U.S. Treasury
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months		(2)
Gross Unrealized Losses - More than twelve months		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months		634
Fair Value - More than twelve months		0
Government-sponsored enterprises
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(934)	(126)
Gross Unrealized Losses - More than twelve months	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	28,533	14,084
Fair Value - More than twelve months	0	0
Government-sponsored mortgage-backed and collateralized mortgage obligations
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(1,763)	(832)
Gross Unrealized Losses - More than twelve months	(43)	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	146,098	144,820
Fair Value - More than twelve months	3,827	0
SBA asset-backed securities
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Gross Unrealized Losses - Less than twelve months	(104)	(59)
Gross Unrealized Losses - More than twelve months	(108)	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Fair Value - Less than twelve months	9,157	15,958
Fair Value - More than twelve months	$ 5,053	$ 0

Securities - Narrative (Details

Securities - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2015USD ($)	Dec. 31, 2016USD ($)mutual_fund	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, transferred security, at carrying value	$ 196,300
Available-for sale securities, transferred security, unrealized gain (loss)	$ 666
Proceeds for securities available for sale		$ 97,824	$ 99,522	$ 362,941
AFS securities, gross realized gain		2,300	2,000	4,500
AFS securities, gross realized loss		$ 981	56	$ 1,700
Depreciation, percentage of amortized cost basis (less than)		2.00%
Number of mutual funds with unrealized losses | mutual_fund		3
Gross unrealized losses		$ 2,517	3,497
Government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Securities available for sale pledged as collateral, amortized cost		27,300	46,200
Securities available for sale pledged as collateral, at fair value		$ 27,000	$ 46,000
Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Depreciation, percentage of amortized cost basis (less than)		6.00%
Gross unrealized losses		$ 2,500
Accumulated Net Investment Gain (Loss) | Held-to-maturity Securities
Schedule of Available-for-sale Securities [Line Items]
Other comprehensive income (loss), held-to-maturity securities adjustment, before tax		$ 337

Loans and The Allowance for L57

Loans and The Allowance for Loan Losses - Summary of Loan balances (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 1,929,028	$ 1,539,176
Allowance for loan losses	(18,750)	(17,102)
Discount and fair value adjustments on purchased loans	(1,846)	(1,959)
Deferred loan costs and fees, net	4,439	3,160
Loans, net	1,912,871	1,523,275
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,693,513	1,318,313
1-4 Family Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	851,154	599,938
Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	78,719	77,399
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	687,289	561,203
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	76,351	79,773
Commercial Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	206,234	182,677
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 29,281	$ 38,186

Loans and The Allowance for L58

Loans and The Allowance for Loan Losses - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	$ 89.7	$ 39.8
Transferor's continuing involvement, arrangements of financial support, amount	3.8
1-4 Family Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged to secure debt	759.9	508.5
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance	56	30.6
Loans pledged to secure debt	$ 293.1	$ 133.2

Loans and The Allowance for L59

Loans and The Allowance for Loan Losses - Activity in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for Credit Losses, beginning balance	$ 17,102	$ 12,973	$ 9,671
Provision (credit) for loan losses	4,885	4,090	3,381
Loans charged-off	(3,475)	(43)	(79)
Recoveries	238	82	0
Allowance for Credit Losses, ending balance	18,750	17,102	12,973
1-4 Family Residential
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for Credit Losses, beginning balance	3,916	3,222	2,835
Provision (credit) for loan losses	830	612	405
Loans charged-off	0	0	(18)
Recoveries	100	82	0
Allowance for Credit Losses, ending balance	4,846	3,916	3,222
Home Equity
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for Credit Losses, beginning balance	636	340	247
Provision (credit) for loan losses	(99)	296	93
Loans charged-off	0	0	0
Recoveries	0	0	0
Allowance for Credit Losses, ending balance	537	636	340
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for Credit Losses, beginning balance	7,147	3,551	2,608
Provision (credit) for loan losses	1,447	3,596	943
Loans charged-off	(321)	0	0
Recoveries	101	0	0
Allowance for Credit Losses, ending balance	8,374	7,147	3,551
Construction
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for Credit Losses, beginning balance	1,364	1,056	303
Provision (credit) for loan losses	(11)	308	753
Loans charged-off	0	0	0
Recoveries	0	0	0
Allowance for Credit Losses, ending balance	1,353	1,364	1,056
Commercial Business
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for Credit Losses, beginning balance	2,839	3,410	2,416
Provision (credit) for loan losses	3,428	(571)	994
Loans charged-off	(3,098)	0	0
Recoveries	37	0	0
Allowance for Credit Losses, ending balance	3,206	2,839	3,410
Consumer
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for Credit Losses, beginning balance	772	736	574
Provision (credit) for loan losses	(282)	79	223
Loans charged-off	(56)	(43)	(61)
Recoveries	0	0	0
Allowance for Credit Losses, ending balance	434	772	736
Unallocated
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for Credit Losses, beginning balance	428	658	688
Provision (credit) for loan losses	(428)	(230)	(30)
Loans charged-off	0	0	0
Recoveries	0	0	0
Allowance for Credit Losses, ending balance	$ 0	$ 428	$ 658

Loans and The Allowance for L60

Loans and The Allowance for Loan Losses - Additional Activity in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to impaired loans	$ 17	$ 404
Allowance related to non-impaired loans	18,733	16,698
Total allowance for loan losses	18,750	17,102	$ 12,973	$ 9,671
Impaired loans	9,231	11,170
Non-impaired loans	1,919,797	1,528,006
Total loans	1,929,028	1,539,176
1-4 Family Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to impaired loans	17	0
Allowance related to non-impaired loans	4,829	3,916
Total allowance for loan losses	4,846	3,916	3,222	2,835
Impaired loans	6,726	6,114
Non-impaired loans	844,428	593,824
Total loans	851,154	599,938
Home Equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to impaired loans	0	0
Allowance related to non-impaired loans	537	636
Total allowance for loan losses	537	636	340	247
Impaired loans	1,153	270
Non-impaired loans	77,566	77,129
Total loans	78,719	77,399
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to impaired loans	0	384
Allowance related to non-impaired loans	8,374	6,763
Total allowance for loan losses	8,374	7,147	3,551	2,608
Impaired loans	941	4,631
Non-impaired loans	686,348	556,572
Total loans	687,289	561,203
Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to impaired loans	0	0
Allowance related to non-impaired loans	1,353	1,364
Total allowance for loan losses	1,353	1,364	1,056	303
Impaired loans	0	0
Non-impaired loans	76,351	79,773
Total loans	76,351	79,773
Commercial Business
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to impaired loans	0	10
Allowance related to non-impaired loans	3,206	2,829
Total allowance for loan losses	3,206	2,839	3,410	2,416
Impaired loans	241	10
Non-impaired loans	205,993	182,667
Total loans	206,234	182,677
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to impaired loans	0	10
Allowance related to non-impaired loans	434	762
Total allowance for loan losses	434	772	736	574
Impaired loans	170	145
Non-impaired loans	29,111	38,041
Total loans	29,281	38,186
Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance related to impaired loans	0	0
Allowance related to non-impaired loans	0	428
Total allowance for loan losses	0	428	$ 658	$ 688
Impaired loans	0	0
Non-impaired loans	0	0
Total loans	$ 0	$ 0

Loans and The Allowance for L61

Loans and The Allowance for Loan Losses - Summary of Past Due and Non-accrual loans, by class (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 11,591	$ 5,978
Loans on Non-accrual	8,983	10,744
1-4 Family Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,279	3,277
Loans on Non-accrual	6,478	5,688
Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,723	1,226
Loans on Non-accrual	1,153	270
Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,393	1,249
Loans on Non-accrual	941	4,631
Commercial Business
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,009	23
Loans on Non-accrual	241	10
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	187	203
Loans on Non-accrual	170	145
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,600	3,344
30-59 Days Past Due | 1-4 Family Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	584	2,287
30-59 Days Past Due | Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	452	1,031
30-59 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,393	0
30-59 Days Past Due | Commercial Business
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,996	23
30-59 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	175	3
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	887	1,348
60-89 Days Past Due | 1-4 Family Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	373	0
60-89 Days Past Due | Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	496	19
60-89 Days Past Due | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	1,249
60-89 Days Past Due | Commercial Business
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13	0
60-89 Days Past Due | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5	80
Past Due 90 Days or More
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,104	1,286
Past Due 90 Days or More | 1-4 Family Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,322	990
Past Due 90 Days or More | Home Equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	775	176
Past Due 90 Days or More | Commercial Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Past Due 90 Days or More | Commercial Business
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	0
Past Due 90 Days or More | Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 7	$ 120

Loans and The Allowance for L62

Loans and The Allowance for Loan Losses - Summary of Impaired Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Recorded Investment
Recorded Investment, without a valuation allowance	$ 9,110	$ 6,419
Recorded investment, with valuation allowance		4,751
Recorded investment, total	9,231	11,170
Unpaid Principal Balance
Unpaid Principal Balance, without a valuation allowance	12,917	7,288
Unpaid Principal Balance, with a valuation allowance		4,752
Unpaid Principal Balance, total	13,230	12,040
Related Allowance	17	404
1-4 Family Residential
Recorded Investment
Recorded Investment, without a valuation allowance	6,605	6,114
Recorded investment, with valuation allowance	121
Unpaid Principal Balance
Unpaid Principal Balance, without a valuation allowance	7,023	6,824
Unpaid Principal Balance, with a valuation allowance	313
Related Allowance	17
Home Equity
Recorded Investment
Recorded Investment, without a valuation allowance	1,153	270
Unpaid Principal Balance
Unpaid Principal Balance, without a valuation allowance	1,225	425
Commercial Real Estate
Recorded Investment
Recorded Investment, without a valuation allowance	941
Recorded investment, with valuation allowance		4,631
Unpaid Principal Balance
Unpaid Principal Balance, without a valuation allowance	1,207
Unpaid Principal Balance, with a valuation allowance		4,631
Related Allowance		384
Commercial Business
Recorded Investment
Recorded Investment, without a valuation allowance	241
Recorded investment, with valuation allowance		10
Unpaid Principal Balance
Unpaid Principal Balance, without a valuation allowance	3,279
Unpaid Principal Balance, with a valuation allowance		11
Related Allowance		10
Consumer
Recorded Investment
Recorded Investment, without a valuation allowance	170	35
Recorded investment, with valuation allowance		110
Unpaid Principal Balance
Unpaid Principal Balance, without a valuation allowance	$ 183	39
Unpaid Principal Balance, with a valuation allowance		110
Related Allowance		$ 10

Loans and The Allowance for L63

Loans and The Allowance for Loan Losses - Summary of Average Recorded Investments and Interest Income of Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, without a valuation allowance	$ 11,030	$ 6,450	$ 4,586
Interest Income Recognized, without a valuation allowance	751	452	232
Consumer Excluding Consumer Other Portfolio Segment | 1-4 Family Residential
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, without a valuation allowance	6,451	4,869	4,076
Interest Income Recognized, without a valuation allowance	449	270	213
Consumer Excluding Consumer Other Portfolio Segment | Home Equity
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, without a valuation allowance	555	575	476
Interest Income Recognized, without a valuation allowance	29	14	17
Consumer Excluding Consumer Other Portfolio Segment | Commercial Real Estate
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, without a valuation allowance	3,192	926
Interest Income Recognized, without a valuation allowance	206	161
Commercial Business
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, without a valuation allowance	672	2
Interest Income Recognized, without a valuation allowance	55	1
Consumer
Financing Receivable, Impaired [Line Items]
Average Recorded Investment, without a valuation allowance	160	78	34
Interest Income Recognized, without a valuation allowance	$ 12	$ 6	$ 2

Loans and The Allowance for L64

Loans and The Allowance for Loan Losses - Summary of Loan by Risk Rating (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 1,929,028	$ 1,539,176
1-4 Family Residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	851,154	599,938
Home Equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	78,719	77,399
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	687,289	561,203
Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	76,351	79,773
Commercial Business
Financing Receivable, Recorded Investment [Line Items]
Total loans	206,234	182,677
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	29,281	38,186
Loans rated 1 - 6
Financing Receivable, Recorded Investment [Line Items]
Total loans	938,280	812,346
Loans rated 1 - 6 | 1-4 Family Residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,054	1,950
Loans rated 1 - 6 | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	293	465
Loans rated 1 - 6 | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	671,872	548,360
Loans rated 1 - 6 | Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	76,351	79,773
Loans rated 1 - 6 | Commercial Business
Financing Receivable, Recorded Investment [Line Items]
Total loans	188,706	181,792
Loans rated 1 - 6 | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	4	6
Loans rated 7
Financing Receivable, Recorded Investment [Line Items]
Total loans	31,857	13,421
Loans rated 7 | 1-4 Family Residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,514	4,461
Loans rated 7 | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	967	321
Loans rated 7 | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,720	7,765
Loans rated 7 | Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 7 | Commercial Business
Financing Receivable, Recorded Investment [Line Items]
Total loans	17,510	874
Loans rated 7 | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	146	0
Loans rated 8
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,452	6,963
Loans rated 8 | 1-4 Family Residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,442	1,592
Loans rated 8 | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	258	144
Loans rated 8 | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,697	5,078
Loans rated 8 | Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 8 | Commercial Business
Financing Receivable, Recorded Investment [Line Items]
Total loans	18	0
Loans rated 8 | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	37	149
Loans rated 9
Financing Receivable, Recorded Investment [Line Items]
Total loans	645	712
Loans rated 9 | 1-4 Family Residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	645	701
Loans rated 9 | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 9 | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 9 | Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 9 | Commercial Business
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	11
Loans rated 9 | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 10
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 10 | 1-4 Family Residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 10 | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 10 | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 10 | Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 10 | Commercial Business
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans rated 10 | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans not rated
Financing Receivable, Recorded Investment [Line Items]
Total loans	949,794	705,734
Loans not rated | 1-4 Family Residential
Financing Receivable, Recorded Investment [Line Items]
Total loans	843,499	591,234
Loans not rated | Home Equity
Financing Receivable, Recorded Investment [Line Items]
Total loans	77,201	76,469
Loans not rated | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans not rated | Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans not rated | Commercial Business
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Loans not rated | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 29,094	$ 38,031

Premises and Equipment (Details

Premises and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 33,925	$ 29,895
Less accumulated depreciation and amortization	(11,891)	(9,880)
Premises and equipment, net	22,034	20,015
Depreciation and amortization of premises and equipment	2,000	1,800	$ 1,500
Land
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	4,087	4,087
Buildings
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 10,322	10,322
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	40 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 9,334	7,727
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	10 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 3,874	2,601
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	3 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	5 years
Technology equipment
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 6,139	5,088
Technology equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life (in years)	1 year
Technology equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life (in years)	3 years
Construction in progress
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 169	$ 70

Deposits - Summary of Deposit B

Deposits - Summary of Deposit Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Banking and Thrift [Abstract]
NOW and demand	$ 331,508	$ 288,143
Regular savings	262,984	287,344
Money market	573,204	368,050
Brokered money market	53,357	41,807
Total non-certificate accounts	1,221,053	985,344
Term certificates of $250,000 or more	77,550	65,364
Term certificates less than $250,000	262,564	246,614
Brokered certificates of deposit	247,520	136,527
Total certificate accounts	587,634	448,505
Total deposits	$ 1,808,687	$ 1,433,849

Deposits - Schedule of Contract

Deposits - Schedule of Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Time Deposits, Fiscal Year Maturity [Abstract]
Amount - 2017	$ 372,461
Amount - 2018	88,220
Amount - 2019	68,928
Amount - 2020	38,393
Amount - 2021	19,632
Total certificate accounts	$ 587,634	$ 448,505
Weighted Average Rate of Time Deposits [Abstract]
Weighted Average Rate - 2017	0.67%
Weighted Average Rate - 2018	1.26%
Weighted Average Rate - 2019	1.69%
Weighted Average Rate - 2020	1.90%
Weighted Average Rate - 2021	1.76%
Weighted Average Rate	1.00%

Borrowings - Additional Informa

Borrowings - Additional Information (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Federal Home Loan Bank of Boston
Debt Instrument [Line Items]
FFHLB advances with an original maturity of less than one year	$ 146,000,000	$ 205,000,000
Weighted average rate (percent)	0.76%	0.41%
Line of Credit | Federal Home Loan Bank of Boston
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 7,700,000	$ 7,700,000
Line of credit, amount outstanding	0
Unsecured Federal Funds Line of Credit | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	42,000,000	39,000,000
Line of credit, amount outstanding	$ 0	$ 0

Borrowings - FHLB Advances Fisc

Borrowings - FHLB Advances Fiscal Year Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Federal Home Loan Bank, Advances, Fiscal Year Maturity [Abstract]
2,016	$ 0	$ 10,000
2,017	15,000	15,000
2,018	20,000	20,000
2,019	25,000	0
2,020	15,000	10,000
2,021	30,000	0
Total FHLB advances	$ 105,000	$ 55,000
Federal Home Loan Bank, Advances, Maturities Summary, Average Interest Rate of Amounts Due [Abstract]
2,016	0.00%	2.29%
2,017	1.99%	1.99%
2,018	2.12%	2.23%
2,019	1.20%	0.00%
2,020	1.49%	1.65%
2,021	0.28%	0.00%
Weighted average rate	1.27%	2.07%

Income Taxes - Provisions (Bene

Income Taxes - Provisions (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current tax provision:
Federal									$ 3,617	$ 2,933	$ 2,695
State									306	206	240
Current income tax provision									3,923	3,139	2,935
Deferred tax provision (benefit):
Federal									55	7	(3,183)
State									47	(148)	(1,014)
Federal and State									102	(141)	(4,197)
Change in valuation reserve									(220)	(161)	640
Deferred income tax benefit									(118)	(302)	(3,557)
Provision (benefit) for income taxes	$ 1,323	$ 891	$ 721	$ 870	$ 587	$ 923	$ 689	$ 638	$ 3,805	$ 2,837	$ (622)

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal statutory rate									35.00%	34.00%	34.00%
Statutory federal tax provision (benefit) at 34%									$ 4,236	$ 3,429	$ (274)
Increase (decrease) resulting from:
State taxes, net of federal tax benefit									233	39	(511)
Dividends received deduction									(41)	(211)	(201)
Tax-exempt bank-owned life insurance									(528)	(351)	(404)
Tax-exempt interest									(189)	(222)	(277)
Change in valuation reserve									(220)	(161)	640
Nondeductible IPO costs									0	0	202
Equity incentives									339	52	0
Amortization of low income housing partnership									219	0	0
Tax credits utilized									(286)	(45)	0
Accrual adjustment									207	13	0
Statutory rate change for net deferred tax asset from 34% to 35%									(289)	0	0
Other, net									124	294	203
Provision (benefit) for income taxes	$ 1,323	$ 891	$ 721	$ 870	$ 587	$ 923	$ 689	$ 638	$ 3,805	$ 2,837	$ (622)
Effective tax rates									30.50%	28.20%	77.30%

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Examination [Line Items]
Deferred tax assets, gross	$ 14,958	$ 15,279
Valuation reserve	(1,790)	(1,966)
Deferred tax assets, net	13,168	13,313
Deferred tax liabilities	(3,022)	(2,648)
Net deferred tax asset	10,146	10,665	$ 6,233	$ 2,831
Federal
Income Tax Examination [Line Items]
Deferred tax assets, gross	11,700	12,091
Deferred tax liabilities	(2,427)	(2,138)
State
Income Tax Examination [Line Items]
Deferred tax assets, gross	3,258	3,188
Deferred tax liabilities	$ (595)	$ (510)

Income Taxes - Tax Effect on De

Income Taxes - Tax Effect on Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Depreciation and amortization	$ 747	$ 929
Employee benefit plans and share-based compensation plans	571	901
Allowance for loan losses	7,660	6,831
Contribution carryover	2,317	2,675
Net unrealized loss on securities held as, or transferred from, available for sale	893	1,748
Net unrealized losses on defined benefit pension plan	1,270	1,052
Deferred rent expense	123	28
Other	302	131
Valuation reserve	(1,790)	(1,966)
Deferred tax liabilities:
Deferred loan origination costs	(1,947)	(1,664)
Net deferred tax asset	$ 10,146	$ 10,665	$ 6,233	$ 2,831

Income Taxes - Changes in Defer

Income Taxes - Changes in Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) In Deferred Taxes [Roll Forward]
Balance at beginning of year	$ 10,665	$ 6,233	$ 2,831
Deferred tax benefit	118	302	3,557
Tax effect of changes in accumulated other comprehensive income	(637)	4,130	(155)
Balance at end of year	$ 10,146	$ 10,665	$ 6,233

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Examination [Line Items]
Deferred tax assets, valuation allowance	$ 1,790,000	$ 1,966,000
Bad debt reserve for tax purposes of qualified lender, percentage of reserve subject taxation	150.00%
Income taxes, penalties and interest expense	$ 22,000	$ 0	$ 0
Federal
Income Tax Examination [Line Items]
Bad debt reserve for tax purposes of qualified lender	1,300,000
Deferred income tax liability not recognized	$ 514,000

Income Taxes - Change in Valuat

Income Taxes - Change in Valuation Allowance (Details) - Valuation Allowance of Deferred Tax Assets $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	$ (1,966)
Change through the income statement	220
Change through other comprehensive income	(44)
Balance at end of year	(1,790)
Federal
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	(200)
Change through the income statement	200
Change through other comprehensive income	0
Balance at end of year	0
State
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	(1,766)
Change through the income statement	20
Change through other comprehensive income	(44)
Balance at end of year	$ (1,790)

Equity - Additional Information

Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 11, 2014	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2015	Sep. 22, 2011
Class of Stock [Line Items]
Tier 1 capital conservation buffer common equity to RWA (percent) (greater than)		0.625%		2.50%
Tier 1 capital conservation buffer common equity capital to RWA, phasing period (years)		3 years
Preferred stock, shares issued		0	0		18,724
Liquidation value					$ 1,000
Preferred stock		$ 0	$ 0		$ 18,700
Preferred stock, redemption amount	$ 18,700
Payments for repurchase of redeemable preferred stock	$ 18,700
Preferred stock, shares authorized		50,000,000	50,000,000
Preferred stock, par value (dollars per share)		$ 0	$ 0
Preferred stock, shares outstanding		0	0
Retained earnings, unappropriated		$ 148,000
Funds available for loans or advances from the Bank		30,100
Blue Hills Bank
Class of Stock [Line Items]
Equity restrictions		$ 154,200

Equity - Minimum Required Capit

Equity - Minimum Required Capital (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Total capital (to risk weighted assets)
Actual - Total Capital to Risk Weighted Assets	$ 395,325	$ 407,444
Actual - Total Capital to Risk Weighted Assets (percent)	20.50%	24.80%
Minimum Capital Requirement - Total Capital to Risk Weighted Assets	$ 154,471	$ 131,231
Minimum Capital Requirement - Total Capital to Risk Weighted Assets (percent)	8.00%	8.00%
Minimum to Be Well Capitalized - Total Capital to Risk Weighted Assets	$ 193,089	$ 164,039
Minimum to Be Well Capitalized - Total Capital to Risk Weighted Assets (percent)	10.00%	10.00%
Tier 1 capital (to risk weighted assets)
Actual - Tier 1 Capital to Risk Weighted Assets	$ 376,575	$ 390,342
Actual - Tier 1 Capital to Risk Weighted Assets (percent)	19.50%	23.80%
Minimum Capital Requirement - Tier 1 Capital to Risk Weighted Assets	$ 115,854	$ 98,423
Minimum Capital Requirement - Tier 1 Capital to Risk Weighted Assets (percent)	6.00%	6.00%
Minimum to Be Well Capitalized - Tier 1 Capital to Risk Weighted Assets	$ 154,471	$ 131,231
Minimum to Be Well Capitalized - Tier 1 Capital to Risk Weighted Assets (percent)	8.00%	8.00%
Common equity Tier 1 (to risk weighted assets)
Actual - Common Equity to Risk Weighted Assets	$ 376,575	$ 390,342
Actual - Common Equity to Risk Weighted Assets (percent)	19.50%	23.80%
Minimum Capital Requirement - Common Equity to Risk Weighted Assets	$ 86,890	$ 73,818
Minimum Capital Requirement - Common Equity to Risk Weighted Assets (percent)	4.50%	4.50%
Minimum to Be Well Capitalized - Common Equity to Risk Weighted Assets	$ 125,508	$ 106,625
Minimum to Be Well Capitalized - Common Equity to Risk Weighted Assets (percent)	6.50%	6.50%
Tier 1 capital (to average assets)
Actual - Tier 1 Capital to Average Assets	$ 376,575	$ 390,342
Actual - Tier 1 Capital to Average Assets (percent)	16.00%	19.60%
Minimum Capital Requirement - Tier 1 Capital to Average Assets	$ 94,166	$ 79,658
Minimum Capital Requirement - Tier 1 Capital to Average Assets (percent)	4.00%	4.00%
Minimum To Be Well Capitalized - Tier 1 Capital to Average Assets	$ 117,708	$ 99,573
Minimum To Be Well Capitalized - Tier 1 Capital to Average Assets (percent)	5.00%	5.00%
Blue Hills Bank
Total capital (to risk weighted assets)
Actual - Total Capital to Risk Weighted Assets	$ 313,457	$ 296,309
Actual - Total Capital to Risk Weighted Assets (percent)	16.30%	18.10%
Minimum Capital Requirement - Total Capital to Risk Weighted Assets	$ 154,196	$ 130,832
Minimum Capital Requirement - Total Capital to Risk Weighted Assets (percent)	8.00%	8.00%
Minimum to Be Well Capitalized - Total Capital to Risk Weighted Assets	$ 192,745	$ 163,540
Minimum to Be Well Capitalized - Total Capital to Risk Weighted Assets (percent)	10.00%	10.00%
Tier 1 capital (to risk weighted assets)
Actual - Tier 1 Capital to Risk Weighted Assets	$ 294,707	$ 279,207
Actual - Tier 1 Capital to Risk Weighted Assets (percent)	15.30%	17.10%
Minimum Capital Requirement - Tier 1 Capital to Risk Weighted Assets	$ 115,647	$ 98,124
Minimum Capital Requirement - Tier 1 Capital to Risk Weighted Assets (percent)	6.00%	6.00%
Minimum to Be Well Capitalized - Tier 1 Capital to Risk Weighted Assets	$ 154,196	$ 130,832
Minimum to Be Well Capitalized - Tier 1 Capital to Risk Weighted Assets (percent)	8.00%	8.00%
Common equity Tier 1 (to risk weighted assets)
Actual - Common Equity to Risk Weighted Assets	$ 294,707	$ 279,207
Actual - Common Equity to Risk Weighted Assets (percent)	15.30%	17.10%
Minimum Capital Requirement - Common Equity to Risk Weighted Assets	$ 86,735	$ 73,593
Minimum Capital Requirement - Common Equity to Risk Weighted Assets (percent)	4.50%	4.50%
Minimum to Be Well Capitalized - Common Equity to Risk Weighted Assets	$ 125,284	$ 106,301
Minimum to Be Well Capitalized - Common Equity to Risk Weighted Assets (percent)	6.50%	6.50%
Tier 1 capital (to average assets)
Actual - Tier 1 Capital to Average Assets	$ 294,707	$ 279,207
Actual - Tier 1 Capital to Average Assets (percent)	12.50%	14.00%
Minimum Capital Requirement - Tier 1 Capital to Average Assets	$ 94,099	$ 79,867
Minimum Capital Requirement - Tier 1 Capital to Average Assets (percent)	4.00%	4.00%
Minimum To Be Well Capitalized - Tier 1 Capital to Average Assets	$ 117,623	$ 99,608
Minimum To Be Well Capitalized - Tier 1 Capital to Average Assets (percent)	5.00%	5.00%

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 01, 2015	Jul. 21, 2014	Dec. 15, 2013	Jan. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Employer contribution					$ 470	$ 0	$ 0
401(k) Plan, minimum service period required to be a participant (months)						3 months
401(k) Employer non-elective contribution based on earnings (percent)	3.00%		3.00%
401(k) Employer elective contribution based on earnings (percent)	2.00%		2.00%
401(k) plan expense	4.00%					3.00%
401(k) Employer matching contribution, percent match, first 3%	100.00%
401(k) Employer matching contribution, percent match, remaining 2%	50.00%
401(k) Employer matching contribution (percent)					784	$ 610	465
Short-term Incentive Compensation expense					$ 2,500	2,300	3,000
Employee stock ownership plan, shares		2,277,345			2,277,345
Shares issued (in dollars per share)		$ 10			$ 10
ESOP, term of loan (years)					30 years
ESOP, interest rate (percent)					3.75%
ESOP, number of annual committed-to-be-released shares					75,912
ESOP, number of suspense shares fair value					$ 38,400	32,500
ESOP expense					$ 1,130	1,063	993
Subsequent Event
Defined Benefit Plan Disclosure [Line Items]
Employer contribution				$ 1,100
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, minimum required age					21 years
Defined benefit plan, minimum hours of service required					1000 hours
Defined benefit plan, required period to perform service (years)					12 months
Net periodic pension cost (benefit)					$ (27)	(234)	$ (1,218)
SERP
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, required period to perform service (years)					5 years
Shares paid for tax withholdings for share based compensation					27,956
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation, minimum (percent)					40.00%
Target plan asset allocation, maximum (percent)					64.00%
Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation, minimum (percent)					15.00%
Target plan asset allocation, maximum (percent)					25.00%
Other Investments
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation, minimum (percent)					25.00%
Target plan asset allocation, maximum (percent)					41.00%
Parent Company
Defined Benefit Plan Disclosure [Line Items]
ESOP, loan balance					$ 20,995	$ 21,459

Employee Benefit Plans - Accumu

Employee Benefit Plans - Accumulated Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in plan assets:
Employer contribution	$ 470	$ 0	$ 0
Pension Plan
Change in plan assets:
Fair value of plan assets at beginning of year	8,814	9,443	9,535
Actual return (loss) on plan assets	847	(304)	391
Benefits paid	(320)	(325)	(483)
Fair value of plan assets at end of year	9,811	8,814	9,443
Change in benefit obligation:
Benefit obligation at beginning of year	10,772	10,135	9,287
Service cost	0	0	484
Interest cost	422	401	407
Actuarial loss	1,022	561	2,230
Benefits paid	(320)	(325)	(483)
Curtailment gain	0	0	(1,790)
Benefit obligation at end of year	11,896	10,772	10,135
Funded status and accrued liability at end of year	(2,085)	(1,958)	(692)
Accumulated benefit obligation at end of year	$ 11,896	$ 10,772	$ 10,135

Employee Benefit Plans - Benefi

Employee Benefit Plans - Benefit Obligation Assumptions Used (Details)	Dec. 31, 2016	Dec. 31, 2015
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.86%	4.01%

Employee Benefit Plans - Net Pe

Employee Benefit Plans - Net Periodic Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain	$ 0	$ 0	$ (1,304)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	484
Interest cost	422	401	407
Expected return on plan assets	(720)	(745)	(735)
Amortization of net actuarial loss (gain)	271	110	(70)
Curtailment gain	0	0	(1,304)
Net periodic pension benefit	$ (27)	$ (234)	$ (1,218)

Employee Benefit Plans - Net 83

Employee Benefit Plans - Net Periodic Pension Costs Assumptions Used (Details) - Pension Plan	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.01%	4.00%	4.25%
Expected long-term rate of return on plan assets	8.00%	8.00%	8.00%

Employee Benefit Plans - Fair V

Employee Benefit Plans - Fair Value of Pension Plan Assets (Details) - Pension Plan - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Investments measure in the fair value hierarchy	$ 3,943
Investments measured at net asset value	5,868
Total plan investment assets, at fair value	9,811	$ 8,814	$ 9,443	$ 9,535
Level 1
Defined Benefit Plan Disclosure [Line Items]
Investments measure in the fair value hierarchy	3,943
Total plan investment assets, at fair value	3,943	3,888
Level 2
Defined Benefit Plan Disclosure [Line Items]
Investments measure in the fair value hierarchy	0
Total plan investment assets, at fair value	0	4,266
Level 3
Defined Benefit Plan Disclosure [Line Items]
Investments measure in the fair value hierarchy	0
Total plan investment assets, at fair value	0	660
Collective funds
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	681	5,392
Collective funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	681	1,126
Collective funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	0	4,266
Collective funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	0	0
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	1,929	1,566
Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	1,929	1,566
Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	0	0
Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	0	0
Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	1,209	1,046
Mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	1,209	1,046
Mutual funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	0	0
Mutual funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	0	0
Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	124	150
Short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	124	150
Short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	0	0
Short-term investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value	$ 0	0
Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value		660
Hedge funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value		0
Hedge funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value		0
Hedge funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan investment assets, at fair value		$ 660

Employee Benefit Plans - Expect

Employee Benefit Plans - Expected Benefit Payments (Details) $ in Thousands	Dec. 31, 2016USD ($)
Compensation and Retirement Disclosure [Abstract]
2,017	$ 785
2,018	1,087
2,019	614
2,020	710
2,021	930
2022-2026	$ 3,223

Employee Benefit Plans - Employ

Employee Benefit Plans - Employee Stock Ownership Plan (Details) - shares	Dec. 31, 2016	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Allocated	149,613	75,912
Committed to be allocated	75,912	75,912
Unallocated	2,049,608	2,124,846
Total	2,275,133	2,276,670

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	2,846,681
Expected life (years)	6 years 6 months	6 years 6 months
Vesting period (years)	5 years	5 years
Share-based compensation expense	$ 2,100,000	$ 473,000	$ 0
Tax benefit related to share-based compensation expense	$ 502,000	112,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized	1,138,673
Share-based compensation expense	$ 2,800,000	651,000	$ 0
Tax benefit related to share-based compensation expense	$ 987,000	$ 228,000
Granted (shares)	31,450
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (shares)	40,000
Maximum | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (years)	10 years

Stock-Based Compensation - Fair

Stock-Based Compensation - Fair Value Assumptions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (shares)	55,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (shares)	55,000	2,434,000
Vesting period (years)	5 years	5 years
Expected volatility (percent)	28.47%	28.85%
Expected life (years)	6 years 6 months	6 years 6 months
Expected dividend yield (percent)	0.58%	0.54%
Risk free interest rate (percent)	1.38%	1.55%
Fair value per option (dollars per share)	$ 4.02	$ 4.23

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance (shares)	2,434,000
Granted (shares)	55,000
Forfeited (shares)	(36,450)
Exercised (shares)	(2,880)
Ending balance (shares)	2,449,670	2,434,000
Outstanding and expected to vest at end of period (shares)	2,449,670
Exercisable at end of period (shares)	478,390
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance, weighted average exercise price (dollars per share)	$ 14.07
Granted, weighted average exercise price (dollars per share)	13.80
Forfeited, weighted average exercise price (dollars per share)	14.07
Exercised, weighted average exercise price (dollars per share)	14.07
Ending balance, weighted average exercise price (dollars per share)	14.06	$ 14.07
Outstanding and expected to vest at end of period, weighted average exercise price (dollars per share)	14.06
Exercisable at end of period, weighted average exercise price (dollars per share)	$ 14.07
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, weighted average remaining contractual term (years)	8 years 9 months 7 days
Outstanding and expected to vest, weighted average remaining contractual term (years)	8 years 9 months 7 days
Exercisable, weighted average remaining contractual term (years)	3 years 9 months 11 days
Outstanding, aggregate intrinsic value	$ 11,479,306
Outstanding and expected to vest, aggregate intrinsic value	11,479,306
Exercisable, aggregate intrinsic value	$ 2,238,865
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Granted (shares)	55,000	2,434,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Unrecognized compensation cost at December 31, 2016	$ 7,827,000
Weighted average remaining recognition period (years) at December 31, 2016	3 years 9 months 11 days

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Activity (Details) - Restricted Stock $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (shares) | shares	983,175
Granted (shares) | shares	31,450
Vested (shares) | shares	(186,755)
Forfeited (shares) | shares	(11,800)
Ending balance (shares) | shares	816,070
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance, weighted average exercise price (dollars per share) | $ / shares	$ 14.07
Granted, weighted average exercise price (dollars per share) | $ / shares	13.83
Vested, weighted average exercise price (dollars per share) | $ / shares	14.07
Forfeited, weighted average exercise price (dollars per share) | $ / shares	14.07
Ending balance, weighted average exercise price (dollars per share) | $ / shares	$ 14.06
Unrecognized compensation cost, inclusive of directors' fees at December 31, 2016 | $	$ 10,645
Weighted average remaining recognition period (years) at December 31, 2016	3 years 9 months 11 days

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income (loss)	$ 3,998	$ 1,630	$ 1,358	$ 1,667	$ 2,412	$ 1,810	$ 1,699	$ 1,306	$ 8,653	$ 7,227	$ (183)
Average number of common shares outstanding (shares)									27,464,996	28,460,077
Less: Average unvested restricted stock awards (shares)									(957,364)	(231,652)
Less: Average unallocated ESOP shares (shares)									(2,087,227)	(2,163,478)
Average number of common shares outstanding used to calculate basic earnings per common share (shares)	23,919,483	24,129,512	24,575,211	25,066,086	25,500,755	26,183,381	26,293,560	26,274,738	24,420,405	26,064,947
Effect of dilutive unvested restricted stock awards (shares)									120,524	4,642
Average number of common shares outstanding used to calculate diluted earnings per common share (shares)	24,032,613	24,307,540	24,699,794	25,132,441	25,554,961	26,183,381	26,293,560	26,274,738	24,540,929	26,069,589
Basic earnings per share (dollars per share)	$ 0.17	$ 0.07	$ 0.06	$ 0.07	$ 0.09	$ 0.07	$ 0.06	$ 0.05	$ 0.35	$ 0.28
Diluted earnings per share (dollars per share)	$ 0.17	$ 0.07	$ 0.05	$ 0.07	$ 0.09	$ 0.07	$ 0.06	$ 0.05	$ 0.35	$ 0.28
Antidilutive securities excluded from computation of earnings per share (shares)									2,486,000	2,434,000

Commitments and Contingencies -

Commitments and Contingencies - Credit Related Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Commitments to originate loans
Other Commitments [Line Items]
Financial instruments with off-balance-sheet risk	$ 51,622	$ 69,554
Letters of credit
Other Commitments [Line Items]
Financial instruments with off-balance-sheet risk	3,277	3,571
Undisbursed construction loans
Other Commitments [Line Items]
Financial instruments with off-balance-sheet risk	96,169	80,336
Commercial Business
Other Commitments [Line Items]
Financial instruments with off-balance-sheet risk	164,185	128,748
Home equity
Other Commitments [Line Items]
Financial instruments with off-balance-sheet risk	55,344	44,968
Consumer
Other Commitments [Line Items]
Financial instruments with off-balance-sheet risk	$ 15,995	$ 16,033

Commitments and Contingencies93

Commitments and Contingencies - Operating Lease Commitments (Details) $ in Thousands	Dec. 31, 2016USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,017	$ 2,530
2,018	2,665
2,019	2,479
2,020	2,398
2,021	2,288
Thereafter	12,408
Total future minimum payments due	$ 24,768

Commitments and Contingencies94

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	Jan. 01, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Commitments [Line Items]
Operating leases, rental expense		$ 2,200	$ 1,600	$ 1,100
Renewal term		30 years
Chief Executive Officer
Other Commitments [Line Items]
Employment agreement, initial term (in years)		3 years
Employment agreement, automatic extension period (in years)		1 year
President
Other Commitments [Line Items]
Employment agreement, initial term (in years)		3 years
Employment agreement, automatic extension period (in years)		1 year
Boston Waterfront Music Venue Naming Rights Agreement
Other Commitments [Line Items]
Contractual obligation, period	10 years
Other commitment contractual obligation	$ 390	$ 430	$ 410	$ 390
Contractual obligation, annual increase (percentage)	5.00%

On Balance Sheet Derivative I95

On Balance Sheet Derivative Instruments and Hedging Activities (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative Asset, notional amount	$ 435,353	$ 290,846
Derivative Asset, fair value	9,024	7,962
Derivative Liability, notional amount	452,533	295,244
Derivative Liability, fair value	8,988	8,489
Interest Rate Swap
Derivatives, Fair Value [Line Items]
Derivative Asset, notional amount	419,488	282,546
Derivative Asset, fair value	9,016	7,956
Derivative Liability, notional amount	419,488	282,546
Derivative Liability, fair value	8,932	8,411
Other Contract
Derivatives, Fair Value [Line Items]
Derivative Asset, notional amount	15,865	8,300
Derivative Asset, fair value	8	6
Derivative Liability, notional amount	33,045	12,698
Derivative Liability, fair value	$ 56	$ 78

On Balance Sheet Derivative I96

On Balance Sheet Derivative Instruments and Hedging Activities - Additional Information (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Notional amount	$ 435,353	$ 290,846
Derivative Gains, fair value	9,024	7,962
Derivative Losses, fair value	8,988	$ 8,489
Mortgage loan commitments
Derivative [Line Items]
Notional amount	6,800
Derivative Gains, fair value	111
Derivative Losses, fair value	3
Forward loan sale commitment
Derivative [Line Items]
Notional amount	9,500
Derivative Gains, fair value	15
Derivative Losses, fair value	$ 74

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets
Debt securities	$ 161,668	$ 184,114
Marketable equity securities	43,168	47,576
Recurring
Assets
Debt securities	161,668	184,114
Marketable equity securities	43,168	47,576
Derivative assets		7,962
Total assets	213,986	239,652
Liabilities
Derivative liabilities	9,065	8,489
Recurring | Level 1
Assets
Debt securities	0	0
Marketable equity securities	43,168	47,576
Derivative assets		0
Total assets	43,168	47,576
Liabilities
Derivative liabilities	0	0
Recurring | Level 2
Assets
Debt securities	161,668	184,114
Marketable equity securities	0	0
Derivative assets		7,962
Total assets	170,692	192,076
Liabilities
Derivative liabilities	8,988	8,489
Recurring | Level 3
Assets
Debt securities	0	0
Marketable equity securities	0	0
Derivative assets		0
Total assets	126	0
Liabilities
Derivative liabilities	77	0
Interest Rate Swap | Level 1
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Interest Rate Swap | Level 2
Assets
Derivative assets	9,024	7,962
Liabilities
Derivative liabilities	8,988	8,489
Interest Rate Swap | Level 3
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	$ 0
Interest Rate Swap | Recurring
Assets
Derivative assets	9,024
Liabilities
Derivative liabilities	8,988
Interest Rate Swap | Recurring | Level 1
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Interest Rate Swap | Recurring | Level 2
Assets
Derivative assets	9,024
Liabilities
Derivative liabilities	8,988
Interest Rate Swap | Recurring | Level 3
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Forward loan sale commitment | Level 1
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Forward loan sale commitment | Level 2
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Forward loan sale commitment | Level 3
Assets
Derivative assets	15
Liabilities
Derivative liabilities	74
Forward loan sale commitment | Recurring
Assets
Derivative assets	15
Liabilities
Derivative liabilities	74
Forward loan sale commitment | Recurring | Level 1
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Forward loan sale commitment | Recurring | Level 2
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Forward loan sale commitment | Recurring | Level 3
Assets
Derivative assets	15
Liabilities
Derivative liabilities	74
Mortgage loan commitments | Level 1
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Mortgage loan commitments | Level 2
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Mortgage loan commitments | Level 3
Assets
Derivative assets	111
Liabilities
Derivative liabilities	3
Mortgage loan commitments | Recurring
Assets
Derivative assets	111
Liabilities
Derivative liabilities	3
Mortgage loan commitments | Recurring | Level 1
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Mortgage loan commitments | Recurring | Level 2
Assets
Derivative assets	0
Liabilities
Derivative liabilities	0
Mortgage loan commitments | Recurring | Level 3
Assets
Derivative assets	111
Liabilities
Derivative liabilities	$ 3

Other Comprehensive Income - Co

Other Comprehensive Income - Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net-of-tax amount	$ (4,069)	$ (5,188)
Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized loss	(3,482)	(2,858)
Tax effect	1,270	1,052
Net-of-tax amount	(2,212)	(1,806)
Available-for-sale Securities | Accumulated Net Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized loss	(3,087)	(5,701)
Tax effect	1,007	1,945
Net-of-tax amount	(2,080)	(3,756)	$ 3,392	$ 1,983
Held-to-maturity Securities | Accumulated Net Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized loss	337	571
Tax effect	(114)	(197)
Net-of-tax amount	$ 223	$ 374	$ 0	$ 0

Fair Value Measurements - Ass99

Fair Value Measurements - Assets and Liabilities Measure at Fair Value on a Nonrecurring Basis (Details) - Nonrecurring - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ (2,911)	$ (404)	$ (18)
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	136	4,752
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 0	$ 0

Other Comprehensive Income - Ch

Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ (5,188)
Unrealized gains on securities reclassified as held to maturity		0	$ (666)	$ 0
Amortization of amounts previously recorded upon transfer to held-to-maturity from available-for-sale	[1]	(234)	(95)	0
Tax effects		(637)	4,130	(155)
Other comprehensive income (loss)		1,119	(7,765)	112
Ending balance		(4,069)	(5,188)
Actuarial gain expected to be included in AOCI		358
Defined Benefit Pension Plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(1,806)	(815)	482
Other comprehensive income (loss) before reclassifications		(895)	(1,610)	(2,090)
Realized gains reclassified		0	0	0
Amortization of actuarial losses		271	110	(70)
Tax effects		218	509	863
Other comprehensive income (loss)		(406)	(991)	(1,297)
Ending balance		(2,212)	(1,806)	(815)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(5,188)	2,577	2,465
Other comprehensive income (loss) before reclassifications		2,954	(9,942)	2,852
Realized gains reclassified		(1,235)	(1,968)	(2,515)
Amortization of actuarial losses		271	110	(70)
Unrealized gains on securities reclassified as held to maturity			0
Amortization of amounts previously recorded upon transfer to held-to-maturity from available-for-sale		(234)	(95)
Tax effects		(637)	4,130	(155)
Other comprehensive income (loss)		1,119	(7,765)	112
Ending balance		(4,069)	(5,188)	2,577
Available-for-sale Securities | Accumulated Net Investment Gain (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(3,756)	3,392	1,983
Other comprehensive income (loss) before reclassifications		3,849	(8,332)	4,942
Realized gains reclassified		(1,235)	(1,968)	(2,515)
Unrealized gains on securities reclassified as held to maturity			(666)
Amortization of amounts previously recorded upon transfer to held-to-maturity from available-for-sale		0	0
Tax effects		(938)	3,818	(1,018)
Other comprehensive income (loss)		1,676	(7,148)	1,409
Ending balance		(2,080)	(3,756)	3,392
Held-to-maturity Securities | Accumulated Net Investment Gain (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		374	0	0
Other comprehensive income (loss) before reclassifications		0	0	0
Realized gains reclassified		0	0	0
Unrealized gains on securities reclassified as held to maturity			666
Amortization of amounts previously recorded upon transfer to held-to-maturity from available-for-sale		(234)	(95)
Tax effects		83	(197)	0
Other comprehensive income (loss)		(151)	374	0
Ending balance		$ 223	$ 374	$ 0
[1]	Amounts are included in interest income on securities in the consolidated statements of operations. Income tax expense associated with the amortization amount for the years ended December 31, 2016 and 2015 was $83,000 and $35,000, respectively.

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Fair Value, Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial assets:
Securities available for sale	$ 204,836	$ 231,690
Securities held to maturity	201,027	200,141
Carrying Amount
Financial assets:
Cash and cash equivalents	30,496	33,298
Securities available for sale	204,836	231,690
Securities held to maturity	201,027	200,141
Federal Home Loan Bank stock	13,352	13,567
Loans and loans held for sale, net	1,915,632	1,536,152
Accrued interest receivable	6,057	5,344
Financial liabilities:
Deposits	1,808,687	1,433,849
Borrowings	251,000	260,000
Estimate of Fair Value Measurement
Financial assets:
Cash and cash equivalents	30,496	33,298
Securities available for sale	204,836	231,690
Securities held to maturity	198,093	199,226
Federal Home Loan Bank stock	13,352	13,567
Loans and loans held for sale, net	1,903,978	1,538,809
Accrued interest receivable	6,057	5,344
Financial liabilities:
Deposits	1,808,629	1,434,179
Borrowings	250,648	260,244
Level 1
Financial assets:
Cash and cash equivalents	30,496	33,298
Securities available for sale	43,168	47,576
Securities held to maturity	0	634
Federal Home Loan Bank stock	0	0
Loans and loans held for sale, net	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Borrowings	0	0
Level 2
Financial assets:
Cash and cash equivalents	0	0
Securities available for sale	161,668	184,114
Securities held to maturity	198,093	198,592
Federal Home Loan Bank stock	0	0
Loans and loans held for sale, net	0	0
Accrued interest receivable	0	0
Financial liabilities:
Deposits	0	0
Borrowings	250,648	260,244
Level 3
Financial assets:
Cash and cash equivalents	0	0
Securities available for sale	0	0
Securities held to maturity	0	0
Federal Home Loan Bank stock	13,352	13,567
Loans and loans held for sale, net	1,903,978	1,538,809
Accrued interest receivable	6,057	5,344
Financial liabilities:
Deposits	1,808,629	1,434,179
Borrowings	0	0
Interest Rate Swap | Carrying Amount
Financial liabilities:
Derivative assets	9,024	7,962
Derivative liabilities	8,988	8,489
Interest Rate Swap | Estimate of Fair Value Measurement
Financial liabilities:
Derivative assets	9,024	7,962
Derivative liabilities	8,988	8,489
Interest Rate Swap | Level 1
Financial liabilities:
Derivative assets	0	0
Derivative liabilities	0	0
Interest Rate Swap | Level 2
Financial liabilities:
Derivative assets	9,024	7,962
Derivative liabilities	8,988	8,489
Interest Rate Swap | Level 3
Financial liabilities:
Derivative assets	0	0
Derivative liabilities	0	$ 0
Forward loan sale commitment | Carrying Amount
Financial liabilities:
Derivative assets	15
Derivative liabilities	74
Forward loan sale commitment | Estimate of Fair Value Measurement
Financial liabilities:
Derivative assets	15
Derivative liabilities	74
Forward loan sale commitment | Level 1
Financial liabilities:
Derivative assets	0
Derivative liabilities	0
Forward loan sale commitment | Level 2
Financial liabilities:
Derivative assets	0
Derivative liabilities	0
Forward loan sale commitment | Level 3
Financial liabilities:
Derivative assets	15
Derivative liabilities	74
Mortgage loan commitments | Carrying Amount
Financial liabilities:
Derivative assets	111
Derivative liabilities	3
Mortgage loan commitments | Estimate of Fair Value Measurement
Financial liabilities:
Derivative assets	111
Derivative liabilities	3
Mortgage loan commitments | Level 1
Financial liabilities:
Derivative assets	0
Derivative liabilities	0
Mortgage loan commitments | Level 2
Financial liabilities:
Derivative assets	0
Derivative liabilities	0
Mortgage loan commitments | Level 3
Financial liabilities:
Derivative assets	111
Derivative liabilities	$ 3

Condensed Financial Statemen102

Condensed Financial Statements of Parent Company (Condensed Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets [Abstract]
Total cash and cash equivalents	$ 30,496	$ 33,298
Other assets	23,537	20,060
Assets	2,469,692	2,114,343
Liabilities and Equity [Abstract]
Accrued expenses	23,098	21,665
Stockholders' equity	386,907	398,829	$ 411,606	$ 171,534
Total liabilities and stockholders' equity	2,469,692	2,114,343
Parent Company
Assets [Abstract]
Cash balances at Blue Hills Bank	66,326	100,965
Total cash and cash equivalents	66,326	100,965
Investment in subsidiaries	328,201	311,357
Other assets	13,499	7,993
Assets	408,026	420,315
Liabilities and Equity [Abstract]
Liability to ESOP	20,995	21,459
Accrued expenses	124	27
Stockholders' equity	386,907	398,829
Total liabilities and stockholders' equity	$ 408,026	$ 420,315

Condensed Financial Statemen103

Condensed Financial Statements of Parent Company (Condensed Statement of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Income Statements, Captions [Line Items]
Loss before income taxes and equity in undistributed net income of subsidiaries									$ 12,458	$ 10,064	$ (805)
Applicable income tax benefit	$ 1,323	$ 891	$ 721	$ 870	$ 587	$ 923	$ 689	$ 638	3,805	2,837	(622)
Net income (loss)	$ 3,998	$ 1,630	$ 1,358	$ 1,667	$ 2,412	$ 1,810	$ 1,699	$ 1,306	8,653	7,227	(183)
Parent Company
Condensed Income Statements, Captions [Line Items]
Loss before income taxes and equity in undistributed net income of subsidiaries									(2,478)	(1,860)	(9,432)
Applicable income tax benefit									(758)	(1,112)	(3,277)
Loss before equity in income of subsidiaries									(1,720)	(748)	(6,155)
Equity in undistributed net income of subsidiaries									10,373	7,975	5,972
Net income (loss)									$ 8,653	$ 7,227	$ (183)

Condensed Financial Statemen104

Condensed Financial Statements of Parent Company (Condensed Statement of Cash Flow) (Details) - USD ($) $ in Thousands	Jul. 21, 2014	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income (loss)		$ 3,998	$ 1,630	$ 1,358	$ 1,667	$ 2,412	$ 1,810	$ 1,699	$ 1,306	$ 8,653	$ 7,227	$ (183)
Charitable Foundation contribution										0	0	7,000
Excess tax benefit from deferred and stock based compensation										(105)	(166)	0
Net change in other assets										(3,477)	(1,153)	(7,033)
Net change in other liabilities										914	(8,495)	14,220
Net cash provided by operating activities										17,564	6,389	16,124
Cash flows from investing activities:
Net cash used in investing activities										(358,512)	(424,944)	(111,393)
Cash flows from financing activities:
Net proceeds from issuance of common stock	$ 277,700									0	0	274,143
Redemption of SBLF preferred stock										0	0	(18,724)
Excess tax benefit from deferred and stock based compensation										105	166	0
Repurchase of common stock										(24,432)	(13,121)	0
Share redemption for tax withholdings on deferred compensation obligation										0	(439)	0
Proceeds from exercise of stock options										40	0	0
Common and preferred stock dividends paid										0	0	(439)
Net cash provided by financing activities										338,146	391,707	115,099
Net change in cash and cash equivalents										(2,802)	(26,848)	19,830
Cash and cash equivalents at beginning of year					33,298				60,146	33,298	60,146	40,316
Cash and cash equivalents at end of year		30,496				33,298				30,496	33,298	60,146
Parent Company
Cash flows from operating activities:
Net income (loss)										8,653	7,227	(183)
Equity in undistributed net income of subsidiaries										(10,373)	(7,975)	(5,972)
Charitable Foundation contribution										0	0	6,943
Excess tax benefit from deferred and stock based compensation										(105)	(166)	0
Net change in other assets										11,625	(1,157)	(1,731)
Net change in other liabilities										97	(241)	267
Net cash provided by operating activities										9,897	(2,312)	(676)
Cash flows from investing activities:
Investment in Blue Hills Bank										(16,844)	(3,929)	(161,820)
Net cash used in investing activities										(16,844)	(3,929)	(161,820)
Cash flows from financing activities:
Net proceeds from issuance of common stock										0	0	274,143
Redemption of SBLF preferred stock										0	0	(18,724)
Repurchase of common stock										(24,432)	(13,121)
Share redemption for tax withholdings on deferred compensation obligation										(730)	(439)
Proceeds from exercise of stock options										40	0
Common and preferred stock dividends paid										(2,675)	(1,032)	(439)
Net cash provided by financing activities										(27,692)	(14,426)	254,980
Net change in cash and cash equivalents										(34,639)	(20,667)	92,484
Cash and cash equivalents at beginning of year					$ 100,965				$ 121,632	100,965	121,632	29,148
Cash and cash equivalents at end of year		$ 66,326				$ 100,965				$ 66,326	$ 100,965	$ 121,632

Selected Quarterly Financial105

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Interest and dividend income	$ 19,434	$ 17,685	$ 16,356	$ 16,063	$ 17,071	$ 15,418	$ 13,130	$ 12,682	$ 69,538	$ 58,301	$ 49,275
Interest expense	3,484	3,190	3,040	2,862	2,499	2,213	2,015	2,017	12,576	8,744	6,898
Net interest and dividend income	15,950	14,495	13,316	13,201	14,572	13,205	11,115	10,665	56,962	49,557	42,377
Provision for loan losses	927	2,872	1,113	(27)	1,949	1,318	544	279	4,885	4,090	3,381
Other noninterest income	3,509	3,834	2,147	1,621	2,179	1,456	2,210	866
Realized securities gains (losses), net	298	298	664	(244)	145	238	267	1,318
Total noninterest income	3,807	4,132	2,811	1,377	2,324	1,694	2,477	2,184	12,127	8,679	9,607
Total noninterest expense	13,509	13,234	12,935	12,068	11,948	10,848	10,660	10,626	51,746	44,082	49,408
Provision (benefit) for income taxes	1,323	891	721	870	587	923	689	638	3,805	2,837	(622)
Net income (loss)	$ 3,998	$ 1,630	$ 1,358	$ 1,667	$ 2,412	$ 1,810	$ 1,699	$ 1,306	$ 8,653	$ 7,227	$ (183)
Basic earnings per share (dollars per share)	$ 0.17	$ 0.07	$ 0.06	$ 0.07	$ 0.09	$ 0.07	$ 0.06	$ 0.05	$ 0.35	$ 0.28
Diluted earnings per share (dollars per share)	$ 0.17	$ 0.07	$ 0.05	$ 0.07	$ 0.09	$ 0.07	$ 0.06	$ 0.05	$ 0.35	$ 0.28
Weighted average common shares (basic) (shares)	23,919,483	24,129,512	24,575,211	25,066,086	25,500,755	26,183,381	26,293,560	26,274,738	24,420,405	26,064,947
Weighted average common shares (diluted) (shares)	24,032,613	24,307,540	24,699,794	25,132,441	25,554,961	26,183,381	26,293,560	26,274,738	24,540,929	26,069,589

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 17, 2017	Feb. 03, 2017	Feb. 28, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Subsequent Event [Line Items]
Gross unrealized losses				$ 2,517	$ 3,497
Net loss realized on sale of securities				(1,280)	(1,968)	$ (2,822)
Global asset allocation
Subsequent Event [Line Items]
Gross unrealized losses				$ 2,498	$ 3,484
Subsequent Event
Subsequent Event [Line Items]
Cash and stock held in escrow			$ 653
Subsequent Event | Global asset allocation
Subsequent Event [Line Items]
Proceeds from sale of securities	$ 42,400
Gross unrealized losses	1,100
Net loss realized on sale of securities	$ 1,100
Subsequent Event | NRS
Subsequent Event [Line Items]
Gain on investment conversion			$ 5,900
Subsequent Event | CBU | 1196 Corp. | NRS
Subsequent Event [Line Items]
Shares owned (in shares)		5,000
Cash received per share owned (in usd per share)		$ 319.04
Stock received per share owned (in shares)		14.876