Century Bancorp (CNBKA) 10-Q 7 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Registrant Name	CENTURY BANCORP, INC.
Entity Central Index Key	0000812348
Entity Filer Category	Accelerated Filer
Entity Tax Identification Number	04-2498617
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Trading Symbol	CNBKA
Entity Address, State or Province	MA
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	0-15752
Entity Incorporation, State or Country Code	MA
Entity Address, City or Town	MEDFORD
Entity Address, Address Line One	400 MYSTIC AVENUE
Entity Address, Postal Zip Code	02155
City Area Code	781
Local Phone Number	391-4000
Title of 12(b) Security	Class A Common Stock
Security Exchange Name	NASDAQ
Class A Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,658,569
Class B Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		1,909,340

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets
Cash and due from banks	$ 116,242	$ 136,735
Federal funds sold and interest-bearing deposits in other banks	500,521	237,265
Total cash and cash equivalents	616,763	374,000
Securities available-for-sale, amortized cost $263,089 and $282,273, respectively	263,898	282,448
Securities held-to-maturity, fair value $3,222,903 and $2,579,103, respectively	3,217,176	2,509,088
Federal Home Loan Bank of Boston, stock at cost	13,361	13,361
Equity securities, amortized cost $1,635 and $1,635, respectively	1,722	1,668
Loans, net:
Total loans, net	2,992,762	2,995,829
Less: allowance for loan losses	34,952	35,486
Net loans	2,957,810	2,960,343
Bank premises and equipment	39,750	39,062
Accrued interest receivable	13,981	13,283
Goodwill	2,714	2,714
Other assets	162,149	162,867
Total assets	7,289,324	6,358,834
Deposits:
Demand deposits	1,321,084	1,103,878
Savings and NOW deposits	2,269,617	1,728,092
Money market accounts	2,324,557	2,074,108
Time deposits	480,784	546,143
Total deposits	6,396,042	5,452,221
Securities sold under agreements to repurchase	228,755	232,090
Other borrowed funds	151,769	177,009
Subordinated debentures	36,083	36,083
Due to broker	1,310
Other liabilities	94,033	91,022
Total liabilities	6,907,992	5,988,425
Stockholders' Equity
Preferred Stock – $1.00 par value; 100,000 shares authorized; no shares issued and outstanding
Additional paid-in capital	12,292	12,292
Retained earnings	388,638	378,699
Stockholders' equity before adjustment of accumulated other comprehensive income (loss)	406,498	396,559
Unrealized gains on securities available-for-sale, net of taxes	594	130
Unrealized losses on securities transferred to held-to-maturity, net of taxes	(1,107)	(1,221)
Pension liability, net of taxes	(24,653)	(25,059)
Total accumulated other comprehensive loss, net of taxes	(25,166)	(26,150)
Total stockholders' equity	381,332	370,409
Total liabilities and stockholders' equity	7,289,324	6,358,834
Construction and land development [Member]
Loans, net:
Total loans, net	7,854	10,909
Commercial and industrial [Member]
Loans, net:
Total loans, net	1,315,295	1,314,245
Municipal [Member]
Loans, net:
Total loans, net	137,073	137,607
Commercial real estate [Member]
Loans, net:
Total loans, net	796,660	789,836
Residential real estate [Member]
Loans, net:
Total loans, net	460,123	448,436
Consumer and overdrafts [Member]
Loans, net:
Total loans, net	19,987	20,439
Home equity [Member]
Loans, net:
Total loans, net	255,770	274,357
Class A Common Stock [Member]
Stockholders' Equity
Common stock value	3,657	3,656
Total stockholders' equity	3,657	3,656
Class B Common Stock [Member]
Stockholders' Equity
Common stock value	1,911	1,912
Total stockholders' equity	$ 1,911	$ 1,912

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Amortized cost	$ 263,089	$ 282,273
Held-to-maturity securities, fair value	3,222,903	2,579,103
Equity securities, amortized cost	$ 1,635	$ 1,635
Preferred stock, par value	$ 1	$ 1
Preferred stock, shares authorized	100,000	100,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Class A Common Stock [Member]
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	3,656,469	3,655,469
Class B Common Stock [Member]
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	5,000,000	5,000,000
Common stock, shares issued	1,911,440	1,912,440

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest income
Loans	$ 21,605	$ 22,199
Securities held-to-maturity	13,117	15,293
Securities available-for-sale	630	1,693
Federal funds sold and interest-bearing deposits in other banks	179	610
Total interest income	35,531	39,795
Interest expense
Savings and NOW deposits	1,118	3,725
Money market accounts	2,886	5,572
Time deposits	1,581	3,172
Securities sold under agreements to repurchase	141	626
Other borrowed funds and subordinated debentures	1,238	1,499
Total interest expense	6,964	14,594
Net interest income	28,567	25,201
(Credit) provision for loan losses	(550)	1,075
Net interest income after (credit) provision for loan losses	29,117	24,126
Other operating income
Service charges on deposit accounts	2,218	2,296
Lockbox fees	996	930
Other income	989	1,084
Total other operating income	4,203	4,310
Operating expenses
Salaries and employee benefits	12,250	11,371
Occupancy	1,702	1,515
Equipment	949	837
Other	5,970	4,450
Total operating expenses	20,871	18,173
Income before income taxes	12,449	10,263
Provision for income taxes	1,679	597
Net income	$ 10,770	$ 9,666
Class A Common Stock [Member]
Share data:
Weighted average number of shares outstanding, basic	3,656,469	3,652,349
Weighted average number of shares outstanding, diluted	5,567,909	5,567,909
Basic earnings per share	$ 2.34	$ 2.10
Diluted earnings per share	$ 1.93	$ 1.74
Class B Common Stock [Member]
Share data:
Weighted average number of shares outstanding, basic	1,911,440	1,915,560
Weighted average number of shares outstanding, diluted	1,911,440	1,915,560
Basic earnings per share	$ 1.17	$ 1.05
Diluted earnings per share	$ 1.17	$ 1.05

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 10,770	$ 9,666
Unrealized gains (losses) on securities:
Unrealized gains (losses) arising during period	464	(1,531)
Total unrealized gains (losses) on securities	464	(1,531)
Accretion of net unrealized losses transferred	114	164
Defined benefit pension plans:
Amortization of prior service cost and loss included in net periodic benefit cost	406	360
Other comprehensive income (loss)	984	(1,007)
Comprehensive income	$ 11,754	$ 8,659

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Class A Common Stock [Member]	Class B Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member]Class A Common Stock [Member]	Retained Earnings [Member]Class B Common Stock [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning balance at Dec. 31, 2019	$ 332,581	$ 3,651	$ 1,917	$ 12,292	$ 338,980			$ (24,259)
Net income	9,666				9,666
Other comprehensive income, net of tax:
Unrealized holding gains (losses) arising during period, net of taxes	(1,531)							(1,531)
Accretion of unrealized losses on securities transferred to held-to-maturity, net of taxes	164							164
Pension liability adjustment, net of taxes	360							360
Conversion of Class B Common Stock to Class A Common Stock		1	(1)
Cash dividends		(438)	(115)			$ (438)	$ (115)
Ending balance at Mar. 31, 2020	340,687	3,652	1,916	12,292	348,093			(25,266)
Beginning balance at Dec. 31, 2020	370,409	3,656	1,912	12,292	378,699			(26,150)
Net income	10,770				10,770
Other comprehensive income, net of tax:
Unrealized holding gains (losses) arising during period, net of taxes	464							464
Accretion of unrealized losses on securities transferred to held-to-maturity, net of taxes	114							114
Pension liability adjustment, net of taxes	406							406
Conversion of Class B Common Stock to Class A Common Stock		1	(1)
Cash dividends		(658)	(173)			$ (658)	$ (173)
Ending balance at Mar. 31, 2021	$ 381,332	$ 3,657	$ 1,911	$ 12,292	$ 388,638			$ (25,166)

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Unrealized holding (losses) gains arising during period, taxes	$ 170	$ 548
Accretion of net unrealized losses on securities transferred during the period, taxes	41	58
Pension liability adjustment, taxes	$ 159	$ 141
Conversion of Class B Common Stock to Class A Common Stock, shares	1,000	1,400
Class A Common Stock [Member]
Cash dividends, per share	$ 0.18	$ 12
Class B Common Stock [Member]
Cash dividends, per share	$ 0.09	$ 6

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 10,770	$ 9,666
Adjustments to reconcile net income to net cash provided by operating activities:
Net (gain) loss on equity securities	(54)	79
(Credit) provision for loan losses	(550)	1,075
Deferred income taxes	(1,007)	(114)
Net depreciation and amortization (accretion)	528	(578)
(Increase) decrease in accrued interest receivable	(699)	112
Decrease in other assets	898	2,359
Increase (decrease) in other liabilities	5,325	(336)
Net cash provided by operating activities	15,211	12,263
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from redemptions of Federal Home Loan Bank of Boston stock		6,831
Purchase of Federal Home Loan Bank of Boston stock		(4,601)
Proceeds from calls/maturities of securities available-for-sale	25,993	20,734
Purchase of securities available-for-sale	(6,770)	(39,719)
Proceeds from calls/maturities of securities held-to-maturity	257,255	123,723
Purchase of securities held-to-maturity	(964,868)	(70,171)
Net decrease (increase) in loans	3,092	(72,621)
Bank owned life insurance purchases		(6,000)
Capital expenditures	(1,565)	(3,084)
Net cash used in investing activities	(686,863)	(44,908)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net (decrease) increase in time deposits	(65,359)	57,402
Net increase in demand, savings, money market and NOW deposits	1,009,180	104,999
Cash dividends	(831)	(553)
Net decrease in securities sold under agreements to repurchase	(3,335)	(46,050)
Net decrease in other borrowed funds	(25,240)	(58,835)
Net cash provided by financing activities	914,415	56,963
Net increase in cash and cash equivalents	242,763	24,318
Cash and cash equivalents at beginning of period	374,000	258,693
Cash and cash equivalents at end of period	616,763	283,011
Cash paid (received) during the period for:
Interest	7,127	14,711
Income taxes	1,075	300
Change in unrealized gains (losses) on securities available-for-sale, net of taxes	464	(1,531)
Change in unrealized losses on securities transferred to held-to-maturity, net of taxes	114	164
Pension liability adjustment, net of taxes	406	360
Change in due to broker	$ 1,310	$ 5,500

Basis of Financial Statement Pr

Basis of Financial Statement Presentation	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Financial Statement Presentation	Note 1. Basis of Financial Statement Presentation The consolidated financial statements include the accounts of Century Bancorp, Inc. (the “Company”) and its wholly owned subsidiary, Century Bank and Trust Company (the “Bank”). The consolidated financial statements also include the accounts of the Bank’s wholly owned subsidiaries, Century Subsidiary Investments, Inc. (“CSII”), Century Subsidiary Investments, Inc. II (“CSII II”), Century Subsidiary Investments, Inc. III (“CSII III”) and Century Financial Services Inc. (“CFSI”). CSII, CSII II, and CSII III are engaged in buying, selling and holding investment securities. CFSI has the power to engage in financial agency, securities brokerage, and investment and financial advisory services and related securities credit. The Company also owns 100% of Century Bancorp Capital Trust II (“CBCT II”). The entity is an unconsolidated subsidiary of the Company. All significant intercompany accounts and transactions have been eliminated in consolidation. The Company provides a full range of banking services to individual, business and municipal customers in Massachusetts, New Hampshire, Rhode Island, Connecticut, New York, Virginia, Washington D.C, and Pennsylvania. As a bank holding company, the Company is subject to the regulation and supervision of the Board of Governors of the Federal Reserve System (the “Federal Reserve Board”). The Bank, a state chartered financial institution, is subject to supervision and regulation by applicable state and federal banking agencies, including the Federal Reserve Board, the Federal Deposit Insurance Corporation (the “FDIC”) and the Massachusetts Commissioner of Banks. The Bank is also subject to various requirements and restrictions under federal and state law, including requirements to maintain reserves against deposits, restrictions on the types and amounts of loans that may be granted and the interest that may be charged thereon, and limitations on the types of investments that may be made and the types of services that may be offered. Various consumer laws and regulations also affect the operations of the Bank. In addition to the impact of regulation, commercial banks are affected significantly by the actions of the Federal Reserve Board as it attempts to control the money supply and credit availability in order to influence the economy. All aspects of the Company’s business are highly competitive. The Company faces aggressive competition from other lending institutions and from numerous other providers of financial services. The Company has one reportable operating segment. The financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America and general practices within the banking industry. In preparing the financial statements, 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 revenues and expenses for the period. Actual results could differ from those estimates. The Company’s Quarterly Report on Form 10-Q 10-K Material estimates that are susceptible to change in the near term relate to the allowance for loan losses. Management believes that the allowance for loan losses is adequate based on a review of factors, including historical charge-off COVID-19

Securities Available-for-Sale

Securities Available-for-Sale	3 Months Ended
	Mar. 31, 2021
Text Block [Abstract]
Securities Available-for-Sale	Note 2. Securities Available-for-Sale March 31, 2021 December 31, 2020 Amortized Gross Gross Fair Amortized Gross Gross Fair (in thousands) SBA Backed Securities $ 43,154 $ — $ 299 $ 42,855 $ 44,328 $ — $ 289 $ 44,039 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 165,846 1,097 132 166,811 177,239 819 317 177,741 Privately Issued Residential Mortgage-Backed Securities 321 5 — 326 330 2 4 328 Obligations Issued by States and Political Subdivisions 45,668 — — 45,668 52,276 — — 52,276 Other Debt Securities 8,100 178 40 8,238 8,100 24 60 8,064 Total $ 263,089 $ 1,280 $ 471 $ 263,898 $ 282,273 $ 845 $ 670 $ 282,448 Included in SBA Backed Securities, and U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities are securities at fair value pledged to secure public deposits and repurchase agreements amounting to $172,427,000 and $183,269,000 at March 31, 2021 and December 31, 2020, respectively. Also included in securities available-for-sale available-for-sale Debt securities of U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities primarily refer to debt securities of Fannie Mae and Freddie Mac. The following table shows the maturity distribution of the Company’s securities available-for-sale Amortized Fair (in thousands) Within one year $ 48,041 $ 48,047 After one but within five years 104,714 105,250 After five but within ten years 89,033 89,484 More than 10 years 21,301 21,117 Total $ 263,089 $ 263,898 The weighted average remaining life of investment securities available-for-sale As of March 31, 2021 and December 31, 2020, management concluded that the unrealized losses of its investment securities are temporary in nature since they are not related to the underlying credit quality of the issuers, and the Company does not intend to sell these debt securities and it is not more likely than not that it will be required to sell these debt securities before the anticipated recovery of its remaining amortized cost. In making its other-than-temporary impairment evaluation, the Company considered that the principal and interest on these securities are from issuers that are investment grade. The unrealized loss on SBA Backed Securities, U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities related primarily to interest rates and not credit quality, and because the Company has the ability and intent to hold these investments until recovery of fair value, which may be maturity, the Company does not consider these investments to be other-than-temporarily impaired at March 31, 2021 or December 31, 2020. In evaluating the underlying credit quality of a security, management considers several factors such as the credit rating of the obligor and the issuer, if applicable. Internal reviews of issuer financial statements are performed as deemed necessary. In the case of privately issued mortgage-backed securities, the performance of the underlying loans is analyzed as deemed necessary to determine the estimated future cash flows of the securities. Factors considered include the level of subordination, current and estimated future default rates, current and estimated prepayment rates, estimated loss severity rates, geographic concentrations and origination dates of underlying loans. The following table shows the temporarily impaired securities of the Company’s available-for-sale March 31, 2021 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) SBA Backed Securities $ — $ — $ 42,856 $ 299 $ 42,856 $ 299 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed 346 5 17,288 127 17,634 132 Privately Issued Residential Mortgage-Backed — — — — — — Obligations Issued by States and Political Subdivisions — — — — — — Other Debt Securities 2,461 39 1,299 1 3,760 40 Total temporarily impaired securities $ 2,807 $ 44 $ 61,443 $ 427 $ 64,250 $ 471 The following table shows the temporarily impaired securities of the Company’s available-for-sale December 31, 2020 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) SBA Backed Securities $ 13,839 $ 42 $ 30,200 $ 247 $ 44,039 $ 289 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed 18,188 50 33,617 267 51,805 317 Privately Issued Residential Mortgage-Backed Securities — — 210 4 210 4 Obligations Issued by States and Political Subdivisions — — — — — — Other Debt Securities 3,942 58 1,298 2 5,240 60 Total temporarily impaired securities $ 35,969 $ 150 $ 65,325 $ 520 $ 101,294 $ 670

Investment Securities Held-to-M

Investment Securities Held-to-Maturity	3 Months Ended
	Mar. 31, 2021
Text Block [Abstract]
Investment Securities Held-to-Maturity	Note 3. Investment Securities Held-to-Maturity March 31, 2021 December 31, 2020 Amortized Gross Gross Estimated Amortized Gross Gross Estimated Fair (in thousands) U.S. Government Sponsored Enterprises $ 381,077 $ 218 $ 9,017 $ 372,278 $ 244,220 $ 389 $ 866 $ 243,743 SBA Backed Securities 36,330 1,142 — 37,472 37,783 2,002 — 39,785 U.S. Government Sponsored Enterprises Mortgage- Backed 2,799,769 45,772 32,388 2,813,153 2,227,085 69,522 1,032 2,295,575 Total $ 3,217,176 $ 47,132 $ 41,405 $ 3,222,903 $ 2,509,088 $ 71,913 $ 1,898 $ 2,579,103 Included in total investment securities held-to-maturity held-to-maturity At March 31, 2021 and December 31, 2020, all mortgage-backed securities are obligations of U.S. Government Sponsored Enterprises. Debt securities of U.S. Government Sponsored Enterprises and U.S. Government Sponsored Enterprises Mortgage-Backed Securities primarily refer to debt securities of Fannie Mae and Freddie Mac. The following table shows the maturity distribution of the Company’s securities held-to-maturity Amortized Fair (in thousands) Within one year $ 84,709 $ 85,698 After one but within five years 1,707,454 1,738,266 After five but within ten years 1,425,013 1,398,939 More than ten years — — Total $ 3,217,176 $ 3,222,903 The weighted average remaining life of investment securities held-to-maturity As of March 31, 2021 and December 31, 2020, management concluded that the unrealized losses of its investment securities are temporary in nature since they are not related to the underlying credit quality of the issuers, and the Company does not intend to sell these debt securities and it is not more likely than not that it will be required to sell these debt securities before the anticipated recovery of their remaining amortized costs. In making its other-than-temporary impairment evaluation, the Company considered the fact that the principal and interest on these securities are from issuers that are investment grade. The unrealized loss on U.S. Government Sponsored Enterprises, SBA Backed Securities, and U.S. Government Sponsored Enterprises Mortgage-Backed Securities related primarily to interest rates and not credit quality, and because the Company does not intend to sell any of these securities and it is not more likely than not that it will be required to sell these securities before the anticipated recovery of the remaining amortized cost, the Company does not consider these investments to be other-than-temporarily impaired at March 31, 2021 or December 31, 2020. In evaluating the underlying credit quality of a security, management considers several factors such as the credit rating of the obligor and the issuer, if applicable. Internal reviews of issuer financial statements are performed as deemed necessary. The following table shows the temporarily impaired securities of the Company’s held-to-maturity March 31, 2021 Less Than 12 Months 12 Months or Longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) US Government Sponsored Enterprises $ 346,560 $ 9,017 $ — $ — $ 346,560 $ 9,017 SBA Backed Securities — — — — — — U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 1,332,059 32,388 — — 1,332,059 32,388 Total temporarily impaired securities $ 1,678,619 $ 41,405 $ — $ — $ 1,678,619 $ 41,405 The following table shows the temporarily impaired securities of the Company’s held-to-maturity December 31, 2020 Less Than 12 Months 12 Months or Longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Government Sponsored Enterprises $ 162,870 $ 866 $ — $ — $ 162,870 $ 866 SBA Backed Securities — — — — — — U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 302,401 1,032 — — 302,401 1,032 Total temporarily impaired securities $ 465,271 $ 1,898 $ — $ — $ 465,271 $ 1,898

Allowance for Loan Losses

Allowance for Loan Losses	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Allowance for Loan Losses	Note 4. Allowance for Loan Losses The Company maintains an allowance for loan losses in an amount determined by management on the basis of the character of the loans, loan performance, financial condition of borrowers, the value of collateral securing loans and other relevant factors. The following table summarizes the changes in the Company’s allowance for loan losses for the periods indicated. Three months ended 2021 2020 (in thousands) Allowance for loan losses, beginning of period $ 35,486 $ 29,585 Loans charged off (67 ) (62 ) Recoveries on loans previously charged-off 83 206 Net recoveries (charge-offs) 16 144 (Credit) provision charged to expense (550 ) 1,075 Allowance for loan losses, end of period $ 34,952 $ 30,804 Further information pertaining to the allowance for loan losses for the three months ending March 31, 2021 is as follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total (in thousands) Allowance for loan losses: Balance at December 31, 2020 $ 429 $ 16,713 $ 2,804 $ 11,751 $ 2,111 $ 241 $ 1,208 $ 229 $ 35,486 Charge-offs — — — — — (67 ) — — (67 ) Recoveries — 3 — — — 80 — — 83 (Credit) provision (136 ) (246 ) 33 (96 ) (44 ) (60 ) (159 ) 158 (550 ) Ending balance at $ 293 $ 16,470 $ 2,837 $ 11,655 $ 2,067 $ 194 $ 1,049 $ 387 $ 34,952 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 125 $ — $ 74 $ — $ — $ — $ — $ 199 Amount of allowance for loan losses for loans not deemed to be impaired $ 293 $ 16,345 $ 2,837 $ 11,581 $ 2,067 $ 194 $ 1,049 $ 387 $ 34,753 Loans: Ending balance $ 7,854 $ 1,315,295 $ 137,073 $ 796,660 $ 460,123 $ 19,987 $ 255,770 $ — $ 2,992,762 Loans deemed to be impaired $ — $ 357 $ — $ 2,300 $ — $ — $ — $ — $ 2,657 Loans not deemed to be impaired $ 7,854 $ 1,314,938 $ 137,073 $ 794,360 $ 460,123 $ 19,987 $ 255,770 $ — $ 2,990,105 Further information pertaining to the allowance for loan losses for the three months ending March 31, 2020 is as follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total (in thousands) Allowance for loan losses: Balance at December 31, 2019 $ 331 $ 11,596 $ 2,566 $ 11,464 $ 2,194 $ 312 $ 1,065 $ 57 $ 29,585 Charge-offs — (5 ) — — — (57 ) — — (62 ) Recoveries — 164 — — — 37 5 — 206 Provision (85 ) 673 323 (343 ) 255 4 67 181 1,075 Ending balance at $ 246 $ 12,428 $ 2,889 $ 11,121 $ 2,449 $ 296 $ 1,137 $ 238 $ 30,804 Amount of allowance for loan losses $ — $ — $ — $ 85 $ — $ — $ — $ — $ 85 Amount of allowance for loan losses $ 246 $ 12,428 $ 2,889 $ 11,036 $ 2,449 $ 296 $ 1,137 $ 238 $ 30,719 Loans: Ending balance $ 6,493 $ 867,599 $ 141,588 $ 761,464 $ 393,338 $ 21,039 $ 307,373 $ — $ 2,498,894 Loans deemed to be impaired $ — $ 623 $ — $ 2,322 $ — $ — $ — $ — $ 2,945 Loans not deemed to be impaired $ 6,493 $ 866,976 $ 141,588 $ 759,142 $ 393,338 $ 21,039 $ 307,373 $ — $ 2,495,949 There was a credit to the provision for losses of $550,000 for the quarter ended March 31, 2021, compared to a provision of $1,075,000 for the quarter ended March 31, 2020. The credit provision for the first quarter of 2021 was primarily attributable to a decline in loan balances exclusive of U.S. Small Business Administration (“SBA”) Payroll Protection Program (“PPP”) loans and a reduction in specific allocations to the allowance for loan losses. As of March 31, 2021, PPP loans totaled approximately 1,117 loans for approximately $213,000,000. These types of loans are categorized as commercial and industrial and are 100% guaranteed by the SBA and require no allowance for loan losses. The provision for the first quarter of 2020 was primarily the result of provisions related to the onset of the COVID-19 The Company utilizes a six grade internal loan rating system for commercial real estate, construction, commercial, and municipal loans as follows: Loans rated 1-3 Loans in this category are considered “pass” rated loans with low to average risk. Loans rated 4 (Monitor): These loans represent classified loans that management is closely monitoring for credit quality. These loans have had or may have minor credit quality deterioration as of March 31, 2021 and December 31, 2020. Loans rated 5 (Substandard): Substandard loans represent classified loans that management is closely monitoring for credit quality. These loans have had more significant credit quality deterioration as of March 31, 2021 and December 31, 2020. Loans rated 6 (Doubtful): Doubtful loans represent classified loans that management is closely monitoring for credit quality. These loans had more significant credit quality deterioration as of March 31, 2021 and December 31, 2020 and full collectability is doubtful. Impaired: Impaired loans represent classified loans that management is closely monitoring for credit quality. A loan is classified as impaired when it is probable that the Company will be unable to collect all amounts due. The following table presents the Company’s loans by risk rating at March 31, 2021. Construction and Commercial Municipal Commercial Grade: (in thousands) 1-3 $ 7,854 $ 1,310,993 $ 137,073 $ 770,872 4 (Monitor) — 3,945 — 23,488 5 (Substandard) — — — — 6 (Doubtful) — — — — Impaired — 357 — 2,300 Total $ 7,854 $ 1,315,295 $ 137,073 $ 796,660 The following table presents the Company’s loans by risk rating at December 31, 2020. Construction and Commercial Municipal Commercial Grade: (in thousands) 1-3 $ 10,909 $ 1,309,861 $ 137,607 $ 761,101 4 (Monitor) — 3,945 — 23,795 5 (Substandard) — — — — 6 (Doubtful) — — — — Impaired — 439 — 4,940 Total $ 10,909 $ 1,314,245 $ 137,607 $ 789,836 Credit ratings issued by national organizations were utilized as credit quality indicators as presented in the following table at March 31, 2021 and are included within the total loan portfolio. Commercial Municipal Commercial Total (in thousands) Credit Rating: Aaa – Aa3 $ 705,387 $ 73,758 $ 36,519 $ 815,664 A1 – A3 182,559 7,103 145,096 334,758 Baa1 – Baa3 50,000 51,132 146,930 248,062 Ba2 — 5,080 — 5,080 Total $ 937,946 $ 137,073 $ 328,545 $ 1,403,564 Credit ratings issued by national organizations were utilized as credit quality indicators as presented in the following table at December 31, 2020. Commercial Municipal Commercial Total (in thousands) Credit Rating: Aaa – Aa3 $ 710,955 $ 74,291 $ 38,035 $ 823,281 A1 – A3 183,123 7,103 145,583 335,809 Baa1 – Baa3 50,000 51,133 140,905 242,038 Ba2 — 5,080 — 5,080 Total $ 944,078 $ 137,607 $ 324,523 $ 1,406,208 The Company utilized payment performance as credit quality indicators for the loan types listed below. Further information pertaining to the allowance for loan losses at March 31, 2021 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 7,854 $ 7,854 Commercial and industrial — 297 — 297 1,314,998 1,315,295 Municipal — — — — 137,073 137,073 Commercial real estate — 261 — 261 796,399 796,660 Residential real estate 1,373 188 — 1,561 458,562 460,123 Consumer and overdrafts 12 7 — 19 19,968 19,987 Home equity 1,325 189 — 1,514 254,256 255,770 Total $ 2,710 $ 942 $ — $ 3,652 $ 2,989,110 $ 2,992,762 Further information pertaining to the allowance for loan losses at December 31, 2020 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 10,909 $ 10,909 Commercial and industrial 56 297 90 443 1,313,802 1,314,245 Municipal — — — — 137,607 137,607 Commercial real estate — 2,881 — 2,881 786,955 789,836 Residential real estate 390 527 — 917 447,519 448,436 Consumer and overdrafts 21 1 — 22 20,417 20,439 Home equity 1,001 290 — 1,291 273,066 274,357 Total $ 1,468 $ 3,996 $ 90 $ 5,554 $ 2,990,275 $ 2,995,829 Impaired loans A loan is impaired when, based on current information and events, it is probable that a creditor will be unable to collect all amounts due according to the contractual terms of the loan agreement. When a loan is impaired, the Company measures impairment based on the present value of expected future cash flows discounted at the loan’s effective interest rate, except that as a practical expedient, the Company measures impairment based on a loan’s observable market price or the fair value of the collateral if the loan is collateral dependent. Loans are charged-off charged-off The following is information pertaining to impaired loans for March 31, 2021: Carrying Unpaid Required Average Value Months Interest Income Months (in thousands) With no required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 4 5 — 7 — Municipal — — — — — Commercial real estate 261 296 — 267 — Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 265 $ 301 $ — $ 274 $ — With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 353 373 125 374 1 Municipal — — — — — Commercial real estate 2,039 2,169 74 3,354 20 Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 2,392 $ 2,542 $ 199 $ 3,728 $ 21 Total: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 357 378 125 381 1 Municipal — — — — — Commercial real estate 2,300 2,465 74 3,621 20 Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 2,657 $ 2,843 $ 199 $ 4,002 $ 21 The following is information pertaining to impaired loans for March 31, 2020: Carrying Unpaid Required Average Value Months Interest Income Months (in thousands) With no required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 623 641 — 582 1 Municipal — — — — — Commercial real estate 155 185 — 157 — Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 778 $ 826 $ — $ 739 $ 1 With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial — — — 113 1 Municipal — — — — — Commercial real estate 2,167 2,290 85 2,176 22 Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 2,167 $ 2,290 $ 85 $ 2,289 $ 23 Total: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 623 641 — 695 2 Municipal — — — — — Commercial real estate 2,322 2,475 85 2,333 22 Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 2,945 $ 3,116 $ 85 $ 3,028 $ 24 Troubled debt restructurings (“TDR”) are identified as modifications in which a concession was granted to a customer who was having financial difficulties. This concession may be below market rate, longer amortization/term, or a lower payment amount. The present value calculation of the modifications did not result in an increase in the allowance for these loans beyond any previously established allocations. There was no TDR made during the three-month period ended March 31, 2021. Also, there were no commitments to lend additional funds to TDR borrowers. There were no TDRs that subsequently defaulted during the first three months of 2021. Under Section 4013 of the CARES Act, loans less than 30 days past due as of December 31, 2019 will be considered current for COVID-19 COVID-19 COVID-19 As of March 31, 2021, and as a result of COVID-19 There was no TDR made during the three-month period ended March 31, 2020. Also, there were no commitments to lend additional funds to TDR borrowers. There were no TDRs that subsequently defaulted during the first three months of 2020.

Reclassifications Out of Accumu

Reclassifications Out of Accumulated Other Comprehensive Income	3 Months Ended
	Mar. 31, 2021
Text Block [Abstract]
Reclassifications Out of Accumulated Other Comprehensive Income	Note 5. Reclassifications Out of Accumulated Other Comprehensive Income Amount Reclassified from Accumulated Other Comprehensive Income Details about Accumulated Other Comprehensive Income Components Three Three Affected Line Item in the Statement (in thousands) Accretion of unrealized losses transferred $ (155 ) $ (222 ) Interest on securities held-to-maturity 41 58 Provision for income taxes $ (114 ) $ (164 ) Net income Amortization of defined benefit pension items Prior-service costs $ (54 ) $ (29 )(b) Salaries and employee benefits Actuarial gains (losses) (511 ) (472 )(b) Salaries and employee benefits Total before tax (565 ) (501 ) Income before taxes Tax (expense) or benefit 159 141 Provision for income taxes Net of tax $ (406 ) $ (360 ) Net income (a) Amount in parentheses indicates reductions to net income. (b) These accumulated other comprehensive income components are included in the computation of net periodic pension cost(see Employee Benefits footnote (Note 7) for additional details).

Earnings Per Share ("EPS")

Earnings Per Share ("EPS")	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings Per Share ("EPS")	Note 6. Earnings per Share (“EPS”) Class A and Class B shares participate equally in undistributed earnings. Under the Company’s Articles of Organization, the holders of Class A Common Stock are entitled to receive dividends per share equal to at least 200% of dividends paid, if any, from time to time, on each share of Class B Common Stock. Diluted EPS includes the dilutive effect of common stock equivalents and assumes the conversion of all Class B common stock; basic EPS excludes all common stock equivalents. The Company had no common stock equivalents outstanding for the periods ended March 31, 2021 and 2020. The following table is a reconciliation of basic EPS and diluted EPS. Three Months Ended (in thousands except share and per share data) 2021 2020 Basic EPS Computation: Numerator: Net income, Class A $ 8,538 $ 7,658 Net income, Class B 2,232 2,008 Denominator: Weighted average shares outstanding, Class A 3,656,469 3,652,349 Weighted average shares outstanding, Class B 1,911,440 1,915,560 Basic EPS, Class A $ 2.34 $ 2.10 Basic EPS, Class B 1.17 1.05 Diluted EPS Computation: Numerator: Net income, Class A $ 8,538 $ 7,658 Net income, Class B 2,232 2,008 Total net income, for diluted EPS, Class A computation 10,770 9,666 Denominator: Weighted average shares outstanding, basic, Class A 3,656,469 3,652,349 Weighted average shares outstanding, Class B 1,911,440 1,915,560 Weighted average shares outstanding diluted, Class A 5,567,909 5,567,909 Weighted average shares outstanding, Class B 1,911,440 1,915,560 Diluted EPS, Class A $ 1.93 $ 1.74 Diluted EPS, Class B 1.17 1.05

Employee Benefits

Employee Benefits	3 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Employee Benefits	Note 7. Employee Benefits The Company provides pension benefits to its employees under a noncontributory, defined benefit plan which is funded on a current basis in compliance with the requirements of the Employee Retirement Income Security Act of 1974 (“ERISA”) and recognizes costs over the estimated employee service period. The Company also has the Century Bancorp, Inc. Supplemental Executive Retirement and Insurance Plan (the “Supplemental Plan”) which is limited to certain officers and employees of the Company. The Supplemental Plan is accrued on a current basis and recognizes costs over the estimated employee service period. Executive officers of the Company and its subsidiaries who have at least one year of service may participate in the Supplemental Plan. The Supplemental Plan is voluntary, and participants are required to contribute to its cost. Life insurance policies, which are owned by the Company, are purchased covering the lives of each participant. Components of Net Periodic Benefit Cost for the Three Months Ended March 31, Pension Benefits Supplemental Insurance/ 2021 2020 2021 2020 (in thousands) Service cos t $ 379 $ 344 $ 363 $ 353 Interest 434 450 434 466 Expected return on plan assets (1,062 ) (952 ) — — Recognized prior service cost (benefit) — — 54 29 Recognized net actuarial losses 241 261 269 211 Net periodic benefit (credit) cost $ (8 ) $ 103 $ 1,120 $ 1,059 Approximately $371,000 and $465,000 of costs other than service costs, from the table above, are included in other expenses with the remaining cost included in salaries and employee benefits, for the three months ended March 31, 2021 and 2020, respectively. Contributions The Company has contributed $1,302,000 to the Defined Benefit Pension Plan in 2021.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 8. Fair Value Measurements The Company follows FASB ASC 820-10, 2016-1, (Subtopic 825-10) Recognition and Measurement of Financial Assets and Financial Liabilities 820-10 Level I – Quoted prices are available in active markets for identical assets or liabilities as of the reported date. The type of financial instruments included in Level I are highly liquid cash instruments with quoted prices such as G-7 Level II – Pricing inputs are other than quoted prices in active markets, which are either directly or indirectly observable as of the reported date. The nature of these financial instruments include cash instruments for which quoted prices are available but traded less frequently, derivative instruments whose fair value have been derived using a model where inputs to the model are directly observable in the market or can be derived principally from or corroborated by observable market data, and instruments that are fair valued using other financial instruments, the parameters of which can be directly observed. Instruments which are generally included in this category are corporate bonds and loans, mortgage whole loans, municipal bonds, and OTC derivatives. Level III – Instruments that have little to no pricing observability as of the reported date. These financial instruments do not have two-way The results of the fair value hierarchy as of March 31, 2021, are as follows: Securities AFS Fair Value Measurements Using Carrying Quoted Prices Significant Significant (in thousands) SBA Backed Securities $ 42,855 $ — $ 42,855 $ — U.S. Government Agency and Sponsored Mortgage-Backed Securities 166,811 — 166,811 — Privately Issued Residential Mortgage- Backed 326 — 326 — Obligations Issued by States and Political Subdivisions 45,668 — — 45,668 Other Debt Securities 8,238 — 8,238 — Total $ 263,898 $ — $ 218,230 $ 45,668 Equity Securities $ 1,722 $ 376 $ 1,346 $ — Financial Instruments Measured at Fair Value on a Non-recurring Basis Impaired Loans $ 558 $ — $ — $ 558 The results of the fair value hierarchy as of December 31, 2020, are as follows: Securities AFS Fair Value Measurements Using Carrying Quoted Prices Assets Significant Significant (in thousands) Financial Instruments Measured at Fair Value on a Recurring Basis SBA Backed Securities $ 44,039 $ — $ 44,039 $ — U.S. Government Agency and Sponsored Mortgage-Backed Securities 177,741 — 177,741 — Privately Issued Residential Mortgage- 328 — 328 — Obligations Issued by States and Political Subdivisions 52,276 — — 52,276 Other Debt Securities 8,064 — 8,064 — Total $ 282,448 $ — $ 230,172 $ 52,276 Equity Securities $ 1,668 $ 303 $ 1,365 $ — Financial Instruments Measured at Fair Value on a Non-recurring Basis Impaired Loans $ 3,178 $ — $ — $ 3,178 Impaired loan balances represent those collateral dependent loans where management has estimated the credit loss by comparing the loan’s carrying value against the expected realizable fair value of the collateral. Fair value is generally determined through a review process that includes independent appraisals, discounted cash flows, or other external assessments of the underlying collateral, which generally include various Level 3 inputs which are not observable. The Company discounts the fair values, as appropriate, based on management’s observations of the local real estate market for loans in this category. Appraisals, discounted cash flows and real estate tax assessments are reviewed quarterly. There is no specific policy regarding how frequently appraisals will be updated. Adjustments are made to appraisals and real estate tax assessments based on management’s estimate of changes in real estate values. All impaired loans have been reviewed during the past quarter using either a discounted cash flow analysis, appraisal of collateral or other type of real estate tax assessment. The types of adjustments that are made to specific provisions (credits) related to impaired loans recognized for the three-month period ended March 31, 2021 amounted to ($375,000) and amounted to $501,000 for the year ended December 31, 2020. There were no transfers between level 1, 2 and 3 for the three months ended March 31, 2021 and the year ended December 31, 2020. There were no liabilities measured at fair value on a recurring or nonrecurring basis during the three months ended March 31, 2021 and the year ended December 31, 2021. The following table presents additional information about assets measured at fair value on a recurring and nonrecurring basis for which the Company has utilized Level 3 inputs to determine fair value (dollars in thousands) at March 31, 2021. Management continues to monitor the assumptions used to value the assets listed below. Asset Fair Value Valuation Technique Unobservable Input Unobservable Input Securities AFS (1) $ 45,668 Discounted cash flow Discount rate 0% - 1.0% (2) Impaired Loans $ 558 Appraisal of collateral (3) Appraisal adjustments (4) 0%—22% discount The following table presents additional information about assets measured at fair value on a recurring and nonrecurring basis for which the Company has utilized Level 3 inputs to determine fair value (dollars in thousands) at December 31, 2020. Management continues to monitor the assumptions used to value the assets listed below. Asset Fair Value Valuation Technique Unobservable Input Unobservable Input Securities AFS (1) $ 52,276 Discounted cash flow Discount rate 0% - 1.0% (2) Impaired Loans $ 3,178 Appraisal of collateral (3) Appraisal adjustments (4) 0%-17% discount (1) Municipal securities generally have maturities of one year or less and, therefore, the amortized cost equates to the fair value. (2) Weighted averages. (3) Fair value is generally determined through independent appraisals of the underlying collateral, which generally include various Level 3 inputs which are not identifiable. (4) Appraisals may be adjusted by management for qualitative factors such as economic conditions and estimated expenses. The changes in Level 3 securities for the three-month period ended March 31, 2021 are shown in the table below: Obligations Issued by States & Balance at December 31, 2020 $ 52,276 Purchases 6,770 Maturities and calls (13,353 ) Amortization (25 ) Balance at March 31, 2021 $ 45,668 The amortized cost of Level 3 securities was $45,668,000 at March 31, 2021 with an unrealized loss of $0. The securities in this category are generally municipal securities with no readily determinable fair value. Management evaluated the fair value of these securities based on an evaluation of the underlying issuer, prevailing rates and market liquidity. The changes in Level 3 securities for the three-month period ended March 31, 2020 are shown in the table below: Obligations Issued by States & Subdivisions Balance at December 31, 2019 $ 13,301 Purchases 9,372 Maturities and calls (5,449 ) Amortization — Changes in fair value — Balance at March 31, 2020 $ 17,224 The amortized cost of Level 3 securities was $17,224,000 at March 31, 2020 with an unrealized loss of $0. The securities in this category are generally municipal securities with no readily determinable fair value. Management evaluated the fair value of these securities based on an evaluation of the underlying issuer, prevailing rates and market liquidity. The fair value of impaired loans decreased by $2,624,000, for the first three months of 2021, mainly attributable to one loan that was paid down. The fair value of impaired loans decreased by $269,000, for the first three months of 2020, mainly attributable to one loan that was paid down. There were no liabilities measured at fair value on a recurring or nonrecurring basis during the three-month period ended March 31, 2020.

Fair Values of Financial Instru

Fair Values of Financial Instruments	3 Months Ended
	Mar. 31, 2021
Investments, All Other Investments [Abstract]
Fair Values of Financial Instruments	Note 9. Fair Values of Financial Instruments The following methods and assumptions were used by the Company in estimating fair values of its financial instruments. Excluded from this disclosure are all non-financial The assumptions used below are expected to approximate those that market participants would use in valuing these financial instruments. Fair value estimates are made at a specific point in time, based on available market information and judgments about the financial instrument, including estimates of timing, amount of expected future cash flows and the credit standing of the issuer. Such estimates do not consider the tax impact of the realization of unrealized gains or losses. In some cases, the fair value estimates cannot be substantiated by comparison to independent markets. In addition, the disclosed fair value may not be realized in the immediate settlement of the financial instrument. Care should be exercised in deriving conclusions about our business, its value or financial position based on the fair value information of financial instruments presented below. Securities Held-to-Maturity The fair values of these securities were based on quoted market prices, where available, as provided by third-party investment portfolio pricing vendors. If quoted market prices were not available, fair values provided by the vendors were based on quoted market prices of comparable instruments in active markets and/or based on a matrix pricing methodology which employs The Bond Market Association’s standard calculations for cash flow and price/yield analysis, live benchmark bond pricing and terms/condition data available from major pricing sources. Management regards the inputs and methods used by third party pricing vendors to be “Level 2 inputs and methods” as defined in the “fair value hierarchy” provided by FASB. Loans The fair value of loans is estimated using the exit price notion consistent with Topic 820, Fair Value Measurement. Fair value is determined based on a discounted cash flow analysis. The discounted cash flow analysis was based on the contractual maturity of the loan and market indications of rates, prepayment speeds, defaults and credit risk. For certain non-performing Time Deposits The fair value of time deposits was estimated using a discounted cash flow approach that applies prevailing market interest rates for similar maturity instruments. The fair values of the Company’s time deposit liabilities do not take into consideration the value of the Company’s long-term relationships with depositors, which may have significant value. Other Borrowed Funds The fair value of other borrowed funds is based on the discounted value of contractual cash flows. The discount rate used is estimated based on the rates currently offered for other borrowed funds of similar remaining maturities. Subordinated Debentures The fair value of subordinated debentures is based on the discounted value of contractual cash flows. The discount rate used is estimated based on the rates currently offered for other subordinated debentures of similar remaining maturities. The following presents (in thousands) the carrying amount, estimated fair value, and placement in the fair value hierarchy of the Company’s financial instruments as of March 31, 2021 and December 31, 2020. This table excludes financial instruments for which the carrying amount approximates fair value. Financial assets for which the fair value approximates carrying value include cash and cash equivalents, short-term investments, FHLBB stock and accrued interest receivable. Financial liabilities for which the fair value approximates carrying value include non-maturity March 31, 2021 Carrying Estimated Fair Value Level 2 Level 3 (in thousands) Financial assets: Securities held-to-maturity $ 3,217,176 $ 3,222,903 $ — $ 3,222,903 $ — Loans (1) 2,957,810 2,877,220 — — 2,877,220 Financial liabilities: Time deposits 480,784 479,087 — 479,087 — Other borrowed funds 151,769 155,001 — 155,001 — Subordinated debentures 36,083 36,083 — 36,083 — December 31, 2020 Financial assets: Securities held-to-maturity $ 2,509,088 $ 2,579,103 $ — $ 2,579,103 $ — Loans (1) 2,960,343 2,902,390 — — 2,902,390 Financial liabilities: Time deposits 546,143 556,470 — 556,470 — Other borrowed funds 177,009 183,000 — 183,000 — Subordinated debentures 36,083 36,083 — 36,083 — (1) Comprised of loans (including collateral dependent impaired loans), net of deferred loan costs and the allowance for loanlosses. Limitations Fair value estimates are made at a specific point in time, based on relevant market information and information about the type of financial instrument. These estimates do not reflect any premium or discount that could result from offering for sale at one time the Bank’s entire holdings of a particular financial instrument. Because no active market exists for some of the Bank’s financial instruments, fair value estimates are based on judgments regarding future expected loss experience, cash flows, current economic conditions, risk characteristics and other factors. These estimates are subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. Changes in assumptions and changes in the loan, debt and interest rate markets could significantly affect the estimates. Further, the income tax ramifications related to the realization of the unrealized gains and losses can have a significant effect on the fair value estimates and have not been considered.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Note 10. Revenue from Contracts with Customers Revenue from contracts with customers in the scope of ASC Topic 606 is measured based on the consideration specified in the contract with a customer, and excludes amounts collected on behalf of third parties. The Company recognizes revenue from contracts with customers when it satisfies its performance obligations. The Company’s performance obligations are typically satisfied as services are rendered, and our contracts do not include multiple performance obligations. Payment is generally collected at the time services are rendered, or monthly. Unsatisfied performance obligations at the report date are not material to our consolidated financial statements. The Company pays sales commissions to its employees in accordance with certain incentive plans. The Company expenses sales commissions when incurred if we do not expect to recover these costs from the terms of the contract with the customer. Sales commissions are included in compensation expense. In certain cases, other parties are involved with providing products and services to our customers. If the Company is a principal in the transaction (providing goods or services itself), revenues are reported based on the gross consideration received from the customer and any related expenses are reported gross in noninterest expense. If the Company is an agent in the transaction (arranging for another party to provide goods or services), the Company reports its net fee or commission retained as revenue. Waivers and reversals are recorded as a reduction of revenue either when the revenue is recognized by the Company or at the time the waiver or reversal is earned by the customer. A. Nature of goods and services The vast majority of the Company’s revenue is specifically out-of-scope in-scope, a. Revenue earned at a point in time – Examples of revenue earned at a point in time are ATM transaction fees, wire transfer fees, “non-sufficient b. Revenue earned over time – The Company earns revenue from contracts with customers in a variety of ways in which the revenue is earned over a period of time – generally monthly or quarterly. Examples of this type of revenue are deposit account service fees, lockbox fees, investment management fees, merchant referral services, and safe deposit box fees. Account service charges, management fees and referral fees are recognized on a monthly basis while any transaction based income is recorded as the activity occurs. Revenue is primarily based on the number and type of transactions or assets managed and is generally derived from transactional information accumulated by our systems. Revenue is recorded in the same period as the related transactions occur or services are rendered to the customer. B. Disaggregation of revenue The following table presents total revenues as presented in the Consolidated Statements of Income and the related amounts which are from contracts with customers within the scope of Topic 606. As illustrated here, the vast majority of our revenues are specifically excluded from the scope of Topic 606. Three Months Revenue from Three Months Revenue from (dollars in thousands) Total net interest income $ 28,567 $ — $ 25,201 $ — Noninterest income: Service charges on deposit accounts 2,218 2,218 2,296 2,296 Lockbox fees 996 996 930 930 Other income 989 695 1,084 599 Total noninterest income 4,203 3,909 4,310 3,825 Total net revenues $ 32,770 $ 3,909 $ 29,511 $ 3,825 The following table provides information about receivables with customers. (dollars in thousands) March 31, 2021 December 31, 2020 Receivables, which are included in “Other assets” $ 1,393 $ 1,397

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	Note 11. Leases The Company has operating leases primarily for branch locations as well as data processing centers. The Company’s operating leases have remaining lease terms of 1 year to 31 years, some of which include options to extend the leases for up to 10 years, and some of which include options to terminate the leases within 1 year. The Company also has one sublease for part of a data processing center that the Company currently leases from a lessor. The sublease expires in 2022 with an option to terminate and no option to extend. Lease income, for the sublease, totaled approximately $10,000 for the three months ended March 31, 2021. Variable lease costs include costs that are not included in the lease liability. The components of lease expense were as follows: (in thousands) Three Months Three Months Operating lease cost $ 560 $ 546 Variable lease cost 153 133 Total lease cost $ 713 $ 679 Supplemental cash flow information related to leases was as follows: (in thousands) (in Three Months Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 541 $ 529 Right-of-use Operating leases $ — $ — Supplemental balance sheet information related to leases was as follows: 3/31/2021 12/31/2020 (in thousands, except lease term and discount rate) Operating Leases: Operating lease right-of-use $ 13,262 $ 13,713 Operating lease liabilities $ 13,496 $ 13,935 Weighted Average Remaining Lease Term: Operating Leases 10 Years 10 Years Weighted Average Discount Rate: Operating Leases 3.1 % 3.1 % The Company has payment obligations under a number of non-cancelable A summary of future minimum rental payments under such leases as the dates indicated follows: Minimum Rental Payments March 31, 2021 December 31, 2020 Year Ending December 31, (in thousands) 2021 $ 1,612 $ 2,156 2022 1,995 1,995 2023 1,962 1,962 2024 1,692 1,692 2025 1,471 1,471 Thereafter 7,394 7,394 Total lease payments $ 16,126 $ 16,670 Less imputed interest (2,630 ) (2,735 ) Present value of lease liability $ 13,496 $ 13,935 March 31, 2021 minimum rental payments represent nine months of rental payments remaining in calendar year 2021.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	Note 12. Subsequent Events Proposed Transaction with Eastern Bankshares, Inc. On April 7, 2021, the Company and Eastern Bankshares, Inc. (“Eastern” ) (NASDAQ: EBC) entered into an Agreement and Plan of Merger pursuant to which, through a series of transactions, Eastern will acquire the Company in a cash transaction for total consideration valued at approximately $642 million. Under the terms of the Agreement and Plan of Merger, (i) each holder of Class A common stock will receive a cash payment of $115.28 per share of Class A common stock and (ii) each holder of Class B common stock will receive a cash payment of $115.28 per share of Class B common stock. The transaction is expected to close in the fourth quarter of 2021 and is subject to customary closing conditions, including approval by the shareholders of the Company and required regulatory approvals.

Securities Available-for-Sale (

Securities Available-for-Sale (Tables)	3 Months Ended
	Mar. 31, 2021
Text Block [Abstract]
Summary of Securities Available-for-Sale	March 31, 2021 December 31, 2020 Amortized Gross Gross Fair Amortized Gross Gross Fair (in thousands) SBA Backed Securities $ 43,154 $ — $ 299 $ 42,855 $ 44,328 $ — $ 289 $ 44,039 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 165,846 1,097 132 166,811 177,239 819 317 177,741 Privately Issued Residential Mortgage-Backed Securities 321 5 — 326 330 2 4 328 Obligations Issued by States and Political Subdivisions 45,668 — — 45,668 52,276 — — 52,276 Other Debt Securities 8,100 178 40 8,238 8,100 24 60 8,064 Total $ 263,089 $ 1,280 $ 471 $ 263,898 $ 282,273 $ 845 $ 670 $ 282,448
Estimated Maturity Distribution of Securities Available-for-Sale	The following table shows the maturity distribution of the Company’s securities available-for-sale Amortized Fair (in thousands) Within one year $ 48,041 $ 48,047 After one but within five years 104,714 105,250 After five but within ten years 89,033 89,484 More than 10 years 21,301 21,117 Total $ 263,089 $ 263,898
Continuous Unrealized Loss Position for 12 Months or Less and 12 Months and Longer	The following table shows the temporarily impaired securities of the Company’s available-for-sale March 31, 2021 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) SBA Backed Securities $ — $ — $ 42,856 $ 299 $ 42,856 $ 299 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed 346 5 17,288 127 17,634 132 Privately Issued Residential Mortgage-Backed — — — — — — Obligations Issued by States and Political Subdivisions — — — — — — Other Debt Securities 2,461 39 1,299 1 3,760 40 Total temporarily impaired securities $ 2,807 $ 44 $ 61,443 $ 427 $ 64,250 $ 471 The following table shows the temporarily impaired securities of the Company’s available-for-sale December 31, 2020 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) SBA Backed Securities $ 13,839 $ 42 $ 30,200 $ 247 $ 44,039 $ 289 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed 18,188 50 33,617 267 51,805 317 Privately Issued Residential Mortgage-Backed Securities — — 210 4 210 4 Obligations Issued by States and Political Subdivisions — — — — — — Other Debt Securities 3,942 58 1,298 2 5,240 60 Total temporarily impaired securities $ 35,969 $ 150 $ 65,325 $ 520 $ 101,294 $ 670

Investment Securities Held-to_2

Investment Securities Held-to-Maturity (Tables)	3 Months Ended
	Mar. 31, 2021
Text Block [Abstract]
Summary of Held-to-Maturity Securities	March 31, 2021 December 31, 2020 Amortized Gross Gross Estimated Amortized Gross Gross Estimated Fair (in thousands) U.S. Government Sponsored Enterprises $ 381,077 $ 218 $ 9,017 $ 372,278 $ 244,220 $ 389 $ 866 $ 243,743 SBA Backed Securities 36,330 1,142 — 37,472 37,783 2,002 — 39,785 U.S. Government Sponsored Enterprises Mortgage- Backed 2,799,769 45,772 32,388 2,813,153 2,227,085 69,522 1,032 2,295,575 Total $ 3,217,176 $ 47,132 $ 41,405 $ 3,222,903 $ 2,509,088 $ 71,913 $ 1,898 $ 2,579,103
Company's Securities Held-to-Maturity	The following table shows the maturity distribution of the Company’s securities held-to-maturity Amortized Fair (in thousands) Within one year $ 84,709 $ 85,698 After one but within five years 1,707,454 1,738,266 After five but within ten years 1,425,013 1,398,939 More than ten years — — Total $ 3,217,176 $ 3,222,903
Unrealized Market Loss of Securities	The following table shows the temporarily impaired securities of the Company’s held-to-maturity March 31, 2021 Less Than 12 Months 12 Months or Longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) US Government Sponsored Enterprises $ 346,560 $ 9,017 $ — $ — $ 346,560 $ 9,017 SBA Backed Securities — — — — — — U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 1,332,059 32,388 — — 1,332,059 32,388 Total temporarily impaired securities $ 1,678,619 $ 41,405 $ — $ — $ 1,678,619 $ 41,405 The following table shows the temporarily impaired securities of the Company’s held-to-maturity December 31, 2020 Less Than 12 Months 12 Months or Longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Government Sponsored Enterprises $ 162,870 $ 866 $ — $ — $ 162,870 $ 866 SBA Backed Securities — — — — — — U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 302,401 1,032 — — 302,401 1,032 Total temporarily impaired securities $ 465,271 $ 1,898 $ — $ — $ 465,271 $ 1,898

Allowance for Loan Losses (Tabl

Allowance for Loan Losses (Tables)	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Analysis of the allowance for loan losses	The following table summarizes the changes in the Company’s allowance for loan losses for the periods indicated. Three months ended 2021 2020 (in thousands) Allowance for loan losses, beginning of period $ 35,486 $ 29,585 Loans charged off (67 ) (62 ) Recoveries on loans previously charged-off 83 206 Net recoveries (charge-offs) 16 144 (Credit) provision charged to expense (550 ) 1,075 Allowance for loan losses, end of period $ 34,952 $ 30,804
Summary of Allowance for Loan Losses	Further information pertaining to the allowance for loan losses for the three months ending March 31, 2021 is as follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total (in thousands) Allowance for loan losses: Balance at December 31, 2020 $ 429 $ 16,713 $ 2,804 $ 11,751 $ 2,111 $ 241 $ 1,208 $ 229 $ 35,486 Charge-offs — — — — — (67 ) — — (67 ) Recoveries — 3 — — — 80 — — 83 (Credit) provision (136 ) (246 ) 33 (96 ) (44 ) (60 ) (159 ) 158 (550 ) Ending balance at $ 293 $ 16,470 $ 2,837 $ 11,655 $ 2,067 $ 194 $ 1,049 $ 387 $ 34,952 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 125 $ — $ 74 $ — $ — $ — $ — $ 199 Amount of allowance for loan losses for loans not deemed to be impaired $ 293 $ 16,345 $ 2,837 $ 11,581 $ 2,067 $ 194 $ 1,049 $ 387 $ 34,753 Loans: Ending balance $ 7,854 $ 1,315,295 $ 137,073 $ 796,660 $ 460,123 $ 19,987 $ 255,770 $ — $ 2,992,762 Loans deemed to be impaired $ — $ 357 $ — $ 2,300 $ — $ — $ — $ — $ 2,657 Loans not deemed to be impaired $ 7,854 $ 1,314,938 $ 137,073 $ 794,360 $ 460,123 $ 19,987 $ 255,770 $ — $ 2,990,105 Further information pertaining to the allowance for loan losses for the three months ending March 31, 2020 is as follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total (in thousands) Allowance for loan losses: Balance at December 31, 2019 $ 331 $ 11,596 $ 2,566 $ 11,464 $ 2,194 $ 312 $ 1,065 $ 57 $ 29,585 Charge-offs — (5 ) — — — (57 ) — — (62 ) Recoveries — 164 — — — 37 5 — 206 Provision (85 ) 673 323 (343 ) 255 4 67 181 1,075 Ending balance at $ 246 $ 12,428 $ 2,889 $ 11,121 $ 2,449 $ 296 $ 1,137 $ 238 $ 30,804 Amount of allowance for loan losses $ — $ — $ — $ 85 $ — $ — $ — $ — $ 85 Amount of allowance for loan losses $ 246 $ 12,428 $ 2,889 $ 11,036 $ 2,449 $ 296 $ 1,137 $ 238 $ 30,719 Loans: Ending balance $ 6,493 $ 867,599 $ 141,588 $ 761,464 $ 393,338 $ 21,039 $ 307,373 $ — $ 2,498,894 Loans deemed to be impaired $ — $ 623 $ — $ 2,322 $ — $ — $ — $ — $ 2,945 Loans not deemed to be impaired $ 6,493 $ 866,976 $ 141,588 $ 759,142 $ 393,338 $ 21,039 $ 307,373 $ — $ 2,495,949
Loans by Risk Rating	The following table presents the Company’s loans by risk rating at March 31, 2021. Construction and Commercial Municipal Commercial Grade: (in thousands) 1-3 $ 7,854 $ 1,310,993 $ 137,073 $ 770,872 4 (Monitor) — 3,945 — 23,488 5 (Substandard) — — — — 6 (Doubtful) — — — — Impaired — 357 — 2,300 Total $ 7,854 $ 1,315,295 $ 137,073 $ 796,660
Loans by Credit Rating	Credit ratings issued by national organizations were utilized as credit quality indicators as presented in the following table at March 31, 2021 and are included within the total loan portfolio. Commercial Municipal Commercial Total (in thousands) Credit Rating: Aaa – Aa3 $ 705,387 $ 73,758 $ 36,519 $ 815,664 A1 – A3 182,559 7,103 145,096 334,758 Baa1 – Baa3 50,000 51,132 146,930 248,062 Ba2 — 5,080 — 5,080 Total $ 937,946 $ 137,073 $ 328,545 $ 1,403,564 Credit ratings issued by national organizations were utilized as credit quality indicators as presented in the following table at December 31, 2020. Commercial Municipal Commercial Total (in thousands) Credit Rating: Aaa – Aa3 $ 710,955 $ 74,291 $ 38,035 $ 823,281 A1 – A3 183,123 7,103 145,583 335,809 Baa1 – Baa3 50,000 51,133 140,905 242,038 Ba2 — 5,080 — 5,080 Total $ 944,078 $ 137,607 $ 324,523 $ 1,406,208
Aging of Past Due Loan Losses	Further information pertaining to the allowance for loan losses at March 31, 2021 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 7,854 $ 7,854 Commercial and industrial — 297 — 297 1,314,998 1,315,295 Municipal — — — — 137,073 137,073 Commercial real estate — 261 — 261 796,399 796,660 Residential real estate 1,373 188 — 1,561 458,562 460,123 Consumer and overdrafts 12 7 — 19 19,968 19,987 Home equity 1,325 189 — 1,514 254,256 255,770 Total $ 2,710 $ 942 $ — $ 3,652 $ 2,989,110 $ 2,992,762 Further information pertaining to the allowance for loan losses at December 31, 2020 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 10,909 $ 10,909 Commercial and industrial 56 297 90 443 1,313,802 1,314,245 Municipal — — — — 137,607 137,607 Commercial real estate — 2,881 — 2,881 786,955 789,836 Residential real estate 390 527 — 917 447,519 448,436 Consumer and overdrafts 21 1 — 22 20,417 20,439 Home equity 1,001 290 — 1,291 273,066 274,357 Total $ 1,468 $ 3,996 $ 90 $ 5,554 $ 2,990,275 $ 2,995,829
Information Pertaining to Impaired Loans	The following is information pertaining to impaired loans for March 31, 2021: Carrying Unpaid Required Average Value Months Interest Income Months (in thousands) With no required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 4 5 — 7 — Municipal — — — — — Commercial real estate 261 296 — 267 — Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 265 $ 301 $ — $ 274 $ — With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 353 373 125 374 1 Municipal — — — — — Commercial real estate 2,039 2,169 74 3,354 20 Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 2,392 $ 2,542 $ 199 $ 3,728 $ 21 Total: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 357 378 125 381 1 Municipal — — — — — Commercial real estate 2,300 2,465 74 3,621 20 Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 2,657 $ 2,843 $ 199 $ 4,002 $ 21 The following is information pertaining to impaired loans for March 31, 2020: Carrying Unpaid Required Average Value Months Interest Income Months (in thousands) With no required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 623 641 — 582 1 Municipal — — — — — Commercial real estate 155 185 — 157 — Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 778 $ 826 $ — $ 739 $ 1 With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial — — — 113 1 Municipal — — — — — Commercial real estate 2,167 2,290 85 2,176 22 Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 2,167 $ 2,290 $ 85 $ 2,289 $ 23 Total: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 623 641 — 695 2 Municipal — — — — — Commercial real estate 2,322 2,475 85 2,333 22 Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 2,945 $ 3,116 $ 85 $ 3,028 $ 24 Troubled debt restructurings (“TDR”) are identified as modifications in which a concession was granted to a customer who was having financial difficulties. This concession may be below market rate, longer amortization/term, or a lower payment amount. The present value calculation of the modifications did not result in an increase in the allowance for these loans beyond any previously established allocations. There was no TDR made during the three-month period ended March 31, 2021. Also, there were no commitments to lend additional funds to TDR borrowers. There were no TDRs that subsequently defaulted during the first three months of 2021. Under Section 4013 of the CARES Act, loans less than 30 days past due as of December 31, 2019 will be considered current for COVID-19 COVID-19 COVID-19

Reclassifications Out of Accu_2

Reclassifications Out of Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2021
Text Block [Abstract]
Reclassifications Out of Accumulated Other Comprehensive Income	Amount Reclassified from Accumulated Other Comprehensive Income Details about Accumulated Other Comprehensive Income Components Three Three Affected Line Item in the Statement (in thousands) Accretion of unrealized losses transferred $ (155 ) $ (222 ) Interest on securities held-to-maturity 41 58 Provision for income taxes $ (114 ) $ (164 ) Net income Amortization of defined benefit pension items Prior-service costs $ (54 ) $ (29 )(b) Salaries and employee benefits Actuarial gains (losses) (511 ) (472 )(b) Salaries and employee benefits Total before tax (565 ) (501 ) Income before taxes Tax (expense) or benefit 159 141 Provision for income taxes Net of tax $ (406 ) $ (360 ) Net income

Earnings per share ("EPS") (Tab

Earnings per share ("EPS") (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Reconciliation of Basic EPS and Diluted EPS	The following table is a reconciliation of basic EPS and diluted EPS. Three Months Ended (in thousands except share and per share data) 2021 2020 Basic EPS Computation: Numerator: Net income, Class A $ 8,538 $ 7,658 Net income, Class B 2,232 2,008 Denominator: Weighted average shares outstanding, Class A 3,656,469 3,652,349 Weighted average shares outstanding, Class B 1,911,440 1,915,560 Basic EPS, Class A $ 2.34 $ 2.10 Basic EPS, Class B 1.17 1.05 Diluted EPS Computation: Numerator: Net income, Class A $ 8,538 $ 7,658 Net income, Class B 2,232 2,008 Total net income, for diluted EPS, Class A computation 10,770 9,666 Denominator: Weighted average shares outstanding, basic, Class A 3,656,469 3,652,349 Weighted average shares outstanding, Class B 1,911,440 1,915,560 Weighted average shares outstanding diluted, Class A 5,567,909 5,567,909 Weighted average shares outstanding, Class B 1,911,440 1,915,560 Diluted EPS, Class A $ 1.93 $ 1.74 Diluted EPS, Class B 1.17 1.05

Employee Benefits (Tables)

Employee Benefits (Tables)	3 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost	Components of Net Periodic Benefit Cost for the Three Months Ended March 31, Pension Benefits Supplemental Insurance/ 2021 2020 2021 2020 (in thousands) Service cos t $ 379 $ 344 $ 363 $ 353 Interest 434 450 434 466 Expected return on plan assets (1,062 ) (952 ) — — Recognized prior service cost (benefit) — — 54 29 Recognized net actuarial losses 241 261 269 211 Net periodic benefit (credit) cost $ (8 ) $ 103 $ 1,120 $ 1,059

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Financial Instruments Measured at Fair Value on a Recurring and Non-recurring Basis	The results of the fair value hierarchy as of March 31, 2021, are as follows: Securities AFS Fair Value Measurements Using Carrying Quoted Prices Significant Significant (in thousands) SBA Backed Securities $ 42,855 $ — $ 42,855 $ — U.S. Government Agency and Sponsored Mortgage-Backed Securities 166,811 — 166,811 — Privately Issued Residential Mortgage- Backed 326 — 326 — Obligations Issued by States and Political Subdivisions 45,668 — — 45,668 Other Debt Securities 8,238 — 8,238 — Total $ 263,898 $ — $ 218,230 $ 45,668 Equity Securities $ 1,722 $ 376 $ 1,346 $ — Financial Instruments Measured at Fair Value on a Non-recurring Basis Impaired Loans $ 558 $ — $ — $ 558 The results of the fair value hierarchy as of December 31, 2020, are as follows: Securities AFS Fair Value Measurements Using Carrying Quoted Prices Assets Significant Significant (in thousands) Financial Instruments Measured at Fair Value on a Recurring Basis SBA Backed Securities $ 44,039 $ — $ 44,039 $ — U.S. Government Agency and Sponsored Mortgage-Backed Securities 177,741 — 177,741 — Privately Issued Residential Mortgage- 328 — 328 — Obligations Issued by States and Political Subdivisions 52,276 — — 52,276 Other Debt Securities 8,064 — 8,064 — Total $ 282,448 $ — $ 230,172 $ 52,276 Equity Securities $ 1,668 $ 303 $ 1,365 $ — Financial Instruments Measured at Fair Value on a Non-recurring Basis Impaired Loans $ 3,178 $ — $ — $ 3,178
Assets Measured at Fair Value	The following table presents additional information about assets measured at fair value on a recurring and nonrecurring basis for which the Company has utilized Level 3 inputs to determine fair value (dollars in thousands) at March 31, 2021. Management continues to monitor the assumptions used to value the assets listed below. Asset Fair Value Valuation Technique Unobservable Input Unobservable Input Securities AFS (1) $ 45,668 Discounted cash flow Discount rate 0% - 1.0% (2) Impaired Loans $ 558 Appraisal of collateral (3) Appraisal adjustments (4) 0%—22% discount The following table presents additional information about assets measured at fair value on a recurring and nonrecurring basis for which the Company has utilized Level 3 inputs to determine fair value (dollars in thousands) at December 31, 2020. Management continues to monitor the assumptions used to value the assets listed below. Asset Fair Value Valuation Technique Unobservable Input Unobservable Input Securities AFS (1) $ 52,276 Discounted cash flow Discount rate 0% - 1.0% (2) Impaired Loans $ 3,178 Appraisal of collateral (3) Appraisal adjustments (4) 0%-17% discount (1) Municipal securities generally have maturities of one year or less and, therefore, the amortized cost equates to the fair value. (2) Weighted averages. (3) Fair value is generally determined through independent appraisals of the underlying collateral, which generally include various Level 3 inputs which are not identifiable. (4) Appraisals may be adjusted by management for qualitative factors such as economic conditions and estimated expenses.
Changes in Level 3 Securities	The changes in Level 3 securities for the three-month period ended March 31, 2021 are shown in the table below: Obligations Issued by States & Balance at December 31, 2020 $ 52,276 Purchases 6,770 Maturities and calls (13,353 ) Amortization (25 ) Balance at March 31, 2021 $ 45,668 The changes in Level 3 securities for the three-month period ended March 31, 2020 are shown in the table below: Obligations Issued by States & Subdivisions Balance at December 31, 2019 $ 13,301 Purchases 9,372 Maturities and calls (5,449 ) Amortization — Changes in fair value — Balance at March 31, 2020 $ 17,224

Fair Values of Financial Inst_2

Fair Values of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
Investments, All Other Investments [Abstract]
Carrying Amounts and Fair Values of Company's Financial Instruments	March 31, 2021 Carrying Estimated Fair Value Level 2 Level 3 (in thousands) Financial assets: Securities held-to-maturity $ 3,217,176 $ 3,222,903 $ — $ 3,222,903 $ — Loans (1) 2,957,810 2,877,220 — — 2,877,220 Financial liabilities: Time deposits 480,784 479,087 — 479,087 — Other borrowed funds 151,769 155,001 — 155,001 — Subordinated debentures 36,083 36,083 — 36,083 — December 31, 2020 Financial assets: Securities held-to-maturity $ 2,509,088 $ 2,579,103 $ — $ 2,579,103 $ — Loans (1) 2,960,343 2,902,390 — — 2,902,390 Financial liabilities: Time deposits 546,143 556,470 — 556,470 — Other borrowed funds 177,009 183,000 — 183,000 — Subordinated debentures 36,083 36,083 — 36,083 — (1) Comprised of loans (including collateral dependent impaired loans), net of deferred loan costs and the allowance for loanlosses.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Schedule of Revenue From Contracts	The following table presents total revenues as presented in the Consolidated Statements of Income and the related amounts which are from contracts with customers within the scope of Topic 606. As illustrated here, the vast majority of our revenues are specifically excluded from the scope of Topic 606. Three Months Revenue from Three Months Revenue from (dollars in thousands) Total net interest income $ 28,567 $ — $ 25,201 $ — Noninterest income: Service charges on deposit accounts 2,218 2,218 2,296 2,296 Lockbox fees 996 996 930 930 Other income 989 695 1,084 599 Total noninterest income 4,203 3,909 4,310 3,825 Total net revenues $ 32,770 $ 3,909 $ 29,511 $ 3,825
Information about Receivables with Customers	The following table provides information about receivables with customers. (dollars in thousands) March 31, 2021 December 31, 2020 Receivables, which are included in “Other assets” $ 1,393 $ 1,397

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Components of lease expense	The components of lease expense were as follows: (in thousands) Three Months Three Months Operating lease cost $ 560 $ 546 Variable lease cost 153 133 Total lease cost $ 713 $ 679
Supplemental cash flow information related to leases	Supplemental cash flow information related to leases was as follows: (in thousands) (in Three Months Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 541 $ 529 Right-of-use Operating leases $ — $ —
Supplemental balance sheet information related to leases	Supplemental balance sheet information related to leases was as follows: 3/31/2021 12/31/2020 (in thousands, except lease term and discount rate) Operating Leases: Operating lease right-of-use $ 13,262 $ 13,713 Operating lease liabilities $ 13,496 $ 13,935 Weighted Average Remaining Lease Term: Operating Leases 10 Years 10 Years Weighted Average Discount Rate: Operating Leases 3.1 % 3.1 %
Summary of Future Payments of Lease Liabilities	A summary of future minimum rental payments under such leases as the dates indicated follows: Minimum Rental Payments March 31, 2021 December 31, 2020 Year Ending December 31, (in thousands) 2021 $ 1,612 $ 2,156 2022 1,995 1,995 2023 1,962 1,962 2024 1,692 1,692 2025 1,471 1,471 Thereafter 7,394 7,394 Total lease payments $ 16,126 $ 16,670 Less imputed interest (2,630 ) (2,735 ) Present value of lease liability $ 13,496 $ 13,935

Basis of Financial Statement _2

Basis of Financial Statement Presentation - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021Segment
Number of Reportable Segments	1
Century Bancorp Capital Trust II [Member]
Equity ownership interest	100.00%

Securities Available-for-Sale -

Securities Available-for-Sale - Summary of Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 263,089	$ 282,273
Gross Unrealized Gains	1,280	845
Gross Unrealized Losses	471	670
Total, Fair Value	263,898	282,448
SBA Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,154	44,328
Gross Unrealized Gains	0	0
Gross Unrealized Losses	299	289
Total, Fair Value	42,855	44,039
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	165,846	177,239
Gross Unrealized Gains	1,097	819
Gross Unrealized Losses	132	317
Total, Fair Value	166,811	177,741
Privately Issued Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	321	330
Gross Unrealized Gains	5	2
Gross Unrealized Losses	0	4
Total, Fair Value	326	328
Obligations Issued by States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,668	52,276
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Total, Fair Value	45,668	52,276
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,100	8,100
Gross Unrealized Gains	178	24
Gross Unrealized Losses	40	60
Total, Fair Value	$ 8,238	$ 8,064

Securities Available-for-Sale_2

Securities Available-for-Sale - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021USD ($)Security	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)Security
Schedule of Available-for-sale Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 2,038,453,000		$ 1,866,989,000
Securities available-for-sale are securities at fair value pledged for borrowing	28,830,000		$ 29,885,000
Securities at floating rate or adjustable rate	210,125,000
Sales of securities available for sale	$ 0	$ 0
Securities AFS [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted average remaining life of investment securities available-for-sale	5 years
Number of securities, temporarily impaired for less than 12 months | Security	3		13
Number of securities, temporarily impaired for 12 months or longer | Security	27		21
Number of securities, temporarily impaired, total | Security	151		153
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 172,427,000		$ 183,269,000

Securities Available-for-Sale_3

Securities Available-for-Sale - Estimated Maturity Distribution of Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 48,041
After one but within five years, Amortized Cost	104,714
After five but within ten years, Amortized Cost	89,033
More than 10 years, Amortized Cost	21,301
Amortized Cost	263,089	$ 282,273
Within one year, Fair Value	48,047
After one but within five years, Fair Value	105,250
After five but within ten years, Fair Value	89,484
More than 10 years, Fair Value	21,117
Total, Fair Value	$ 263,898	$ 282,448

Securities Available-for-Sale_4

Securities Available-for-Sale - Continuous Unrealized Loss Position for 12 Months or Less and 12 Months and Longer (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	$ 2,807	$ 35,969
Less Than 12 Months, Unrealized Losses	44	150
12 Months or Longer, Fair Value	61,443	65,325
12 Months or Longer, Unrealized Losses	427	520
Total, Fair Value	64,250	101,294
Total, Unrealized Losses	471	670
SBA Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	0	13,839
Less Than 12 Months, Unrealized Losses	0	42
12 Months or Longer, Fair Value	42,856	30,200
12 Months or Longer, Unrealized Losses	299	247
Total, Fair Value	42,856	44,039
Total, Unrealized Losses	299	289
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	346	18,188
Less Than 12 Months, Unrealized Losses	5	50
12 Months or Longer, Fair Value	17,288	33,617
12 Months or Longer, Unrealized Losses	127	267
Total, Fair Value	17,634	51,805
Total, Unrealized Losses	132	317
Privately Issued Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
12 Months or Longer, Fair Value	0	210
12 Months or Longer, Unrealized Losses	0	4
Total, Fair Value	0	210
Total, Unrealized Losses	0	4
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	2,461	3,942
Less Than 12 Months, Unrealized Losses	39	58
12 Months or Longer, Fair Value	1,299	1,298
12 Months or Longer, Unrealized Losses	1	2
Total, Fair Value	3,760	5,240
Total, Unrealized Losses	$ 40	$ 60

Investment Securities Held-to_3

Investment Securities Held-to-Maturity - Summary of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 3,217,176	$ 2,509,088
Gross Unrealized Gains	47,132	71,913
Gross Unrealized Losses	41,405	1,898
Estimated Fair Value	3,222,903	2,579,103
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	381,077	244,220
Gross Unrealized Gains	218	389
Gross Unrealized Losses	9,017	866
Estimated Fair Value	372,278	243,743
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	36,330	37,783
Gross Unrealized Gains	1,142	2,002
Gross Unrealized Losses	0	0
Estimated Fair Value	37,472	39,785
U.S. Government Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,799,769	2,227,085
Gross Unrealized Gains	45,772	69,522
Gross Unrealized Losses	32,388	1,032
Estimated Fair Value	$ 2,813,153	$ 2,295,575

Investment Securities Held-to_4

Investment Securities Held-to-Maturity - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021USD ($)Security	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)Security
Schedule of Held-to-maturity Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 2,038,453,000		$ 1,866,989,000
Securities held to maturity at floating rate or adjustable rate	81,000
Commercial Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Sales of held-to-maturity securities	$ 0	$ 0
Held-to-Maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Weighted average remaining life of investment securities held-to-maturity	3 years 7 months 6 days
Number of securities, temporarily impaired for less than 12 months | Security	156		53
Number of securities, temporarily impaired for 12 months or longer | Security	0		0
Number of securities, temporarily impaired, total | Security	655		600
Held-to-Maturity Securities [Member] | U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Weighted average remaining life	$ 320,611,000
Federal Home Loan Bank [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities pledged for borrowing at the Federal Home Loan Bank	$ 484,029,000		$ 537,367,000

Investment Securities Held-to_5

Investment Securities Held-to-Maturity - Company's Securities Held-to-Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 84,709
After one but within five years, Amortized Cost	1,707,454
After five but within ten years, Amortized Cost	1,425,013
More than ten years, Amortized Cost	0
Amortized Cost	3,217,176	$ 2,509,088
Within one year, Fair Value	85,698
After one but within five years, Fair Value	1,738,266
After five but within ten years, Fair Value	1,398,939
More than ten years, Fair Value	0
Estimated Fair Value	$ 3,222,903	$ 2,579,103

Investment Securities Held-to_6

Investment Securities Held-to-Maturity - Unrealized Market Loss of Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	$ 1,678,619	$ 465,271
Less Than 12 Months, Unrealized Losses	41,405	1,898
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total, Fair Value	1,678,619	465,271
Total, Unrealized Losses	41,405	1,898
US Government Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	346,560	162,870
Less Than 12 Months, Unrealized Losses	9,017	866
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total, Fair Value	346,560	162,870
Total, Unrealized Losses	9,017	866
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	0	0
Less Than 12 Months, Unrealized Losses	0	0
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total, Fair Value	0	0
Total, Unrealized Losses	0	0
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	1,332,059	302,401
Less Than 12 Months, Unrealized Losses	32,388	1,032
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total, Fair Value	1,332,059	302,401
Total, Unrealized Losses	$ 32,388	$ 1,032

Allowance for Loan Losses - Ana

Allowance for Loan Losses - Analysis of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Receivables [Abstract]
Allowance for loan losses, beginning of period	$ 35,486	$ 29,585
Loans charged off	(67)	(62)
Recoveries on loans previously charged-off	83	206
Net recoveries (charge-offs)	16	144
(Credit) provision charged to expense	(550)	1,075
Allowance for loan losses, end of period	$ 34,952	$ 30,804

Allowance for Loan Losses - Sum

Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Allowance for Loan Losses:
Allowance for loan losses, beginning of period	$ 35,486	$ 29,585
Charge-offs	(67)	(62)
Recoveries	83	206
(Credit) provision	(550)	1,075
Allowance for loan losses, end of period	34,952	30,804
Amount of allowance for loan losses for loans deemed to be impaired	199	85
Amount of allowance for loan losses for loans not deemed to be impaired	34,753	30,719
Loans:
Total loans, net	2,992,762	2,498,894	$ 2,995,829
Loans deemed to be impaired	2,657	2,945
Loans not deemed to be impaired	2,990,105	2,495,949
Construction and Land Development [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of period	429	331
(Credit) provision	(136)	(85)
Allowance for loan losses, end of period	293	246
Amount of allowance for loan losses for loans not deemed to be impaired	293	246
Loans:
Total loans, net	7,854	6,493	10,909
Loans not deemed to be impaired	7,854	6,493
Commercial and Industrial [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of period	16,713	11,596
Charge-offs		(5)
Recoveries	3	164
(Credit) provision	(246)	673
Allowance for loan losses, end of period	16,470	12,428
Amount of allowance for loan losses for loans deemed to be impaired	125	0
Amount of allowance for loan losses for loans not deemed to be impaired	16,345	12,428
Loans:
Total loans, net	1,315,295	867,599	1,314,245
Loans deemed to be impaired	357	623
Loans not deemed to be impaired	1,314,938	866,976
Municipal [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of period	2,804	2,566
(Credit) provision	33	323
Allowance for loan losses, end of period	2,837	2,889
Amount of allowance for loan losses for loans not deemed to be impaired	2,837	2,889
Loans:
Total loans, net	137,073	141,588	137,607
Loans not deemed to be impaired	137,073	141,588
Commercial Real Estate [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of period	11,751	11,464
(Credit) provision	(96)	(343)
Allowance for loan losses, end of period	11,655	11,121
Amount of allowance for loan losses for loans deemed to be impaired	74	85
Amount of allowance for loan losses for loans not deemed to be impaired	11,581	11,036
Loans:
Total loans, net	796,660	761,464	789,836
Loans deemed to be impaired	2,300	2,322
Loans not deemed to be impaired	794,360	759,142
Residential Real Estate [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of period	2,111	2,194
(Credit) provision	(44)	255
Allowance for loan losses, end of period	2,067	2,449
Amount of allowance for loan losses for loans not deemed to be impaired	2,067	2,449
Loans:
Total loans, net	460,123	393,338	448,436
Loans not deemed to be impaired	460,123	393,338
Consumer [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of period	241	312
Charge-offs	(67)	(57)
Recoveries	80	37
(Credit) provision	(60)	4
Allowance for loan losses, end of period	194	296
Amount of allowance for loan losses for loans not deemed to be impaired	194	296
Loans:
Total loans, net	19,987	21,039	20,439
Loans not deemed to be impaired	19,987	21,039
Home Equity [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of period	1,208	1,065
Recoveries		5
(Credit) provision	(159)	67
Allowance for loan losses, end of period	1,049	1,137
Amount of allowance for loan losses for loans not deemed to be impaired	1,049	1,137
Loans:
Total loans, net	255,770	307,373	$ 274,357
Loans not deemed to be impaired	255,770	307,373
Unallocated [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of period	229	57
(Credit) provision	158	181
Allowance for loan losses, end of period	387	238
Amount of allowance for loan losses for loans not deemed to be impaired	$ 387	$ 238

Allowance for Loan Losses - Loa

Allowance for Loan Losses - Loans by Risk Rating (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Loans by risk rating
Financing Receivable, Net	$ 2,992,762	$ 2,995,829	$ 2,498,894
Construction and Land Development [Member]
Loans by risk rating
Financing Receivable, Net	7,854	10,909	6,493
Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	1,315,295	1,314,245	867,599
Municipal [Member]
Loans by risk rating
Financing Receivable, Net	137,073	137,607	141,588
Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	796,660	789,836	$ 761,464
1-3 (Pass) [Member] | Construction and Land Development [Member]
Loans by risk rating
Financing Receivable, Net	7,854	10,909
1-3 (Pass) [Member] | Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	1,310,993	1,309,861
1-3 (Pass) [Member] | Municipal [Member]
Loans by risk rating
Financing Receivable, Net	137,073	137,607
1-3 (Pass) [Member] | Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	770,872	761,101
4 (Monitor) [Member] | Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	3,945	3,945
4 (Monitor) [Member] | Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	23,488	23,795
Impaired [Member] | Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	357	439
Impaired [Member] | Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	$ 2,300	$ 4,940

Allowance for Loan Losses - L_2

Allowance for Loan Losses - Loans by Credit Rating (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	$ 1,403,564	$ 1,406,208
Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	815,664	823,281
A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	334,758	335,809
Baa1 - Baa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	248,062	242,038
Ba2 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	5,080	5,080
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	937,946	944,078
Commercial and Industrial [Member] | Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	705,387	710,955
Commercial and Industrial [Member] | A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	182,559	183,123
Commercial and Industrial [Member] | Baa1 - Baa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	50,000	50,000
Municipal [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	137,073	137,607
Municipal [Member] | Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	73,758	74,291
Municipal [Member] | A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	7,103	7,103
Municipal [Member] | Baa1 - Baa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	51,132	51,133
Municipal [Member] | Ba2 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	5,080	5,080
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	328,545	324,523
Commercial Real Estate [Member] | Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	36,519	38,035
Commercial Real Estate [Member] | A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	145,096	145,583
Commercial Real Estate [Member] | Baa1 - Baa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	$ 146,930	$ 140,905

Allowance for Loan Losses - Agi

Allowance for Loan Losses - Aging of Past Due Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	$ 2,710	$ 1,468
Non Accrual	942	3,996
Accruing Greater Than 90 Days	0	90
Total Past Due	3,652	5,554
Current Loans	2,989,110	2,990,275
Total loans, net	2,992,762	2,995,829	$ 2,498,894
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current Loans	7,854	10,909
Total loans, net	7,854	10,909	6,493
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	0	56
Non Accrual	297	297
Accruing Greater Than 90 Days	0	90
Total Past Due	297	443
Current Loans	1,314,998	1,313,802
Total loans, net	1,315,295	1,314,245	867,599
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current Loans	137,073	137,607
Total loans, net	137,073	137,607	141,588
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Non Accrual	261	2,881
Total Past Due	261	2,881
Current Loans	796,399	786,955
Total loans, net	796,660	789,836	761,464
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	1,373	390
Non Accrual	188	527
Total Past Due	1,561	917
Current Loans	458,562	447,519
Total loans, net	460,123	448,436	393,338
Consumer and overdrafts [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	12	21
Non Accrual	7	1
Total Past Due	19	22
Current Loans	19,968	20,417
Total loans, net	19,987	20,439	21,039
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	1,325	1,001
Non Accrual	189	290
Total Past Due	1,514	1,291
Current Loans	254,256	273,066
Total loans, net	$ 255,770	$ 274,357	$ 307,373

Allowance for Loan Losses - Inf

Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 265	$ 778
With no required reserve recorded, Unpaid Balance Principal	301	826
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	274	739
With no required reserve recorded, Interest Income	0	1
With required reserve recorded, Carrying Value	2,392	2,167
With required reserve recorded, Unpaid Balance Principal	2,542	2,290
With required reserve recorded, Required Reserve	199	85
With required reserve recorded, Average Carrying Value Recognized	3,728	2,289
With required reserve recorded, Interest Income	21	23
Carrying Value	2,657	2,945
Unpaid Balance Principal	2,843	3,116
With required reserve recorded, Required Reserve	199	85
Average Carrying Value Recognized	4,002	3,028
Interest Income	21	24
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	4	623
With no required reserve recorded, Unpaid Balance Principal	5	641
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	7	582
With no required reserve recorded, Interest Income	0	1
With required reserve recorded, Carrying Value	353	0
With required reserve recorded, Unpaid Balance Principal	373	0
With required reserve recorded, Required Reserve	125	0
With required reserve recorded, Average Carrying Value Recognized	374	113
With required reserve recorded, Interest Income	1	1
Carrying Value	357	623
Unpaid Balance Principal	378	641
With required reserve recorded, Required Reserve	125	0
Average Carrying Value Recognized	381	695
Interest Income	1	2
Municipal [Member] | Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	261	155
With no required reserve recorded, Unpaid Balance Principal	296	185
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	267	157
With required reserve recorded, Carrying Value	2,039	2,167
With required reserve recorded, Unpaid Balance Principal	2,169	2,290
With required reserve recorded, Required Reserve	74	85
With required reserve recorded, Average Carrying Value Recognized	3,354	2,176
With required reserve recorded, Interest Income	20	22
Carrying Value	2,300	2,322
Unpaid Balance Principal	2,465	2,475
With required reserve recorded, Required Reserve	74	85
Average Carrying Value Recognized	3,621	2,333
Interest Income	20	22
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	0
Average Carrying Value Recognized	0	0
Interest Income		0
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	$ 0	$ 0

Allowance for Loan Losses - Add

Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021USD ($)Loans	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Provision for credit losses	$ (550,000)	$ 1,075,000
Loans receivable	2,992,762,000		$ 2,995,829,000
Allowances for loan losses	$ 34,952,000	$ 30,804,000	$ 35,486,000	$ 29,585,000
Extended Maturity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Description Of Covid Nineteen Loan Modifications Aggregating Deferral Principal	As of March 31, 2021, and as a result of COVID-19 loan modifications, the Company had modifications of 8 loans aggregating $36,152,000, primarily consisting of short-term payment deferrals. Of these modifications, $36,152,000, or 100%, were performing in accordance with their modified terms.
Loans Insured or Guaranteed by US Government Authorities [Member] | US Small Business Administration Payroll Protection Programme [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of loans covered by a sponsored programme | Loans	1,117
Loans receivable	$ 213,000,000
Percentage of loans covered by a sponsored programme guaranteed	100.00%
Allowances for loan losses	$ 0

Reclassifications Out of Accu_3

Reclassifications Out of Accumulated Other Comprehensive Income - Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Provision for income taxes	$ (1,679)	$ (597)
Net income	10,770	9,666
Salaries and employee benefits	(12,250)	(11,371)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Accretion of Unrealized Losses Transferred [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains on sales of securities	(155)	(222)
Provision for income taxes	41	58
Net income	(114)	(164)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Prior-Service Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	(54)	(29)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	(511)	(472)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Amortization of Defined Benefit Pension Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before taxes	(565)	(501)
Provision for income taxes	159	141
Net income	$ (406)	$ (360)

Earnings Per Share ("EPS") - Ad

Earnings Per Share ("EPS") - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021
Class A Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Class A common stock entitled dividend per share percent in comparison to Class B common stock	200.00%

Earnings Per Share ("EPS") - Re

Earnings Per Share ("EPS") - Reconciliation of Basic EPS and Diluted EPS (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 10,770	$ 9,666
Class A Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 8,538	$ 7,658
Weighted average shares outstanding, basic	3,656,469	3,652,349
Basic earnings per share	$ 2.34	$ 2.10
Net income	$ 8,538	$ 7,658
Weighted average shares outstanding, diluted	5,567,909	5,567,909
Diluted earnings per share	$ 1.93	$ 1.74
Class B Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 2,232	$ 2,008
Weighted average shares outstanding, basic	1,911,440	1,915,560
Basic earnings per share	$ 1.17	$ 1.05
Net income	$ 2,232	$ 2,008
Weighted average shares outstanding, diluted	1,911,440	1,915,560
Diluted earnings per share	$ 1.17	$ 1.05

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail) - USD ($)	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	$ 371,000	$ 465,000
Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 1,302,000

Employee Benefits - Components

Employee Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Pension Plan [Member]
Components of net periodic benefit cost
Service cost	$ 379	$ 344
Interest cost	434	450
Expected return on plan assets	(1,062)	(952)
Recognized net losses	241	261
Net periodic benefit cost (credit)	(8)	103
Supplemental Insurance/ Retirement Plan [Member]
Components of net periodic benefit cost
Service cost	363	353
Interest cost	434	466
Recognized prior service cost	54	29
Recognized net losses	269	211
Net periodic benefit cost (credit)	$ 1,120	$ 1,059

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments Measured at Fair Value on a Recurring and Non-recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	$ 263,898	$ 282,448
Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	218,230	230,172
Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	45,668	52,276
Financial Instruments Measured at Fair Value on a Non-recurring Basis Impaired Loans	558	3,178
SBA Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	42,855	44,039
SBA Backed Securities [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	42,855	44,039
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	166,811	177,741
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	166,811	177,741
Privately Issued Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	326	328
Privately Issued Residential Mortgage-Backed Securities [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	326	328
Obligations Issued by States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	45,668	52,276
Obligations Issued by States and Political Subdivisions [Member] | Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	45,668	52,276
Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	8,238	8,064
Other Debt Securities [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	8,238	8,064
Equity Securities [Member] | Fair Value Measurements, Level 1 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments Measured at Fair Value on a Non Recurring Basis Equity Securities	376	303
Equity Securities [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments Measured at Fair Value on a Non Recurring Basis Equity Securities	1,346	1,365
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	263,898	282,448
Financial Instruments Measured at Fair Value on a Non-recurring Basis Impaired Loans	558	3,178
Carrying Value [Member] | SBA Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	42,855	44,039
Carrying Value [Member] | U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	166,811	177,741
Carrying Value [Member] | Privately Issued Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	326	328
Carrying Value [Member] | Obligations Issued by States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	45,668	52,276
Carrying Value [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	8,238	8,064
Carrying Value [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments Measured at Fair Value on a Non Recurring Basis Equity Securities	$ 1,722	$ 1,668

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Specific adjustments to impaired loans recognized	$ 375,000		$ 501,000
Amortized cost of Level 3 securities	1,635,000		1,635,000
Liabilities measured at fair value on a recurring or nonrecurring basis	0	$ 0	0
Transfers between level 1, 2 and 3	0		$ 0
Impaired Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of loans	2,624,000,000	269,000,000
Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized cost of Level 3 securities	45,668,000	17,224,000
Unrealized loss	$ 0	$ 0

Fair Value Measurements - Asset

Fair Value Measurements - Assets Measured at Fair Value (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Securities AFS [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Fair Value	$ 45,668	$ 52,276
Valuation Technique	Discounted cash flow	Discounted cash flow
Unobservable Input	Discount rate	Discount rate
Impaired Loans [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Fair Value	$ 558	$ 3,178
Valuation Technique	Appraisal of collateral	Appraisal of collateral
Unobservable Input	Appraisal adjustments	Appraisal adjustments
Minimum [Member] | Securities AFS [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Unobservable Input Value or Range	0.00%
Securities AFS, Unobservable Input Value or Range		0
Minimum [Member] | Impaired Loans [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Unobservable Input Value or Range	0.00%
Impaired Loans, Unobservable Input Value or Range		0
Maximum [Member] | Securities AFS [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Unobservable Input Value or Range	1.00%
Securities AFS, Unobservable Input Value or Range		1
Maximum [Member] | Impaired Loans [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Unobservable Input Value or Range	22.00%
Impaired Loans, Unobservable Input Value or Range		17

Fair Value Measurements - Ass_2

Fair Value Measurements - Assets Measured at Fair Value (Parenthetical) (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Municipal [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities maturity period	one year or less	one year or less

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Level 3 Securities (Detail) - Obligations Issued by States and Political Subdivisions [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 52,276	$ 13,301
Purchases	6,770	9,372
Maturities and calls	(13,353)	(5,449)
Amortization	(25)	0
Ending Balance	$ 45,668	$ 17,224

Fair Values of Financial Inst_3

Fair Values of Financial Instruments - Carrying Amount and Fair Value of Company's Financial Instruments (Detail) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020
Financial assets:
Securities held-to-maturity		$ 3,217,176	$ 2,509,088
Loans		2,957,810	2,960,343
Financial liabilities:
Time deposits		480,784	546,143
Other borrowed funds		151,769	177,009
Subordinated debentures		36,083	36,083
Carrying Value [Member]
Financial assets:
Securities held-to-maturity		3,217,176	2,509,088
Loans	[1]	2,957,810	2,960,343
Financial liabilities:
Time deposits		480,784	546,143
Other borrowed funds		151,769	177,009
Subordinated debentures		36,083	36,083
Estimated Fair Value [Member]
Financial assets:
Securities held-to-maturity		3,222,903	2,579,103
Loans	[1]	2,877,220	2,902,390
Financial liabilities:
Time deposits		479,087	556,470
Other borrowed funds		155,001	183,000
Subordinated debentures		36,083	36,083
Fair Value Measurements, Level 2 Inputs [Member]
Financial assets:
Securities held-to-maturity		3,222,903	2,579,103
Financial liabilities:
Time deposits		479,087	556,470
Other borrowed funds		155,001	183,000
Subordinated debentures		36,083	36,083
Fair Value Measurements, Level 3 Inputs [Member]
Financial assets:
Loans	[1]	$ 2,877,220	$ 2,902,390
[1]	Comprised of loans (including collateral dependent impaired loans), net of deferred loan costs and the allowance for loanlosses.

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Schedule of Revenue from Contracts (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Total net interest income	$ 28,567	$ 25,201
Noninterest income:
Service charges on deposit accounts	2,218	2,296
Lockbox fees	996	930
Other income	989	1,084
Total noninterest income	4,203	4,310
ASU 2014-09 [Member]
Disaggregation of Revenue [Line Items]
Total net interest income	28,567	25,201
Noninterest income:
Service charges on deposit accounts	2,218	2,296
Lockbox fees	996	930
Other income	989	1,084
Total noninterest income	4,203	4,310
Total net revenues	32,770	29,511
ASU 2014-09 [Member] | Revenue Guidance Contracts in Scope of Topic 606 [Member]
Noninterest income:
Service charges on deposit accounts	2,218	2,296
Lockbox fees	996	930
Other income	695	599
Total noninterest income	3,909	3,825
Total net revenues	$ 3,909	$ 3,825

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Information about Receivables with Customers (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Other Assets [Member]
Disaggregation of Revenue [Line Items]
Receivables, which are included in "Other assets"	$ 1,393	$ 1,397

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating lease option to extend	options to extend the leases for up to 10 years, and some of which include options to terminate the leases within 1 year.
Sublease Income	$ 10,000
Sublease option to terminate	The sublease expires in 2022 with an option to terminate and no option to extend.
Lease expense	$ 713,000	$ 679,000
Lease rental income	165,000	168,000
Barry R Sloane [Member]
Lease expense	$ 111,000	$ 109,000
Maximum [Member]
Operating lease remaining lease term	31 years
Minimum [Member]
Operating lease remaining lease term	1 year

Leases - Components of lease ex

Leases - Components of lease expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating lease cost	$ 560	$ 546
Variable lease cost	153	133
Total lease cost	$ 713	$ 679

Leases - Supplemental cash flow

Leases - Supplemental cash flow information related to leases (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 541	$ 529
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	$ 0	$ 0

Leases - Supplemental balance s

Leases - Supplemental balance sheet information related to leases (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Operating Leases:
Operating lease right-of-use assets	$ 13,262	$ 13,713
Operating lease liabilities	$ 13,496	$ 13,935
Weighted Average Remaining Lease Term:
Operating Leases	10 years	10 years
Weighted Average Discount Rate:
Operating Leases	3.10%	3.10%

Leases - Summary of Future Paym

Leases - Summary of Future Payments of Lease Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Leases [Abstract]
2021	$ 1,612	$ 2,156
2022	1,995	1,995
2023	1,962	1,962
2024	1,692	1,692
2025	1,471	1,471
Thereafter	7,394	7,394
Total lease payments	16,126	16,670
Less imputed interest	2,630	2,735
Present value of lease liability	$ 13,496	$ 13,935

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] - Eastern Bankshares Inc [Member] $ / shares in Units, $ in Millions	Apr. 07, 2021USD ($)$ / shares
Subsequent Event [Line Items]
Cash consideration | $	$ 642
Class A Common Stock [Member]
Subsequent Event [Line Items]
Busniess combinaton cash payment for common stock held per share	$ 115.28
Class B Common Stock [Member]
Subsequent Event [Line Items]
Busniess combinaton cash payment for common stock held per share	$ 115.28