Century Bancorp (CNBKA) 10-Q 8 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	CNBKA
Entity Registrant Name	CENTURY BANCORP INC
Entity Central Index Key	812,348
Current Fiscal Year End Date	--03-31
Entity Filer Category	Accelerated Filer
Class A Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,608,029
Class B Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		1,959,880

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 64,544	$ 77,199
Federal funds sold and interest-bearing deposits in other banks	186,125	279,231
Total cash and cash equivalents	250,669	356,430
Securities available-for-sale, amortized cost $371,013 and $395,947, respectively	370,976	395,831
Securities held-to-maturity, fair value $1,760,498 and $1,668,827, respectively	1,817,633	1,701,233
Federal Home Loan Bank of Boston, stock at cost	20,050	21,779
Equity securities, amortized cost $ 1,635 and $1,635, respectively	1,654	1,663
Loans, net:
Construction and land development	17,583	18,931
Commercial and industrial	758,621	763,807
Municipal	104,044	106,599
Commercial real estate	726,440	732,491
Residential real estate	300,941	287,731
Consumer	18,635	18,458
Home equity	260,179	247,345
Overdrafts	704	582
Total loans, net	2,187,147	2,175,944
Less: allowance for loan losses	26,695	26,255
Net loans	2,160,452	2,149,689
Bank premises and equipment	23,220	23,527
Accrued interest receivable	10,844	11,179
Goodwill	2,714	2,714
Other assets	118,470	121,527
Total assets	4,776,682	4,785,572
Deposits:
Demand deposits	715,032	736,020
Savings and NOW deposits	1,409,157	1,367,358
Money market accounts	1,195,785	1,188,228
Time deposits	615,822	625,361
Total deposits	3,935,796	3,916,967
Securities sold under agreements to repurchase	141,560	158,990
Other borrowed funds	317,054	347,778
Subordinated debentures	36,083	36,083
Due to broker	10,011
Other liabilities	67,978	65,457
Total liabilities	4,508,482	4,525,275
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	274,636	263,666
Stockholders' equity before adjustment of accumulated other comprehensive income (loss)	292,496	281,526
Unrealized losses on securities available-for-sale, net of taxes	(32)	(62)
Unrealized losses on securities transferred to held-to-maturity, net of taxes	(3,270)	(3,050)
Pension liability, net of taxes	(20,994)	(18,117)
Total accumulated other comprehensive loss, net of taxes	(24,296)	(21,229)
Total stockholders' equity	268,200	260,297
Total liabilities and stockholders' equity	4,776,682	4,785,572
Class A Common Stock [Member]
Stockholders' Equity
Common stock,Value	3,608	3,606
Total stockholders' equity	3,608	3,606
Class B Common Stock [Member]
Stockholders' Equity
Common stock,Value	1,960	1,962
Total stockholders' equity	$ 1,960	$ 1,962

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Amortized cost	$ 371,013	$ 395,947
Held-to-maturity securities, fair value	1,760,498	1,668,827
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	$ 1,000	$ 1,000
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	3,608,029	3,605,829
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	1,959,880	1,962,080

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest income
Loans	$ 18,267	$ 15,100
Securities held-to-maturity	10,288	9,535
Securities available-for-sale	1,992	1,611
Federal funds sold and interest-bearing deposits in other banks	883	393
Total interest income	31,430	26,639
Interest expense
Savings and NOW deposits	2,223	1,227
Money market accounts	2,453	1,274
Time deposits	2,363	1,651
Securities sold under agreements to repurchase	181	103
Other borrowed funds and subordinated debentures	1,742	1,928
Total interest expense	8,962	6,183
Net interest income	22,468	20,456
Provision for loan losses	450	400
Net interest income after provision for loan losses	22,018	20,056
Other operating income
Service charges on deposit accounts	2,067	2,016
Lockbox fees	791	771
Net gains on sales of securities	197
Gains on sales of mortgage loans		101
Other income	1,138	1,021
Total other operating income	4,193	3,909
Operating expenses
Salaries and employee benefits	11,225	10,794
Occupancy	1,637	1,741
Equipment	794	706
FDIC assessments	383	438
Other	3,962	4,046
Total operating expenses	18,001	17,725
Income before income taxes	8,210	6,240
Provision for income taxes	501	144
Net income	$ 7,709	$ 6,096
Class A Common Stock [Member]
Share data:
Weighted average number of shares outstanding, basic	3,608,029	3,600,729
Weighted average number of shares outstanding, diluted	5,567,909	5,567,909
Basic earnings per share	$ 1.68	$ 1.33
Diluted earnings per share	$ 1.38	$ 1.09
Class B Common Stock [Member]
Share data:
Weighted average number of shares outstanding, basic	1,959,880	1,967,180
Weighted average number of shares outstanding, diluted	1,959,880	1,967,180
Basic earnings per share	$ 0.84	$ 0.66
Diluted earnings per share	$ 0.84	$ 0.66

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 7,709	$ 6,096
Unrealized gains (losses) on securities:
Unrealized (losses) gains arising during period	213	135
Less: reclassification adjustment for gains included in net income	(142)
Total unrealized (losses) gains on securities	71	135
Accretion of net unrealized losses transferred	381	373
Defined benefit pension plans:
Amortization of prior service cost and loss included in net periodic benefit cost	293	232
Other comprehensive income	745	740
Comprehensive income	$ 8,454	$ 6,836

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, 2016	$ 240,041	$ 3,601	$ 1,967	$ 12,292	$ 243,565			$ (21,384)
Net income	6,096				6,096
Other comprehensive income, net of tax:
Unrealized holding (losses) gains arising during period, net of taxes	135							135
Accretion of net unrealized losses transferred during the period, net of taxes	373							373
Pension liability adjustment, net of taxes	232							232
Cash dividends						$ (432)	$ (432)
Ending balance at Mar. 31, 2017	246,328	3,601	1,967	12,292	249,112			(20,644)
Beginning balance at Dec. 31, 2017	260,297	3,606	1,962	12,292	263,666			(21,229)
Net income	7,709				7,709
Other comprehensive income, net of tax:
Unrealized holding (losses) gains arising during period, net of taxes	71							71
Accretion of net unrealized losses transferred during the period, net of taxes	381							381
Pension liability adjustment, net of taxes	293							293
Adoption of ASU 2018-2, Income Statement-Reporting Comprehensive Income (Topic 220) - Reclassification of Certain Tax Effects from AOCI					3,783			(3,783)
Adoption of ASU 2016-1, Financial Instruments - Overall (Subtopic 825-10) Recognition and Measurement of Financial Assets and Financial Liabilities					29			(29)
Conversion of Class B Common Stock to Class A Common Stock		2	(2)
Cash dividends						$ (434)	$ (434)
Ending balance at Mar. 31, 2018	$ 268,200	$ 3,608	$ 1,960	$ 12,292	$ 274,636			$ (24,296)

Consolidated Statements of Cha7

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Unrealized holding (losses) gains arising during period, net of taxes	$ 9	$ 88
Realized net gains	197
Accretion of net unrealized losses transferred during the period, taxes	139	287
Pension liability adjustment, taxes	$ 114	$ 155
Class A Common Stock [Member]
Conversion of Class B Common Stock to Class A Common Stock, shares	2,200
Cash dividends, per share	$ 0.12	$ 0.12
Class B Common Stock [Member]
Conversion of Class B Common Stock to Class A Common Stock, shares	2,200
Cash dividends, per share	$ 0.06	$ 0.06

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 7,709	$ 6,096
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sales of mortgage loans		(101)
Net gains on sales of securities	(197)
Net loss on equity securities	9
Provision for loan losses	450	400
Deferred income taxes	(680)	(1,165)
Net depreciation and amortization	592	887
Decrease (increase) in accrued interest receivable	335	(542)
Decrease (increase) in other assets	3,076	(1,690)
Increase in other liabilities	2,926	2,493
Net cash provided by operating activities	14,220	6,378
Purchase of short-term investments		1,082
Proceeds from redemptions of Federal Home Loan Bank of Boston stock	3,464	714
Purchase of Federal Home Loan Bank of Boston stock	(1,735)
Proceeds from calls/maturities of securities available-for-sale	31,527	41,155
Proceeds from sales of securities available-for-sale	17,871	0
Purchase of securities available-for-sale	(19,336)	(51,606)
Proceeds from calls/maturities of securities held-to-maturity	59,409	62,537
Purchase of securities held-to-maturity	(169,974)	(217,463)
Proceeds from life insurance policies	375
Net increase in loans	(11,198)	(124,327)
Proceeds from sales of portfolio loans		7,899
Capital expenditures	(508)	(897)
Net cash used in investing activities	(90,105)	(280,906)
Net (decrease) increase in time deposits	(9,539)	42,102
Net increase in demand, savings, money market and NOW deposits	28,368	48,142
Cash dividends	(551)	(549)
Net (decrease) increase in securities sold under agreements to repurchase	(17,430)	7,640
Net (decrease) increase in other borrowed funds	(30,724)	8,500
Net cash (used in) provided by financing activities	(29,876)	105,835
Net decrease in cash and cash equivalents	(105,761)	(168,693)
Cash and cash equivalents at beginning of period	356,430	236,151
Cash and cash equivalents at end of period	250,669	67,458
Cash paid during the period for:
Interest	9,008	6,232
Income taxes	225	210
Change in unrealized gains (losses) on securities available-for-sale, net of taxes	71	135
Change in unrealized losses on securities transferred to held-to-maturity, net of taxes	381	373
Pension liability adjustment, net of taxes	293	$ 232
Change in due to (from) to broker	$ 10,011

Basis of Financial Statement Pr

Basis of Financial Statement Presentation	3 Months Ended
	Mar. 31, 2018
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, and New York. As a bank holding company, the Company is subject to the regulation and supervision of 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 Commonwealth of 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 independent appraisals and review of other factors, including historical charge-off

Securities Available-for-Sale

Securities Available-for-Sale	3 Months Ended
	Mar. 31, 2018
Text Block [Abstract]
Securities Available-for-Sale	Note 2. Securities Available-for-Sale March 31, 2018 December 31, 2017 Amortized Gross Gross Fair Value Amortized Gross Gross Fair (in thousands) U.S. Treasury $ 2,000 $ — $ 19 $ 1,981 $ 1,999 $ — $ 15 $ 1,984 U.S. Government Sponsored Enterprises 3,934 — 13 3,921 — — — — SBA Backed Securities 79,118 — 335 78,783 81,065 46 161 80,950 U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities 200,364 668 271 200,761 225,537 556 317 225,776 Privately Issued Residential Mortgage-Backed Securities 823 4 8 819 897 4 9 892 Obligations Issued by States and Political Subdivisions 81,174 — 66 81,108 82,849 — 249 82,600 Other Debt Securities 3,600 46 43 3,603 3,600 68 39 3,629 Total $ 371,013 $ 718 $ 755 $ 370,976 $ 395,947 $ 674 $ 790 $ 395,831 Included in SBA Backed Securities and U.S. Government Sponsored Enterprise 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 $217,340,000 and $216,353,000 at March 31, 2018 and December 31, 2017, respectively. Also included in securities available-for-sale available-for-sale available-for-sales Debt securities of U.S. Government Sponsored Enterprises and 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 $ 72,533 $ 72,531 After one but within five years 96,860 96,793 After five but within ten years 130,698 130,957 More than 10 years 70,922 70,695 Total $ 371,013 $ 370,976 The weighted average remaining life of investment securities available-for-sale As of March 31, 2018 and December 31, 2017, 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 U.S. Treasury, SBA Backed Securities, U.S. Government Sponsored Enterprises, U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities, Privately Issued Residential Mortgage-Backed Securities, Obligations Issued by States and Political Subdivisions, and Other Debt 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. 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. In the case of marketable equity securities, the severity of the unrealized loss, the length of time the unrealized loss has existed, and the issuer’s financial performance are considered. The following table shows the temporarily impaired securities of the Company’s available-for-sale March 31, 2018 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Treasury $ 1,981 $ 19 $ — $ — $ 1,981 $ 19 U.S. Government Sponsored Enterprises 3,921 13 — — 3,921 13 SBA Backed Securities 39,032 112 39,752 223 78,784 335 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 46,317 38 46,305 233 92,622 271 Privately Issued Residential Mortgage-Backed Securities — — 582 8 582 8 Obligations Issued by States and Political Subdivisions — — 4,643 66 4,643 66 Other Debt Securities 400 1 457 42 857 43 Total temporarily impaired securities $ 91,651 $ 183 $ 91,739 $ 572 $ 183,390 $ 755 The following table shows the temporarily impaired securities of the Company’s available-for-sale December 31, 2017 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Treasury $ 1,984 $ 15 $ — $ — $ 1,984 $ 15 U.S. Government Sponsored Enterprises $ — $ — $ — $ — — — SBA Backed Securities 18,378 55 40,911 106 59,289 161 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 40,394 123 59,336 194 99,730 317 Privately Issued Residential Mortgage-Backed Securities — — 633 9 633 9 Obligations Issued by States and Political Subdivisions — — 4,458 249 4,458 249 Other Debt Securities 400 — 461 39 861 39 Total temporarily impaired securities $ 61,156 $ 193 $ 105,799 $ 597 $ 166,955 $ 790

Investment Securities Held-to-M

Investment Securities Held-to-Maturity	3 Months Ended
	Mar. 31, 2018
Text Block [Abstract]
Investment Securities Held-to-Maturity	Note 3. Investment Securities Held-to-Maturity March 31, 2018 December 31, 2017 Amortized Gross Gross Estimated Amortized Gross Gross Estimated (in thousands) U.S. Government Sponsored Enterprises $ 139,780 $ 18 $ 922 $ 138,876 $ 104,653 $ 341 $ 472 $ 104,522 SBA Backed Securities 56,188 — 2,005 54,183 57,235 20 1,271 55,984 U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities 1,621,665 610 54,836 1,567,439 1,539,345 2,261 33,285 1,508,321 Total $ 1,817,633 $ 628 $ 57,763 $ 1,760,498 $ 1,701,233 $ 2,622 $ 35,028 $ 1,668,827 Included in U.S. Government and Agency Securities are securities pledged to secure public deposits and repurchase agreements at fair value amounting to $1,216,741,000 and $1,262,708,000 at March 31, 2018 and December 31, 2017, respectively. Also included are securities pledged for borrowing at the Federal Home Loan Bank of Boston at fair value amounting to $465,541,000 and $382,120,000 at March 31, 2018 and December 31, 2017, respectively. There were no sales of held-to-maturity At March 31, 2018 and December 31, 2017, all mortgage-backed securities are obligations of U.S. Government Agencies and Government Sponsored Enterprises. Debt securities of U.S. Government Sponsored Enterprises and 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 held-to-maturity Amortized Fair (in thousands) Within one year $ 24,860 $ 24,840 After one but within five years 1,184,354 1,150,251 After five but within ten years 605,293 582,422 More than ten years 3,126 2,985 Total $ 1,817,633 $ 1,760,498 The weighted average remaining life of investment securities held-to-maturity As of March 31, 2018 and December 31, 2017, 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 likely 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 Agency and Sponsored Enterprise 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 likely 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 March 31, 2018 and December 31, 2017. 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, 2018 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 $ 84,390 $ 583 $ 14,662 $ 339 $ 99,052 $ 922 SBA Backed Securities 21,384 592 32,798 1,413 54,182 2,005 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 682,644 14,431 815,823 40,405 1,498,467 54,836 Total temporarily impaired securities $ 788,418 $ 15,606 $ 863,283 $ 42,157 $ 1,651,701 $ 57,763 The following table shows the temporarily impaired securities of the Company’s held-to-maturity December 31, 2017 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 $ 15,257 $ 239 $ 14,768 $ 233 $ 30,025 $ 472 SBA Backed Securities 19,457 142 33,750 1,129 53,207 1,271 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 519,481 5,920 814,712 27,365 1,334,193 33,285 Total temporarily impaired securities $ 554,195 $ 6,301 $ 863,230 $ 28,727 $ 1,417,425 $ 35,028

Allowance for Loan Losses

Allowance for Loan Losses	3 Months Ended
	Mar. 31, 2018
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 2018 2017 (in thousands) Allowance for loan losses, beginning of period $ 26,255 $ 24,406 Loans charged off (87 ) (96 ) Recoveries on loans previously charged-off 77 117 Net recoveries (charge-offs) (10 ) 21 Provision charged to expense 450 400 Allowance for loan losses, end of period $ 26,695 $ 24,827 Further information pertaining to the allowance for loan losses for the three months ending March 31, 2018 follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total Allowance for loan losses: (in thousands) Balance at December 31, 2017 $ 1,645 $ 9,651 $ 1,720 $ 9,728 $ 1,873 $ 373 $ 989 $ 276 $ 26,255 Charge-offs — (5 ) — — — (82 ) — — (87 ) Recoveries — 23 — — — 54 — — 77 Provision (207 ) (5 ) — 59 586 (24 ) 78 (37 ) 450 Ending balance at March 31, 2018 $ 1,438 $ 9,664 $ 1,720 $ 9,787 $ 2,459 $ 321 $ 1,067 $ 239 $ 26,695 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 12 $ — $ 94 $ 580 $ — $ — $ — $ 686 Amount of allowance for loan losses for loans not deemed to be impaired $ 1,438 $ 9,652 $ 1,720 $ 9,693 $ 1,879 $ 321 $ 1,067 $ 239 $ 26,009 Loans: Ending balance $ 17,583 $ 758,621 $ 104,044 $ 726,440 $ 300,941 $ 19,339 $ 260,179 $ — $ 2,187,147 Loans deemed to be impaired $ — $ 522 $ — $ 2,528 $ 2,774 $ — $ — $ — $ 5,824 Loans not deemed to be impaired $ 17,583 $ 758,099 $ 104,044 $ 723,912 $ 298,167 $ 19,339 $ 260,179 $ — $ 2,181,323 Further information pertaining to the allowance for loan losses for the three months ending March 31, 2017 follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total Allowance for loan losses: (in thousands) Balance at December 31, 2016 $ 1,012 $ 6,972 $ 1,612 $ 11,135 $ 1,698 $ 582 $ 1,102 $ 293 $ 24,406 Charge-offs — — — — — (96 ) — — (96 ) Recoveries — 19 — — 2 96 — — 117 Provision (139 ) 378 287 81 (29 ) (130 ) (52 ) 4 400 Ending balance at March 31, 2017 $ 873 $ 7,369 $ 1,899 $ 11,216 $ 1,671 $ 452 $ 1,050 $ 297 $ 24,827 Amount of allowance for loan losses for loans deemed to be impaired $ 2 $ 21 $ — $ 130 $ 6 $ — $ — $ — $ 159 Amount of allowance for loan losses for loans not deemed to be impaired $ 871 $ 7,348 $ 1,899 $ 11,086 $ 1,665 $ 452 $ 1,050 $ 297 $ 24,668 Loans: Ending balance $ 10,773 $ 649,326 $ 153,447 $ 732,151 $ 264,442 $ 11,573 $ 218,782 $ — $ 2,040,494 Loans deemed to be impaired $ 93 $ 378 $ — $ 3,123 $ 190 $ — $ — $ — $ 3,784 Loans not deemed to be impaired $ 10,680 $ 648,948 $ 153,447 $ 729,028 $ 264,252 $ 11,573 $ 218,782 $ — $ 2,036,710 The Company utilizes a six grade internal loan rating system for commercial real estate, construction and commercial 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, 2018 and December 31, 2017. 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, 2018 and December 31, 2017. 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, 2018 and December 31, 2017 and are doubtful for full collection. 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, 2018. Construction Commercial Municipal Commercial Grade: (in thousands) 1-3 $ 17,583 $ 752,853 $ 104,044 $ 699,363 4 (Monitor) — 5,246 — 24,549 5 (Substandard) — — — — 6 (Doubtful) — — — — Impaired — 522 — 2,528 Total $ 17,583 $ 758,621 $ 104,044 $ 726,440 The following table presents the Company’s loans by risk rating at December 31, 2017. Construction Commercial Municipal Commercial Grade: (in thousands) 1-3 $ 18,931 $ 758,093 $ 106,599 $ 705,235 4 (Monitor) — 5,366 — 24,702 5 (Substandard) — — — — 6 (Doubtful) — — — — Impaired — 348 — 2,554 Total $ 18,931 $ 763,807 $ 106,599 $ 732,491 The Company has increased its exposure to larger loans to large institutions with publically available credit ratings beginning in 2015. These ratings are tracked as a credit quality indicator for these loans. Credit ratings issued by national organizations were utilized as credit quality indicators as presented in the following table at March 31, 2018 and are included within the total loan portfolio. Commercial Municipal Commercial Total Credit Rating: (in thousands) Aaa – Aa3 $ 477,230 $ 59,024 $ 43,667 $ 579,921 A1 – A3 195,449 7,635 128,211 331,295 Baa1 – Baa3 — 26,970 121,125 148,095 Ba2 — 8,165 — 8,165 Total $ 672,679 $ 101,794 $ 293,003 $ 1,067,476 Credit ratings issued by national organizations were utilized as credit quality indicators as presented in the following table at December 31, 2017. Commercial Municipal Commercial Total Credit Rating: (in thousands) Aaa – Aa3 $ 478,905 $ 62,029 $ 45,066 $ 586,000 A1 – A3 195,599 7,635 128,554 331,788 Baa1 – Baa3 — 26,970 122,000 148,970 Ba2 — 8,165 — 8,165 Total $ 674,504 $ 104,799 $ 295,620 $ 1,074,923 The Company utilized payment performance as credit quality indicators for the loan types listed below. The indicators are depicted in the table “aging of past due loans,” below. Further information pertaining to the allowance for loan losses at March 31, 2018 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 17,583 $ 17,583 Commercial and industrial 242 198 — 440 758,181 758,621 Municipal — — — — 104,044 104,044 Commercial real estate 1,713 211 — 1,924 724,516 726,440 Residential real estate 1,270 186 — 1,456 299,485 300,941 Consumer and overdrafts 8 2 — 10 19,329 19,339 Home equity 704 789 — 1,493 258,686 260,179 Total $ 3,937 $ 1,386 $ — $ 5,323 $ 2,181,824 $ 2,187,147 Further information pertaining to the allowance for loan losses at December 31, 2017 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 18,931 $ 18,931 Commercial and industrial 65 44 — 109 763,698 763,807 Municipal — — — — 106,599 106,599 Commercial real estate 672 215 — 887 731,604 732,491 Residential real estate 4,282 724 — 5,006 282,725 287,731 Consumer and overdrafts 5 6 — 11 19,029 19,040 Home equity 618 695 — 1,313 246,032 247,345 Total $ 5,642 $ 1,684 $ — $ 7,326 $ 2,168,618 $ 2,175,944 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, 2018: Carrying Unpaid Required Average Interest With no required reserve recorded: (in thousands) Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 27 214 — 49 — Municipal — — — — — Commercial real estate 210 231 — 265 — Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 237 $ 445 $ — $ 314 $ — With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 495 511 12 388 5 Municipal — — — — — Commercial real estate 2,318 2,430 94 2,278 23 Residential real estate 2,774 2,774 580 3,827 6 Consumer — — — — — Home equity — — — — — Total $ 5,587 $ 5,715 $ 686 $ 6,493 $ 34 Total: Construction and land development $ — $ — $ — $ —2 $ — Commercial and industrial 522 725 12 437 5 Municipal — — — — — Commercial real estate 2,528 2,661 94 2,543 23 Residential real estate 2,774 2,774 580 3,827 6 Consumer — — — — — Home equity — — — — — Total $ 5,824 $ 6,160 $ 686 $ 6,807 $ 34 The following is information pertaining to impaired loans for March 31, 2017: Carrying Unpaid Required Average Interest With no required reserve recorded: (in thousands) Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 41 229 — 43 — Municipal — — — — — Commercial real estate 588 588 — 589 9 Residential real estate 84 174 — 87 2 Consumer — — — — — Home equity — — — — — Total $ 713 $ 991 $ — $ 719 $ 11 With required reserve recorded: Construction and land development $ 93 $ 108 $ 2 $ 93 $ — Commercial and industrial 337 352 21 339 4 Municipal — — — — — Commercial real estate 2,535 2,642 130 2,548 23 Residential real estate 106 106 6 107 1 Consumer — — — — — Home equity — — — — — Total $ 3,071 $ 3,208 $ 159 $ 3,087 $ 28 Total: Construction and land development $ 93 $ 108 $ 2 $ 93 $ — Commercial and industrial 378 581 21 382 4 Municipal — — — — — Commercial real estate 3,123 3,230 130 3,137 32 Residential real estate 190 280 6 194 3 Consumer — — — — — Home equity — — — — — Total $ 3,784 $ 4,199 $ 159 $ 3,806 $ 39 Troubled Debt Restructurings are identified as a modification 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 modification did not result in an increase in the allowance for these loans beyond any previously established allocations. There was one residential real estate loan and one consumer loan that were modified during the first quarter of 2018. The loans were modified by reducing the interest rates as well as extending the terms on both loans. The pre-modification pre-modification There was no troubled debt restructuring that occurred during the three month period ended March 31, 2017. Also, there were no commitments to lend additional funds to troubled debt restructuring borrowers. There were no troubled debt restructurings that subsequently defaulted during the first three months of 2017 and 2018.

Reclassifications Out of Accumu

Reclassifications Out of Accumulated Other Comprehensive Income	3 Months Ended
	Mar. 31, 2018
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 Months Ended March 31, 2018 Three Months Ended March 31, 2017 Affected Line Item in the Statement where Net Income is Presented (in thousands) Unrealized gains and losses onavailable-for-sale $ 197 $ — Net gains on sales of investments (55 ) — Provision for income taxes $ 142 $ — Net income Accretion of unrealized losses transferred $ (520 ) $ (662 ) Interest on securities held-to-maturity 139 289 Provision for income taxes $ (381 ) $ (373 ) Net income Amortization of defined benefit pension items Prior-service costs $ (4 ) $ (3 )(b) Salaries and employee benefits Actuarial gains (losses) (403 ) (384 )(b) Salaries and employee benefits Total before tax (407 ) (387 ) Income before taxes Tax (expense) or benefit 114 155 Provision for income taxes Net of tax $ (293 ) $ (232 ) 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, 2018
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; basic EPS excludes all common stock equivalents. The Company had no common stock equivalents outstanding for the periods ended March 31, 2018 and 2017. The following table is a reconciliation of basic EPS and diluted EPS. Three Months Ended (in thousands except share and per share data) 2018 2017 Basic EPS Computation: Numerator: Net income, Class A $ 6,062 $ 4,788 Net income, Class B 1,647 1,308 Denominator: Weighted average shares outstanding, Class A 3,608,029 3,600,729 Weighted average shares outstanding, Class B 1,959,880 1,967,180 Basic EPS, Class A $ 1.68 $ 1.33 Basic EPS, Class B 0.84 0.66 Diluted EPS Computation: Numerator: Net income, Class A $ 6,062 $ 4,788 Net income, Class B 1,647 1,308 Total net income, for diluted EPS, Class A computation 7,709 6,096 Denominator: Weighted average shares outstanding, basic, Class A 3,608,029 3,600,729 Weighted average shares outstanding, Class B 1,959,880 1,967,180 Weighted average shares outstanding diluted, Class A 5,567,909 5,567,909 Weighted average shares outstanding, Class B 1,959,880 1,967,180 Diluted EPS, Class A $ 1.38 $ 1.09 Diluted EPS, Class B 0.84 0.66

Employee Benefits

Employee Benefits	3 Months Ended
	Mar. 31, 2018
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 a Supplemental Executive Insurance/Retirement 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, Defined Benefit Supplemental Insurance/ 2018 2017 2018 2017 (in thousands) Service cost $ 353 $ 310 $ 277 $ 395 Interest 370 362 346 345 Expected return on plan assets (954 ) (746 ) — — Recognized prior service cost (benefit) (25 ) (26 ) 29 29 Recognized net actuarial losses 227 226 176 159 Net periodic benefit (credit) cost $ (29 ) $ 126 $ 828 $ 928 As a result of the adoption of ASU 2017-07, Contributions The Company does not intend to contribute to the Defined Benefit Pension Plan in 2018.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 8. Fair Value Measurements The Company follows FASB ASC 820-10, Fair Value Measurements and Disclosures 2016-1, 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 non-investment The results of the fair value hierarchy as of March 31, 2018, are as follows: Financial Instruments Measured at Fair Value on a Recurring Basis: Securities AFS Fair Value Measurements Using Carrying Quoted Prices Significant Significant (in thousands) U.S. Treasury $ 1,981 $ — $ 1,981 $ — U.S. Government Sponsored Enterprises 3,921 — 3,921 — SBA Backed Securities 78,783 — 78,783 — U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities 200,761 — 200,761 — Privately Issued Residential Mortgage-Backed Securities 819 — 819 — Obligations Issued by States and Political Subdivisions 81,108 — 4,643 76,465 Other Debt Securities 3,603 — 3,603 — Total $ 370,976 $ — $ 294,511 $ 76,465 Financial Instruments Measured at Fair Value on a Non-recurring Impaired Loans $ 3,084 $ — $ — $ 3,084 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. Within the past twelve months there have been no updated appraisals, however, 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) relate to impaired loans recognized for the three month period ended March 31, 2018 amounted to $581,000. 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). Management continues to monitor the assumptions used to value the assets listed below. Asset Fair Value Valuation Technique Unobservable Input Unobservable Input Value or Range Securities AFS (4) $ 76,465 Discounted cash flow Discount rate 1.6%-4.4% (3) Impaired Loans $ 3,084 Appraisal of collateral (1) Appraisal adjustments (2) 0%-30% discount (1) Fair value is generally determined through independent appraisals of the underlying collateral, which generally include various Level 3 inputs which are not identifiable. (2) Appraisals may be adjusted by management for qualitative factors such as economic conditions and estimated expenses. (3) Weighted averages. (4) Municipal securities generally have maturities of one year or less and, therefore, the amortized cost equates to the fair value. There was one auction rate security whose fair value is based on the evaluation of the underlying issuer, prevailing interest rates and market liquidity. The changes in Level 3 securities for the three month period ended March 31, 2018 are shown in the table below: Auction Rate Obligations Equity Total (in thousands) Balance at December 31, 2017 $ 4,459 $ 78,141 $ — $ 82,600 Purchases — 20,416 — 20,416 Maturities and calls — (22,068 ) — (22,068 ) Transfer (4,459 ) — — (4,459 ) Amortization — (24 ) — (24 ) Changes in fair value — — — — Balance at March 31, 2018 $ — $ 76,465 $ — $ 76,465 The amortized cost of Level 3 securities was $76,465,000 at March 31, 2018 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. There was one transfer of a security from level 3 to level 2 for the three months ended March 31, 2018 as a result of increased trading activity and quoted market prices. There were no liabilities measured at fair value on a recurring or nonrecurring basis during the three month period ended March 31, 2018. The changes in Level 3 securities for the three month period ended March 31, 2017, are shown in the table below: Auction Rate Obligations Equity Total (in thousands) Balance at December 31, 2016 $ 4,298 $ 160,578 $ — $ 164,876 Purchases — 23,088 — 23,088 Maturities and calls — (24,565 ) — (24,565 ) Amortization — (62 ) — (62 ) Changes in fair value — — — — Balance at March 31, 2017 $ 4,298 $ 159,039 $ — $ 163,337 The amortized cost of Level 3 securities was $163,742,000 at March 31, 2017 with an unrealized loss of $405,000. The securities in this category are generally equity investments, municipal securities with no readily determinable fair value or failed auction rate securities. Management evaluated the fair value of these securities based on an evaluation of the underlying issuer, prevailing rates and market liquidity. The results of the fair value hierarchy as of December 31, 2017, are as follows: Financial Instruments Measured at Fair Value on a Recurring Basis: Securities AFS Fair Value Measurements Using Carrying Quoted Prices Significant Significant (in thousands) U.S. Treasury $ 1,984 $ — $ 1,984 $ — U.S. Government Sponsored Enterprises — — — — SBA Backed Securities 80,950 — 80,950 — U.S. Government Agency and Sponsored Mortgage-Backed Securities 225,776 — 225,776 — Privately Issued Residential Mortgage-Backed Securities 892 — 892 — Obligations Issued by States and Political Subdivisions 82,600 — — 82,600 Other Debt Securities 3,629 — 3,629 — Total $ 395,831 $ — $ 313,231 $ 82,600 Financial Instruments Measured at Fair Value on a Non-recurring Impaired Loans $ 246 $ — $ — $ 246 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 identifiable. 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. Within the past twelve months there have been no updated appraisals, however, 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) relate to impaired loans recognized for 2017 for the estimated credit loss amounted to $3,000. There were no transfers between level 1, 2 and 3 for the year ended December 31, 2017. There were no liabilities measured at fair value on a recurring or nonrecurring basis during the year ended December 31, 2017. 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). Management continues to monitor the assumptions used to value the assets listed below. Asset Fair Value Valuation Technique Unobservable Input Unobservable Input Value or Range Securities AFS (4) $ 82,600 Discounted cash flow Discount rate 1.0%-3.5% (3) Impaired Loans $ 246 Appraisal of collateral (1) Appraisal adjustments (2) 0%-30% discount (1) Fair value is generally determined through independent appraisals of the underlying collateral, which generally include various Level 3 inputs which are not identifiable. (2) Appraisals may be adjusted by management for qualitative factors such as economic conditions and estimated expenses. (3) Weighted averages (4) Municipal securities generally have maturities of one year or less and, therefore, the amortized cost equates to the fair value. There was one auction rate security whose fair value is based on the evaluation of the underlying issuer, prevailing interest rates and market liquidity.

Fair Values of Financial Instru

Fair Values of Financial Instruments	3 Months Ended
	Mar. 31, 2018
Investments, All Other Investments [Abstract]
Fair Values of Financial Instruments	Note 9. Fair Values of Financial Instruments The following methods were used by the Company in estimating fair values of its financial instruments. Excluded from this disclosure are all nonfinancial instruments. Accordingly, the aggregate fair value amounts presented do not represent the underlying value of the Company. 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. The fair value of loans is estimated using the exit price notion consistent with Topic 820, Fair Value Measurement. 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, 2018 and December 31, 2017. This table excludes financial instruments for which the carrying amount approximates fair value as these assets and liabilities that are due within one year. 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, 2018 Carrying Estimated Fair Value Level 2 Level 3 (in thousands) Financial assets: Securities held-to-maturity $ 1,817,633 $ 1,760,498 $ — $ 1,760,498 $ — Loans (1) 2,160,452 2,106,013 — — 2,106,013 Financial liabilities: Time deposits 615,822 613,788 — 613,788 — Other borrowed funds 317,054 315,791 — 315,791 — Subordinated debentures 36,083 36,083 — — 36,083 December 31, 2017 Financial assets: Securities held-to-maturity $ 1,701,233 $ 1,668,827 $ — $ 1,668,827 $ — Loans (1) 2,149,689 2,094,517 — — 2,094,517 Financial liabilities: Time deposits 625,361 627,517 — 627,517 — Other borrowed funds 347,778 349,364 — 349,364 — 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 loan losses.

Recent Accounting Developments

Recent Accounting Developments	3 Months Ended
	Mar. 31, 2018
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Developments	Note 10. Recent Accounting Developments Recently Adopted Accounting Standards Updates Effective January 1, 2018, the following new accounting guidance was adopted by the Company: In February 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-03, 825-10) 2016-1. In February 2018, the FASB issued Accounting Standards Update (“ASU”) 2018-02, In May 2017, the FASB issued ASU 2017-09, In March 2017, the FASB issued ASU 2017-07, In February 2017, the FASB issued ASU 2017-05, 610-20). 610-20, Effective January 1, 2018, the Company adopted ASU 2014-09 2014-09 The vast majority of the Company’s revenue is interest income on loans, investment securities and deposits at other financial institutions which are specifically outside the scope of ASU 2014-09. 2014-09 non-interest In November 2016, the FASB issued ASU 2016-18, Restricted Cash. beginning-of-period end-of-period In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments. In January 2016, FASB issued ASU 2016-1, 825-10) Recognition and Measurement of Financial Assets and Financial Liabilities. Accounting Standards Issued but not yet Adopted The following list identifies ASUs applicable to the Company that have been issued by the FASB but are not yet effective: In July 2017, FASB issued ASU 2017-11, 2017-11 In March 2017, the FASB issued ASU 2017-08, 310-20) In January 2017, the FASB issued ASU 2017-04, In June 2016, the FASB issued ASU 2016-13, In February 2016, the FASB issued ASU 2016-02,

Revenue from Contracts with Cus

Revenue from Contracts with Customers	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Customers	Note 11. 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. Change in accounting policy The Company adopted Topic 606 Revenue from Contracts with Customers The Company applied Topic 606 using the cumulative effect method. Therefore, the comparative information has not been adjusted and continues to be reported under Topic 605. There was no cumulative effect adjustment as of January 1, 2018, and there were no material changes to the financial statements at or for the three months ended March 31, 2018 as a result of adopting Topic 606. B. Practical Expedients The Company applies the practical expedient in paragraph 606-10-50-14 The Company applies the practical expedient in paragraph 606-10-32-18 C. 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, NSF fees, credit and debit card interchange fees and foreign exchange transaction fees. Revenue is generally derived from transactional information accumulated by our systems and is recognized as revenue immediately as the transactions occur or upon providing the service to complete the customer’s transaction. The Company is the principal in each of these contracts, with the exception of credit and debit card interchange fees, in which case we are acting as the agent and record revenue net of expenses paid to the principal. 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. D. 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 March 31, 2018 Revenue from Three Months Revenue from (dollars in thousands) Total interest income $ 22,468 $ — $ 20,456 $ — Noninterest income: Service charges on deposit accounts 2,067 2,067 2,016 2,016 Lockbox fees 791 791 771 771 Net gains on sales of securities 197 — — — Gains on sales of mortgage loans — — 101 — Other income 1,138 719 1,021 603 Total noninterest income 4,193 3,577 3,909 3,390 Total revenues $ 26,661 $ 3,577 $ 24,365 $ 3,390 March 31, December 31, (dollars in thousands) Receivables, which are included in “Other assets” $ 1,161 $ 1,009

Recent Accounting Developments

Recent Accounting Developments (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Developments	Recent Accounting Developments Recently Adopted Accounting Standards Updates Effective January 1, 2018, the following new accounting guidance was adopted by the Company: In February 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-03, 825-10) 2016-1. In February 2018, the FASB issued Accounting Standards Update (“ASU”) 2018-02, In May 2017, the FASB issued ASU 2017-09, In March 2017, the FASB issued ASU 2017-07, In February 2017, the FASB issued ASU 2017-05, 610-20). 610-20, Effective January 1, 2018, the Company adopted ASU 2014-09 2014-09 The vast majority of the Company’s revenue is interest income on loans, investment securities and deposits at other financial institutions which are specifically outside the scope of ASU 2014-09. 2014-09 non-interest In November 2016, the FASB issued ASU 2016-18, Restricted Cash. beginning-of-period end-of-period In August 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments. In January 2016, FASB issued ASU 2016-1, 825-10) Recognition and Measurement of Financial Assets and Financial Liabilities. Accounting Standards Issued but not yet Adopted The following list identifies ASUs applicable to the Company that have been issued by the FASB but are not yet effective: In July 2017, FASB issued ASU 2017-11, 2017-11 In March 2017, the FASB issued ASU 2017-08, 310-20) In January 2017, the FASB issued ASU 2017-04, In June 2016, the FASB issued ASU 2016-13, In February 2016, the FASB issued ASU 2016-02,

Securities Available-for-Sale (

Securities Available-for-Sale (Tables)	3 Months Ended
	Mar. 31, 2018
Text Block [Abstract]
Summary of Securities Available-for-Sale	March 31, 2018 December 31, 2017 Amortized Gross Gross Fair Value Amortized Gross Gross Fair (in thousands) U.S. Treasury $ 2,000 $ — $ 19 $ 1,981 $ 1,999 $ — $ 15 $ 1,984 U.S. Government Sponsored Enterprises 3,934 — 13 3,921 — — — — SBA Backed Securities 79,118 — 335 78,783 81,065 46 161 80,950 U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities 200,364 668 271 200,761 225,537 556 317 225,776 Privately Issued Residential Mortgage-Backed Securities 823 4 8 819 897 4 9 892 Obligations Issued by States and Political Subdivisions 81,174 — 66 81,108 82,849 — 249 82,600 Other Debt Securities 3,600 46 43 3,603 3,600 68 39 3,629 Total $ 371,013 $ 718 $ 755 $ 370,976 $ 395,947 $ 674 $ 790 $ 395,831
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 $ 72,533 $ 72,531 After one but within five years 96,860 96,793 After five but within ten years 130,698 130,957 More than 10 years 70,922 70,695 Total $ 371,013 $ 370,976
Continuous Unrealized Loss Position for Less than 12 Months and 12 Months or Longer	The following table shows the temporarily impaired securities of the Company’s available-for-sale March 31, 2018 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Treasury $ 1,981 $ 19 $ — $ — $ 1,981 $ 19 U.S. Government Sponsored Enterprises 3,921 13 — — 3,921 13 SBA Backed Securities 39,032 112 39,752 223 78,784 335 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 46,317 38 46,305 233 92,622 271 Privately Issued Residential Mortgage-Backed Securities — — 582 8 582 8 Obligations Issued by States and Political Subdivisions — — 4,643 66 4,643 66 Other Debt Securities 400 1 457 42 857 43 Total temporarily impaired securities $ 91,651 $ 183 $ 91,739 $ 572 $ 183,390 $ 755 The following table shows the temporarily impaired securities of the Company’s available-for-sale December 31, 2017 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Treasury $ 1,984 $ 15 $ — $ — $ 1,984 $ 15 U.S. Government Sponsored Enterprises $ — $ — $ — $ — — — SBA Backed Securities 18,378 55 40,911 106 59,289 161 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 40,394 123 59,336 194 99,730 317 Privately Issued Residential Mortgage-Backed Securities — — 633 9 633 9 Obligations Issued by States and Political Subdivisions — — 4,458 249 4,458 249 Other Debt Securities 400 — 461 39 861 39 Total temporarily impaired securities $ 61,156 $ 193 $ 105,799 $ 597 $ 166,955 $ 790

Investment Securities Held-to22

Investment Securities Held-to-Maturity (Tables)	3 Months Ended
	Mar. 31, 2018
Text Block [Abstract]
Summary of Held-to-Maturity Securities	March 31, 2018 December 31, 2017 Amortized Gross Gross Estimated Amortized Gross Gross Estimated (in thousands) U.S. Government Sponsored Enterprises $ 139,780 $ 18 $ 922 $ 138,876 $ 104,653 $ 341 $ 472 $ 104,522 SBA Backed Securities 56,188 — 2,005 54,183 57,235 20 1,271 55,984 U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities 1,621,665 610 54,836 1,567,439 1,539,345 2,261 33,285 1,508,321 Total $ 1,817,633 $ 628 $ 57,763 $ 1,760,498 $ 1,701,233 $ 2,622 $ 35,028 $ 1,668,827
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 $ 24,860 $ 24,840 After one but within five years 1,184,354 1,150,251 After five but within ten years 605,293 582,422 More than ten years 3,126 2,985 Total $ 1,817,633 $ 1,760,498
Unrealized Market Loss of Securities	The following table shows the temporarily impaired securities of the Company’s held-to-maturity March 31, 2018 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 $ 84,390 $ 583 $ 14,662 $ 339 $ 99,052 $ 922 SBA Backed Securities 21,384 592 32,798 1,413 54,182 2,005 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 682,644 14,431 815,823 40,405 1,498,467 54,836 Total temporarily impaired securities $ 788,418 $ 15,606 $ 863,283 $ 42,157 $ 1,651,701 $ 57,763 The following table shows the temporarily impaired securities of the Company’s held-to-maturity December 31, 2017 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 $ 15,257 $ 239 $ 14,768 $ 233 $ 30,025 $ 472 SBA Backed Securities 19,457 142 33,750 1,129 53,207 1,271 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 519,481 5,920 814,712 27,365 1,334,193 33,285 Total temporarily impaired securities $ 554,195 $ 6,301 $ 863,230 $ 28,727 $ 1,417,425 $ 35,028

Allowance for Loan Losses (Tabl

Allowance for Loan Losses (Tables)	3 Months Ended
	Mar. 31, 2018
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 2018 2017 (in thousands) Allowance for loan losses, beginning of period $ 26,255 $ 24,406 Loans charged off (87 ) (96 ) Recoveries on loans previously charged-off 77 117 Net recoveries (charge-offs) (10 ) 21 Provision charged to expense 450 400 Allowance for loan losses, end of period $ 26,695 $ 24,827
Summary of Allowance for Loan Losses	Further information pertaining to the allowance for loan losses for the three months ending March 31, 2018 follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total Allowance for loan losses: (in thousands) Balance at December 31, 2017 $ 1,645 $ 9,651 $ 1,720 $ 9,728 $ 1,873 $ 373 $ 989 $ 276 $ 26,255 Charge-offs — (5 ) — — — (82 ) — — (87 ) Recoveries — 23 — — — 54 — — 77 Provision (207 ) (5 ) — 59 586 (24 ) 78 (37 ) 450 Ending balance at March 31, 2018 $ 1,438 $ 9,664 $ 1,720 $ 9,787 $ 2,459 $ 321 $ 1,067 $ 239 $ 26,695 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 12 $ — $ 94 $ 580 $ — $ — $ — $ 686 Amount of allowance for loan losses for loans not deemed to be impaired $ 1,438 $ 9,652 $ 1,720 $ 9,693 $ 1,879 $ 321 $ 1,067 $ 239 $ 26,009 Loans: Ending balance $ 17,583 $ 758,621 $ 104,044 $ 726,440 $ 300,941 $ 19,339 $ 260,179 $ — $ 2,187,147 Loans deemed to be impaired $ — $ 522 $ — $ 2,528 $ 2,774 $ — $ — $ — $ 5,824 Loans not deemed to be impaired $ 17,583 $ 758,099 $ 104,044 $ 723,912 $ 298,167 $ 19,339 $ 260,179 $ — $ 2,181,323 Further information pertaining to the allowance for loan losses for the three months ending March 31, 2017 follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total Allowance for loan losses: (in thousands) Balance at December 31, 2016 $ 1,012 $ 6,972 $ 1,612 $ 11,135 $ 1,698 $ 582 $ 1,102 $ 293 $ 24,406 Charge-offs — — — — — (96 ) — — (96 ) Recoveries — 19 — — 2 96 — — 117 Provision (139 ) 378 287 81 (29 ) (130 ) (52 ) 4 400 Ending balance at March 31, 2017 $ 873 $ 7,369 $ 1,899 $ 11,216 $ 1,671 $ 452 $ 1,050 $ 297 $ 24,827 Amount of allowance for loan losses for loans deemed to be impaired $ 2 $ 21 $ — $ 130 $ 6 $ — $ — $ — $ 159 Amount of allowance for loan losses for loans not deemed to be impaired $ 871 $ 7,348 $ 1,899 $ 11,086 $ 1,665 $ 452 $ 1,050 $ 297 $ 24,668 Loans: Ending balance $ 10,773 $ 649,326 $ 153,447 $ 732,151 $ 264,442 $ 11,573 $ 218,782 $ — $ 2,040,494 Loans deemed to be impaired $ 93 $ 378 $ — $ 3,123 $ 190 $ — $ — $ — $ 3,784 Loans not deemed to be impaired $ 10,680 $ 648,948 $ 153,447 $ 729,028 $ 264,252 $ 11,573 $ 218,782 $ — $ 2,036,710
Loans by Risk Rating	The following table presents the Company’s loans by risk rating at March 31, 2018. Construction Commercial Municipal Commercial Grade: (in thousands) 1-3 $ 17,583 $ 752,853 $ 104,044 $ 699,363 4 (Monitor) — 5,246 — 24,549 5 (Substandard) — — — — 6 (Doubtful) — — — — Impaired — 522 — 2,528 Total $ 17,583 $ 758,621 $ 104,044 $ 726,440 The following table presents the Company’s loans by risk rating at December 31, 2017. Construction Commercial Municipal Commercial Grade: (in thousands) 1-3 $ 18,931 $ 758,093 $ 106,599 $ 705,235 4 (Monitor) — 5,366 — 24,702 5 (Substandard) — — — — 6 (Doubtful) — — — — Impaired — 348 — 2,554 Total $ 18,931 $ 763,807 $ 106,599 $ 732,491
Loans by Credit Rating	the following table at March 31, 2018 and are included within the total loan portfolio. Commercial Municipal Commercial Total Credit Rating: (in thousands) Aaa – Aa3 $ 477,230 $ 59,024 $ 43,667 $ 579,921 A1 – A3 195,449 7,635 128,211 331,295 Baa1 – Baa3 — 26,970 121,125 148,095 Ba2 — 8,165 — 8,165 Total $ 672,679 $ 101,794 $ 293,003 $ 1,067,476 Credit ratings issued by national organizations were utilized as credit quality indicators as presented in the following table at December 31, 2017. Commercial Municipal Commercial Total Credit Rating: (in thousands) Aaa – Aa3 $ 478,905 $ 62,029 $ 45,066 $ 586,000 A1 – A3 195,599 7,635 128,554 331,788 Baa1 – Baa3 — 26,970 122,000 148,970 Ba2 — 8,165 — 8,165 Total $ 674,504 $ 104,799 $ 295,620 $ 1,074,923
Aging of Past Due Loan Losses	Further information pertaining to the allowance for loan losses at March 31, 2018 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 17,583 $ 17,583 Commercial and industrial 242 198 — 440 758,181 758,621 Municipal — — — — 104,044 104,044 Commercial real estate 1,713 211 — 1,924 724,516 726,440 Residential real estate 1,270 186 — 1,456 299,485 300,941 Consumer and overdrafts 8 2 — 10 19,329 19,339 Home equity 704 789 — 1,493 258,686 260,179 Total $ 3,937 $ 1,386 $ — $ 5,323 $ 2,181,824 $ 2,187,147 Further information pertaining to the allowance for loan losses at December 31, 2017 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 18,931 $ 18,931 Commercial and industrial 65 44 — 109 763,698 763,807 Municipal — — — — 106,599 106,599 Commercial real estate 672 215 — 887 731,604 732,491 Residential real estate 4,282 724 — 5,006 282,725 287,731 Consumer and overdrafts 5 6 — 11 19,029 19,040 Home equity 618 695 — 1,313 246,032 247,345 Total $ 5,642 $ 1,684 $ — $ 7,326 $ 2,168,618 $ 2,175,944
Information Pertaining to Impaired Loans	The following is information pertaining to impaired loans for March 31, 2018: Carrying Unpaid Required Average Interest With no required reserve recorded: (in thousands) Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 27 214 — 49 — Municipal — — — — — Commercial real estate 210 231 — 265 — Residential real estate — — — — — Consumer — — — — — Home equity — — — — — Total $ 237 $ 445 $ — $ 314 $ — With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 495 511 12 388 5 Municipal — — — — — Commercial real estate 2,318 2,430 94 2,278 23 Residential real estate 2,774 2,774 580 3,827 6 Consumer — — — — — Home equity — — — — — Total $ 5,587 $ 5,715 $ 686 $ 6,493 $ 34 Total: Construction and land development $ — $ — $ — $ —2 $ — Commercial and industrial 522 725 12 437 5 Municipal — — — — — Commercial real estate 2,528 2,661 94 2,543 23 Residential real estate 2,774 2,774 580 3,827 6 Consumer — — — — — Home equity — — — — — Total $ 5,824 $ 6,160 $ 686 $ 6,807 $ 34 The following is information pertaining to impaired loans for March 31, 2017: Carrying Unpaid Required Average Interest With no required reserve recorded: (in thousands) Construction and land development $ — $ — $ — $ — $ — Commercial and industrial 41 229 — 43 — Municipal — — — — — Commercial real estate 588 588 — 589 9 Residential real estate 84 174 — 87 2 Consumer — — — — — Home equity — — — — — Total $ 713 $ 991 $ — $ 719 $ 11 With required reserve recorded: Construction and land development $ 93 $ 108 $ 2 $ 93 $ — Commercial and industrial 337 352 21 339 4 Municipal — — — — — Commercial real estate 2,535 2,642 130 2,548 23 Residential real estate 106 106 6 107 1 Consumer — — — — — Home equity — — — — — Total $ 3,071 $ 3,208 $ 159 $ 3,087 $ 28 Total: Construction and land development $ 93 $ 108 $ 2 $ 93 $ — Commercial and industrial 378 581 21 382 4 Municipal — — — — — Commercial real estate 3,123 3,230 130 3,137 32 Residential real estate 190 280 6 194 3 Consumer — — — — — Home equity — — — — — Total $ 3,784 $ 4,199 $ 159 $ 3,806 $ 39

Reclassifications Out of Accu24

Reclassifications Out of Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2018
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 Months Ended March 31, 2018 Three Months Ended March 31, 2017 Affected Line Item in the Statement where Net Income is Presented (in thousands) Unrealized gains and losses onavailable-for-sale $ 197 $ — Net gains on sales of investments (55 ) — Provision for income taxes $ 142 $ — Net income Accretion of unrealized losses transferred $ (520 ) $ (662 ) Interest on securities held-to-maturity 139 289 Provision for income taxes $ (381 ) $ (373 ) Net income Amortization of defined benefit pension items Prior-service costs $ (4 ) $ (3 )(b) Salaries and employee benefits Actuarial gains (losses) (403 ) (384 )(b) Salaries and employee benefits Total before tax (407 ) (387 ) Income before taxes Tax (expense) or benefit 114 155 Provision for income taxes Net of tax $ (293 ) $ (232 ) 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") (Tab

Earnings per Share ("EPS") (Tables)	3 Months Ended
	Mar. 31, 2018
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) 2018 2017 Basic EPS Computation: Numerator: Net income, Class A $ 6,062 $ 4,788 Net income, Class B 1,647 1,308 Denominator: Weighted average shares outstanding, Class A 3,608,029 3,600,729 Weighted average shares outstanding, Class B 1,959,880 1,967,180 Basic EPS, Class A $ 1.68 $ 1.33 Basic EPS, Class B 0.84 0.66 Diluted EPS Computation: Numerator: Net income, Class A $ 6,062 $ 4,788 Net income, Class B 1,647 1,308 Total net income, for diluted EPS, Class A computation 7,709 6,096 Denominator: Weighted average shares outstanding, basic, Class A 3,608,029 3,600,729 Weighted average shares outstanding, Class B 1,959,880 1,967,180 Weighted average shares outstanding diluted, Class A 5,567,909 5,567,909 Weighted average shares outstanding, Class B 1,959,880 1,967,180 Diluted EPS, Class A $ 1.38 $ 1.09 Diluted EPS, Class B 0.84 0.66

Employee Benefits (Tables)

Employee Benefits (Tables)	3 Months Ended
	Mar. 31, 2018
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost	Defined Benefit Supplemental Insurance/ 2018 2017 2018 2017 (in thousands) Service cost $ 353 $ 310 $ 277 $ 395 Interest 370 362 346 345 Expected return on plan assets (954 ) (746 ) — — Recognized prior service cost (benefit) (25 ) (26 ) 29 29 Recognized net actuarial losses 227 226 176 159 Net periodic benefit (credit) cost $ (29 ) $ 126 $ 828 $ 928

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
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, 2018, are as follows: Financial Instruments Measured at Fair Value on a Recurring Basis: Securities AFS Fair Value Measurements Using Carrying Quoted Prices Significant Significant (in thousands) U.S. Treasury $ 1,981 $ — $ 1,981 $ — U.S. Government Sponsored Enterprises 3,921 — 3,921 — SBA Backed Securities 78,783 — 78,783 — U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities 200,761 — 200,761 — Privately Issued Residential Mortgage-Backed Securities 819 — 819 — Obligations Issued by States and Political Subdivisions 81,108 — 4,643 76,465 Other Debt Securities 3,603 — 3,603 — Total $ 370,976 $ — $ 294,511 $ 76,465 Financial Instruments Measured at Fair Value on a Non-recurring Impaired Loans $ 3,084 $ — $ — $ 3,084 The results of the fair value hierarchy as of December 31, 2017, are as follows: Financial Instruments Measured at Fair Value on a Recurring Basis: Securities AFS Fair Value Measurements Using Carrying Quoted Prices Significant Significant (in thousands) U.S. Treasury $ 1,984 $ — $ 1,984 $ — U.S. Government Sponsored Enterprises — — — — SBA Backed Securities 80,950 — 80,950 — U.S. Government Agency and Sponsored Mortgage-Backed Securities 225,776 — 225,776 — Privately Issued Residential Mortgage-Backed Securities 892 — 892 — Obligations Issued by States and Political Subdivisions 82,600 — — 82,600 Other Debt Securities 3,629 — 3,629 — Total $ 395,831 $ — $ 313,231 $ 82,600 Financial Instruments Measured at Fair Value on a Non-recurring Impaired Loans $ 246 $ — $ — $ 246
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). Management continues to monitor the assumptions used to value the assets listed below. Asset Fair Value Valuation Technique Unobservable Input Unobservable Input Value or Range Securities AFS (4) $ 76,465 Discounted cash flow Discount rate 1.6%-4.4% (3) Impaired Loans $ 3,084 Appraisal of collateral (1) Appraisal adjustments (2) 0%-30% discount (1) Fair value is generally determined through independent appraisals of the underlying collateral, which generally include various Level 3 inputs which are not identifiable. (2) Appraisals may be adjusted by management for qualitative factors such as economic conditions and estimated expenses. (3) Weighted averages. (4) Municipal securities generally have maturities of one year or less and, therefore, the amortized cost equates to the fair value. There was one auction rate security whose fair value is based on the evaluation of the underlying issuer, prevailing interest rates and market liquidity. 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). Management continues to monitor the assumptions used to value the assets listed below. Asset Fair Value Valuation Technique Unobservable Input Unobservable Input Value or Range Securities AFS (4) $ 82,600 Discounted cash flow Discount rate 1.0%-3.5% (3) Impaired Loans $ 246 Appraisal of collateral (1) Appraisal adjustments (2) 0%-30% discount (1) Fair value is generally determined through independent appraisals of the underlying collateral, which generally include various Level 3 inputs which are not identifiable. (2) Appraisals may be adjusted by management for qualitative factors such as economic conditions and estimated expenses. (3) Weighted averages (4) Municipal securities generally have maturities of one year or less and, therefore, the amortized cost equates to the fair value. There was one auction rate security whose fair value is based on the evaluation of the underlying issuer, prevailing interest rates and market liquidity.
Changes in Level 3 Securities	The changes in Level 3 securities for the three month period ended March 31, 2018 are shown in the table below: Auction Rate Obligations Equity Total (in thousands) Balance at December 31, 2017 $ 4,459 $ 78,141 $ — $ 82,600 Purchases — 20,416 — 20,416 Maturities and calls — (22,068 ) — (22,068 ) Transfer (4,459 ) — — (4,459 ) Amortization — (24 ) — (24 ) Changes in fair value — — — — Balance at March 31, 2018 $ — $ 76,465 $ — $ 76,465 The changes in Level 3 securities for the three month period ended March 31, 2017, are shown in the table below: Auction Rate Obligations Equity Total (in thousands) Balance at December 31, 2016 $ 4,298 $ 160,578 $ — $ 164,876 Purchases — 23,088 — 23,088 Maturities and calls — (24,565 ) — (24,565 ) Amortization — (62 ) — (62 ) Changes in fair value — — — — Balance at March 31, 2017 $ 4,298 $ 159,039 $ — $ 163,337

Fair Values of Financial Inst28

Fair Values of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Investments, All Other Investments [Abstract]
Carrying Amounts and Fair Values of Company's Financial Instruments	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, 2018 and December 31, 2017. This table excludes financial instruments for which the carrying amount approximates fair value as these assets and liabilities that are due within one year. 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, 2018 Carrying Estimated Fair Value Level 2 Level 3 (in thousands) Financial assets: Securities held-to-maturity $ 1,817,633 $ 1,760,498 $ — $ 1,760,498 $ — Loans (1) 2,160,452 2,106,013 — — 2,106,013 Financial liabilities: Time deposits 615,822 613,788 — 613,788 — Other borrowed funds 317,054 315,791 — 315,791 — Subordinated debentures 36,083 36,083 — — 36,083 December 31, 2017 Financial assets: Securities held-to-maturity $ 1,701,233 $ 1,668,827 $ — $ 1,668,827 $ — Loans (1) 2,149,689 2,094,517 — — 2,094,517 Financial liabilities: Time deposits 625,361 627,517 — 627,517 — Other borrowed funds 347,778 349,364 — 349,364 — 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 loan losses.

Revenue from Contracts with C29

Revenue from Contracts with Customers (Tables)	3 Months Ended
	Mar. 31, 2018
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 March 31, 2018 Revenue from Three Months Revenue from (dollars in thousands) Total interest income $ 22,468 $ — $ 20,456 $ — Noninterest income: Service charges on deposit accounts 2,067 2,067 2,016 2,016 Lockbox fees 791 791 771 771 Net gains on sales of securities 197 — — — Gains on sales of mortgage loans — — 101 — Other income 1,138 719 1,021 603 Total noninterest income 4,193 3,577 3,909 3,390 Total revenues $ 26,661 $ 3,577 $ 24,365 $ 3,390
Information about Receivables with Customers	March 31, December 31, (dollars in thousands) Receivables, which are included in “Other assets” $ 1,161 $ 1,009

Basis of Financial Statement 30

Basis of Financial Statement Presentation - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018Segment
Basis Of Presentation [Line Items]
Number of reportable segments	1
Century Bancorp Capital Trust II [Member]
Basis Of Presentation [Line Items]
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, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 371,013	$ 395,947
Gross Unrealized Gains	718	674
Gross Unrealized Losses	755	790
Total, Fair Value	370,976	395,831
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,000	1,999
Gross Unrealized Losses	19	15
Total, Fair Value	1,981	1,984
U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,934
Gross Unrealized Losses	13
Total, Fair Value	3,921
SBA Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	79,118	81,065
Gross Unrealized Gains		46
Gross Unrealized Losses	335	161
Total, Fair Value	78,783	80,950
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	200,364	225,537
Gross Unrealized Gains	668	556
Gross Unrealized Losses	271	317
Total, Fair Value	200,761	225,776
Privately Issued Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	823	897
Gross Unrealized Gains	4	4
Gross Unrealized Losses	8	9
Total, Fair Value	819	892
Obligations Issued by States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	81,174	82,849
Gross Unrealized Losses	66	249
Total, Fair Value	81,108	82,600
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,600	3,600
Gross Unrealized Gains	46	68
Gross Unrealized Losses	43	39
Total, Fair Value	$ 3,603	$ 3,629

Securities Available-for-Sale32

Securities Available-for-Sale - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018USD ($)Security	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)Security
Schedule of Available-for-sale Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 1,216,741,000		$ 1,262,708,000
Securities available-for-sale are securities at fair value pledged for borrowing	58,870,000		$ 67,780,000
Gross gains on sales of securities	197,000
Proceeds from sales of securities available-for-sale	17,871,000	$ 0
Federal Home Loan Bank [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross gains on sales of securities	$ 197,000
Securities AFS [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted average remaining life of investment securities available-for-sale	5 years 7 months 6 days
Number of securities, temporarily impaired for less than 12 months | Security	23		16
Number of securities, temporarily impaired for 12 months or longer | Security	22		28
Number of securities, temporarily impaired, total | Security	181		249
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	$ 217,340,000		$ 216,353,000
U.S. Government Sponsored Enterprises [Member] | Securities AFS [Member]
Schedule of Available-for-sale Securities [Line Items]
Weighted average remaining life	$ 3,934,000

Securities Available-for-Sale33

Securities Available-for-Sale - Maturity Distribution of Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 72,533
After one but within five years, Amortized Cost	96,860
After five but within ten years, Amortized Cost	130,698
More than 10 years, Amortized Cost	70,922
Amortized Cost	371,013	$ 395,947
Within one year, Fair Value	72,531
After one but within five years, Fair Value	96,793
After five but within ten years, Fair Value	130,957
More than 10 years, Fair Value	70,695
Total, Fair Value	$ 370,976	$ 395,831

Securities Available-for-Sale34

Securities Available-for-Sale - Continuous Unrealized Loss Position for Less than 12 Months and 12 Months or Longer (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	$ 91,651	$ 61,156
Less Than 12 Months, Unrealized Losses	183	193
12 Months or Longer, Fair Value	91,739	105,799
12 Months or Longer, Unrealized Losses	572	597
Total, Fair Value	183,390	166,955
Total, Unrealized Losses	755	790
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	1,981	1,984
Less Than 12 Months, Unrealized Losses	19	15
Total, Fair Value	1,981	1,984
Total, Unrealized Losses	19	15
U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	3,921
Less Than 12 Months, Unrealized Losses	13
Total, Fair Value	3,921
Total, Unrealized Losses	13
SBA Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	39,032	18,378
Less Than 12 Months, Unrealized Losses	112	55
12 Months or Longer, Fair Value	39,752	40,911
12 Months or Longer, Unrealized Losses	223	106
Total, Fair Value	78,784	59,289
Total, Unrealized Losses	335	161
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	46,317	40,394
Less Than 12 Months, Unrealized Losses	38	123
12 Months or Longer, Fair Value	46,305	59,336
12 Months or Longer, Unrealized Losses	233	194
Total, Fair Value	92,622	99,730
Total, Unrealized Losses	271	317
Privately Issued Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
12 Months or Longer, Fair Value	582	633
12 Months or Longer, Unrealized Losses	8	9
Total, Fair Value	582	633
Total, Unrealized Losses	8	9
Obligations Issued by States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
12 Months or Longer, Fair Value	4,643	4,458
12 Months or Longer, Unrealized Losses	66	249
Total, Fair Value	4,643	4,458
Total, Unrealized Losses	66	249
Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	400	400
Less Than 12 Months, Unrealized Losses	1
12 Months or Longer, Fair Value	457	461
12 Months or Longer, Unrealized Losses	42	39
Total, Fair Value	857	861
Total, Unrealized Losses	$ 43	$ 39

Investment Securities Held-to35

Investment Securities Held-to-Maturity - Summary of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 1,817,633	$ 1,701,233
Gross Unrealized Gains	628	2,622
Gross Unrealized Losses	57,763	35,028
Estimated Fair Value	1,760,498	1,668,827
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	139,780	104,653
Gross Unrealized Gains	18	341
Gross Unrealized Losses	922	472
Estimated Fair Value	138,876	104,522
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	56,188	57,235
Gross Unrealized Gains		20
Gross Unrealized Losses	2,005	1,271
Estimated Fair Value	54,183	55,984
U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,621,665	1,539,345
Gross Unrealized Gains	610	2,261
Gross Unrealized Losses	54,836	33,285
Estimated Fair Value	$ 1,567,439	$ 1,508,321

Investment Securities Held-to36

Investment Securities Held-to-Maturity - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018USD ($)Security	Dec. 31, 2017USD ($)Security
Schedule of Held-to-maturity Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements | $	$ 1,216,741,000	$ 1,262,708,000
Held-to-Maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Weighted average remaining life of investment securities held-to-maturity	4 years 6 months
Number of securities, temporarily impaired for less than 12 months | Security	182	117
Number of securities, temporarily impaired for 12 months or longer | Security	174	168
Number of securities, temporarily impaired, total | Security	423	404
Held-to-Maturity Securities [Member] | U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Weighted average remaining life | $	$ 44,996,000
Federal Home Loan Bank [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities pledged for borrowing at the Federal Home Loan Bank | $	$ 465,541,000	$ 382,120,000

Investment Securities Held-to37

Investment Securities Held-to-Maturity - Company's Securities Held-to-Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 24,860
After one but within five years, Amortized Cost	1,184,354
After five but within ten years, Amortized Cost	605,293
More than ten years, Amortized Cost	3,126
Amortized Cost	1,817,633	$ 1,701,233
Within one year, Fair Value	24,840
After one but within five years, Fair Value	1,150,251
After five but within ten years, Fair Value	582,422
More than ten years, Fair Value	2,985
Estimated Fair Value	$ 1,760,498	$ 1,668,827

Investment Securities Held-to38

Investment Securities Held-to-Maturity - Unrealized Market Loss of Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	$ 788,418	$ 554,195
Less Than 12 Months, Unrealized Losses	15,606	6,301
12 Months or Longer, Fair Value	863,283	863,230
12 Months or Longer, Unrealized Losses	42,157	28,727
Total, Fair Value	1,651,701	1,417,425
Total, Unrealized Losses	57,763	35,028
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	84,390	15,257
Less Than 12 Months, Unrealized Losses	583	239
12 Months or Longer, Fair Value	14,662	14,768
12 Months or Longer, Unrealized Losses	339	233
Total, Fair Value	99,052	30,025
Total, Unrealized Losses	922	472
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	21,384	19,457
Less Than 12 Months, Unrealized Losses	592	142
12 Months or Longer, Fair Value	32,798	33,750
12 Months or Longer, Unrealized Losses	1,413	1,129
Total, Fair Value	54,182	53,207
Total, Unrealized Losses	2,005	1,271
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	682,644	519,481
Less Than 12 Months, Unrealized Losses	14,431	5,920
12 Months or Longer, Fair Value	815,823	814,712
12 Months or Longer, Unrealized Losses	40,405	27,365
Total, Fair Value	1,498,467	1,334,193
Total, Unrealized Losses	$ 54,836	$ 33,285

Allowance for Loan Losses - Ana

Allowance for Loan Losses - Analysis of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Receivables [Abstract]
Allowance for loan losses, beginning of period	$ 26,255	$ 24,406
Loans charged off	(87)	(96)
Recoveries on loans previously charged-off	77	117
Net recoveries (charge-offs)	(10)	21
Provision charged to expense	450	400
Allowance for loan losses, end of period	$ 26,695	$ 24,827

Allowance for Loan Losses - Sum

Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Allowance for loan losses:
Allowance for loan losses, beginning of period	$ 26,255	$ 24,406
Charge-offs	(87)	(96)
Recoveries	77	117
Provision	450	400
Allowance for loan losses, end of period	26,695	24,827
Amount of allowance for loan losses for loans deemed to be impaired	686	159
Amount of allowance for loan losses for loans not deemed to be impaired	26,009	24,668
Loans:
Total loans, net	2,187,147	2,040,494	$ 2,175,944
Loans deemed to be impaired	5,824	3,784
Loans not deemed to be impaired	2,181,323	2,036,710
Construction and Land Development [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,645	1,012
Provision	(207)	(139)
Allowance for loan losses, end of period	1,438	873
Amount of allowance for loan losses for loans deemed to be impaired		2
Amount of allowance for loan losses for loans not deemed to be impaired	1,438	871
Loans:
Total loans, net	17,583	10,773	18,931
Loans deemed to be impaired		93
Loans not deemed to be impaired	17,583	10,680
Commercial and Industrial [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	9,651	6,972
Charge-offs	(5)
Recoveries	23	19
Provision	(5)	378
Allowance for loan losses, end of period	9,664	7,369
Amount of allowance for loan losses for loans deemed to be impaired	12	21
Amount of allowance for loan losses for loans not deemed to be impaired	9,652	7,348
Loans:
Total loans, net	758,621	649,326	763,807
Loans deemed to be impaired	522	378
Loans not deemed to be impaired	758,099	648,948
Municipal [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,720	1,612
Provision		287
Allowance for loan losses, end of period	1,720	1,899
Amount of allowance for loan losses for loans not deemed to be impaired	1,720	1,899
Loans:
Total loans, net	104,044	153,447	106,599
Loans not deemed to be impaired	104,044	153,447
Commercial Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	9,728	11,135
Provision	59	81
Allowance for loan losses, end of period	9,787	11,216
Amount of allowance for loan losses for loans deemed to be impaired	94	130
Amount of allowance for loan losses for loans not deemed to be impaired	9,693	11,086
Loans:
Total loans, net	726,440	732,151	732,491
Loans deemed to be impaired	2,528	3,123
Loans not deemed to be impaired	723,912	729,028
Residential Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,873	1,698
Recoveries		2
Provision	586	(29)
Allowance for loan losses, end of period	2,459	1,671
Amount of allowance for loan losses for loans deemed to be impaired	580	6
Amount of allowance for loan losses for loans not deemed to be impaired	1,879	1,665
Loans:
Total loans, net	300,941	264,442	287,731
Loans deemed to be impaired	2,774	190
Loans not deemed to be impaired	298,167	264,252
Consumer [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	373	582
Charge-offs	(82)	(96)
Recoveries	54	96
Provision	(24)	(130)
Allowance for loan losses, end of period	321	452
Amount of allowance for loan losses for loans deemed to be impaired	1
Amount of allowance for loan losses for loans not deemed to be impaired	321	452
Loans:
Total loans, net	19,339	11,573	19,040
Loans not deemed to be impaired	19,339	11,573
Home Equity [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	989	1,102
Provision	78	(52)
Allowance for loan losses, end of period	1,067	1,050
Amount of allowance for loan losses for loans not deemed to be impaired	1,067	1,050
Loans:
Total loans, net	260,179	218,782	$ 247,345
Loans not deemed to be impaired	260,179	218,782
Unallocated [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	276	293
Provision	(37)	4
Allowance for loan losses, end of period	239	297
Amount of allowance for loan losses for loans not deemed to be impaired	$ 239	$ 297

Allowance for Loan Losses - Loa

Allowance for Loan Losses - Loans by Risk Rating (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Loans by risk rating
Financing Receivable, Net	$ 2,187,147	$ 2,175,944	$ 2,040,494
Construction and Land Development [Member]
Loans by risk rating
Financing Receivable, Net	17,583	18,931	10,773
Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	758,621	763,807	649,326
Municipal [Member]
Loans by risk rating
Financing Receivable, Net	104,044	106,599	153,447
Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	726,440	732,491	$ 732,151
1-3 (Pass) [Member] | Construction and Land Development [Member]
Loans by risk rating
Financing Receivable, Net	17,583	18,931
1-3 (Pass) [Member] | Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	752,853	758,093
1-3 (Pass) [Member] | Municipal [Member]
Loans by risk rating
Financing Receivable, Net	104,044	106,599
1-3 (Pass) [Member] | Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	699,363	705,235
4 (Monitor) [Member] | Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	5,246	5,366
4 (Monitor) [Member] | Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	24,549	24,702
Impaired [Member] | Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	522	348
Impaired [Member] | Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	$ 2,528	$ 2,554

Allowance for Loan Losses - L42

Allowance for Loan Losses - Loans by Credit Rating (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	$ 1,067,476	$ 1,074,923
Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	579,921	586,000
A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	331,295	331,788
Baa1 - Baa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	148,095	148,970
Ba2 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	8,165	8,165
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	672,679	674,504
Commercial and Industrial [Member] | Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	477,230	478,905
Commercial and Industrial [Member] | A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	195,449	195,599
Municipal [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	101,794	104,799
Municipal [Member] | Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	59,024	62,029
Municipal [Member] | A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	7,635	7,635
Municipal [Member] | Baa1 - Baa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	26,970	26,970
Municipal [Member] | Ba2 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	8,165	8,165
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	293,003	295,620
Commercial Real Estate [Member] | Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	43,667	45,066
Commercial Real Estate [Member] | A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	128,211	128,554
Commercial Real Estate [Member] | Baa1 - Baa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	$ 121,125	$ 122,000

Allowance for Loan Losses - Agi

Allowance for Loan Losses - Aging of Past Due Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	$ 3,937	$ 5,642
Non Accrual	1,386	1,684
Accruing Greater than 90 Days	0	0
Total Past Due	5,323	7,326
Current Loans	2,181,824	2,168,618
Total loans, net	2,187,147	2,175,944	$ 2,040,494
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing Greater than 90 Days	0	0
Current Loans	17,583	18,931
Total loans, net	17,583	18,931	10,773
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	242	65
Non Accrual	198	44
Accruing Greater than 90 Days	0	0
Total Past Due	440	109
Current Loans	758,181	763,698
Total loans, net	758,621	763,807	649,326
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing Greater than 90 Days	0	0
Current Loans	104,044	106,599
Total loans, net	104,044	106,599	153,447
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	1,713	672
Non Accrual	211	215
Accruing Greater than 90 Days	0	0
Total Past Due	1,924	887
Current Loans	724,516	731,604
Total loans, net	726,440	732,491	732,151
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	1,270	4,282
Non Accrual	186	724
Accruing Greater than 90 Days	0	0
Total Past Due	1,456	5,006
Current Loans	299,485	282,725
Total loans, net	300,941	287,731	264,442
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	8	5
Non Accrual	2	6
Accruing Greater than 90 Days	0	0
Total Past Due	10	11
Current Loans	19,329	19,029
Total loans, net	19,339	19,040	11,573
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	704	618
Non Accrual	789	695
Accruing Greater than 90 Days	0	0
Total Past Due	1,493	1,313
Current Loans	258,686	246,032
Total loans, net	$ 260,179	$ 247,345	$ 218,782

Allowance for Loan Losses - Inf

Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 237	$ 713
With no required reserve recorded, Unpaid Balance Principal	445	991
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	314	719
With no required reserve recorded, Interest Income		11
With required reserve recorded, Carrying Value	5,587	3,071
With required reserve recorded, Unpaid Balance Principal	5,715	3,208
With required reserve recorded, Required Reserve	686	159
With required reserve recorded, Average Carrying Value Recognized	6,493	3,087
With required reserve recorded, Interest Income	34	28
Carrying Value	5,824	3,784
Unpaid Balance Principal	6,160	4,199
With required reserve recorded, Required Reserve	686	159
Average Carrying Value Recognized	6,807	3,806
Interest Income	34	39
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
With required reserve recorded, Carrying Value		93
With required reserve recorded, Unpaid Balance Principal		108
With required reserve recorded, Required Reserve		2
With required reserve recorded, Average Carrying Value Recognized		93
Carrying Value		93
Unpaid Balance Principal		108
With required reserve recorded, Required Reserve		2
Average Carrying Value Recognized	2	93
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	27	41
With no required reserve recorded, Unpaid Balance Principal	214	229
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	49	43
With required reserve recorded, Carrying Value	495	337
With required reserve recorded, Unpaid Balance Principal	511	352
With required reserve recorded, Required Reserve	12	21
With required reserve recorded, Average Carrying Value Recognized	388	339
With required reserve recorded, Interest Income	5	4
Carrying Value	522	378
Unpaid Balance Principal	725	581
With required reserve recorded, Required Reserve	12	21
Average Carrying Value Recognized	437	382
Interest Income	5	4
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	210	588
With no required reserve recorded, Unpaid Balance Principal	231	588
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized	265	589
With no required reserve recorded, Interest Income		9
With required reserve recorded, Carrying Value	2,318	2,535
With required reserve recorded, Unpaid Balance Principal	2,430	2,642
With required reserve recorded, Required Reserve	94	130
With required reserve recorded, Average Carrying Value Recognized	2,278	2,548
With required reserve recorded, Interest Income	23	23
Carrying Value	2,528	3,123
Unpaid Balance Principal	2,661	3,230
With required reserve recorded, Required Reserve	94	130
Average Carrying Value Recognized	2,543	3,137
Interest Income	23	32
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value		84
With no required reserve recorded, Unpaid Balance Principal		174
With no required reserve recorded, Required Reserve	0	0
With no required reserve recorded, Average Carrying Value Recognized		87
With no required reserve recorded, Interest Income		2
With required reserve recorded, Carrying Value	2,774	106
With required reserve recorded, Unpaid Balance Principal	2,774	106
With required reserve recorded, Required Reserve	580	6
With required reserve recorded, Average Carrying Value Recognized	3,827	107
With required reserve recorded, Interest Income	6	1
Carrying Value	2,774	190
Unpaid Balance Principal	2,774	280
With required reserve recorded, Required Reserve	580	6
Average Carrying Value Recognized	3,827	194
Interest Income	6	3
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0
With required reserve recorded, Required Reserve	1
With required reserve recorded, Required Reserve	1
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, 2018USD ($)ContractContracts	Mar. 31, 2017USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Specific reserves	$ 686,000	$ 159,000
Commitment to lend additional funds to TDR borrowers	0
Troubled debt restructurings, subsequently defaulted	$ 0	0
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of troubled debt restructurings | Contracts	1
Pre-modification outstanding recorded investment	$ 2,675,000
Post-modification outstanding recorded investment	2,675,000
Specific reserves	580,000	$ 6,000
Residential Real Estate [Member] | Restructured Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Specific reserves	$ 575,000
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of troubled debt restructurings | Contract	1
Pre-modification outstanding recorded investment	$ 17,000
Post-modification outstanding recorded investment	17,000
Specific reserves	$ 1,000

Reclassifications Out of Accu46

Reclassifications Out of Accumulated Other Comprehensive Income - Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains on sales of securities	$ 197
Provision for income taxes	(501)	$ (144)
Net income	7,709	6,096
Salaries and employee benefits	(11,225)	(10,794)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains on sales of securities	197
Provision for income taxes	(55)
Net income	142
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	(520)	(662)
Provision for income taxes	139	289
Net income	(381)	(373)
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	(4)	(3)
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	(403)	(384)
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	(407)	(387)
Provision for income taxes	114	155
Net income	$ (293)	$ (232)

Earnings per Share ("EPS") - Ad

Earnings per Share ("EPS") - Additional Information (Detail) - shares	Mar. 31, 2018	Mar. 31, 2017
Class A Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Number of Stock options outstanding	0	0

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, 2018	Mar. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 7,709	$ 6,096
Class A Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 6,062	$ 4,788
Weighted average shares outstanding, basic	3,608,029	3,600,729
Basic earnings per share	$ 1.68	$ 1.33
Net income	$ 6,062	$ 4,788
Weighted average shares outstanding, diluted	5,567,909	5,567,909
Diluted earnings per share	$ 1.38	$ 1.09
Class B Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 1,647	$ 1,308
Weighted average shares outstanding, basic	1,959,880	1,967,180
Basic earnings per share	$ 0.84	$ 0.66
Net income	$ 1,647	$ 1,308
Weighted average shares outstanding, diluted	1,959,880	1,967,180
Diluted earnings per share	$ 0.84	$ 0.66

Employee Benefits - Components

Employee Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 353	$ 310
Interest	370	362
Expected return on plan assets	(954)	(746)
Recognized prior service cost (benefit)	(25)	(26)
Recognized net actuarial losses	227	226
Net periodic benefit (credit) cost	(29)	126
Supplemental Insurance/ Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	277	395
Interest	346	345
Recognized prior service cost (benefit)	29	29
Recognized net actuarial losses	176	159
Net periodic benefit (credit) cost	$ 828	$ 928

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Employer expected contribution to Pension Plan in 2018	$ 0
ASU 2017-07 [Member]
Defined Benefit Plan Disclosure [Line Items]
Reclassification from salaries and employee benefits to other expenses	$ 169,000	$ 349,000

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, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	$ 370,976	$ 395,831
Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS		313,231
Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS		82,600
Financial Instruments Measured at Fair Value on a Non-recurring Basis
Impaired Loans	3,084	246
Impaired Loans	3,084	246
U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,981	1,984
U.S. Treasury [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,981	1,984
SBA Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	78,783	80,950
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	78,783	80,950
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	200,761	225,776
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	200,761	225,776
Privately Issued Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	819	892
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	819	892
Obligations Issued by States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	81,108	82,600
Obligations Issued by States and Political Subdivisions [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	4,643
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	76,465	82,600
Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,603	3,629
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	3,603	3,629
Equity Securities [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	294,511
Equity Securities [Member] | Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	76,465
U.S. Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,921
U.S. Government Sponsored Enterprises [Member] | Fair Value Measurements, Level 2 Inputs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,921
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS		395,831
Financial Instruments Measured at Fair Value on a Non-recurring Basis
Impaired Loans	3,084	246
Impaired Loans	3,084	246
Carrying Value [Member] | U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,981	1,984
Carrying Value [Member] | SBA Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	78,783	80,950
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	200,761	225,776
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	819	892
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	81,108	82,600
Carrying Value [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,603	$ 3,629
Carrying Value [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	370,976
Carrying Value [Member] | U.S. Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	$ 3,921

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Specific adjustments to impaired loans recognized	$ 581,000	$ 3,000
Amortized cost of Level 3 securities	1,635,000	1,635,000
Transfers between level 1, 2 and 3	1	0
Liabilities measured at fair value on a recurring or nonrecurring basis	0	$ 0
Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized cost of Level 3 securities	76,465,000		$ 163,742,000
Unrealized loss	$ 0		$ 405,000

Fair Value Measurements - Asset

Fair Value Measurements - Assets Measured at Fair Value (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Securities AFS [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Fair Value	$ 76,465	$ 82,600
Valuation Technique	Discounted cash flow
Unobservable Input	Discount rate
Impaired Loans [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Fair Value	$ 3,084	$ 246
Valuation Technique	Appraisal of collateral
Unobservable Input	Appraisal adjustments
Minimum [Member] | Securities AFS [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Unobservable Input Value or Range	1.60%	1.00%
Minimum [Member] | Impaired Loans [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Unobservable Input Value or Range	0.00%	0.00%
Maximum [Member] | Securities AFS [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Unobservable Input Value or Range	4.40%	3.50%
Maximum [Member] | Impaired Loans [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Unobservable Input Value or Range	30.00%	30.00%

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Level 3 Securities (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 82,600	$ 164,876
Purchases	20,416	23,088
Maturities and calls	(22,068)	(24,565)
Transfer	(4,459)
Amortization	(24)	(62)
Changes in fair value	0	0
Ending Balance	76,465	163,337
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	4,459	4,298
Transfer	(4,459)
Changes in fair value	0	0
Ending Balance		4,298
Obligations Issued by States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	78,141	160,578
Purchases	20,416	23,088
Maturities and calls	(22,068)	(24,565)
Amortization	(24)	(62)
Changes in fair value	0	0
Ending Balance	76,465	159,039
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in fair value	$ 0	$ 0

Fair Value Measurements - Ass55

Fair Value Measurements - Assets Measured at Fair Value (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2017
Municipal [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities maturity period	one year or less

Fair Values of Financial Inst56

Fair Values of Financial Instruments - Carrying Amount and Fair Value of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial assets:
Securities held-to-maturity	$ 1,817,633	$ 1,701,233
Loans	2,160,452	2,149,689
Financial liabilities:
Time deposits	615,822	625,361
Other borrowed funds	317,054	347,778
Subordinated debentures	36,083	36,083
Carrying Value [Member]
Financial assets:
Securities held-to-maturity	1,817,633	1,701,233
Loans	2,160,452	2,149,689
Financial liabilities:
Time deposits	615,822	625,361
Other borrowed funds	317,054	347,778
Subordinated debentures	36,083	36,083
Estimated Fair Value [Member]
Financial assets:
Securities held-to-maturity	1,760,498	1,668,827
Loans	2,106,013	2,094,517
Financial liabilities:
Time deposits	613,788	627,517
Other borrowed funds	315,791	349,364
Subordinated debentures	36,083	36,083
Fair Value Measurements, Level 2 Inputs [Member]
Financial assets:
Securities held-to-maturity	1,760,498	1,668,827
Financial liabilities:
Time deposits	613,788	627,517
Other borrowed funds	315,791	349,364
Fair Value Measurements, Level 3 Inputs [Member]
Financial assets:
Loans	2,106,013	2,094,517
Financial liabilities:
Subordinated debentures	$ 36,083	$ 36,083

Recent Accounting Development57

Recent Accounting Developments - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended
	Feb. 28, 2018	Aug. 31, 2016	Jan. 31, 2016	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in investing activities				$ (90,105,000)	$ (280,906,000)
Decrease in operating activities				$ 14,220,000	$ 6,378,000
ASU 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassified from accumulated other comprehensive income to retained earnings	$ 3,800,000
ASU 2016-15 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in investing activities		$ 375,000
Decrease in operating activities		$ (375,000)
ASU 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassified from accumulated other comprehensive income to retained earnings			$ 29,000

Revenue from Contracts with C58

Revenue from Contracts with Customers - Schedule of Revenue from Contracts (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Total interest income	$ 22,468	$ 20,456
Noninterest income:
Service charges on deposit accounts	2,067	2,016
Lockbox fees	791	771
Net gains on sales of securities	197
Gains on sales of mortgage loans		101
Other income	1,138	1,021
Total noninterest income	4,193	3,909
ASU 2014-09 [Member]
Disaggregation of Revenue [Line Items]
Total interest income	22,468	20,456
Noninterest income:
Service charges on deposit accounts	2,067	2,016
Lockbox fees	791	771
Net gains on sales of securities	197
Gains on sales of mortgage loans		101
Other income	1,138	1,021
Total noninterest income	4,193	3,909
Total revenues	26,661	24,365
ASU 2014-09 [Member] | Revenue Guidance Contracts in Scope of Topic 606 [Member]
Noninterest income:
Service charges on deposit accounts	2,067	2,016
Lockbox fees	791	771
Other income	719	603
Total noninterest income	3,577	3,390
Total revenues	$ 3,577	$ 3,390

Revenue from Contracts with C59

Revenue from Contracts with Customers - Information about Receivables with Customers (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Other Assets [Member]
Disaggregation of Revenue [Line Items]
Receivables, which are included in "Other assets"	$ 1,161	$ 1,009