Century Bancorp (CNBKA) 10-Q 8 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	CNBKA
Entity Registrant Name	CENTURY BANCORP INC
Entity Central Index Key	812,348
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Class A Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,608,329
Class B Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		1,959,580

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 68,945	$ 77,199
Federal funds sold and interest-bearing deposits in other banks	142,345	279,231
Total cash and cash equivalents	211,290	356,430
Securities available-for-sale, amortized cost $366,385 and $395,947, respectively	366,503	395,831
Securities held-to-maturity, fair value $1,795,117 and $1,668,827, respectively	1,875,752	1,701,233
Federal Home Loan Bank of Boston, stock at cost	22,743	21,779
Equity securities, amortized cost $1,616 and $1,616, respectively	1,616	1,663
Loans, net:
Construction and land development	12,434	18,931
Commercial and industrial	783,960	763,807
Municipal	94,532	106,599
Commercial real estate	730,265	732,491
Residential real estate	335,114	287,731
Consumer	20,677	18,458
Home equity	283,818	247,345
Overdrafts	539	582
Total loans, net	2,261,339	2,175,944
Less: allowance for loan losses	28,545	26,255
Net loans	2,232,794	2,149,689
Bank premises and equipment	24,023	23,527
Accrued interest receivable	12,878	11,179
Goodwill	2,714	2,714
Other assets	120,110	121,527
Total assets	4,870,423	4,785,572
Deposits:
Demand deposits	731,095	736,020
Savings and NOW deposits	1,359,334	1,367,358
Money market accounts	1,294,092	1,188,228
Time deposits	579,886	625,361
Total deposits	3,964,407	3,916,967
Securities sold under agreements to repurchase	140,490	158,990
Other borrowed funds	372,606	347,778
Subordinated debentures	36,083	36,083
Due to broker	897
Other liabilities	69,063	65,457
Total liabilities	4,583,546	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	292,114	263,666
Stockholders' equity before adjustment of accumulated other comprehensive income (loss)	309,974	281,526
Unrealized losses on securities available-for-sale, net of taxes	92	(62)
Unrealized losses on securities transferred to held-to-maturity, net of taxes	(2,779)	(3,050)
Pension liability, net of taxes	(20,410)	(18,117)
Total accumulated other comprehensive loss, net of taxes	(23,097)	(21,229)
Total stockholders' equity	286,877	260,297
Total liabilities and stockholders' equity	4,870,423	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	Sep. 30, 2018	Dec. 31, 2017
Amortized cost	$ 366,385	$ 395,947
Held-to-maturity securities, fair value	1,795,117	1,668,827
Equity securities, amortized cost	$ 1,616	$ 1,616
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	3,608,329	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	1,959,580	1,962,080

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest income
Loans	$ 20,167	$ 16,658	$ 57,613	$ 48,668
Securities held-to-maturity	11,507	9,447	32,930	28,806
Securities available-for-sale	2,500	1,809	6,821	5,143
Federal funds sold and interest-bearing deposits in other banks	591	607	2,239	1,349
Total interest income	34,765	28,521	99,603	83,966
Interest expense
Savings and NOW deposits	2,972	1,727	7,778	4,454
Money market accounts	3,652	1,395	9,039	3,903
Time deposits	2,571	2,095	7,465	5,648
Securities sold under agreements to repurchase	288	129	657	352
Other borrowed funds and subordinated debentures	2,078	1,822	5,793	5,695
Total interest expense	11,561	7,168	30,732	20,052
Net interest income	23,204	21,353	68,871	63,914
Provision for loan losses		450	900	1,340
Net interest income after provision for loan losses	23,204	20,903	67,971	62,574
Other operating income
Lockbox fees	892	735	2,304	2,367
Net gains on sales of securities	105	47	302	47
Gains on sales of mortgage loans				370
Other income	1,035	1,071	3,210	3,179
Total other operating income	4,169	3,942	12,084	12,142
Operating expenses
Salaries and employee benefits	10,570	9,933	32,331	31,097
Occupancy	1,481	1,427	4,579	4,663
Equipment	781	782	2,355	2,245
FDIC assessments	368	340	1,110	1,218
Other	4,148	3,723	12,133	11,904
Total operating expenses	17,348	16,205	52,508	51,127
Income before income taxes	10,025	8,640	27,547	23,589
Provision for income taxes	444	617	1,259	1,313
Net income	$ 9,581	$ 8,023	$ 26,288	$ 22,276
Class A Common Stock [Member]
Share data:
Weighted average number of shares outstanding, basic	3,608,329	3,605,829	3,608,129	3,603,429
Weighted average number of shares outstanding, diluted	5,567,909	5,567,909	5,567,909	5,567,909
Basic earnings per share	$ 2.09	$ 1.75	$ 5.73	$ 4.86
Diluted earnings per share	$ 1.72	$ 1.44	$ 4.72	$ 4
Class B Common Stock [Member]
Share data:
Weighted average number of shares outstanding, basic	1,959,580	1,962,080	1,959,780	1,964,480
Weighted average number of shares outstanding, diluted	1,959,580	1,962,080	1,959,780	1,964,480
Basic earnings per share	$ 1.04	$ 0.87	$ 2.86	$ 2.43
Diluted earnings per share	$ 1.04	$ 0.87	$ 2.86	$ 2.43
Deposit Account [Member]
Other operating income
Service charges on deposit accounts	$ 2,137	$ 2,089	$ 6,268	$ 6,179

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 9,581	$ 8,023	$ 26,288	$ 22,276
Unrealized gains (losses) on securities:
Unrealized (losses) gains arising during period	(88)	122	412	455
Less: reclassification adjustment for gains included in net income	(76)	(28)	(217)	(28)
Total unrealized (losses) gains on securities	(164)	94	195	427
Accretion of net unrealized losses transferred	238	223	872	856
Defined benefit pension plans:
Amortization of prior service cost and loss included in net periodic benefit cost	292	233	877	698
Other comprehensive income	366	550	1,944	1,981
Comprehensive income	$ 9,947	$ 8,573	$ 28,232	$ 24,257

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	22,276				22,276
Other comprehensive income, net of tax:
Unrealized holding (losses) gains arising during period, net of taxes	427							427
Accretion of net unrealized losses transferred during the period, net of taxes	856							856
Pension liability adjustment, net of taxes	698							698
Conversion of Class B Common Stock to Class A Common Stock		5	(5)
Cash dividends						$ (1,297)	$ (353)
Ending balance at Sep. 30, 2017	262,648	3,606	1,962	12,292	264,191			(19,403)
Beginning balance at Dec. 31, 2017	260,297	3,606	1,962	12,292	263,666			(21,229)
Net income	26,288				26,288
Other comprehensive income, net of tax:
Unrealized holding (losses) gains arising during period, net of taxes	195							195
Accretion of net unrealized losses transferred during the period, net of taxes	872							872
Pension liability adjustment, net of taxes	877							877
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						$ (1,299)	$ (353)
Ending balance at Sep. 30, 2018	$ 286,877	$ 3,608	$ 1,960	$ 12,292	$ 292,114			$ (23,097)

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Unrealized holding (losses) gains arising during period, net of taxes	$ 39	$ 282
Realized net gains	302	47
Accretion of net unrealized losses transferred during the period, taxes	314	1,022
Pension liability adjustment, taxes	$ 342	$ 465
Class A Common Stock [Member]
Conversion of Class B Common Stock to Class A Common Stock, shares	2,500	5,100
Cash dividends, per share	$ 0.36	$ 0.36
Class B Common Stock [Member]
Conversion of Class B Common Stock to Class A Common Stock, shares	2,500	5,100
Cash dividends, per share	$ 0.18	$ 0.18

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 26,288	$ 22,276
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sales of mortgage loans		(370)
Net gains on sales of securities	(302)	(47)
Net loss on equity securities	47
Provision for loan losses	900	1,340
Deferred income taxes	(1,270)	(3,477)
Net depreciation and amortization	1,116	2,444
Increase in accrued interest receivable	(1,699)	(281)
Decrease (increase) in other assets	1,542	(1,478)
Increase in other liabilities	4,825	4,076
Net cash provided by operating activities	31,447	24,483
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from maturities of short-term investments		3,183
Proceeds from redemptions of Federal Home Loan Bank of Boston stock	13,619	7,175
Purchase of Federal Home Loan Bank of Boston stock	(14,583)	(8,070)
Proceeds from calls/maturities of securities available-for-sale	111,922	211,576
Proceeds from sales of securities available-for-sale	27,517	18,133
Purchase of securities available-for-sale	(108,871)	(111,777)
Proceeds from calls/maturities of securities held-to-maturity	187,009	231,953
Purchase of securities held-to-maturity	(358,824)	(230,813)
Proceeds from life insurance policies	375
Net increase in loans	(83,967)	(215,063)
Proceeds from sales of portfolio loans		26,701
Capital expenditures	(2,900)	(2,881)
Net cash used in investing activities	(228,703)	(69,883)
CASH FLOWS FROM FINANCING ACTIVITIES:
Net (decrease) increase in time deposits	(45,475)	128,920
Net (decrease) increase in demand, savings, money market and NOW deposits	92,915	(176,456)
Cash dividends	(1,652)	(1,650)
Net (decrease) increase in securities sold under agreements to repurchase	(18,500)	46,568
Net increase in other borrowed funds	24,828	65,000
Net cash provided by financing activities	52,116	62,382
Net (decrease) increase in cash and cash equivalents	(145,140)	16,982
Cash and cash equivalents at beginning of period	356,430	236,151
Cash and cash equivalents at end of period	211,290	253,133
Cash paid during the period for:
Interest	30,680	20,255
Income taxes	590	4,830
Change in unrealized gains (losses) on securities available-for-sale, net of taxes	195	427
Change in unrealized losses on securities transferred to held-to-maturity, net of taxes	872	856
Pension liability adjustment, net of taxes	877	698
Change in due to (from) to broker	$ 897	$ 5,911

Basis of Financial Statement Pr

Basis of Financial Statement Presentation	9 Months Ended
	Sep. 30, 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	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Securities Available-for-Sale	Note 2. Securities Available-for-Sale September 30, 2018 December 31, 2017 Amortized Gross Gross Fair Amortized Gross Gross Fair (in thousands) U.S. Treasury $ 1,999 $ — $ 13 $ 1,986 $ 1,999 $ — $ 15 $ 1,984 U.S. Government Sponsored Enterprises 3,942 — 53 3,889 — — — — SBA Backed Securities 71,417 — 293 71,124 81,065 46 161 80,950 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 168,760 666 211 169,215 225,537 556 317 225,776 Privately Issued Residential Mortgage-Backed Securities 720 4 9 715 897 4 9 892 Obligations Issued by States and Political Subdivisions 115,947 62 — 116,009 82,849 — 249 82,600 Other Debt Securities 3,600 21 56 3,565 3,600 68 39 3,629 Total $ 366,385 $ 753 $ 635 $ 366,503 $ 395,947 $ 674 $ 790 $ 395,831 Included in SBA Backed Securities, 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 $210,362,000 and $216,353,000 at September 30, 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 $ 115,302 $ 115,282 After one but within five years 60,862 60,682 After five but within ten years 156,425 156,782 More than 10 years 33,796 33,757 Total $ 366,385 $ 366,503 The weighted average remaining life of investment securities available-for-sale As of September 30, 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 September 30, 2018 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Treasury $ — $ — $ 1,986 $ 13 $ 1,986 $ 13 U.S. Government Sponsored Enterprises 3,889 53 — — 3,889 53 SBA Backed Securities 25,567 42 45,557 251 71,124 293 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 31,311 60 26,032 151 57,343 211 Privately Issued Residential Mortgage-Backed Securities — — 524 9 524 9 Obligations Issued by States and Political Subdivisions — — — — — — Other Debt Securities — — 744 56 744 56 Total temporarily impaired securities $ 60,767 $ 155 $ 74,843 $ 480 $ 135,610 $ 635 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 54 40,911 107 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 1 461 38 861 39 Total temporarily impaired securities $ 61,156 $ 193 $ 105,799 $ 597 $ 166,955 $ 790

Investment Securities Held-to-M

Investment Securities Held-to-Maturity	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Investment Securities Held-to-Maturity	Note 3. Investment Securities Held-to-Maturity September 30, 2018 December 31, 2017 Amortized Gross Gross Estimated Amortized Gross Gross Estimated (in thousands) U.S. Treasury $ 9,903 $ — $ 3 $ 9,900 $ — $ — $ — $ — U.S. Government Sponsored Enterprises 167,968 — 2,152 165,816 104,653 341 472 104,522 SBA Backed Securities 53,576 — 2,759 50,817 57,235 20 1,271 55,984 U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities 1,644,305 139 75,860 1,568,584 1,539,345 2,261 33,285 1,508,321 Total $ 1,875,752 $ 139 $ 80,774 $ 1,795,117 $ 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 $1,267,793,000 and $1,262,708,000 at September 30, 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 $515,979,000 and $382,120,000 at September 30, 2018 and December 31, 2017, respectively. There were no sales of held-to-maturity At September 30, 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 $ 39,091 $ 38,932 After one but within five years 1,210,561 1,163,813 After five but within ten years 622,996 589,508 More than ten years 3,104 2,864 Total $ 1,875,752 $ 1,795,117 The weighted average remaining life of investment securities held-to-maturity As of September 30, 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 the rise in 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 September 30, 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 September 30, 2018 Less Than 12 Months 12 Months or Longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Treasury $ 9,900 $ 3 $ — $ — $ 9,900 $ 3 U.S. Government Sponsored Enterprises 135,760 1,171 29,517 981 165,277 2,152 SBA Backed Securities 2,487 75 48,330 2,684 50,817 2,759 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 557,866 13,733 997,268 62,127 1,555,134 75,860 Total temporarily impaired securities $ 706,013 $ 14,982 $ 1,075,115 $ 65,792 $ 1,781,128 $ 80,774 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	9 Months Ended
	Sep. 30, 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 Nine months ended 2018 2017 2018 2017 (in thousands) Allowance for loan losses, beginning of period $ 27,144 $ 25,289 $ 26,255 $ 24,406 Loans charged off (89 ) (95 ) (247 ) (292 ) Recoveries on loans previously charged-off 1,490 54 1,637 244 Net recoveries (charge-offs) 1,401 (41 ) 1,390 (48 ) Provision charged to expense — 450 900 1,340 Allowance for loan losses, end of period $ 28,545 $ 25,698 $ 28,545 $ 25,698 Further information pertaining to the allowance for loan losses for the three months ending September 30, 2018 follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total Allowance for loan losses: (in thousands) Balance at June 30, 2018 $ 633 $ 10,384 $ 1,704 $ 10,209 $ 2,493 $ 336 $ 1,078 $ 307 $ 27,144 Charge-offs — (11 ) — — — (78 ) — — (89 ) Recoveries 1,432 16 — — — 42 — — 1,490 Provision (1,155 ) 895 84 415 (182 ) 32 (28 ) (61 ) — Ending balance at September 30, 2018 $ 910 $ 11,284 $ 1,788 $ 10,624 $ 2,311 $ 332 $ 1,050 $ 246 $ 28,545 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 93 $ — $ 95 $ 350 $ — $ — $ — $ 538 Amount of allowance for loan losses for loans not deemed to be impaired $ 910 $ 11,191 $ 1,788 $ 10,529 $ 1,961 $ 332 $ 1,050 $ 246 $ 28,007 Loans: Ending balance $ 12,434 $ 783,960 $ 94,532 $ 730,265 $ 335,114 $ 21,216 $ 283,818 $ — $ 2,261,339 Loans deemed to be impaired $ — $ 660 $ — $ 2,680 $ 2,675 $ — $ — $ — $ 6,015 Loans not deemed to be impaired $ 12,434 $ 783,300 $ 94,532 $ 727,585 $ 332,439 $ 21,216 $ 283,818 $ — $ 2,255,324 Further information pertaining to the allowance for loan losses for the nine months ending September 30, 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 — (16 ) — — — (231 ) — — (247 ) Recoveries 1,432 49 — — — 156 — — 1,637 Provision (2,167 ) 1,600 68 896 438 34 61 (30 ) 900 Ending balance at September 30, 2018 $ 910 $ 11,284 $ 1,788 $ 10,624 $ 2,311 $ 332 $ 1,050 $ 246 $ 28,545 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 93 $ — $ 95 $ 350 $ — $ — $ — $ 538 Amount of allowance for loan losses for loans not deemed to be impaired $ 910 $ 11,191 $ 1,788 $ 10,529 $ 1,961 $ 332 $ 1,050 $ 246 $ 28,007 Loans: Ending balance $ 12,434 $ 783,960 $ 94,532 $ 730,265 $ 335,114 $ 21,216 $ 283,818 $ — $ 2,261,339 Loans deemed to be impaired $ — $ 660 $ — $ 2,680 $ 2,675 $ — $ — $ — $ 6,015 Loans not deemed to be impaired $ 12,434 $ 783,300 $ 94,532 $ 727,585 $ 332,439 $ 21,216 $ 283,818 $ — $ 2,255,324 During the nine months ending September 30, 2018, the Company’s provision was primarily attributable to an increase in residential real estate balances and increased qualitative allocations for commercial and industrial and commercial real estate loans, offset, somewhat by the recovery of a construction loan previously charged-off charged-off Further information pertaining to the allowance for loan losses for the three months ending September 30, 2017 follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total Allowance for loan losses: (in thousands) Balance at June 30, 2017 $ 1,137 $ 7,563 $ 1,859 $ 11,028 $ 2,118 $ 195 $ 1,146 $ 243 $ 25,289 Charge-offs — (20 ) — — — (75 ) — — (95 ) Recoveries — 9 — — — 45 — — 54 Provision 323 1,297 265 (1,491 ) (45 ) 220 (103 ) (16 ) 450 Ending balance at September 30, 2017 $ 1,460 $ 8,849 $ 2,124 $ 9,537 $ 2,073 $ 385 $ 1,043 $ 227 $ 25,698 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 8 $ — $ 111 $ 67 $ — $ — $ — $ 186 Amount of allowance for loan losses for loans not deemed to be impaired $ 1,460 $ 8,841 $ 2,124 $ 9,426 $ 2,006 $ 385 $ 1,043 $ 227 $ 25,512 Loans: Ending balance $ 16,779 $ 702,646 $ 128,412 $ 735,844 $ 272,588 $ 19,284 $ 237,094 $ — $ 2,112,647 Loans deemed to be impaired $ — $ 366 $ — $ 2,583 $ 4,318 $ — $ — $ — $ 7,267 Loans not deemed to be impaired $ 16,779 $ 702,280 $ 128,412 $ 733,261 $ 268,270 $ 19,284 $ 237,094 $ — $ 2,105,380 Further information pertaining to the allowance for loan losses for the nine months ending September 30, 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 — (49 ) — — — (243 ) — — (292 ) Recoveries — 63 — — 2 179 — — 244 Provision 448 1,863 512 (1,598 ) 373 (133 ) (59 ) (66 ) 1,340 Ending balance at September 30, 2017 $ 1,460 $ 8,849 $ 2,124 $ 9,537 $ 2,073 $ 385 $ 1,043 $ 227 $ 25,698 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 8 $ — $ 111 $ 67 $ — $ — $ — $ 186 Amount of allowance for loan losses for loans not deemed to be impaired $ 1,460 $ 8,841 $ 2,124 $ 9,426 $ 2,006 $ 385 $ 1,043 $ 227 $ 25,512 Loans: Ending balance $ 16,779 $ 702,646 $ 128,412 $ 735,844 $ 272,588 $ 19,284 $ 237,094 $ — $ 2,112,647 Loans deemed to be impaired $ — $ 366 $ — $ 2,583 $ 4,318 $ — $ — $ — $ 7,267 Loans not deemed to be impaired $ 16,779 $ 702,280 $ 128,412 $ 733,261 $ 268,270 $ 19,284 $ 237,094 $ — $ 2,105,380 During the nine months ending September 30, 2017, the Company’s provision was primarily attributable to an increase in commercial and industrial, construction and land development, and residential real estate balances offset, somewhat, by changes in historical loss rates and qualitative factors. During the three months ending September 30, 2017 the Company’s provision was primarily attributable to an increase in commercial and industrial loan balances offset, somewhat, by changes in historical loss rates and qualitative factors. 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 September 30, 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 September 30, 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 September 30, 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 September 30, 2018. Construction Commercial Municipal Commercial Grade: (in thousands) 1-3 $ 12,434 $ 779,165 $ 94,532 $ 703,039 4 (Monitor) — 4,135 — 24,546 5 (Substandard) — — — — 6 (Doubtful) — — — — Impaired — 660 — 2,680 Total $ 12,434 $ 783,960 $ 94,532 $ 730,265 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 September 30, 2018 and are included within the total loan portfolio. Commercial Municipal Commercial Total Credit Rating: (in thousands) Aaa – Aa3 $ 492,117 $ 57,958 $ 43,106 $ 593,181 A1 – A3 194,465 995 110,191 305,651 Baa1 – Baa3 — 26,970 119,409 146,379 Ba2 — 6,810 — 6,810 Total $ 686,582 $ 92,733 $ 272,706 $ 1,052,021 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 September 30, 2018 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 12,434 $ 12,434 Commercial and industrial 322 346 — 668 783,292 783,960 Municipal — — — — 94,532 94,532 Commercial real estate 980 196 — 1,176 729,089 730,265 Residential real estate 1,668 2,678 372 4,718 330,396 335,114 Consumer and overdrafts 15 10 — 25 21,191 21,216 Home equity 752 499 99 1,350 282,468 283,818 Total $ 3,737 $ 3,729 $ 471 $ 7,937 $ 2,253,402 $ 2,261,339 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 September 30, 2018: Carrying Unpaid Required Average Interest Average Interest With no required reserve recorded: (in thousands) Construction and land development $ — $ — $ — $ — $ — $ — $ — Commercial and industrial 84 282 — 56 — 47 — Municipal — — — — — — — Commercial real estate 196 219 — 280 — 267 — Residential real estate — — — — — — — Consumer — — — — — — — Home equity — — — — — — — Total $ 280 $ 501 $ — $ 336 $ — $ 314 $ — With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — $ — $ — Commercial and industrial 576 593 93 589 5 490 14 Municipal — — — — — — — Commercial real estate 2,484 2,597 95 2,262 24 2,278 71 Residential real estate 2,675 2,675 350 2,675 — 3,136 80 Consumer — — — — — — — Home equity — — — — — — — Total $ 5,735 $ 5,865 $ 538 $ 5,526 $ 29 $ 5,904 $ 165 Total: Construction and land development $ — $ — $ — $ — $ — $ — $ — Commercial and industrial 660 875 93 645 5 537 14 Municipal — — — — — — — Commercial real estate 2,680 2,816 95 2,542 24 2,545 71 Residential real estate 2,675 2,675 350 2,675 — 3,136 80 Consumer — — — — — — — Home equity — — — — — — — Total $ 6,015 $ 6,366 $ 538 $ 5,862 $ 29 $ 6,218 $ 165 The following is information pertaining to impaired loans for September 30, 2017: Carrying Unpaid Required Average Interest Average Interest With no required reserve recorded: (in thousands) Construction and land development $ — $ — $ — $ — $ — $ — $ — Commercial and industrial 54 261 — 60 — 49 — Municipal — — — — — — — Commercial real estate 91 109 — 45 — 313 — Residential real estate 72 163 — 75 2 81 5 Consumer — — — — — — — Home equity — — — — — — — Total $ 217 $ 533 $ — $ 180 $ 2 $ 443 $ 5 With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — $ 56 $ — Commercial and industrial 312 328 8 319 4 328 12 Municipal — — — — — — — Commercial real estate 2,492 2,599 111 2,547 22 2,542 69 Residential real estate 4,246 4,247 67 4,257 19 1,767 36 Consumer — — — — — — — Home equity — — — — — — — Total $ 7,050 $ 7,174 $ 186 $ 7,123 $ 45 $ 4,693 $ 117 Total: Construction and land development $ — $ — $ — $ — $ — $ 56 $ — Commercial and industrial 366 589 8 379 4 377 12 Municipal — — — — — — — Commercial real estate 2,583 2,708 111 2,592 22 2,855 69 Residential real estate 4,318 4,410 67 4,332 21 1,848 41 Consumer — — — — — — — Home equity — — — — — — — Total $ 7,267 $ 7,707 $ 186 $ 7,303 $ 47 $ 5,136 $ 122 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 nine month period ended September 30, 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 nine months of 2017.

Reclassifications Out of Accumu

Reclassifications Out of Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 30, 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 Three Three Affected Line Item in the Statement where Net Income is Presented (in thousands) Unrealized gains and losses on available-for-sale $ 105 $ 47 Net gains on sales of investments Tax (expense) or benefit (29 ) (19 ) Provision for income taxes Net of tax $ 76 $ 28 Net income Accretion of unrealized losses transferred $ (323 ) $ (554 ) Interest on securities held-to-maturity Tax (expense) or benefit 85 331 Provision for income taxes Net of tax $ (238 ) $ (223 ) Net income Amortization of defined benefit pension items Prior-service costs $ (4 ) $ (3 )(b) Salaries and employee benefits Actuarial gains (losses) (402 ) (385 )(b) Salaries and employee benefits Total before tax (406 ) (388 ) Income before taxes Tax (expense) or benefit 114 155 Provision for income taxes Net of tax $ (292 ) $ (233 ) Net income Details about Accumulated Other Nine Nine Affected Line Item in the Statement where Net Income is Presented (in thousands) Unrealized gains and losses on available-for-sale $ 302 $ 47 Net gains on sales of investments Tax (expense) or benefit (85 ) (19 ) Provision for income taxes Net of tax $ 217 $ 28 Net income Accretion of unrealized losses transferred $ (1,186 ) $ (1,878 ) Interest on securities held-to-maturity Tax (expense) or benefit 314 1,022 Provision for income taxes Net of tax $ (872 ) $ (856 ) Net income Amortization of defined benefit pension items Prior-service costs $ (12 ) $ (8 )(b) Salaries and employee benefits Actuarial gains (losses) (1,207 ) (1,155 )(b) Salaries and employee benefits Total before tax (1,219 ) (1,163 ) Income before taxes Tax (expense) or benefit 342 465 Provision for income taxes Net of tax $ (877 ) $ (698 ) 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")	9 Months Ended
	Sep. 30, 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 September 30, 2018 and 2017. The following table is a reconciliation of basic EPS and diluted EPS. Three Months Ended Nine Months Ended (in thousands except share and per share data) 2018 2017 2018 2017 Basic EPS Computation: Numerator: Net income, Class A $ 7,535 $ 6,307 $ 20,674 $ 17,505 Net income, Class B 2,046 1,716 5,614 4,771 Denominator: Weighted average shares outstanding, Class A 3,608,329 3,605,829 3,608,129 3,603,429 Weighted average shares outstanding, Class B 1,959,580 1,962,080 1,959,780 1,964,480 Basic EPS, Class A $ 2.09 $ 1.75 $ 5.73 $ 4.86 Basic EPS, Class B 1.04 0.87 2.86 2.43 Diluted EPS Computation: Numerator: Net income, Class A $ 7,535 $ 6,307 $ 20,674 $ 17,505 Net income, Class B 2,046 1,716 5,614 4,771 Total net income, for diluted EPS, Class A computation 9,581 8,023 26,288 22,276 Denominator: Weighted average shares outstanding, basic, Class A 3,608,329 3,605,829 3,608,129 3,603,429 Weighted average shares outstanding, Class B 1,959,580 1,962,080 1,959,780 1,964,480 Weighted average shares outstanding diluted, Class A 5,567,909 5,567,909 5,567,909 5,567,909 Weighted average shares outstanding, Class B 1,959,580 1,962,080 1,959,780 1,964,480 Diluted EPS, Class A $ 1.72 $ 1.44 $ 4.72 $ 4.00 Diluted EPS, Class B 1.04 0.87 2.86 2.43

Employee Benefits

Employee Benefits	9 Months Ended
	Sep. 30, 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 September 30, Pension Benefits Supplemental Insurance/ 2018 2017 2018 2017 (in thousands) Service cost $ 353 $ 310 $ 277 $ 395 Interest 371 362 346 345 Expected return on plan assets (954 ) (746 ) — — Recognized prior service cost (benefit) (25 ) (26 ) 29 29 Recognized net actuarial losses 226 226 176 159 Net periodic benefit (credit) cost $ (29 ) $ 126 $ 828 $ 928 Components of Net Periodic Benefit Cost for the Six Months Ended June 30, Pension Benefits Supplemental Insurance/ 2018 2017 2018 2017 (in thousands) Service cost $ 1,059 $ 930 $ 831 $ 1,184 Interest 1,111 1,087 1,040 1,035 Expected return on plan assets (2,863 ) (2,238 ) — — Recognized prior service cost (benefit) (75 ) (78 ) 87 87 Recognized net actuarial losses 680 678 527 477 Net periodic benefit (credit) cost $ (88 ) $ 379 $ 2,485 $ 2,783 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	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 8. Fair Value Measurements The Company follows FASB ASC 820-10, 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 September 30, 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 $ 1,986 $ — $ 1,986 $ — U.S. Government Sponsored Enterprises 3,889 — 3,889 — SBA Backed Securities 71,124 — 71,124 — U.S. Government Agency and Sponsored Mortgage-Backed Securities 169,215 — 169,215 — Privately Issued Residential Mortgage-Backed Securities 715 — 715 — Obligations Issued by States and Political Subdivisions 116,009 — 4,775 111,234 Other Debt Securities 3,565 — 3,565 — Total $ 366,503 $ — $ 255,269 $ 111,234 Financial Instruments Measured at Fair Value on a Non-recurring Impaired Loans $ 3,107 $ — $ — $ 3,107 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 (credits) provisions relate to impaired loans recognized for the three and nine month periods ended September 30, 2018 amounted to $(187,000) and $427,000, respectively. 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 Securities AFS (4) $ 111,234 Discounted cash flow Discount rate 2.0%-4.5% (3) Impaired Loans $ 3,107 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. The changes in Level 3 securities for the nine month period ended September 30, 2018 are shown in the table below: Auction Rate Obligations & Political Total (in thousands) Balance at December 31, 2017 $ 4,459 $ 78,141 $ 82,600 Purchases — 105,837 105,837 Maturities and calls — (72,640 ) (72,640 ) Transfer (4,459 ) — (4,459 ) Amortization — (104 ) (104 ) Changes in fair value — — — Balance at September 30, 2018 $ — $ 111,234 $ 111,234 The amortized cost of Level 3 securities was $111,234,000 at September 30, 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 nine months ended September 30, 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 nine month period ended September 30, 2018. The changes in Level 3 securities for the nine month period ended September 30, 2017, are shown in the table below: Auction Rate Obligations Total (in thousands) Balance at December 31, 2016 $ 4,298 $ 160,578 $ 164,876 Purchases — 61,393 61,393 Maturities and calls — (146,869 ) (146,869 ) Amortization — (155 ) (155 ) Changes in fair value — — — Balance at September 30, 2017 $ 4,298 $ 74,947 $ 79,245 The amortized cost of Level 3 securities was $79,655,000 at September 30, 2017 with an unrealized loss of $410,000. The securities in this category are generally 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 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	9 Months Ended
	Sep. 30, 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 September 30, 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 September 30, 2018 Carrying Estimated Fair Value Level 2 Level 3 (in thousands) Financial assets: Securities held-to-maturity $ 1,875,752 $ 1,795,117 $ — $ 1,795,117 $ — Loans (1) 2,232,794 2,188,606 — — 2,188,606 Financial liabilities: Time deposits 579,886 577,531 — 577,531 — Other borrowed funds 372,606 371,531 — 371,531 — 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	9 Months Ended
	Sep. 30, 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 March 2018 Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2018-05: In February 2018, the FASB issued ASU 2018-03, 825-10) 2016-1. In February 2018, the FASB issued 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 August 2018, FASB issued ASU 2018-15, 350-40): internal-use In August 2018, FASB issued ASU 2018-14, 715-20): In August 2018, FASB issued ASU 2018-13, In July 2017, FASB issued ASU 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, In July 2018, ASU 2018-10, 2018-10”) 2016-02. Also 2018-11, 2018-11”) Securities and Exchange Commission (SEC) ruling: In August 2018, the SEC issued a final rule that amends certain of the Commission’s disclosure requirements “that have become redundant, duplicative, overlapping, outdated, or superseded, in light of other Commission disclosure requirements, U.S. GAAP, or changes in the information environment.” The financial reporting implications of the final rule’s amendments may vary by company, but the changes are generally expected to reduce or eliminate some of an SEC registrant’s disclosure requirements. In limited circumstances, however, the amendments may expand those requirements, including those related to interim disclosures about changes in stockholders’ equity. Under the requirements, registrants must now analyze changes in stockholders’ equity, in the form of a reconciliation, for “the current and comparative year-to-date year-to-date 10-Q.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	9 Months Ended
	Sep. 30, 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 month and nine months ended September 30, 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. Nine Revenue from Nine Revenue from (dollars in thousands) Total net interest income $ 68,871 $ — $ 63,914 $ — Noninterest income: Service charges on deposit accounts 6,268 6,268 6,179 6,179 Lockbox fees 2,304 2,304 2,367 2,367 Net gains on sales of securities 302 — 47 — Gains on sales of mortgage loans — — 370 — Other income 3,210 2,215 3,179 2,048 Total noninterest income 12,084 10,787 12,142 10,594 Total revenues $ 80,955 $ 10,787 $ 76,056 $ 10,594 Three Revenue from Three Revenue from (dollars in thousands) Total net interest income $ 23,204 $ — $ 21,353 $ — Noninterest income: Service charges on deposit accounts 2,137 2,137 2,089 2,089 Lockbox fees 892 892 735 735 Net gains on sales of securities 105 — 47 — Gains on sales of mortgage loans — — — — Other income 1,035 751 1,071 712 Total noninterest income 4,169 3,780 3,942 3,536 Total revenues $ 27,373 $ 3,780 $ 25,295 $ 3,536 The following table provides information about receivables with customers. (dollars in thousands) September 30, 2018 December 31, 2017 Receivables, which are included in “Other assets” $ 1,095 $ 1,009

Securities Available-for-Sale (

Securities Available-for-Sale (Tables)	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Summary of Securities Available-for-Sale	September 30, 2018 December 31, 2017 Amortized Gross Gross Fair Amortized Gross Gross Fair (in thousands) U.S. Treasury $ 1,999 $ — $ 13 $ 1,986 $ 1,999 $ — $ 15 $ 1,984 U.S. Government Sponsored Enterprises 3,942 — 53 3,889 — — — — SBA Backed Securities 71,417 — 293 71,124 81,065 46 161 80,950 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 168,760 666 211 169,215 225,537 556 317 225,776 Privately Issued Residential Mortgage-Backed Securities 720 4 9 715 897 4 9 892 Obligations Issued by States and Political Subdivisions 115,947 62 — 116,009 82,849 — 249 82,600 Other Debt Securities 3,600 21 56 3,565 3,600 68 39 3,629 Total $ 366,385 $ 753 $ 635 $ 366,503 $ 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 $ 115,302 $ 115,282 After one but within five years 60,862 60,682 After five but within ten years 156,425 156,782 More than 10 years 33,796 33,757 Total $ 366,385 $ 366,503
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 September 30, 2018 Less than 12 months 12 months or longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Treasury $ — $ — $ 1,986 $ 13 $ 1,986 $ 13 U.S. Government Sponsored Enterprises 3,889 53 — — 3,889 53 SBA Backed Securities 25,567 42 45,557 251 71,124 293 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 31,311 60 26,032 151 57,343 211 Privately Issued Residential Mortgage-Backed Securities — — 524 9 524 9 Obligations Issued by States and Political Subdivisions — — — — — — Other Debt Securities — — 744 56 744 56 Total temporarily impaired securities $ 60,767 $ 155 $ 74,843 $ 480 $ 135,610 $ 635 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 54 40,911 107 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 1 461 38 861 39 Total temporarily impaired securities $ 61,156 $ 193 $ 105,799 $ 597 $ 166,955 $ 790

Investment Securities Held-to_2

Investment Securities Held-to-Maturity (Tables)	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Summary of Held-to-Maturity Securities	September 30, 2018 December 31, 2017 Amortized Gross Gross Estimated Amortized Gross Gross Estimated (in thousands) U.S. Treasury $ 9,903 $ — $ 3 $ 9,900 $ — $ — $ — $ — U.S. Government Sponsored Enterprises 167,968 — 2,152 165,816 104,653 341 472 104,522 SBA Backed Securities 53,576 — 2,759 50,817 57,235 20 1,271 55,984 U.S. Government Agency and Sponsored Enterprises Mortgage-Backed Securities 1,644,305 139 75,860 1,568,584 1,539,345 2,261 33,285 1,508,321 Total $ 1,875,752 $ 139 $ 80,774 $ 1,795,117 $ 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 $ 39,091 $ 38,932 After one but within five years 1,210,561 1,163,813 After five but within ten years 622,996 589,508 More than ten years 3,104 2,864 Total $ 1,875,752 $ 1,795,117
Unrealized Market Loss of Securities	The following table shows the temporarily impaired securities of the Company’s held-to-maturity September 30, 2018 Less Than 12 Months 12 Months or Longer Total Temporarily Impaired Investments Fair Unrealized Fair Unrealized Fair Unrealized (in thousands) U.S. Treasury $ 9,900 $ 3 $ — $ — $ 9,900 $ 3 U.S. Government Sponsored Enterprises 135,760 1,171 29,517 981 165,277 2,152 SBA Backed Securities 2,487 75 48,330 2,684 50,817 2,759 U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities 557,866 13,733 997,268 62,127 1,555,134 75,860 Total temporarily impaired securities $ 706,013 $ 14,982 $ 1,075,115 $ 65,792 $ 1,781,128 $ 80,774 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)	9 Months Ended
	Sep. 30, 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 Nine months ended 2018 2017 2018 2017 (in thousands) Allowance for loan losses, beginning of period $ 27,144 $ 25,289 $ 26,255 $ 24,406 Loans charged off (89 ) (95 ) (247 ) (292 ) Recoveries on loans previously charged-off 1,490 54 1,637 244 Net recoveries (charge-offs) 1,401 (41 ) 1,390 (48 ) Provision charged to expense — 450 900 1,340 Allowance for loan losses, end of period $ 28,545 $ 25,698 $ 28,545 $ 25,698
Summary of Allowance for Loan Losses	Further information pertaining to the allowance for loan losses for the three months ending September 30, 2018 follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total Allowance for loan losses: (in thousands) Balance at June 30, 2018 $ 633 $ 10,384 $ 1,704 $ 10,209 $ 2,493 $ 336 $ 1,078 $ 307 $ 27,144 Charge-offs — (11 ) — — — (78 ) — — (89 ) Recoveries 1,432 16 — — — 42 — — 1,490 Provision (1,155 ) 895 84 415 (182 ) 32 (28 ) (61 ) — Ending balance at September 30, 2018 $ 910 $ 11,284 $ 1,788 $ 10,624 $ 2,311 $ 332 $ 1,050 $ 246 $ 28,545 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 93 $ — $ 95 $ 350 $ — $ — $ — $ 538 Amount of allowance for loan losses for loans not deemed to be impaired $ 910 $ 11,191 $ 1,788 $ 10,529 $ 1,961 $ 332 $ 1,050 $ 246 $ 28,007 Loans: Ending balance $ 12,434 $ 783,960 $ 94,532 $ 730,265 $ 335,114 $ 21,216 $ 283,818 $ — $ 2,261,339 Loans deemed to be impaired $ — $ 660 $ — $ 2,680 $ 2,675 $ — $ — $ — $ 6,015 Loans not deemed to be impaired $ 12,434 $ 783,300 $ 94,532 $ 727,585 $ 332,439 $ 21,216 $ 283,818 $ — $ 2,255,324 Further information pertaining to the allowance for loan losses for the nine months ending September 30, 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 — (16 ) — — — (231 ) — — (247 ) Recoveries 1,432 49 — — — 156 — — 1,637 Provision (2,167 ) 1,600 68 896 438 34 61 (30 ) 900 Ending balance at September 30, 2018 $ 910 $ 11,284 $ 1,788 $ 10,624 $ 2,311 $ 332 $ 1,050 $ 246 $ 28,545 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 93 $ — $ 95 $ 350 $ — $ — $ — $ 538 Amount of allowance for loan losses for loans not deemed to be impaired $ 910 $ 11,191 $ 1,788 $ 10,529 $ 1,961 $ 332 $ 1,050 $ 246 $ 28,007 Loans: Ending balance $ 12,434 $ 783,960 $ 94,532 $ 730,265 $ 335,114 $ 21,216 $ 283,818 $ — $ 2,261,339 Loans deemed to be impaired $ — $ 660 $ — $ 2,680 $ 2,675 $ — $ — $ — $ 6,015 Loans not deemed to be impaired $ 12,434 $ 783,300 $ 94,532 $ 727,585 $ 332,439 $ 21,216 $ 283,818 $ — $ 2,255,324 Further information pertaining to the allowance for loan losses for the three months ending September 30, 2017 follows: Construction Commercial Municipal Commercial Residential Consumer Home Unallocated Total Allowance for loan losses: (in thousands) Balance at June 30, 2017 $ 1,137 $ 7,563 $ 1,859 $ 11,028 $ 2,118 $ 195 $ 1,146 $ 243 $ 25,289 Charge-offs — (20 ) — — — (75 ) — — (95 ) Recoveries — 9 — — — 45 — — 54 Provision 323 1,297 265 (1,491 ) (45 ) 220 (103 ) (16 ) 450 Ending balance at September 30, 2017 $ 1,460 $ 8,849 $ 2,124 $ 9,537 $ 2,073 $ 385 $ 1,043 $ 227 $ 25,698 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 8 $ — $ 111 $ 67 $ — $ — $ — $ 186 Amount of allowance for loan losses for loans not deemed to be impaired $ 1,460 $ 8,841 $ 2,124 $ 9,426 $ 2,006 $ 385 $ 1,043 $ 227 $ 25,512 Loans: Ending balance $ 16,779 $ 702,646 $ 128,412 $ 735,844 $ 272,588 $ 19,284 $ 237,094 $ — $ 2,112,647 Loans deemed to be impaired $ — $ 366 $ — $ 2,583 $ 4,318 $ — $ — $ — $ 7,267 Loans not deemed to be impaired $ 16,779 $ 702,280 $ 128,412 $ 733,261 $ 268,270 $ 19,284 $ 237,094 $ — $ 2,105,380 Further information pertaining to the allowance for loan losses for the nine months ending September 30, 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 — (49 ) — — — (243 ) — — (292 ) Recoveries — 63 — — 2 179 — — 244 Provision 448 1,863 512 (1,598 ) 373 (133 ) (59 ) (66 ) 1,340 Ending balance at September 30, 2017 $ 1,460 $ 8,849 $ 2,124 $ 9,537 $ 2,073 $ 385 $ 1,043 $ 227 $ 25,698 Amount of allowance for loan losses for loans deemed to be impaired $ — $ 8 $ — $ 111 $ 67 $ — $ — $ — $ 186 Amount of allowance for loan losses for loans not deemed to be impaired $ 1,460 $ 8,841 $ 2,124 $ 9,426 $ 2,006 $ 385 $ 1,043 $ 227 $ 25,512 Loans: Ending balance $ 16,779 $ 702,646 $ 128,412 $ 735,844 $ 272,588 $ 19,284 $ 237,094 $ — $ 2,112,647 Loans deemed to be impaired $ — $ 366 $ — $ 2,583 $ 4,318 $ — $ — $ — $ 7,267 Loans not deemed to be impaired $ 16,779 $ 702,280 $ 128,412 $ 733,261 $ 268,270 $ 19,284 $ 237,094 $ — $ 2,105,380
Loans by Risk Rating	The following table presents the Company’s loans by risk rating at September 30, 2018. Construction Commercial Municipal Commercial Grade: (in thousands) 1-3 $ 12,434 $ 779,165 $ 94,532 $ 703,039 4 (Monitor) — 4,135 — 24,546 5 (Substandard) — — — — 6 (Doubtful) — — — — Impaired — 660 — 2,680 Total $ 12,434 $ 783,960 $ 94,532 $ 730,265 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	Credit ratings issued by national organizations were utilized as credit quality indicators as presented in the following table at September 30, 2018 and are included within the total loan portfolio. Commercial Municipal Commercial Total Credit Rating: (in thousands) Aaa – Aa3 $ 492,117 $ 57,958 $ 43,106 $ 593,181 A1 – A3 194,465 995 110,191 305,651 Baa1 – Baa3 — 26,970 119,409 146,379 Ba2 — 6,810 — 6,810 Total $ 686,582 $ 92,733 $ 272,706 $ 1,052,021 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 September 30, 2018 follows: Accruing 30-89 Days Non Accruing Total Current Total (in thousands) Construction and land development $ — $ — $ — $ — $ 12,434 $ 12,434 Commercial and industrial 322 346 — 668 783,292 783,960 Municipal — — — — 94,532 94,532 Commercial real estate 980 196 — 1,176 729,089 730,265 Residential real estate 1,668 2,678 372 4,718 330,396 335,114 Consumer and overdrafts 15 10 — 25 21,191 21,216 Home equity 752 499 99 1,350 282,468 283,818 Total $ 3,737 $ 3,729 $ 471 $ 7,937 $ 2,253,402 $ 2,261,339 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 September 30, 2018: Carrying Unpaid Required Average Interest Average Interest With no required reserve recorded: (in thousands) Construction and land development $ — $ — $ — $ — $ — $ — $ — Commercial and industrial 84 282 — 56 — 47 — Municipal — — — — — — — Commercial real estate 196 219 — 280 — 267 — Residential real estate — — — — — — — Consumer — — — — — — — Home equity — — — — — — — Total $ 280 $ 501 $ — $ 336 $ — $ 314 $ — With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — $ — $ — Commercial and industrial 576 593 93 589 5 490 14 Municipal — — — — — — — Commercial real estate 2,484 2,597 95 2,262 24 2,278 71 Residential real estate 2,675 2,675 350 2,675 — 3,136 80 Consumer — — — — — — — Home equity — — — — — — — Total $ 5,735 $ 5,865 $ 538 $ 5,526 $ 29 $ 5,904 $ 165 Total: Construction and land development $ — $ — $ — $ — $ — $ — $ — Commercial and industrial 660 875 93 645 5 537 14 Municipal — — — — — — — Commercial real estate 2,680 2,816 95 2,542 24 2,545 71 Residential real estate 2,675 2,675 350 2,675 — 3,136 80 Consumer — — — — — — — Home equity — — — — — — — Total $ 6,015 $ 6,366 $ 538 $ 5,862 $ 29 $ 6,218 $ 165 The following is information pertaining to impaired loans for September 30, 2017: Carrying Unpaid Required Average Interest Average Interest With no required reserve recorded: (in thousands) Construction and land development $ — $ — $ — $ — $ — $ — $ — Commercial and industrial 54 261 — 60 — 49 — Municipal — — — — — — — Commercial real estate 91 109 — 45 — 313 — Residential real estate 72 163 — 75 2 81 5 Consumer — — — — — — — Home equity — — — — — — — Total $ 217 $ 533 $ — $ 180 $ 2 $ 443 $ 5 With required reserve recorded: Construction and land development $ — $ — $ — $ — $ — $ 56 $ — Commercial and industrial 312 328 8 319 4 328 12 Municipal — — — — — — — Commercial real estate 2,492 2,599 111 2,547 22 2,542 69 Residential real estate 4,246 4,247 67 4,257 19 1,767 36 Consumer — — — — — — — Home equity — — — — — — — Total $ 7,050 $ 7,174 $ 186 $ 7,123 $ 45 $ 4,693 $ 117 Total: Construction and land development $ — $ — $ — $ — $ — $ 56 $ — Commercial and industrial 366 589 8 379 4 377 12 Municipal — — — — — — — Commercial real estate 2,583 2,708 111 2,592 22 2,855 69 Residential real estate 4,318 4,410 67 4,332 21 1,848 41 Consumer — — — — — — — Home equity — — — — — — — Total $ 7,267 $ 7,707 $ 186 $ 7,303 $ 47 $ 5,136 $ 122

Reclassifications Out of Accu_2

Reclassifications Out of Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Reclassifications Out of Accumulated Other Comprehensive Income	Amount Reclassified from Accumulated Other Comprehensive Income Details about Accumulated Other Three Three Affected Line Item in the Statement where Net Income is Presented (in thousands) Unrealized gains and losses on available-for-sale $ 105 $ 47 Net gains on sales of investments Tax (expense) or benefit (29 ) (19 ) Provision for income taxes Net of tax $ 76 $ 28 Net income Accretion of unrealized losses transferred $ (323 ) $ (554 ) Interest on securities held-to-maturity Tax (expense) or benefit 85 331 Provision for income taxes Net of tax $ (238 ) $ (223 ) Net income Amortization of defined benefit pension items Prior-service costs $ (4 ) $ (3 )(b) Salaries and employee benefits Actuarial gains (losses) (402 ) (385 )(b) Salaries and employee benefits Total before tax (406 ) (388 ) Income before taxes Tax (expense) or benefit 114 155 Provision for income taxes Net of tax $ (292 ) $ (233 ) Net income Details about Accumulated Other Nine Nine Affected Line Item in the Statement where Net Income is Presented (in thousands) Unrealized gains and losses on available-for-sale $ 302 $ 47 Net gains on sales of investments Tax (expense) or benefit (85 ) (19 ) Provision for income taxes Net of tax $ 217 $ 28 Net income Accretion of unrealized losses transferred $ (1,186 ) $ (1,878 ) Interest on securities held-to-maturity Tax (expense) or benefit 314 1,022 Provision for income taxes Net of tax $ (872 ) $ (856 ) Net income Amortization of defined benefit pension items Prior-service costs $ (12 ) $ (8 )(b) Salaries and employee benefits Actuarial gains (losses) (1,207 ) (1,155 )(b) Salaries and employee benefits Total before tax (1,219 ) (1,163 ) Income before taxes Tax (expense) or benefit 342 465 Provision for income taxes Net of tax $ (877 ) $ (698 ) 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)	9 Months Ended
	Sep. 30, 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 Nine Months Ended (in thousands except share and per share data) 2018 2017 2018 2017 Basic EPS Computation: Numerator: Net income, Class A $ 7,535 $ 6,307 $ 20,674 $ 17,505 Net income, Class B 2,046 1,716 5,614 4,771 Denominator: Weighted average shares outstanding, Class A 3,608,329 3,605,829 3,608,129 3,603,429 Weighted average shares outstanding, Class B 1,959,580 1,962,080 1,959,780 1,964,480 Basic EPS, Class A $ 2.09 $ 1.75 $ 5.73 $ 4.86 Basic EPS, Class B 1.04 0.87 2.86 2.43 Diluted EPS Computation: Numerator: Net income, Class A $ 7,535 $ 6,307 $ 20,674 $ 17,505 Net income, Class B 2,046 1,716 5,614 4,771 Total net income, for diluted EPS, Class A computation 9,581 8,023 26,288 22,276 Denominator: Weighted average shares outstanding, basic, Class A 3,608,329 3,605,829 3,608,129 3,603,429 Weighted average shares outstanding, Class B 1,959,580 1,962,080 1,959,780 1,964,480 Weighted average shares outstanding diluted, Class A 5,567,909 5,567,909 5,567,909 5,567,909 Weighted average shares outstanding, Class B 1,959,580 1,962,080 1,959,780 1,964,480 Diluted EPS, Class A $ 1.72 $ 1.44 $ 4.72 $ 4.00 Diluted EPS, Class B 1.04 0.87 2.86 2.43

Employee Benefits (Tables)

Employee Benefits (Tables)	9 Months Ended
	Sep. 30, 2018
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost	Components of Net Periodic Benefit Cost for the Three Months Ended September 30, Pension Benefits Supplemental Insurance/ 2018 2017 2018 2017 (in thousands) Service cost $ 353 $ 310 $ 277 $ 395 Interest 371 362 346 345 Expected return on plan assets (954 ) (746 ) — — Recognized prior service cost (benefit) (25 ) (26 ) 29 29 Recognized net actuarial losses 226 226 176 159 Net periodic benefit (credit) cost $ (29 ) $ 126 $ 828 $ 928 Components of Net Periodic Benefit Cost for the Six Months Ended June 30, Pension Benefits Supplemental Insurance/ 2018 2017 2018 2017 (in thousands) Service cost $ 1,059 $ 930 $ 831 $ 1,184 Interest 1,111 1,087 1,040 1,035 Expected return on plan assets (2,863 ) (2,238 ) — — Recognized prior service cost (benefit) (75 ) (78 ) 87 87 Recognized net actuarial losses 680 678 527 477 Net periodic benefit (credit) cost $ (88 ) $ 379 $ 2,485 $ 2,783

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 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 $ 1,986 $ — $ 1,986 $ — U.S. Government Sponsored Enterprises 3,889 — 3,889 — SBA Backed Securities 71,124 — 71,124 — U.S. Government Agency and Sponsored Mortgage-Backed Securities 169,215 — 169,215 — Privately Issued Residential Mortgage-Backed Securities 715 — 715 — Obligations Issued by States and Political Subdivisions 116,009 — 4,775 111,234 Other Debt Securities 3,565 — 3,565 — Total $ 366,503 $ — $ 255,269 $ 111,234 Financial Instruments Measured at Fair Value on a Non-recurring Impaired Loans $ 3,107 $ — $ — $ 3,107 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 Securities AFS (4) $ 111,234 Discounted cash flow Discount rate 2.0%-4.5% (3) Impaired Loans $ 3,107 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. 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 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 nine month period ended September 30, 2018 are shown in the table below: Auction Rate Obligations & Political Total (in thousands) Balance at December 31, 2017 $ 4,459 $ 78,141 $ 82,600 Purchases — 105,837 105,837 Maturities and calls — (72,640 ) (72,640 ) Transfer (4,459 ) — (4,459 ) Amortization — (104 ) (104 ) Changes in fair value — — — Balance at September 30, 2018 $ — $ 111,234 $ 111,234 The changes in Level 3 securities for the nine month period ended September 30, 2017, are shown in the table below: Auction Rate Obligations Total (in thousands) Balance at December 31, 2016 $ 4,298 $ 160,578 $ 164,876 Purchases — 61,393 61,393 Maturities and calls — (146,869 ) (146,869 ) Amortization — (155 ) (155 ) Changes in fair value — — — Balance at September 30, 2017 $ 4,298 $ 74,947 $ 79,245

Fair Values of Financial Inst_2

Fair Values of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 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 September 30, 2018 Carrying Estimated Fair Value Level 2 Level 3 (in thousands) Financial assets: Securities held-to-maturity $ 1,875,752 $ 1,795,117 $ — $ 1,795,117 $ — Loans (1) 2,232,794 2,188,606 — — 2,188,606 Financial liabilities: Time deposits 579,886 577,531 — 577,531 — Other borrowed funds 372,606 371,531 — 371,531 — 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 C_2

Revenue from Contracts with Customers (Tables)	9 Months Ended
	Sep. 30, 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. Nine Revenue from Nine Revenue from (dollars in thousands) Total net interest income $ 68,871 $ — $ 63,914 $ — Noninterest income: Service charges on deposit accounts 6,268 6,268 6,179 6,179 Lockbox fees 2,304 2,304 2,367 2,367 Net gains on sales of securities 302 — 47 — Gains on sales of mortgage loans — — 370 — Other income 3,210 2,215 3,179 2,048 Total noninterest income 12,084 10,787 12,142 10,594 Total revenues $ 80,955 $ 10,787 $ 76,056 $ 10,594 Three Revenue from Three Revenue from (dollars in thousands) Total net interest income $ 23,204 $ — $ 21,353 $ — Noninterest income: Service charges on deposit accounts 2,137 2,137 2,089 2,089 Lockbox fees 892 892 735 735 Net gains on sales of securities 105 — 47 — Gains on sales of mortgage loans — — — — Other income 1,035 751 1,071 712 Total noninterest income 4,169 3,780 3,942 3,536 Total revenues $ 27,373 $ 3,780 $ 25,295 $ 3,536
Information about Receivables with Customers	The following table provides information about receivables with customers. (dollars in thousands) September 30, 2018 December 31, 2017 Receivables, which are included in “Other assets” $ 1,095 $ 1,009

Basis of Financial Statement _2

Basis of Financial Statement Presentation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 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	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 366,385	$ 395,947
Gross Unrealized Gains	753	674
Gross Unrealized Losses	635	790
Total, Fair Value	366,503	395,831
U.S. Treasury [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,999	1,999
Gross Unrealized Losses	13	15
Total, Fair Value	1,986	1,984
U.S. Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,942
Gross Unrealized Losses	53
Total, Fair Value	3,889
SBA Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	71,417	81,065
Gross Unrealized Gains		46
Gross Unrealized Losses	293	161
Total, Fair Value	71,124	80,950
U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	168,760	225,537
Gross Unrealized Gains	666	556
Gross Unrealized Losses	211	317
Total, Fair Value	169,215	225,776
Privately Issued Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	720	897
Gross Unrealized Gains	4	4
Gross Unrealized Losses	9	9
Total, Fair Value	715	892
Obligations Issued by States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	115,947	82,849
Gross Unrealized Gains	62
Gross Unrealized Losses		249
Total, Fair Value	116,009	82,600
Other Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,600	3,600
Gross Unrealized Gains	21	68
Gross Unrealized Losses	56	39
Total, Fair Value	$ 3,565	$ 3,629

Securities Available-for-Sale_2

Securities Available-for-Sale - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)Security	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Security	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)Security
Debt Securities, Available-for-sale [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 1,267,793,000		$ 1,267,793,000		$ 1,262,708,000
Gross gains on sales of securities	105,000	$ 47,000	302,000	$ 47,000
Proceeds from sales of securities available-for-sale			27,517,000	$ 18,133,000
Federal Home Loan Bank [Member]
Debt Securities, Available-for-sale [Line Items]
Securities available-for-sale are securities at fair value pledged for borrowing	$ 35,852,000		$ 35,852,000		$ 67,780,000
Securities AFS [Member]
Debt Securities, Available-for-sale [Line Items]
Weighted average remaining life of investment securities available-for-sale			4 years 10 months 24 days
Number of securities, temporarily impaired for less than 12 months | Security	13		13		16
Number of securities, temporarily impaired for 12 months or longer | Security	25		25		28
Number of securities, temporarily impaired, total | Security	195		195		249
U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 210,362,000		$ 210,362,000		$ 216,353,000
U.S. Government Sponsored Enterprises [Member] | Securities AFS [Member]
Debt Securities, Available-for-sale [Line Items]
Weighted average remaining life	$ 3,942,000		$ 3,942,000

Securities Available-for-Sale_3

Securities Available-for-Sale - Maturity Distribution of Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 115,302
After one but within five years, Amortized Cost	60,862
After five but within ten years, Amortized Cost	156,425
More than 10 years, Amortized Cost	33,796
Amortized Cost	366,385	$ 395,947
Within one year, Fair Value	115,282
After one but within five years, Fair Value	60,682
After five but within ten years, Fair Value	156,782
More than 10 years, Fair Value	33,757
Total, Fair Value	$ 366,503	$ 395,831

Securities Available-for-Sale_4

Securities Available-for-Sale - Continuous Unrealized Loss Position for Less than 12 Months and 12 Months or Longer (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	$ 60,767	$ 61,156
Less Than 12 Months, Unrealized Losses	155	193
12 Months or Longer, Fair Value	74,843	105,799
12 Months or Longer, Unrealized Losses	480	597
Total, Fair Value	135,610	166,955
Total, Unrealized Losses	635	790
U.S. Treasury [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value		1,984
Less Than 12 Months, Unrealized Losses		15
12 Months or Longer, Fair Value	1,986
12 Months or Longer, Unrealized Losses	13
Total, Fair Value	1,986	1,984
Total, Unrealized Losses	13	15
U.S. Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	3,889
Less Than 12 Months, Unrealized Losses	53
Total, Fair Value	3,889
Total, Unrealized Losses	53
SBA Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	25,567	18,378
Less Than 12 Months, Unrealized Losses	42	54
12 Months or Longer, Fair Value	45,557	40,911
12 Months or Longer, Unrealized Losses	251	107
Total, Fair Value	71,124	59,289
Total, Unrealized Losses	293	161
U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value	31,311	40,394
Less Than 12 Months, Unrealized Losses	60	123
12 Months or Longer, Fair Value	26,032	59,336
12 Months or Longer, Unrealized Losses	151	194
Total, Fair Value	57,343	99,730
Total, Unrealized Losses	211	317
Privately Issued Residential Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
12 Months or Longer, Fair Value	524	633
12 Months or Longer, Unrealized Losses	9	9
Total, Fair Value	524	633
Total, Unrealized Losses	9	9
Obligations Issued by States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
12 Months or Longer, Fair Value		4,458
12 Months or Longer, Unrealized Losses		249
Total, Fair Value		4,458
Total, Unrealized Losses		249
Other Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, Fair Value		400
Less Than 12 Months, Unrealized Losses		1
12 Months or Longer, Fair Value	744	461
12 Months or Longer, Unrealized Losses	56	38
Total, Fair Value	744	861
Total, Unrealized Losses	$ 56	$ 39

Investment Securities Held-to_3

Investment Securities Held-to-Maturity - Summary of Held-to-Maturity Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 1,875,752	$ 1,701,233
Gross Unrealized Gains	139	2,622
Gross Unrealized Losses	80,774	35,028
Estimated Fair Value	1,795,117	1,668,827
U.S. Treasury [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	9,903
Gross Unrealized Losses	3
Estimated Fair Value	9,900
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	167,968	104,653
Gross Unrealized Gains		341
Gross Unrealized Losses	2,152	472
Estimated Fair Value	165,816	104,522
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	53,576	57,235
Gross Unrealized Gains		20
Gross Unrealized Losses	2,759	1,271
Estimated Fair Value	50,817	55,984
U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,644,305	1,539,345
Gross Unrealized Gains	139	2,261
Gross Unrealized Losses	75,860	33,285
Estimated Fair Value	$ 1,568,584	$ 1,508,321

Investment Securities Held-to_4

Investment Securities Held-to-Maturity - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018USD ($)Security	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)Security
Schedule of Held-to-maturity Securities [Line Items]
Securities at fair value pledged to secure public deposits and repurchase agreements	$ 1,267,793,000		$ 1,262,708,000
Sales of held-to-maturity securities	$ 0	$ 0
Held-to-Maturity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Weighted average remaining life of investment securities held-to-maturity	4 years 6 months
Number of securities, temporarily impaired for less than 12 months | Security	176		117
Number of securities, temporarily impaired for 12 months or longer | Security	232		168
Number of securities, temporarily impaired, total | Security	446		404
Held-to-Maturity Securities [Member] | U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Weighted average remaining life	$ 82,990,000
Federal Home Loan Bank [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities pledged for borrowing at the Federal Home Loan Bank	$ 515,979,000		$ 382,120,000

Investment Securities Held-to_5

Investment Securities Held-to-Maturity - Company's Securities Held-to-Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 39,091
After one but within five years, Amortized Cost	1,210,561
After five but within ten years, Amortized Cost	622,996
More than ten years, Amortized Cost	3,104
Amortized Cost	1,875,752	$ 1,701,233
Within one year, Fair Value	38,932
After one but within five years, Fair Value	1,163,813
After five but within ten years, Fair Value	589,508
More than ten years, Fair Value	2,864
Estimated Fair Value	$ 1,795,117	$ 1,668,827

Investment Securities Held-to_6

Investment Securities Held-to-Maturity - Unrealized Market Loss of Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	$ 706,013	$ 554,195
Less Than 12 Months, Unrealized Losses	14,982	6,301
12 Months or Longer, Fair Value	1,075,115	863,230
12 Months or Longer, Unrealized Losses	65,792	28,727
Total, Fair Value	1,781,128	1,417,425
Total, Unrealized Losses	80,774	35,028
U.S. Government Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	135,760	15,257
Less Than 12 Months, Unrealized Losses	1,171	239
12 Months or Longer, Fair Value	29,517	14,768
12 Months or Longer, Unrealized Losses	981	233
Total, Fair Value	165,277	30,025
Total, Unrealized Losses	2,152	472
SBA Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	2,487	19,457
Less Than 12 Months, Unrealized Losses	75	142
12 Months or Longer, Fair Value	48,330	33,750
12 Months or Longer, Unrealized Losses	2,684	1,129
Total, Fair Value	50,817	53,207
Total, Unrealized Losses	2,759	1,271
U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	557,866	519,481
Less Than 12 Months, Unrealized Losses	13,733	5,920
12 Months or Longer, Fair Value	997,268	814,712
12 Months or Longer, Unrealized Losses	62,127	27,365
Total, Fair Value	1,555,134	1,334,193
Total, Unrealized Losses	75,860	$ 33,285
U.S. Treasury [Member]
Schedule of Held-to-maturity Securities [Line Items]
Less Than 12 Months, Fair Value	9,900
Less Than 12 Months, Unrealized Losses	3
Total, Fair Value	9,900
Total, Unrealized Losses	$ 3

Allowance for Loan Losses - Ana

Allowance for Loan Losses - Analysis of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Receivables [Abstract]
Allowance for loan losses, beginning of period	$ 27,144	$ 25,289	$ 26,255	$ 24,406
Loans charged off	(89)	(95)	(247)	(292)
Recoveries on loans previously charged-off	1,490	54	1,637	244
Net recoveries (charge-offs)	1,401	(41)	1,390	(48)
Provision charged to expense		450	900	1,340
Allowance for loan losses, end of period	$ 28,545	$ 25,698	$ 28,545	$ 25,698

Allowance for Loan Losses - Sum

Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Allowance for loan losses:
Allowance for loan losses, beginning of period	$ 27,144,000	$ 25,289,000	$ 26,255,000	$ 24,406,000
Charge-offs	(89,000)	(95,000)	(247,000)	(292,000)
Recoveries	1,490,000	54,000	1,637,000	244,000
Provision		450,000	900,000	1,340,000
Allowance for loan losses, end of period	28,545,000	25,698,000	28,545,000	25,698,000
Amount of allowance for loan losses for loans deemed to be impaired	538,000	186,000	538,000	186,000
Amount of allowance for loan losses for loans not deemed to be impaired	28,007,000	25,512,000	28,007,000	25,512,000
Loans:
Total loans, net	2,261,339,000	2,112,647,000	2,261,339,000	2,112,647,000	$ 2,175,944,000
Loans deemed to be impaired	6,015,000	7,267,000	6,015,000	7,267,000
Loans not deemed to be impaired	2,255,324,000	2,105,380,000	2,255,324,000	2,105,380,000
Construction and Land Development [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	633,000	1,137,000	1,645,000	1,012,000
Recoveries	1,432,000		1,432,000
Provision	(1,155,000)	323,000	(2,167,000)	448,000
Allowance for loan losses, end of period	910,000	1,460,000	910,000	1,460,000
Amount of allowance for loan losses for loans not deemed to be impaired	910,000	1,460,000	910,000	1,460,000
Loans:
Total loans, net	12,434,000	16,779,000	12,434,000	16,779,000	18,931,000
Loans not deemed to be impaired	12,434,000	16,779,000	12,434,000	16,779,000
Commercial and Industrial [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	10,384,000	7,563,000	9,651,000	6,972,000
Charge-offs	(11,000)	(20,000)	(16,000)	(49,000)
Recoveries	16,000	9,000	49,000	63,000
Provision	895,000	1,297,000	1,600,000	1,863,000
Allowance for loan losses, end of period	11,284,000	8,849,000	11,284,000	8,849,000
Amount of allowance for loan losses for loans deemed to be impaired	93,000	8,000	93,000	8,000
Amount of allowance for loan losses for loans not deemed to be impaired	11,191,000	8,841,000	11,191,000	8,841,000
Loans:
Total loans, net	783,960,000	702,646,000	783,960,000	702,646,000	763,807,000
Loans deemed to be impaired	660,000	366,000	660,000	366,000
Loans not deemed to be impaired	783,300,000	702,280,000	783,300,000	702,280,000
Municipal [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,704,000	1,859,000	1,720,000	1,612,000
Provision	84,000	265,000	68,000	512,000
Allowance for loan losses, end of period	1,788,000	2,124,000	1,788,000	2,124,000
Amount of allowance for loan losses for loans not deemed to be impaired	1,788,000	2,124,000	1,788,000	2,124,000
Loans:
Total loans, net	94,532,000	128,412,000	94,532,000	128,412,000	106,599,000
Loans not deemed to be impaired	94,532,000	128,412,000	94,532,000	128,412,000
Commercial Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	10,209,000	11,028,000	9,728,000	11,135,000
Provision	415,000	(1,491,000)	896,000	(1,598,000)
Allowance for loan losses, end of period	10,624,000	9,537,000	10,624,000	9,537,000
Amount of allowance for loan losses for loans deemed to be impaired	95,000	111,000	95,000	111,000
Amount of allowance for loan losses for loans not deemed to be impaired	10,529,000	9,426,000	10,529,000	9,426,000
Loans:
Total loans, net	730,265,000	735,844,000	730,265,000	735,844,000	732,491,000
Loans deemed to be impaired	2,680,000	2,583,000	2,680,000	2,583,000
Loans not deemed to be impaired	727,585,000	733,261,000	727,585,000	733,261,000
Residential Real Estate [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	2,493,000	2,118,000	1,873,000	1,698,000
Recoveries				2,000
Provision	(182,000)	(45,000)	438,000	373,000
Allowance for loan losses, end of period	2,311,000	2,073,000	2,311,000	2,073,000
Amount of allowance for loan losses for loans deemed to be impaired	350,000	67,000	350,000	67,000
Amount of allowance for loan losses for loans not deemed to be impaired	1,961,000	2,006,000	1,961,000	2,006,000
Loans:
Total loans, net	335,114,000	272,588,000	335,114,000	272,588,000	287,731,000
Loans deemed to be impaired	2,675,000	4,318,000	2,675,000	4,318,000
Loans not deemed to be impaired	332,439,000	268,270,000	332,439,000	268,270,000
Consumer [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	336,000	195,000	373,000	582,000
Charge-offs	(78,000)	(75,000)	(231,000)	(243,000)
Recoveries	42,000	45,000	156,000	179,000
Provision	32,000	220,000	34,000	(133,000)
Allowance for loan losses, end of period	332,000	385,000	332,000	385,000
Amount of allowance for loan losses for loans deemed to be impaired	1,000		1,000
Amount of allowance for loan losses for loans not deemed to be impaired	332,000	385,000	332,000	385,000
Loans:
Total loans, net	21,216,000	19,284,000	21,216,000	19,284,000	19,040,000
Loans not deemed to be impaired	21,216,000	19,284,000	21,216,000	19,284,000
Home Equity [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	1,078,000	1,146,000	989,000	1,102,000
Provision	(28,000)	(103,000)	61,000	(59,000)
Allowance for loan losses, end of period	1,050,000	1,043,000	1,050,000	1,043,000
Amount of allowance for loan losses for loans not deemed to be impaired	1,050,000	1,043,000	1,050,000	1,043,000
Loans:
Total loans, net	283,818,000	237,094,000	283,818,000	237,094,000	$ 247,345,000
Loans not deemed to be impaired	283,818,000	237,094,000	283,818,000	237,094,000
Unallocated [Member]
Allowance for loan losses:
Allowance for loan losses, beginning of period	307,000	243,000	276,000	293,000
Provision	(61,000)	(16,000)	(30,000)	(66,000)
Allowance for loan losses, end of period	246,000	227,000	246,000	227,000
Amount of allowance for loan losses for loans not deemed to be impaired	$ 246,000	$ 227,000	$ 246,000	$ 227,000

Allowance for Loan Losses - Loa

Allowance for Loan Losses - Loans by Risk Rating (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Loans by risk rating
Financing Receivable, Net	$ 2,261,339	$ 2,175,944	$ 2,112,647
Construction and Land Development [Member]
Loans by risk rating
Financing Receivable, Net	12,434	18,931	16,779
Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	783,960	763,807	702,646
Municipal [Member]
Loans by risk rating
Financing Receivable, Net	94,532	106,599	128,412
Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	730,265	732,491	$ 735,844
1-3 (Pass) [Member] | Construction and Land Development [Member]
Loans by risk rating
Financing Receivable, Net	12,434	18,931
1-3 (Pass) [Member] | Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	779,165	758,093
1-3 (Pass) [Member] | Municipal [Member]
Loans by risk rating
Financing Receivable, Net	94,532	106,599
1-3 (Pass) [Member] | Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	703,039	705,235
4 (Monitor) [Member] | Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	4,135	5,366
4 (Monitor) [Member] | Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	24,546	24,702
Impaired [Member] | Commercial and Industrial [Member]
Loans by risk rating
Financing Receivable, Net	660	348
Impaired [Member] | Commercial Real Estate [Member]
Loans by risk rating
Financing Receivable, Net	$ 2,680	$ 2,554

Allowance for Loan Losses - L_2

Allowance for Loan Losses - Loans by Credit Rating (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	$ 1,052,021	$ 1,074,923
Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	593,181	586,000
A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	305,651	331,788
Baa1 - Baa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	146,379	148,970
Ba2 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	6,810	8,165
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	686,582	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	492,117	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	194,465	195,599
Municipal [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	92,733	104,799
Municipal [Member] | Aaa - Aa3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	57,958	62,029
Municipal [Member] | A1 - A3 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	995	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	6,810	8,165
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable net of deferred income credit quality	272,706	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	43,106	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	110,191	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	$ 119,409	$ 122,000

Allowance for Loan Losses - Agi

Allowance for Loan Losses - Aging of Past Due Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	$ 3,737	$ 5,642
Non Accrual	3,729	1,684
Accruing Greater than 90 Days	471
Total Past Due	7,937	7,326
Current Loans	2,253,402	2,168,618
Total loans, net	2,261,339	2,175,944	$ 2,112,647
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current Loans	12,434	18,931
Total loans, net	12,434	18,931	16,779
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	322	65
Non Accrual	346	44
Total Past Due	668	109
Current Loans	783,292	763,698
Total loans, net	783,960	763,807	702,646
Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Current Loans	94,532	106,599
Total loans, net	94,532	106,599	128,412
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	980	672
Non Accrual	196	215
Total Past Due	1,176	887
Current Loans	729,089	731,604
Total loans, net	730,265	732,491	735,844
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	1,668	4,282
Non Accrual	2,678	724
Accruing Greater than 90 Days	372
Total Past Due	4,718	5,006
Current Loans	330,396	282,725
Total loans, net	335,114	287,731	272,588
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	15	5
Non Accrual	10	6
Total Past Due	25	11
Current Loans	21,191	19,029
Total loans, net	21,216	19,040	19,284
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Accruing 30-89 Days Past Due	752	618
Non Accrual	499	695
Accruing Greater than 90 Days	99
Total Past Due	1,350	1,313
Current Loans	282,468	246,032
Total loans, net	$ 283,818	$ 247,345	$ 237,094

Allowance for Loan Losses - Inf

Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	$ 280,000	$ 217,000	$ 280,000	$ 217,000
With no required reserve recorded, Unpaid Balance Principal	501,000	533,000	501,000	533,000
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	336,000	180,000	314,000	443,000
With no required reserve recorded, Interest Income		2,000		5,000
With required reserve recorded, Carrying Value	5,735,000	7,050,000	5,735,000	7,050,000
With required reserve recorded, Unpaid Balance Principal	5,865,000	7,174,000	5,865,000	7,174,000
With required reserve recorded, Required Reserve	538,000	186,000	538,000	186,000
With required reserve recorded, Average Carrying Value Recognized	5,526,000	7,123,000	5,904,000	4,693,000
With required reserve recorded, Interest Income	29,000	45,000	165,000	117,000
Carrying Value	6,015,000	7,267,000	6,015,000	7,267,000
Unpaid Balance Principal	6,366,000	7,707,000	6,366,000	7,707,000
With required reserve recorded, Required Reserve	538,000	186,000	538,000	186,000
Average Carrying Value Recognized	5,862,000	7,303,000	6,218,000	5,136,000
Interest Income	29,000	47,000	165,000	122,000
Construction and Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0	0	0
With required reserve recorded, Average Carrying Value Recognized				56,000
Average Carrying Value Recognized				56,000
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	84,000	54,000	84,000	54,000
With no required reserve recorded, Unpaid Balance Principal	282,000	261,000	282,000	261,000
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	56,000	60,000	47,000	49,000
With required reserve recorded, Carrying Value	576,000	312,000	576,000	312,000
With required reserve recorded, Unpaid Balance Principal	593,000	328,000	593,000	328,000
With required reserve recorded, Required Reserve	93,000	8,000	93,000	8,000
With required reserve recorded, Average Carrying Value Recognized	589,000	319,000	490,000	328,000
With required reserve recorded, Interest Income	5,000	4,000	14,000	12,000
Carrying Value	660,000	366,000	660,000	366,000
Unpaid Balance Principal	875,000	589,000	875,000	589,000
With required reserve recorded, Required Reserve	93,000	8,000	93,000	8,000
Average Carrying Value Recognized	645,000	379,000	537,000	377,000
Interest Income	5,000	4,000	14,000	12,000
Municipal [Member] | Municipal [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0	0	0
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value	196,000	91,000	196,000	91,000
With no required reserve recorded, Unpaid Balance Principal	219,000	109,000	219,000	109,000
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized	280,000	45,000	267,000	313,000
With required reserve recorded, Carrying Value	2,484,000	2,492,000	2,484,000	2,492,000
With required reserve recorded, Unpaid Balance Principal	2,597,000	2,599,000	2,597,000	2,599,000
With required reserve recorded, Required Reserve	95,000	111,000	95,000	111,000
With required reserve recorded, Average Carrying Value Recognized	2,262,000	2,547,000	2,278,000	2,542,000
With required reserve recorded, Interest Income	24,000	22,000	71,000	69,000
Carrying Value	2,680,000	2,583,000	2,680,000	2,583,000
Unpaid Balance Principal	2,816,000	2,708,000	2,816,000	2,708,000
With required reserve recorded, Required Reserve	95,000	111,000	95,000	111,000
Average Carrying Value Recognized	2,542,000	2,592,000	2,545,000	2,855,000
Interest Income	24,000	22,000	71,000	69,000
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Carrying Value		72,000		72,000
With no required reserve recorded, Unpaid Balance Principal		163,000		163,000
With no required reserve recorded, Required Reserve	0	0	0	0
With no required reserve recorded, Average Carrying Value Recognized		75,000		81,000
With no required reserve recorded, Interest Income		2,000		5,000
With required reserve recorded, Carrying Value	2,675,000	4,246,000	2,675,000	4,246,000
With required reserve recorded, Unpaid Balance Principal	2,675,000	4,247,000	2,675,000	4,247,000
With required reserve recorded, Required Reserve	350,000	67,000	350,000	67,000
With required reserve recorded, Average Carrying Value Recognized	2,675,000	4,257,000	3,136,000	1,767,000
With required reserve recorded, Interest Income		19,000	80,000	36,000
Carrying Value	2,675,000	4,318,000	2,675,000	4,318,000
Unpaid Balance Principal	2,675,000	4,410,000	2,675,000	4,410,000
With required reserve recorded, Required Reserve	350,000	67,000	350,000	67,000
Average Carrying Value Recognized	2,675,000	4,332,000	3,136,000	1,848,000
Interest Income		21,000	80,000	41,000
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	0	0	0	0
With required reserve recorded, Required Reserve	1,000		1,000
With required reserve recorded, Required Reserve	1,000		1,000
Home Equity [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
With no required reserve recorded, Required Reserve	$ 0	$ 0	$ 0	$ 0

Allowance for Loan Losses - Add

Allowance for Loan Losses - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Mar. 31, 2018ContractContracts	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items]
Specific reserves		$ 538,000	$ 186,000
Troubled debt restructurings, subsequently defaulted			0
Commitment to lend additional funds to TDR borrowers			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		350,000	$ 67,000
Residential Real Estate [Member] | Restructured Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Specific reserves		350,000
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
Troubled debt restructurings, subsequently defaulted		$ 2,675,000

Reclassifications Out of Accu_3

Reclassifications Out of Accumulated Other Comprehensive Income - Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gains on sales of securities	$ 105	$ 47	$ 302	$ 47
Provision for income taxes	(444)	(617)	(1,259)	(1,313)
Net income	9,581	8,023	26,288	22,276
Actuarial gains (losses)	(10,570)	(9,933)	(32,331)	(31,097)
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	105	47	302	47
Provision for income taxes	(29)	(19)	(85)	(19)
Net income	76	28	217	28
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	(323)	(554)	(1,186)	(1,878)
Provision for income taxes	85	331	314	1,022
Net income	(238)	(223)	(872)	(856)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Prior-Service Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial gains (losses)	(4)	(3)	(12)	(8)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Actuarial Gains (Losses) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial gains (losses)	(402)	(385)	(1,207)	(1,155)
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	(406)	(388)	(1,219)	(1,163)
Provision for income taxes	114	155	342	465
Net income	$ (292)	$ (233)	$ (877)	$ (698)

Earnings per Share ("EPS") - Ad

Earnings per Share ("EPS") - Additional Information (Detail) - shares	Sep. 30, 2018	Sep. 30, 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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 9,581	$ 8,023	$ 26,288	$ 22,276
Class A Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 7,535	$ 6,307	$ 20,674	$ 17,505
Weighted average shares outstanding, basic	3,608,329	3,605,829	3,608,129	3,603,429
Basic earnings per share	$ 2.09	$ 1.75	$ 5.73	$ 4.86
Net income	$ 7,535	$ 6,307	$ 20,674	$ 17,505
Weighted average shares outstanding, diluted	5,567,909	5,567,909	5,567,909	5,567,909
Diluted earnings per share	$ 1.72	$ 1.44	$ 4.72	$ 4
Class B Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income	$ 2,046	$ 1,716	$ 5,614	$ 4,771
Weighted average shares outstanding, basic	1,959,580	1,962,080	1,959,780	1,964,480
Basic earnings per share	$ 1.04	$ 0.87	$ 2.86	$ 2.43
Net income	$ 2,046	$ 1,716	$ 5,614	$ 4,771
Weighted average shares outstanding, diluted	1,959,580	1,962,080	1,959,780	1,964,480
Diluted earnings per share	$ 1.04	$ 0.87	$ 2.86	$ 2.43

Employee Benefits - Components

Employee Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension benefits.
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 353	$ 310	$ 1,059	$ 930
Interest	371	362	1,111	1,087
Expected return on plan assets	(954)	(746)	(2,863)	(2,238)
Recognized prior service cost (benefit)	(25)	(26)	(75)	(78)
Recognized net actuarial losses	226	226	680	678
Net periodic benefit (credit) cost	(29)	126	(88)	379
Supplemental Insurance/ Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	277	395	831	1,184
Interest	346	345	1,040	1,035
Recognized prior service cost (benefit)	29	29	87	87
Recognized net actuarial losses	176	159	527	477
Net periodic benefit (credit) cost	$ 828	$ 928	$ 2,485	$ 2,783

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 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	$ 508,000	$ 1,047,000

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments Measured at Fair Value on a Recurring and Non-recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	$ 366,503	$ 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	3,107	246
Impaired Loans	3,107	246
U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,986	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	1,986	1,984
SBA Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	71,124	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	71,124	80,950
U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	169,215	225,776
U.S. Government Agency and Sponsored Enterprise 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	169,215	225,776
Privately Issued Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	715	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	715	892
Obligations Issued by States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	116,009	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	4,775
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	111,234	82,600
Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,565	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	3,565	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	255,269
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	111,234
U.S. Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,889
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	3,889
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	3,107	246
Impaired Loans	3,107	246
Carrying Value [Member] | U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	1,986	1,984
Carrying Value [Member] | SBA Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	71,124	80,950
Carrying Value [Member] | U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	169,215	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	715	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	116,009	82,600
Carrying Value [Member] | Other Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	3,565	$ 3,629
Carrying Value [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	366,503
Carrying Value [Member] | U.S. Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities AFS	$ 3,889

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2018USD ($)Security	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Specific adjustments to impaired loans recognized	$ (187,000)	$ 427,000	$ 3,000
Amortized cost of Level 3 securities	1,616,000	$ 1,616,000	1,616,000
Number of securities transfered from level 3 to level 2 | Security		1
Liabilities measured at fair value on a recurring or nonrecurring basis	0	$ 0	0
Transfers between level 1, 2 and 3			$ 0
Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Amortized cost of Level 3 securities	111,234,000	111,234,000		$ 79,655,000
Unrealized loss	$ 0	$ 0		$ 410,000

Fair Value Measurements - Asset

Fair Value Measurements - Assets Measured at Fair Value (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)
Securities AFS [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Fair Value	$ 111,234	$ 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	$ 3,107	$ 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]
Securities AFS, Unobservable Input Value or Range	2	1
Minimum [Member] | Impaired Loans [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Impaired Loans, Unobservable Input Value or Range	0	0
Maximum [Member] | Securities AFS [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities AFS, Unobservable Input Value or Range	4.5	3.5
Maximum [Member] | Impaired Loans [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Impaired Loans, Unobservable Input Value or Range	30	30

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Level 3 Securities (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 82,600	$ 164,876
Purchases	105,837	61,393
Maturities and calls	(72,640)	(146,869)
Transfer	(4,459)
Amortization	(104)	(155)
Changes in fair value	0	0
Balance at September 30, 2018	111,234	79,245
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
Balance at September 30, 2018		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	105,837	61,393
Maturities and calls	(72,640)	(146,869)
Amortization	(104)	(155)
Changes in fair value	0	0
Balance at September 30, 2018	$ 111,234	$ 74,947

Fair Value Measurements - Ass_2

Fair Value Measurements - Assets Measured at Fair Value (Parenthetical) (Detail)	9 Months Ended
	Sep. 30, 2018
Municipal [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Securities maturity period	one year or less

Fair Values of Financial Inst_3

Fair Values of Financial Instruments - Carrying Amount and Fair Value of Company's Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial assets:
Securities held-to-maturity	$ 1,875,752	$ 1,701,233
Loans	2,232,794	2,149,689
Financial liabilities:
Time deposits	579,886	625,361
Other borrowed funds	372,606	347,778
Subordinated debentures	36,083	36,083
Carrying Value [Member]
Financial assets:
Securities held-to-maturity	1,875,752	1,701,233
Loans	2,232,794	2,149,689
Financial liabilities:
Time deposits	579,886	625,361
Other borrowed funds	372,606	347,778
Subordinated debentures	36,083	36,083
Estimated Fair Value [Member]
Financial assets:
Securities held-to-maturity	1,795,117	1,668,827
Loans	2,188,606	2,094,517
Financial liabilities:
Time deposits	577,531	627,517
Other borrowed funds	371,531	349,364
Subordinated debentures	36,083	36,083
Fair Value Measurements, Level 2 Inputs [Member]
Financial assets:
Securities held-to-maturity	1,795,117	1,668,827
Financial liabilities:
Time deposits	577,531	627,517
Other borrowed funds	371,531	349,364
Fair Value Measurements, Level 3 Inputs [Member]
Financial assets:
Loans	2,188,606	2,094,517
Financial liabilities:
Subordinated debentures	$ 36,083	$ 36,083

Recent Accounting Developments

Recent Accounting Developments - Additional Information (Detail) - USD ($)	1 Months Ended
	Feb. 28, 2018	Aug. 31, 2016	Jan. 31, 2016
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 C_3

Revenue from Contracts with Customers - Schedule of Revenue from Contracts (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total net interest income	$ 23,204	$ 21,353	$ 68,871	$ 63,914
Noninterest income:
Lockbox fees	892	735	2,304	2,367
Net gains on sales of securities	105	47	302	47
Gains on sales of mortgage loans				370
Other income	1,035	1,071	3,210	3,179
Total noninterest income	4,169	3,942	12,084	12,142
Deposit Account [Member]
Noninterest income:
Service charges on deposit accounts	2,137	2,089	6,268	6,179
ASU 2014-09 [Member]
Disaggregation of Revenue [Line Items]
Total net interest income	23,204	21,353	68,871	63,914
Noninterest income:
Lockbox fees	892	735	2,304	2,367
Net gains on sales of securities	105	47	302	47
Gains on sales of mortgage loans				370
Other income	1,035	1,071	3,210	3,179
Total noninterest income	4,169	3,942	12,084	12,142
Total revenues	27,373	25,295	80,955	76,056
ASU 2014-09 [Member] | Deposit Account [Member]
Noninterest income:
Service charges on deposit accounts	2,137	2,089	6,268	6,179
ASU 2014-09 [Member] | Revenue Guidance Contracts in Scope of Topic 606 [Member]
Noninterest income:
Lockbox fees	892	735	2,304	2,367
Other income	751	712	2,215	2,048
Total noninterest income	3,780	3,536	10,787	10,594
Total revenues	3,780	3,536	10,787	10,594
ASU 2014-09 [Member] | Revenue Guidance Contracts in Scope of Topic 606 [Member] | Deposit Account [Member]
Noninterest income:
Service charges on deposit accounts	$ 2,137	$ 2,089	$ 6,268	$ 6,179

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Information about Receivables with Customers (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Other Assets [Member]
Disaggregation of Revenue [Line Items]
Receivables, which are included in "Other assets"	$ 1,095	$ 1,009