Century Bancorp (CNBKA) 10-Q 7 Nov 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014	Oct. 31, 2014	Oct. 31, 2014
		Class A Common Stock [Member]	Class B Common Stock [Member]
Document Information [Line Items]	'	'	'
Document Type	'10-Q	'	'
Amendment Flag	'false	'	'
Document Period End Date	30-Sep-14	'	'
Document Fiscal Year Focus	'2014	'	'
Document Fiscal Period Focus	'Q3	'	'
Trading Symbol	'CNBKA	'	'
Entity Registrant Name	'CENTURY BANCORP INC	'	'
Entity Central Index Key	'0000812348	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	3,600,729	1,967,180

Consolidated_Balance_Sheets_un

Consolidated Balance Sheets (unaudited) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets	'	'
Cash and due from banks	$57,425	$59,956
Federal funds sold and interest-bearing deposits in other banks	103,537	34,722
Total cash and cash equivalents	160,962	94,678
Short-term investments	2,125	4,617
Securities available-for-sale, amortized cost $489,876 and $465,943, respectively	490,683	464,245
Securities held-to-maturity, fair value $1,463,535 and $1,464,449, respectively	1,471,137	1,487,884
Federal Home Loan Bank of Boston stock, at cost	22,231	18,072
Loans held-for-sale	16,279	'
Loans, net:	'	'
Commercial and industrial	152,823	76,675
Municipal	36,624	32,737
Construction and land development	25,339	33,058
Commercial real estate	695,074	696,317
Residential real estate	268,927	286,041
Home equity	147,593	130,277
Consumer and other	10,253	9,658
Total loans, net	1,336,633	1,264,763
Less: allowance for loan losses	22,469	20,941
Net loans	1,314,164	1,243,822
Bank premises and equipment	23,451	23,400
Accrued interest receivable	6,317	6,539
Goodwill	2,714	2,714
Other assets	87,350	85,183
Total assets	3,597,413	3,431,154
Deposits:	'	'
Demand deposits	496,583	475,862
Savings and NOW deposits	1,015,626	992,796
Money Market Accounts	907,457	864,957
Time deposits	370,779	382,224
Total deposits	2,790,445	2,715,839
Securities sold under agreements to repurchase	195,100	214,440
Other borrowed funds	337,500	255,144
Subordinated debentures	36,083	36,083
Due to broker	7,613	'
Other liabilities	35,078	33,176
Total liabilities	3,401,819	3,254,682
Stockholders' Equity	'	'
Preferred stock - $1.00 par value; 100,000 shares authorized; no shares issued and outstanding	0	0
Additional paid-in capital	12,250	11,932
Retained earnings	195,338	180,747
Stockholders' equity before adjustment of accumulated other comprehensive income (loss)	213,155	198,235
Unrealized gains (losses) on securities available-for-sale, net of taxes	464	-1,045
Unrealized losses on securities transferred to held-to-maturity, net of taxes	-11,143	-13,667
Pension liability, net of taxes	-6,882	-7,051
Total accumulated other comprehensive loss, net of taxes	-17,561	-21,763
Total stockholders' equity	195,594	176,472
Total liabilities and stockholders' equity	3,597,413	3,431,154
Class A Common Stock [Member]	'	'
Stockholders' Equity	'	'
Common stock value	3,600	3,580
Total stockholders' equity	3,600	3,580
Class B Common Stock [Member]	'	'
Stockholders' Equity	'	'
Common stock value	1,967	1,976
Total stockholders' equity	$1,967	$1,976

Consolidated_Balance_Sheets_un1

Consolidated Balance Sheets (unaudited) (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Amortized cost	$489,876	$465,943
Held-to-maturity securities, fair value	$1,463,535	$1,464,449
Preferred stock, par value	$1	$1
Preferred stock, shares authorized	100,000	100,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Class A Common Stock [Member]	'	'
Common stock, par value	$1	$1
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	3,599,729	3,580,404
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	1,967,180	1,976,180

Consolidated_Statements_of_Inc

Consolidated Statements of Income (unaudited) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Interest income	'	'	'	'
Loans	$12,708	$12,856	$37,768	$36,734
Securities held-to-maturity	8,104	6,181	23,904	9,120
Securities available-for-sale	752	1,392	2,366	12,580
Federal funds sold and interest-bearing deposits in other banks	60	120	271	384
Total interest income	21,624	20,549	64,309	58,818
Interest expense	'	'	'	'
Savings and NOW deposits	642	674	1,911	1,933
Money market accounts	725	681	2,033	1,795
Time deposits	1,089	1,089	3,315	3,657
Securities sold under agreements to repurchase	90	89	284	268
Other borrowed funds and subordinated debentures	2,333	2,218	6,753	6,310
Total interest expense	4,879	4,751	14,296	13,963
Net interest income	16,745	15,798	50,013	44,855
Provision for loan losses	600	750	1,650	2,250
Net interest income after provision for loan losses	16,145	15,048	48,363	42,605
Other operating income	'	'	'	'
Service charges on deposit accounts	2,022	2,064	6,068	6,040
Lockbox fees	723	736	2,345	2,346
Net gains on sales of investments	'	1,001	'	2,665
Gains on sales of mortgage loans held for sale	133	247	221	1,238
Other income	880	726	2,209	2,140
Total other operating income	3,758	4,774	10,843	14,429
Operating expenses	'	'	'	'
Salaries and employee benefits	8,681	8,858	26,332	25,858
Occupancy	1,341	1,240	4,105	3,715
Equipment	552	554	1,709	1,746
FDIC assessments	502	462	1,476	1,312
Other	2,900	2,881	8,602	8,491
Total operating expenses	13,976	13,995	42,224	41,122
Income before income taxes	5,927	5,827	16,982	15,912
Provision for income taxes	221	308	745	891
Net income	5,706	5,519	16,237	15,021
Class A Common Stock [Member]	'	'	'	'
Operating expenses	'	'	'	'
Net income	4,480	4,324	12,741	11,760
Share data:	'	'	'	'
Weighted average number of shares outstanding, basic	3,594,583	3,578,400	3,588,728	3,574,109
Weighted average number of shares outstanding, diluted	5,563,278	5,558,031	5,559,909	5,557,783
Basic earnings per share	$1.25	$1.21	$3.55	$3.29
Diluted earnings per share	$1.03	$0.99	$2.92	$2.70
Class B Common Stock [Member]	'	'	'	'
Operating expenses	'	'	'	'
Net income	$1,226	$1,195	$3,496	$3,261
Share data:	'	'	'	'
Weighted average number of shares outstanding, basic	1,967,180	1,978,180	1,969,647	1,982,413
Weighted average number of shares outstanding, diluted	1,967,180	1,978,180	1,969,647	1,982,413
Basic earnings per share	$0.62	$0.60	$1.78	$1.64
Diluted earnings per share	$0.62	$0.60	$1.78	$1.64

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (unaudited) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]	'	'	'	'
Net income	$5,706	$5,519	$16,237	$15,021
Unrealized gains (losses) on securities:	'	'	'	'
Unrealized gains (losses) arising and transferred during period	1,004	-4,968	1,509	-25,857
Less: reclassification adjustment for gains included in net income	'	-1,001	'	-2,665
Total unrealized gains (losses) on securities	1,004	-5,969	1,509	-28,522
Accretion of net unrealized losses transferred	792	910	2,524	910
Defined benefit pension plans:	'	'	'	'
Amortization of prior service cost and loss included in net periodic benefit cost	56	173	169	520
Other comprehensive income (loss)	1,852	-4,886	4,202	-27,092
Comprehensive income (loss)	$7,558	$633	$20,439	($12,071)

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Shareholders' Equity (unaudited) (USD $)	Total	Class A Common Stock [Member]	Class B Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
In Thousands, unless otherwise specified						Class A Common Stock [Member]	Class B Common Stock [Member]
Beginning balance at Dec. 31, 2012	$179,990	$3,568	$1,986	$11,891	$162,892	'	'	($347)
Net income	15,021	11,760	3,261	'	15,021	'	'	'
Other comprehensive income, net of tax:	'	'	'	'	'	'	'	'
Unrealized holding (losses) gains arising during period, net of taxes	-28,522	'	'	'	'	'	'	-12,969
Unrealized losses on securities transferred to held-to-maturity net of $9,206 in taxes	-14,643	'	'	'	'	'	'	-14,643
Pension liability adjustment, net of taxes	520	'	'	'	'	'	'	520
Conversion of class B common stock to class A common stock	'	8	-8	'	'	'	'	'
Stock options exercised	43	2	'	41	'	'	'	'
Cash dividends	'	-1,285	-357	'	'	-1,285	-357	'
Ending balance at Sep. 30, 2013	166,320	3,578	1,978	11,932	176,271	'	'	-27,439
Beginning balance at Jun. 30, 2013	'	'	'	'	'	'	'	'
Net income	5,519	4,324	1,195	'	'	'	'	'
Other comprehensive income, net of tax:	'	'	'	'	'	'	'	'
Unrealized holding (losses) gains arising during period, net of taxes	-5,969	'	'	'	'	'	'	'
Ending balance at Sep. 30, 2013	166,320	3,578	1,978	'	'	'	'	'
Beginning balance at Dec. 31, 2013	176,472	3,580	1,976	11,932	180,747	'	'	-21,763
Net income	16,237	12,741	3,496	'	16,237	'	'	'
Other comprehensive income, net of tax:	'	'	'	'	'	'	'	'
Unrealized holding (losses) gains arising during period, net of taxes	1,509	'	'	'	'	'	'	1,509
Accretion of unrealized losses on securities transferred to held-to-maturity, net of in taxes	2,524	'	'	'	'	'	'	2,524
Unrealized losses on securities transferred to held-to-maturity net of $9,206 in taxes	2,524	'	'	'	'	'	'	'
Pension liability adjustment, net of taxes	169	'	'	'	'	'	'	169
Conversion of class B common stock to class A common stock	'	9	-9	'	'	'	'	'
Stock options exercised	329	11	'	318	'	'	'	'
Cash dividends	'	'	'	'	'	-1,290	-356	'
Ending balance at Sep. 30, 2014	195,594	3,600	1,967	12,250	195,338	'	'	-17,561
Beginning balance at Jun. 30, 2014	'	'	'	'	'	'	'	'
Net income	5,706	4,480	1,226	'	'	'	'	'
Other comprehensive income, net of tax:	'	'	'	'	'	'	'	'
Unrealized holding (losses) gains arising during period, net of taxes	1,004	'	'	'	'	'	'	'
Ending balance at Sep. 30, 2014	$195,594	$3,600	$1,967	'	'	'	'	'

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Shareholders' Equity (unaudited) (Parenthetical) (USD $)	9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Unrealized holding (losses) gains arising during period, taxes	$996	$8,266
Realized net gains	'	2,665
Accretion of unrealized losses on securities transferred to held-to-maturity, taxes	1,485	'
Unrealized losses on securities transferred to held-to-maturity, taxes	'	9,206
Pension liability adjustment, taxes	$113	$346
Conversion of class B common stock to class A common stock, shares	9,000	8,700
Stock options exercised, shares	10,325	1,625
Class A Common Stock [Member]	'	'
Cash dividends paid, per share	$0.36	$0.36
Class B Common Stock [Member]	'	'
Cash dividends paid, per share	$0.18	$0.18

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (unaudited) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:	'	'
Net income	$16,237	$15,021
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Gain on sales of mortgage loans held for sale	-221	-1,238
Net gain on sales of investments	'	-2,665
Provision for loan losses	1,650	2,250
Deferred income taxes	-2,648	-1,297
Net depreciation and amortization	2,337	4,421
Decrease (increase) in accrued interest receivable	222	-265
Increase in other assets	-2,238	-4,321
Increase in other liabilities	2,184	3,527
Net cash provided by operating activities	17,523	15,433
CASH FLOWS FROM INVESTING ACTIVITIES:	'	'
Proceeds from maturities of short-term investments	3,561	16,317
Purchase of short-term investments	-1,069	-8,561
Proceeds from calls/maturities of securities available-for-sale	112,242	228,212
Proceeds from sales of securities available-for-sale	'	216,078
Purchase of securities available-for-sale	-132,953	-536,612
Proceeds from calls/maturities of securities held-to-maturity	183,533	79,249
Purchase of securities held-to-maturity	-163,064	-190,718
Net increase in loans	-101,378	-182,406
Proceeds from sales of portfolio loans	13,364	64,219
Capital expenditures	-1,780	-1,232
Net cash used in investing activities	-87,544	-315,454
CASH FLOWS FROM FINANCING ACTIVITIES:	'	'
Net decrease in time deposits	-11,445	-68,433
Net increase in demand, savings, money market and NOW deposits	86,051	311,489
Net proceeds from exercise of stock options	329	43
Cash dividends	-1,646	-1,642
Net decrease in securities sold under agreements to repurchase	-19,340	-6,230
Net increase in other borrowed funds	82,356	46,000
Net cash provided by financing activities	136,305	281,227
Net increase (decrease) in cash and cash equivalents	66,284	-18,794
Cash and cash equivalents at beginning of period	94,678	152,283
Cash and cash equivalents at end of period	160,962	133,489
Cash paid during the period for:	'	'
Cash paid during the period for interest	14,295	13,993
Cash paid during the period for income taxes	2,807	2,898
Change in unrealized gains (losses) on securities available-for-sale, net of taxes	1,509	-28,522
Change in unrealized losses on securities transferred to held-to-maturity, net of taxes	2,524	-14,643
Pension liability adjustment, net of taxes	169	520
Due to broker	7,613	3,086
Transfer of securities available-for-sale to held-to-maturity	'	$987,037

Basis_of_Financial_Statement_P

Basis of Financial Statement Presentation	9 Months Ended
	Sep. 30, 2014
Accounting Policies [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. 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 should be read in conjunction with the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2013, as filed with the Securities and Exchange Commission.
	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 rates with additional allocations based on risk factors for each category and general economic factors. While management uses available information to recognize loan losses, future additions to the allowance for loan losses may be necessary based on changes in economic conditions. In addition, regulatory agencies periodically review the Company’s allowance for loan losses. Such agencies may require the Company to recognize additions to the allowance for loan losses based on their judgments about information available to them at the time of their examination.
	Certain reclassifications are made to prior-year amounts whenever necessary to conform with the current-year presentation.

Recent_Market_Developments

Recent Market Developments	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Recent Market Developments	'
	Note 2. Recent Market Developments
	The financial services industry continues to face challenges in the aftermath of the recent national and global economic crisis. Since June 2009, the U.S. economy has been recovering from the most severe recession and financial crisis since the Great Depression. There have been some improvements in private sector employment, industrial production and U.S. exports; nevertheless, the pace of economic recovery has been slow. Financial markets have improved since the depths of the crisis but are still unsettled and volatile. There is continued concern about the U.S. economic outlook.
	On July 21, 2010, the Dodd-Frank Wall Street Reform and Consumer Protection Act (the “Act”) became law. The Act was intended to address many issues arising in the recent financial crisis and is exceedingly broad in scope, affecting many aspects of bank and financial market regulation. The Act requires, or permits by implementing regulation, enhanced prudential standards for banks and bank holding companies inclusive of capital, leverage, liquidity, concentration and exposure measures. In addition, traditional bank regulatory principles such as restrictions on transactions with affiliates and insiders were enhanced. The Act also contains reforms of consumer mortgage lending practices and creates a Bureau of Consumer Financial Protection, which is granted broad authority over consumer financial practices of banks and others. It is expected as the specific new or incremental requirements applicable to the Company become effective that the costs and difficulties of remaining compliant with all such requirements will increase. The Act broadens the base for FDIC assessments to average consolidated assets less tangible equity of financial institutions and also permanently raises the current standard maximum FDIC deposit insurance amount to $250,000. The Act extended unlimited deposit insurance on non-interest bearing transaction accounts through December 31, 2012. In addition, the Act added a new Section 13 to the Bank Holding Company Act, the so-called “Volcker Rule,” (the “Rule”) which generally restricts certain banking entities such as the Company and its subsidiaries or affiliates, from engaging in proprietary trading activities and owning equity in or sponsoring any private equity or hedge fund. The Rule became effective July 21, 2012. The final implementing regulations for the Rule were issued by various regulatory agencies in December, 2013 and under an extended conformance regulation compliance must be achieved by July 21, 2015. Under the Rule, the Company may be restricted from engaging in proprietary trading, investing in third party hedge or private equity funds or sponsoring new funds unless it qualifies for an exemption from the rule. The Company has little involvement in prohibited proprietary trading or investment activities in covered funds and the Company does not expect that complying with the requirements of the Rule will have any material effect on the Company’s financial condition or results of operation.
	On September 29, 2009, the FDIC adopted a Notice of Proposed Rulemaking (NPR) that would require insured institutions to prepay their estimated quarterly risk-based assessments for the fourth quarter of 2009 and for all of 2010, 2011 and 2012. The FDIC Board voted to adopt a uniform three-basis point increase in assessment rates effective on January 1, 2011, and extend the restoration period from seven to eight years. This rule was finalized on November 2, 2009. The Company’s quarterly risk-based deposit insurance assessments were paid from this amount until June 30, 2013. The Company received a refund of $2.4 million of prepaid FDIC assessments in June 2013.
	Federal banking regulators have issued risk-based capital guidelines, which assign risk factors to asset categories and off-balance-sheet items. Also, the Basel Committee has issued capital standards entitled “Basel III: A global regulatory framework for more resilient banks and banking systems” (“Basel III”). The Federal Reserve Board has finalized its rule implementing the Basel III regulatory capital framework. The rule, that will come into effect in January 2015, sets the Basel III minimum regulatory capital requirements for all organizations. It includes a new common equity Tier I ratio of 4.5 percent of risk-weighted assets, raises the minimum Tier I capital ratio from 4 percent to 6 percent of risk-weighted assets and would set a new conservation buffer of 2.5 percent of risk-weighted assets. The Company has analyzed the final rules; the implementation of the framework will not have a material impact on the Company’s financial condition or results of operations.

Stock_Option_Accounting

Stock Option Accounting	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Stock Option Accounting	'
	Note 3. Stock Option Accounting
	Stock option activity under the Company’s stock option plan for the nine months ended September 30, 2014 is as follows:
		Amount			Weighted
					Average
					Exercise Price
	Shares under option:
	Outstanding at beginning of year		20,225		$	31.82
	Exercised		(10,325	)		31.83
	Forfeited		(8,900	)		31.83
	Outstanding at end of period		1,000		$	31.6
	Exercisable at end of period		1,000		$	31.6
	Available to be granted at end of period		233,784
	On September 30, 2014, the outstanding options to purchase 1,000 shares of Class A common stock has an exercise price of $31.60 with a weighted average exercise price of $31.60 and a weighted average remaining contractual life of 13 days. The intrinsic value of options exercisable at September 30, 2014 had an aggregate value of $3,020. The intrinsic value of options exercised at September 30, 2014 had an aggregate value of $28,807.
	The Company uses the fair value method to account for stock options. All of the Company’s stock options are vested and there were no options granted during the first nine months of 2014.

Securities_AvailableforSale

Securities Available-for-Sale	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Securities Available-for-Sale	'
	Note 4. Securities Available-for-Sale
		September 30, 2014								December 31, 2013
		Amortized		Gross		Gross		Fair		Amortized		Gross		Gross		Fair
		Cost		Unrealized		Unrealized		Value		Cost		Unrealized		Unrealized		Value
				Gains		Losses						Gains		Losses
		( In thousands)
	U.S. Treasury	$	1,999	$	2	$	—	$	2,001	$	1,997	$	1	$	—	$	1,998
	U.S. Government Sponsored Enterprises		—		—		—		—		9,995		9		—		10,004
	Small Business Administration		6,787		42		—		6,829		7,270		32		—		7,302
	U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities		391,721		2,185		623		393,283		404,103		588		1,501		403,190
	Privately Issued Residential Mortgage Backed Securities		1,993		9		11		1,991		2,294		6		23		2,277
	Obligations Issued by States and Political Subdivisions		83,749		2		873		82,878		37,578		15		870		36,723
	Other Debt Securities		3,300		5		109		3,196		2,300		—		125		2,175
	Equity Securities		327		178		—		505		406		170		—		576
	Total	$	489,876	$	2,423	$	1,616	$	490,683	$	465,943	$	821	$	2,519	$	464,245
	During the third quarter of 2013, securities available-for-sale with an amortized cost of $1,012,370,000 were transferred to securities held-to-maturity at their fair value of $987,037,000 in response to rising interest rates. Rising interest rates have the potential to increase unrealized losses on the available-for-sale portfolio. The transfer was implemented to lessen the effects of rising interest rates.
	Included in 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 $333,036,000 and $368,137,000 at September 30, 2014 and December 31, 2013, respectively. Also included in securities available-for-sale are securities pledged for borrowing at the Federal Home Loan Bank of Boston amounting to $21,706,000 and $12,214,000 at September 30, 2014 and December 31, 2013, respectively. There were no realized gains on sales of investments for the nine months ended September 30, 2014. The Company realized gross gains of $2,665,000 from the proceeds of $216,078,000 from the sales of available-for-sale securities for the nine months ended September 30, 2013.
	Debt securities of Government Sponsored Enterprises 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 at September 30, 2014.
		Amortized		Fair
		Cost		Value
		( In thousands)
	Within one year	$	77,321	$	77,322
	After one but within five years		175,594		176,505
	After five but within ten years		226,116		226,788
	More than 10 years		9,018		8,172
	Non-maturing		1,827		1,896
	Total	$	489,876	$	490,683
	The weighted average remaining life of investment securities available-for-sale at September 30, 2014 was 4.4 years. The contractual maturities, which were used in the table above, of mortgage-backed securities, will differ from the actual maturities, due to the ability of the issuers to prepay underlying obligations.
	As of September 30, 2014 and December 31, 2013, 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 the fact that the principal and interest on these securities are from issuers that are investment grade. The change in the unrealized losses on the state and municipal securities and the nonagency mortgage-backed securities was primarily caused by changes in credit spreads and liquidity issues in the marketplace.
	The unrealized loss on U.S. Government Sponsored Enterprises and U.S. Government Sponsored Enterprises Mortgage Backed Securities related primarily to interest rates and not credit quality and because the Company has the ability and intent to hold these investments until recovery of fair value, which may be maturity. The Company does not consider these investments to be other-than-temporarily impaired.
	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 portfolio at September 30, 2014. This table shows the unrealized market loss of securities that have been in a continuous unrealized loss position for 12 months or less and a continuous loss position for 12 months and longer. There are 3 and 17 securities that are temporarily impaired for less than 12 months and for 12 months or longer, respectively, out of a total of 257 holdings at September 30, 2014.
		September 30, 2014
		Less than 12 months				12 months or longer				Total
	Temporarily Impaired Investments	Fair Value		Unrealized		Fair Value		Unrealized		Fair Value		Unrealized
				Losses				Losses				Losses
		(In thousands)
	U.S. Government Sponsored Enterprises	$	—	$	—	$	—	$	—	$	—	$	—
	U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities		20,768		99		99,716		524		120,484		623
	Privately Issued Residential Mortgage Backed Securities		—		—		737		11		737		11
	Obligations Issued by States and Political Subdivisions		—		—		3,820		873		3,820		873
	Other Debt Securities		—		—		1,390		109		1,390		109
	Total temporarily impaired securities	$	20,768	$	99	$	105,663	$	1,517	$	126,431	$	1,616
	The following table shows the temporarily impaired securities of the Company’s available-for-sale portfolio at December 31, 2013. This table shows the unrealized market loss of securities that have been in a continuous unrealized loss position for 12 months or less and a continuous loss position for 12 months and longer. There are 47 and 7 securities that are temporarily impaired for less than 12 months and for 12 months or longer, respectively, out of a total of 234 holdings at December 31, 2013.
		December 31, 2013
		Less than 12 months				12 months or longer				Total
	Temporarily Impaired Investments	Fair Value		Unrealized		Fair Value		Unrealized		Fair Value		Unrealized
				Losses				Losses				Losses
		(In thousands)
	U.S. Government Sponsored Enterprises	$	—	$	—	$	—	$	—	$	—	$	—
	U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities		289,709		1, 352		24,557		149		314,266		1,501
	Privately Issued Residential Mortgage Backed Securities		1,486		23		—		—		1,486		23
	Obligations Issued by States and Political Subdivisions		—		—		3,820		870		3,820		870
	Other Debt Securities		—		—		1,376		125		1,376		125
	Total temporarily impaired securities	$	291,195	$	1,375	$	29,753	$	1,144	$	320,948	$	2,519

Investment_Securities_HeldtoMa

Investment Securities Held-to-Maturity	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Investment Securities Held-to-Maturity	'
	Note 5. Investment Securities Held-to-Maturity
		September 30, 2014								December 31, 2013
		Amortized		Gross		Gross		Estimated		Amortized		Gross		Gross		Estimated
		Cost		Unrealized		Unrealized		Fair		Cost		Unrealized		Unrealized		Fair
				Gains		Losses		Value				Gains		Losses		Value
		(In thousands)
	U.S. Government Sponsored Enterprises	$	291,158	$	1,377	$	870	$	291,665	$	291,779	$	185	$	5,043	$	286,921
	U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities		1,179,979		6,408		14,517		1,171,870		1,196,105		2,239		20,816		1,177,528
	Total	$	1,471,137	$	7,785	$	15,387	$	1,463,535	$	1,487,884	$	2,424	$	25,859	$	1,464,449
	Included in U.S. Government and Agency Securities are securities pledged to secure public deposits and repurchase agreements at fair value amounting to $839,764,000 and $732,144,000 at September 30, 2014 and December 31, 2013, respectively. Also included are securities pledged for borrowing at the Federal Home Loan Bank of Boston at fair value amounting to $466,789,000 and $510,060,000 at September 30, 2014 and December 31, 2013, respectively.
	At September 30, 2014 and December 31, 2013, all mortgage-backed securities are obligations of U.S. Government Agencies and Government Sponsored Enterprises. Government Sponsored Enterprises 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 at September 30, 2014.
		Amortized		Fair
		Cost		Value
		( In thousands)
	Within one year	$	4,168	$	4,230
	After one but within five years		988,565		983,567
	After five but within ten years		477,606		474,921
	More than ten years		798		817
	Total	$	1,471,137	$	1,463,535
	The weighted average remaining life of investment securities held-to-maturity at September 30, 2014 was 4.7 years. Included in the weighted average remaining life calculation at September 30, 2014 were $213,343,000 of U.S. Government Sponsored Enterprises obligations that are callable at the discretion of the issuer. The actual maturities, which were used in the table above, of mortgage-backed securities, will differ from the contractual maturities, due to the ability of the issuers to prepay underlying obligations.
	As of September 30, 2014 and December 31, 2013, 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 Agency and Sponsored Enterprises Mortgage-Backed Securities related primarily to interest rates and not credit quality, and because the Company does not intend to sell any of these securities and it is not 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 at September 30, 2014 and December 31, 2013.
	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 portfolio at September 30, 2014. This table shows the unrealized market loss of securities that have been in a continuous unrealized loss position for 12 months or less and a continuous loss position for 12 months and longer. There are 84 and 53 securities that are temporarily impaired for less than 12 months and for 12 months or longer, respectively, out of a total of 305 holdings at September 30, 2014.
		September 30, 2014
		Less Than 12 Months				12 Months or Longer				Total
	Temporarily Impaired Investments	Fair Value		Unrealized		Fair Value		Unrealized		Fair Value		Unrealized
				Losses				Losses				Losses
		(Dollars in thousands)
	U.S. Government Sponsored Enterprises	$	105,032	$	507	$	14,637	$	363	$	119,669	$	870
	U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities		422,503		4,626		346,611		9,891		769,114		14,517
	Total temporarily impaired securities	$	527,535	$	5,133	$	361,248	$	10,254	$	888,783	$	15,387
	The following table shows the temporarily impaired securities of the Company’s held-to-maturity portfolio at December 31, 2013. This table shows the unrealized market loss of securities that have been in a continuous unrealized loss position for 12 months or less and a continuous loss position for 12 months and longer. There are 191 and 13 securities that are temporarily impaired for less than 12 months and for 12 months or longer, respectively, out of a total of 300 holdings at December 31, 2013.
		December 31, 2013
		Less Than 12 Months				12 Months or Longer				Total
	Temporarily Impaired Investments	Fair Value		Unrealized		Fair Value		Unrealized		Fair Value		Unrealized
				Losses				Losses				Losses
		( In thousands)
	U.S. Government Sponsored Enterprises	$	232,535	$	5,043	$	—	$	—	$	232,535	$	5,043
	U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities		931,180		18,654		80,362		2,162		1,011,542		20,816
	Total temporarily impaired securities	$	1,163,715	$	23,697	$	80,362	$	2,162	$	1,244,077	$	25,859

Allowance_for_Loan_Losses

Allowance for Loan Losses	9 Months Ended
	Sep. 30, 2014
Receivables [Abstract]	'
Allowance for Loan Losses	'
	Note 6. 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
		September 30,						September 30,
		2014			2013			2014			2013
		(in thousands)
	Allowance for loan losses, beginning of period	$	21,722		$	20,500		$	20,941		$	19,197
	Loans charged off		(163	)		(149	)		(705	)		(682	)
	Recoveries on loans previously charged-off		310			149			583			485
	Net charge-offs		147			—			(122	)		(197	)
	Provision charged to expense		600			750			1,650			2,250
	Allowance for loan losses, end of period	$	22,469		$	21,250		$	22,469		$	21,250
	Further information pertaining to the allowance for loan losses for the three months ending September 30, 2014 follows:
		Construction			Commercial			Commercial			Residential			Consumer			Home			Unallocated			Total
		and Land			and			Real			Real						Equity
		Development			Industrial			Estate			Estate
		(Dollars in thousands)
	Allowance for loan losses:
	Balance at June 30, 2014	$	2,045		$	2,915		$	11,975		$	1,927		$	428		$	915		$	1,517		$	21,722
	Charge-offs		—			(37	)		—			—			(126	)		—			—			(163	)
	Recoveries		—			115			1			6			106			82			—			310
	Provision		(39	)		2,396			(1,116	)		(132	)		46			(41	)		(514	)		600
	Ending balance at September 30, 2014	$	2,006		$	5,389		$	10,860		$	1,801		$	454		$	956		$	1,003		$	22,469
	Amount of allowance for loan losses for loans deemed to be impaired	$	272		$	348		$	648		$	152		$	—		$	93		$	—			1,513
	Amount of allowance for loan losses for loans not deemed to be impaired	$	1,734		$	5,041		$	10,212		$	1,649		$	454		$	863		$	1,003		$	20,956
	Loans:
	Ending balance	$	25,339		$	181,627		$	702,894		$	268,927		$	10,253		$	147,593		$	—		$	1,336,633
	Loans deemed to be impaired	$	354		$	1,096		$	4,740		$	1,549		$	—		$	93		$	—		$	7,832
	Loans not deemed to be impaired	$	24,985		$	180,531		$	698,154		$	267,378		$	10,253		$	147,500		$	—		$	1,328,801
	Further information pertaining to the allowance for loan losses for the nine months ending September 30, 2014 follows:
		Construction			Commercial			Commercial			Residential			Consumer			Home			Unallocated			Total
		and Land			and			Real			Real						Equity
		Development			Industrial			Estate			Estate
		(Dollars in thousands)
	Allowance for loan losses:
	Balance at December 31, 2013	$	2,174		$	2,989		$	11,218		$	2,006		$	432		$	959		$	1,163		$	20,941
	Charge-offs		(250	)		(51	)		—			—			(404	)		—			—			(705	)
	Recoveries		—			164			5			26			305			83			—			583
	Provision		82			2,287			(363	)		(231	)		121			(86	)		(160	)		1,650
	Ending balance at September 30, 2014	$	2,006		$	5,389		$	10,860		$	1,801		$	454		$	956		$	1,003		$	22,469
	Amount of allowance for loan losses for loans deemed to be impaired	$	272		$	348		$	648		$	152		$	—		$	93		$	—			1,513
	Amount of allowance for loan losses for loans not deemed to be impaired	$	1,734		$	5,041		$	10,212		$	1,649		$	454		$	863		$	1,003		$	20,956
	Loans:
	Ending balance	$	25,339		$	181,627		$	702,894		$	268,927		$	10,253		$	147,593		$	—		$	1,336,633
	Loans deemed to be impaired	$	354		$	1,096		$	4,740		$	1,549		$	—		$	93		$	—		$	7,832
	Loans not deemed to be impaired	$	24,985		$	180,531		$	698,154		$	267,378		$	10,253		$	147,500		$	—		$	1,328,801
	Further information pertaining to the allowance for loan losses for the three months ending September 30, 2013 follows:
		Construction			Commercial			Commercial			Residential			Consumer			Home			Unallocated			Total
		and Land			and			Real			Real						Equity
		Development			Industrial			Estate			Estate
		(Dollars in thousands)
	Allowance for loan losses:
	Balance at June 30, 2013	$	3,241		$	3,215		$	9,424		$	2,030		$	363		$	932		$	1,295		$	20,500
	Charge-offs		—			—			—			—			(149	)		—			—			(149	)
	Recoveries		—			42			2			4			101			—			—			149
	Provision		(114	)		(534	)		1,162			176			76			17			(33	)		750
	Ending balance at September 30, 2013	$	3,127		$	2,723		$	10,588		$	2,210		$	391		$	949		$	1		$	21,250
																					,262
	Amount of allowance for loan losses for loans deemed to be impaired	$	1,000		$	90		$	445		$	139		$	—		$	95		$	—			1,769
	Amount of allowance for loan losses for loans not deemed to be impaired	$	2,127		$	2,633		$	10,143		$	2,071		$	391		$	854		$	1,262		$	19,481
	Loans:
	Ending balance	$	32,750		$	87,468		$	666,166		$	309,291		$	8,728		$	126,645		$	—		$	1,231,048
Loans deemed to be impaired	$	1,500		$	1,132		$	4,688		$	1,151		$	—		$	95		$	—		$	8,566
Loans not deemed to be impaired	$	31,250		$	86,336		$	661,478		$	308,140		$	8,728		$	126,550		$	—		$	1,222,482
Further information pertaining to the allowance for loan losses for the nine months ending September 30, 2013 follows:
	Construction			Commercial			Commercial			Residential			Consumer			Home			Unallocated			Total
	and Land			and			Real			Real						Equity
	Development			Industrial			Estate			Estate
	(Dollars in thousands)
Allowance for loan losses:
Balance at December 31, 2012	$	3,041		$	3,118		$	9,065		$	1,994		$	333		$	886		$	760		$	19,197
Charge-offs		—			(234	)		—			—			(448	)		—			—			(682	)
Recoveries		—			163			5			9			307			1			—			485
Provision		86			(324	)		1,518			207			199			62			502			2,250
Ending balance at September 30, 2013	$	3,127		$	2,723		$	10,588		$	2,210		$	391		$	949		$	1		$	21,250
																				,262
Amount of allowance for loan losses for loans deemed to be impaired	$	1,000		$	90		$	445		$	139		$	—		$	95		$	—			1,769
Amount of allowance for loan losses for loans not deemed to be impaired	$	2,127		$	2,633		$	10,143		$	2,071		$	391		$	854		$	1,262		$	19,481
Loans:
Ending balance	$	32,750		$	87,468		$	666,166		$	309,291		$	8,728		$	126,645		$	—		$	1,231,048
Loans deemed to be impaired	$	1,500		$	1,132		$	4,688		$	1,151		$	—		$	95		$	—		$	8,566
Loans not deemed to be impaired	$	31,250		$	86,336		$	661,478		$	308,140		$	8,728		$	126,550		$	—		$	1,222,482
The Company utilizes a six grade internal loan rating system for commercial real estate, construction and commercial loans as follows:
Loans rated 1-3 (Pass):
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, 2014 and December 31, 2013.
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, 2014 and December 31, 2013.
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, 2014 and December 31, 2013 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, 2014.
	Construction			Commercial			Commercial
	and land			and			real
	development			industrial			estate
	(Dollars in thousands)
Grade:
1-3 (Pass)	$	17,808		$	180,059		$	697,509
4 (Monitor)		7,177			472			645
5 (Substandard)		—			—			—
6 (Doubtful)		—			—			—
Impaired		354			1,096			4,740
Total	$	25,339		$	181,627		$	702,894
The following table presents the Company’s loans by risk rating at December 31, 2013.
	Construction			Commercial			Commercial
	and land			and			real
	development			industrial			estate
	(Dollars in thousands)
Grade:
1-3 (Pass)	$	25,138		$	90,563		$	707,461
4 (Monitor)		7,312			472			1,346
5 (Substandard)		—			—			—
6 (Doubtful)		—			—			—
Impaired		608			1,367			4,520
Total	$	33,058		$	92,402		$	713,327
The Company utilized payment performance as credit quality indicators for residential real estate, consumer and overdrafts, and the home equity portfolio. 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, 2014 follows:
	Accruing			Non Accrual			Accrual			Total			Current Loans			Total
	30-89 Days						Greater			Past Due
	Past Due						Than
							90 Days
							(Dollars in thousands)
Construction and land development	$	—		$	354		$	—		$	354		$	24,985		$	25,339
Commercial and industrial		895			418			—			1,313			180,314			181,627
Commercial real estate		1,608			2,787			—			4,395			698,499			702,894
Residential real estate		378			2,197			—			2,575			266,352			268,927
Consumer and overdrafts		5			8			—			13			10,240			10,253
Home equity		1,072			254			—			1,326			146,267			147,593
Total	$	3,958		$	6,018		$	—		$	9,976		$	1,326,657		$	1,336,633
Further information pertaining to the allowance for loan losses at December 31, 2013 follows:
	Accruing			Non Accrual			Accrual			Total			Current Loans			Total
	30-89 Days						Greater			Past Due
	Past Due						Than
							90
							Days
							(Dollars in thousands)
Construction and land development	$	—		$	500		$	—		$	500		$	32,558		$	33,058
Commercial and industrial		112			706			—			818			91,584			92,402
Commercial real estate		1,496			306			—			1,802			711,525			713,327
Residential real estate		2,232			1,034			—			3,266			282,775			286,041
Consumer and overdrafts		11			3			—			14			9,644			9,658
Home equity		1,710			—			—			1,710			128,567			130,277
Total	$	5,561		$	2,549		$	—		$	8,110		$	1,256,653		$	1,264,763
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 when management believes that the collectability of the loan’s principal is not probable. The specific factors that management considers in making the determination that the collectability of the loan’s principal is not probable include; the delinquency status of the loan, the fair value of the collateral, if secured, and the financial strength of the borrower and/or guarantors. For collateral dependent loans, the amount of the recorded investment in a loan that exceeds the fair value of the collateral is charged-off against the allowance for loan losses in lieu of an allocation of a specific allowance amount when such an amount has been identified definitively as uncollectible. The Company’s policy for recognizing interest income on impaired loans is contained within Note 1 of the consolidated financial statements contained in the Company’s Annual Report for the fiscal year ended December 31, 2013.
The following is information pertaining to impaired loans for September 30, 2014:
	Carrying			Unpaid			Required			Average			Interest			Average			Interest
	Value			Principal			Reserve			Carrying Value			Income			Carrying Value			Income
				Balance						For 3 Months			Recognized For			For 9 Months			Recognized For
										Ending 9/30/14			3 Months			Ending 9/30/14			9 Months
													Ending 9/30/14						Ending 9/30/14
	(Dollars in thousands)
With no required reserve recorded:
Construction and land development	$	—		$	—		$	—		$	—		$	—		$	225		$	—
Commercial and industrial		11			42			—			11			—			53			—
Commercial real estate		392			396			—			396			—			175			—
Residential real estate		—			—			—			18			—			72			—
Consumer		—			—			—			—			—			—			—
Home equity		—			—			—			—			—			—			—
Total	$	403		$	438		$	—		$	425		$	—		$	525		$	—
With required reserve recorded:
Construction and land development	$	354		$	3,400		$	272		$	355		$	—		$	207		$	—
Commercial and industrial		1,085			1,337			348			1,078			8			1,095			24
Commercial real estate		4,348			4,440			648			4,492			39			4,443			113
Residential real estate		1,549			1,549			152			1,536			3			1,193			8
Consumer		—			—			—			—			—			—			—
Home equity		93			93			93			93			—			94			—
Total	$	7,429		$	10,819		$	1,513		$	7,554		$	50		$	7,032		$	145
Total:
Construction and land development	$	354		$	3,400		$	272		$	355		$	—		$	432		$	—
Commercial and industrial		1,096			1,379			348			1,089			8			1,148			24
Commercial real estate		4,740			4,836			648			4,888			39			4,618			113
Residential real estate		1,549			1,549			152			1,554			3			1,265			8
Consumer		—			—			—			—			—			—			—
Home equity		93			93			93			93			—			94			—
Total	$	7,832		$	11,257		$	1,513		$	7,979		$	50		$	7,557		$	145
The following is information pertaining to impaired loans for September 30, 2013:
	Carrying Value			Unpaid			Required			Average			Interest			Average			Interest
				Principal			Reserve			Carrying Value			Income			Carrying Value			Income
				Balance						For 3 Months			Recognized For			For 9 Months			Recognized For
										Ending 9/30/13			3 Months			Ending 9/30/13			9 Months
													Ending 9/30/13						Ending 9/30/13
	(Dollars in thousands)
With no required reserve recorded:
Construction and land development	$	—		$	—		$	—		$	—		$	—		$	—		$	—
Commercial and industrial		264			294			—			239			—			390			1
Commercial real estate		218			218			—			126			—			133			—
Residential real estate		254			263			—			260			—			145			—
Consumer		—			—			—			—			—			—			—
Home equity		—			—			—			—			—			—			—
Total	$	736		$	775		$	—		$	625		$	1		$	668		$	1
With required reserve recorded:
Construction and land development	$	1,500		$	3,292		$	1,000		$	1,500		$	—		$	1,500		$	—
Commercial and industrial		868			1,101			90			885			12			864			29
Commercial real estate		4,470			4,558			445			2,796			26			2,394			72
Residential real estate		897			979			139			901			—			853			—
Consumer		—			—			—			—			—			—			—
Home equity		95			95			95			95			—			96			—
Total	$	7,830		$	10,025		$	1,769		$	6,177		$	38		$	5,707		$	101
Total:
Construction and land development	$	1,500		$	3,292		$	1,000		$	1,500		$	—		$	1,500		$	—
Commercial and industrial		1,132			1,395			90			1,124			12			1,254			30
Commercial real estate		4,688			4,776			445			2,922			26			2,527			72
Residential real estate		1,151			1,242			139			1,161			—			998			—
Consumer		—			—			—			—			—			—			—
Home equity		95			95			95			95			—			96			—
Total	$	8,566		$	10,800		$	1,769		$	6,802		$	38		$	6,375		$	102
Troubled Debt Restructurings were identified as a modification in which a concession was granted to a customer who is having financial difficulties. This concession may be below market rate, longer amortization/term, and 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 commercial real estate troubled debt restructuring, totaling $2.2 million during the period ended September 30, 2014, that subsequently defaulted. There was one commercial and industrial troubled debt restructuring that occurred during the three and nine month period ended September 30, 2014. The pre-modification and post-modification outstanding recorded investment amounted to $23,811 and $23,761, respectively. The term of the loan was extended and the financial impact of the modification for the performing commercial and industrial loan was a $50 increase in principal payments for the quarter and year-to-date ended September 30, 2014.
Troubled Debt Restructurings occurring during the three and nine month periods ended September 30, 2013:
	Number			Pre-modification			Post-
	of			outstanding			modification
	Contracts			recorded			outstanding
				investment			recorded
							investment
	(Dollars in thousands)
Construction and land development		1		$	108		$	108
Commercial and industrial		1			41			41
Commercial real estate		1			2,247			2,242
Total		3		$	2,396		$	2,391
The loans were modified, for the loans, by reducing interest rates as well as extending term for the commercial and industrial loan. The financial impact of the modifications for performing commercial and industrial loans were $366 reduction in principal and $217 reduction in interest payments for the quarter and year-to-date ended September 30, 2013. The financial impact of the modifications for performing commercial real estate loans were $1,786 increase in principal and $7,907 reduction in interest payments for the quarter and year-to-date ended September 30, 2013. The financial impact of the modifications for performing construction and land development loans were $530 reduction in principal and $415 reduction in interest payments for the quarter and year-to-date ended September 30, 2013.

Reclassifications_Out_of_Accum

Reclassifications Out of Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Reclassifications Out of Accumulated Other Comprehensive Income	'
	Note 7. Reclassifications Out of Accumulated Other Comprehensive Income (a)
	Amount Reclassified from Accumulated Other Comprehensive Income
	Details about Accumulated		Three Months Ended			Three Months Ended			Affected Line Item
	Other Comprehensive		September 30, 2014			September 30, 2013			in the Statement
	Income Components								Where Net Income
									is Presented
			(in thousands)
	Unrealized gains and losses on available-for-sale securities
			$	—		$	1,001		Net gains on sales of investments
				—			(387	)	Provision for income taxes
			$	—		$	614		Net income
	Accretion of unrealized losses transferred
			$	1,216		$	1,485		Securities held-to-maturity
				(424	)		(575	)	Provision for income taxes
			$	792		$	910		Net income
	Amortization of defined benefit pension items
	Prior-service costs		$	(3	)(b)	$	(3	)	Salaries and employee benefits
	Actuarial gains (losses)			(91	)(b)		(287	)	Salaries and employee benefits
	Total before tax			(94	)		(290	)	Income before taxes
	Tax (expense) or benefit			38			117		Provision for income taxes
	Net of tax		$	(56	)	$	(173	)	Net income
	Total reclassifications for the period		$	736		$	1,351		Net income, net of tax
	Details about Accumulated		Nine Months Ended			Nine Months Ended			Affected Line Item
	Other Comprehensive		September 30, 2014			September 30, 2013			in the Statement
	Income Components								Where Net Income
									is Presented
			(in thousands)
	Unrealized gains and losses on available-for-sale securities
			$	—		$	2,665		Net gains on sales of investments
				—			(1,035	)	Provision for income taxes
			$	—		$	1,630		Net income
	Accretion of unrealized losses transferred
			$	4,009		$	1,485		Securities held-to-maturity
				(1,485	)		(575	)	Provision for income taxes
			$	2,524		$	910		Net income
	Amortization of defined benefit pension items
	Prior-service costs		$	(8	)(b)	$	(8	)	Salaries and employee benefits
	Actuarial gains (losses)			(274	)(b)		(859	)	Salaries and employee benefits
	Total before tax			(282	)		(867	)	Income before taxes
	Tax (expense) or benefit			113			347		Provision for income taxes
	Net of tax		$	(169	)	$	(520	)	Net income
	Total reclassifications for the period		$	2,355		$	2,020		Net income, net of tax
	(a)	Amounts in parentheses indicate debits to profit/loss.
	(b)	These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see employee benefits footnote (Note 9) for additional details).

Earnings_per_Share_EPS

Earnings per Share ("EPS")	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Earnings per Share ("EPS")	'
	Note 8. 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 only common stock equivalents for the Company are the stock options discussed below. The dilutive effect of these stock options for 2014 and 2013 was an increase of 1,534 and 1,162 shares, respectively.
	The following table is a reconciliation of basic EPS and diluted EPS for the three and nine months ended September 30,
		Three Months Ended				Nine Months Ended
		September 30				September 30,
		2014		2013		2014		2013
	(in thousands except share and per share data)
	Basic EPS Computation:
	Numerator:
	Net income, Class A	$	4,480	$	4,324	$	12,741	$	11,760
	Net income, Class B		1,226		1,195		3,496		3,261
	Denominator:
	Weighted average shares outstanding, Class A		3,594,583		3,578,400		3,588,728		3,574,109
	Weighted average shares outstanding, Class B		1,967,180		1,987,180		1,969,647		1,982,413
	Basic EPS, Class A	$	1.25	$	1.21	$	3.55	$	3.29
	Basic EPS, Class B		0.62		0.6		1.78		1.64
	Diluted EPS Computation:
	Numerator:
	Net income, Class A	$	4,480	$	4,324	$	12,741	$	11,760
	Net income, Class B		1,226		1,195		3,496		3,261
	Total net income, for diluted EPS, Class A computation		5,706		5,519		16,237		15,021
	Denominator:
	Weighted average shares outstanding, basic, Class A		3,594,583		3,578,400		3,588,728		3,574,109
	Weighted average shares outstanding, Class B		1,967,180		1,978,180		1,969,647		1,982,413
	Dilutive effect of Class A stock options		1,515		1,451		1,534		1,261
	Weighted average shares outstanding diluted, Class A		5,563,278		5,558,031		5,559,909		5,557,783
	Weighted average shares outstanding, Class B		1,967,180		1,978,180		1,969,647		1,982,413
	Diluted EPS, Class A	$	1.03	$	0.99	$	2.92	$	2.7
	Diluted EPS, Class B		0.62		0.6		1.78		1.64

Employee_Benefits

Employee Benefits	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Employee Benefits	'
	Note 9. 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 (Credit) for the Three Months Ended September 30,
		Pension Benefits						Supplemental
								Insurance/
								Retirement
								Plan
		2014			2013			2014		2013
		(In thousands)
	Service cost	$	258		$	299		$	389	$	381
	Interest		367			314			331		267
	Expected return on plan assets		(636	)		(470	)		—		—
	Recognized prior service cost (benefit)		(26	)		(26	)		29		29
	Recognized net actuarial losses		3			158			88		129
	Net periodic benefit (credit) cost	$	(34	)	$	275		$	837	$	806
	Components of Net Periodic Benefit Cost (Credit) for the Nine Months Ended September 30,
		Pension Benefits						Supplemental
								Insurance/
								Retirement Plan
		2014			2013			2014		2013
		(In thousands)
	Service cost	$	775		$	897		$	1,166	$	1,144
	Interest		1,100			942			994		803
	Expected return on plan assets		(1,907	)		(1,410	)		—		—
	Recognized prior service cost (benefit)		(78	)		(78	)		86		86
	Recognized net actuarial losses		9			473			266		386
	Net periodic benefit (credit) cost	$	(101	)	$	824		$	2,512	$	2,419
	Contributions
	As of June 30, 2014, $920,000 has been contributed. The Company does not anticipate making any additional contributions.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Note 10. Fair Value Measurements
	The Company follows FASB ASC 820-10, Fair Value Measurements and Disclosures, (formerly SFAS 157, “Fair Value Measurements,”) which among other things, requires enhanced disclosures about assets and liabilities carried at fair value. ASC 820-10 establishes a hierarchal disclosure framework associated with the level of pricing observability utilized in measuring financial instruments at fair value. The three broad levels of the hierarchy are as follows:
	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 government, agency securities, listed equities and money market securities, as well as listed derivative instruments.
	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 markets and are measured using management’s best estimate of fair value, where the inputs into the determination of fair value require significant management judgment or estimation. Instruments that are included in this category generally include certain commercial mortgage loans, certain private equity investments, distressed debt, non-investment grade residual interests in securitizations, as well as certain highly structured OTC derivative contracts.
	The results of the fair value hierarchy as of September 30, 2014, are as follows:
	Financial Instruments Measured at Fair Value on a Recurring Basis:
			Securities AFS Fair Value Measurements Using
			Carrying		Quoted Prices			Significant			Significant
			Value		In Active			Observable			Other
					Markets for			Inputs			Unobservable
					Identical			(Level 2)			Inputs
					Assets						(Level 3)
					(Level 1)
			(In thousands)
	U.S. Treasury		$	2,001	$	—		$	2,001		$	—
	U.S. Government Sponsored Enterprises			—		—			—			—
	SBA Backed Securities			6,829		—			6,829			—
	U.S. Government Agency and Sponsored Mortgage Backed Securities			393,283		—			393,283			—
	Privately Issued Residential Mortgage Backed Securities			1,991		—			1,991			—
	Obligations Issued by States and Political Subdivisions			82,878		—			403			82,475
	Other Debt Securities			3,196		1,005			2,191			—
	Equity Securities			505		294			—			211
	Total		$	490,683	$	1,299		$	406,698		$	82,686
	Financial Instruments Measured at Fair Value on a Non-recurring Basis:
	Impaired Loans			4,680		—			—			4,680
	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 or other type of real estate tax assessment. The types of adjustments that are made to specific provisions (credits) relate to impaired loans recognized for the three-month period and nine-month periods ended September 30, 2014 amounted to $483,000 and $999,000, respectively.
	There were no transfers between level 1 and 2 for the three months ended September 30, 2014. There were no liabilities measured at fair value on a recurring or nonrecurring basis during the six month period ended September 30, 2014.
	The following table presents additional information about assets measured at fair value on a recurring and nonrecurring basis for which the Company has utilized Level 3 inputs to determine fair value (dollars in thousands). Management continues to monitor the assumptions used to value the assets listed below.
	Asset		Fair Value		Valuation Technique		Unobservable Input	Unobservable Input
								Value or Range
	Securities AFS(4)		$	82,686	Discounted cash flow		Discount rate	0% -1% (3)
	Impaired Loans			4,680	Appraisal of collateral (1)		Appraisal adjustments (2)	0%-25% 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, 2014 are shown in the table below:
			Auction Rate		Obligations			Equity			Total
			Securities		Issued by States			Securities
					& Political
					Subdivisions
			(In thousands)
	Balance at December 31, 2013		$	3,820	$	32,487		$	290		$	36,597
	Purchases			—		86,378			—			86,378
	Maturities and calls			—		(40,206	)		(79	)		(40,285	)
	Amortization			—		(4	)		—			(4	)
	Changes in fair value			—		—			—			—
	Balance at September 30, 2014		$	3,820	$	78,655		$	211		$	82,686
	The amortized cost of Level 3 securities was $83,559,000 at September 30, 2014 with an unrealized loss of $872,000. The securities in this category are generally equity investments, municipal securities with no readily determinable fair value or failed auction rate securities. Management evaluated the fair value of these securities based on an evaluation of the underlying issuer, prevailing rates and market liquidity.
	The changes in Level 3 securities for the nine-month period ended September 30, 2013, are shown in the table below:
			Auction Rate		Obligations			Equity			Total
			Securities		Issued by States			Securities
					& Political
					Subdivisions
			(In thousands)
	Balance at December 31, 2012		$	3,963	$	49,477		$	342		$	53,782
	Purchases			—		43,807			—			43,807
	Maturities and calls			—		(57,036	)		(51	)		(57,087	)
	Amortization			—		(23	)		—			(23	)
	Changes in fair value			—		—			—			—
	Balance at September 30, 2013		$	3,963	$	36,225		$	291		$	40,479
The amortized cost of Level 3 securities was $41,204,000 at September 30, 2013 with an unrealized loss of $725,000. The securities in this category are generally equity investments, municipal securities with no readily determinable fair value or failed auction rate securities. Management evaluated the fair value of these securities based on an evaluation of the underlying issuer, prevailing rates and market liquidity.

Fair_Values_of_Financial_Instr

Fair Values of Financial Instruments	9 Months Ended
	Sep. 30, 2014
Investments, All Other Investments [Abstract]	'
Fair Values of Financial Instruments	'
	Note 11. Fair Values of Financial Instruments
	The following methods and assumptions were used by the Company in estimating fair values of its financial instruments. Excluded from this disclosure are all nonfinancial instruments. Accordingly, the aggregate fair value amounts presented do not represent the underlying value of the Company.
	The assumptions used below are expected to approximate those that market participants would use in valuing these financial instruments.
	Fair value estimates are made at a specific point in time, based on available market information and judgments about the financial instrument, including estimates of timing, amount of expected future cash flows and the credit standing of the issuer. Such estimates do not consider the tax impact of the realization of unrealized gains or losses. In some cases, the fair value estimates cannot be substantiated by comparison to independent markets. In addition, the disclosed fair value may not be realized in the immediate settlement of the financial instrument. Care should be exercised in deriving conclusions about our business, its value or financial position based on the fair value information of financial instruments presented below.
	Securities held-to-maturity: The fair values of these securities were based on quoted market prices, where available, as provided by third-party investment portfolio pricing vendors. If quoted market prices were not available, fair values provided by the vendors were based on quoted market prices of comparable instruments in active markets and/or based on a matrix pricing methodology which employs The Bond Market Association’s standard calculations for cash flow and price/yield analysis, live benchmark bond pricing and terms/condition data available from major pricing sources. Management regards the inputs and methods used by third party pricing vendors to be “Level 2 inputs and methods” as defined in the “fair value hierarchy” provided by FASB.
	Loans: For variable-rate loans, that reprice frequently and with no significant change in credit risk, fair values are based on carrying amounts. The fair value of other loans is estimated using discounted cash flow analysis, based on interest rates currently being offered for loans with similar terms to borrowers of similar credit quality. Incremental credit risk for nonperforming loans has been considered.
	Time deposits: The fair value of time deposits was estimated using a discounted cash flow approach that applies prevailing market interest rates for similar maturity instruments. The fair values of the Company’s time deposit liabilities do not take into consideration the value of the Company’s long-term relationships with depositors, which may have significant value.
	Other borrowed funds: The fair value of other borrowed funds is based on the discounted value of contractual cash flows. The discount rate used is estimated based on the rates currently offered for other borrowed funds of similar remaining maturities.
	Subordinated debentures: The fair value of subordinated debentures is based on the discounted value of contractual cash flows. The discount rate used is estimated based on the rates currently offered for other subordinated debentures of similar remaining maturities.
	The following presents (in thousands) the carrying amount, estimated fair value, and placement in the fair value hierarchy of the Company’s financial instruments as of September 30, 2014 and December 31, 2013. This table excludes financial instruments for which the carrying amount approximates fair value. Financial assets for which the fair value approximates carrying value include cash and cash equivalents, short-term investments, FHLBB stock and accrued interest receivable. Financial liabilities for which the fair value approximates carrying value include non-maturity deposits, short-term borrowings and accrued interest payable.
							Fair Value Measurements
			Carrying Amount		Estimated Fair		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
					Value
	September 30, 2014
	(in thousands)
	Financial assets:
	Securities held-to-maturity		$	1,471,137	$	1,463,535	$	—	$	1,463,535	$	—
	Loans (1)			1,314,164		1,291,746		—		—		1,291,746
	Financial liabilities:
	Time deposits			370,779		375,650		—		375,650		—
	Other borrowed funds			337,500		340,500		—		340,500		—
	Subordinated debentures			36,083		36,083		—		—		36,083
	December 31, 2013
	Financial assets:
	Securities held-to-maturity			1,487,884		1,464,449		—		1,464,449		—
	Loans (1)			1,243,822		1,214,192		—		—		1,214,192
	Financial liabilities:
	Time deposits			382,224		386,742		—		386,742		—
	Other borrowed funds			255,144		254,736		—		254,736		—
	Subordinated debentures			36,083		39,503		—		—		39,503
	-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, 2014
Accounting Changes and Error Corrections [Abstract]	'
Recent Accounting Developments	'
	Note 12. Recent Accounting Developments
	In December 2011, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2011-11, Balance Sheet (Topic 210), Disclosures about Offsetting Assets and Liabilities. ASU 2011-11 requires an entity to disclose information about offsetting and related arrangements to enable users of financial statements to understand the effect of those arrangements on its financial position, and to allow investors to better compare financial statements prepared under U.S. GAAP with financial statements prepared under IFRS. The new standards are effective for annual periods beginning January 1, 2013, and interim periods within those annual periods. Retrospective application is required. The Company implemented the provisions of ASU 2011-11 as of January 1, 2013. The adoption of this pronouncement did not have a material effect on the consolidated financial statements.
	In February 2013, the FASB issued ASU 2013-02, Comprehensive Income (Topic 220) Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income. ASU 2013-02 requires an entity to report the effect of significant reclassifications out of accumulated other comprehensive income on the respective line items in net income or as a separate disclosure in the notes to the financial statements. The new standard is effective for annual periods beginning January 1, 2013, and interim periods within those annual periods. The Company has presented a separate footnote (Note 7) as a result of this pronouncement.
	In January 2014, the FASB issued ASU 2014-04, Receivables-Troubled Debt Restructurings by Creditors (Subtopic 310-40) Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure. The amendments in this update clarify that an in substance repossession or foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (1) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (2) the borrower conveying all interest in the residential real estate property to the creditor to satisfy that loan through completion of a deed in lieu of foreclosure or through a similar legal agreement. The amendments in this update are effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2014. The Company has assessed the impact of ASU 2014-04 and the adoption of this amendment will not have a material impact on the Company’s financial statements.
	In June 2014, the FASB issued ASU 2014-11, Transfers and Servicing (Topic 860) Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures. This ASU eliminates sale accounting for repurchase-to-maturity transactions and supersedes the guidance under which a transfer of a financial asset and a contemporaneous repurchase financing could be accounted for on a combined basis as a forward agreement. In addition, the ASU requires a new disclosure for transactions economically similar to repurchase agreements in which the transferor retains substantially all of the exposure to the economic return on the transferred financial assets throughout the term of the transaction. The ASU is effective for annual periods beginning after December 15, 2014 and interim periods beginning after December 15, 2015; early application is not permitted. The Company is currently assessing the applicability of this ASU and has not determined the impact, if any, as of September 30, 2014.
	In August 2014, the FASB issued ASU 2014-14, Receivables—Troubled Debt Restructurings by Creditors (Subtopic 310-40) Classification of Certain Government-Guaranteed Mortgage Loans upon Foreclosure. This ASU which will require creditors to derecognize certain foreclosed government-guaranteed mortgage loans and to recognize a separate other receivable that is measured at the amount the creditor expects to recover from the guarantor, and to treat the guarantee and the receivable as a single unit of account. ASU 2014-14 is effective for public business entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2014. For entities other than public business entities, the ASU is effective for annual periods ending after December 15, 2015, and interim periods beginning after December 15, 2015. An entity can elect a prospective or a modified retrospective transition method, but must use the same transition method that it elected under FASB ASU No. 2014-04, Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure. Early adoption, including adoption in an interim period, is permitted if the entity already adopted ASU 2014-04. The Company has assessed the impact of ASU 2014-14 and the adoption of this amendment will not have a material impact on the Company’s financial statements.

Fair_Value_Measurements_Polici

Fair Value Measurements (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Changes and Error Corrections [Abstract]	'
Fair Value Measurements and Disclosures	'
	The Company follows FASB ASC 820-10, Fair Value Measurements and Disclosures, (formerly SFAS 157, “Fair Value Measurements,”) which among other things, requires enhanced disclosures about assets and liabilities carried at fair value. ASC 820-10 establishes a hierarchal disclosure framework associated with the level of pricing observability utilized in measuring financial instruments at fair value. The three broad levels of the hierarchy are as follows:
	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 government, agency securities, listed equities and money market securities, as well as listed derivative instruments.
	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 markets and are measured using management’s best estimate of fair value, where the inputs into the determination of fair value require significant management judgment or estimation. Instruments that are included in this category generally include certain commercial mortgage loans, certain private equity investments, distressed debt, non-investment grade residual interests in securitizations, as well as certain highly structured OTC derivative contracts.
Disclosures about Offsetting Assets and Liabilities	'
	In December 2011, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2011-11, Balance Sheet (Topic 210), Disclosures about Offsetting Assets and Liabilities. ASU 2011-11 requires an entity to disclose information about offsetting and related arrangements to enable users of financial statements to understand the effect of those arrangements on its financial position, and to allow investors to better compare financial statements prepared under U.S. GAAP with financial statements prepared under IFRS. The new standards are effective for annual periods beginning January 1, 2013, and interim periods within those annual periods. Retrospective application is required. The Company implemented the provisions of ASU 2011-11 as of January 1, 2013. The adoption of this pronouncement did not have a material effect on the consolidated financial statements.
Comprehensive Income	'
	In February 2013, the FASB issued ASU 2013-02, Comprehensive Income (Topic 220) Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income. ASU 2013-02 requires an entity to report the effect of significant reclassifications out of accumulated other comprehensive income on the respective line items in net income or as a separate disclosure in the notes to the financial statements. The new standard is effective for annual periods beginning January 1, 2013, and interim periods within those annual periods. The Company has presented a separate footnote (Note 7) as a result of this
Debt Restructuring	'
	In January 2014, the FASB issued ASU 2014-04, Receivables-Troubled Debt Restructurings by Creditors (Subtopic 310-40) Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure. The amendments in this update clarify that an in substance repossession or foreclosure occurs, and a creditor is considered to have received physical possession of residential real estate property collateralizing a consumer mortgage loan, upon either (1) the creditor obtaining legal title to the residential real estate property upon completion of a foreclosure or (2) the borrower conveying all interest in the residential real estate property to the creditor to satisfy that loan through completion of a deed in lieu of foreclosure or through a similar legal agreement. The amendments in this update are effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2014. The Company has assessed the impact of ASU 2014-04 and the adoption of this amendment will not have a material impact on the Company’s financial statements.
Transfer and Servicing of Financial Assets	'
	In June 2014, the FASB issued ASU 2014-11, Transfers and Servicing (Topic 860) Repurchase-to-Maturity Transactions, Repurchase Financings, and Disclosures. This ASU eliminates sale accounting for repurchase-to-maturity transactions and supersedes the guidance under which a transfer of a financial asset and a contemporaneous repurchase financing could be accounted for on a combined basis as a forward agreement. In addition, the ASU requires a new disclosure for transactions economically similar to repurchase agreements in which the transferor retains substantially all of the exposure to the economic return on the transferred financial assets throughout the term of the transaction. The ASU is effective for annual periods beginning after December 15, 2014 and interim periods beginning after December 15, 2015; early application is not permitted. The Company is currently assessing the applicability of this ASU and has not determined the impact, if any, as of September 30, 2014.
Government Guaranteed Mortgage Loans	'
	In August 2014, the FASB issued ASU 2014-14, Receivables—Troubled Debt Restructurings by Creditors (Subtopic 310-40) Classification of Certain Government-Guaranteed Mortgage Loans upon Foreclosure. This ASU which will require creditors to derecognize certain foreclosed government-guaranteed mortgage loans and to recognize a separate other receivable that is measured at the amount the creditor expects to recover from the guarantor, and to treat the guarantee and the receivable as a single unit of account. ASU 2014-14 is effective for public business entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2014. For entities other than public business entities, the ASU is effective for annual periods ending after December 15, 2015, and interim periods beginning after December 15, 2015. An entity can elect a prospective or a modified retrospective transition method, but must use the same transition method that it elected under FASB ASU No. 2014-04, Reclassification of Residential Real Estate Collateralized Consumer Mortgage Loans upon Foreclosure. Early adoption, including adoption in an interim period, is permitted if the entity already adopted ASU 2014-04. The Company has assessed the impact of ASU 2014-14 and the adoption of this amendment will not have a material impact on the Company’s financial statements.

Stock_Option_Accounting_Tables

Stock Option Accounting (Tables)	9 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Summary of Stock Option Activity under Stock Option Plan	'
	Stock option activity under the Company’s stock option plan for the nine months ended September 30, 2014 is as follows:
		Amount			Weighted
					Average
					Exercise Price
	Shares under option:
	Outstanding at beginning of year		20,225		$	31.82
	Exercised		(10,325	)		31.83
	Forfeited		(8,900	)		31.83
	Outstanding at end of period		1,000		$	31.6
	Exercisable at end of period		1,000		$	31.6
	Available to be granted at end of period		233,784

Securities_AvailableforSale_Ta

Securities Available-for-Sale (Tables)	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Summary of Securities Available-for-Sale	'
		September 30, 2014								December 31, 2013
		Amortized		Gross		Gross		Fair		Amortized		Gross		Gross		Fair
		Cost		Unrealized		Unrealized		Value		Cost		Unrealized		Unrealized		Value
				Gains		Losses						Gains		Losses
		( In thousands)
	U.S. Treasury	$	1,999	$	2	$	—	$	2,001	$	1,997	$	1	$	—	$	1,998
	U.S. Government Sponsored Enterprises		—		—		—		—		9,995		9		—		10,004
	Small Business Administration		6,787		42		—		6,829		7,270		32		—		7,302
	U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities		391,721		2,185		623		393,283		404,103		588		1,501		403,190
	Privately Issued Residential Mortgage Backed Securities		1,993		9		11		1,991		2,294		6		23		2,277
	Obligations Issued by States and Political Subdivisions		83,749		2		873		82,878		37,578		15		870		36,723
	Other Debt Securities		3,300		5		109		3,196		2,300		—		125		2,175
	Equity Securities		327		178		—		505		406		170		—		576
	Total	$	489,876	$	2,423	$	1,616	$	490,683	$	465,943	$	821	$	2,519	$	464,245
Maturity Distribution of Securities Available-for-Sale	'
	The following table shows the maturity distribution of the Company’s securities available-for-sale at September 30, 2014.
		Amortized		Fair
		Cost		Value
		( In thousands)
	Within one year	$	77,321	$	77,322
	After one but within five years		175,594		176,505
	After five but within ten years		226,116		226,788
	More than 10 years		9,018		8,172
	Non-maturing		1,827		1,896
	Total	$	489,876	$	490,683
Continuous Unrealized Loss Position for 12 Months or Less and 12 Months or Longer	'
	The following table shows the temporarily impaired securities of the Company’s available-for-sale portfolio at September 30, 2014. This table shows the unrealized market loss of securities that have been in a continuous unrealized loss position for 12 months or less and a continuous loss position for 12 months and longer. There are 3 and 17 securities that are temporarily impaired for less than 12 months and for 12 months or longer, respectively, out of a total of 257 holdings at September 30, 2014.
		September 30, 2014
		Less than 12 months				12 months or longer				Total
	Temporarily Impaired Investments	Fair Value		Unrealized		Fair Value		Unrealized		Fair Value		Unrealized
				Losses				Losses				Losses
		(In thousands)
	U.S. Government Sponsored Enterprises	$	—	$	—	$	—	$	—	$	—	$	—
	U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities		20,768		99		99,716		524		120,484		623
	Privately Issued Residential Mortgage Backed Securities		—		—		737		11		737		11
	Obligations Issued by States and Political Subdivisions		—		—		3,820		873		3,820		873
	Other Debt Securities		—		—		1,390		109		1,390		109
	Total temporarily impaired securities	$	20,768	$	99	$	105,663	$	1,517	$	126,431	$	1,616
	The following table shows the temporarily impaired securities of the Company’s available-for-sale portfolio at December 31, 2013. This table shows the unrealized market loss of securities that have been in a continuous unrealized loss position for 12 months or less and a continuous loss position for 12 months and longer. There are 47 and 7 securities that are temporarily impaired for less than 12 months and for 12 months or longer, respectively, out of a total of 234 holdings at December 31, 2013.
		December 31, 2013
		Less than 12 months				12 months or longer				Total
	Temporarily Impaired Investments	Fair Value		Unrealized		Fair Value		Unrealized		Fair Value		Unrealized
				Losses				Losses				Losses
		(In thousands)
	U.S. Government Sponsored Enterprises	$	—	$	—	$	—	$	—	$	—	$	—
	U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities		289,709		1, 352		24,557		149		314,266		1,501
	Privately Issued Residential Mortgage Backed Securities		1,486		23		—		—		1,486		23
	Obligations Issued by States and Political Subdivisions		—		—		3,820		870		3,820		870
	Other Debt Securities		—		—		1,376		125		1,376		125
	Total temporarily impaired securities	$	291,195	$	1,375	$	29,753	$	1,144	$	320,948	$	2,519

Investment_Securities_HeldtoMa1

Investment Securities Held-to-Maturity (Tables)	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Summary of Held-to-Maturity Securities	'
		September 30, 2014								December 31, 2013
		Amortized		Gross		Gross		Estimated		Amortized		Gross		Gross		Estimated
		Cost		Unrealized		Unrealized		Fair		Cost		Unrealized		Unrealized		Fair
				Gains		Losses		Value				Gains		Losses		Value
		(In thousands)
	U.S. Government Sponsored Enterprises	$	291,158	$	1,377	$	870	$	291,665	$	291,779	$	185	$	5,043	$	286,921
	U.S. Government Agency and Sponsored Enterprises Mortgage Backed Securities		1,179,979		6,408		14,517		1,171,870		1,196,105		2,239		20,816		1,177,528
	Total	$	1,471,137	$	7,785	$	15,387	$	1,463,535	$	1,487,884	$	2,424	$	25,859	$	1,464,449
Company's Securities Held-to-Maturity	'
	The following table shows the maturity distribution of the Company’s securities held-to-maturity at September 30, 2014.
		Amortized		Fair
		Cost		Value
		( In thousands)
	Within one year	$	4,168	$	4,230
	After one but within five years		988,565		983,567
	After five but within ten years		477,606		474,921
	More than ten years		798		817
	Total	$	1,471,137	$	1,463,535
Unrealized Market Loss of Securities	'
	The following table shows the temporarily impaired securities of the Company’s held-to-maturity portfolio at September 30, 2014. This table shows the unrealized market loss of securities that have been in a continuous unrealized loss position for 12 months or less and a continuous loss position for 12 months and longer. There are 84 and 53 securities that are temporarily impaired for less than 12 months and for 12 months or longer, respectively, out of a total of 305 holdings at September 30, 2014.
		September 30, 2014
		Less Than 12 Months				12 Months or Longer				Total
	Temporarily Impaired Investments	Fair Value		Unrealized		Fair Value		Unrealized		Fair Value		Unrealized
				Losses				Losses				Losses
		(Dollars in thousands)
	U.S. Government Sponsored Enterprises	$	105,032	$	507	$	14,637	$	363	$	119,669	$	870
	U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities		422,503		4,626		346,611		9,891		769,114		14,517
	Total temporarily impaired securities	$	527,535	$	5,133	$	361,248	$	10,254	$	888,783	$	15,387
	The following table shows the temporarily impaired securities of the Company’s held-to-maturity portfolio at December 31, 2013. This table shows the unrealized market loss of securities that have been in a continuous unrealized loss position for 12 months or less and a continuous loss position for 12 months and longer. There are 191 and 13 securities that are temporarily impaired for less than 12 months and for 12 months or longer, respectively, out of a total of 300 holdings at December 31, 2013.
		December 31, 2013
		Less Than 12 Months				12 Months or Longer				Total
	Temporarily Impaired Investments	Fair Value		Unrealized		Fair Value		Unrealized		Fair Value		Unrealized
				Losses				Losses				Losses
		( In thousands)
	U.S. Government Sponsored Enterprises	$	232,535	$	5,043	$	—	$	—	$	232,535	$	5,043
	U.S. Government Agency and Sponsored Enterprise Mortgage-Backed Securities		931,180		18,654		80,362		2,162		1,011,542		20,816
	Total temporarily impaired securities	$	1,163,715	$	23,697	$	80,362	$	2,162	$	1,244,077	$	25,859

Allowance_for_Loan_Losses_Tabl

Allowance for Loan Losses (Tables)	9 Months Ended
	Sep. 30, 2014
Receivables [Abstract]	'
Summary of Changes in 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
		September 30,						September 30,
		2014			2013			2014			2013
		(in thousands)
	Allowance for loan losses, beginning of period	$	21,722		$	20,500		$	20,941		$	19,197
	Loans charged off		(163	)		(149	)		(705	)		(682	)
	Recoveries on loans previously charged-off		310			149			583			485
	Net charge-offs		147			—			(122	)		(197	)
	Provision charged to expense		600			750			1,650			2,250
	Allowance for loan losses, end of period	$	22,469		$	21,250		$	22,469		$	21,250
Summary of Allowance for Loan Losses	'
	Further information pertaining to the allowance for loan losses for the three months ending September 30, 2014 follows:
		Construction			Commercial			Commercial			Residential			Consumer			Home			Unallocated			Total
		and Land			and			Real			Real						Equity
		Development			Industrial			Estate			Estate
		(Dollars in thousands)
	Allowance for loan losses:
	Balance at June 30, 2014	$	2,045		$	2,915		$	11,975		$	1,927		$	428		$	915		$	1,517		$	21,722
	Charge-offs		—			(37	)		—			—			(126	)		—			—			(163	)
	Recoveries		—			115			1			6			106			82			—			310
	Provision		(39	)		2,396			(1,116	)		(132	)		46			(41	)		(514	)		600
	Ending balance at September 30, 2014	$	2,006		$	5,389		$	10,860		$	1,801		$	454		$	956		$	1,003		$	22,469
	Amount of allowance for loan losses for loans deemed to be impaired	$	272		$	348		$	648		$	152		$	—		$	93		$	—			1,513
	Amount of allowance for loan losses for loans not deemed to be impaired	$	1,734		$	5,041		$	10,212		$	1,649		$	454		$	863		$	1,003		$	20,956
	Loans:
	Ending balance	$	25,339		$	181,627		$	702,894		$	268,927		$	10,253		$	147,593		$	—		$	1,336,633
	Loans deemed to be impaired	$	354		$	1,096		$	4,740		$	1,549		$	—		$	93		$	—		$	7,832
	Loans not deemed to be impaired	$	24,985		$	180,531		$	698,154		$	267,378		$	10,253		$	147,500		$	—		$	1,328,801
	Further information pertaining to the allowance for loan losses for the nine months ending September 30, 2014 follows:
		Construction			Commercial			Commercial			Residential			Consumer			Home			Unallocated			Total
		and Land			and			Real			Real						Equity
		Development			Industrial			Estate			Estate
		(Dollars in thousands)
	Allowance for loan losses:
	Balance at December 31, 2013	$	2,174		$	2,989		$	11,218		$	2,006		$	432		$	959		$	1,163		$	20,941
	Charge-offs		(250	)		(51	)		—			—			(404	)		—			—			(705	)
	Recoveries		—			164			5			26			305			83			—			583
	Provision		82			2,287			(363	)		(231	)		121			(86	)		(160	)		1,650
	Ending balance at September 30, 2014	$	2,006		$	5,389		$	10,860		$	1,801		$	454		$	956		$	1,003		$	22,469
	Amount of allowance for loan losses for loans deemed to be impaired	$	272		$	348		$	648		$	152		$	—		$	93		$	—			1,513
	Amount of allowance for loan losses for loans not deemed to be impaired	$	1,734		$	5,041		$	10,212		$	1,649		$	454		$	863		$	1,003		$	20,956
	Loans:
	Ending balance	$	25,339		$	181,627		$	702,894		$	268,927		$	10,253		$	147,593		$	—		$	1,336,633
	Loans deemed to be impaired	$	354		$	1,096		$	4,740		$	1,549		$	—		$	93		$	—		$	7,832
	Loans not deemed to be impaired	$	24,985		$	180,531		$	698,154		$	267,378		$	10,253		$	147,500		$	—		$	1,328,801
	Further information pertaining to the allowance for loan losses for the three months ending September 30, 2013 follows:
		Construction			Commercial			Commercial			Residential			Consumer			Home			Unallocated			Total
		and Land			and			Real			Real						Equity
		Development			Industrial			Estate			Estate
		(Dollars in thousands)
	Allowance for loan losses:
	Balance at June 30, 2013	$	3,241		$	3,215		$	9,424		$	2,030		$	363		$	932		$	1,295		$	20,500
	Charge-offs		—			—			—			—			(149	)		—			—			(149	)
	Recoveries		—			42			2			4			101			—			—			149
	Provision		(114	)		(534	)		1,162			176			76			17			(33	)		750
	Ending balance at September 30, 2013	$	3,127		$	2,723		$	10,588		$	2,210		$	391		$	949		$	1		$	21,250
																					,262
	Amount of allowance for loan losses for loans deemed to be impaired	$	1,000		$	90		$	445		$	139		$	—		$	95		$	—			1,769
	Amount of allowance for loan losses for loans not deemed to be impaired	$	2,127		$	2,633		$	10,143		$	2,071		$	391		$	854		$	1,262		$	19,481
	Loans:
	Ending balance	$	32,750		$	87,468		$	666,166		$	309,291		$	8,728		$	126,645		$	—		$	1,231,048
	Loans deemed to be impaired	$	1,500		$	1,132		$	4,688		$	1,151		$	—		$	95		$	—		$	8,566
	Loans not deemed to be impaired	$	31,250		$	86,336		$	661,478		$	308,140		$	8,728		$	126,550		$	—		$	1,222,482
	Further information pertaining to the allowance for loan losses for the nine months ending September 30, 2013 follows:
		Construction			Commercial			Commercial			Residential			Consumer			Home			Unallocated			Total
		and Land			and			Real			Real						Equity
		Development			Industrial			Estate			Estate
		(Dollars in thousands)
	Allowance for loan losses:
	Balance at December 31, 2012	$	3,041		$	3,118		$	9,065		$	1,994		$	333		$	886		$	760		$	19,197
	Charge-offs		—			(234	)		—			—			(448	)		—			—			(682	)
	Recoveries		—			163			5			9			307			1			—			485
	Provision		86			(324	)		1,518			207			199			62			502			2,250
	Ending balance at September 30, 2013	$	3,127		$	2,723		$	10,588		$	2,210		$	391		$	949		$	1		$	21,250
,262
Amount of allowance for loan losses for loans deemed to be impaired	$	1,000		$	90		$	445		$	139		$	—		$	95		$	—			1,769
Amount of allowance for loan losses for loans not deemed to be impaired	$	2,127		$	2,633		$	10,143		$	2,071		$	391		$	854		$	1,262		$	19,481
Loans:
Ending balance	$	32,750		$	87,468		$	666,166		$	309,291		$	8,728		$	126,645		$	—		$	1,231,048
Loans deemed to be impaired	$	1,500		$	1,132		$	4,688		$	1,151		$	—		$	95		$	—		$	8,566
Loans not deemed to be impaired	$	31,250		$	86,336		$	661,478		$	308,140		$	8,728		$	126,550		$	—		$	1,222,482
Loans by Risk Rating	'
	The following table presents the Company’s loans by risk rating at September 30, 2014.
		Construction			Commercial			Commercial
		and land			and			real
		development			industrial			estate
		(Dollars in thousands)
	Grade:
	1-3 (Pass)	$	17,808		$	180,059		$	697,509
	4 (Monitor)		7,177			472			645
	5 (Substandard)		—			—			—
	6 (Doubtful)		—			—			—
	Impaired		354			1,096			4,740
	Total	$	25,339		$	181,627		$	702,894
	The following table presents the Company’s loans by risk rating at December 31, 2013.
		Construction			Commercial			Commercial
		and land			and			real
		development			industrial			estate
		(Dollars in thousands)
	Grade:
	1-3 (Pass)	$	25,138		$	90,563		$	707,461
	4 (Monitor)		7,312			472			1,346
	5 (Substandard)		—			—			—
	6 (Doubtful)		—			—			—
	Impaired		608			1,367			4,520
	Total	$	33,058		$	92,402		$	713,327
Aging of Past Due Loan Losses	'
	Further information pertaining to the allowance for loan losses at September 30, 2014 follows:
		Accruing			Non Accrual			Accrual			Total			Current Loans			Total
		30-89 Days						Greater			Past Due
		Past Due						Than
								90 Days
								(Dollars in thousands)
	Construction and land development	$	—		$	354		$	—		$	354		$	24,985		$	25,339
	Commercial and industrial		895			418			—			1,313			180,314			181,627
	Commercial real estate		1,608			2,787			—			4,395			698,499			702,894
	Residential real estate		378			2,197			—			2,575			266,352			268,927
	Consumer and overdrafts		5			8			—			13			10,240			10,253
	Home equity		1,072			254			—			1,326			146,267			147,593
	Total	$	3,958		$	6,018		$	—		$	9,976		$	1,326,657		$	1,336,633
	Further information pertaining to the allowance for loan losses at December 31, 2013 follows:
		Accruing			Non Accrual			Accrual			Total			Current Loans			Total
		30-89 Days						Greater			Past Due
		Past Due						Than
								90
								Days
								(Dollars in thousands)
	Construction and land development	$	—		$	500		$	—		$	500		$	32,558		$	33,058
	Commercial and industrial		112			706			—			818			91,584			92,402
	Commercial real estate		1,496			306			—			1,802			711,525			713,327
	Residential real estate		2,232			1,034			—			3,266			282,775			286,041
	Consumer and overdrafts		11			3			—			14			9,644			9,658
	Home equity		1,710			—			—			1,710			128,567			130,277
	Total	$	5,561		$	2,549		$	—		$	8,110		$	1,256,653		$	1,264,763
Information Pertaining to Impaired Loans	'
	The following is information pertaining to impaired loans for September 30, 2014:
		Carrying			Unpaid			Required			Average			Interest			Average			Interest
		Value			Principal			Reserve			Carrying Value			Income			Carrying Value			Income
					Balance						For 3 Months			Recognized For			For 9 Months			Recognized For
											Ending 9/30/14			3 Months			Ending 9/30/14			9 Months
														Ending 9/30/14						Ending 9/30/14
		(Dollars in thousands)
	With no required reserve recorded:
	Construction and land development	$	—		$	—		$	—		$	—		$	—		$	225		$	—
	Commercial and industrial		11			42			—			11			—			53			—
	Commercial real estate		392			396			—			396			—			175			—
	Residential real estate		—			—			—			18			—			72			—
	Consumer		—			—			—			—			—			—			—
	Home equity		—			—			—			—			—			—			—
	Total	$	403		$	438		$	—		$	425		$	—		$	525		$	—
	With required reserve recorded:
	Construction and land development	$	354		$	3,400		$	272		$	355		$	—		$	207		$	—
	Commercial and industrial		1,085			1,337			348			1,078			8			1,095			24
	Commercial real estate		4,348			4,440			648			4,492			39			4,443			113
	Residential real estate		1,549			1,549			152			1,536			3			1,193			8
	Consumer		—			—			—			—			—			—			—
	Home equity		93			93			93			93			—			94			—
	Total	$	7,429		$	10,819		$	1,513		$	7,554		$	50		$	7,032		$	145
	Total:
	Construction and land development	$	354		$	3,400		$	272		$	355		$	—		$	432		$	—
	Commercial and industrial		1,096			1,379			348			1,089			8			1,148			24
	Commercial real estate		4,740			4,836			648			4,888			39			4,618			113
	Residential real estate		1,549			1,549			152			1,554			3			1,265			8
	Consumer		—			—			—			—			—			—			—
	Home equity		93			93			93			93			—			94			—
	Total	$	7,832		$	11,257		$	1,513		$	7,979		$	50		$	7,557		$	145
	The following is information pertaining to impaired loans for September 30, 2013:
		Carrying Value			Unpaid			Required			Average			Interest			Average			Interest
					Principal			Reserve			Carrying Value			Income			Carrying Value			Income
					Balance						For 3 Months			Recognized For			For 9 Months			Recognized For
											Ending 9/30/13			3 Months			Ending 9/30/13			9 Months
														Ending 9/30/13						Ending 9/30/13
		(Dollars in thousands)
	With no required reserve recorded:
	Construction and land development	$	—		$	—		$	—		$	—		$	—		$	—		$	—
	Commercial and industrial		264			294			—			239			—			390			1
	Commercial real estate		218			218			—			126			—			133			—
	Residential real estate		254			263			—			260			—			145			—
	Consumer		—			—			—			—			—			—			—
	Home equity		—			—			—			—			—			—			—
	Total	$	736		$	775		$	—		$	625		$	1		$	668		$	1
	With required reserve recorded:
	Construction and land development	$	1,500		$	3,292		$	1,000		$	1,500		$	—		$	1,500		$	—
	Commercial and industrial		868			1,101			90			885			12			864			29
	Commercial real estate		4,470			4,558			445			2,796			26			2,394			72
	Residential real estate		897			979			139			901			—			853			—
	Consumer		—			—			—			—			—			—			—
	Home equity		95			95			95			95			—			96			—
	Total	$	7,830		$	10,025		$	1,769		$	6,177		$	38		$	5,707		$	101
	Total:
	Construction and land development	$	1,500		$	3,292		$	1,000		$	1,500		$	—		$	1,500		$	—
	Commercial and industrial		1,132			1,395			90			1,124			12			1,254			30
	Commercial real estate		4,688			4,776			445			2,922			26			2,527			72
	Residential real estate		1,151			1,242			139			1,161			—			998			—
	Consumer		—			—			—			—			—			—			—
	Home equity		95			95			95			95			—			96			—
	Total	$	8,566		$	10,800		$	1,769		$	6,802		$	38		$	6,375		$	102
Troubled Debt Restructurings	'
	Troubled Debt Restructurings occurring during the three and nine month periods ended September 30, 2013:
		Number			Pre-modification			Post-
		of			outstanding			modification
		Contracts			recorded			outstanding
					investment			recorded
								investment
		(Dollars in thousands)
	Construction and land development		1		$	108		$	108
	Commercial and industrial		1			41			41
	Commercial real estate		1			2,247			2,242
	Total		3		$	2,396		$	2,391

Reclassifications_Out_of_Accum1

Reclassifications Out of Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Reclassifications Out of Accumulated Other Comprehensive Income	'
	Amount Reclassified from Accumulated Other Comprehensive Income
	Details about Accumulated		Three Months Ended			Three Months Ended			Affected Line Item
	Other Comprehensive		September 30, 2014			September 30, 2013			in the Statement
	Income Components								Where Net Income
									is Presented
			(in thousands)
	Unrealized gains and losses on available-for-sale securities
			$	—		$	1,001		Net gains on sales of investments
				—			(387	)	Provision for income taxes
			$	—		$	614		Net income
	Accretion of unrealized losses transferred
			$	1,216		$	1,485		Securities held-to-maturity
				(424	)		(575	)	Provision for income taxes
			$	792		$	910		Net income
	Amortization of defined benefit pension items
	Prior-service costs		$	(3	)(b)	$	(3	)	Salaries and employee benefits
	Actuarial gains (losses)			(91	)(b)		(287	)	Salaries and employee benefits
	Total before tax			(94	)		(290	)	Income before taxes
	Tax (expense) or benefit			38			117		Provision for income taxes
	Net of tax		$	(56	)	$	(173	)	Net income
	Total reclassifications for the period		$	736		$	1,351		Net income, net of tax
	Details about Accumulated		Nine Months Ended			Nine Months Ended			Affected Line Item
	Other Comprehensive		September 30, 2014			September 30, 2013			in the Statement
	Income Components								Where Net Income
									is Presented
			(in thousands)
	Unrealized gains and losses on available-for-sale securities
			$	—		$	2,665		Net gains on sales of investments
				—			(1,035	)	Provision for income taxes
			$	—		$	1,630		Net income
	Accretion of unrealized losses transferred
			$	4,009		$	1,485		Securities held-to-maturity
				(1,485	)		(575	)	Provision for income taxes
			$	2,524		$	910		Net income
	Amortization of defined benefit pension items
	Prior-service costs		$	(8	)(b)	$	(8	)	Salaries and employee benefits
	Actuarial gains (losses)			(274	)(b)		(859	)	Salaries and employee benefits
	Total before tax			(282	)		(867	)	Income before taxes
	Tax (expense) or benefit			113			347		Provision for income taxes
	Net of tax		$	(169	)	$	(520	)	Net income
	Total reclassifications for the period		$	2,355		$	2,020		Net income, net of tax
	(a)	Amounts in parentheses indicate debits to profit/loss.
	(b)	These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see employee benefits footnote (Note 9) for additional details).

Earnings_per_Share_EPS_Tables

Earnings per Share ("EPS") (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Reconciliation of Basic EPS and Diluted EPS	'
	The following table is a reconciliation of basic EPS and diluted EPS for the three and nine months ended September 30,
		Three Months Ended				Nine Months Ended
		September 30				September 30,
		2014		2013		2014		2013
	(in thousands except share and per share data)
	Basic EPS Computation:
	Numerator:
	Net income, Class A	$	4,480	$	4,324	$	12,741	$	11,760
	Net income, Class B		1,226		1,195		3,496		3,261
	Denominator:
	Weighted average shares outstanding, Class A		3,594,583		3,578,400		3,588,728		3,574,109
	Weighted average shares outstanding, Class B		1,967,180		1,987,180		1,969,647		1,982,413
	Basic EPS, Class A	$	1.25	$	1.21	$	3.55	$	3.29
	Basic EPS, Class B		0.62		0.6		1.78		1.64
	Diluted EPS Computation:
	Numerator:
	Net income, Class A	$	4,480	$	4,324	$	12,741	$	11,760
	Net income, Class B		1,226		1,195		3,496		3,261
	Total net income, for diluted EPS, Class A computation		5,706		5,519		16,237		15,021
	Denominator:
	Weighted average shares outstanding, basic, Class A		3,594,583		3,578,400		3,588,728		3,574,109
	Weighted average shares outstanding, Class B		1,967,180		1,978,180		1,969,647		1,982,413
	Dilutive effect of Class A stock options		1,515		1,451		1,534		1,261
	Weighted average shares outstanding diluted, Class A		5,563,278		5,558,031		5,559,909		5,557,783
	Weighted average shares outstanding, Class B		1,967,180		1,978,180		1,969,647		1,982,413
	Diluted EPS, Class A	$	1.03	$	0.99	$	2.92	$	2.7
	Diluted EPS, Class B		0.62		0.6		1.78		1.64

Employee_Benefits_Tables

Employee Benefits (Tables)	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Components of Net Periodic Benefit Cost (Credit)	'
	Components of Net Periodic Benefit Cost (Credit) for the Three Months Ended September 30,
		Pension Benefits						Supplemental
								Insurance/
								Retirement
								Plan
		2014			2013			2014		2013
		(In thousands)
	Service cost	$	258		$	299		$	389	$	381
	Interest		367			314			331		267
	Expected return on plan assets		(636	)		(470	)		—		—
	Recognized prior service cost (benefit)		(26	)		(26	)		29		29
	Recognized net actuarial losses		3			158			88		129
	Net periodic benefit (credit) cost	$	(34	)	$	275		$	837	$	806
	Components of Net Periodic Benefit Cost (Credit) for the Nine Months Ended September 30,
		Pension Benefits						Supplemental
								Insurance/
								Retirement Plan
		2014			2013			2014		2013
		(In thousands)
	Service cost	$	775		$	897		$	1,166	$	1,144
	Interest		1,100			942			994		803
	Expected return on plan assets		(1,907	)		(1,410	)		—		—
	Recognized prior service cost (benefit)		(78	)		(78	)		86		86
	Recognized net actuarial losses		9			473			266		386
	Net periodic benefit (credit) cost	$	(101	)	$	824		$	2,512	$	2,419

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2014
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, 2014, are as follows:
	Financial Instruments Measured at Fair Value on a Recurring Basis:
			Securities AFS Fair Value Measurements Using
			Carrying		Quoted Prices			Significant			Significant
			Value		In Active			Observable			Other
					Markets for			Inputs			Unobservable
					Identical			(Level 2)			Inputs
					Assets						(Level 3)
					(Level 1)
			(In thousands)
	U.S. Treasury		$	2,001	$	—		$	2,001		$	—
	U.S. Government Sponsored Enterprises			—		—			—			—
	SBA Backed Securities			6,829		—			6,829			—
	U.S. Government Agency and Sponsored Mortgage Backed Securities			393,283		—			393,283			—
	Privately Issued Residential Mortgage Backed Securities			1,991		—			1,991			—
	Obligations Issued by States and Political Subdivisions			82,878		—			403			82,475
	Other Debt Securities			3,196		1,005			2,191			—
	Equity Securities			505		294			—			211
	Total		$	490,683	$	1,299		$	406,698		$	82,686
	Financial Instruments Measured at Fair Value on a Non-recurring Basis:
	Impaired Loans			4,680		—			—			4,680
Assets Measured at Fair Value	'
	The following table presents additional information about assets measured at fair value on a recurring and nonrecurring basis for which the Company has utilized Level 3 inputs to determine fair value (dollars in thousands). Management continues to monitor the assumptions used to value the assets listed below.
	Asset		Fair Value		Valuation Technique		Unobservable Input	Unobservable Input
								Value or Range
	Securities AFS(4)		$	82,686	Discounted cash flow		Discount rate	0% -1% (3)
	Impaired Loans			4,680	Appraisal of collateral (1)		Appraisal adjustments (2)	0%-25% 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.
Changes in Level 3 Securities	'
	The changes in Level 3 securities for the nine-month period ended September 30, 2014 are shown in the table below:
			Auction Rate		Obligations			Equity			Total
			Securities		Issued by States			Securities
					& Political
					Subdivisions
			(In thousands)
	Balance at December 31, 2013		$	3,820	$	32,487		$	290		$	36,597
	Purchases			—		86,378			—			86,378
	Maturities and calls			—		(40,206	)		(79	)		(40,285	)
	Amortization			—		(4	)		—			(4	)
	Changes in fair value			—		—			—			—
	Balance at September 30, 2014		$	3,820	$	78,655		$	211		$	82,686
	The changes in Level 3 securities for the nine-month period ended September 30, 2013, are shown in the table below:
			Auction Rate		Obligations			Equity			Total
			Securities		Issued by States			Securities
					& Political
					Subdivisions
			(In thousands)
	Balance at December 31, 2012		$	3,963	$	49,477		$	342		$	53,782
	Purchases			—		43,807			—			43,807
	Maturities and calls			—		(57,036	)		(51	)		(57,087	)
	Amortization			—		(23	)		—			(23	)
	Changes in fair value			—		—			—			—
	Balance at September 30, 2013		$	3,963	$	36,225		$	291		$	40,479

Fair_Values_of_Financial_Instr1

Fair Values of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2014
Investments, All Other Investments [Abstract]	'
Carrying Amount and Fair Value 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, 2014 and December 31, 2013. This table excludes financial instruments for which the carrying amount approximates fair value. Financial assets for which the fair value approximates carrying value include cash and cash equivalents, short-term investments, FHLBB stock and accrued interest receivable. Financial liabilities for which the fair value approximates carrying value include non-maturity deposits, short-term borrowings and accrued interest payable.
							Fair Value Measurements
			Carrying Amount		Estimated Fair		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
					Value
	September 30, 2014
	(in thousands)
	Financial assets:
	Securities held-to-maturity		$	1,471,137	$	1,463,535	$	—	$	1,463,535	$	—
	Loans (1)			1,314,164		1,291,746		—		—		1,291,746
	Financial liabilities:
	Time deposits			370,779		375,650		—		375,650		—
	Other borrowed funds			337,500		340,500		—		340,500		—
	Subordinated debentures			36,083		36,083		—		—		36,083
	December 31, 2013
	Financial assets:
	Securities held-to-maturity			1,487,884		1,464,449		—		1,464,449		—
	Loans (1)			1,243,822		1,214,192		—		—		1,214,192
	Financial liabilities:
	Time deposits			382,224		386,742		—		386,742		—
	Other borrowed funds			255,144		254,736		—		254,736		—
	Subordinated debentures			36,083		39,503		—		—		39,503
	-1	Comprised of loans (including collateral dependent impaired loans), net of deferred loan costs and the allowance for loan losses.

Basis_of_Financial_Statement_P1

Basis of Financial Statement Presentation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2014
	Segment
Accounting Policies [Abstract]	'
Equity ownership interest	100.00%
Number of reportable segments	1

Recent_Market_Developments_Add

Recent Market Developments - Additional Information (Detail) (USD $)	0 Months Ended	9 Months Ended
	Nov. 02, 2009	Sep. 30, 2014	Jun. 30, 2013
Recent Market Development [Line Items]	'	'	'
FDIC deposit insurance amount	'	$250,000	'
Uniform increase in assessment rates effective on January 1, 2011	0.03%	'	'
Refund amount received by company	'	'	$2,400,000
Common equity Tier 1 ratio as percentage of risk-weighted assets	'	4.50%	'
Minimum Tier 1 capital ratio as percentage of risk-weighted assets	'	4.00%	'
Revised minimum Tier 1 capital ratio as percentage of risk-weighted assets	'	6.00%	'
Tier 1 capital conservation buffer as percentage of risk-weighted assets	'	2.50%	'
Minimum [Member]	'	'	'
Recent Market Development [Line Items]	'	'	'
Restoration period	'7 years	'	'
Maximum [Member]	'	'	'
Recent Market Development [Line Items]	'	'	'
Restoration period	'8 years	'	'

Stock_Option_Accounting_Summar

Stock Option Accounting - Summary of Stock Option Activity under Stock Option Plan (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Shares under option:	'	'
Outstanding at beginning of year, Amount	20,225	'
Exercised, Amount	-10,325	-1,625
Forfeited, Amount	-8,900	'
Outstanding at end of period, Amount	1,000	'
Exercisable at end of period, Amount	1,000	'
Available to be granted at end of period, Amount	233,784	'
Outstanding at beginning of year, Weighted Average Exercise Price	$31.82	'
Exercised, Weighted Average Exercise Price	$31.83	'
Forfeited, Weighted Average Exercise Price	$31.83	'
Outstanding at end of period, Weighted Average Exercise Price	$31.60	'
Exercisable at end of period, Weighted Average Exercise Price	$31.60	'

Stock_Option_Accounting_Additi

Stock Option Accounting - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of outstanding options	1,000	20,225
Weighted average exercise price	$31.60	$31.82
Options granted	0	'
Class A Common Stock [Member]	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Number of outstanding options	1,000	'
Exercise prices of shares outstanding, minimum	$31.60	'
Weighted average exercise price	$31.60	'
Weighted average remaining contractual life	'13 days	'
Intrinsic value of options exercisable	$3,020	'
Intrinsic value of options exercised	$28,807	'

Securities_AvailableforSale_Su

Securities Available-for-Sale - Summary of Securities Available-for-Sale (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	$489,876	$465,943
Gross Unrealized Gains	2,423	821
Gross Unrealized Losses	1,616	2,519
Total, Fair Value	490,683	464,245
U.S. Treasury [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	1,999	1,997
Gross Unrealized Gains	2	1
Total, Fair Value	2,001	1,998
U.S. Government Sponsored Enterprises [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	'	9,995
Gross Unrealized Gains	'	9
Total, Fair Value	'	10,004
SBA Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	6,787	7,270
Gross Unrealized Gains	42	32
Total, Fair Value	6,829	7,302
U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	391,721	404,103
Gross Unrealized Gains	2,185	588
Gross Unrealized Losses	623	1,501
Total, Fair Value	393,283	403,190
Privately Issued Residential Mortgage Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	1,993	2,294
Gross Unrealized Gains	9	6
Gross Unrealized Losses	11	23
Total, Fair Value	1,991	2,277
Obligations Issued by States and Political Subdivisions [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	83,749	37,578
Gross Unrealized Gains	2	15
Gross Unrealized Losses	873	870
Total, Fair Value	82,878	36,723
Other Debt Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	3,300	2,300
Gross Unrealized Gains	5	'
Gross Unrealized Losses	109	125
Total, Fair Value	3,196	2,175
Equity Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized cost	327	406
Gross Unrealized Gains	178	170
Total, Fair Value	$505	$576

Securities_AvailableforSale_Ad

Securities Available-for-Sale - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended						9 Months Ended
	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013
				Securities AFS [Member]	Securities AFS [Member]	U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]	U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]	Federal Home Loan Bank of Boston [Member]	Federal Home Loan Bank of Boston [Member]
				Security	Security
Schedule of Available-for-sale Securities [Line Items]	'	'	'	'	'	'	'	'	'
Securities available-for-sale with an amortized cost	$1,012,370,000	'	'	'	'	'	'	'	'
Securities held-to-maturity at their fair value	987,037,000	'	987,037,000	'	'	'	'	'	'
Securities at fair value pledged to secure public deposits and repurchase agreements	'	'	'	'	'	333,036,000	368,137,000	'	'
Securities available-for-sale are securities pledged for borrowing	'	'	'	'	'	'	'	21,706,000	12,214,000
Realized gains on sales of investments	'	'	'	'	'	'	'	0	'
Realized gross gain	1,001,000	'	2,665,000	'	'	'	'	'	'
Proceeds from sales of securities available-for-sale	'	'	$216,078,000	'	'	'	'	'	'
Weighted average remaining life of investment securities available-for-sale	'	'4 years 4 months 24 days	'	'	'	'	'	'	'
Number of securities, temporarily impaired for less than 12 months	'	'	'	3	47	'	'	'	'
Number of securities, temporarily impaired for 12 months or longer	'	'	'	17	7	'	'	'	'
Number of securities, temporarily impaired, total	'	'	'	257	234	'	'	'	'

Securities_AvailableforSale_Ma

Securities Available-for-Sale - Maturity Distribution of Securities Available-for-Sale (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Investments, Debt and Equity Securities [Abstract]	'	'
Within one year, Amortized Cost	$77,321	'
After one but within five years, Amortized Cost	175,594	'
After five but within ten years, Amortized Cost	226,116	'
More than 10 years, Amortized Cost	9,018	'
Non-maturing, Amortized Cost	1,827	'
Amortized cost	489,876	465,943
Within one year, Fair Value	77,322	'
After one but within five years, Fair Value	176,505	'
After five but within ten years, Fair Value	226,788	'
More than 10 years, Fair Value	8,172	'
Non-maturing, Fair Value	1,896	'
Total, Fair Value	$490,683	$464,245

Securities_AvailableforSale_Co

Securities Available-for-Sale - Continuous Unrealized Loss Position for 12 Months or Less and 12 Months or Longer (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
Less than 12 months, Fair Value	$20,768	$291,195
Less than 12 months, Unrealized Losses	99	1,375
12 months or longer, Fair Value	105,663	29,753
12 months or longer, Unrealized Losses	1,517	1,144
Total, Fair Value	126,431	320,948
Total, Unrealized Losses	1,616	2,519
U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Less than 12 months, Fair Value	20,768	289,709
Less than 12 months, Unrealized Losses	99	1,352
12 months or longer, Fair Value	99,716	24,557
12 months or longer, Unrealized Losses	524	149
Total, Fair Value	120,484	314,266
Total, Unrealized Losses	623	1,501
Privately Issued Residential Mortgage Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Less than 12 months, Fair Value	'	1,486
Less than 12 months, Unrealized Losses	'	23
12 months or longer, Fair Value	737	'
12 months or longer, Unrealized Losses	11	'
Total, Fair Value	737	1,486
Total, Unrealized Losses	11	23
Obligations Issued by States and Political Subdivisions [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
12 months or longer, Fair Value	3,820	3,820
12 months or longer, Unrealized Losses	873	870
Total, Fair Value	3,820	3,820
Total, Unrealized Losses	873	870
Other Debt Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
12 months or longer, Fair Value	1,390	1,376
12 months or longer, Unrealized Losses	109	125
Total, Fair Value	1,390	1,376
Total, Unrealized Losses	$109	$125

Investment_Securities_HeldtoMa2

Investment Securities Held-to-Maturity - Unrealized Gain (Losses) on Securities (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	$1,471,137	$1,487,884
Gross Unrealized Gains	7,785	2,424
Gross Unrealized Losses	15,387	25,859
Estimated Fair Value	1,463,535	1,464,449
U.S. Government Sponsored Enterprises [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	291,158	291,779
Gross Unrealized Gains	1,377	185
Gross Unrealized Losses	870	5,043
Estimated Fair Value	291,665	286,921
U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	1,179,979	1,196,105
Gross Unrealized Gains	6,408	2,239
Gross Unrealized Losses	14,517	20,816
Estimated Fair Value	$1,171,870	$1,177,528

Investment_Securities_HeldtoMa3

Investment Securities Held-to-Maturity - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]	'	'
Securities pledged for borrowing at the Federal Home Loan Bank of Boston	$1,463,535,000	$1,464,449,000
Weighted average remaining life of investment securities held-to-maturity	'4 years 8 months 12 days	'
Held-to-Maturity Securities [Member]	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Number of securities, temporarily impaired for less than 12 months	84	191
Number of securities, temporarily impaired for 12 months or longer	53	13
Number of securities, temporarily impaired, total	305	300
Federal Home Loan Bank of Boston [Member]	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Securities pledged for borrowing at the Federal Home Loan Bank of Boston	466,789,000	510,060,000
U.S. Government Sponsored Enterprises [Member]	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Securities at fair value pledged to secure public deposits and repurchase agreements	839,764,000	732,144,000
Securities pledged for borrowing at the Federal Home Loan Bank of Boston	291,665,000	286,921,000
Weighted average remaining life	$213,343,000	'

Investment_Securities_HeldtoMa4

Investment Securities Held-to-Maturity - Company's Securities Held-to-Maturity (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Investments, Debt and Equity Securities [Abstract]	'	'
Within one year, Amortized Cost	$4,168	'
After one but within five years, Amortized Cost	988,565	'
After five but within ten years, Amortized Cost	477,606	'
More than ten years, Amortized Cost	798	'
Total, Amortized Cost	1,471,137	1,487,884
Within one year, Fair Value	4,230	'
After one but within five years, Fair Value	983,567	'
After five but within ten years, Fair Value	474,921	'
More than ten years, Fair Value	817	'
Estimated Fair Value	$1,463,535	$1,464,449

Investment_Securities_HeldtoMa5

Investment Securities Held-to-Maturity - Unrealized Market Loss of Securities (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Held-to-maturity Securities [Line Items]	'	'
Less Than 12 Months, Fair Value	$527,535	$1,163,715
Less Than 12 Months, Unrealized Losses	5,133	23,697
12 Months or Longer, Fair Value	361,248	80,362
12 Months or Longer, Unrealized Losses	10,254	2,162
Total, Fair Value	888,783	1,244,077
Total, Unrealized Losses	15,387	25,859
U.S. Government Sponsored Enterprises [Member]	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Less Than 12 Months, Fair Value	105,032	232,535
Less Than 12 Months, Unrealized Losses	507	5,043
12 Months or Longer, Fair Value	14,637	'
12 Months or Longer, Unrealized Losses	363	'
Total, Fair Value	119,669	232,535
Total, Unrealized Losses	870	5,043
U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Less Than 12 Months, Fair Value	422,503	931,180
Less Than 12 Months, Unrealized Losses	4,626	18,654
12 Months or Longer, Fair Value	346,611	80,362
12 Months or Longer, Unrealized Losses	9,891	2,162
Total, Fair Value	769,114	1,011,542
Total, Unrealized Losses	$14,517	$20,816

Allowance_for_Loan_Losses_Summ

Allowance for Loan Losses - Summary of Changes in Allowance for Loan Losses (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Receivables [Abstract]	'	'	'	'
Allowance for loan losses, beginning of period	$21,722	$20,500	$20,941	$19,197
Loans charged off	-163	-149	-705	-682
Recoveries on loans previously charged-off	310	149	583	485
Net charge-offs	147	'	-122	-197
Provision charged to expense	600	750	1,650	2,250
Allowance for loan losses, end of period	$22,469	$21,250	$22,469	$21,250

Allowance_for_Loan_Losses_Summ1

Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Allowance for loan losses:	'	'	'	'	'
Allowance for loan losses, beginning of period	$21,722	$20,500	$20,941	$19,197	'
Charge-offs	-163	-149	-705	-682	'
Recoveries	310	149	583	485	'
Provision	600	750	1,650	2,250	'
Allowance for loan losses, end of period	22,469	21,250	22,469	21,250	'
Amount of allowance for loan losses for loans deemed to be impaired	1,513	1,769	1,513	1,769	'
Amount of allowance for loan losses for loans not deemed to be impaired	20,956	19,481	20,956	19,481	'
Loans:	'	'	'	'	'
Total loans, net	1,336,633	1,231,048	1,336,633	1,231,048	1,264,763
Loans deemed to be impaired	7,832	8,566	7,832	8,566	'
Loans not deemed to be impaired	1,328,801	1,222,482	1,328,801	1,222,482	'
Construction and Land Development [Member]	'	'	'	'	'
Allowance for loan losses:	'	'	'	'	'
Allowance for loan losses, beginning of period	2,045	3,241	2,174	3,041	'
Charge-offs	'	'	-250	'	'
Provision	-39	-114	82	86	'
Allowance for loan losses, end of period	2,006	3,127	2,006	3,127	'
Amount of allowance for loan losses for loans deemed to be impaired	272	1,000	272	1,000	'
Amount of allowance for loan losses for loans not deemed to be impaired	1,734	2,127	1,734	2,127	'
Loans:	'	'	'	'	'
Total loans, net	25,339	32,750	25,339	32,750	33,058
Loans deemed to be impaired	354	1,500	354	1,500	'
Loans not deemed to be impaired	24,985	31,250	24,985	31,250	'
Commercial and Industrial [Member]	'	'	'	'	'
Allowance for loan losses:	'	'	'	'	'
Allowance for loan losses, beginning of period	2,915	3,215	2,989	3,118	'
Charge-offs	-37	'	-51	-234	'
Recoveries	115	42	164	163	'
Provision	2,396	-534	2,287	-324	'
Allowance for loan losses, end of period	5,389	2,723	5,389	2,723	'
Amount of allowance for loan losses for loans deemed to be impaired	348	90	348	90	'
Amount of allowance for loan losses for loans not deemed to be impaired	5,041	2,633	5,041	2,633	'
Loans:	'	'	'	'	'
Total loans, net	181,627	87,468	181,627	87,468	92,402
Loans deemed to be impaired	1,096	1,132	1,096	1,132	'
Loans not deemed to be impaired	180,531	86,336	180,531	86,336	'
Commercial Real Estate [Member]	'	'	'	'	'
Allowance for loan losses:	'	'	'	'	'
Allowance for loan losses, beginning of period	11,975	9,424	11,218	9,065	'
Recoveries	1	2	5	5	'
Provision	-1,116	1,162	-363	1,518	'
Allowance for loan losses, end of period	10,860	10,588	10,860	10,588	'
Amount of allowance for loan losses for loans deemed to be impaired	648	445	648	445	'
Amount of allowance for loan losses for loans not deemed to be impaired	10,212	10,143	10,212	10,143	'
Loans:	'	'	'	'	'
Total loans, net	702,894	666,166	702,894	666,166	713,327
Loans deemed to be impaired	4,740	4,688	4,740	4,688	'
Loans not deemed to be impaired	698,154	661,478	698,154	661,478	'
Residential Real Estate [Member]	'	'	'	'	'
Allowance for loan losses:	'	'	'	'	'
Allowance for loan losses, beginning of period	1,927	2,030	2,006	1,994	'
Recoveries	6	4	26	9	'
Provision	-132	176	-231	207	'
Allowance for loan losses, end of period	1,801	2,210	1,801	2,210	'
Amount of allowance for loan losses for loans deemed to be impaired	152	139	152	139	'
Amount of allowance for loan losses for loans not deemed to be impaired	1,649	2,071	1,649	2,071	'
Loans:	'	'	'	'	'
Total loans, net	268,927	309,291	268,927	309,291	286,041
Loans deemed to be impaired	1,549	1,151	1,549	1,151	'
Loans not deemed to be impaired	267,378	308,140	267,378	308,140	'
Consumer [Member]	'	'	'	'	'
Allowance for loan losses:	'	'	'	'	'
Allowance for loan losses, beginning of period	428	363	432	333	'
Charge-offs	-126	-149	-404	-448	'
Recoveries	106	101	305	307	'
Provision	46	76	121	199	'
Allowance for loan losses, end of period	454	391	454	391	'
Amount of allowance for loan losses for loans deemed to be impaired	'	'	'	'	'
Amount of allowance for loan losses for loans not deemed to be impaired	454	391	454	391	'
Loans:	'	'	'	'	'
Total loans, net	10,253	8,728	10,253	8,728	9,658
Loans deemed to be impaired	'	'	'	'	'
Loans not deemed to be impaired	10,253	8,728	10,253	8,728	'
Home Equity [Member]	'	'	'	'	'
Allowance for loan losses:	'	'	'	'	'
Allowance for loan losses, beginning of period	915	932	959	886	'
Recoveries	82	'	83	1	'
Provision	-41	17	-86	62	'
Allowance for loan losses, end of period	956	949	956	949	'
Amount of allowance for loan losses for loans deemed to be impaired	93	95	93	95	'
Amount of allowance for loan losses for loans not deemed to be impaired	863	854	863	854	'
Loans:	'	'	'	'	'
Total loans, net	147,593	126,645	147,593	126,645	130,277
Loans deemed to be impaired	93	95	93	95	'
Loans not deemed to be impaired	147,500	126,550	147,500	126,550	'
Unallocated [Member]	'	'	'	'	'
Allowance for loan losses:	'	'	'	'	'
Allowance for loan losses, beginning of period	1,517	1,295	1,163	760	'
Provision	-514	-33	-160	502	'
Allowance for loan losses, end of period	1,003	'	1,003	'	'
Amount of allowance for loan losses for loans not deemed to be impaired	$1,003	$1,262	$1,003	$1,262	'

Allowance_for_Loan_Losses_Loan

Allowance for Loan Losses - Loans by Risk Rating (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Loans by risk rating	'	'	'
Financing Receivable, Net	$1,336,633	$1,264,763	$1,231,048
Construction and Land Development [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	25,339	33,058	32,750
Construction and Land Development [Member] | 1-3 (Pass) [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	17,808	25,138	'
Construction and Land Development [Member] | 4 (Monitor) [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	7,177	7,312	'
Construction and Land Development [Member] | Impaired [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	354	608	'
Commercial and Industrial [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	181,627	92,402	87,468
Commercial and Industrial [Member] | 1-3 (Pass) [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	180,059	90,563	'
Commercial and Industrial [Member] | 4 (Monitor) [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	472	472	'
Commercial and Industrial [Member] | Impaired [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	1,096	1,367	'
Commercial Real Estate [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	702,894	713,327	666,166
Commercial Real Estate [Member] | 1-3 (Pass) [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	697,509	707,461	'
Commercial Real Estate [Member] | 4 (Monitor) [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	645	1,346	'
Commercial Real Estate [Member] | Impaired [Member]	'	'	'
Loans by risk rating	'	'	'
Financing Receivable, Net	$4,740	$4,520	'

Allowance_for_Loan_Losses_Agin

Allowance for Loan Losses - Aging of Past Due Loan Losses (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Thousands, unless otherwise specified
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'
Accruing 30-89 Days Past Due	$3,958	$5,561	'
Non Accrual	6,018	2,549	'
Total Past Due	9,976	8,110	'
Current Loans	1,326,657	1,256,653	'
Total loans, net	1,336,633	1,264,763	1,231,048
Construction and Land Development [Member]	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'
Non Accrual	354	500	'
Total Past Due	354	500	'
Current Loans	24,985	32,558	'
Total loans, net	25,339	33,058	32,750
Commercial and Industrial [Member]	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'
Accruing 30-89 Days Past Due	895	112	'
Non Accrual	418	706	'
Total Past Due	1,313	818	'
Current Loans	180,314	91,584	'
Total loans, net	181,627	92,402	87,468
Commercial Real Estate [Member]	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'
Accruing 30-89 Days Past Due	1,608	1,496	'
Non Accrual	2,787	306	'
Total Past Due	4,395	1,802	'
Current Loans	698,499	711,525	'
Total loans, net	702,894	713,327	666,166
Residential Real Estate [Member]	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'
Accruing 30-89 Days Past Due	378	2,232	'
Non Accrual	2,197	1,034	'
Total Past Due	2,575	3,266	'
Current Loans	266,352	282,775	'
Total loans, net	268,927	286,041	309,291
Consumer [Member]	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'
Accruing 30-89 Days Past Due	5	11	'
Non Accrual	8	3	'
Total Past Due	13	14	'
Current Loans	10,240	9,644	'
Total loans, net	10,253	9,658	8,728
Home Equity [Member]	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'
Accruing 30-89 Days Past Due	1,072	1,710	'
Non Accrual	254	'	'
Total Past Due	1,326	1,710	'
Current Loans	146,267	128,567	'
Total loans, net	$147,593	$130,277	$126,645

Allowance_for_Loan_Losses_Info

Allowance for Loan Losses - Information Pertaining to Impaired Loans (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
With no required reserve recorded, Carrying Value	$403	$736	$403	$736
With no required reserve recorded, Unpaid Balance Principal	438	775	438	775
With no required reserve recorded, Required Reserve	'	'	'	'
With no required reserve recorded, Average Carrying Value	425	625	525	668
With no required reserve recorded, Interest Income Recognized	'	1	'	1
With required reserve recorded, Carrying Value	7,429	7,830	7,429	7,830
With required reserve recorded, Unpaid Balance Principal	10,819	10,025	10,819	10,025
With required reserve recorded, Required Reserve	1,513	1,769	1,513	1,769
With required reserve recorded, Average Carrying Value	7,554	6,177	7,032	5,707
With required reserve recorded, Interest Income Recognized	50	38	145	101
Carrying Value	7,832	8,566	7,832	8,566
Unpaid Principal Balance	11,257	10,800	11,257	10,800
With required reserve recorded, Required Reserve	1,513	1,769	1,513	1,769
Average Carrying Value	7,979	6,802	7,557	6,375
Interest Income Recognized	50	38	145	102
Construction and Land Development [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
With no required reserve recorded, Required Reserve	'	'	'	'
With no required reserve recorded, Average Carrying Value	'	'	225	'
With no required reserve recorded, Interest Income Recognized	'	'	'	'
With required reserve recorded, Carrying Value	354	1,500	354	1,500
With required reserve recorded, Unpaid Balance Principal	3,400	3,292	3,400	3,292
With required reserve recorded, Required Reserve	272	1,000	272	1,000
With required reserve recorded, Average Carrying Value	355	1,500	207	1,500
Carrying Value	354	1,500	354	1,500
Unpaid Principal Balance	3,400	3,292	3,400	3,292
With required reserve recorded, Required Reserve	272	1,000	272	1,000
Average Carrying Value	355	1,500	432	1,500
Commercial and Industrial [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
With no required reserve recorded, Carrying Value	11	264	11	264
With no required reserve recorded, Unpaid Balance Principal	42	294	42	294
With no required reserve recorded, Required Reserve	'	'	'	'
With no required reserve recorded, Average Carrying Value	11	239	53	390
With no required reserve recorded, Interest Income Recognized	'	'	'	1
With required reserve recorded, Carrying Value	1,085	868	1,085	868
With required reserve recorded, Unpaid Balance Principal	1,337	1,101	1,337	1,101
With required reserve recorded, Required Reserve	348	90	348	90
With required reserve recorded, Average Carrying Value	1,078	885	1,095	864
With required reserve recorded, Interest Income Recognized	8	12	24	29
Carrying Value	1,096	1,132	1,096	1,132
Unpaid Principal Balance	1,379	1,395	1,379	1,395
With required reserve recorded, Required Reserve	348	90	348	90
Average Carrying Value	1,089	1,124	1,148	1,254
Interest Income Recognized	8	12	24	30
Commercial Real Estate [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
With no required reserve recorded, Carrying Value	392	218	392	218
With no required reserve recorded, Unpaid Balance Principal	396	218	396	218
With no required reserve recorded, Required Reserve	'	'	'	'
With no required reserve recorded, Average Carrying Value	396	126	175	133
With no required reserve recorded, Interest Income Recognized	'	'	'	'
With required reserve recorded, Carrying Value	4,348	4,470	4,348	4,470
With required reserve recorded, Unpaid Balance Principal	4,440	4,558	4,440	4,558
With required reserve recorded, Required Reserve	648	445	648	445
With required reserve recorded, Average Carrying Value	4,492	2,796	4,443	2,394
With required reserve recorded, Interest Income Recognized	39	26	113	72
Carrying Value	4,740	4,688	4,740	4,688
Unpaid Principal Balance	4,836	4,776	4,836	4,776
With required reserve recorded, Required Reserve	648	445	648	445
Average Carrying Value	4,888	2,922	4,618	2,527
Interest Income Recognized	39	26	113	72
Residential Real Estate [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
With no required reserve recorded, Carrying Value	'	254	'	254
With no required reserve recorded, Unpaid Balance Principal	'	263	'	263
With no required reserve recorded, Required Reserve	'	'	'	'
With no required reserve recorded, Average Carrying Value	18	260	72	145
With no required reserve recorded, Interest Income Recognized	'	'	'	'
With required reserve recorded, Carrying Value	1,549	897	1,549	897
With required reserve recorded, Unpaid Balance Principal	1,549	979	1,549	979
With required reserve recorded, Required Reserve	152	139	152	139
With required reserve recorded, Average Carrying Value	1,536	901	1,193	853
With required reserve recorded, Interest Income Recognized	3	'	8	'
Carrying Value	1,549	1,151	1,549	1,151
Unpaid Principal Balance	1,549	1,242	1,549	1,242
With required reserve recorded, Required Reserve	152	139	152	139
Average Carrying Value	1,554	1,161	1,265	998
Interest Income Recognized	3	'	8	'
Consumer [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
With no required reserve recorded, Required Reserve	'	'	'	'
With no required reserve recorded, Interest Income Recognized	'	'	'	'
With required reserve recorded, Required Reserve	'	'	'	'
Carrying Value	'	'	'	'
Unpaid Principal Balance	'	'	'	'
With required reserve recorded, Required Reserve	'	'	'	'
Average Carrying Value	'	'	'	'
Interest Income Recognized	'	'	'	'
Home Equity [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
With no required reserve recorded, Required Reserve	'	'	'	'
With no required reserve recorded, Interest Income Recognized	'	'	'	'
With required reserve recorded, Carrying Value	93	95	93	95
With required reserve recorded, Unpaid Balance Principal	93	95	93	95
With required reserve recorded, Required Reserve	93	95	93	95
With required reserve recorded, Average Carrying Value	93	95	94	96
Carrying Value	93	95	93	95
Unpaid Principal Balance	93	95	93	95
With required reserve recorded, Required Reserve	93	95	93	95
Average Carrying Value	$93	$95	$94	$96

Allowance_for_Loan_Losses_Addi

Allowance for Loan Losses - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
	TDRs	Contracts	TDRs	Contracts
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Number of troubled debt restructurings	'	3	'	3
Pre-modification outstanding recorded investment	'	$2,396,000	'	$2,396,000
Post-modification outstanding recorded investment	'	2,391,000	'	2,391,000
Commercial Real Estate [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Troubled debt restructurings, subsequently defaulted	'	'	2,200,000	'
Number of troubled debt restructurings	'	1	1	1
Pre-modification outstanding recorded investment	'	2,247,000	'	2,247,000
Post-modification outstanding recorded investment	'	2,242,000	'	2,242,000
Financing allowance increase in principal	'	1,786,000	'	1,786,000
Financing allowance reduction in interest payments	'	7,907,000	'	7,907,000
Commercial and Industrial [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Number of troubled debt restructurings	1	1	1	1
Pre-modification outstanding recorded investment	'	41,000	23,811,000	41,000
Post-modification outstanding recorded investment	'	41,000	23,761,000	41,000
Financing allowance increase in principal	50,000	'	50,000	'
Financing allowance reduction in principal	'	366,000	'	366,000
Financing allowance reduction in interest payments	'	217,000	'	217,000
Construction and Land Development [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Number of troubled debt restructurings	'	1	'	1
Pre-modification outstanding recorded investment	'	108,000	'	108,000
Post-modification outstanding recorded investment	'	108,000	'	108,000
Financing allowance reduction in principal	'	530,000	'	530,000
Financing allowance reduction in interest payments	'	$415,000	'	$415,000

Allowance_for_Loan_Losses_Summ2

Allowance for Loan Losses - Summary of Troubled Debt Restructurings (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
	TDRs	Contracts	TDRs	Contracts
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Number of Contracts	'	3	'	3
Pre-modification outstanding recorded investment	'	$2,396	'	$2,396
Post- modification outstanding recorded investment	'	2,391	'	2,391
Construction and Land Development [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Number of Contracts	'	1	'	1
Pre-modification outstanding recorded investment	'	108	'	108
Post- modification outstanding recorded investment	'	108	'	108
Commercial and Industrial [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Number of Contracts	1	1	1	1
Pre-modification outstanding recorded investment	'	41	23,811	41
Post- modification outstanding recorded investment	'	41	23,761	41
Commercial Real Estate [Member]	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Number of Contracts	'	1	1	1
Pre-modification outstanding recorded investment	'	2,247	'	2,247
Post- modification outstanding recorded investment	'	$2,242	'	$2,242

Reclassifications_Out_of_Accum2

Reclassifications Out of Accumulated Other Comprehensive Income - Reclassifications Out of Accumulated Other Comprehensive Income (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Net gains on sales of investments	'	$1,001	'	$2,665
Securities held-to-maturity	8,104	6,181	23,904	9,120
Provision for income taxes	-221	-308	-745	-891
Net income	5,706	5,519	16,237	15,021
Salaries and employee benefits	-8,681	-8,858	-26,332	-25,858
Reclassification Out of Accumulated Other Comprehensive Income [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Net income	736	1,351	2,355	2,020
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 investments	'	1,001	'	2,665
Provision for income taxes	'	-387	'	-1,035
Net income	'	614	'	1,630
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Accretion of Unrealized Losses Transferred [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Securities held-to-maturity	1,216	1,485	4,009	1,485
Provision for income taxes	-424	-575	-1,485	-575
Net income	792	910	2,524	910
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Prior-Service Costs [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Salaries and employee benefits	-3	-3	-8	-8
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Actuarial Gains (Losses) [Member]	'	'	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'	'	'
Salaries and employee benefits	-91	-287	-274	-859
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	-94	-290	-282	-867
Provision for income taxes	38	117	113	347
Net income	($56)	($173)	($169)	($520)

Earnings_Per_Share_EPS_Additio

Earnings Per Share ("EPS") - Additional Information (Detail) (Class A Common Stock [Member])	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]	'	'	'	'
Dilutive effect of stock options, increment in shares	1,515	1,451	1,534	1,261
Minimum [Member]	'	'	'	'
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]	'	'	'	'
Percentage of dividends paid	'	'	200.00%	'

Earnings_Per_Share_EPS_Reconci

Earnings Per Share ("EPS") - Reconciliation of Basic EPS and Diluted EPS (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]	'	'	'	'
Net income	$5,706	$5,519	$16,237	$15,021
Class A Common Stock [Member]	'	'	'	'
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]	'	'	'	'
Net income	4,480	4,324	12,741	11,760
Weighted average shares outstanding, basic	3,594,583	3,578,400	3,588,728	3,574,109
Basic earnings per share	$1.25	$1.21	$3.55	$3.29
Dilutive effect of Class A stock options	1,515	1,451	1,534	1,261
Weighted average shares outstanding, diluted	5,563,278	5,558,031	5,559,909	5,557,783
Diluted earnings per share	$1.03	$0.99	$2.92	$2.70
Class B Common Stock [Member]	'	'	'	'
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]	'	'	'	'
Net income	$1,226	$1,195	$3,496	$3,261
Weighted average shares outstanding, basic	1,967,180	1,978,180	1,969,647	1,982,413
Basic earnings per share	$0.62	$0.60	$1.78	$1.64
Weighted average shares outstanding, diluted	1,967,180	1,978,180	1,969,647	1,982,413
Diluted earnings per share	$0.62	$0.60	$1.78	$1.64

Employee_Benefits_Additional_I

Employee Benefits - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2014
Compensation and Retirement Disclosure [Abstract]	'
Number of years service to participate in supplemental plan	'1 year
Current fiscal year contribution to pension plan	$920,000
Additional contributions to pension plan in remainder of current fiscal year	$0

Employee_Benefits_Components_o

Employee Benefits - Components of Net Periodic Benefit Cost (Credit) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension Benefits [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Service cost	$258	$299	$775	$897
Interest	367	314	1,100	942
Expected return on plan assets	-636	-470	-1,907	-1,410
Recognized prior service cost (benefit)	-26	-26	-78	-78
Recognized net actuarial losses	3	158	9	473
Net periodic benefit (credit) cost	-34	275	-101	824
Supplemental Insurance/ Retirement Plan [Member]	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'
Service cost	389	381	1,166	1,144
Interest	331	267	994	803
Recognized prior service cost (benefit)	29	29	86	86
Recognized net actuarial losses	88	129	266	386
Net periodic benefit (credit) cost	$837	$806	$2,512	$2,419

Fair_Value_Measurements_Financ

Fair Value Measurements - Financial Instruments Measured at Fair Value on a Recurring and Non-recurring Basis (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	$490,683	$464,245
Fair Value Measurements, Level 1 Inputs [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	1,299	'
Fair Value Measurements, Level 2 Inputs [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	406,698	'
Fair Value Measurements, Level 3 Inputs [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	82,686	'
U.S. Treasury [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	2,001	1,998
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	2,001	'
SBA Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	6,829	7,302
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	6,829	'
U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	393,283	403,190
U.S. Government Agency and Sponsored 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	393,283	'
Privately Issued Residential Mortgage Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	1,991	2,277
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	1,991	'
Obligations Issued by States and Political Subdivisions [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	82,878	36,723
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	403	'
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	82,475	'
Other Debt Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	3,196	2,175
Other Debt Securities [Member] | Fair Value Measurements, Level 1 Inputs [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	1,005	'
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	2,191	'
Equity Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	505	576
Equity Securities [Member] | Fair Value Measurements, Level 1 Inputs [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	294	'
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	211	'
Impaired Loans [Member] | Fair Value Measurements, Level 3 Inputs [Member]	'	'
Financial Instruments Measured at Fair Value on a Non-recurring Basis	'	'
Impaired Loans	4,680	'
Carrying Value [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	490,683	'
Carrying Value [Member] | U.S. Treasury [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	2,001	'
Carrying Value [Member] | SBA Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	6,829	'
Carrying Value [Member] | U.S. Government Agency and Sponsored Mortgage Backed Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	393,283	'
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	1,991	'
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	82,878	'
Carrying Value [Member] | Other Debt Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	3,196	'
Carrying Value [Member] | Equity Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Securities AFS	505	'
Carrying Value [Member] | Impaired Loans [Member]	'	'
Financial Instruments Measured at Fair Value on a Non-recurring Basis	'	'
Impaired Loans	$4,680	'

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013
			Fair Value Measurements, Level 3 Inputs [Member]	Fair Value Measurements, Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'	'	'
Specific adjustments to impaired loans recognized	$483,000	$999,000	'	'
Transfers between level 1 and 2	0	0	'	'
Liabilities measured at fair value on a recurring or nonrecurring basis	0	0	'	'
Amortized cost of Level 3 securities	'	'	83,559,000	41,204,000
Unrealized loss	'	'	$872,000	$725,000

Fair_Value_Measurements_Assets

Fair Value Measurements - Assets Measured at Fair Value (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014
Securities AFS [Member]	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'
Fair Value	$82,686
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	$4,680
Valuation Technique	'Appraisal of collateral
Unobservable Input	'Appraisal adjustments
Minimum [Member] | Securities AFS [Member]	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'
Unobservable Input Value or Range	0.00%
Minimum [Member] | Impaired Loans [Member]	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'
Unobservable Input Value or Range	0.00%
Maximum [Member] | Securities AFS [Member]	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'
Unobservable Input Value or Range	1.00%
Maximum [Member] | Impaired Loans [Member]	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'
Unobservable Input Value or Range	25.00%

Fair_Value_Measurements_Assets1

Fair Value Measurements - Assets Measured at Fair Value (Parenthetical) (Detail) (Municipal Notes [Member])	9 Months Ended
	Sep. 30, 2014
Municipal Notes [Member]	'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'
Securities maturity period	'one year or less

Fair_Value_Measurements_Change

Fair Value Measurements - Changes in Level 3 Securities (Detail) (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	$36,597	$53,782
Purchases	86,378	43,807
Maturities and calls	-40,285	-57,087
Amortization	-4	-23
Changes in fair value	'	'
Ending Balance	82,686	40,479
Auction Rate Securities [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	3,820	3,963
Changes in fair value	'	'
Ending Balance	3,820	3,963
Obligations Issued by States and Political Subdivisions [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	32,487	49,477
Purchases	86,378	43,807
Maturities and calls	-40,206	-57,036
Amortization	-4	-23
Changes in fair value	'	'
Ending Balance	78,655	36,225
Equity Securities [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'
Beginning Balance	290	342
Maturities and calls	-79	-51
Changes in fair value	'	'
Ending Balance	$211	$291

Fair_Values_of_Financial_Instr2

Fair Values of Financial Instruments - Carrying Amount and Fair Value of Company's Financial Instruments (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Financial assets:	'	'
Securities held-to-maturity	$1,471,137	$1,487,884
Loans	1,314,164	1,243,822
Financial liabilities:	'	'
Time deposits	370,779	382,224
Other borrowed funds	337,500	255,144
Subordinated debentures	36,083	36,083
Carrying Value [Member]	'	'
Financial assets:	'	'
Securities held-to-maturity	1,471,137	1,487,884
Loans	1,314,164	1,243,822
Financial liabilities:	'	'
Time deposits	370,779	382,224
Other borrowed funds	337,500	255,144
Subordinated debentures	36,083	36,083
Estimated Fair Value [Member]	'	'
Financial assets:	'	'
Securities held-to-maturity	1,463,535	1,464,449
Loans	1,291,746	1,214,192
Financial liabilities:	'	'
Time deposits	375,650	386,742
Other borrowed funds	340,500	254,736
Subordinated debentures	36,083	39,503
Fair Value Measurements, Level 2 Inputs [Member]	'	'
Financial assets:	'	'
Securities held-to-maturity	1,463,535	1,464,449
Financial liabilities:	'	'
Time deposits	375,650	386,742
Other borrowed funds	340,500	254,736
Fair Value Measurements, Level 3 Inputs [Member]	'	'
Financial assets:	'	'
Loans	1,291,746	1,214,192
Financial liabilities:	'	'
Subordinated debentures	$36,083	$39,503