NBT Bancorp (NBTB) 10-K 2 Mar 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 13, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Entity Registrant Name	NBT BANCORP INC
Entity Central Index Key	790359
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$1,001,148,554
Entity Common Stock, Shares Outstanding		44,213,717
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets
Cash and due from banks	$139,635	$157,625
Short-term interest bearing accounts	7,001	1,301
Securities available for sale, at fair value	1,013,171	1,364,881
Securities held to maturity (fair value $454,994 and $113,276)	454,361	117,283
Trading securities	7,793	5,779
Federal Reserve and Federal Home Loan Bank stock	32,626	46,864
Loans	5,595,271	5,406,795
Less allowance for loan losses	66,359	69,434
Net loans	5,528,912	5,337,361
Premises and equipment, net	89,258	88,327
Goodwill	263,634	264,997
Intangible assets, net	20,317	25,557
Bank owned life insurance	114,251	114,966
Other assets	126,967	127,234
Total assets	7,797,926	7,652,175
Liabilities
Demand (noninterest bearing)	1,838,622	1,645,641
Savings, NOW, and money market	3,417,160	3,223,441
Time	1,043,823	1,021,142
Total deposits	6,299,605	5,890,224
Short-term borrowings	316,802	456,042
Long-term debt	130,945	308,823
Junior subordinated debt	101,196	101,196
Other liabilities	85,197	79,321
Total liabilities	6,933,745	6,835,606
Stockholders' equity
Preferred stock, $0.01 par value; authorized 2,500,000 shares at December 31, 2014 and 2013	0	0
Common stock, $0.01 par value. Authorized 100,000,000 shares at December 31, 2014 and December 31, 2013; issued 49,651,494 at December 31, 2014 and December 31, 2013	497	497
Additional paid-in-capital	576,504	574,152
Retained earnings	423,956	385,787
Accumulated other comprehensive loss	-17,027	-16,765
Common stock in treasury, at cost, 5,755,040 and 6,138,444 shares at December 31, 2014 and 2013, respectively	-119,749	-127,102
Total stockholders' equity	864,181	816,569
Total liabilities and stockholders' equity	$7,797,926	$7,652,175

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Assets
Securities held to maturity fair value	$454,994	$113,276
Stockholders' equity
Preferred stock, par value (in dollars per share)	$0.01	$0.01
Preferred stock, shares authorized (in shares)	2,500,000	2,500,000
Common stock, par value (in dollars per share)	$0.01	$0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	49,651,494	49,651,494
Common stock in treasury, at cost (in shares)	5,755,040	6,138,444

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest, fee, and dividend income
Interest and fees on loans and leases	$243,324	$238,672	$208,458
Securities available for sale	24,464	25,510	27,005
Securities held to maturity	5,261	2,660	2,378
Other	2,032	1,881	1,556
Total interest, fee, and dividend income	275,081	268,723	239,397
Interest expense
Deposits	13,638	16,290	18,848
Short-term borrowings	845	515	188
Long-term debt	6,555	11,755	14,428
Trust preferred debentures	2,165	2,084	1,730
Total interest expense	23,203	30,644	35,194
Net interest income	251,878	238,079	204,203
Provision for loan and lease losses	19,539	22,424	20,269
Net interest income after provision for loan and lease losses	232,339	215,655	183,934
Noninterest income
Insurance and other financial services revenue	24,517	24,447	22,387
Service charges on deposit accounts	17,941	19,307	18,225
ATM and debit card fees	17,135	15,558	12,358
Retirement plan administration fees	12,129	11,497	10,097
Trust	18,950	16,682	9,172
Bank owned life insurance income	5,349	3,793	3,077
Net securities gains	92	1,426	599
Gain on the sale of Springstone investment	19,401	0	0
Other	10,513	10,505	11,412
Total noninterest income	126,027	103,215	87,327
Noninterest expense
Salaries and employee benefits	119,667	113,580	104,815
Occupancy	22,128	20,720	17,415
Data processing and communications	16,137	15,353	13,437
Professional fees and outside services	14,426	13,309	10,463
Equipment	12,658	11,493	9,627
Office supplies and postage	6,983	6,563	6,489
FDIC expenses	4,944	4,960	3,832
Advertising	2,831	3,204	2,889
Amortization of intangible assets	5,047	4,872	3,394
Loan collection and other real estate owned	3,248	2,619	2,560
Merger expenses	0	12,364	2,608
Prepayment penalties on long-term debt	17,902	0	0
Other	20,092	19,890	16,358
Total noninterest expense	246,063	228,927	193,887
Income before income tax expense	112,303	89,943	77,374
Income tax expense	37,229	28,196	22,816
Net income	$75,074	$61,747	$54,558
Earnings per share
Basic (in dollars per share)	$1.71	$1.47	$1.63
Diluted (in dollars per share)	$1.69	$1.46	$1.62

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$75,074	$61,747	$54,558
Other comprehensive (loss) income, net of tax
Unrealized net holding gains (losses) arising during the year (pre-tax amounts of $18,069, ($41,059), and ($2,471)	11,447	-24,794	-1,492
Reclassification adjustment for net gains related to securities available for sale included in net income (pre-tax amounts of $92, $1,426, and $599)	-56	-861	-362
Amortization of unrealized net gains and losses related to the reclassification of available for sale investment securities to held to maturity (pre-tax amounts of ($421), $0, and $0)	-257	0	0
Amortization of prior service cost and actuarial gains (pre-tax amounts of $75, $2,790, and $3,593)	46	1,601	2,092
(Increase) Decrease in prior service cost and unrecognized actuarial loss (pre-tax amounts of ($19,245), $21,923, and $(24))	-11,442	13,169	-14
Total other comprehensive (loss) income	-262	-10,885	224
Comprehensive income	$74,812	$50,862	$54,782

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other comprehensive (loss) income, before tax
Unrealized net holding (losses) gains arising during the period, pre-tax amounts	$18,069	($41,059)	($2,471)
Reclassification adjustment for net gains related to securities available for sale included in net income, pre-tax amounts	92	1,426	599
Amortization of unrealized net gains and losses related to the reclassification of available for sale investment securities to held to maturity, pre-tax amounts	-421	0	0
Amortization of prior service cost and actuarial gains, pre-tax amounts	75	2,790	3,593
Decrease (Increase) in prior service costs and unrecognized actuarial loss, pre-tax amounts	($19,245)	$21,923	($24)

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Stockholders' Equity (USD $)	Common Stock [Member]	Additional Paid-in-Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Common Stock in Treasury [Member]	Total
In Thousands
Beginning Balance at Dec. 31, 2011	$380	$317,329	$329,981	($6,104)	($103,476)	$538,110
Net income	0	0	54,558	0	0	54,558
Cash dividends	0	0	-26,712	0	0	-26,712
Purchases of treasury shares	0	0	0	0	-15,490	-15,490
Net issuance of shares for acquisition	13	25,811	0	0	0	25,824
Net issuance of shares to employee stock plans, including tax benefit	0	-812	-269	0	2,476	1,395
Stock-based compensation	0	4,364	0	0	0	4,364
Other comprehensive income	0	0	0	224	0	224
Ending Balance at Dec. 31, 2012	393	346,692	357,558	-5,880	-116,490	582,273
Net income	0	0	61,747	0	0	61,747
Cash dividends	0	0	-33,518	0	0	-33,518
Purchases of treasury shares	0	0	0	0	-12,459	-12,459
Net issuance of shares for acquisition	104	225,447	0	0	-5,779	219,772
Net issuance of shares to employee stock plans, including tax benefit	0	-2,292	0	0	7,626	5,334
Stock-based compensation	0	4,305	0	0	0	4,305
Other comprehensive income	0	0	0	-10,885	0	-10,885
Ending Balance at Dec. 31, 2013	497	574,152	385,787	-16,765	-127,102	816,569
Net income	0	0	75,074	0	0	75,074
Cash dividends	0	0	-36,905	0	0	-36,905
Purchases of treasury shares	0	0	0	0	-72	-72
Net issuance of shares to employee stock plans, including tax benefit	0	-1,169	0	0	7,425	6,256
Stock-based compensation	0	3,521	0	0	0	3,521
Other comprehensive income	0	0	0	-262	0	-262
Ending Balance at Dec. 31, 2014	$497	$576,504	$423,956	($17,027)	($119,749)	$864,181

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Consolidated Statements of Changes in Stockholders' Equity [Abstract]
Cash dividends - per share (in dollars per share)	$0.84	$0.81	$0.80
Purchase of treasury shares (in shares)	3,288	584,925	769,568
Net issuance of shares for acquisition (in shares)	0	10,346,363	1,269,592
Treasury stock reissued in acquisition of Alliance (in shares)	0	408,957	0
Net issuance of shares to employee stock plans, including tax benefit (in shares)	386,692	385,219	118,616

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net income	$75,074,000	$61,747,000	$54,558,000
Adjustments to reconcile net income to net cash provided by operating activities
Provision for loan and lease losses	19,539,000	22,424,000	20,269,000
Depreciation and amortization of premises and equipment	8,324,000	7,948,000	6,276,000
Net accretion on securities	3,216,000	5,058,000	2,408,000
Amortization of intangible assets	5,047,000	4,872,000	3,394,000
Stock based compensation	3,521,000	4,305,000	4,364,000
Bank owned life insurance income	-5,349,000	-3,793,000	-3,077,000
Trading security purchases	-1,626,000	-1,085,000	-753,000
Unrealized (gains) losses in trading securities	-388,000	-776,000	-103,000
Deferred income tax benefit	8,347,000	2,344,000	-10,000
Proceeds from sale of loans held for sale	7,050,000	71,342,000	65,160,000
Originations and purchases of loans held for sale	-10,215,000	-66,512,000	-66,252,000
Net gains on sales of loans held for sale	-17,000	-1,288,000	-2,469,000
Net security gains	-92,000	-1,426,000	-599,000
Net gains on sales of other real estate owned	-459,000	-1,106,000	-988,000
Gain on sale of equity investment	-19,401,000	0	0
Prepayment penalties on long-term debt	17,903,000	0	0
Net decrease (increase) in other assets	-27,949,000	20,463,000	6,804,000
Net (decrease) increase in other liabilities	5,286,000	-5,219,000	-128,000
Net cash provided by operating activities	87,811,000	119,298,000	88,854,000
Investing activities
Net cash provided by acquisitions	0	80,883,000	52,871,000
Securities available for sale:
Proceeds from maturities, calls, and principal paydowns	236,133,000	376,509,000	573,828,000
Proceeds from sales	189,000	27,593,000	1,790,000
Purchases	-197,652,000	-353,714,000	-483,858,000
Securities held to maturity:
Proceeds from maturities, calls, and principal paydowns	44,756,000	34,413,000	31,506,000
Purchases	-49,479,000	-84,621,000	-20,193,000
Other:
Net increase in loans	-212,238,000	-255,318,000	-277,530,000
Proceeds from FHLB stock redemption	78,441,000	27,409,000	0
Purchases of Federal Reserve and FHLB stock	-64,203,000	-36,366,000	-1,886,000
Proceeds from bank owned life insurance	6,064,000	0	0
Purchases of premises and equipment, net	-9,003,000	-5,766,000	-6,994,000
Proceeds from sales of equity investment	19,639,000	0	0
Proceeds from sales of other real estate owned	3,612,000	5,224,000	3,616,000
Net cash used in investing activities	-143,741,000	-183,754,000	-126,850,000
Financing activities
Net (decrease) increase in deposits	409,381,000	-7,545,000	135,095,000
Net increase (decrease) in short-term borrowings	-139,240,000	271,497,000	-18,651,000
Proceeds from issuance of long-term debt	120,051,000	0	0
Repayments of long-term debt	-315,831,000	-163,595,000	-3,354,000
Proceeds from the issuance of shares to employee benefit plans and other stock plans	6,256,000	5,334,000	1,395,000
Purchase of treasury stock	-72,000	-12,459,000	-15,490,000
Cash dividends and payment for fractional shares	-36,905,000	-33,518,000	-26,712,000
Net cash provided by financing activities	43,640,000	59,714,000	72,283,000
Net (decrease) increase in cash and cash equivalents	-12,290,000	-4,742,000	34,287,000
Cash and cash equivalents at beginning of year	158,926,000	163,668,000	129,381,000
Cash and cash equivalents at end of year	146,636,000	158,926,000	163,668,000
Cash paid during the period for:
Interest	23,387,000	31,307,000	35,344,000
Income taxes, net of refund	38,912,000	20,848,000	25,512,000
Noncash investing activities:
Loans transferred to other real estate owned	4,330,000	4,746,000	2,734,000
Preferred stock acquired from sale of equity investment	2,762,000	0	0
Transfer of available for sale securities to held to maturity portfolio	332,115,000	0	0
Acquisitions:
Fair value of assets acquired	0	1,505,490,000	258,467,000
Fair value of liabilities assumed	0	1,285,718,000	285,012,000
Fair value of debt issued in purchase combination	$0	$0	$502,000

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Summary of Significant Accounting Policies [Abstract]
Summary of Significant Accounting Policies	(1)  Summary of Significant Accounting Policies
	The accounting and reporting policies of NBT Bancorp Inc. (“NBT Bancorp”) and its subsidiaries, NBT Bank, National Association (“NBT Bank”), NBT Holdings, Inc., and NBT Financial Services, Inc., conform, in all material respects, to U.S. generally accepted accounting principles (“GAAP”) and to general practices within the banking industry. Collectively, NBT Bancorp and its subsidiaries are referred to herein as “the Company.”
	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from these estimates.
	Estimates associated with the allowance for loan losses, income taxes, pension expense, fair values of financial instruments, status of contingencies and other-than-temporary impairment on investments are particularly susceptible to material change in the near term.
	The following is a description of significant policies and practices:
	Consolidation
	The accompanying consolidated financial statements include the accounts of NBT Bancorp and its wholly owned subsidiaries mentioned above.  All material intercompany transactions have been eliminated in consolidation. Amounts previously reported in the consolidated financial statements are reclassified whenever necessary to conform to the current year’s presentation. In the “Parent Company Financial Information,” the investment in subsidiaries is recorded using the equity method of accounting.
	The Company determines whether it has a controlling financial interest in an entity by first evaluating whether the entity is a voting interest entity or a variable interest entity under GAAP. Voting interest entities are entities in which the total equity investment at risk is sufficient to enable the entity to finance itself independently and provides the equity holders with the obligation to absorb losses, the right to receive residual returns and the right to make decisions about the entity’s activities. The Company consolidates voting interest entities in which it has all, or at least a majority of, the voting interest. As defined in applicable accounting standards, variable interest entities (“VIEs”) are entities that lack one or more of the characteristics of a voting interest entity. A controlling financial interest in a VIE is present when the Company has both the power and ability to direct the activities of the VIE that most significantly impact the VIE's economic performance and an obligation to absorb losses or the right to receive benefits that could potentially be significant to the VIE. The Company’s wholly owned subsidiaries CNBF Capital Trust I, NBT Statutory Trust I, NBT Statutory Trust II, Alliance Financial Capital Trust I and Alliance Financial Capital Trust II are VIEs for which the Company is not the primary beneficiary. Accordingly, the accounts of these entities are not included in the Company’s consolidated financial statements.
	Segment Report
	The Company’s operations are primarily in the community banking industry and include the provision of traditional banking services.  The Company also provides other services through its subsidiaries such as insurance, retirement plan administration, and trust administration. The Company operates solely in the geographical regions of central and upstate New York, northeastern Pennsylvania, western Massachusetts, southern New Hampshire, Vermont, and the greater Portland, Maine area.  The Company has no reportable operating segments.
	Cash Equivalents
	The Company considers amounts due from correspondent banks, cash items in process of collection, and institutional money market mutual funds to be cash equivalents for purposes of the consolidated statements of cash flows.
	Securities
	The Company classifies its securities at date of purchase as either available for sale, held to maturity or trading.  Held to maturity debt securities are those that the Company has the ability and intent to hold until maturity.  Trading securities are securities purchased with the intent to sell within a short period of time, and unrealized gains and losses are included in earnings.  Available for sale securities are securities that are not classified as a held to maturity or trading securities. Available for sale securities are recorded at fair value. Unrealized holding gains and losses, net of the related tax effect, on available for sale securities are excluded from earnings and are reported in stockholders’ equity and the statement of comprehensive income as a component of accumulated other comprehensive income or loss. Held to maturity securities are recorded at amortized cost. Trading securities are recorded at fair value, with net unrealized gains and losses recognized in income.  Transfers of securities between categories are recorded at fair value at the date of transfer. Declines in the fair value of held-to-maturity and available-for-sale securities below their cost that are deemed to be other than temporary are reflected in earnings as realized losses or in other comprehensive income, depending on whether the Company intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss.  If the Company intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss, the other-than-temporary impairment shall be recognized in earnings equal to the entire difference between the investment’s amortized cost basis and its fair value at the balance sheet date.  If the Company does not intend to sell the security and it is not more likely than not that the entity will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss, the other-than-temporary impairment shall be separated into (a) the amount representing the credit loss and (b) the amount related to all other factors.  The amount of the total other-than-temporary impairment related to the credit loss shall be recognized in earnings. The amount of the total other-than-temporary impairment related to other factors shall be recognized in other comprehensive income, net of applicable taxes.
	In estimating other-than-temporary impairment losses, management considers, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer, and (iii) the historical and implied volatility of the fair value of the security.
	Non-marketable equity securities are carried at cost.
	Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the interest method. Dividend and interest income are recognized when earned. Realized gains and losses on securities sold are derived using the specific identification  method for determining the cost of securities sold.
	Investments in Federal Reserve Bank (“FRB”) and Federal Home Loan Bank (“FHLB”) stock are required for membership in those organizations and are carried at cost since there is no market value available.  The FHLB New York continues to pay dividends and repurchase stock.  As such, the Company has not recognized any impairment on its holdings of FHLB stock.
	Loans
	Loans are recorded at their current unpaid principal balance, net of unearned income and unamortized loan fees and expenses, which are amortized under the effective interest method over the estimated lives of the loans. Interest income on loans is accrued based on the principal amount outstanding.
	For all loan classes within the Company’s loan portfolio, loans are placed on nonaccrual status when timely collection of principal and interest in accordance with contractual terms is doubtful. Loans are transferred to nonaccrual status generally when principal or interest payments become ninety days delinquent, unless the loan is well secured and in the process of collection, or sooner when management concludes circumstances indicate that borrowers may be unable to meet contractual principal or interest payments.  When a loan is transferred to a nonaccrual status, all interest previously accrued in the current period but not collected is reversed against interest income in that period. Interest accrued in a prior period and not collected is charged-off against the allowance for loan losses.
	If ultimate repayment of a nonaccrual loan is expected, any payments received are applied in accordance with contractual terms. If ultimate repayment of principal is not expected, any payment received on a nonaccrual loan is applied to principal until ultimate repayment becomes expected.  For all loan classes within the Company’s loan portfolio, nonaccrual loans are returned to accrual status when they become current as to principal and interest and demonstrate a period of performance under the contractual terms and, in the opinion of management, are fully collectible as to principal and interest.  For loans in all portfolios, the principal amount is charged off in full or in part as soon as management determines, based on available facts, that the collection of principal in full is improbable.  For commercial loans, management considers specific facts and circumstances relative to individual credits in making such a determination.  For consumer and residential loan classes, management uses specific guidance and thresholds from the Federal Financial Institutions Examination Council’s Uniform Retail Credit Classification and Account Management Policy.
	Commercial type loans are considered impaired when it is probable that the borrower will not repay the loan according to the original contractual terms of the loan agreement, and all loan types are considered impaired if the loan is restructured in a troubled debt restructuring (“TDR”).  In determining that we will be unable to collect all principal and interest payments due in accordance with the contractual terms of the loan agreements, we consider factors such as payment history and changes in the financial condition of individual borrowers, local economic conditions, historical loss experience and the conditions of the various markets in which the collateral may be liquidated.
	A loan is considered to be a TDR when the Company grants a concession to the borrower because of the borrower’s financial condition that the Company would not otherwise consider. Such concessions include the reduction of interest rates, forgiveness of all or a portion of principal or interest, or other modifications at interest rates that are less than the current market rate for new obligations with similar risk. TDR loans are nonaccrual loans; however, they can be returned to accrual status after a period of performance, generally evidenced by six months of compliance with their modified terms.
	When the Company modifies a loan, management evaluates any possible impairment based on the present value of the expected future cash flows, discounted at the contractual interest rate of the original loan agreement, except when the sole (remaining) source of repayment for the loan is the operation or liquidation of the collateral.  In these cases, management uses the current fair value of the collateral, less selling costs, instead of discounted cash flows.  If management determines that the value of the modified loan is less than the recorded investment in the loan (net of previous charge-offs, deferred loan fees or costs and unamortized premium or discount), impairment is recognized by segment or class of loan as applicable, through an allowance estimate or a charge-off to the allowance.  Segment and class status is determined by the loan’s classification at origination.
	Acquired Loans
	Acquired loans are initially measured at fair value as of the acquisition date without carryover of historical allowance for loan losses.
	For loans that meet the criteria stipulated in ASC 310-30, the Company shall recognize the accretable yield, which is defined as the excess of all cash flows expected at acquisition over the initial fair value of the loan, as interest income on a level-yield basis over the expected remaining life of the loan. The excess of the loan's contractually required payments over the cash flows expected to be collected is the nonaccretable difference. The nonaccretable difference shall not be recognized as an adjustment of yield, a loss accrual, or a valuation allowance. Decreases in the expected cash flows in subsequent periods require the establishment of an allowance for loan losses. Improvements in expected cash flows in future periods result in a reduction of the nonaccretable discount, with such amount reclassified as part of the accretable yield and subsequently recognized in interest income over the remaining lives of the acquired loans on a level-yield basis if the amount and timing of future cash flows is reasonably estimable.
	Acquired loans that met the criteria for nonaccrual of interest prior to the acquisition are considered performing upon acquisition, regardless of whether the customer is contractually delinquent, if the Company can reasonably estimate the timing and amount of the expected cash flows on such loans and if the Company expects to fully collect the new carrying value of the loans. As such, the Company may no longer consider the loan to be nonaccrual or nonperforming and may accrue interest on these loans, including the impact of any accretable yield. As such, charge-offs on acquired loans are first applied to the nonaccretable difference and then to any allowance for loan losses recognized subsequent to acquisition.
	For loans that meet the criteria stipulated in ASC 310-20, the Company shall amortize/accrete into interest income the premium/discount determined at the date of purchase on a level-yield basis over the life of the loan. Subsequent to the acquisition date, the methods utilized to estimate the required allowance for loan losses are similar to originated loans.  Loans accounted for under ASC 310-20 are placed on nonaccrual status when past due in accordance with the Company's nonaccrual policy.
	An acquired loan may be resolved either through receipt of payment (in full or in part) from the borrower, the sale of the loan to a third party, or foreclosure of the collateral. In the event of a sale of the loan, a gain or loss on sale is recognized and reported within noninterest income based on the difference between the sales proceeds and the carrying amount of the loan. In other cases, individual loans are removed from the pool based on comparing the amount received from its resolution (fair value of the underlying collateral less costs to sell in the case of a foreclosure) with its outstanding balance. Any difference between these amounts is recorded as a charge-off through the allowance for loan losses.  Acquired loans subject to modification are not removed from the pool even if those loans would otherwise be deemed troubled debt restructurings as the pool, and not the individual loan, represents the unit of account.
	Allowance for Loan Losses
	The allowance for loan losses is the amount which, in the opinion of management, is necessary to absorb probable losses inherent in the loan portfolio. The allowance is determined based upon numerous considerations, including local and regional conditions, the growth and composition of the loan portfolio  with  respect to the mix between the various types of loans and their related risk characteristics, a review of the value of collateral supporting the loans, comprehensive reviews of the loan portfolio by the independent loan review staff and management, as well as consideration of volume and trends of delinquencies, nonperforming loans, and loan charge-offs.  Loan losses are charged off against the allowance, while recoveries of amounts previously charged off are credited to the allowance.  As a result of tests of adequacy, required additions to the allowance for loan losses are made periodically by charges to the provision for loan losses.
	The allowance for loan losses related to impaired loans specifically allocated for impairment is based on discounted cash flows using the loan’s initial effective interest rate or the fair value of the collateral for certain loans where repayment of the loan is expected to be provided solely by the underlying collateral (collateral dependent loans). The Company’s impaired loans are generally collateral dependent. The Company considers the estimated cost to sell, on a discounted basis, when determining the fair value of collateral in the measurement of impairment if those costs are expected to reduce the cash flows available to repay or otherwise satisfy the loans.
	The allowance for loan losses for homogeneous non impaired loans is calculated using a systematic methodology with both a quantitative and a qualitative analysis that is applied on a quarterly basis. For purposes of our allowance methodology, the loan portfolio is segmented as described in Note 5, Allowance for Loan Loss and Credit Quality of Loans. Each segment has a distinct set of risk characteristics monitored by management. We further assess and monitor risk and performance at a more disaggregated level which includes our internal risk grading system for the commercial segments.
	We first apply historical loss rates to pools of loans with similar risk characteristics. Loss rates are calculated by historical charge-offs that have occurred within each pool of loans over the loss emergence period, or LEP. The LEP is an estimate of the average amount of time from the point at which a loss is incurred on a loan to the point at which the loss is confirmed. In general, the LEP will be shorter in an economic slowdown or recession and longer during times of economic stability or growth, as customers are better able to delay loss confirmation after a potential loss event has occurred. In conjunction with our annual review of the ALL assumptions, we update our study of LEPs for each portfolio segment using our loan charge-off history. Another key assumption is the look-back period, or LBP, which represents the historical data period utilized to calculate loss rates.
	After consideration of the historic loss analysis, management applies additional qualitative adjustments so that the allowance for loan losses is reflective of the inherent losses that exist in the loan portfolio at the balance sheet date. Qualitative adjustments are made based upon past loss experience; size, trend, composition, and nature of loans; changes in lending policies and procedures, including underwriting standards and collection, charge-offs and recoveries; trends experienced in nonperforming and delinquent loans; current economic conditions in the Company’s market; portfolio concentrations that may affect loss experience across one of more components of the portfolio; the effect of external factors such as competition, legal and regulatory requirements; and the experience, ability, and depth of lending management and staff. The evaluation of the various components of the allowance for loan losses requires considerable judgment in order to estimate inherent loss exposures. In addition, various regulatory agencies, as an integral component of their examination process, periodically review the Company’s allowance for loan losses. Such agencies may require the Company to make loan grade changes as well as recognize additions to the allowance based on their examinations.
	Management believes that the allowance for loan losses is adequate.  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 or changes in the values of properties securing loans in the process of foreclosure. In addition, various regulatory agencies, as an integral part of their examination process, 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 which may not be currently available to management.
	Premises and Equipment
	Premises and equipment are stated at cost, less accumulated depreciation.  Depreciation of premises and equipment is determined using the straight-line method over the estimated useful lives of the respective assets. Expenditures for maintenance, repairs, and minor replacements are charged to expense as incurred.
	Other Real Estate Owned
	OREO consists of properties acquired through foreclosure or by acceptance of a deed in lieu of foreclosure. These assets are recorded at the lower of fair value of the asset acquired less estimated costs to sell or “cost” (defined as the fair value at initial foreclosure). At the time of foreclosure, or when foreclosure occurs in-substance, the excess, if any, of the loan over the fair market value of the assets received, less estimated selling costs, is charged to the allowance for loan losses and any subsequent valuation write-downs are charged to other expense.  In connection with the determination of the allowance for loan losses and the valuation of other real estate owned, management obtains appraisals for properties.  Operating costs associated with the properties are charged to expense as incurred. Gains on the sale of OREO are included in income when title has passed and the sale has met the minimum down payment requirements prescribed by GAAP.  The balance of OREO at December 31, 2014 and 2013 was approximately $4.0 million and $2.9 million, respectively, and is recorded in Other Assets on the Consolidated Balance Sheet.
	Goodwill and Other Intangible Assets
	Goodwill and intangible assets that have indefinite useful lives are not amortized, but are tested at least annually for impairment. Intangible assets that have finite useful lives are amortized over their useful lives.  Core deposit intangibles and trust intangibles at the Company are amortized using the sum-of-the-years’-digits method.  Covenants not to compete are amortized on a straight-line basis.  Customer lists are amortized using an accelerated method.
	When facts and circumstances indicate potential impairment of amortizable intangible assets, the Company evaluates the recoverability of the asset carrying value, using estimates of undiscounted future cash flows over the remaining asset life. Any impairment loss is measured by the excess of carrying value over fair value. Goodwill impairment tests are performed on an annual basis or when events or circumstances dictate. In these tests, the fair values of each reporting unit, or segment, is compared to the carrying amount of that reporting unit in order to determine if impairment is indicated. If so, the implied fair value of the reporting unit’s goodwill is compared to its carrying amount and the impairment loss is measured by the excess of the carrying value over fair value.
	Bank-Owned Life Insurance
	The Bank has purchased life insurance policies on certain employees, key executives and directors. Bank-owned life insurance is recorded at the amount that can be realized under the insurance contract at the balance sheet date, which is the cash surrender value adjusted for other charges or other amounts due that are probable at settlement.
	Treasury Stock
	Treasury stock acquisitions are recorded at cost. Subsequent sales of treasury stock are recorded on an average cost basis. Gains on the sale of treasury stock are credited to additional paid-in-capital. Losses on the sale of treasury stock are charged to additional paid-in-capital to the extent of previous gains, otherwise charged to retained earnings.
	Income Taxes
	Income taxes are accounted for under the asset and liability method. Deferred income taxes are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases.  Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred taxes of a change in tax rates is recognized in income in the period that includes the enactment date.  The Company recognizes interest accrued and penalties related to unrecognized tax benefits in income tax expense.
	Tax positions are recognized as a benefit only if it is “more likely than not” that the tax position would be sustained in a tax examination, with a tax examination being presumed to occur. The amount recognized is the largest amount of tax benefit that is greater than 50 percent likely of being realized on examination. For tax positions not meeting the “more likely than not” test, no tax benefit is recorded.
	Stock-Based Compensation
	We maintain various long-term incentive stock benefit plans under which we grant stock options, restricted stock awards, and restricted stock units to certain directors and key employees.  We recognize compensation expense in our income statement over the requisite service period, based on the grant-date fair value of the award.  For restricted stock awards and units, we recognize compensation expense ratably over the vesting period for the fair value of the award, measured at the grant date.  The fair values of options are estimated using the Black-Scholes option pricing model.
	The Company’s stock-based employee compensation plan is described in Note 14 “Stock-Based Compensation,” of this Report.
	Interest Rate Swaps
	The Bank offers interest rate swap agreements to its customers.  These agreements allow the Bank’s customers to effectively fix the interest rate on a variable rate loan by entering into a separate agreement.  Simultaneous with the execution of such an agreement with a customer, the Bank enters into a matching interest rate swap agreement with an unrelated third party provider, which allows the Bank to continue to receive the historical variable rate under the loan agreement with the customer.  The agreement with the third party is not a hedge contract therefore changes in fair value are recorded through earnings.  Assets and liabilities associated with the agreements are recorded in other assets and other liabilities on the balance sheet.  Gains and losses are recorded as other noninterest income.  The Bank is not subject to any fee or penalty should the customer elect to terminate the interest rate swap agreement prior to maturity.  The Bank is exposed to credit loss equal to the fair value of the derivatives (not the notional amount of the derivatives) in the event of nonperformance by the counterparty to the interest rate swap agreements.  Additionally, the Bank receives a fee from the customer that is recognized when the Bank has fulfilled its obligations under each agreement, which is generally upon execution of the agreement with the Bank’s customer.  Since the terms of the thirty three interest rate swap agreements with the customers are identical to the related swaps with the third party, the income statement impact to the Bank is generally limited to the fees it receives from the customer.
	Other Financial Instruments
	The Company is a party to certain other financial instruments with off-balance-sheet risk such as commitments to extend credit, unused lines of credit, as well as certain mortgage loans sold to investors with recourse. The Company’s policy is to record such instruments when funded.
	Standby letters of credit are conditional commitments issued to guarantee the performance of a customer to a third party.  The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loan facilities to customers.  Under the standby letters of credit, the Company is required to make payments to the beneficiary of the letters of credit upon request by the beneficiary contingent upon the customer's failure to perform under the terms of the underlying contract with the beneficiary.  Standby letters of credit typically have one year expirations with an option to renew upon annual review.  The Company typically receives a fee for these transactions.  The fair value of stand-by letters of credit is recorded upon inception.
	Loan Sales and Loan Servicing
	The Company originates and services residential mortgage loans for consumers and sells 15-year, 20-year and 30-year residential real estate mortgages in the secondary market when the interest rate environment is determined to be favorable by management, while retaining servicing rights on the sold loans.  Loan sales are recorded when the sales are funded.  Mortgage servicing rights are recorded at fair value upon sale of the loan.  Loans held for sale are recorded at the lower of cost or market.
	Repurchase Agreements
	Repurchase agreements are accounted for as secured financing transactions since the Company maintains effective control over the transferred securities and the transfer meets the other criteria for such accounting.  Obligations to repurchase securities sold are reflected as a liability in the Consolidated Balance Sheets.  The securities underlying the agreements are delivered to a custodial account for the benefit of the dealer or bank with whom each transaction is executed.  The dealers or banks, who may sell, loan or otherwise dispose of such securities to other parties in the normal course of their operations, agree to resell to the Company the same securities at the maturities of the agreements.
Earnings Per Share
Basic earnings per share (EPS) excludes dilution and is computed by dividing income available to common stockholders by the weighted average number of common shares outstanding for the period. Diluted EPS reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the entity (such as the Company’s dilutive stock options and restricted stock).
Subsequent Events
The Company has evaluated subsequent events for potential recognition and/or disclosure and there were none identified.
Comprehensive Income
At the Company, comprehensive income represents net income plus other comprehensive income (loss), which consists primarily of the net change in unrealized gains or losses on securities available for sale for the period and changes in the funded status of employee benefit plans. Accumulated other comprehensive (loss) income represents the net unrealized gains or losses on securities available for sale and the previously unrecognized portion of the funded status of employee benefit plans, net of income taxes, as of the consolidated balance sheet dates.
Pension Costs
The Company maintains a noncontributory, defined benefit pension plan covering substantially all employees, as well as supplemental employee retirement plans covering certain executives and a defined benefit postretirement healthcare plan that covers certain employees.  Costs associated with these plans, based on actuarial computations of current and future benefits for employees, are charged to current operating expenses.
Trust Operations
Assets held by the Company in a fiduciary or agency capacity for its customers are not included in the accompanying consolidated balance sheets, since such assets are not assets of the Company.  Trust income is recognized on the accrual method based on contractual rates applied to the balances of trust accounts.
Fair Value Measurements
Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value measurements are not adjusted for transaction costs.  A fair value hierarchy prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (level 1 measurements) and the lowest priority to unobservable inputs (level 3 measurements). The three levels of the fair value hierarchy are described below:
Level 1 - Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities;
Level 2 -  Quoted prices for similar assets or liabilities in active markets, quoted prices in markets that are not active, or inputs that are observable, either directly or indirectly, for substantially the full term of the asset or liability;
Level 3 - Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity).
A financial instrument’s level within the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement.
The types of instruments valued based on quoted market prices in active markets include most U.S. government and agency securities, many other sovereign government obligations, liquid mortgage products, active listed equities and most money market securities. Such instruments are generally classified within level 1 or level 2 of the fair value hierarchy.  The Company does not adjust the quoted price for such instruments.
The types of instruments valued based on quoted prices in markets that are not active, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency include most investment-grade and high-yield corporate bonds, less liquid mortgage products, less liquid agency securities, less liquid listed equities, state, municipal and provincial obligations, and certain physical commodities. Such instruments are generally classified within level 2 of the fair value hierarchy.
Level 3 is for positions that are not traded in active markets or are subject to transfer restrictions, valuations are adjusted to reflect illiquidity and/or non-transferability, and such adjustments are generally based on available market evidence. In the absence of such evidence, management’s best estimate will be used. Management’s best estimate consists of both internal and external support on certain Level 3 investments. Subsequent to inception, management only changes level 3 inputs and assumptions when corroborated by evidence such as transactions in similar instruments, completed or pending third-party transactions in the underlying investment or comparable entities, subsequent rounds of financing, recapitalizations and other transactions across the capital structure, offerings in the equity or debt markets, and changes in financial ratios or cash flows.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2014
Acquisitions [Abstract]
Acquisitions	(2)  Acquisitions
	Acquisition of Alliance Financial Corporation
	On March 8, 2013, the Company acquired Alliance Financial Corporation (“Alliance”), the parent company of Alliance Bank, N.A., for total consideration of $226 million.  As part of the acquisition, Alliance was merged with and into the Company and Alliance Bank, with 26 branch locations in the central New York counties of Onondaga, Cortland, Madison, Oneida and Oswego, was merged with and into the Bank.  The merger with Alliance enabled the Company to expand its footprint into demographically attractive and contiguous markets located in the aforementioned New York counties.  Alliance operations were integrated into the Company and were included in the Consolidated Statements of Income from the date of acquisition.
	Other Goodwill Adjustments
	During the twelve months ended December 31, 2014, the Company recorded deferred tax adjustments totaling approximately ($1.0) million and valuation adjustments totaling ($0.4) related to the 2013 acquisition of Alliance resulting in a decrease in goodwill of approximately ($1.4) million in 2014.  During the twelve months ended December 31, 2013, the Company recorded a deferred tax adjustment related to the 2012 acquisition of Hampshire First Bank resulting in a decrease in goodwill of approximately $(1.0) million.  In addition, the Company recorded a goodwill adjustment of approximately $0.1 million related to the 2012 acquisition of a financial services company.

Securities

Securities	12 Months Ended
	Dec. 31, 2014
Securities [Abstract]
Securities	(3) Securities
	The amortized cost, estimated fair value, and unrealized gains and losses of securities available for sale are as follows:
	(In thousands)	Amortized cost		Unrealized gains			Unrealized losses		Estimated fair value
	31-Dec-14
	U.S. Treasury	$	23,041	$	70		$	-	$	23,111
	Federal agency		332,193		327			2,606		329,914
	State & municipal		37,035		587			52		37,570
	Mortgage-backed:
	Government-sponsored enterprises		339,190		7,597			224		346,563
	U.S. government agency securities		17,367		863			66		18,164
	Collateralized mortgage obligations:
	Government-sponsored enterprises		199,837		1,828			234		201,431
	U.S. government agency securities		40,237		497			36		40,698
	Other securities		12,818		3,054			152		15,720
	Total securities available for sale	$	1,001,718	$	14,823		$	3,370	$	1,013,171
	31-Dec-13
	U.S. Treasury	$	43,279	$	337		$	-	$	43,616
	Federal agency		285,880		343			7,308		278,915
	State & municipal		113,435		1,842			1,612		113,665
	Mortgage-backed:
	Government-sponsored enterprises		337,666		5,788			2,131		341,323
	U.S. government securities		21,924		1,002			85		22,841
	Collateralized mortgage obligations:
	Government-sponsored enterprises		521,257		1,777			18,141		504,893
	U.S. government securities		43,943		794			102		44,635
	Other securities		12,367		2,854			228		14,993
	Total securities available for sale	$	1,379,751	$	14,737		$	29,607	$	1,364,881
	The following table sets forth information with regard to sales transactions of securities available for sale:
		Years ended December 31
	(In thousands)	2014		2013			2012
	Proceeds from sales	$	189	$	27,593		$	1,790
	Gross realized gains	$	49	$	1,283		$	442
	Gross realized losses		-		-			-
	Net securities gains	$	49	$	1,283		$	442
	In addition to gains (losses) from sales transactions, the Company also recorded gains from calls on securities available for sale of approximately $0.1 million for the year ended December 31, 2014, $0.1 million for the year ended December 31, 2013, and $0.2 million for the year ended December 31, 2012.
	At December 31, 2014 and 2013, securities available for sale and held to maturity with amortized costs totaling $1.4 billion and $1.4 billion, respectively, were pledged to secure public deposits and for other purposes required or permitted by law.  Additionally, at December 31, 2014, securities available for sale and held to maturity with an amortized cost of $208.8 million were pledged as collateral for securities sold under the repurchase agreements.
	The amortized cost, estimated fair value, and unrealized gains and losses of securities held to maturity are as follows:
	(In thousands)	Amortized		Unrealized			Unrealized		Estimated
		cost		gains			losses		fair value
	31-Dec-14
	Mortgage-backed	$	755	$	113		$	-	$	868
	Collateralized mortgage obligations		317,628		1,934			1,965		317,597
	State & municipal		135,978		674			123		136,529
	Total securities held to maturity	$	454,361	$	2,721		$	2,088	$	454,994
	31-Dec-13
	Mortgage-backed	$	953	$	128		$	-	$	1,081
	Collateralized mortgage obligations		62,025		-			4,569		57,456
	State & municipal		54,305		442			8		54,739
	Total securities held to maturity	$	117,283	$	570		$	4,577	$	113,276
	At December 31, 2014 and 2013, all of the mortgaged-backed securities held to maturity were comprised of U.S. government agency securities.
	The following table sets forth information with regard to investment securities with unrealized losses at December 31, 2014 and 2013, segregated according to the length of time the securities had been in a continuous unrealized loss position:
		Less than 12 months							12 months or longer							Total
	Security Type:	Fair		Unrealized			Number		Fair		Unrealized			Number		Fair		Unrealized			Number
		Value		losses			of		Value		losses			of		Value		losses			of
							Positions							Positions							Positions
	31-Dec-14
	Investment securities available for sale:
	Federal agency	$	66,528	$	(226	)		8	$	198,151	$	(2,380	)		16	$	264,679	$	(2,606	)		24
	State & municipal		8,818		(42	)		33		1,321		(10	)		5		10,139		(52	)		38
	Mortgage-backed		10,400		(36	)		10		35,565		(254	)		31		45,965		(290	)		41
	Collateralized mortgage obligations		57,682		(196	)		8		6,598		(74	)		4		64,280		(270	)		12
	Other securities		-		-			-		3,201		(152	)		2		3,201		(152	)		2
	Total securities with unrealized losses	$	143,428	$	(500	)		59	$	244,836	$	(2,870	)		58	$	388,264	$	(3,370	)		117
	31-Dec-14
Investment securities held to maturity:
Collateralized mortgage obligations	$	26,052	$	(49	)		2	$	46,415	$	(1,916	)		4	$	72,467	$	(1,965	)		6
State & municipal		43,514		(116	)		110		1,619		(7	)		6		45,133		(123	)		116
Total securities with unrealized losses	$	69,566	$	(165	)		112	$	48,034	$	(1,923	)		10	$	117,600	$	(2,088	)		122
31-Dec-13
Investment securities available for sale:
Federal agency	$	233,935	$	(6,927	)		20	$	9,619	$	(381	)		1	$	243,554	$	(7,308	)		21
State & municipal		50,328		(1,612	)		177		-		-			-		50,328		(1,612	)		177
Mortgage-backed		143,080		(2,216	)		79		-		-			-		143,080		(2,216	)		79
Collateralized mortgage obligations		379,273		(18,243	)		36		-		-			-		379,273		(18,243	)		36
Other securities		5,490		(203	)		2		223		(25	)		1		5,713		(228	)		3
Total securities with unrealized losses	$	812,106	$	(29,201	)		314	$	9,842	$	(406	)		2	$	821,948	$	(29,607	)		316
31-Dec-13
Investment securities held to maturity:
Collateralized mortgage obligations	$	57,456	$	(4,569	)		5	$	-	$	-			-	$	57,456	$	(4,569	)		5
State & municipal		1,012		(8	)		1		-		-			-		1,012		(8	)		1
Total securities with unrealized losses	$	58,468	$	(4,577	)		6	$	-	$	-			-	$	58,468	$	(4,577	)		6
Management has the intent to hold the securities classified as held to maturity until they mature, at which time it is believed the Company will receive full value for the securities. Furthermore, as of December 31, 2014, management also had intent to hold, and will not be required to sell, the securities classified as available for sale for a period of time sufficient for a recovery of cost, which may be until maturity.  The unrealized losses are due to increases in market interest rates over the yields available at the time the underlying securities were purchased. When necessary, the Company has performed a discounted cash flow analysis to determine whether or not it will receive the contractual principal and interest on certain securities.  The fair value is expected to recover as the bonds approach their maturity date or repricing date or if market yields for such investments decline.  As of December 31, 2014, management believes the impairments detailed in the table above are temporary and no other-than-temporary impairment losses have been realized in the Company’s consolidated statements of income.
During 2014, the Company transferred approximately $340 million in securities from the available for sale portfolio to the held to maturity portfolio, which had unrealized losses at the time of transfer of approximately $8.3 million. This unrealized loss is amortized into interest income over the lives of the transferred securities.
The following tables set forth information with regard to contractual maturities of debt securities at December 31, 2014:
(In thousands)	Amortized		Estimated fair
	cost		value
Debt securities classified as available for sale
Within one year	$	28,193	$	28,310
From one to five years		356,696		356,107
From five to ten years		160,816		163,924
After ten years		443,195		449,110
	$	988,900	$	997,451
Debt securities classified as held to maturity
Within one year	$	22,999	$	23,075
From one to five years		15,506		15,606
From five to ten years		87,326		87,640
After ten years		328,530		328,673
	$	454,361	$	454,994
Maturities of mortgage-backed, CMOs and asset-backed securities are stated based on their estimated average lives.  Actual maturities may differ from estimated average lives or contractual maturities because, in certain cases, borrowers have the right to call or prepay obligations with or without call or prepayment penalties.
Except for U.S. Government securities, there were no holdings, when taken in the aggregate, of any single issuer that exceeded 10% of consolidated stockholders’ equity at December 31, 2014 and December 31, 2013.

Loans

Loans	12 Months Ended
	Dec. 31, 2014
Loans [Abstract]
Loans	(4)  Loans
	A summary of loans, net of deferred fees and origination costs, by category is as follows:
		At December 31,
	(In thousands)	2014			2013
	Residential real estate mortgages	$	1,115,589		$	1,041,637
	Commercial		839,770			859,026
	Commercial real estate		1,442,989			1,328,313
	Real estate construction and development		83,750			93,247
	Agricultural and agricultural real estate mortgages		107,195			112,035
	Consumer		1,436,382			1,352,638
	Home equity		569,596			619,899
	Total loans	$	5,595,271		$	5,406,795
	Included in the above loans are net deferred loan origination costs totaling $35.6 million and $31.8 million at December 31, 2014 and 2013, respectively.  The Company had residential loans held for sale totaling $3.2 million as of December 31, 2014 and $0.1 million as of December 31, 2013.
	At December 31, 2014 and 2013, the Company serviced $23.4 million and $15.7 million, respectively, of agricultural loans sold with recourse.  Due to sufficient collateral on these loans, no reserve is considered necessary at December 31, 2014 and 2013.
	FHLB advances are collateralized by a blanket lien on the Company’s residential real estate mortgages.
	In the ordinary course of business, the Company has made loans at prevailing rates and terms to directors, officers, and other related parties. Such loans, in management’s opinion, do not present more than the normal risk of collectability or incorporate other unfavorable features. The aggregate amount of loans outstanding to qualifying related parties and changes during the years are summarized as follows:
	(In thousands)	2014			2013
	Balance at January 1	$	3,372		$	2,790
	New loans		522			569
	Adjustment due to change in composition of related parties		253			376
	Repayments		(571	)		(363	)
	Balance at December 31	$	3,576		$	3,372

Allowance_for_Loan_Losses_and_

Allowance for Loan Losses and Credit Quality of Loans	12 Months Ended
	Dec. 31, 2014
Allowance for Loan Losses and Credit Quality of Loans [Abstract]
Allowance for Loan Losses and Credit Quality of Loans and Leases	(5)  Allowance for Loan Losses and Credit Quality of Loans
	Allowance for Loan Losses
	The allowance for loan losses is maintained at a level estimated by management to provide adequately for risk of probable losses inherent in the current loan portfolio. The adequacy of the allowance for loan losses is continuously monitored. It is assessed for adequacy using a methodology designed to ensure the level of the allowance reasonably reflects the loan portfolio’s risk profile. It is evaluated to ensure that it is sufficient to absorb all reasonably estimable credit losses inherent in the current loan portfolio.
	To develop and document a systematic methodology for determining the allowance for loan losses, the Company has divided the loan portfolio into three segments, each with different risk characteristics and methodologies for assessing risk. Those segments are further segregated between our loans accounted for under the amortized cost method (referred to as “originated” loans) and loans acquired in a business combination (referred to as “acquired” loans). Prior to 2013, separate disclosures for acquired loans were not significant and were included with originated loans in the Company’s asset quality disclosures. Each portfolio segment is broken down into class segments where appropriate. Class segments contain unique measurement attributes, risk characteristics and methods for monitoring and assessing risk that are necessary to develop the allowance for loan losses. Unique characteristics such as borrower type, loan type, collateral type, and risk characteristics define each class segment. The following table illustrates the portfolio and class segments for the Company’s loan portfolio:
	Portfolio	Class
	Commercial Loans	Commercial
		Commercial Real Estate
		Agricultural
		Agricultural Real Estate
		Business Banking
	Consumer Loans	Indirect
		Home Equity
		Direct
	Residential Real Estate Mortgages
	COMMERCIAL LOANS
	Commercial – The Company offers a variety of loan options to meet the specific needs of our commercial customers including term loans, time notes and lines of credit. Such loans are made available to businesses for working capital such as inventory and receivables, business expansion and equipment purchases. Generally, a collateral lien is placed on equipment or other assets owned by the borrower. These loans carry a higher risk than commercial real estate loans by the nature of the underlying collateral, which can be business assets such as equipment and accounts receivable and is generally less liquid than real estate. To reduce the risk, management also attempts to secure real estate as collateral and obtain personal guarantees of the borrowers.
	Commercial Real Estate – The Company offers commercial real estate loans to finance real estate purchases, refinancings, expansions and improvements to commercial properties. Commercial real estate loans are made to finance the purchases of real property which generally consists of real estate with completed structures. These commercial real estate loans are secured by first liens on the real estate, which may include apartments, commercial structures, housing businesses, healthcare facilities, and other non owner-occupied facilities. These loans are typically less risky than commercial loans, since they are secured by real estate and buildings. The Company’s underwriting analysis includes credit verification, independent appraisals, a review of the borrower's financial condition, and a detailed analysis of the borrower’s underlying cash flows. These loans are typically originated in amounts of no more than 80% of the appraised value of the property.
	Agricultural – The Company offers a variety of agricultural loans to meet the needs of our agricultural customers including term loans, time notes, and lines of credit. These loans are made to purchase livestock, purchase and modernize equipment, and finance seasonal crop expenses. Generally, a collateral lien is placed on the livestock, equipment, produce inventories, and/or receivables owned by the borrower. These loans may carry a higher risk than commercial and agricultural real estate loans due to the industry price volatility and the perishable nature of the underlying collateral. To reduce these risks, management may attempt to secure these loans with additional real estate collateral, obtain personal guarantees of the borrowers, or obtain government loan guarantees to provide further support.
	Agricultural Real Estate – The Company offers real estate loans to our agricultural customers to finance farm related real estate purchases, refinancings, expansions, and improvements to agricultural properties. Agricultural real estate loans are made to finance the purchases and improvements of farm properties that generally consist of barns, production facilities, and land. The agricultural real estate loans are secured by first liens on the farm real estate. Because they are secured by land and buildings, these loans may be less risky than agricultural loans. The Company's underwriting analysis includes credit verification, independent appraisals, a review of the borrower's financial condition, and a detailed analysis of the borrower’s underlying cash flows. These loans are typically originated in amounts of no more than 75% of the appraised value of the property. Government loan guarantees may be obtained to provide further support.
	Business Banking - The Company offers a variety of loan options to meet the specific needs of our small business customers including term loans, small business mortgages and lines of credit. Such loans are generally less than $500 thousand and are made available to businesses for working capital such as inventory and receivables, business expansion, equipment purchases, and agricultural needs. Generally, a collateral lien is placed on equipment or other assets owned by the borrower such as inventory and/or receivables. These loans carry a higher risk than commercial loans due to the smaller size of the borrower and lower levels of capital. To reduce the risk, the Company obtains personal guarantees of the owners for a majority of the loans.
	CONSUMER LOANS
	Indirect – The Company maintains relationships with many dealers primarily in the communities that we serve. Through these relationships, the company finances the purchases of automobiles and recreational vehicles (such as campers, boats, etc.) indirectly through dealer relationships. Approximately 70% of the indirect relationships represent automobile financing. Most of these loans carry a fixed rate of interest with principal repayment terms typically ranging from three to six years, based upon the nature of the collateral and the size of the loan. The majority of indirect consumer loans are underwritten on a secured basis using the underlying collateral being financed.
	Home Equity – The Company offers fixed home equity loans as well as home equity lines of credit to consumers to finance home improvements, debt consolidation, education and other uses. Consumers are able to borrower up to 85% of the equity in their homes. The Company originates home equity lines of credit and second mortgage loans (loans secured by a second lien position on one-to-four-family residential real estate). These loans carry a higher risk than first mortgage residential loans as they are in a second position with respect to collateral. Risk is reduced through underwriting criteria, which include credit verification, appraisals, a review of the borrower's financial condition, and personal cash flows. A security interest, with title insurance when necessary, is taken in the underlying real estate.
	Direct – The Company offers a variety of consumer installment loans to finance vehicle purchases, mobile home purchases and personal expenditures. Most of these loans carry a fixed rate of interest with principal repayment terms typically ranging from one to ten years, based upon the nature of the collateral and the size of the loan. The majority of consumer loans are underwritten on a secured basis using the underlying collateral being financed or a customer's deposit account. In addition to installment loans, the Company also offers personal lines of credit and overdraft protection. A minimal amount of loans are unsecured, which carry a higher risk of loss.
	RESIDENTIAL REAL ESTATE LOANS
	Residential real estate loans consist primarily of loans secured by first or second deeds of trust on primary residences. We originate adjustable-rate and fixed-rate, one-to-four-family residential real estate loans for the construction, purchase or refinancing of a mortgage. These loans are collateralized by owner-occupied properties located in the Company’s market area. When market conditions are favorable, for longer term, fixed-rate residential mortgages without escrow, the Company retains the servicing, but sells the right to receive principal and interest to Freddie Mac when market conditions are favorable.  This practice allows the Company to manage interest rate risk, liquidity risk, and credit risk. Loans on one-to-four-family residential real estate are generally originated in amounts of no more than 85% of the purchase price or appraised value (whichever is lower), or have private mortgage insurance. Mortgage title insurance and hazard insurance are normally required. Construction loans have a unique risk, because they are secured by an incomplete dwelling. This risk is reduced through periodic site inspections, including one at each loan draw period.
	Allowance for Loan Loss Calculation
	Management considers the accounting policy relating to the allowance for loan losses to be a critical accounting policy given the inherent uncertainty in evaluating the levels of the allowance required to cover credit losses in the portfolio and the material effect that such judgments can have on the consolidated results of operations.
	In addition, various regulatory agencies, as an integral component of their examination process, periodically review the Company’s allowance for loan losses. Such agencies may require the Company to make loan grade changes as well as recognize additions to the allowance based on their examinations.
	After a thorough consideration of the factors discussed above, any required additions to the allowance for loan losses are made periodically by charges to the provision for loan losses. These charges are necessary to maintain the allowance at a level which management believes is reasonably reflective of overall inherent risk of probable loss in the portfolio. While management uses available information to recognize losses on loans, additions to the allowance may fluctuate from one reporting period to another. These fluctuations are reflective of changes in risk associated with portfolio content and/or changes in management’s assessment of any or all of the determining factors discussed above.
	The following table illustrates the changes in the allowance for loan losses by portfolio segment for the years ended December 31, 2014, 2013 and 2012:
	Allowance for Loan Losses
	(in thousands)
			Commercial				Consumer				Residential				Unallocated			Total
			Loans				Loans				Real Estate
											Mortgages
	Balance as of December 31, 2013		$	35,090			$	27,694			$	6,520			$	130		$	69,434
	Charge-offs			(9,414	)			(16,642	)			(1,417	)			-			(27,473	)
	Recoveries			1,774				2,800				285				-			4,859
	Provision			4,983				12,868				1,742				(54	)		19,539
	Ending Balance as of December 31, 2014		$	32,433			$	26,720			$	7,130			$	76		$	66,359
	Balance as of December 31, 2012		$	35,624			$	27,162			$	6,252			$	296		$	69,334
	Charge-offs			(10,459	)			(15,459	)			(1,771	)			-			(27,689	)
	Recoveries			1,957				3,136				272				-			5,365
	Provision			7,968				12,855				1,767				(166	)		22,424
	Ending Balance as of December 31, 2013		$	35,090			$	27,694			$	6,520			$	130		$	69,434
	Balance as of December 31, 2011		$	38,831			$	26,049			$	6,249			$	205		$	71,334
	Charge-offs			(8,750	)			(15,848	)			(1,906	)			-			(26,504	)
	Recoveries			1,641				2,556				38				-			4,235
	Provision			3,902				14,405				1,871				91			20,269
	Ending Balance as of December 31, 2012		$	35,624			$	27,162			$	6,252			$	296		$	69,334
	For acquired loans, to the extent that we experience deterioration in borrower credit quality resulting in a decrease in our expected cash flows subsequent to acquisition of the loans, an allowance for loan losses would be established based on our estimate of future credit losses over the remaining life of the loans.  As of December 31, 2014 the allowance for loan losses for the acquired loan portfolio totaled $0.5 million. There was no allowance for the acquired loan portfolio as of December 31, 2013.  Net charge-offs related to acquired loans totaled approximately $4.8 million and $0.4 million during the years ended December 31, 2014 and December 31, 2013, respectively, and are included in the table above.
	The following table illustrates the allowance for loan losses and the recorded investment by portfolio segment as of December 31, 2014 and 2013:
	Allowance for Loan Losses and Recorded Investment in Loans
	(in thousands)
			Commercial				Consumer				Residential				Unallocated			Total
			Loans				Loans				Real Estate
											Mortgages
	As of December 31, 2014
	Allowance for loan losses		$	32,433			$	26,720			$	7,130			$	76		$	66,359
	Allowance for loans individually evaluated for impairment			1,100				-				-							1,100
	Allowance for loans collectively evaluated for impairment		$	31,333			$	26,720			$	7,130			$	76		$	65,259
	Ending balance of loans		$	2,473,702			$	2,005,980			$	1,115,589						$	5,595,271
	Ending balance of originated loans individually evaluated for impairment			11,079				5,498				3,544							20,121
Ending balance of acquired loans individually evaluated for impairment			5,675				-				-							5,675
Ending balance of acquired loans collectively evaluated for impairment			327,656				147,256				266,747							741,659
Ending balance of originated loans collectively evaluated for impairment		$	2,129,292			$	1,853,226			$	845,298						$	4,827,816
As of December 31, 2013
Allowance for loan losses		$	35,090			$	27,694			$	6,520			$	130		$	69,434
Allowance for loans individually evaluated for impairment			715				-				-							715
Allowance for loans collectively evaluated for impairment		$	34,375			$	27,694			$	6,520			$	130		$	68,719
Ending balance of loans		$	2,392,621			$	1,972,537			$	1,041,637						$	5,406,795
Ending balance of originated loans individually evaluated for impairment			16,120				3,248				2,012							21,380
Ending balance of acquired loans individually evaluated for impairment			10,060				-				-							10,060
Ending balance of acquired loans collectively evaluated for impairment			392,329				219,587				308,416							920,332
Ending balance of originated loans collectively evaluated for impairment		$	1,974,112			$	1,749,702			$	731,209						$	4,455,023
The following table illustrates the Company’s nonaccrual loans by loan class as of December 31, 2014 and 2013:
(In thousands)		31-Dec-14				31-Dec-13
ORIGINATED
Commercial Loans
Commercial		$	1,012			$	3,669
Commercial Real Estate			4,127				7,834
Agricultural			817				1,135
Agricultural Real Estate			565				961
Business Banking			6,910				5,701
			13,431				19,300
Consumer Loans
Indirect			1,964				1,461
Home Equity			6,596				5,931
Direct			84				86
			8,644				7,478
Residential Real Estate Mortgages			8,770				7,105
		$	30,845			$	33,883
ACQUIRED
Commercial Loans
Commercial		$	3,009			$	6,599
Commercial Real Estate			2,666				3,559
Business Banking			665				1,340
			6,340				11,498
Consumer Loans
Indirect			106				93
Home Equity			557				570
Direct			33				49
			696				712
Residential Real Estate Mortgages			3,193				3,872
		$	10,229			$	16,082
TOTAL NONACCRUAL LOANS		$	41,074			$	49,965
The following table sets forth information with regard to past due and nonperforming loans by loan class:
Age Analysis of Past Due Financing Receivables
As of December 31, 2014
(in thousands)
		31-60 Days				61-90 Days				Greater				Total			Non-Accrual				Current		Recorded Total
		Past Due				Past Due				Than				Past Due									Loans
		Accruing				Accruing				90 Days				Accruing
										Past Due
										Accruing
ORIGINATED
Commercial Loans
Commercial		$	-			$	735			$	-			$	735		$	1,012			$	613,400	$	615,147
Commercial Real Estate			192				-				-				192			4,127				1,064,549		1,068,868
Agricultural			-				-				-				-			817				32,130		32,947
Agricultural Real Estate			19				-				-				19			565				24,390		24,974
Business Banking			799				235				84				1,118			6,910				390,407		398,435
			1,010				970				84				2,064			13,431				2,124,876		2,140,371
Consumer Loans
Indirect			16,434				3,154				1,991				21,579			1,964				1,286,507		1,310,050
Home Equity			4,591				1,428				821				6,840			6,596				479,444		492,880
Direct			560				157				52				769			84				54,941		55,794
			21,585				4,739				2,864				29,188			8,644				1,820,892		1,858,724
Residential Real Estate Mortgages			2,901				96				1,256				4,253			8,770				835,819		848,842
		$	25,496			$	5,805			$	4,204			$	35,505		$	30,845			$	4,781,587	$	4,847,937
ACQUIRED
Commercial Loans
Commercial		$	-			$	-			$	-			$	-		$	3,009			$	72,255	$	75,264
Commercial Real Estate			-				-				-				-			2,666				197,222		199,888
Business Banking			5				15				-				20			665				57,494		58,179
			5				15				-				20			6,340				326,971		333,331
Consumer Loans
Indirect			518				5				54				577			106				64,540		65,223
Home Equity			190				60				5				255			557				75,904		76,716
Direct			31				-				7				38			33				5,246		5,317
			739				65				66				870			696				145,690		147,256
Residential Real Estate Mortgages			1,162				265				671				2,098			3,193				261,456		266,747
		$	1,906			$	345			$	737			$	2,988		$	10,229			$	734,117	$	747,334
Total Loans		$	27,402			$	6,150			$	4,941			$	38,493		$	41,074			$	5,515,704	$	5,595,271
Age Analysis of Past Due Financing Receivables
As of December 31, 2013
(in thousands)
		31-60 Days				61-90 Days				Greater				Total			Non-Accrual				Current		Recorded Total
		Past Due				Past Due				Than				Past Due									Loans
		Accruing				Accruing				90 Days				Accruing
										Past Due
										Accruing
ORIGINATED
Commercial Loans
Commercial		$	105			$	247			$	-			$	352		$	3,669			$	612,402	$	616,423
Commercial Real Estate			1,366				-				-				1,366			7,834				925,116		934,316
Agricultural			150				21				-				171			1,135				63,856		65,162
Agricultural Real Estate			519				-				-				519			961				35,172		36,652
Business Banking			1,228				122				105				1,455			5,701				330,523		337,679
			3,368				390				105				3,863			19,300				1,967,069		1,990,232
Consumer Loans
Indirect			14,093				2,878				1,583				18,554			1,461				1,141,829		1,161,844
Home Equity			6,033				1,888				1,115				9,036			5,931				517,856		532,823
Direct			679				125				46				850			86				57,347		58,283
			20,805				4,891				2,744				28,440			7,478				1,717,032		1,752,950
Residential Real Estate Mortgages			3,951				379				808				5,138			7,105				720,978		733,221
		$	28,124			$	5,660			$	3,657			$	37,441		$	33,883			$	4,405,079	$	4,476,403
ACQUIRED
Commercial Loans
Commercial		$	24			$	-			$	-			$	24		$	6,599			$	96,603	$	103,226
Commercial Real Estate			-				-				-				-			3,559				225,455		229,014
Business Banking			320				2				-				322			1,340				68,487		70,149
			344				2				-				346			11,498				390,545		402,389
Consumer Loans
Indirect			939				113				71				1,123			93				123,870		125,086
Home Equity			753				63				-				816			570				85,690		87,076
Direct			76				56				9				141			49				7,235		7,425
			1,768				232				80				2,080			712				216,795		219,587
Residential Real Estate Mortgages			1,725				-				-				1,725			3,872				302,819		308,416
		$	3,837			$	234			$	80			$	4,151		$	16,082			$	910,159	$	930,392
Total Loans		$	31,961			$	5,894			$	3,737			$	41,592		$	49,965			$	5,315,238	$	5,406,795
There were no material commitments to extend further credit to borrowers with nonperforming loans.
The methodology used to establish the allowance for loan losses on impaired loans incorporates specific allocations on loans analyzed individually.  Classified loans, including all TDRs and nonaccrual commercial loans that are graded substandard or below, with outstanding balances of $500 thousand or more are evaluated for impairment through the Company’s quarterly status review process.  In determining that we will be unable to collect all principal and interest payments due in accordance with the contractual terms of the loan agreements, we consider factors such as payment history and changes in the financial condition of individual borrowers, local economic conditions, historical loss experience and the conditions of the various markets in which the collateral may be liquidated.  For loans that are evaluated for impairment, impairment is measured by one of three methods: 1) the fair value of collateral less cost to sell, 2) present value of expected future cash flows or 3) the loan’s observable market price.  These impaired loans are reviewed on a quarterly basis for changes in the measurement of impairment.  For impaired loans measured using the present value of expected cash flow method, any change to the previously recognized impairment loss is recognized as a change to the allowance account and recorded in the consolidated statement of income as a component of the provision for credit losses.
The following provides additional information on loans specifically evaluated for impairment for the years ended December 31, 2014 and 2013
Impaired Loans
		31-Dec-14												31-Dec-13
(in thousands)		Recorded				Unpaid			Related					Recorded			Unpaid			Related
		Investment				Principal			Allowance					Investment			Principal			Allowance
		Balance				Balance								Balance			Balance
		(Book)				(Legal)								(Book)			(Legal)
ORIGINATED
With no related allowance recorded:
Commercial Loans
Commercial		$	1,748			$	1,901							$	4,721		$	4,777
Commercial Real Estate			4,505				4,520								4,613			5,164
Agricultural			20				26								125			195
Agricultural Real Estate			1,147				1,441								1,431			1,708
Business Banking			896				1,301								210			602
Total Commercial Loans			8,316				9,189								11,100			12,446
Consumer Loans
Home Equity			5,498				6,033								3,248			3,472
Residential Real Estate Mortgages			3,544				3,959								2,012			2,255
Total			17,358				19,181								16,360			18,173
With an allowance recorded:
Commercial Loans
Commercial Real Estate			2,763				4,611				600				5,020			6,877				715
ACQUIRED
With no related allowance recorded:
Commercial Loans
Commercial			-				-								6,501			6,538
Commercial Real Estate			2,666				3,830								3,559			3,842
Total Commercial Loans			2,666				3,830								10,060			10,380
With an  allowance recorded:
Commercial Loans
Commercial			3,009				4,668				500				-			-				-
Total		$	25,796			$	32,290			$	1,100			$	31,440		$	35,430			$	715
The following table summarizes the average recorded investments on loans specifically evaluated for impairment and the interest income recognized for the years ended December 31, 2014, 2013 and 2012:
		31-Dec-14								31-Dec-13							31-Dec-12
(in thousands)		Average				Interest Income				Average				Interest Income			Average				Interest Income
		Recorded				Recognized				Recorded				Recognized			Recorded				Recognized
		Investment				Accrual				Investment				Accrual			Investment				Accrual
ORIGINATED
Commercial Loans
Commercial		$	1,954			$	115			$	3,488			$	-		$	6,682			$	56
Commercial Real Estate			9,679				169				11,085				95			4,944				230
Agricultural			91				1				1,035				1			1,767				43
Agricultural Real Estate			1,346				46				1,067				47			922				72
Business Banking			610				55				127				61			68				65
Consumer Loans
Home Equity			5,198				267				3,120				145			1,877				123
Residential Real Estate Mortgages			3,039				119				2,085				69			1,143				54
ACQUIRED
Commercial Loans
Commercial			5,756				-				-				-			-				-
Commercial Real Estate			3,386				-				1,310				-			-				-
Total		$	31,059			$	772			$	23,317			$	418		$	17,403			$	643
While we continue to adhere to prudent underwriting standards, as a lender we may be adversely impacted by general economic weaknesses and, in particular, a sharp downturn in the housing market nationally.  Decreases in real estate values could adversely affect the value of property used as collateral for our loans.  Adverse changes in the economy may have a negative effect on the ability of our borrowers to make timely loan payments, which would have an adverse impact on our earnings.  A further increase in loan delinquencies would decrease our net interest income and adversely impact our loan loss experience, causing increases in our provision and allowance for loan losses.
The Company has developed an internal loan grading system to evaluate and quantify the Bank’s loan portfolio with respect to quality and risk.  The system focuses on, among other things, financial strength of borrowers, experience and depth of management, primary and secondary sources of repayment, payment history, nature of the business, outlook on particular industries.  The internal grading system enables the Company to monitor the quality of the entire loan portfolio on a continuous basis and provide management with an early warning system, enabling recognition and response to problem loans and potential problem loans.
Commercial Grading System
For commercial and agricultural loans, the Company uses a grading system that relies on quantifiable and measurable characteristics when available.  This would include comparison of financial strength to available industry averages, comparison of transaction factors (loan terms and conditions) to loan policy, and comparison of credit history to stated repayment terms and industry averages. Some grading factors are necessarily more subjective such as economic and industry factors, regulatory environment, and management.  The grading system for commercial and agricultural loans is as follows:
	●	Doubtful
A doubtful loan has a high probability of total or substantial loss, but because of specific pending events that may strengthen the asset, its classification as loss is deferred. Doubtful borrowers are usually in default, lack adequate liquidity or capital, and lack the resources necessary to remain an operating entity. Pending events can include mergers, acquisitions, liquidations, capital injections, the perfection of liens on additional collateral, the valuation of collateral, and refinancing. Generally, pending events should be resolved within a relatively short period and the ratings will be adjusted based on the new information. Because of high probability of loss, nonaccrual treatment is required for doubtful assets.
	●	Substandard
Substandard loans have a high probability of payment default, or they have other well-defined weaknesses. They require more intensive supervision by bank management. Substandard loans are generally characterized by current or expected unprofitable operations, inadequate debt service coverage, inadequate liquidity, or marginal capitalization. Repayment may depend on collateral or other credit risk mitigants. For some substandard loans, the likelihood of full collection of interest and principal may be in doubt and should be placed on nonaccrual. Although substandard assets in the aggregate will have a distinct potential for loss, an individual asset’s loss potential does not have to be distinct for the asset to be rated substandard.
●        Special Mention
Special Mention loans have potential weaknesses that may, if not checked or corrected, weaken the asset or inadequately protect the Company’s position at some future date. These loans pose elevated risk, but their weakness does not yet justify a substandard classification. Borrowers may be experiencing adverse operating trends (declining revenues or margins) or may be struggling with an ill-proportioned balance sheet (e.g., increasing inventory without an increase in sales, high leverage, tight liquidity). Adverse economic or market conditions, such as interest rate increases or the entry of a new competitor, may also support a special mention rating. Although a Special Mention loan has a higher probability of default than a pass asset, its default is not imminent.
●        Pass
Loans graded as Pass encompass all loans not graded as Doubtful, Substandard, or Special Mention.  Pass loans are in compliance with loan covenants, and payments are generally made as agreed.  Pass loans range from superior quality to fair quality.
Business Banking Grading System
Business Banking loans are graded as either Classified or Non-classified:
●        Classified
Classified loans are inadequately protected by the current worth and paying capacity of the obligor or, if applicable, the collateral pledged.   These loans have a well-defined weakness, or weaknesses, that jeopardize the liquidation of the debt, or in some cases make collection or liquidation in full, on the basis of currently existing facts, conditions, and values, highly questionable and improbable. They are characterized by the distinct possibility that the Company will sustain some loss if the deficiencies are not corrected. Classified loans have a high probability of payment default, or a high probability of total or substantial loss.  These loans require more intensive supervision by management and are generally characterized by current or expected unprofitable operations, inadequate debt service coverage, inadequate liquidity, or marginal capitalization.  Repayment may depend on collateral or other credit risk mitigants.  When the likelihood of full collection of interest and principal may be in doubt; classified loans are considered to have a nonaccrual status.   In some cases, classified loans are considered uncollectible and of such little value that their continuance as assets is not warranted.
●       Non-classified
Loans graded as Non-classified encompass all loans not graded as Classified.  Non-classified loans are in compliance with loan covenants, and payments are generally made as agreed.
Consumer and Residential Mortgage Grading System
Consumer and Residential Mortgage loans are graded as either Performing or Nonperforming.   Nonperforming loans are loans that are 1) over 90 days past due and interest is still accruing or 2) on nonaccrual status.  All loans not meeting any of these three criteria are considered Performing.
The following tables illustrate the Company’s credit quality by loan class for the years ended December 31, 2014 and 2013:
Credit Quality Indicators
31-Dec-14
(In thousands)
ORIGINATED
Commercial Credit Exposure
By Internally Assigned Grade:	Commercial			Commercial			Agricultural			Agricultural			Total
				Real Estate						Real Estate
Pass	$	$570,884		$	1,023,856		$	30,481		$	23,443		$	1,648,664
Special Mention		6,022			17,341			275			42			23,680
Substandard		38,241			27,671			2,183			1,489			69,584
Doubtful		-			-			8			-			8
Total	$	615,147		$	1,068,868		$	32,947		$	24,974		$	1,741,936
Business Banking Credit Exposure
By Internally Assigned Grade:	Business Banking									Total
Non-classified	$	379,445								$	379,445
Classified		18,990									18,990
Total	$	398,435								$	398,435
Consumer Credit Exposure
By Payment Activity:	Indirect			Home Equity			Direct			Total
Performing	$	1,306,095		$	485,463		$	55,658		$	1,847,216
Nonperforming		3,955			7,417			136			11,508
Total	$	1,310,050		$	492,880		$	55,794		$	1,858,724
Residential Mortgage Credit Exposure
By Payment Activity:	Residential			Total
	Mortgage
Performing	$	838,816		$	838,816
Nonperforming		10,026			10,026
Total	$	848,842		$	848,842
Credit Quality Indicators
31-Dec-14
(In thousands)
ACQUIRED
Commercial Credit Exposure
By Internally Assigned Grade:	Commercial			Commercial			Agricultural			Total
				Real Estate
Pass	$	63,630		$	186,036		$	-		$	249,666
Special Mention		2,840			2,646			-			5,486
Substandard		8,794			11,206			-			20,000
Doubtful		-			-			-			-
Total	$	75,264		$	199,888		$	-		$	275,152
Business Banking Credit Exposure
By Internally Assigned Grade:	Business Banking			Total
Non-classified	$	53,264		$	53,264
Classified		4,915			4,915
Total	$	58,179		$	58,179
Consumer Credit Exposure
By Payment Activity:	Indirect			Home Equity			Direct			Total
Performing	$	65,063		$	76,154		$	5,277		$	146,494
Nonperforming		160			562			40			762
Total	$	65,223		$	76,716		$	5,317		$	147,256
Residential Mortgage Credit Exposure
By Payment Activity:	Residential Mortgage			Total
Performing	$	262,883		$	262,883
Nonperforming		3,864			3,864
Total	$	266,747		$	266,747
Credit Quality Indicators
31-Dec-13
(In thousands)
Commercial Credit Exposure
By Internally Assigned Grade:		Commercial				Commercial				Agricultural				Agricultural			Total
						Real Estate								Real Estate
Pass		$	576,079			$	878,411			$	60,043			$	33,136		$	1,547,669
Special Mention			16,836				22,777				381				43			40,037
Substandard			23,508				33,128				4,726				3,473			64,835
Doubtful			-				-				12				-			12
Total		$	616,423			$	934,316			$	65,162			$	36,652		$	1,652,553
Business Banking Credit Exposure
By Internally Assigned Grade:	Business Banking									Total
Non-classified	$	319,578								$	319,578
Classified		18,101									18,101
Total	$	337,679								$	337,679
Consumer Credit Exposure
By Payment Activity:	Indirect			Home Equity			Direct			Total
Performing	$	1,158,800		$	525,777		$	58,151		$	1,742,728
Nonperforming		3,044			7,046			132			10,222
Total	$	1,161,844		$	532,823		$	58,283		$	1,752,950
Residential Mortgage Credit Exposure
By Payment Activity:	Residential			Total
	Mortgage
Performing	$	725,308		$	725,308
Nonperforming		7,913			7,913
Total	$	733,221		$	733,221
Credit Quality Indicators
31-Dec-13
(In thousands)
ACQUIRED
Commercial Credit Exposure
By Internally Assigned Grade:	Commercial			Commercial			Agricultural			Total
				Real Estate
Pass	$	85,692		$	205,010		$	-		$	290,702
Special Mention		2,230			6,183			-			8,413
Substandard		15,304			17,821			-			33,125
Doubtful		-			-			-			-
Total	$	103,226		$	229,014		$	-		$	332,240
Business Banking Credit Exposure
By Internally Assigned Grade:	Business Banking			Total
Non-classified	$	65,437		$	65,437
Classified		4,712			4,712
Total	$	70,149		$	70,149
Consumer Credit Exposure
By Payment Activity:	Indirect			Home Equity			Direct			Total
Performing	$	124,922		$	86,506		$	7,367		$	218,795
Nonperforming		164			570			58			792
Total	$	125,086		$	87,076		$	7,425		$	219,587
Residential Mortgage Credit Exposure
By Payment Activity:	Residential Mortgage			Total
Performing	$	304,544		$	304,544
Nonperforming		3,872			3,872
Total	$	308,416		$	308,416
Troubled Debt Restructuring
Troubled debt restructurings made during the year ended December 31, 2014 consisted of three business banking loans totaling $0.9 million, 9 home equity loans totaling $0.3 million, one indirect consumer loan totaling less than $0.1 million, 47 direct consumer loans totaling $3.0 million and 27 residential real estate mortgages totaling $2.7 million.  During the year ended December 31, 2014, there was one indirect consumer loan classified as TDRs totaling less than $0.1 million, one home equity loan classified as a TDR totaling less than $0.1 million, 5 direct consumer loans classified as TDRs totaling $0.2 million, and six residential real estate mortgages classified as TDRs totaling $0.4 million that subsequently defaulted on their renegotiated terms.
Troubled debt restructurings made during the year ended December 31, 2013 consisted of four commercial loans totaling $7.0 million, 23 home equity loans totaling $1.0 million, and six residential real estate mortgages totaling $0.5 million.  During the year ended December 31, 2013, there was one commercial loan classified as a TDR totaling $0.9 million and eight home equity loans classified as TDRs totaling $0.4 million that subsequently defaulted on their renegotiated terms.
Substantially all modifications include one or a combination of the following: an extension of the maturity date at a stated rate of interest lower than the current market rate for new debt with similar risk; temporary reduction in the interest rate; or change in scheduled payment amount.

Premises_and_Equipment_Net

Premises and Equipment, Net	12 Months Ended
	Dec. 31, 2014
Premises and Equipment, Net [Abstract]
Premises and Equipment, Net	(6) Premises and Equipment, Net
	A summary of premises and equipment follows:
		December 31,
	(In thousands)	2014		2013
	Land, buildings, and improvements	$	122,400	$	120,098
	Equipment		58,835		55,729
	Premises and equipment before accumulated depreciation		181,235		175,827
	Accumulated depreciation		91,977		87,500
	Total premises and equipment	$	89,258	$	88,327
	Buildings and improvements are depreciated based on useful lives of 15 to 40 years.  Equipment is depreciated based on useful lives of three to ten years.
	Rental expense included in occupancy expense amounted to $8.0 million in 2014, $7.5 million in 2013, and $6.4 million in 2012. The future minimum rental payments related to noncancelable operating leases with original terms of one year or more are as follows at December 31, 2014 (in thousands):
	Future Minimum Rental Payments
	2015	$	7,369
	2016		7,215
	2017		6,811
	2018		6,122
	2019		5,655
	Thereafter		26,257
	Total	$	59,429

Goodwill_and_other_Intangible_

Goodwill and other Intangible Assets	12 Months Ended
	Dec. 31, 2014
Goodwill and other Intangible Assets [Abstract]
Goodwill and other Intangible Assets	(7) Goodwill and Other Intangible Assets
	A summary of goodwill is as follows:
	(In thousands)
	1-Jan-14	$	264,997
	Goodwill Adjustments		(1,363	)
	31-Dec-14	$	263,634
	1-Jan-13	$	152,373
	Goodwill Acquired		112,624
	31-Dec-13	$	264,997
	The Company has intangible assets with definite useful lives capitalized on its consolidated balance sheet in the form of core deposit and other identified intangible assets.  These intangible assets are amortized over their estimated useful lives, which range primarily from one to twelve years.
	A summary of core deposit and other intangible assets follows:
		December 31,
	(In thousands)	2014			2013
	Core deposit intangibles
	Gross carrying amount	$	19,401		$	19,401
	Less: accumulated amortization		12,522			10,083
	Net carrying amount		6,879			9,318
	Identified intangible assets
	Gross carrying amount		28,316			28,509
	Less: accumulated amortization		14,878			12,270
	Net carrying amount		13,438			16,239
	Total intangibles
	Gross carrying amount		47,717			47,910
	Less: accumulated amortization		27,400			22,353
	Net carrying amount	$	20,317		$	25,557
	Amortization expense on intangible assets with definite useful lives totaled $5.0 million for 2014, $4.9 million for 2013 and $3.4 million for 2012.  Amortization expense on intangible assets with definite useful lives is expected to total $4.8 million for 2015, $3.3 million for 2016, $2.8 million for 2017, $2.2 million for 2018, $1.7 million for 2019 and $3.7million thereafter.  Other identified intangible assets include customer lists, non-competes, and trademark intangibles, of which $1.8 million will not amortize.

Deposits

Deposits	12 Months Ended
	Dec. 31, 2014
Deposits [Abstract]
Deposits	(8)  Deposits
	The following table sets forth the maturity distribution of time deposits at December 31, 2014 (in thousands):
	Time deposits
	Within one year	$	464,853
	After one but within two years		132,999
	After two but within three years		143,142
	After three but within four years		80,804
	After four but within five years		204,492
	After five years		17,533
	Total	$	1,043,823
	Time deposits of $100,000 or more aggregated $269.8 million and $375.4 million December 31, 2014 and 2013, respectively.

ShortTerm_Borrowings

Short-Term Borrowings	12 Months Ended
	Dec. 31, 2014
Short-Term Borrowings [Abstract]
Short-Term Borrowings	(9) Short-Term Borrowings
	Short-term borrowings totaled $316.8 million and $456.0 million at December 31, 2014 and 2013, respectively, and consist of Federal funds purchased and securities sold under repurchase agreements, which generally represent overnight borrowing transactions, and other short-term borrowings, primarily FHLB advances, with original maturities of one year or less.
	The Company had unused lines of credit with the FHLB available for short-term financing of approximately $958 million and $497 million at December 31, 2014 and 2013, respectively. Borrowings on these lines are secured by FHLB stock, certain securities and one-to-four family first lien mortgage loans. Securities collateralizing repurchase agreements are held in safekeeping by nonaffiliated  financial  institutions and are under the Company’s control.
	Information related to short-term borrowings is summarized as follows:
	(In thousands)	2014			2013			2012
	Federal funds purchased
	Balance at year-end	$	68,000		$	130,000		$	10,000
	Average during the year		110,154			39,907			12,658
	Maximum month end balance		183,000			130,000			60,000
	Weighted average rate during the year		0.29	%		0.26	%		0.27	%
	Weighted average rate at December 31		0.34	%		0.18	%		0.27	%
	Securities sold under repurchase agreements
	Balance at year-end	$	148,802		$	176,042		$	152,941
	Average during the year		165,858			169,352			153,084
	Maximum month end balance		182,861			185,871			165,977
	Weighted average rate during the year		0.06	%		0.06	%		0.1	%
	Weighted average rate at December 31		0.06	%		0.05	%		0.1	%
	Other short-term borrowings
	Balance at year-end	$	100,000		$	150,000		$	-
	Average during the year		106,438			71,589			-
	Maximum month end balance		320,000			210,000			-
	Weighted average rate during the year		0.4	%		0.43	%		0	%
	Weighted average rate at December 31		0.36	%		0.55	%		0	%
	See Note 3 for additional information regarding securities pledged as collateral for securities sold under the repurchase agreements.

LongTerm_Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2014
Long-Term Debt [Abstract]
Long-Term Debt	(10) Long-Term Debt
	Long-term debt consists of obligations having an original maturity at issuance of more than one year. A majority of the Company’s long-term debt is comprised of FHLB advances collateralized by the FHLB stock owned by the Company, certain of its mortgage-backed securities and a blanket lien on its residential real estate mortgage loans.  A summary as of December 31, 2014 and 2013 is as follows:
	(In thousands)	As of December 31, 2014										As of December 31, 2013
	Maturity	Amount		Weighted Average Rate			Callable Amount		Weighted Average Rate			Amount		Weighted Average Rate			Callable Amount		Weighted Average Rate
	2014		-		-			-		-			12,460		1.33	%		-		-
	2015		217		-			-		-			308		-			-		-
	2016		50,626		2.91	%		30,000		4.15	%		90,313		3.52	%		70,000		4.21	%
	2017		40,000		2.68	%		25,000		3.48	%		115,312		3.55	%		75,000		3.73	%
	2018		40,000		2.57	%		25,000		3.15	%		90,313		3.26	%		75,000		3.61	%
	2021		102		4	%		-		-			117		4	%		-		-
		$	130,945				$	80,000				$	308,823				$	220,000

Junior_Subordinated_Debt

Junior Subordinated Debt	12 Months Ended
	Dec. 31, 2014
Junior Subordinated Debt [Abstract]
Junior Subordinated Debt	(11) Junior Subordinated Debt
	The Company sponsors five business trusts, CNBF Capital Trust I, NBT Statutory Trust I, NBT Statutory Trust II, Alliance Financial Capital Trust I and Alliance Financial Capital Trust II.  The trusts were formed for the purpose of issuing company-obligated mandatorily redeemable preferred securities to third-party investors and investing in the proceeds from the sale of such preferred securities solely in junior subordinated debt securities of the Company.  The debentures held by each trust are the sole assets of that trust.  These five statutory business trusts are collectively referred herein to as “the Trusts.”  The Company guarantees, on a limited basis, payments of distributions on the trust preferred securities and payments on redemption of the trust preferred securities.  The Trusts are variable interest entities (“VIEs”) for which the Company is not the primary beneficiary, as defined by U.S. GAAP.  In accordance with U.S. GAAP, the accounts of the Trusts are not included in the Company’s consolidated financial statements. See Note 1 — Summary of Significant Accounting Policies for additional information about the Company’s consolidation policy.
	As of December 31, 2014, the Trusts had the following issues of trust preferred debentures, all held by the Trusts, outstanding (dollars in thousands):
	Description	Issuance Date	Trust Preferred Securities Outstanding		Interest Rate	Trust Preferred Debt Owed To Trust		Final Maturity Date
	CNBF Capital Trust I	August 1999	$	18,000	3-month LIBOR plus 2.75%	$	18,720	Aug-29
	NBT Statutory Trust I	November 2005		5,000	3-month LIBOR plus 1.40%		5,155	Dec-35
	NBT Statutory Trust II	Feb-06		50,000	3-month LIBOR plus 1.40%		51,547	Mar-36
	Alliance Financial Capital Trust I	Dec-03		10,000	3-month LIBOR plus 2.85%		10,310	Jan-34
	Alliance Financial Capital Trust II	Sep-06		15,000	3-month LIBOR plus 1.65%		15,464	Sep-36
	The Company’s junior subordinated debentures include amounts related to the Company’s NBT Statutory Trust I and II as well as junior subordinated debentures associated with one statutory trust affiliates that were acquired from our merger with CNB Financial Corp. and two statutory trusts acquired from Alliance (the “Trusts”). The Trusts qualify as variable interest entities and were formed to issue mandatorily redeemable trust preferred securities to investors and loan the proceeds to us for general corporate purposes. The Trusts hold, as their sole assets, junior subordinated debentures of the Company with face amounts totaling $98 million at December 31, 2014. The Company owns all of the common securities of the Trusts and have accordingly recorded $3.2 million in equity method investments classified as other assets in our Consolidated Balance Sheets at December 31, 2014. The Company owns all of the common stock of the Trusts, which have issued trust preferred securities in conjunction with the Company issuing trust preferred debentures to the Trusts. The terms of the trust preferred debentures are substantially the same as the terms of the trust preferred securities.
	The Company’s junior subordinated debentures are redeemable prior to the maturity date at our option upon each trust’s stated option repurchase dates, and from time to time thereafter. These debentures are also redeemable in whole at any time upon the occurrence of specific events defined within the trust indenture. Our obligations under the debentures and related documents, taken together, constitute a full and unconditional guarantee by the Company of the issuers’ obligations under the trust preferred securities.  The Company owns all of the common stock of the Trusts, which have issued trust preferred securities in conjunction with the Company issuing trust preferred debentures to the Trusts. The terms of the trust preferred debentures are substantially the same as the terms of the trust preferred securities.
	With respect to the Trusts, the Company has the right to defer payments of interest on the debentures issued to the Trusts at any time or from time to time for a period of up to ten consecutive semi-annual periods with respect to each deferral period. Under the terms of the debentures, if in certain circumstances there is an event of default under the debentures or the Company elects to defer interest on the debentures, the Company may not, with certain exceptions, declare or pay any dividends or distributions on its capital stock or purchase or acquire any of its capital stock.
	Despite the fact that the Trusts are not included in the Company’s consolidated financial statements, $97 million of the $101 million in trust preferred securities issued by these subsidiary trusts is included in the Tier 1 capital of the Company for regulatory capital purposes as allowed by the Federal Reserve Board (NBT Bank owns $1.0 million of CNBF Trust I securities).  The Dodd-Frank Act requires bank holding companies with assets greater than $500 million to be subject to the same capital requirements as insured depository institutions, meaning, for instance, that such bank holding companies will not be able to count trust preferred securities issued after May 19, 2010 as Tier 1 capital.  The aforementioned Trusts are grandfathered with respect to this enactment based on their date of issuance.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Taxes [Abstract]
Income Taxes	(12) Income Taxes
	The significant components of income tax expense attributable to operations are:
		Years ended December 31,
	(In thousands)	2014			2013			2012
	Current
	Federal	$	26,059		$	23,536		$	21,011
	State		2,823			2,316			1,815
			28,882			25,852			22,826
	Deferred
	Federal		6,648			2,334			(13	)
	State		1,699			10			3
			8,347			2,344			(10	)
	Total income tax expense	$	37,229		$	28,196		$	22,816
	Not included in the above table are items that were recorded to stockholders’ equity of approximately $(1.1) million, $7.0 million, and $(0.1) million for 2014, 2013, and 2012, respectively, relating to deferred taxes on the unrealized (gain) loss on available for sale securities, tax benefits recognized with respect to stock options exercised, and deferred taxes related to pension plans.
	The tax effects of temporary differences that give rise to significant portions of the deferred tax assets and deferred tax liabilities are as follows:
		December 31,
	(In thousands)	2014			2013
	Deferred tax assets
	Allowance for loan losses	$	25,689		$	26,729
	Deferred compensation		8,744			7,931
	Postretirement benefit obligation		2,377			2,596
	Unrealized losses on securities available for sale		-			5,900
	Accrued liabilities		1,778			3,265
	Stock-based compensation expense		6,457			7,862
	Equipment leasing		1,416			1,661
	Other		1,325			2,125
	Total deferred tax assets		47,786			58,069
	Deferred tax liabilities
	Pension and executive retirement		12,192			17,417
	Fair value adjustments from acquisitions		1,243			2,070
	Unrealized gains on securities available for sale		1,331			-
	Premises and equipment, primarily due to accelerated depreciation		2,491			2,270
	Deferred loan costs		1,460			1,624
	Intangible amortization		14,162			12,007
	Other		390			892
	Total deferred tax liabilities		33,269			36,280
	Net deferred tax asset at year-end		14,517			21,789
	Net deferred tax asset at beginning of year		21,789			11,115
	(Decrease) Increase in net deferred tax asset	$	(7,272	)	$	10,674
	Realization of deferred tax assets is dependent upon the generation of future taxable income or the existence of sufficient taxable income within the available carryback period.  A valuation allowance is provided when it is more likely than not that some portion of the deferred tax asset will not be realized.  Based on available evidence, gross deferred tax assets will ultimately be realized and a valuation allowance was not deemed necessary at December 31, 2014 and 2013.
	At December 31, 2014, 2013, and 2012 the Company had no ASC 740-10 unrecognized tax benefits.   The Company does not expect the total amount of unrecognized tax benefits to significantly increase within the next twelve months.   During 2012 there was a reduction of reserves for Federal tax benefits for expiration of the statute of limitations of prior years’ tax filings.  As a result, unrecognized tax benefits were reduced $0.9 million for 2012 with a reduction of tax expense of $0.8 million in 2012.
	The Company is no longer subject to U.S. Federal tax examination by tax authorities for years prior to 2010 and New York State for years prior to 2010.  The Company recognizes interest expense penalties related to unrecognized tax benefits, if any, in income tax expense.
	The following is a reconciliation of the provision for income taxes to the amount computed by applying the applicable Federal statutory rate of 35 % to income before taxes:
		Years ended December 31
	(In thousands)	2014			2013			2012
	Federal income tax at statutory rate	$	39,306		$	31,482		$	27,081
	Tax exempt income		(2,250	)		(2,433	)		(2,536	)
	Net increase in CSV of life insurance		(1,734	)		(1,166	)		(908	)
	Low income housing tax credits		(880	)		(819	)		(629	)
	State taxes, net of federal tax benefit		2,939			1,512			1,182
	Other, net		(152	)		(380	)		(1,374	)
	Income tax expense	$	37,229		$	28,196		$	22,816

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2014
Employee Benefit Plans [Abstract]
Employee Benefit Plans	(13) Employee Benefit Plans
	Defined Benefit Postretirement Plans
	The Company has a qualified, noncontributory, defined benefit pension plan (“the Plan”) covering substantially all of its employees at December 31, 2014. Benefits paid from the plan are based on age, years of service, compensation, social security benefits, and are determined in accordance with defined formulas. The Company’s policy is to fund the pension plan in accordance with ERISA standards. Assets of the plan are invested in bonds and publicly traded stocks and mutual funds. Prior to January 1, 2000, the Plan was a traditional defined benefit plan based on final average compensation.  On January 1, 2000, the Plan was converted to a cash balance plan with grandfathering provisions for existing participants.  Effective March 1, 2013, the pension plan was amended.  Benefit accruals for participants who, as of January 1, 2000, elected to continue participating in the traditional defined benefit plan design were frozen as of March 1, 2013.
	The Company assumed a noncontributory, defined benefit pension plan in the Alliance acquisition.  This plan covers certain Alliance full-time employees who met eligibility requirements on October 6, 2006, at which time all benefits were frozen.  Under this plan, retirement benefits are primarily a function of both the years of service and the level of compensation.  Effective May 1, 2013, this plan was merged into the Plan.  The merging of the plans required a valuation as of the merger date and resulted in a $2.4 million adjustment to accumulated other comprehensive income in 2013.  The merging of the plans did not have a significant impact on the Company’s financial statements and related footnotes.
	In addition to the Plan, the Company provides supplemental employee retirement plans to certain current and former executives.  The Company also assumed supplemental retirement plans for certain current and former executives in the Alliance acquisition.
	The supplemental employee retirement plans and the defined benefit pension plan are collectively referred to herein as “Pension Benefits.”
	Also, the Company provides certain health care benefits for retired employees.  Benefits are accrued over the employees’ active service period. Only employees that were employed by NBT Bank on or before January 1, 2000 are eligible to receive postretirement health care benefits.  The plan is contributory for participating retirees, requiring participants to absorb certain deductibles and coinsurance amounts with contributions adjusted annually to reflect cost sharing provisions and benefit limitations called for in the plan. Employees become eligible for these benefits if they reach normal retirement age while working for the Company.  For eligible employees described above, the Company funds the cost of postretirement health care as benefits are paid. The Company elected to recognize the transition obligation on a delayed basis over twenty years.  In addition, the Company assumed post-retirement medical life insurance benefits for certain Alliance employees, retirees and their spouses, if applicable, in the Alliance acquisition.  These postretirement benefits are referred to herein as “Other Benefits.”
	Accounting standards require an employer to: (1) recognize the overfunded or underfunded status of defined benefit postretirement plans, which is measured as the difference between plan assets at fair value and the benefit obligation, as an asset or liability in its balance sheet; (2) recognize changes in that funded status in the year in which the changes occur through comprehensive income; and (3) measure the defined benefit plan assets and obligations as of the date of its year-end balance sheet.
	The components of accumulated other comprehensive loss, which have not yet been recognized as components of net periodic benefit cost, related to pensions and other postretirement benefits at December 31, 2014 are summarized below.
	The Company expects that $2.4 million in net actuarial loss and $0.2 million in prior service costs will be recognized as components of net periodic benefit cost in 2015.
		Pension Benefits								Other Benefits
	(In thousands)	2014				2013				2014				2013
	Net actuarial loss		$	28,767			$	11,286			$	2,929			$	1,628
	Prior service cost			97				118				(314	)			(521	)
	Total amounts recognized in accumulated other comprehensive loss (pre-tax)		$	28,864			$	11,404			$	2,615			$	1,107
	A December 31 measurement date is used for the pension, supplemental pension and postretirement benefit plans.  The following table sets forth changes in benefit obligations, changes in plan assets, and the funded status of the pension plans and other postretirement benefits:
			Pension Benefits								Other Benefits
	(In thousands)		2014				2013				2014				2013
	Change in benefit obligation
	Benefit obligation at beginning of year		$	85,667			$	85,130			$	7,428			$	4,071
	Service cost			2,290				2,493				16				23
	Interest cost			4,142				3,223				347				286
	Plan participants' contributions			-				-				266				269
	Actuarial(gain) loss			12,501				(10,853	)			1,452				(369	)
	Amendments			-				-				-				(54	)
	Acquisition			-				10,958				-				3,928
	Benefits paid			(6,044	)			(5,284	)			(799	)			(726	)
	Projected benefit obligation at end of year			98,556				85,667				8,710				7,428
	Change in plan assets
	Fair value of plan assets at beginning of year			118,574				99,705				-				-
	Actual return on plan assets			3,950				18,451				-				-
	Acquisition			-				4,994				-				-
	Employer contributions			752				708				533				457
	Plan participants' contributions			-				-				266				269
	Benefits paid			(6,044	)			(5,284	)			(799	)			(726	)
	Fair value of plan assets at end of year			117,232				118,574				-				-
	Funded status at year end		$	18,676			$	32,907			$	(8,710	)		$	(7,428	)
	An asset is recognized for an overfunded plan and a liability is recognized for an underfunded plan.  The accumulated benefit obligation for pension benefits was $98.6 million and $85.7 million at December 31, 2014 and 2013, respectively.  The accumulated benefit obligation for other postretirement benefits was $8.7 million and $7.4 million at December 31, 2014 and 2013, respectively.  The funded status of the pension and other postretirement benefit plans has been recognized as follows in the consolidated balance sheets at December 31, 2014 and 2013.
		Pension Benefits								Other Benefits
	(In thousands)	2014				2013				2014				2013
	Other assets		$	39,044			$	48,189			$	-			$	-
	Other liabilities			(20,368	)			(15,282	)			(8,710	)			(7,428	)
	Funded status		$	18,676			$	32,907			$	(8,710	)		$	(7,428	)
	The following assumptions were used to determine the benefit obligation and the net periodic pension cost for the years indicated:
			Years ended December 31,
			2014				2013				2012
	Weighted average assumptions:
	The following assumptions were used to determine benefit obligations:
	Discount rate			4.19% - 4.30	%			4.90%-5.05	%			3.5	%
	Expected long-term return on plan assets			7.5	%			7.5	%			7.5	%
	Rate of compensation increase			3.00%-3.75	%			3	%			3	%
	The following assumptions were used to determine net periodic pension cost:
	Discount rate			4.90%-5.05	%			3.5	%			4.1	%
	Expected long-term return on plan assets			7.5	%			7.5	%			7.5	%
	Rate of compensation increase			3.00%-3.75	%			3	%			3	%
	Net periodic benefit cost and other amounts recognized in other comprehensive income (loss) for the years ended December 31 included the following components:
			Pension Benefits												Other Benefits
	(In thousands)		2014				2013				2012				2014			2013			2012
	Components of net periodic benefit cost
	Service cost		$	2,290			$	2,493			$	3,122			$	16		$	23		$	20
	Interest cost			4,142				3,223				3,145				347			286			155
	Expected return on plan assets			(8,681	)			(7,804	)			(6,686	)			-			-			-
	Amortization of prior service cost			23				23				283				(206	)		(205	)		(202	)
	Amortization of unrecognized net loss			79				2,692				3,330				151			280			182
Net periodic pension cost		$	(2,147	)		$	627			$	3,194			$	308		$	384		$	155
Other changes in plan assets and benefit obligations recognized in other comprehensive income (pre-tax)
Net loss (gain)		$	17,233			$	(21,500	)		$	894			$	1,452		$	(369	)	$	136
Prior service cost			-				-				(1,006	)			-			(54	)		-
Amortization of prior service cost			(23	)			(23	)			(283	)			206			205			202
Amortization of unrecognized net gain			(79	)			(2,692	)			(3,330	)			(151	)		(280	)		(182	)
Total recognized in other comprehensive loss (income)			17,131				(24,215	)			(3,725	)			1,507			(498	)		156
Total recognized in net periodic benefit cost and other comprehensive income (loss) - pre-tax		$	14,984			$	(23,588	)		$	(531	)		$	1,815		$	(114	)	$	311
The following table sets forth estimated future benefit payments for the pension plans and other postretirement benefit plans:
(In thousands)		Pension				Other
		Benefits				Benefits
2015			6,011				538
2016			6,221				549
2017			9,473				571
2018			7,100				592
2019			6,953				578
2020 - 2024			40,351				2,881
The Company is not required to make contributions to the defined benefit plan in 2015.
For measurement purposes, the annual rates of increase in the per capita cost of covered medical and prescription drug benefits for fiscal year 2014 were assumed to be 7.0 to 9.0 percent. The rates were assumed to decrease gradually to 3.9 percent for fiscal year 2075 and remain at that level thereafter.  Assumed health care cost trend rates have a significant effect on amounts reported for health care plans. A one-percentage point change in the health care trend rates would have the following effects as of and for the year ended December 31, 2014:
(In thousands)		One Percentage point increase				One Percentage point decrease
Increase (decrease) on total service and interest cost components		$	39			$	(33	)
Increase (decrease) on postretirement accumulated benefit obligation			895				(764	)
Plan Investment Policy
The Company’s key investment objectives in managing its defined benefit plan assets are to ensure that present and future benefit obligations to all participants and beneficiaries are met as they become due; to provide a total return that, over the long-term, maximizes the ratio of the plan assets to liabilities, while minimizing the present value of required Company contributions, at the appropriate levels of risk; to meet statutory requirements and regulatory agencies’ requirements; and to satisfy applicable accounting standards.  The Company periodically evaluates the asset allocations, funded status, rate of return assumption and contribution strategy for satisfaction of our investment objectives.
The target and actual allocations expressed as a percentage of the defined benefit pension plan’s assets are as follows:
		Target 2014				2014				2013
Cash and cash equivalents			0 - 20	%			4	%			6	%
Fixed income securities			20 - 40	%			38	%			27	%
Equities			40 - 80	%			58	%			67	%
Total							100	%			100	%
Only high-quality bonds are to be included in the portfolio.  All issues that are rated lower than A by Standard and Poor’s are to be excluded.  Equity securities at December 31, 2014 and 2013 do not include any Company common stock.
The following table presents the financial instruments recorded at fair value on a recurring basis by the Plan as of December 31, 2014 and 2013:
(In thousands)		Quoted Prices in Active Markets for				Significant				Balance
		Identical Assets				Other				as of
		(Level 1)				Observable Inputs				31-Dec-14
						(Level 2)
Cash and cash equivalents		$	4,423			$	-			$	4,423
Foreign equity mutual funds			38,581				-				38,581
Equity mutual funds			29,718				-				29,718
U.S. government bonds			-				4,420				4,420
Corporate bonds			-				40,090				40,090
Totals		$	72,722			$	44,510			$	117,232
(In thousands)		Quoted Prices in Active Markets for Identical Assets				Significant				Balance
		(Level 1)				Other				as of
						Observable Inputs				31-Dec-13
						(Level 2)
Cash and cash equivalents		$	7,533			$	-			$	7,533
Foreign equity mutual funds			15,653				-				15,653
Equity mutual funds			16,727				-				16,727
U.S. government bonds			-				9,355				9,355
Corporate bonds			-				19,665				19,665
Common stock			44,532				-				44,532
Municipal bonds and notes			-				1,451				1,451
Foreign bonds and notes			-				1,392				1,392
Foreign equity			2,266				-				2,266
Totals		$	86,711			$	31,863			$	118,574
The plan had no financial instruments recorded at fair value on a nonrecurring basis as of December 31, 2014.
Determination of Assumed Rate of Return
The expected long-term rate-of-return on assets was 7.5% at December 31, 2014 and December 31, 2013.  This assumption represents the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the projected benefit obligation.  The assumption has been determined by reflecting expectations regarding future rates of return for the portfolio considering the asset distribution and related historical rates of return.  The appropriateness of the assumption is reviewed annually.
Employee 401(k) and Employee Stock Ownership Plans
The Company maintains a 401(k) and employee stock ownership plan (the “401(k) Plan”).  The Company contributes to the 401(k) Plan based on employees’ contributions out of their annual salaries.  In addition, the Company may also make discretionary contributions to the 401(k) Plan based on profitability.  Participation in the 401(k) Plan is contingent upon certain age and service requirements.  The employer contributions associated with the 401(k) Plan were $2.2 million in 2014, $2.1 million in 2013, and $1.8 million in 2012.

StockBased_Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2014
Stock-Based Compensation [Abstract]
Stock-Based Compensation	(14) Stock-Based Compensation
	In April 2008, the Company adopted the NBT Bancorp Inc. 2008 Omnibus Incentive Plan (the “Plan”). Under the terms of the Plan, options and other equity-based awards are granted to directors and employees to increase their direct proprietary interest in the operations and success of the Company.  The Plan assumed all prior equity-based incentive plans and any new equity-based awards are granted under the terms of the Plan.  Under terms of the Plan, stock options are granted to purchase shares of the Company’s common stock at a price equal to the fair market value of the common stock on the date of the grant. Options granted have a vesting period of four years and terminate ten years from the date of the grant.  Shares issued as a result of stock option exercises and vesting of restricted shares and stock unit awards are funded from the Company’s treasury stock.  Restricted shares granted under the Plan vest after five years for employees and three years for non-employee directors.  Restricted stock units granted under the Plan may have different terms and conditions.  Performance shares and units granted under the Plan for executives may have different terms and conditions.  Since 2011, the Company primarily grants restricted stock unit awards.  Stock option grants since that time were reloads of existing grants.
	The following table summarizes information concerning stock options outstanding at December 31, 2014:
		Number of Shares			Weighted average exercise price		Weighted Average Remaining Contractual Term (in yrs)			Aggregate Intrinsic Value
	Outstanding at January 1, 2014		1,341,500		$	22.98
	Granted		3,296			24.8
	Exercised		(290,243	)		22.58
	Forfeited		(105	)		20.19
	Expired		(16,106	)		22.36
	Outstanding at December 31, 2014		1,038,342		$	23.1			3.4		$	3,353,951
	Exercisable at December 31, 2014		1,031,726		$	23.09			3.37		$	3,342,258
	Expected to Vest		5,249		$	24.5			7.32		$	9,354
	Total stock-based compensation expense for stock option awards totaled $0.1 million, $0.2 million, and $0.5 million for the years ended December 31, 2014, 2013, and 2012, respectively.  Cash proceeds, tax benefits and intrinsic value related to total stock options exercised is as follows:
		Years ended December 31,
	(dollars in thousands)	2014			2013			2012
	Proceeds from stock options exercised	$	6,554		$	7,927		$	1,908
	Tax benefits related to stock options exercised		313			178			8
	Intrinsic value of stock options exercised		789			905			498
	Fair value of shares vested during the year		393			766			1,656
	The Company has outstanding restricted and deferred stock awards granted from various plans at December 31, 2014. The Company recognized $4.2 million, $3.8 million, and $3.7 million in stock-based compensation expense related to these stock awards for the years ended December 31, 2014, 2013, and 2012, respectively.  Tax benefits recognized with respect to restricted stock awards and stock units were $2.9 million, $2.4 million and $1.5 million for the years ended December 31, 2014, 2013 and 2012, respectively.  Unrecognized compensation cost related to restricted stock awards and stock units totaled $4.4 million at December 31, 2014 and will be recognized over 1.7 years on a weighted average basis.  Shares issued are funded from the Company’s treasury stock.  The following table summarizes information for unvested restricted stock awards outstanding as of December 31, 2014:
		Number			Weighted-
		of			Average
		Shares			Grant Date Fair
					Value
	Unvested Restricted Stock Awards
	Unvested at January 1, 2014		66,650		$	23.15
	Forfeited		-			-
	Vested		(14,650	)		22.16
	Unvested at December 31, 2014		52,000		$	23.43
	The following table summarizes information for unvested restricted stock units outstanding as of December 31, 2014:
		Number			Weighted-
		of			Average
		Shares			Grant Date Fair
					Value
	Unvested Restricted Stock Units
	Unvested at January 1, 2014		539,850		$	27.36
	Forfeited		(5,090	)		-
	Vested		(105,013	)		-
	Granted		209,228			24.11
	Unvested at December 31, 2014		638,975		$	31.01
	The Company has 3.8 million securities remaining available to be granted as part of the Plan at December 31, 2014.

Stockholders_Equity

Stockholders Equity	12 Months Ended
	Dec. 31, 2014
Stockholders Equity [Abstract]
Stockholders Equity	(15)  Stockholders’ Equity
	In accordance with accounting standards, unrealized gains on available for sale securities and unrecognized actuarial gains or losses and prior service costs associated with the Company’s pension and postretirement benefit plans are included in accumulated other comprehensive loss, net of tax.  For the years ended December 31, components of accumulated other comprehensive loss are:
	(In thousands)	2014			2013
	Unrecognized prior service cost and net actuarial loss on pension plans	$	(19,181	)	$	(7,785	)
	Unrealized net holding gains (losses) on available for sale securities		2,154			(8,980	)
	Accumulated other comprehensive loss	$	(17,027	)	$	(16,765	)
	Certain restrictions exist regarding the ability of the subsidiary bank to transfer funds to the Company in the form of cash dividends. The approval of the Office of Comptroller of the Currency (OCC) is required to pay dividends when a bank fails to meet certain minimum regulatory capital standards or when such dividends are in excess of a subsidiary bank's earnings retained in the current year plus retained net profits for the preceding two years as specified in applicable OCC regulations..  At December 31, 2014, approximately $88.7 million of the total stockholders’ equity of the Bank was available for payment of dividends to the Company without approval by the OCC. The Bank’s ability to pay dividends also is subject to the Bank being in compliance with regulatory capital requirements.  The Bank is currently in compliance with these requirements. Under the State of Delaware General Corporation Law, the Company may declare and pay dividends either out of accumulated net retained earnings or capital surplus.
	Under a previously disclosed stock repurchase plan, the Company purchased 3,288 shares of its common stock during the twelve month period ended December 31, 2014, for a total of $0.1 million at an average price of $22.02 per share.  This plan expired on December 31, 2014.  On October 27, 2014, the NBT Board of Directors authorized a new repurchase program for NBT to repurchase up to an additional 1,000,000 shares of its outstanding common stock.  This plan expires on December 31, 2016.

Regulatory_Capital_Requirement

Regulatory Capital Requirements	12 Months Ended
	Dec. 31, 2014
Regulatory Capital Requirements [Abstract]
Regulatory Capital Requirements	(16)  Regulatory Capital Requirements
	The Company and NBT Bank are subject to various regulatory capital requirements administered by the federal banking agencies.  Failure to meet minimum capital requirements can initiate certain mandatory and possibly additional discretionary actions by regulators that, if undertaken, could have a direct material effect on the consolidated financial statements. Under capital adequacy guidelines and the regulatory framework for prompt corrective action, NBT Bank must meet specific capital guidelines that involve quantitative measures of NBT Bank’s assets, liabilities, and certain off-balance sheet items as calculated under regulatory accounting practices. The capital amounts and classifications are also subject to qualitative judgments by the regulators about components, risk weightings, and other factors.
	Quantitative measures established by regulation to ensure capital adequacy require the Company and NBT Bank to maintain minimum amounts and ratios (set forth in the table below) of total and Tier 1 Capital to risk-weighted assets and of Tier 1 capital to average assets. As of December 31, 2014 and 2013, the Company and NBT Bank meet all capital adequacy requirements to which they were subject.
	Under their prompt corrective action regulations, regulatory authorities are required to take certain supervisory actions (and may take additional discretionary actions) with respect to an undercapitalized institution. Such actions could have a direct material effect on an institution’s financial statements.  The regulations establish a framework for the classification of banks into five categories:  well capitalized, adequately capitalized, under capitalized, significantly under capitalized, and critically under capitalized.  As of December 31, 2014, the most recent notification from NBT Bank’s regulators categorized NBT Bank as well capitalized under the regulatory framework for prompt corrective action.  To be categorized as well capitalized NBT Bank must maintain minimum total risk-based, Tier 1 risk-based, and Tier 1 capital to average asset ratios as set forth in the table below. There are no conditions or events since that notification that management believes have changed NBT Bank’s category.
	The Company and NBT Bank’s actual capital amounts and ratios are presented as follows:
		Actual					Regulatory ratio requirements
	(Dollars in thousands)	Amount		Ratio			Minimum			For classification
							capital adequacy			as well capitalized
	As of December 31, 2014
	Total Capital (to risk weighted assets):
	Company	$	777,651		13.5	%		8	%		10	%
	NBT Bank		727,771		12.72	%		8	%		10	%
	Tier I Capital (to risk weighted assets)
	Company		709,965		12.32	%		4	%		6	%
	NBT Bank		660,086		11.54	%		4	%		6	%
	Tier I Capital (to average assets)
	Company		709,965		9.39	%		4	%		5	%
	NBT Bank		660,086		8.79	%		4	%		5	%
	As of December 31, 2013
	Total Capital (to risk weighted assets):
	Company	$	723,580		12.99	%		8	%		10	%
	NBT Bank		686,194		12.41	%		8	%		10	%
	Tier I Capital (to risk weighted assets)
	Company		653,950		11.74	%		4	%		6	%
	NBT Bank		617,038		11.16	%		4	%		6	%
	Tier I Capital (to average assets)
	Company		653,950		8.93	%		4	%		5	%
	NBT Bank		617,038		8.47	%		4	%		5	%

Earnings_Per_Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Earnings Per Share	(17) Earnings Per Share
	The following is a reconciliation of basic and diluted earnings per share for the years presented in the consolidated statements of income:
		Years ended December 31,
		2014								2013								2012
	(In thousands, except per share data)	Net			Weighted		Per share			Net			Weighted		Per share			Net			Weighted		Per share
		income			average		amount			income			average		amount			income			average		amount
					shares								shares								shares
	Basic earnings per share		$	75,074		43,877		$	1.71		$	61,747		41,930		$	1.47		$	54,558		33,379		$	1.63
	Effect of dilutive securities
	Stock based compensation					518								420								340
	Diluted earnings per share		$	75,074		44,395		$	1.69		$	61,747		42,350		$	1.46		$	54,558		33,719		$	1.62
	There were approximately 0.5 million, 1.0 million, and 1.2 million weighted average stock options for the years ended December 31, 2014, 2013, and 2012, respectively, that were not considered in the calculation of diluted earnings per share since the stock options’ exercise prices were greater than the average market price during  these  periods.

Reclassification_Adjustments_O

Reclassification Adjustments Out of Other Comprehensive (Loss) Income	12 Months Ended
	Dec. 31, 2014
Reclassification Adjustments Out of Other Comprehensive Income (Loss) [Abstract]
Reclassification Adjustments Out of Other Comprehensive (Loss) Income	(18) Reclassification Adjustments Out of Other Comprehensive (Loss) Income
	The following table summarizes the reclassification adjustments out of accumulated other comprehensive loss (in thousands):
	Detail About Accumulated Other Comprehensive (Loss)	Amount reclassified from accumulated other comprehensive income (loss)						Affected line item in the consolidated statement of comprehensive income
	Income Components
		Years ended
		31-Dec-14			31-Dec-13
	Available for sale securities:
	Gains on available for sale securities	$	(92	)	$	(1,426	)	Net securities gains
	Amortization of unrealized gains and losses related to securities transfer		(421	)		-		Interest Income
	Tax benefit		200			565		Income tax expense
	Net of tax	$	(313	)	$	(861	)
	Pension and other benefits:
	Amortization of net gains	$	94		$	2,972		Salaries and employee benefits
	Amortization of prior service costs		(19	)		(182	)	Salaries and employee benefits
	Tax expense		29			1,189		Income tax expense
	Net of tax	$	46		$	1,601
	Total reclassifications during the period, net of tax	$	(267	)	$	740

Commitments_and_Contingent_Lia

Commitments and Contingent Liabilities	12 Months Ended
	Dec. 31, 2014
Commitments and Contingent Liabilities [Abstract]
Commitments and Contingent Liabilities	(19) Commitments and Contingent Liabilities
	The Company’s concentrations of credit risk are reflected in the consolidated balance sheets.  The concentrations of credit risk with standby letters of credit, unused lines of credit, commitments to originate new loans and loans sold with recourse generally follow the loan classifications.
	At December 31, 2014, approximately 59% of the Company’s loans were secured by real estate located in central and upstate New York, northeastern Pennsylvania, western Massachusetts, southern New Hampshire, and Vermont.  Accordingly, the ultimate collectability of a substantial portion of the Company’s portfolio is susceptible to changes in market conditions of those areas. Management is not aware of any material concentrations of credit to any industry or individual borrowers.
	The Company is a party to certain financial instruments with off balance sheet risk in the normal course of business to meet the financing needs of its customers.  These financial instruments include commitments to extend credit, unused lines of credit, standby letters of credit, and certain mortgage loans sold to investors with recourse. The Company’s exposure to credit loss in the event of nonperformance by the other party to the commitments to extend credit, unused lines of credit, standby letters of credit, and loans sold with recourse is represented by the contractual amount of those instruments. The credit risk associated with commitments to extend credit and standby and commercial letters of credit is essentially the same as that involved with extending loans to customers and is subject to normal credit policies.  Collateral may be obtained based on management’s assessment of the customer’s creditworthiness.
		At December 31,
	(In thousands)	2014		2013
	Unused lines of credit	$	214,175	$	216,658
	Commitments to extend credits, primarily variable rate		972,912		849,092
	Standby letters of credit		35,244		36,837
	Commercial letters of credit		22,486		41,263
	Loans sold with recourse		23,351		15,741
	Since many loan commitments, standby letters of credit, and guarantees and indemnification contracts expire without being funded in whole or in part, the contract amounts are not necessarily indicative of future cash flows. The Company does not issue any guarantees that would require liability-recognition or disclosure, other than its standby letters of credit.
	The Company guarantees the obligations or performance of customers by issuing stand-by letters of credit to third parties. These stand-by letters of credit are frequently issued in support of third party debt, such as corporate debt issuances, industrial revenue bonds, and municipal securities. The risk involved in issuing stand-by letters of credit is essentially the same as the credit risk involved in extending loan facilities to customers, and letters of credit are subject to the same credit origination, portfolio maintenance and management procedures in effect to monitor other credit and off-balance sheet products. Typically, these instruments have terms of five years or less and expire unused; therefore, the total amounts do not necessarily represent future cash requirements. The fair value of the Company’s stand-by letters of credit at December 31, 2014 and 2013 was not significant.
	The total amount of loans serviced by the Company for unrelated third parties was approximately $626.0 million and $685.6 million at December 31, 2014 and 2013, respectively. At December 31, 2014 and 2013, the Company had approximately $1.5 million and $2.2 million, respectively, of mortgage servicing rights.
	In the normal course of business there are various outstanding legal proceedings. If legal costs are deemed material by management, the Company accrues for the estimated loss from a loss contingency if the information available indicates that it is probable that a liability had been incurred at the date of the financial statements, and the amount of loss can be reasonably estimated.
	The Company is required to maintain reserve balances with the Federal Reserve Bank of New York. The required average total reserve for NBT Bank for the 14-day maintenance period ending December 24, 2014 was $46.9 million.

Fair_Values_of_Financial_Instr

Fair Values of Financial Instruments	12 Months Ended
	Dec. 31, 2014
Fair Values of Financial Instruments [Abstract]
Fair Values of Financial Instruments	(20) Fair Values of Financial Instruments
	The following table sets forth information with regard to estimated fair values of financial instruments at December 31, 2014 and December 31, 2013.  This table excludes financial instruments for which the carrying amount approximates fair value.  Financial instruments for which the fair value approximates carrying value include cash and cash equivalents, securities available for sale, trading securities, accrued interest receivable, non-maturity deposits, short-term borrowings, accrued interest payable, and interest rate swaps.
				31-Dec-14				31-Dec-13
	(In thousands)	Fair Value Hierarchy		Carrying amount		Estimated fair value		Carrying amount		Estimated fair value
	Financial assets
	Securities held to maturity		2	$	454,361	$	454,994	$	117,283	$	113,276
	Net loans		3		5,528,912		5,584,777		5,337,361		5,386,520
	Financial liabilities
	Time deposits		2	$	1,043,823	$	1,038,877	$	1,021,142	$	1,023,982
	Long-term debt		2		130,945		132,562		308,823		325,195
	Junior subordinated debt		2		101,196		103,770		101,196		105,121
	Fair value estimates are made at a specific point in time, based on relevant market information and information about the financial instrument. These estimates do not reflect any premium or discount that could result from offering for sale at one time the Company’s entire holdings of a particular financial instrument. Because no market exists for a significant portion of the Company’s financial instruments, fair value estimates are based on judgments regarding future expected loss experience, current economic conditions, risk characteristics of various financial instruments, and other factors. These estimates are subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. Changes in assumptions could significantly affect the estimates.
	Fair value estimates are based on existing on and off balance sheet financial instruments without attempting to estimate the value of anticipated future business and the value of assets and liabilities that are not considered financial instruments. For example, the Company has a substantial trust and investment management operation that contributes net fee income annually. The trust and investment management operation is not considered a financial instrument, and its value has not been incorporated into the fair value estimates. Other significant assets and liabilities include the benefits resulting from the low-cost funding of deposit liabilities as compared to the cost of borrowing funds in the market, and premises and equipment. In addition, the tax ramifications related to the realization of the unrealized gains and losses can have a significant effect on fair value estimates and have not been considered in the estimate of fair value.
	Securities Held to Maturity
	The fair value of the Company’s investment securities held to maturity is primarily measured using information from a third party pricing service.  The fair value measurements consider observable data that may include dealer quotes, market spreads, cash flows, the U.S. Treasury yield curve, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the bond’s terms and conditions, among other things.
	Net Loans
	The fair value of the Company’s loans was estimated by discounting the expected future cash flows using the current interest rates at which similar loans would be made for the same remaining maturities.  Loans were first segregated by type, and then further segmented into fixed and variable rate and loan quality categories.  Expected future cash flows were projected based on contractual cash flows, adjusted for estimated prepayments.
	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.
	Long-Term Debt
	The fair value of long-term debt was estimated using a discounted cash flow approach that applies prevailing market interest rates for similar maturity instruments.
	Trust Preferred Debentures
	The fair value of trust preferred debentures has been estimated using a discounted cash flow analysis.
	The following table sets forth the Company’s financial assets and liabilities measured on a recurring basis that were accounted for at fair value as of December 31, 2014 and December 31, 2013.  Assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement (in thousands):
		Quoted Prices in		Significant		Significant		Balance
		Active Markets for		Other		Unobservable		as of
		Identical Assets		Observable Inputs		Inputs		31-Dec-14
		(Level 1)		(Level 2)		(Level 3)
	Assets:
	Securities Available for Sale:
	U.S. Treasury	$	23,111	$	-	$	-	$	23,111
	Federal Agency		-		329,914		-		329,914
	State & municipal		-		37,570		-		37,570
	Mortgage-backed		-		364,727		-		364,727
	Collateralized mortgage obligations		-		242,129		-		242,129
	Other securities		7,612		8,108		-		15,720
	Total Securities Available for Sale	$	30,723	$	982,448	$	-	$	1,013,171
	Trading Securities		7,793		-		-		7,793
	Interest Rate Swaps		-		4,707		-		4,707
	Total	$	38,516	$	987,155	$	-	$	1,025,671
	Liabilities:
	Interest Rate Swaps	$	-	$	4,707	$	-	$	4,707
	Total	$	-	$	4,707	$	-	$	4,707
		Quoted Prices in		Significant		Significant		Balance
		Active Markets for		Other		Unobservable		as of
		Identical Assets		Observable Inputs		Inputs		31-Dec-13
		(Level 1)		(Level 2)		(Level 3)
	Assets:
	Securities Available for Sale:
	U.S. Treasury	$	43,616	$	-	$	-	$	43,616
	Federal Agency		-		278,915		-		278,915
	State & municipal		-		113,665		-		113,665
	Mortgage-backed		-		364,164		-		364,164
	Collateralized mortgage obligations		-		549,528		-		549,528
	Other securities		6,796		8,197		-		14,993
	Total Securities Available for Sale	$	50,412	$	1,314,469	$	-	$	1,364,881
	Trading Securities		5,779		-		-		5,779
	Interest Rate Swaps		-		281		-		281
	Total	$	56,191	$	1,314,750	$	-	$	1,370,941
	Liabilities:
	Interest Rate Swaps	$	-	$	281	$	-	$	281
	Total	$	-	$	281	$	-	$	281
	Fair values for securities are based on quoted market prices or dealer quotes, where available.  Where quoted market prices are not available, fair values are based on quoted market prices of comparable instruments.  When necessary, the Company utilizes matrix pricing from a third party pricing vendor to determine fair value pricing.  Matrix prices are based on quoted prices for securities with similar coupons, ratings, and maturities, rather than on specific bids and offers for the designated security.
	The Company enters into interest rate swaps to facilitate customer transactions and meet their financing needs. These swaps are considered derivatives, but are not designated in hedging relationships. These instruments have interest rate and credit risk associated with them. To mitigate the interest rate risk, the Company enters into offsetting interest rate swaps with counterparties. The counterparty swaps are also considered derivatives and are also not designated in hedging relationships. Interest rate swaps are recorded within other assets or other liabilities on the consolidated balance sheet at their estimated fair value. Changes to the fair value of assets and liabilities arising from these derivatives are included, net, in other operating income in the consolidated statement of income.
FASB ASC Topic 820 requires disclosure of assets and liabilities measured and recorded at fair value on a nonrecurring basis.  In accordance with the provisions of FASB ASC Topic 310, the Company had collateral dependent impaired loans with a carrying value of approximately $5.8 million which had specific reserves included in the allowance for loan losses of $1.1 million at December 31, 2014.  The Company uses the fair value of underlying collateral to estimate the specific reserves for collateral dependent impaired loans.  The fair value of underlying collateral is generally determined through independent appraisals, which generally include various Level 3 inputs which are not identifiable. The appraisals may be adjusted by management for qualitative factors such as economic conditions and estimated liquidation expenses ranging from 10% to 35%.  Based on the valuation techniques used, the fair value measurements for collateral dependent impaired loans are classified as Level 3.
FASB ASC Topic 825 gives entities the option to measure eligible financial assets, financial liabilities and Company commitments at fair value (i.e., the fair value option), on an instrument-by-instrument basis, that are otherwise not permitted to be accounted for at fair value under other accounting standards.  The election to use the fair value option is available when an entity first recognizes a financial asset or financial liability or upon entering into a Company commitment.  Subsequent changes in fair value must be recorded in earnings.  As of December 31, 2014 and 2013, the Company did not elect the fair value option for any eligible items.

Sale_of_Equity_Investments

Sale of Equity Investments	12 Months Ended
	Dec. 31, 2014
Sale of Equity Investment [Abstract]
Sale of Equity Investments Disclosure [Text Block]	(21)  Sale of Equity Investment
	On April 17, 2014, NBT Capital Corp., a wholly-owned subsidiary of NBT, sold to LendingClub Corporation, its 20% ownership interest in Springstone Financial, LLC, which NBT originally acquired in exchange for a $3 million investment, as part of LendingClub's acquisition of all of the outstanding equity in Springstone. In total, LendingClub paid the group of selling equityholders a purchase price equal to $140 million in cash and preferred stock. As a result of this sale, the Company recognized a gain of $19.4 million during the second quarter of 2014.  There is $5.2 million in proceeds being held in escrow for indemnification provisions of the sale contract which will be recognized into income in 2015 when the conditions of the contract have been deemed to be satisfied.

Parent_Company_Financial_Infor

Parent Company Financial Information	12 Months Ended
	Dec. 31, 2014
Parent Company Financial Information [Abstract]
Parent Company Financial Information	(22)  Parent Company Financial Information
	Condensed Balance Sheets
		December 31,
	(In thousands)	2014			2013
	Assets
	Cash and cash equivalents	$	3,586		$	3,741
	Securities available for sale, at estimated fair value		11,649			11,008
	Trading securities		6,761			4,742
	Investment in subsidiaries, on equity basis		947,880			896,479
	Other assets		61,829			49,530
	Total assets	$	1,031,705		$	965,500
	Liabilities and Stockholders’ Equity
	Total liabilities	$	167,524		$	148,931
	Stockholders’ equity		864,181			816,569
	Total liabilities and stockholders’ equity	$	1,031,705		$	965,500
	Condensed Income Statements
		Years ended December 31,
	(In thousands)	2014			2013			2012
	Dividends from subsidiaries	$	35,400		$	13,500		$	79,175
	Management fee from subsidiaries		87,116			84,778			78,665
	Securities gains		49			1,273			442
	Interest, dividend and other income		800			636			720
	Total revenue		123,365			100,187			159,002
	Operating expense		89,834			83,679			79,015
	Income before income tax benefit and equity in undistributed income of subsidiaries		33,531			16,508			79,987
	Income tax benefit (expense)		631			(1,046	)		(284	)
	Dividends in excess of income (equity in undistributed income) of subsidiaries		40,912			46,285			(25,145	)
	Net income	$	75,074		$	61,747		$	54,558
	Statements of Cash Flow
		Years ended December 31,
	(In thousands)	2014			2013			2012
	Operating activities
	Net income	$	75,074		$	61,747		$	54,558
	Adjustments to reconcile net income to net cash provided by operating activities
	Stock-based compensation		3,521			4,305			4,364
	Gain on sales of available-for-sale securities		49			1,273			442
	Equity in undistributed income of subsidiaries		(75,824	)		(59,785	)		(54,030	)
	Cash dividend from subsidiaries		35,400			13,500			79,175
	Net change in other liabilities		18,594			(18,077	)		(3,181	)
	Net change in other assets		(25,151	)		14,928			2,030
	Net cash provided by operating activities		31,663			17,891			83,358
	Investing activities
	Purchases of available-for-sale securities		(597	)		-			(4,163	)
	Sales and maturities of available-for-sale securities		140			1,948			1,445
	Net cash provided by (used in) acquisitions		-			2,232			(14,612	)
	Purchases of premises and equipment		(640	)		(782	)		(1,240	)
	Net cash (used in) provided by investing activities		(1,097	)		3,398			(18,570	)
	Financing activities
	Proceeds from the issuance of shares to employee benefit plans and other stock plans		5,943			5,512			1,387
	Payments on long-term debt		-			-			(3,340	)
	Purchases of treasury shares		(72	)		(12,459	)		(15,490	)
	Cash dividends and payments for fractional shares		(36,905	)		(33,518	)		(26,712	)
	Excess tax benefit from exercise of stock options		313			(178	)		8
	Net cash used in financing activities		(30,721	)		(40,643	)		(44,147	)
	Net (decrease) increase in cash and cash equivalents		(155	)		(19,354	)		20,641
	Cash and cash equivalents at beginning of year		3,741			23,095			2,454
	Cash and cash equivalents at end of year	$	3,586		$	3,741		$	23,095
	A statement of changes in stockholders’ equity has not been presented since it is the same as the consolidated statement of changes in stockholders’ equity previously presented.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Summary of Significant Accounting Policies [Abstract]
Consolidation	Consolidation
	The accompanying consolidated financial statements include the accounts of NBT Bancorp and its wholly owned subsidiaries mentioned above.  All material intercompany transactions have been eliminated in consolidation. Amounts previously reported in the consolidated financial statements are reclassified whenever necessary to conform to the current year’s presentation. In the “Parent Company Financial Information,” the investment in subsidiaries is recorded using the equity method of accounting.
	The Company determines whether it has a controlling financial interest in an entity by first evaluating whether the entity is a voting interest entity or a variable interest entity under GAAP. Voting interest entities are entities in which the total equity investment at risk is sufficient to enable the entity to finance itself independently and provides the equity holders with the obligation to absorb losses, the right to receive residual returns and the right to make decisions about the entity’s activities. The Company consolidates voting interest entities in which it has all, or at least a majority of, the voting interest. As defined in applicable accounting standards, variable interest entities (“VIEs”) are entities that lack one or more of the characteristics of a voting interest entity. A controlling financial interest in a VIE is present when the Company has both the power and ability to direct the activities of the VIE that most significantly impact the VIE's economic performance and an obligation to absorb losses or the right to receive benefits that could potentially be significant to the VIE. The Company’s wholly owned subsidiaries CNBF Capital Trust I, NBT Statutory Trust I, NBT Statutory Trust II, Alliance Financial Capital Trust I and Alliance Financial Capital Trust II are VIEs for which the Company is not the primary beneficiary. Accordingly, the accounts of these entities are not included in the Company’s consolidated financial statements.
Segment Report	Segment Report
	The Company’s operations are primarily in the community banking industry and include the provision of traditional banking services.  The Company also provides other services through its subsidiaries such as insurance, retirement plan administration, and trust administration. The Company operates solely in the geographical regions of central and upstate New York, northeastern Pennsylvania, western Massachusetts, southern New Hampshire, Vermont, and the greater Portland, Maine area.  The Company has no reportable operating segments.
Cash Equivalents	Cash Equivalents
	The Company considers amounts due from correspondent banks, cash items in process of collection, and institutional money market mutual funds to be cash equivalents for purposes of the consolidated statements of cash flows.
Securities	Securities
	The Company classifies its securities at date of purchase as either available for sale, held to maturity or trading.  Held to maturity debt securities are those that the Company has the ability and intent to hold until maturity.  Trading securities are securities purchased with the intent to sell within a short period of time, and unrealized gains and losses are included in earnings.  Available for sale securities are securities that are not classified as a held to maturity or trading securities. Available for sale securities are recorded at fair value. Unrealized holding gains and losses, net of the related tax effect, on available for sale securities are excluded from earnings and are reported in stockholders’ equity and the statement of comprehensive income as a component of accumulated other comprehensive income or loss. Held to maturity securities are recorded at amortized cost. Trading securities are recorded at fair value, with net unrealized gains and losses recognized in income.  Transfers of securities between categories are recorded at fair value at the date of transfer. Declines in the fair value of held-to-maturity and available-for-sale securities below their cost that are deemed to be other than temporary are reflected in earnings as realized losses or in other comprehensive income, depending on whether the Company intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss.  If the Company intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss, the other-than-temporary impairment shall be recognized in earnings equal to the entire difference between the investment’s amortized cost basis and its fair value at the balance sheet date.  If the Company does not intend to sell the security and it is not more likely than not that the entity will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss, the other-than-temporary impairment shall be separated into (a) the amount representing the credit loss and (b) the amount related to all other factors.  The amount of the total other-than-temporary impairment related to the credit loss shall be recognized in earnings. The amount of the total other-than-temporary impairment related to other factors shall be recognized in other comprehensive income, net of applicable taxes.
	In estimating other-than-temporary impairment losses, management considers, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer, and (iii) the historical and implied volatility of the fair value of the security.
	Non-marketable equity securities are carried at cost.
	Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the interest method. Dividend and interest income are recognized when earned. Realized gains and losses on securities sold are derived using the specific identification  method for determining the cost of securities sold.
	Investments in Federal Reserve Bank (“FRB”) and Federal Home Loan Bank (“FHLB”) stock are required for membership in those organizations and are carried at cost since there is no market value available.  The FHLB New York continues to pay dividends and repurchase stock.  As such, the Company has not recognized any impairment on its holdings of FHLB stock.
Loans	Loans
	Loans are recorded at their current unpaid principal balance, net of unearned income and unamortized loan fees and expenses, which are amortized under the effective interest method over the estimated lives of the loans. Interest income on loans is accrued based on the principal amount outstanding.
	For all loan classes within the Company’s loan portfolio, loans are placed on nonaccrual status when timely collection of principal and interest in accordance with contractual terms is doubtful. Loans are transferred to nonaccrual status generally when principal or interest payments become ninety days delinquent, unless the loan is well secured and in the process of collection, or sooner when management concludes circumstances indicate that borrowers may be unable to meet contractual principal or interest payments.  When a loan is transferred to a nonaccrual status, all interest previously accrued in the current period but not collected is reversed against interest income in that period. Interest accrued in a prior period and not collected is charged-off against the allowance for loan losses.
	If ultimate repayment of a nonaccrual loan is expected, any payments received are applied in accordance with contractual terms. If ultimate repayment of principal is not expected, any payment received on a nonaccrual loan is applied to principal until ultimate repayment becomes expected.  For all loan classes within the Company’s loan portfolio, nonaccrual loans are returned to accrual status when they become current as to principal and interest and demonstrate a period of performance under the contractual terms and, in the opinion of management, are fully collectible as to principal and interest.  For loans in all portfolios, the principal amount is charged off in full or in part as soon as management determines, based on available facts, that the collection of principal in full is improbable.  For commercial loans, management considers specific facts and circumstances relative to individual credits in making such a determination.  For consumer and residential loan classes, management uses specific guidance and thresholds from the Federal Financial Institutions Examination Council’s Uniform Retail Credit Classification and Account Management Policy.
	Commercial type loans are considered impaired when it is probable that the borrower will not repay the loan according to the original contractual terms of the loan agreement, and all loan types are considered impaired if the loan is restructured in a troubled debt restructuring (“TDR”).  In determining that we will be unable to collect all principal and interest payments due in accordance with the contractual terms of the loan agreements, we consider factors such as payment history and changes in the financial condition of individual borrowers, local economic conditions, historical loss experience and the conditions of the various markets in which the collateral may be liquidated.
	A loan is considered to be a TDR when the Company grants a concession to the borrower because of the borrower’s financial condition that the Company would not otherwise consider. Such concessions include the reduction of interest rates, forgiveness of all or a portion of principal or interest, or other modifications at interest rates that are less than the current market rate for new obligations with similar risk. TDR loans are nonaccrual loans; however, they can be returned to accrual status after a period of performance, generally evidenced by six months of compliance with their modified terms.
	When the Company modifies a loan, management evaluates any possible impairment based on the present value of the expected future cash flows, discounted at the contractual interest rate of the original loan agreement, except when the sole (remaining) source of repayment for the loan is the operation or liquidation of the collateral.  In these cases, management uses the current fair value of the collateral, less selling costs, instead of discounted cash flows.  If management determines that the value of the modified loan is less than the recorded investment in the loan (net of previous charge-offs, deferred loan fees or costs and unamortized premium or discount), impairment is recognized by segment or class of loan as applicable, through an allowance estimate or a charge-off to the allowance.  Segment and class status is determined by the loan’s classification at origination.
Acquired Loans	Acquired Loans
	Acquired loans are initially measured at fair value as of the acquisition date without carryover of historical allowance for loan losses.
	For loans that meet the criteria stipulated in ASC 310-30, the Company shall recognize the accretable yield, which is defined as the excess of all cash flows expected at acquisition over the initial fair value of the loan, as interest income on a level-yield basis over the expected remaining life of the loan. The excess of the loan's contractually required payments over the cash flows expected to be collected is the nonaccretable difference. The nonaccretable difference shall not be recognized as an adjustment of yield, a loss accrual, or a valuation allowance. Decreases in the expected cash flows in subsequent periods require the establishment of an allowance for loan losses. Improvements in expected cash flows in future periods result in a reduction of the nonaccretable discount, with such amount reclassified as part of the accretable yield and subsequently recognized in interest income over the remaining lives of the acquired loans on a level-yield basis if the amount and timing of future cash flows is reasonably estimable.
	Acquired loans that met the criteria for nonaccrual of interest prior to the acquisition are considered performing upon acquisition, regardless of whether the customer is contractually delinquent, if the Company can reasonably estimate the timing and amount of the expected cash flows on such loans and if the Company expects to fully collect the new carrying value of the loans. As such, the Company may no longer consider the loan to be nonaccrual or nonperforming and may accrue interest on these loans, including the impact of any accretable yield. As such, charge-offs on acquired loans are first applied to the nonaccretable difference and then to any allowance for loan losses recognized subsequent to acquisition.
	For loans that meet the criteria stipulated in ASC 310-20, the Company shall amortize/accrete into interest income the premium/discount determined at the date of purchase on a level-yield basis over the life of the loan. Subsequent to the acquisition date, the methods utilized to estimate the required allowance for loan losses are similar to originated loans.  Loans accounted for under ASC 310-20 are placed on nonaccrual status when past due in accordance with the Company's nonaccrual policy.
	An acquired loan may be resolved either through receipt of payment (in full or in part) from the borrower, the sale of the loan to a third party, or foreclosure of the collateral. In the event of a sale of the loan, a gain or loss on sale is recognized and reported within noninterest income based on the difference between the sales proceeds and the carrying amount of the loan. In other cases, individual loans are removed from the pool based on comparing the amount received from its resolution (fair value of the underlying collateral less costs to sell in the case of a foreclosure) with its outstanding balance. Any difference between these amounts is recorded as a charge-off through the allowance for loan losses.  Acquired loans subject to modification are not removed from the pool even if those loans would otherwise be deemed troubled debt restructurings as the pool, and not the individual loan, represents the unit of account.
Allowance for Loan Losses	Allowance for Loan Losses
	The allowance for loan losses is the amount which, in the opinion of management, is necessary to absorb probable losses inherent in the loan portfolio. The allowance is determined based upon numerous considerations, including local and regional conditions, the growth and composition of the loan portfolio  with  respect to the mix between the various types of loans and their related risk characteristics, a review of the value of collateral supporting the loans, comprehensive reviews of the loan portfolio by the independent loan review staff and management, as well as consideration of volume and trends of delinquencies, nonperforming loans, and loan charge-offs.  Loan losses are charged off against the allowance, while recoveries of amounts previously charged off are credited to the allowance.  As a result of tests of adequacy, required additions to the allowance for loan losses are made periodically by charges to the provision for loan losses.
	The allowance for loan losses related to impaired loans specifically allocated for impairment is based on discounted cash flows using the loan’s initial effective interest rate or the fair value of the collateral for certain loans where repayment of the loan is expected to be provided solely by the underlying collateral (collateral dependent loans). The Company’s impaired loans are generally collateral dependent. The Company considers the estimated cost to sell, on a discounted basis, when determining the fair value of collateral in the measurement of impairment if those costs are expected to reduce the cash flows available to repay or otherwise satisfy the loans.
	The allowance for loan losses for homogeneous non impaired loans is calculated using a systematic methodology with both a quantitative and a qualitative analysis that is applied on a quarterly basis. For purposes of our allowance methodology, the loan portfolio is segmented as described in Note 5, Allowance for Loan Loss and Credit Quality of Loans. Each segment has a distinct set of risk characteristics monitored by management. We further assess and monitor risk and performance at a more disaggregated level which includes our internal risk grading system for the commercial segments.
	We first apply historical loss rates to pools of loans with similar risk characteristics. Loss rates are calculated by historical charge-offs that have occurred within each pool of loans over the loss emergence period, or LEP. The LEP is an estimate of the average amount of time from the point at which a loss is incurred on a loan to the point at which the loss is confirmed. In general, the LEP will be shorter in an economic slowdown or recession and longer during times of economic stability or growth, as customers are better able to delay loss confirmation after a potential loss event has occurred. In conjunction with our annual review of the ALL assumptions, we update our study of LEPs for each portfolio segment using our loan charge-off history. Another key assumption is the look-back period, or LBP, which represents the historical data period utilized to calculate loss rates.
	After consideration of the historic loss analysis, management applies additional qualitative adjustments so that the allowance for loan losses is reflective of the inherent losses that exist in the loan portfolio at the balance sheet date. Qualitative adjustments are made based upon past loss experience; size, trend, composition, and nature of loans; changes in lending policies and procedures, including underwriting standards and collection, charge-offs and recoveries; trends experienced in nonperforming and delinquent loans; current economic conditions in the Company’s market; portfolio concentrations that may affect loss experience across one of more components of the portfolio; the effect of external factors such as competition, legal and regulatory requirements; and the experience, ability, and depth of lending management and staff. The evaluation of the various components of the allowance for loan losses requires considerable judgment in order to estimate inherent loss exposures. In addition, various regulatory agencies, as an integral component of their examination process, periodically review the Company’s allowance for loan losses. Such agencies may require the Company to make loan grade changes as well as recognize additions to the allowance based on their examinations.
	Management believes that the allowance for loan losses is adequate.  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 or changes in the values of properties securing loans in the process of foreclosure. In addition, various regulatory agencies, as an integral part of their examination process, 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 which may not be currently available to management.
Premises and Equipment	Premises and Equipment
	Premises and equipment are stated at cost, less accumulated depreciation.  Depreciation of premises and equipment is determined using the straight-line method over the estimated useful lives of the respective assets. Expenditures for maintenance, repairs, and minor replacements are charged to expense as incurred.
Other Real Estate Owned	Other Real Estate Owned
	OREO consists of properties acquired through foreclosure or by acceptance of a deed in lieu of foreclosure. These assets are recorded at the lower of fair value of the asset acquired less estimated costs to sell or “cost” (defined as the fair value at initial foreclosure). At the time of foreclosure, or when foreclosure occurs in-substance, the excess, if any, of the loan over the fair market value of the assets received, less estimated selling costs, is charged to the allowance for loan losses and any subsequent valuation write-downs are charged to other expense.  In connection with the determination of the allowance for loan losses and the valuation of other real estate owned, management obtains appraisals for properties.  Operating costs associated with the properties are charged to expense as incurred. Gains on the sale of OREO are included in income when title has passed and the sale has met the minimum down payment requirements prescribed by GAAP.  The balance of OREO at December 31, 2014 and 2013 was approximately $4.0 million and $2.9 million, respectively, and is recorded in Other Assets on the Consolidated Balance Sheet.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets
	Goodwill and intangible assets that have indefinite useful lives are not amortized, but are tested at least annually for impairment. Intangible assets that have finite useful lives are amortized over their useful lives.  Core deposit intangibles and trust intangibles at the Company are amortized using the sum-of-the-years’-digits method.  Covenants not to compete are amortized on a straight-line basis.  Customer lists are amortized using an accelerated method.
	When facts and circumstances indicate potential impairment of amortizable intangible assets, the Company evaluates the recoverability of the asset carrying value, using estimates of undiscounted future cash flows over the remaining asset life. Any impairment loss is measured by the excess of carrying value over fair value. Goodwill impairment tests are performed on an annual basis or when events or circumstances dictate. In these tests, the fair values of each reporting unit, or segment, is compared to the carrying amount of that reporting unit in order to determine if impairment is indicated. If so, the implied fair value of the reporting unit’s goodwill is compared to its carrying amount and the impairment loss is measured by the excess of the carrying value over fair value.
Bank-Owned Life Insurance	Bank-Owned Life Insurance
	The Bank has purchased life insurance policies on certain employees, key executives and directors. Bank-owned life insurance is recorded at the amount that can be realized under the insurance contract at the balance sheet date, which is the cash surrender value adjusted for other charges or other amounts due that are probable at settlement.
Treasury Stock	Treasury Stock
	Treasury stock acquisitions are recorded at cost. Subsequent sales of treasury stock are recorded on an average cost basis. Gains on the sale of treasury stock are credited to additional paid-in-capital. Losses on the sale of treasury stock are charged to additional paid-in-capital to the extent of previous gains, otherwise charged to retained earnings.
Income Taxes	Income Taxes
	Income taxes are accounted for under the asset and liability method. Deferred income taxes are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases.  Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred taxes of a change in tax rates is recognized in income in the period that includes the enactment date.  The Company recognizes interest accrued and penalties related to unrecognized tax benefits in income tax expense.
	Tax positions are recognized as a benefit only if it is “more likely than not” that the tax position would be sustained in a tax examination, with a tax examination being presumed to occur. The amount recognized is the largest amount of tax benefit that is greater than 50 percent likely of being realized on examination. For tax positions not meeting the “more likely than not” test, no tax benefit is recorded.
Stock-Based Compensation	Stock-Based Compensation
	We maintain various long-term incentive stock benefit plans under which we grant stock options, restricted stock awards, and restricted stock units to certain directors and key employees.  We recognize compensation expense in our income statement over the requisite service period, based on the grant-date fair value of the award.  For restricted stock awards and units, we recognize compensation expense ratably over the vesting period for the fair value of the award, measured at the grant date.  The fair values of options are estimated using the Black-Scholes option pricing model.
	The Company’s stock-based employee compensation plan is described in Note 14 “Stock-Based Compensation,” of this Report.
Interest Rate Swaps	Interest Rate Swaps
	The Bank offers interest rate swap agreements to its customers.  These agreements allow the Bank’s customers to effectively fix the interest rate on a variable rate loan by entering into a separate agreement.  Simultaneous with the execution of such an agreement with a customer, the Bank enters into a matching interest rate swap agreement with an unrelated third party provider, which allows the Bank to continue to receive the historical variable rate under the loan agreement with the customer.  The agreement with the third party is not a hedge contract therefore changes in fair value are recorded through earnings.  Assets and liabilities associated with the agreements are recorded in other assets and other liabilities on the balance sheet.  Gains and losses are recorded as other noninterest income.  The Bank is not subject to any fee or penalty should the customer elect to terminate the interest rate swap agreement prior to maturity.  The Bank is exposed to credit loss equal to the fair value of the derivatives (not the notional amount of the derivatives) in the event of nonperformance by the counterparty to the interest rate swap agreements.  Additionally, the Bank receives a fee from the customer that is recognized when the Bank has fulfilled its obligations under each agreement, which is generally upon execution of the agreement with the Bank’s customer.  Since the terms of the thirty three interest rate swap agreements with the customers are identical to the related swaps with the third party, the income statement impact to the Bank is generally limited to the fees it receives from the customer.
Other Financial Instruments	Other Financial Instruments
	The Company is a party to certain other financial instruments with off-balance-sheet risk such as commitments to extend credit, unused lines of credit, as well as certain mortgage loans sold to investors with recourse. The Company’s policy is to record such instruments when funded.
	Standby letters of credit are conditional commitments issued to guarantee the performance of a customer to a third party.  The credit risk involved in issuing letters of credit is essentially the same as that involved in extending loan facilities to customers.  Under the standby letters of credit, the Company is required to make payments to the beneficiary of the letters of credit upon request by the beneficiary contingent upon the customer's failure to perform under the terms of the underlying contract with the beneficiary.  Standby letters of credit typically have one year expirations with an option to renew upon annual review.  The Company typically receives a fee for these transactions.  The fair value of stand-by letters of credit is recorded upon inception.
Loan Sales and Loan Servicing	Loan Sales and Loan Servicing
	The Company originates and services residential mortgage loans for consumers and sells 15-year, 20-year and 30-year residential real estate mortgages in the secondary market when the interest rate environment is determined to be favorable by management, while retaining servicing rights on the sold loans.  Loan sales are recorded when the sales are funded.  Mortgage servicing rights are recorded at fair value upon sale of the loan.  Loans held for sale are recorded at the lower of cost or market.
Repurchase Agreements	Repurchase Agreements
	Repurchase agreements are accounted for as secured financing transactions since the Company maintains effective control over the transferred securities and the transfer meets the other criteria for such accounting.  Obligations to repurchase securities sold are reflected as a liability in the Consolidated Balance Sheets.  The securities underlying the agreements are delivered to a custodial account for the benefit of the dealer or bank with whom each transaction is executed.  The dealers or banks, who may sell, loan or otherwise dispose of such securities to other parties in the normal course of their operations, agree to resell to the Company the same securities at the maturities of the agreements.
Earnings Per Share	Earnings Per Share
	Basic earnings per share (EPS) excludes dilution and is computed by dividing income available to common stockholders by the weighted average number of common shares outstanding for the period. Diluted EPS reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock or resulted in the issuance of common stock that then shared in the earnings of the entity (such as the Company’s dilutive stock options and restricted stock).
Subsequent Events	Subsequent Events
	The Company has evaluated subsequent events for potential recognition and/or disclosure and there were none identified.
Comprehensive Income	Comprehensive Income
	At the Company, comprehensive income represents net income plus other comprehensive income (loss), which consists primarily of the net change in unrealized gains or losses on securities available for sale for the period and changes in the funded status of employee benefit plans. Accumulated other comprehensive (loss) income represents the net unrealized gains or losses on securities available for sale and the previously unrecognized portion of the funded status of employee benefit plans, net of income taxes, as of the consolidated balance sheet dates.
Pension Costs	Pension Costs
	The Company maintains a noncontributory, defined benefit pension plan covering substantially all employees, as well as supplemental employee retirement plans covering certain executives and a defined benefit postretirement healthcare plan that covers certain employees.  Costs associated with these plans, based on actuarial computations of current and future benefits for employees, are charged to current operating expenses.
Trust Operations	Trust Operations
	Assets held by the Company in a fiduciary or agency capacity for its customers are not included in the accompanying consolidated balance sheets, since such assets are not assets of the Company.  Trust income is recognized on the accrual method based on contractual rates applied to the balances of trust accounts.
Fair Value Measurements	Fair Value Measurements
	Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value measurements are not adjusted for transaction costs.  A fair value hierarchy prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (level 1 measurements) and the lowest priority to unobservable inputs (level 3 measurements). The three levels of the fair value hierarchy are described below:
	Level 1 - Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities;
	Level 2 -  Quoted prices for similar assets or liabilities in active markets, quoted prices in markets that are not active, or inputs that are observable, either directly or indirectly, for substantially the full term of the asset or liability;
	Level 3 - Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity).
	A financial instrument’s level within the fair value hierarchy is based on the lowest level of input that is significant to the fair value measurement.
	The types of instruments valued based on quoted market prices in active markets include most U.S. government and agency securities, many other sovereign government obligations, liquid mortgage products, active listed equities and most money market securities. Such instruments are generally classified within level 1 or level 2 of the fair value hierarchy.  The Company does not adjust the quoted price for such instruments.
	The types of instruments valued based on quoted prices in markets that are not active, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency include most investment-grade and high-yield corporate bonds, less liquid mortgage products, less liquid agency securities, less liquid listed equities, state, municipal and provincial obligations, and certain physical commodities. Such instruments are generally classified within level 2 of the fair value hierarchy.
	Level 3 is for positions that are not traded in active markets or are subject to transfer restrictions, valuations are adjusted to reflect illiquidity and/or non-transferability, and such adjustments are generally based on available market evidence. In the absence of such evidence, management’s best estimate will be used. Management’s best estimate consists of both internal and external support on certain Level 3 investments. Subsequent to inception, management only changes level 3 inputs and assumptions when corroborated by evidence such as transactions in similar instruments, completed or pending third-party transactions in the underlying investment or comparable entities, subsequent rounds of financing, recapitalizations and other transactions across the capital structure, offerings in the equity or debt markets, and changes in financial ratios or cash flows.

Securities_Tables

Securities (Tables)	12 Months Ended
	Dec. 31, 2014
Securities [Abstract]
Amortized cost, estimated fair value, and unrealized gains and losses of securities available for sale	The amortized cost, estimated fair value, and unrealized gains and losses of securities available for sale are as follows:
	(In thousands)	Amortized cost		Unrealized gains			Unrealized losses		Estimated fair value
	31-Dec-14
	U.S. Treasury	$	23,041	$	70		$	-	$	23,111
	Federal agency		332,193		327			2,606		329,914
	State & municipal		37,035		587			52		37,570
	Mortgage-backed:
	Government-sponsored enterprises		339,190		7,597			224		346,563
	U.S. government agency securities		17,367		863			66		18,164
	Collateralized mortgage obligations:
	Government-sponsored enterprises		199,837		1,828			234		201,431
	U.S. government agency securities		40,237		497			36		40,698
	Other securities		12,818		3,054			152		15,720
	Total securities available for sale	$	1,001,718	$	14,823		$	3,370	$	1,013,171
	31-Dec-13
	U.S. Treasury	$	43,279	$	337		$	-	$	43,616
	Federal agency		285,880		343			7,308		278,915
	State & municipal		113,435		1,842			1,612		113,665
	Mortgage-backed:
	Government-sponsored enterprises		337,666		5,788			2,131		341,323
	U.S. government securities		21,924		1,002			85		22,841
	Collateralized mortgage obligations:
	Government-sponsored enterprises		521,257		1,777			18,141		504,893
	U.S. government securities		43,943		794			102		44,635
	Other securities		12,367		2,854			228		14,993
	Total securities available for sale	$	1,379,751	$	14,737		$	29,607	$	1,364,881
Schedule of sales transactions of securities available for sale	The following table sets forth information with regard to sales transactions of securities available for sale:
		Years ended December 31
	(In thousands)	2014		2013			2012
	Proceeds from sales	$	189	$	27,593		$	1,790
	Gross realized gains	$	49	$	1,283		$	442
	Gross realized losses		-		-			-
	Net securities gains	$	49	$	1,283		$	442
Amortized cost, estimated fair value, and unrealized gains and losses of securities held to maturity	The amortized cost, estimated fair value, and unrealized gains and losses of securities held to maturity are as follows:
	(In thousands)	Amortized		Unrealized			Unrealized		Estimated
		cost		gains			losses		fair value
	31-Dec-14
	Mortgage-backed	$	755	$	113		$	-	$	868
	Collateralized mortgage obligations		317,628		1,934			1,965		317,597
	State & municipal		135,978		674			123		136,529
	Total securities held to maturity	$	454,361	$	2,721		$	2,088	$	454,994
	31-Dec-13
	Mortgage-backed	$	953	$	128		$	-	$	1,081
	Collateralized mortgage obligations		62,025		-			4,569		57,456
	State & municipal		54,305		442			8		54,739
	Total securities held to maturity	$	117,283	$	570		$	4,577	$	113,276
Investment securities with unrealized losses	The following table sets forth information with regard to investment securities with unrealized losses at December 31, 2014 and 2013, segregated according to the length of time the securities had been in a continuous unrealized loss position:
		Less than 12 months							12 months or longer							Total
	Security Type:	Fair		Unrealized			Number		Fair		Unrealized			Number		Fair		Unrealized			Number
		Value		losses			of		Value		losses			of		Value		losses			of
							Positions							Positions							Positions
	31-Dec-14
	Investment securities available for sale:
	Federal agency	$	66,528	$	(226	)		8	$	198,151	$	(2,380	)		16	$	264,679	$	(2,606	)		24
	State & municipal		8,818		(42	)		33		1,321		(10	)		5		10,139		(52	)		38
	Mortgage-backed		10,400		(36	)		10		35,565		(254	)		31		45,965		(290	)		41
	Collateralized mortgage obligations		57,682		(196	)		8		6,598		(74	)		4		64,280		(270	)		12
	Other securities		-		-			-		3,201		(152	)		2		3,201		(152	)		2
	Total securities with unrealized losses	$	143,428	$	(500	)		59	$	244,836	$	(2,870	)		58	$	388,264	$	(3,370	)		117
	31-Dec-14
	Investment securities held to maturity:
	Collateralized mortgage obligations	$	26,052	$	(49	)		2	$	46,415	$	(1,916	)		4	$	72,467	$	(1,965	)		6
	State & municipal		43,514		(116	)		110		1,619		(7	)		6		45,133		(123	)		116
	Total securities with unrealized losses	$	69,566	$	(165	)		112	$	48,034	$	(1,923	)		10	$	117,600	$	(2,088	)		122
	31-Dec-13
	Investment securities available for sale:
	Federal agency	$	233,935	$	(6,927	)		20	$	9,619	$	(381	)		1	$	243,554	$	(7,308	)		21
	State & municipal		50,328		(1,612	)		177		-		-			-		50,328		(1,612	)		177
	Mortgage-backed		143,080		(2,216	)		79		-		-			-		143,080		(2,216	)		79
	Collateralized mortgage obligations		379,273		(18,243	)		36		-		-			-		379,273		(18,243	)		36
	Other securities		5,490		(203	)		2		223		(25	)		1		5,713		(228	)		3
	Total securities with unrealized losses	$	812,106	$	(29,201	)		314	$	9,842	$	(406	)		2	$	821,948	$	(29,607	)		316
	31-Dec-13
	Investment securities held to maturity:
	Collateralized mortgage obligations	$	57,456	$	(4,569	)		5	$	-	$	-			-	$	57,456	$	(4,569	)		5
	State & municipal		1,012		(8	)		1		-		-			-		1,012		(8	)		1
	Total securities with unrealized losses	$	58,468	$	(4,577	)		6	$	-	$	-			-	$	58,468	$	(4,577	)		6
Contractual maturities of debt securities	The following tables set forth information with regard to contractual maturities of debt securities at December 31, 2014:
	(In thousands)	Amortized		Estimated fair
		cost		value
	Debt securities classified as available for sale
	Within one year	$	28,193	$	28,310
	From one to five years		356,696		356,107
	From five to ten years		160,816		163,924
	After ten years		443,195		449,110
		$	988,900	$	997,451
	Debt securities classified as held to maturity
	Within one year	$	22,999	$	23,075
	From one to five years		15,506		15,606
	From five to ten years		87,326		87,640
	After ten years		328,530		328,673
		$	454,361	$	454,994

Loans_Tables

Loans (Tables)	12 Months Ended
	Dec. 31, 2014
Loans [Abstract]
Loans, net of deferred fees and origination costs	A summary of loans, net of deferred fees and origination costs, by category is as follows:
		At December 31,
	(In thousands)	2014			2013
	Residential real estate mortgages	$	1,115,589		$	1,041,637
	Commercial		839,770			859,026
	Commercial real estate		1,442,989			1,328,313
	Real estate construction and development		83,750			93,247
	Agricultural and agricultural real estate mortgages		107,195			112,035
	Consumer		1,436,382			1,352,638
	Home equity		569,596			619,899
	Total loans	$	5,595,271		$	5,406,795
Related party loans	The aggregate amount of loans outstanding to qualifying related parties and changes during the years are summarized as follows:
	(In thousands)	2014			2013
	Balance at January 1	$	3,372		$	2,790
	New loans		522			569
	Adjustment due to change in composition of related parties		253			376
	Repayments		(571	)		(363	)
	Balance at December 31	$	3,576		$	3,372

Allowance_for_Loan_Losses_and_1

Allowance for Loan Losses and Credit Quality of Loans (Tables)	12 Months Ended
	Dec. 31, 2014
Allowance for Loan Losses and Credit Quality of Loans [Abstract]
Allowance for loan losses by portfolio	The following table illustrates the changes in the allowance for loan losses by portfolio segment for the years ended December 31, 2014, 2013 and 2012:
	Allowance for Loan Losses
	(in thousands)
			Commercial				Consumer				Residential				Unallocated			Total
			Loans				Loans				Real Estate
											Mortgages
	Balance as of December 31, 2013		$	35,090			$	27,694			$	6,520			$	130		$	69,434
	Charge-offs			(9,414	)			(16,642	)			(1,417	)			-			(27,473	)
	Recoveries			1,774				2,800				285				-			4,859
	Provision			4,983				12,868				1,742				(54	)		19,539
	Ending Balance as of December 31, 2014		$	32,433			$	26,720			$	7,130			$	76		$	66,359
	Balance as of December 31, 2012		$	35,624			$	27,162			$	6,252			$	296		$	69,334
	Charge-offs			(10,459	)			(15,459	)			(1,771	)			-			(27,689	)
	Recoveries			1,957				3,136				272				-			5,365
	Provision			7,968				12,855				1,767				(166	)		22,424
	Ending Balance as of December 31, 2013		$	35,090			$	27,694			$	6,520			$	130		$	69,434
	Balance as of December 31, 2011		$	38,831			$	26,049			$	6,249			$	205		$	71,334
	Charge-offs			(8,750	)			(15,848	)			(1,906	)			-			(26,504	)
	Recoveries			1,641				2,556				38				-			4,235
	Provision			3,902				14,405				1,871				91			20,269
	Ending Balance as of December 31, 2012		$	35,624			$	27,162			$	6,252			$	296		$	69,334
	The following table illustrates the allowance for loan losses and the recorded investment by portfolio segment as of December 31, 2014 and 2013:
	Allowance for Loan Losses and Recorded Investment in Loans
	(in thousands)
			Commercial				Consumer				Residential				Unallocated			Total
			Loans				Loans				Real Estate
											Mortgages
	As of December 31, 2014
	Allowance for loan losses		$	32,433			$	26,720			$	7,130			$	76		$	66,359
	Allowance for loans individually evaluated for impairment			1,100				-				-							1,100
	Allowance for loans collectively evaluated for impairment		$	31,333			$	26,720			$	7,130			$	76		$	65,259
	Ending balance of loans		$	2,473,702			$	2,005,980			$	1,115,589						$	5,595,271
	Ending balance of originated loans individually evaluated for impairment			11,079				5,498				3,544							20,121
	Ending balance of acquired loans individually evaluated for impairment			5,675				-				-							5,675
	Ending balance of acquired loans collectively evaluated for impairment			327,656				147,256				266,747							741,659
	Ending balance of originated loans collectively evaluated for impairment		$	2,129,292			$	1,853,226			$	845,298						$	4,827,816
	As of December 31, 2013
	Allowance for loan losses		$	35,090			$	27,694			$	6,520			$	130		$	69,434
	Allowance for loans individually evaluated for impairment			715				-				-							715
	Allowance for loans collectively evaluated for impairment		$	34,375			$	27,694			$	6,520			$	130		$	68,719
	Ending balance of loans		$	2,392,621			$	1,972,537			$	1,041,637						$	5,406,795
	Ending balance of originated loans individually evaluated for impairment			16,120				3,248				2,012							21,380
	Ending balance of acquired loans individually evaluated for impairment			10,060				-				-							10,060
	Ending balance of acquired loans collectively evaluated for impairment			392,329				219,587				308,416							920,332
	Ending balance of originated loans collectively evaluated for impairment		$	1,974,112			$	1,749,702			$	731,209						$	4,455,023
Past due and nonperforming loans by loan class	The following table illustrates the Company’s nonaccrual loans by loan class as of December 31, 2014 and 2013:
	(In thousands)		31-Dec-14				31-Dec-13
	ORIGINATED
	Commercial Loans
	Commercial		$	1,012			$	3,669
	Commercial Real Estate			4,127				7,834
	Agricultural			817				1,135
	Agricultural Real Estate			565				961
	Business Banking			6,910				5,701
				13,431				19,300
	Consumer Loans
	Indirect			1,964				1,461
	Home Equity			6,596				5,931
	Direct			84				86
				8,644				7,478
	Residential Real Estate Mortgages			8,770				7,105
			$	30,845			$	33,883
	ACQUIRED
	Commercial Loans
	Commercial		$	3,009			$	6,599
	Commercial Real Estate			2,666				3,559
	Business Banking			665				1,340
				6,340				11,498
	Consumer Loans
	Indirect			106				93
	Home Equity			557				570
	Direct			33				49
				696				712
	Residential Real Estate Mortgages			3,193				3,872
			$	10,229			$	16,082
	TOTAL NONACCRUAL LOANS		$	41,074			$	49,965
	The following table sets forth information with regard to past due and nonperforming loans by loan class:
	Age Analysis of Past Due Financing Receivables
	As of December 31, 2014
	(in thousands)
			31-60 Days				61-90 Days				Greater				Total			Non-Accrual				Current		Recorded Total
			Past Due				Past Due				Than				Past Due									Loans
			Accruing				Accruing				90 Days				Accruing
											Past Due
											Accruing
	ORIGINATED
	Commercial Loans
	Commercial		$	-			$	735			$	-			$	735		$	1,012			$	613,400	$	615,147
	Commercial Real Estate			192				-				-				192			4,127				1,064,549		1,068,868
	Agricultural			-				-				-				-			817				32,130		32,947
	Agricultural Real Estate			19				-				-				19			565				24,390		24,974
	Business Banking			799				235				84				1,118			6,910				390,407		398,435
				1,010				970				84				2,064			13,431				2,124,876		2,140,371
	Consumer Loans
	Indirect			16,434				3,154				1,991				21,579			1,964				1,286,507		1,310,050
	Home Equity			4,591				1,428				821				6,840			6,596				479,444		492,880
	Direct			560				157				52				769			84				54,941		55,794
				21,585				4,739				2,864				29,188			8,644				1,820,892		1,858,724
	Residential Real Estate Mortgages			2,901				96				1,256				4,253			8,770				835,819		848,842
			$	25,496			$	5,805			$	4,204			$	35,505		$	30,845			$	4,781,587	$	4,847,937
	ACQUIRED
	Commercial Loans
	Commercial		$	-			$	-			$	-			$	-		$	3,009			$	72,255	$	75,264
	Commercial Real Estate			-				-				-				-			2,666				197,222		199,888
	Business Banking			5				15				-				20			665				57,494		58,179
				5				15				-				20			6,340				326,971		333,331
	Consumer Loans
	Indirect			518				5				54				577			106				64,540		65,223
	Home Equity			190				60				5				255			557				75,904		76,716
Direct			31				-				7				38			33				5,246		5,317
			739				65				66				870			696				145,690		147,256
Residential Real Estate Mortgages			1,162				265				671				2,098			3,193				261,456		266,747
		$	1,906			$	345			$	737			$	2,988		$	10,229			$	734,117	$	747,334
Total Loans		$	27,402			$	6,150			$	4,941			$	38,493		$	41,074			$	5,515,704	$	5,595,271
Age Analysis of Past Due Financing Receivables
As of December 31, 2013
(in thousands)
		31-60 Days				61-90 Days				Greater				Total			Non-Accrual				Current		Recorded Total
		Past Due				Past Due				Than				Past Due									Loans
		Accruing				Accruing				90 Days				Accruing
										Past Due
										Accruing
ORIGINATED
Commercial Loans
Commercial		$	105			$	247			$	-			$	352		$	3,669			$	612,402	$	616,423
Commercial Real Estate			1,366				-				-				1,366			7,834				925,116		934,316
Agricultural			150				21				-				171			1,135				63,856		65,162
Agricultural Real Estate			519				-				-				519			961				35,172		36,652
Business Banking			1,228				122				105				1,455			5,701				330,523		337,679
			3,368				390				105				3,863			19,300				1,967,069		1,990,232
Consumer Loans
Indirect			14,093				2,878				1,583				18,554			1,461				1,141,829		1,161,844
Home Equity			6,033				1,888				1,115				9,036			5,931				517,856		532,823
Direct			679				125				46				850			86				57,347		58,283
			20,805				4,891				2,744				28,440			7,478				1,717,032		1,752,950
Residential Real Estate Mortgages			3,951				379				808				5,138			7,105				720,978		733,221
		$	28,124			$	5,660			$	3,657			$	37,441		$	33,883			$	4,405,079	$	4,476,403
ACQUIRED
Commercial Loans
Commercial		$	24			$	-			$	-			$	24		$	6,599			$	96,603	$	103,226
Commercial Real Estate			-				-				-				-			3,559				225,455		229,014
Business Banking			320				2				-				322			1,340				68,487		70,149
			344				2				-				346			11,498				390,545		402,389
Consumer Loans
Indirect			939				113				71				1,123			93				123,870		125,086
Home Equity			753				63				-				816			570				85,690		87,076
Direct			76				56				9				141			49				7,235		7,425
			1,768				232				80				2,080			712				216,795		219,587
Residential Real Estate Mortgages			1,725				-				-				1,725			3,872				302,819		308,416
		$	3,837			$	234			$	80			$	4,151		$	16,082			$	910,159	$	930,392
Total Loans		$	31,961			$	5,894			$	3,737			$	41,592		$	49,965			$	5,315,238	$	5,406,795
Impaired loans and specific reserve allocations	The following provides additional information on loans specifically evaluated for impairment for the years ended December 31, 2014 and 2013
	Impaired Loans
			31-Dec-14												31-Dec-13
	(in thousands)		Recorded				Unpaid			Related					Recorded			Unpaid			Related
			Investment				Principal			Allowance					Investment			Principal			Allowance
			Balance				Balance								Balance			Balance
			(Book)				(Legal)								(Book)			(Legal)
	ORIGINATED
	With no related allowance recorded:
	Commercial Loans
	Commercial		$	1,748			$	1,901							$	4,721		$	4,777
	Commercial Real Estate			4,505				4,520								4,613			5,164
	Agricultural			20				26								125			195
	Agricultural Real Estate			1,147				1,441								1,431			1,708
	Business Banking			896				1,301								210			602
	Total Commercial Loans			8,316				9,189								11,100			12,446
	Consumer Loans
	Home Equity			5,498				6,033								3,248			3,472
	Residential Real Estate Mortgages			3,544				3,959								2,012			2,255
	Total			17,358				19,181								16,360			18,173
	With an allowance recorded:
	Commercial Loans
	Commercial Real Estate			2,763				4,611				600				5,020			6,877				715
	ACQUIRED
	With no related allowance recorded:
	Commercial Loans
	Commercial			-				-								6,501			6,538
	Commercial Real Estate			2,666				3,830								3,559			3,842
	Total Commercial Loans			2,666				3,830								10,060			10,380
	With an  allowance recorded:
	Commercial Loans
	Commercial			3,009				4,668				500				-			-				-
	Total		$	25,796			$	32,290			$	1,100			$	31,440		$	35,430			$	715
	The following table summarizes the average recorded investments on loans specifically evaluated for impairment and the interest income recognized for the years ended December 31, 2014, 2013 and 2012:
			31-Dec-14								31-Dec-13							31-Dec-12
	(in thousands)		Average				Interest Income				Average				Interest Income			Average				Interest Income
			Recorded				Recognized				Recorded				Recognized			Recorded				Recognized
			Investment				Accrual				Investment				Accrual			Investment				Accrual
	ORIGINATED
	Commercial Loans
	Commercial		$	1,954			$	115			$	3,488			$	-		$	6,682			$	56
	Commercial Real Estate			9,679				169				11,085				95			4,944				230
	Agricultural			91				1				1,035				1			1,767				43
	Agricultural Real Estate			1,346				46				1,067				47			922				72
	Business Banking			610				55				127				61			68				65
	Consumer Loans
	Home Equity			5,198				267				3,120				145			1,877				123
	Residential Real Estate Mortgages			3,039				119				2,085				69			1,143				54
	ACQUIRED
	Commercial Loans
	Commercial			5,756				-				-				-			-				-
	Commercial Real Estate			3,386				-				1,310				-			-				-
	Total		$	31,059			$	772			$	23,317			$	418		$	17,403			$	643
Financing receivable credit quality by loan class	The following tables illustrate the Company’s credit quality by loan class for the years ended December 31, 2014 and 2013:
	Credit Quality Indicators
	31-Dec-14
	(In thousands)
	ORIGINATED
	Commercial Credit Exposure
	By Internally Assigned Grade:	Commercial			Commercial			Agricultural			Agricultural			Total
					Real Estate						Real Estate
	Pass	$	$570,884		$	1,023,856		$	30,481		$	23,443		$	1,648,664
	Special Mention		6,022			17,341			275			42			23,680
	Substandard		38,241			27,671			2,183			1,489			69,584
	Doubtful		-			-			8			-			8
	Total	$	615,147		$	1,068,868		$	32,947		$	24,974		$	1,741,936
	Business Banking Credit Exposure
	By Internally Assigned Grade:	Business Banking									Total
	Non-classified	$	379,445								$	379,445
	Classified		18,990									18,990
	Total	$	398,435								$	398,435
	Consumer Credit Exposure
	By Payment Activity:	Indirect			Home Equity			Direct			Total
	Performing	$	1,306,095		$	485,463		$	55,658		$	1,847,216
	Nonperforming		3,955			7,417			136			11,508
	Total	$	1,310,050		$	492,880		$	55,794		$	1,858,724
	Residential Mortgage Credit Exposure
	By Payment Activity:	Residential			Total
		Mortgage
	Performing	$	838,816		$	838,816
	Nonperforming		10,026			10,026
	Total	$	848,842		$	848,842
	Credit Quality Indicators
	31-Dec-14
	(In thousands)
	ACQUIRED
	Commercial Credit Exposure
	By Internally Assigned Grade:	Commercial			Commercial			Agricultural			Total
					Real Estate
	Pass	$	63,630		$	186,036		$	-		$	249,666
	Special Mention		2,840			2,646			-			5,486
	Substandard		8,794			11,206			-			20,000
	Doubtful		-			-			-			-
	Total	$	75,264		$	199,888		$	-		$	275,152
	Business Banking Credit Exposure
	By Internally Assigned Grade:	Business Banking			Total
	Non-classified	$	53,264		$	53,264
	Classified		4,915			4,915
	Total	$	58,179		$	58,179
	Consumer Credit Exposure
	By Payment Activity:	Indirect			Home Equity			Direct			Total
	Performing	$	65,063		$	76,154		$	5,277		$	146,494
	Nonperforming		160			562			40			762
	Total	$	65,223		$	76,716		$	5,317		$	147,256
	Residential Mortgage Credit Exposure
	By Payment Activity:	Residential Mortgage			Total
	Performing	$	262,883		$	262,883
	Nonperforming		3,864			3,864
	Total	$	266,747		$	266,747
	Credit Quality Indicators
	31-Dec-13
	(In thousands)
	Commercial Credit Exposure
	By Internally Assigned Grade:		Commercial				Commercial				Agricultural				Agricultural			Total
							Real Estate								Real Estate
	Pass		$	576,079			$	878,411			$	60,043			$	33,136		$	1,547,669
	Special Mention			16,836				22,777				381				43			40,037
Substandard			23,508				33,128				4,726				3,473			64,835
Doubtful			-				-				12				-			12
Total		$	616,423			$	934,316			$	65,162			$	36,652		$	1,652,553
Business Banking Credit Exposure
By Internally Assigned Grade:	Business Banking									Total
Non-classified	$	319,578								$	319,578
Classified		18,101									18,101
Total	$	337,679								$	337,679
Consumer Credit Exposure
By Payment Activity:	Indirect			Home Equity			Direct			Total
Performing	$	1,158,800		$	525,777		$	58,151		$	1,742,728
Nonperforming		3,044			7,046			132			10,222
Total	$	1,161,844		$	532,823		$	58,283		$	1,752,950
Residential Mortgage Credit Exposure
By Payment Activity:	Residential			Total
	Mortgage
Performing	$	725,308		$	725,308
Nonperforming		7,913			7,913
Total	$	733,221		$	733,221
Credit Quality Indicators
31-Dec-13
(In thousands)
ACQUIRED
Commercial Credit Exposure
By Internally Assigned Grade:	Commercial			Commercial			Agricultural			Total
				Real Estate
Pass	$	85,692		$	205,010		$	-		$	290,702
Special Mention		2,230			6,183			-			8,413
Substandard		15,304			17,821			-			33,125
Doubtful		-			-			-			-
Total	$	103,226		$	229,014		$	-		$	332,240
Business Banking Credit Exposure
By Internally Assigned Grade:	Business Banking			Total
Non-classified	$	65,437		$	65,437
Classified		4,712			4,712
Total	$	70,149		$	70,149
Consumer Credit Exposure
By Payment Activity:	Indirect			Home Equity			Direct			Total
Performing	$	124,922		$	86,506		$	7,367		$	218,795
Nonperforming		164			570			58			792
Total	$	125,086		$	87,076		$	7,425		$	219,587
Residential Mortgage Credit Exposure
By Payment Activity:	Residential Mortgage			Total
Performing	$	304,544		$	304,544
Nonperforming		3,872			3,872
Total	$	308,416		$	308,416

Premises_and_Equipment_Net_Tab

Premises and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2014
Premises and Equipment, Net [Abstract]
Summary of premises and equipment	A summary of premises and equipment follows:
		December 31,
	(In thousands)	2014		2013
	Land, buildings, and improvements	$	122,400	$	120,098
	Equipment		58,835		55,729
	Premises and equipment before accumulated depreciation		181,235		175,827
	Accumulated depreciation		91,977		87,500
	Total premises and equipment	$	89,258	$	88,327
Future minimum rental payments related to noncancelable operating leases	The future minimum rental payments related to noncancelable operating leases with original terms of one year or more are as follows at December 31, 2014 (in thousands):
	Future Minimum Rental Payments
	2015	$	7,369
	2016		7,215
	2017		6,811
	2018		6,122
	2019		5,655
	Thereafter		26,257
	Total	$	59,429

Goodwill_and_other_Intangible_1

Goodwill and other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and other Intangible Assets [Abstract]
Summary of goodwill	A summary of goodwill is as follows:
	(In thousands)
	1-Jan-14	$	264,997
	Goodwill Adjustments		(1,363	)
	31-Dec-14	$	263,634
	1-Jan-13	$	152,373
	Goodwill Acquired		112,624
	31-Dec-13	$	264,997
Summary of core deposit and other intangible assets	A summary of core deposit and other intangible assets follows:
		December 31,
	(In thousands)	2014			2013
	Core deposit intangibles
	Gross carrying amount	$	19,401		$	19,401
	Less: accumulated amortization		12,522			10,083
	Net carrying amount		6,879			9,318
	Identified intangible assets
	Gross carrying amount		28,316			28,509
	Less: accumulated amortization		14,878			12,270
	Net carrying amount		13,438			16,239
	Total intangibles
	Gross carrying amount		47,717			47,910
	Less: accumulated amortization		27,400			22,353
	Net carrying amount	$	20,317		$	25,557

Deposits_Tables

Deposits (Tables)	12 Months Ended
	Dec. 31, 2014
Deposits [Abstract]
Maturity distribution of time deposits	The following table sets forth the maturity distribution of time deposits at December 31, 2014 (in thousands):
	Time deposits
	Within one year	$	464,853
	After one but within two years		132,999
	After two but within three years		143,142
	After three but within four years		80,804
	After four but within five years		204,492
	After five years		17,533
	Total	$	1,043,823

ShortTerm_Borrowings_Tables

Short-Term Borrowings (Tables)	12 Months Ended
	Dec. 31, 2014
Short-Term Borrowings [Abstract]
Information related to short-term borrowings	Information related to short-term borrowings is summarized as follows:
	(In thousands)	2014			2013			2012
	Federal funds purchased
	Balance at year-end	$	68,000		$	130,000		$	10,000
	Average during the year		110,154			39,907			12,658
	Maximum month end balance		183,000			130,000			60,000
	Weighted average rate during the year		0.29	%		0.26	%		0.27	%
	Weighted average rate at December 31		0.34	%		0.18	%		0.27	%
	Securities sold under repurchase agreements
	Balance at year-end	$	148,802		$	176,042		$	152,941
	Average during the year		165,858			169,352			153,084
	Maximum month end balance		182,861			185,871			165,977
	Weighted average rate during the year		0.06	%		0.06	%		0.1	%
	Weighted average rate at December 31		0.06	%		0.05	%		0.1	%
	Other short-term borrowings
	Balance at year-end	$	100,000		$	150,000		$	-
	Average during the year		106,438			71,589			-
	Maximum month end balance		320,000			210,000			-
	Weighted average rate during the year		0.4	%		0.43	%		0	%
	Weighted average rate at December 31		0.36	%		0.55	%		0	%

LongTerm_Debt_Tables

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Long-Term Debt [Abstract]
Schedule of long-term debt	A summary as of December 31, 2014 and 2013 is as follows:
	(In thousands)	As of December 31, 2014										As of December 31, 2013
	Maturity	Amount		Weighted Average Rate			Callable Amount		Weighted Average Rate			Amount		Weighted Average Rate			Callable Amount		Weighted Average Rate
	2014		-		-			-		-			12,460		1.33	%		-		-
	2015		217		-			-		-			308		-			-		-
	2016		50,626		2.91	%		30,000		4.15	%		90,313		3.52	%		70,000		4.21	%
	2017		40,000		2.68	%		25,000		3.48	%		115,312		3.55	%		75,000		3.73	%
	2018		40,000		2.57	%		25,000		3.15	%		90,313		3.26	%		75,000		3.61	%
	2021		102		4	%		-		-			117		4	%		-		-
		$	130,945				$	80,000				$	308,823				$	220,000

Junior_Subordinated_Debt_Table

Junior Subordinated Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Junior Subordinated Debt [Abstract]
Schedule of debt of VIE where entity is not primary beneficiary	As of December 31, 2014, the Trusts had the following issues of trust preferred debentures, all held by the Trusts, outstanding (dollars in thousands):
	Description	Issuance Date	Trust Preferred Securities Outstanding		Interest Rate	Trust Preferred Debt Owed To Trust		Final Maturity Date
	CNBF Capital Trust I	August 1999	$	18,000	3-month LIBOR plus 2.75%	$	18,720	Aug-29
	NBT Statutory Trust I	November 2005		5,000	3-month LIBOR plus 1.40%		5,155	Dec-35
	NBT Statutory Trust II	Feb-06		50,000	3-month LIBOR plus 1.40%		51,547	Mar-36
	Alliance Financial Capital Trust I	Dec-03		10,000	3-month LIBOR plus 2.85%		10,310	Jan-34
	Alliance Financial Capital Trust II	Sep-06		15,000	3-month LIBOR plus 1.65%		15,464	Sep-36

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Taxes [Abstract]
Components of income tax expense attributable to operations	The significant components of income tax expense attributable to operations are:
		Years ended December 31,
	(In thousands)	2014			2013			2012
	Current
	Federal	$	26,059		$	23,536		$	21,011
	State		2,823			2,316			1,815
			28,882			25,852			22,826
	Deferred
	Federal		6,648			2,334			(13	)
	State		1,699			10			3
			8,347			2,344			(10	)
	Total income tax expense	$	37,229		$	28,196		$	22,816
Components of deferred tax assets and liabilities	The tax effects of temporary differences that give rise to significant portions of the deferred tax assets and deferred tax liabilities are as follows:
		December 31,
	(In thousands)	2014			2013
	Deferred tax assets
	Allowance for loan losses	$	25,689		$	26,729
	Deferred compensation		8,744			7,931
	Postretirement benefit obligation		2,377			2,596
	Unrealized losses on securities available for sale		-			5,900
	Accrued liabilities		1,778			3,265
	Stock-based compensation expense		6,457			7,862
	Equipment leasing		1,416			1,661
	Other		1,325			2,125
	Total deferred tax assets		47,786			58,069
	Deferred tax liabilities
	Pension and executive retirement		12,192			17,417
	Fair value adjustments from acquisitions		1,243			2,070
	Unrealized gains on securities available for sale		1,331			-
	Premises and equipment, primarily due to accelerated depreciation		2,491			2,270
	Deferred loan costs		1,460			1,624
	Intangible amortization		14,162			12,007
	Other		390			892
	Total deferred tax liabilities		33,269			36,280
	Net deferred tax asset at year-end		14,517			21,789
	Net deferred tax asset at beginning of year		21,789			11,115
	(Decrease) Increase in net deferred tax asset	$	(7,272	)	$	10,674
Reconciliation of the provision for income taxes to the amount computed by applying the federal statutory rate	The following is a reconciliation of the provision for income taxes to the amount computed by applying the applicable Federal statutory rate of 35 % to income before taxes:
		Years ended December 31
	(In thousands)	2014			2013			2012
	Federal income tax at statutory rate	$	39,306		$	31,482		$	27,081
	Tax exempt income		(2,250	)		(2,433	)		(2,536	)
	Net increase in CSV of life insurance		(1,734	)		(1,166	)		(908	)
	Low income housing tax credits		(880	)		(819	)		(629	)
	State taxes, net of federal tax benefit		2,939			1,512			1,182
	Other, net		(152	)		(380	)		(1,374	)
	Income tax expense	$	37,229		$	28,196		$	22,816

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Employee Benefit Plans [Abstract]
Components of accumulated other comprehensive income (loss), net periodic benefit cost	The Company expects that $2.4 million in net actuarial loss and $0.2 million in prior service costs will be recognized as components of net periodic benefit cost in 2015.
		Pension Benefits								Other Benefits
	(In thousands)	2014				2013				2014				2013
	Net actuarial loss		$	28,767			$	11,286			$	2,929			$	1,628
	Prior service cost			97				118				(314	)			(521	)
	Total amounts recognized in accumulated other comprehensive loss (pre-tax)		$	28,864			$	11,404			$	2,615			$	1,107
Changes in benefit obligations, changes in plan assets, and the funded status of the pension plans and postretirement benefits	A December 31 measurement date is used for the pension, supplemental pension and postretirement benefit plans.  The following table sets forth changes in benefit obligations, changes in plan assets, and the funded status of the pension plans and other postretirement benefits:
			Pension Benefits								Other Benefits
	(In thousands)		2014				2013				2014				2013
	Change in benefit obligation
	Benefit obligation at beginning of year		$	85,667			$	85,130			$	7,428			$	4,071
	Service cost			2,290				2,493				16				23
	Interest cost			4,142				3,223				347				286
	Plan participants' contributions			-				-				266				269
	Actuarial(gain) loss			12,501				(10,853	)			1,452				(369	)
	Amendments			-				-				-				(54	)
	Acquisition			-				10,958				-				3,928
	Benefits paid			(6,044	)			(5,284	)			(799	)			(726	)
	Projected benefit obligation at end of year			98,556				85,667				8,710				7,428
	Change in plan assets
	Fair value of plan assets at beginning of year			118,574				99,705				-				-
	Actual return on plan assets			3,950				18,451				-				-
	Acquisition			-				4,994				-				-
	Employer contributions			752				708				533				457
	Plan participants' contributions			-				-				266				269
	Benefits paid			(6,044	)			(5,284	)			(799	)			(726	)
	Fair value of plan assets at end of year			117,232				118,574				-				-
	Funded status at year end		$	18,676			$	32,907			$	(8,710	)		$	(7,428	)
Amounts recognized in balance sheet	The funded status of the pension and other postretirement benefit plans has been recognized as follows in the consolidated balance sheets at December 31, 2014 and 2013.
		Pension Benefits								Other Benefits
	(In thousands)	2014				2013				2014				2013
	Other assets		$	39,044			$	48,189			$	-			$	-
	Other liabilities			(20,368	)			(15,282	)			(8,710	)			(7,428	)
	Funded status		$	18,676			$	32,907			$	(8,710	)		$	(7,428	)
Assumptions used to determine benefit obligations and net periodic pension cost	The following assumptions were used to determine the benefit obligation and the net periodic pension cost for the years indicated:
			Years ended December 31,
			2014				2013				2012
	Weighted average assumptions:
	The following assumptions were used to determine benefit obligations:
	Discount rate			4.19% - 4.30	%			4.90%-5.05	%			3.5	%
	Expected long-term return on plan assets			7.5	%			7.5	%			7.5	%
	Rate of compensation increase			3.00%-3.75	%			3	%			3	%
	The following assumptions were used to determine net periodic pension cost:
	Discount rate			4.90%-5.05	%			3.5	%			4.1	%
	Expected long-term return on plan assets			7.5	%			7.5	%			7.5	%
	Rate of compensation increase			3.00%-3.75	%			3	%			3	%
Components of net periodic pension benefits and other benefit costs	Net periodic benefit cost and other amounts recognized in other comprehensive income (loss) for the years ended December 31 included the following components:
			Pension Benefits												Other Benefits
	(In thousands)		2014				2013				2012				2014			2013			2012
	Components of net periodic benefit cost
	Service cost		$	2,290			$	2,493			$	3,122			$	16		$	23		$	20
	Interest cost			4,142				3,223				3,145				347			286			155
	Expected return on plan assets			(8,681	)			(7,804	)			(6,686	)			-			-			-
	Amortization of prior service cost			23				23				283				(206	)		(205	)		(202	)
	Amortization of unrecognized net loss			79				2,692				3,330				151			280			182
	Net periodic pension cost		$	(2,147	)		$	627			$	3,194			$	308		$	384		$	155
	Other changes in plan assets and benefit obligations recognized in other comprehensive income (pre-tax)
	Net loss (gain)		$	17,233			$	(21,500	)		$	894			$	1,452		$	(369	)	$	136
	Prior service cost			-				-				(1,006	)			-			(54	)		-
	Amortization of prior service cost			(23	)			(23	)			(283	)			206			205			202
	Amortization of unrecognized net gain			(79	)			(2,692	)			(3,330	)			(151	)		(280	)		(182	)
	Total recognized in other comprehensive loss (income)			17,131				(24,215	)			(3,725	)			1,507			(498	)		156
	Total recognized in net periodic benefit cost and other comprehensive income (loss) - pre-tax		$	14,984			$	(23,588	)		$	(531	)		$	1,815		$	(114	)	$	311
Estimated future benefit payments for the pension plans and other postretirement benefit plans	The following table sets forth estimated future benefit payments for the pension plans and other postretirement benefit plans:
	(In thousands)		Pension				Other
			Benefits				Benefits
	2015			6,011				538
	2016			6,221				549
	2017			9,473				571
	2018			7,100				592
	2019			6,953				578
	2020 - 2024			40,351				2,881
Effect of one-percentage point change in assumed health care cost trend rates	A one-percentage point change in the health care trend rates would have the following effects as of and for the year ended December 31, 2014:
	(In thousands)		One Percentage point increase				One Percentage point decrease
	Increase (decrease) on total service and interest cost components		$	39			$	(33	)
	Increase (decrease) on postretirement accumulated benefit obligation			895				(764	)
Target and actual allocations of defined benefit pension plan's assets	The target and actual allocations expressed as a percentage of the defined benefit pension plan’s assets are as follows:
			Target 2014				2014				2013
	Cash and cash equivalents			0 - 20	%			4	%			6	%
	Fixed income securities			20 - 40	%			38	%			27	%
	Equities			40 - 80	%			58	%			67	%
	Total							100	%			100	%
Financial instruments recorded at fair value on a recurring basis by the Plan	The following table presents the financial instruments recorded at fair value on a recurring basis by the Plan as of December 31, 2014 and 2013:
	(In thousands)		Quoted Prices in Active Markets for				Significant				Balance
			Identical Assets				Other				as of
			(Level 1)				Observable Inputs				31-Dec-14
							(Level 2)
	Cash and cash equivalents		$	4,423			$	-			$	4,423
	Foreign equity mutual funds			38,581				-				38,581
	Equity mutual funds			29,718				-				29,718
	U.S. government bonds			-				4,420				4,420
	Corporate bonds			-				40,090				40,090
	Totals		$	72,722			$	44,510			$	117,232
	(In thousands)		Quoted Prices in Active Markets for Identical Assets				Significant				Balance
			(Level 1)				Other				as of
							Observable Inputs				31-Dec-13
							(Level 2)
	Cash and cash equivalents		$	7,533			$	-			$	7,533
	Foreign equity mutual funds			15,653				-				15,653
	Equity mutual funds			16,727				-				16,727
	U.S. government bonds			-				9,355				9,355
	Corporate bonds			-				19,665				19,665
	Common stock			44,532				-				44,532
	Municipal bonds and notes			-				1,451				1,451
	Foreign bonds and notes			-				1,392				1,392
	Foreign equity			2,266				-				2,266
	Totals		$	86,711			$	31,863			$	118,574

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2014
Stock-Based Compensation [Abstract]
Stock option activity	The following table summarizes information concerning stock options outstanding at December 31, 2014:
		Number of Shares			Weighted average exercise price		Weighted Average Remaining Contractual Term (in yrs)			Aggregate Intrinsic Value
	Outstanding at January 1, 2014		1,341,500		$	22.98
	Granted		3,296			24.8
	Exercised		(290,243	)		22.58
	Forfeited		(105	)		20.19
	Expired		(16,106	)		22.36
	Outstanding at December 31, 2014		1,038,342		$	23.1			3.4		$	3,353,951
	Exercisable at December 31, 2014		1,031,726		$	23.09			3.37		$	3,342,258
	Expected to Vest		5,249		$	24.5			7.32		$	9,354
Cash proceeds, tax benefits and intrinsic value of stock options exercised	Cash proceeds, tax benefits and intrinsic value related to total stock options exercised is as follows:
		Years ended December 31,
	(dollars in thousands)	2014			2013			2012
	Proceeds from stock options exercised	$	6,554		$	7,927		$	1,908
	Tax benefits related to stock options exercised		313			178			8
	Intrinsic value of stock options exercised		789			905			498
	Fair value of shares vested during the year		393			766			1,656
Unvested restricted awards and unvested restricted units activity	The following table summarizes information for unvested restricted stock awards outstanding as of December 31, 2014:
		Number			Weighted-
		of			Average
		Shares			Grant Date Fair
					Value
	Unvested Restricted Stock Awards
	Unvested at January 1, 2014		66,650		$	23.15
	Forfeited		-			-
	Vested		(14,650	)		22.16
	Unvested at December 31, 2014		52,000		$	23.43
	The following table summarizes information for unvested restricted stock units outstanding as of December 31, 2014:
		Number			Weighted-
		of			Average
		Shares			Grant Date Fair
					Value
	Unvested Restricted Stock Units
	Unvested at January 1, 2014		539,850		$	27.36
	Forfeited		(5,090	)		-
	Vested		(105,013	)		-
	Granted		209,228			24.11
	Unvested at December 31, 2014		638,975		$	31.01

Stockholders_Equity_Tables

Stockholders Equity (Tables)	12 Months Ended
	Dec. 31, 2014
Stockholders Equity [Abstract]
Components of accumulated other comprehensive (loss) income	For the years ended December 31, components of accumulated other comprehensive loss are:
	(In thousands)	2014			2013
	Unrecognized prior service cost and net actuarial loss on pension plans	$	(19,181	)	$	(7,785	)
	Unrealized net holding gains (losses) on available for sale securities		2,154			(8,980	)
	Accumulated other comprehensive loss	$	(17,027	)	$	(16,765	)

Regulatory_Capital_Requirement1

Regulatory Capital Requirements (Tables)	12 Months Ended
	Dec. 31, 2014
Regulatory Capital Requirements [Abstract]
Schedule of compliance with regulatory compliance requirements under banking regulations	The Company and NBT Bank’s actual capital amounts and ratios are presented as follows:
		Actual					Regulatory ratio requirements
	(Dollars in thousands)	Amount		Ratio			Minimum			For classification
							capital adequacy			as well capitalized
	As of December 31, 2014
	Total Capital (to risk weighted assets):
	Company	$	777,651		13.5	%		8	%		10	%
	NBT Bank		727,771		12.72	%		8	%		10	%
	Tier I Capital (to risk weighted assets)
	Company		709,965		12.32	%		4	%		6	%
	NBT Bank		660,086		11.54	%		4	%		6	%
	Tier I Capital (to average assets)
	Company		709,965		9.39	%		4	%		5	%
	NBT Bank		660,086		8.79	%		4	%		5	%
	As of December 31, 2013
	Total Capital (to risk weighted assets):
	Company	$	723,580		12.99	%		8	%		10	%
	NBT Bank		686,194		12.41	%		8	%		10	%
	Tier I Capital (to risk weighted assets)
	Company		653,950		11.74	%		4	%		6	%
	NBT Bank		617,038		11.16	%		4	%		6	%
	Tier I Capital (to average assets)
	Company		653,950		8.93	%		4	%		5	%
	NBT Bank		617,038		8.47	%		4	%		5	%

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Reconciliation of basic and diluted earnings per share	The following is a reconciliation of basic and diluted earnings per share for the years presented in the consolidated statements of income:
		Years ended December 31,
		2014								2013								2012
	(In thousands, except per share data)	Net			Weighted		Per share			Net			Weighted		Per share			Net			Weighted		Per share
		income			average		amount			income			average		amount			income			average		amount
					shares								shares								shares
	Basic earnings per share		$	75,074		43,877		$	1.71		$	61,747		41,930		$	1.47		$	54,558		33,379		$	1.63
	Effect of dilutive securities
	Stock based compensation					518								420								340
	Diluted earnings per share		$	75,074		44,395		$	1.69		$	61,747		42,350		$	1.46		$	54,558		33,719		$	1.62

Reclassification_Adjustments_O1

Reclassification Adjustments Out of Other Comprehensive (Loss) Income (Tables)	12 Months Ended
	Dec. 31, 2014
Reclassification Adjustments Out of Other Comprehensive Income (Loss) [Abstract]
Reclassification out of Accumulated Other Comprehensive Income	The following table summarizes the reclassification adjustments out of accumulated other comprehensive loss (in thousands):
	Detail About Accumulated Other Comprehensive (Loss)	Amount reclassified from accumulated other comprehensive income (loss)						Affected line item in the consolidated statement of comprehensive income
	Income Components
		Years ended
		31-Dec-14			31-Dec-13
	Available for sale securities:
	Gains on available for sale securities	$	(92	)	$	(1,426	)	Net securities gains
	Amortization of unrealized gains and losses related to securities transfer		(421	)		-		Interest Income
	Tax benefit		200			565		Income tax expense
	Net of tax	$	(313	)	$	(861	)
	Pension and other benefits:
	Amortization of net gains	$	94		$	2,972		Salaries and employee benefits
	Amortization of prior service costs		(19	)		(182	)	Salaries and employee benefits
	Tax expense		29			1,189		Income tax expense
	Net of tax	$	46		$	1,601
	Total reclassifications during the period, net of tax	$	(267	)	$	740

Commitments_and_Contingent_Lia1

Commitments and Contingent Liabilities (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingent Liabilities [Abstract]
Schedule of maximum commitments potential obligation	The Company is a party to certain financial instruments with off balance sheet risk in the normal course of business to meet the financing needs of its customers.  These financial instruments include commitments to extend credit, unused lines of credit, standby letters of credit, and certain mortgage loans sold to investors with recourse. The Company’s exposure to credit loss in the event of nonperformance by the other party to the commitments to extend credit, unused lines of credit, standby letters of credit, and loans sold with recourse is represented by the contractual amount of those instruments. The credit risk associated with commitments to extend credit and standby and commercial letters of credit is essentially the same as that involved with extending loans to customers and is subject to normal credit policies.  Collateral may be obtained based on management’s assessment of the customer’s creditworthiness.
		At December 31,
	(In thousands)	2014		2013
	Unused lines of credit	$	214,175	$	216,658
	Commitments to extend credits, primarily variable rate		972,912		849,092
	Standby letters of credit		35,244		36,837
	Commercial letters of credit		22,486		41,263
	Loans sold with recourse		23,351		15,741

Fair_Values_of_Financial_Instr1

Fair Values of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Values of Financial Instruments [Abstract]
Fair Value of Financial Instruments By Balance Sheet Grouping	The following table sets forth information with regard to estimated fair values of financial instruments at December 31, 2014 and December 31, 2013.  This table excludes financial instruments for which the carrying amount approximates fair value.  Financial instruments for which the fair value approximates carrying value include cash and cash equivalents, securities available for sale, trading securities, accrued interest receivable, non-maturity deposits, short-term borrowings, accrued interest payable, and interest rate swaps.
				31-Dec-14				31-Dec-13
	(In thousands)	Fair Value Hierarchy		Carrying amount		Estimated fair value		Carrying amount		Estimated fair value
	Financial assets
	Securities held to maturity		2	$	454,361	$	454,994	$	117,283	$	113,276
	Net loans		3		5,528,912		5,584,777		5,337,361		5,386,520
	Financial liabilities
	Time deposits		2	$	1,043,823	$	1,038,877	$	1,021,142	$	1,023,982
	Long-term debt		2		130,945		132,562		308,823		325,195
	Junior subordinated debt		2		101,196		103,770		101,196		105,121
Fair Value of Financial Assets and Liabilities Measured on a Recurring Basis	The following table sets forth the Company’s financial assets and liabilities measured on a recurring basis that were accounted for at fair value as of December 31, 2014 and December 31, 2013.  Assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement (in thousands):
		Quoted Prices in		Significant		Significant		Balance
		Active Markets for		Other		Unobservable		as of
		Identical Assets		Observable Inputs		Inputs		31-Dec-14
		(Level 1)		(Level 2)		(Level 3)
	Assets:
	Securities Available for Sale:
	U.S. Treasury	$	23,111	$	-	$	-	$	23,111
	Federal Agency		-		329,914		-		329,914
	State & municipal		-		37,570		-		37,570
	Mortgage-backed		-		364,727		-		364,727
	Collateralized mortgage obligations		-		242,129		-		242,129
	Other securities		7,612		8,108		-		15,720
	Total Securities Available for Sale	$	30,723	$	982,448	$	-	$	1,013,171
	Trading Securities		7,793		-		-		7,793
	Interest Rate Swaps		-		4,707		-		4,707
	Total	$	38,516	$	987,155	$	-	$	1,025,671
	Liabilities:
	Interest Rate Swaps	$	-	$	4,707	$	-	$	4,707
	Total	$	-	$	4,707	$	-	$	4,707
		Quoted Prices in		Significant		Significant		Balance
		Active Markets for		Other		Unobservable		as of
		Identical Assets		Observable Inputs		Inputs		31-Dec-13
		(Level 1)		(Level 2)		(Level 3)
	Assets:
	Securities Available for Sale:
	U.S. Treasury	$	43,616	$	-	$	-	$	43,616
	Federal Agency		-		278,915		-		278,915
	State & municipal		-		113,665		-		113,665
	Mortgage-backed		-		364,164		-		364,164
	Collateralized mortgage obligations		-		549,528		-		549,528
	Other securities		6,796		8,197		-		14,993
	Total Securities Available for Sale	$	50,412	$	1,314,469	$	-	$	1,364,881
	Trading Securities		5,779		-		-		5,779
	Interest Rate Swaps		-		281		-		281
	Total	$	56,191	$	1,314,750	$	-	$	1,370,941
	Liabilities:
	Interest Rate Swaps	$	-	$	281	$	-	$	281
	Total	$	-	$	281	$	-	$	281

Parent_Company_Financial_Infor1

Parent Company Financial Information (Tables)	12 Months Ended
	Dec. 31, 2014
Parent Company Financial Information [Abstract]
Parent company financial information	Condensed Balance Sheets
		December 31,
	(In thousands)	2014			2013
	Assets
	Cash and cash equivalents	$	3,586		$	3,741
	Securities available for sale, at estimated fair value		11,649			11,008
	Trading securities		6,761			4,742
	Investment in subsidiaries, on equity basis		947,880			896,479
	Other assets		61,829			49,530
	Total assets	$	1,031,705		$	965,500
	Liabilities and Stockholders’ Equity
	Total liabilities	$	167,524		$	148,931
	Stockholders’ equity		864,181			816,569
	Total liabilities and stockholders’ equity	$	1,031,705		$	965,500
	Condensed Income Statements
		Years ended December 31,
	(In thousands)	2014			2013			2012
	Dividends from subsidiaries	$	35,400		$	13,500		$	79,175
	Management fee from subsidiaries		87,116			84,778			78,665
	Securities gains		49			1,273			442
	Interest, dividend and other income		800			636			720
	Total revenue		123,365			100,187			159,002
	Operating expense		89,834			83,679			79,015
	Income before income tax benefit and equity in undistributed income of subsidiaries		33,531			16,508			79,987
	Income tax benefit (expense)		631			(1,046	)		(284	)
	Dividends in excess of income (equity in undistributed income) of subsidiaries		40,912			46,285			(25,145	)
	Net income	$	75,074		$	61,747		$	54,558
	Statements of Cash Flow
		Years ended December 31,
	(In thousands)	2014			2013			2012
	Operating activities
	Net income	$	75,074		$	61,747		$	54,558
	Adjustments to reconcile net income to net cash provided by operating activities
	Stock-based compensation		3,521			4,305			4,364
	Gain on sales of available-for-sale securities		49			1,273			442
	Equity in undistributed income of subsidiaries		(75,824	)		(59,785	)		(54,030	)
	Cash dividend from subsidiaries		35,400			13,500			79,175
	Net change in other liabilities		18,594			(18,077	)		(3,181	)
	Net change in other assets		(25,151	)		14,928			2,030
	Net cash provided by operating activities		31,663			17,891			83,358
	Investing activities
	Purchases of available-for-sale securities		(597	)		-			(4,163	)
	Sales and maturities of available-for-sale securities		140			1,948			1,445
	Net cash provided by (used in) acquisitions		-			2,232			(14,612	)
	Purchases of premises and equipment		(640	)		(782	)		(1,240	)
	Net cash (used in) provided by investing activities		(1,097	)		3,398			(18,570	)
	Financing activities
	Proceeds from the issuance of shares to employee benefit plans and other stock plans		5,943			5,512			1,387
	Payments on long-term debt		-			-			(3,340	)
	Purchases of treasury shares		(72	)		(12,459	)		(15,490	)
	Cash dividends and payments for fractional shares		(36,905	)		(33,518	)		(26,712	)
	Excess tax benefit from exercise of stock options		313			(178	)		8
	Net cash used in financing activities		(30,721	)		(40,643	)		(44,147	)
	Net (decrease) increase in cash and cash equivalents		(155	)		(19,354	)		20,641
	Cash and cash equivalents at beginning of year		3,741			23,095			2,454
	Cash and cash equivalents at end of year	$	3,586		$	3,741		$	23,095

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
	Agreement
Summary of Significant Accounting Policies [Abstract]
Minimum number of days past due for nonaccrual loan status	90 days
Period of sustained repayment performance for nonperforming TDRs to be returned to performing status	6 months
Balance of OREO	$4	$2.90
Number of interest rate swap agreements	33
Standby letters of credit expiration period	1 year
Mortgage loans on real estate, by loan disclosure	The Company originates and services residential mortgage loans for consumers and sells 15-year, 20-year and 30-year residential real estate mortgages in the secondary market when the interest rate environment is determined to be favorable by management, while retaining servicing rights on the sold loans.

Acquisitions_Details

Acquisitions (Details) (USD $)	0 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 08, 2013	Dec. 31, 2014	Dec. 31, 2013
	Branch
Alliance Financial Corporation [Member]
Business Acquisition [Line Items]
Date of acquisition		8-Mar-13
Total consideration paid	$226
Number of banking centers operated by acquiree	26
Other goodwill adjustments [Abstract]
Deferred tax adjustments		-1
Valuation adjustments		-0.4
Decrease in goodwill		-1.4
Hampshire First Bank [Member]
Other goodwill adjustments [Abstract]
Decrease in goodwill			-1
Acquisition of Financial Services Company [Member]
Other goodwill adjustments [Abstract]
Goodwill adjustment related to business acquisition			$0.10

Securities_Details

Securities (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	Position	Position
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	$1,001,718,000	$1,379,751,000
Unrealized gains	14,823,000	14,737,000
Unrealized losses	3,370,000	29,607,000
Estimated fair value	1,013,171,000	1,364,881,000
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	143,428,000	812,106,000
12 months or longer	244,836,000	9,842,000
Total	388,264,000	821,948,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	-500,000	-29,201,000
12 months or longer	-2,870,000	-406,000
Total	-3,370,000	-29,607,000
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	59	314
12 months or longer	58	2
Total	117	316
Sales transactions of securities available for sale [Abstract]
Proceeds from sales	189,000	27,593,000	1,790,000
Gross realized gains	49,000	1,283,000	442,000
Gross realized losses	0	0	0
Net securities (losses) gains	49,000	1,283,000	442,000
Gains from calls on securities available for sale	100,000	100,000	200,000
Amortized costs of securities available for sale pledged to secure public deposits	1,400,000,000	1,400,000,000
Amortized costs of securities available for sale pledged as collateral for repurchase agreements	208,800,000
Held-to-maturity securities, fair value to amortized cost basis [Abstract]
Amortized cost	454,361,000	117,283,000
Unrealized gains	2,721,000	570,000
Unrealized losses	2,088,000	4,577,000
Total, Estimated Fair Value	454,994,000	113,276,000
Held-to-maturity securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	69,566,000	58,468,000
12 months or longer	48,034,000	0
Total	117,600,000	58,468,000
Held-to-maturity securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	-165,000	-4,577,000
12 months or longer	-1,923,000	0
Total	-2,088,000	-4,577,000
Held-to-maturity securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	112	6
12 months or longer	10	0
Total	122	6
Securities transferred from available for sale portfolio to held to maturity portfolio	340,000,000
Unrealized losses of securities available for sale portfolio before transfer to held to maturity portfolio	8,300,000
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis [Abstract]
Within one year	28,193,000
From one to five years	356,696,000
From five to ten years	160,816,000
After ten years	443,195,000
Total, Amortized Cost	988,900,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Within one year	28,310,000
From one to five years	356,107,000
From five to ten years	163,924,000
After ten years	449,110,000
Total, Fair Value	997,451,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Within one year	22,999,000
From one to five years	15,506,000
From five to ten years	87,326,000
After ten years	328,530,000
Amortized cost	454,361,000	117,283,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Within one year	23,075,000
From one to five years	15,606,000
From five to ten years	87,640,000
After ten years	328,673,000
Total, Estimated Fair Value	454,994,000	113,276,000
Consolidated stockholders' equity threshold percentage that no single issuer of securities exceeded except for U.S. Government securities. (in hundredths)	10.00%	10.00%
Mortgage-Backed [Member]
Held-to-maturity securities, fair value to amortized cost basis [Abstract]
Amortized cost	755,000	953,000
Unrealized gains	113,000	128,000
Unrealized losses	0	0
Total, Estimated Fair Value	868,000	1,081,000
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	755,000	953,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Estimated Fair Value	868,000	1,081,000
State & Municipal [Member]
Held-to-maturity securities, fair value to amortized cost basis [Abstract]
Amortized cost	135,978,000	54,305,000
Unrealized gains	674,000	442,000
Unrealized losses	123,000	8,000
Total, Estimated Fair Value	136,529,000	54,739,000
Held-to-maturity securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	43,514,000	1,012,000
12 months or longer	1,619,000	0
Total	45,133,000	1,012,000
Held-to-maturity securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	-116,000	-8,000
12 months or longer	-7,000	0
Total	-123,000	-8,000
Held-to-maturity securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	110	1
12 months or longer	6	0
Total	116	1
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	135,978,000	54,305,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Estimated Fair Value	136,529,000	54,739,000
Collateralized Mortgage Obligations [Member]
Held-to-maturity securities, fair value to amortized cost basis [Abstract]
Amortized cost	317,628,000	62,025,000
Unrealized gains	1,934,000	0
Unrealized losses	1,965,000	4,569,000
Total, Estimated Fair Value	317,597,000	57,456,000
Held-to-maturity securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	26,052,000	57,456,000
12 months or longer	46,415,000	0
Total	72,467,000	57,456,000
Held-to-maturity securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	-49,000	-4,569,000
12 months or longer	-1,916,000	0
Total	-1,965,000	-4,569,000
Held-to-maturity securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	2	5
12 months or longer	4	0
Total	6	5
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]
Amortized cost	317,628,000	62,025,000
Held-to-maturity Securities, Debt Maturities, Fair Value [Abstract]
Total, Estimated Fair Value	317,597,000	57,456,000
US Treasury [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	23,041,000	43,279,000
Unrealized gains	70,000	337,000
Unrealized losses	0	0
Estimated fair value	23,111,000	43,616,000
Federal Agency [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	332,193,000	285,880,000
Unrealized gains	327,000	343,000
Unrealized losses	2,606,000	7,308,000
Estimated fair value	329,914,000	278,915,000
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	66,528,000	233,935,000
12 months or longer	198,151,000	9,619,000
Total	264,679,000	243,554,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	-226,000	-6,927,000
12 months or longer	-2,380,000	-381,000
Total	-2,606,000	-7,308,000
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	8	20
12 months or longer	16	1
Total	24	21
State & Municipal [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	37,035,000	113,435,000
Unrealized gains	587,000	1,842,000
Unrealized losses	52,000	1,612,000
Estimated fair value	37,570,000	113,665,000
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	8,818,000	50,328,000
12 months or longer	1,321,000	0
Total	10,139,000	50,328,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	-42,000	-1,612,000
12 months or longer	-10,000	0
Total	-52,000	-1,612,000
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	33	177
12 months or longer	5	0
Total	38	177
Mortgage-Backed [Member]
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	10,400,000	143,080,000
12 months or longer	35,565,000	0
Total	45,965,000	143,080,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	-36,000	-2,216,000
12 months or longer	-254,000	0
Total	-290,000	-2,216,000
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	10	79
12 months or longer	31	0
Total	41	79
Mortgage-backed Securities, Issued by US Government-Sponsored Enterprises [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	339,190,000	337,666,000
Unrealized gains	7,597,000	5,788,000
Unrealized losses	224,000	2,131,000
Estimated fair value	346,563,000	341,323,000
Mortgage-backed Securities, Issued by US Government Securities [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	17,367,000	21,924,000
Unrealized gains	863,000	1,002,000
Unrealized losses	66,000	85,000
Estimated fair value	18,164,000	22,841,000
Collateralized Mortgage Obligations [Member]
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	57,682,000	379,273,000
12 months or longer	6,598,000	0
Total	64,280,000	379,273,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	-196,000	-18,243,000
12 months or longer	-74,000	0
Total	-270,000	-18,243,000
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	8	36
12 months or longer	4	0
Total	12	36
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	199,837,000	521,257,000
Unrealized gains	1,828,000	1,777,000
Unrealized losses	234,000	18,141,000
Estimated fair value	201,431,000	504,893,000
Collateralized Mortgage Obligations, U.S. Government Securities [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	40,237,000	43,943,000
Unrealized gains	497,000	794,000
Unrealized losses	36,000	102,000
Estimated fair value	40,698,000	44,635,000
Other Securities [Member]
Available-for-sale securities, fair value to amortized cost basis [Abstract]
Amortized cost	12,818,000	12,367,000
Unrealized gains	3,054,000	2,854,000
Unrealized losses	152,000	228,000
Estimated fair value	15,720,000	14,993,000
Available-for-sale securities in continuous unrealized loss position, fair value [Abstract]
Less than 12 months	0	5,490,000
12 months or longer	3,201,000	223,000
Total	3,201,000	5,713,000
Available-for-sale securities in continuous unrealized loss position, unrealized losses [Abstract]
Less than 12 months	0	-203,000
12 months or longer	-152,000	-25,000
Total	($152,000)	($228,000)
Available-for-sale securities in continuous unrealized loss position, number of positions [Abstract]
Less than 12 months	0	2
12 months or longer	2	1
Total	2	3

Loans_Details

Loans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	$5,595,271,000	$5,406,795,000
Deferred loan origination costs, net	35,600,000	31,800,000
Residential loans held for sale	3,200,000	100,000
Loans and Leases Receivable, Related Parties [Roll Forward]
Balance at January 1	3,372,000	2,790,000
New loans	522,000	569,000
Adjustment due to change in composition of related parties	253,000	376,000
Repayments	-571,000	-363,000
Balance at December 31	3,576,000	3,372,000
Residential Real Estate Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	1,115,589,000	1,041,637,000
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	839,770,000	859,026,000
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	1,442,989,000	1,328,313,000
Real Estate Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	83,750,000	93,247,000
Agricultural and Agricultural Real Estate Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	107,195,000	112,035,000
Loans serviced	23,400,000	15,700,000
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	1,436,382,000	1,352,638,000
Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net Loans	$569,596,000	$619,899,000

Allowance_for_Loan_Losses_and_2

Allowance for Loan Losses and Credit Quality of Loans (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
	Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan portfolio segments	3
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate loan amount, percentage of appraised value or purchase price of the property, maximum (in hundredths)	80.00%
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate loan amount, percentage of appraised value or purchase price of the property, maximum (in hundredths)	75.00%
Business Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Business banking loans, maximum amount	500
Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of automobile financing to indirect relationships with dealers (in hundredths)	70.00%
Principal repayment term of loan, minimum	3 years
Principal repayment term of loan, maximum	6 years
Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Home equity loan amount, percentage of equity in home, maximum (in hundredths)	85.00%
Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal repayment term of loan, minimum	1 year
Principal repayment term of loan, maximum	10 years
Residential Real Estate Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate loan amount, percentage of appraised value or purchase price of the property, maximum (in hundredths)	85.00%

Allowance_for_Loan_Losses_and_3

Allowance for Loan Losses and Credit Quality of Loans, Allowance for Loan Losses (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	$69,434,000	$69,334,000	$71,334,000
Charge-offs	-27,473,000	-27,689,000	-26,504,000
Recoveries	4,859,000	5,365,000	4,235,000
Provision	19,539,000	22,424,000	20,269,000
Balance, end of period	66,359,000	69,434,000	69,334,000
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Allowance for loan losses	66,359,000	69,434,000	69,334,000
Allowance for loans individually evaluated for impairment	1,100,000	715,000
Allowance for loans collectively evaluated for impairment	65,259,000	68,719,000
Ending balance of loans	5,595,271,000	5,406,795,000
Commercial Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	35,090,000	35,624,000	38,831,000
Charge-offs	-9,414,000	-10,459,000	-8,750,000
Recoveries	1,774,000	1,957,000	1,641,000
Provision	4,983,000	7,968,000	3,902,000
Balance, end of period	32,433,000	35,090,000	35,624,000
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Allowance for loan losses	32,433,000	35,090,000	35,624,000
Allowance for loans individually evaluated for impairment	1,100,000	715,000
Allowance for loans collectively evaluated for impairment	31,333,000	34,375,000
Ending balance of loans	2,473,702,000	2,392,621,000
Consumer Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	27,694,000	27,162,000	26,049,000
Charge-offs	-16,642,000	-15,459,000	-15,848,000
Recoveries	2,800,000	3,136,000	2,556,000
Provision	12,868,000	12,855,000	14,405,000
Balance, end of period	26,720,000	27,694,000	27,162,000
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Allowance for loan losses	26,720,000	27,694,000	27,162,000
Allowance for loans individually evaluated for impairment	0	0
Allowance for loans collectively evaluated for impairment	26,720,000	27,694,000
Ending balance of loans	2,005,980,000	1,972,537,000
Residential Real Estate Mortgages [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	6,520,000	6,252,000	6,249,000
Charge-offs	-1,417,000	-1,771,000	-1,906,000
Recoveries	285,000	272,000	38,000
Provision	1,742,000	1,767,000	1,871,000
Balance, end of period	7,130,000	6,520,000	6,252,000
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Allowance for loan losses	7,130,000	6,520,000	6,252,000
Allowance for loans individually evaluated for impairment	0	0
Allowance for loans collectively evaluated for impairment	7,130,000	6,520,000
Ending balance of loans	1,115,589,000	1,041,637,000
Unallocated [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	130,000	296,000	205,000
Charge-offs	0	0	0
Recoveries	0	0	0
Provision	-54,000	-166,000	91,000
Balance, end of period	76,000	130,000	296,000
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Allowance for loan losses	76,000	130,000	296,000
Allowance for loans collectively evaluated for impairment	76,000	130,000
Originated Loans [Member]
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Ending balance of loans	4,847,937,000	4,476,403,000
Ending balance of loans individually evaluated for impairment	20,121,000	21,380,000
Ending balance of loans collectively evaluated for impairment	4,827,816,000	4,455,023,000
Originated Loans [Member] | Commercial Loans [Member]
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Ending balance of loans	2,140,371,000	1,990,232,000
Ending balance of loans individually evaluated for impairment	11,079,000	16,120,000
Ending balance of loans collectively evaluated for impairment	2,129,292,000	1,974,112,000
Originated Loans [Member] | Consumer Loans [Member]
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Ending balance of loans	1,858,724,000	1,752,950,000
Ending balance of loans individually evaluated for impairment	5,498,000	3,248,000
Ending balance of loans collectively evaluated for impairment	1,853,226,000	1,749,702,000
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Ending balance of loans	848,842,000	733,221,000
Ending balance of loans individually evaluated for impairment	3,544,000	2,012,000
Ending balance of loans collectively evaluated for impairment	845,298,000	731,209,000
Acquired Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	0
Charge-offs	-4,800,000	-400,000
Balance, end of period	500	0
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Allowance for loan losses	500	0
Ending balance of loans	747,334,000	930,392,000
Ending balance of loans individually evaluated for impairment	5,675,000	10,060,000
Ending balance of loans collectively evaluated for impairment	741,659,000	920,332,000
Acquired Loans [Member] | Commercial Loans [Member]
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Ending balance of loans	333,331,000	402,389,000
Ending balance of loans individually evaluated for impairment	5,675,000	10,060,000
Ending balance of loans collectively evaluated for impairment	327,656,000	392,329,000
Acquired Loans [Member] | Consumer Loans [Member]
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Ending balance of loans	147,256,000	219,587,000
Ending balance of loans individually evaluated for impairment	0	0
Ending balance of loans collectively evaluated for impairment	147,256,000	219,587,000
Acquired Loans [Member] | Residential Real Estate Mortgages [Member]
Allowance for loan losses and recorded investment by portfolio segment [Abstract]
Ending balance of loans	266,747,000	308,416,000
Ending balance of loans individually evaluated for impairment	0	0
Ending balance of loans collectively evaluated for impairment	$266,747,000	$308,416,000

Allowance_for_Loan_Losses_and_4

Allowance for Loan Losses and Credit Quality of Loans, Past Due Loans (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Aging [Abstract]
Minimum number of days past due for nonaccrual loan status	90 days
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	$27,402	$31,961
61 - 90 Days Past Due Accruing	6,150	5,894
Greater Than 90 Days Past Due Accruing	4,941	3,737
Total Past Due Accruing	38,493	41,592
Non-Accrual	41,074	49,965
Current	5,515,704	5,315,238
Recorded Total Loans and Leases	5,595,271	5,406,795
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Recorded Total Loans and Leases	2,473,702	2,392,621
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Recorded Total Loans and Leases	2,005,980	1,972,537
Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
Recorded Total Loans and Leases	1,115,589	1,041,637
Originated Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	25,496	28,124
61 - 90 Days Past Due Accruing	5,805	5,660
Greater Than 90 Days Past Due Accruing	4,204	3,657
Total Past Due Accruing	35,505	37,441
Non-Accrual	30,845	33,883
Current	4,781,587	4,405,079
Recorded Total Loans and Leases	4,847,937	4,476,403
Originated Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,010	3,368
61 - 90 Days Past Due Accruing	970	390
Greater Than 90 Days Past Due Accruing	84	105
Total Past Due Accruing	2,064	3,863
Non-Accrual	13,431	19,300
Current	2,124,876	1,967,069
Recorded Total Loans and Leases	2,140,371	1,990,232
Originated Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	0	105
61 - 90 Days Past Due Accruing	735	247
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	735	352
Non-Accrual	1,012	3,669
Current	613,400	612,402
Recorded Total Loans and Leases	615,147	616,423
Originated Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	192	1,366
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	192	1,366
Non-Accrual	4,127	7,834
Current	1,064,549	925,116
Recorded Total Loans and Leases	1,068,868	934,316
Originated Loans [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	0	150
61 - 90 Days Past Due Accruing	0	21
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	0	171
Non-Accrual	817	1,135
Current	32,130	63,856
Recorded Total Loans and Leases	32,947	65,162
Originated Loans [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	19	519
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	19	519
Non-Accrual	565	961
Current	24,390	35,172
Recorded Total Loans and Leases	24,974	36,652
Originated Loans [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	799	1,228
61 - 90 Days Past Due Accruing	235	122
Greater Than 90 Days Past Due Accruing	84	105
Total Past Due Accruing	1,118	1,455
Non-Accrual	6,910	5,701
Current	390,407	330,523
Recorded Total Loans and Leases	398,435	337,679
Originated Loans [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	21,585	20,805
61 - 90 Days Past Due Accruing	4,739	4,891
Greater Than 90 Days Past Due Accruing	2,864	2,744
Total Past Due Accruing	29,188	28,440
Non-Accrual	8,644	7,478
Current	1,820,892	1,717,032
Recorded Total Loans and Leases	1,858,724	1,752,950
Originated Loans [Member] | Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	16,434	14,093
61 - 90 Days Past Due Accruing	3,154	2,878
Greater Than 90 Days Past Due Accruing	1,991	1,583
Total Past Due Accruing	21,579	18,554
Non-Accrual	1,964	1,461
Current	1,286,507	1,141,829
Recorded Total Loans and Leases	1,310,050	1,161,844
Originated Loans [Member] | Home Equity Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	4,591	6,033
61 - 90 Days Past Due Accruing	1,428	1,888
Greater Than 90 Days Past Due Accruing	821	1,115
Total Past Due Accruing	6,840	9,036
Non-Accrual	6,596	5,931
Current	479,444	517,856
Recorded Total Loans and Leases	492,880	532,823
Originated Loans [Member] | Direct [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	560	679
61 - 90 Days Past Due Accruing	157	125
Greater Than 90 Days Past Due Accruing	52	46
Total Past Due Accruing	769	850
Non-Accrual	84	86
Current	54,941	57,347
Recorded Total Loans and Leases	55,794	58,283
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	2,901	3,951
61 - 90 Days Past Due Accruing	96	379
Greater Than 90 Days Past Due Accruing	1,256	808
Total Past Due Accruing	4,253	5,138
Non-Accrual	8,770	7,105
Current	835,819	720,978
Recorded Total Loans and Leases	848,842	733,221
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,906	3,837
61 - 90 Days Past Due Accruing	345	234
Greater Than 90 Days Past Due Accruing	737	80
Total Past Due Accruing	2,988	4,151
Non-Accrual	10,229	16,082
Current	734,117	910,159
Recorded Total Loans and Leases	747,334	930,392
Acquired Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	5	344
61 - 90 Days Past Due Accruing	15	2
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	20	346
Non-Accrual	6,340	11,498
Current	326,971	390,545
Recorded Total Loans and Leases	333,331	402,389
Acquired Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	0	24
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	0	24
Non-Accrual	3,009	6,599
Current	72,255	96,603
Recorded Total Loans and Leases	75,264	103,226
Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	0	0
61 - 90 Days Past Due Accruing	0	0
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	0	0
Non-Accrual	2,666	3,559
Current	197,222	225,455
Recorded Total Loans and Leases	199,888	229,014
Acquired Loans [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	5	320
61 - 90 Days Past Due Accruing	15	2
Greater Than 90 Days Past Due Accruing	0	0
Total Past Due Accruing	20	322
Non-Accrual	665	1,340
Current	57,494	68,487
Recorded Total Loans and Leases	58,179	70,149
Acquired Loans [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	739	1,768
61 - 90 Days Past Due Accruing	65	232
Greater Than 90 Days Past Due Accruing	66	80
Total Past Due Accruing	870	2,080
Non-Accrual	696	712
Current	145,690	216,795
Recorded Total Loans and Leases	147,256	219,587
Acquired Loans [Member] | Indirect [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	518	939
61 - 90 Days Past Due Accruing	5	113
Greater Than 90 Days Past Due Accruing	54	71
Total Past Due Accruing	577	1,123
Non-Accrual	106	93
Current	64,540	123,870
Recorded Total Loans and Leases	65,223	125,086
Acquired Loans [Member] | Home Equity Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	190	753
61 - 90 Days Past Due Accruing	60	63
Greater Than 90 Days Past Due Accruing	5	0
Total Past Due Accruing	255	816
Non-Accrual	557	570
Current	75,904	85,690
Recorded Total Loans and Leases	76,716	87,076
Acquired Loans [Member] | Direct [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	31	76
61 - 90 Days Past Due Accruing	0	56
Greater Than 90 Days Past Due Accruing	7	9
Total Past Due Accruing	38	141
Non-Accrual	33	49
Current	5,246	7,235
Recorded Total Loans and Leases	5,317	7,425
Acquired Loans [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,162	1,725
61 - 90 Days Past Due Accruing	265	0
Greater Than 90 Days Past Due Accruing	671	0
Total Past Due Accruing	2,098	1,725
Non-Accrual	3,193	3,872
Current	261,456	302,819
Recorded Total Loans and Leases	$266,747	$308,416

Allowance_for_Loan_Losses_and_5

Allowance for Loan Losses and Credit Quality of Loans, Impaired Loans (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for Loan Losses and Credit Quality of Loans [Abstract]
Minimum balance for classified loans to be evaluated individually for impairment	$500
With an allowance recorded [Abstract]
Recorded investment balance (book)	25,796	31,440
Unpaid principal balance (legal)	32,290	35,430
Related allowance	1,100	715
Average recorded investment	31,059	23,317	17,403
Interest income recognized accrual	772	418	643
Originated Loans [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	17,358	16,360
Unpaid principal balance (legal)	19,181	18,173
Originated Loans [Member] | Commercial Loans [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	8,316	11,100
Unpaid principal balance (legal)	9,189	12,446
Originated Loans [Member] | Commercial [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	1,748	4,721
Unpaid principal balance (legal)	1,901	4,777
With an allowance recorded [Abstract]
Average recorded investment	1,954	3,488	6,682
Interest income recognized accrual	115	0	56
Originated Loans [Member] | Commercial Real Estate [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	4,505	4,613
Unpaid principal balance (legal)	4,520	5,164
With an allowance recorded [Abstract]
Recorded investment balance (book)	2,763	5,020
Unpaid principal balance (legal)	4,611	6,877
Related allowance	600	715
Average recorded investment	9,679	11,085	4,944
Interest income recognized accrual	169	95	230
Originated Loans [Member] | Agricultural [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	20	125
Unpaid principal balance (legal)	26	195
With an allowance recorded [Abstract]
Average recorded investment	91	1,035	1,767
Interest income recognized accrual	1	1	43
Originated Loans [Member] | Agricultural Real Estate [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	1,147	1,431
Unpaid principal balance (legal)	1,441	1,708
With an allowance recorded [Abstract]
Average recorded investment	1,346	1,067	922
Interest income recognized accrual	46	47	72
Originated Loans [Member] | Business Banking [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	896	210
Unpaid principal balance (legal)	1,301	602
With an allowance recorded [Abstract]
Average recorded investment	610	127	68
Interest income recognized accrual	55	61	65
Originated Loans [Member] | Consumer Loans [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	5,498	3,248
Unpaid principal balance (legal)	6,033	3,472
Originated Loans [Member] | Home Equity [Member]
With an allowance recorded [Abstract]
Average recorded investment	5,198	3,120	1,877
Interest income recognized accrual	267	145	123
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	3,544	2,012
Unpaid principal balance (legal)	3,959	2,255
With an allowance recorded [Abstract]
Average recorded investment	3,039	2,085	1,143
Interest income recognized accrual	119	69	54
Acquired Loans [Member] | Commercial Loans [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	2,666	10,060
Unpaid principal balance (legal)	3,830	10,380
Acquired Loans [Member] | Commercial [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	0	6,501
Unpaid principal balance (legal)	0	6,538
With an allowance recorded [Abstract]
Recorded investment balance (book)	3,009	0
Unpaid principal balance (legal)	4,668	0
Related allowance	500	0
Average recorded investment	5,756	0	0
Interest income recognized accrual	0	0	0
Acquired Loans [Member] | Commercial Real Estate [Member]
With no allowance recorded [Abstract]
Recorded investment balance (book)	2,666	3,559
Unpaid principal balance (legal)	3,830	3,842
With an allowance recorded [Abstract]
Average recorded investment	3,386	1,310	0
Interest income recognized accrual	$0	$0	$0

Allowance_for_Loan_Losses_and_6

Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Originated Loans [Member] | Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$1,741,936	$1,652,553
Originated Loans [Member] | Commercial Credit Exposure [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,648,664	1,547,669
Originated Loans [Member] | Commercial Credit Exposure [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	23,680	40,037
Originated Loans [Member] | Commercial Credit Exposure [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	69,584	64,835
Originated Loans [Member] | Commercial Credit Exposure [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8	12
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	615,147	616,423
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	570,884	576,079
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	6,022	16,836
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	38,241	23,508
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,068,868	934,316
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,023,856	878,411
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	17,341	22,777
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	27,671	33,128
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	32,947	65,162
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	30,481	60,043
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	275	381
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,183	4,726
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8	12
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	24,974	36,652
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	23,443	33,136
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	42	43
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,489	3,473
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Originated Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	398,435	337,679
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	379,445	319,578
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	18,990	18,101
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	398,435	337,679
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	379,445	319,578
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	18,990	18,101
Originated Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,858,724	1,752,950
Originated Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,847,216	1,742,728
Originated Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	11,508	10,222
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,310,050	1,161,844
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,306,095	1,158,800
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,955	3,044
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	492,880	532,823
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	485,463	525,777
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,417	7,046
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	55,794	58,283
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	55,658	58,151
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	136	132
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	848,842	733,221
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	838,816	725,308
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	10,026	7,913
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	848,842	733,221
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	838,816	725,308
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	10,026	7,913
Acquired Loans [Member] | Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	275,152	332,240
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	249,666	290,702
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5,486	8,413
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	20,000	33,125
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	75,264	103,226
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	63,630	85,692
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,840	2,230
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8,794	15,304
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	199,888	229,014
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	186,036	205,010
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,646	6,183
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	11,206	17,821
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Acquired Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	58,179	70,149
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	53,264	65,437
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	4,915	4,712
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	58,179	70,149
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	53,264	65,437
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	4,915	4,712
Acquired Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	147,256	219,587
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	146,494	218,795
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	762	792
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	65,223	125,086
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	65,063	124,922
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	160	164
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	76,716	87,076
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	76,154	86,506
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	562	570
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5,317	7,425
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5,277	7,367
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	40	58
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	266,747	308,416
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	262,883	304,544
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,864	3,872
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	266,747	308,416
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	262,883	304,544
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$3,864	$3,872

Allowance_for_Loan_Losses_and_7

Allowance for Loan Losses and Credit Quality of Loans, Troubled Debt Restructurings (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
	Contract	Contract
Commercial Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts		4
Pre-modification outstanding recorded investment		$7
Number of contracts, subsequent default		1
Outstanding recorded investment, subsequent default		0.9
Home Equity [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	9	23
Pre-modification outstanding recorded investment	0.3	1
Number of contracts, subsequent default	1	8
Outstanding recorded investment, subsequent default	0.1	0.4
Residential Real Estate Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	27	6
Pre-modification outstanding recorded investment	2.7	0.5
Number of contracts, subsequent default	6
Outstanding recorded investment, subsequent default	0.4
Business Banking [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	3
Pre-modification outstanding recorded investment	0.9
Indirect Consumer Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	1
Pre-modification outstanding recorded investment	0.1
Number of contracts, subsequent default	1
Outstanding recorded investment, subsequent default	0.1
Direct Consumer Loan [Member]
Financing Receivable, Modifications [Line Items]
Number of contracts	47
Pre-modification outstanding recorded investment	3
Number of contracts, subsequent default	5
Outstanding recorded investment, subsequent default	$0.20

Premises_and_Equipment_Net_Det

Premises and Equipment, Net (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Premises and equipment before accumulated depreciation	$181,235,000	$175,827,000
Accumulated depreciation	91,977,000	87,500,000
Total premises and equipment	89,258,000	88,327,000
Rental expense	8,000,000	7,500,000	6,400,000
Future Minimum Rental Payments [Abstract]
2015	7,369,000
2016	7,215,000
2017	6,811,000
2018	6,122,000
2019	5,655,000
Thereafter	26,257,000
Total	59,429,000
Land, Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment before accumulated depreciation	122,400,000	120,098,000
Equipment [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment before accumulated depreciation	$58,835,000	$55,729,000
Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Building and Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	15 years
Building and Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	40 years

Goodwill_and_other_Intangible_2

Goodwill and other Intangible Assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill [Roll Forward]
Beginning Balance	$264,997,000	$152,373,000
Goodwill acquired	-1,363,000	112,624,000
Ending Balance	263,634,000	264,997,000	152,373,000
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	47,717,000	47,910,000
Less: accumulated amortization	27,400,000	22,353,000
Net carrying amount	20,317,000	25,557,000
Amortization Expense [Abstract]
Amortization of intangible assets	5,047,000	4,872,000	3,394,000
Future Amortization Expense [Abstract]
2015	4,800,000
2016	3,300,000
2017	2,800,000
2018	2,200,000
2019	1,700,000
Thereafter	3,700,000
Indefinite-lived intangible assets (Excluding goodwill)	1,800,000
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset useful life	1 year
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible asset useful life	12 years
Core Deposits Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	19,401,000	19,401,000
Less: accumulated amortization	12,522,000	10,083,000
Net carrying amount	6,879,000	9,318,000
Identified Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	28,316,000	28,509,000
Less: accumulated amortization	14,878,000	12,270,000
Net carrying amount	$13,438,000	$16,239,000

Deposits_Details

Deposits (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Maturities of Time Deposits [Abstract]
Within one year	$464,853,000
After one but within two years	132,999,000
After two but within three years	143,142,000
After three but within four years	80,804,000
After four but within five years	204,492,000
After five years	17,533,000
Total	1,043,823,000	1,021,142,000
Time Deposits, $100,000 or More [Abstract]
Time deposits of $100,000 or more	$269,800,000	$375,400,000

ShortTerm_Borrowings_Details

Short-Term Borrowings (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Short-term Debt [Line Items]
Balance at year-end	$316,802,000	$456,042,000
FHLB, unused lines of credit available for short-term financing	958,000,000	497,000,000
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Balance at year-end	68,000,000	130,000,000	10,000,000
Average during the year	110,154,000	39,907,000	12,658,000
Maximum month end balance	183,000,000	130,000,000	60,000,000
Weighted average rate during the year (in hundredths)	0.29%	0.26%	0.27%
Weighted average rate at December 31 (in hundredths)	0.34%	0.18%	0.27%
Securities Sold under Repurchase Agreements [Member]
Short-term Debt [Line Items]
Balance at year-end	148,802,000	176,042,000	152,941,000
Average during the year	165,858,000	169,352,000	153,084,000
Maximum month end balance	182,861,000	185,871,000	165,977,000
Weighted average rate during the year (in hundredths)	0.06%	0.06%	0.10%
Weighted average rate at December 31 (in hundredths)	0.06%	0.05%	0.10%
Other Short-Term Borrowings [Member]
Short-term Debt [Line Items]
Balance at year-end	100,000,000	150,000,000	0
Average during the year	106,438,000	71,589,000	0
Maximum month end balance	$320,000,000	$210,000,000	$0
Weighted average rate during the year (in hundredths)	0.40%	0.43%	0.00%
Weighted average rate at December 31 (in hundredths)	0.36%	0.55%	0.00%

LongTerm_Debt_Details

Long-Term Debt (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Long-Term Debt by Maturity Periods [Abstract]
Amount	$130,945	$308,823
Callable Amount	80,000	220,000
2013 [Member]
Long-Term Debt by Maturity Periods [Abstract]
Maturity	31-Dec-14
Amount	0	12,460
Weighted Average Rate (in hundredths)	0.00%	1.33%
Callable Amount	0	0
Weighted Average Rate Callable Portion (in hundredths)	0.00%	0.00%
2014 [Member]
Long-Term Debt by Maturity Periods [Abstract]
Maturity	31-Dec-15
Amount	217	308
Weighted Average Rate (in hundredths)	0.00%	0.00%
Callable Amount	0	0
Weighted Average Rate Callable Portion (in hundredths)	0.00%	0.00%
2015 [Member]
Long-Term Debt by Maturity Periods [Abstract]
Maturity	31-Dec-16
Amount	50,626	90,313
Weighted Average Rate (in hundredths)	2.91%	3.52%
Callable Amount	30,000	70,000
Weighted Average Rate Callable Portion (in hundredths)	4.15%	4.21%
2016 [Member]
Long-Term Debt by Maturity Periods [Abstract]
Maturity	31-Dec-17
Amount	40,000	115,312
Weighted Average Rate (in hundredths)	2.68%	3.55%
Callable Amount	25,000	75,000
Weighted Average Rate Callable Portion (in hundredths)	3.48%	3.73%
2017 [Member]
Long-Term Debt by Maturity Periods [Abstract]
Maturity	31-Dec-18
Amount	40,000	90,313
Weighted Average Rate (in hundredths)	2.57%	3.26%
Callable Amount	25,000	75,000
Weighted Average Rate Callable Portion (in hundredths)	3.15%	3.61%
2018 [Member]
Long-Term Debt by Maturity Periods [Abstract]
Maturity	31-Dec-21
Amount	102	117
Weighted Average Rate (in hundredths)	4.00%	4.00%
Callable Amount	$0	$0
Weighted Average Rate Callable Portion (in hundredths)	0.00%	0.00%

Junior_Subordinated_Debt_Detai

Junior Subordinated Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2014
Debt Instrument [Line Items]
Number of statutory business trusts included in the Trusts	5
Minimum assets for bank holding companies to be subject to the same capital requirements as insured depository institutions	$500,000,000
CNBF Capital Trust I Debenture [Member]
Debt Instrument [Line Items]
Issuance Date	1-Aug-99
Trust Preferred Securities Outstanding	18,000,000
Interest Rate	3-month LIBOR plus 2.75%
Trust Preferred Debt Owed To Trust	18,720,000
Final Maturity Date	1-Aug-29
Number of wholly owned Delaware statutory business trusts	1
NBT Statutory Trust I Debenture [Member]
Debt Instrument [Line Items]
Issuance Date	1-Nov-05
Trust Preferred Securities Outstanding	5,000,000
Interest Rate	3-month LIBOR plus 1.40%
Trust Preferred Debt Owed To Trust	5,155,000
Final Maturity Date	1-Dec-35
NBT Statutory Trust II Debenture [Member]
Debt Instrument [Line Items]
Issuance Date	1-Feb-06
Trust Preferred Securities Outstanding	50,000,000
Interest Rate	3-month LIBOR plus 1.40%
Trust Preferred Debt Owed To Trust	51,547,000
Final Maturity Date	1-Mar-36
Alliance Financial Capital Trust I [Member]
Debt Instrument [Line Items]
Issuance Date	1-Dec-03
Trust Preferred Securities Outstanding	10,000,000
Interest Rate	3-month LIBOR plus 2.85%
Trust Preferred Debt Owed To Trust	10,310,000
Final Maturity Date	1-Jan-34
Alliance Financial Capital Trust II [Member]
Debt Instrument [Line Items]
Issuance Date	1-Sep-06
Trust Preferred Securities Outstanding	15,000,000
Interest Rate	3-month LIBOR plus 1.65%
Trust Preferred Debt Owed To Trust	15,464,000
Final Maturity Date	1-Sep-36
NBT Bancorp Inc [Member]
Debt Instrument [Line Items]
Trust equity method investment	1,000,000
Alliance Financial Capital [Member]
Debt Instrument [Line Items]
Number of wholly owned Delaware statutory business trusts	2
Trusts [Member]
Debt Instrument [Line Items]
Trust Preferred Securities Outstanding	98,000,000
Trust Preferred Debt Owed To Trust	101,000,000
Trust equity method investment	3,200,000
Debentures period semi-annual deferral periods	10
Trust preferred securities included in Tier I capital	$97,000,000

Income_Taxes_Details

Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current [Abstract]
Federal	$26,059,000	$23,536,000	$21,011,000
State	2,823,000	2,316,000	1,815,000
Current tax expense (benefit)	28,882,000	25,852,000	22,826,000
Deferred [Abstract]
Federal	6,648,000	2,334,000	-13,000
State	1,699,000	10,000	3,000
Deferred tax expense (benefit)	8,347,000	2,344,000	-10,000
Total income tax expense	37,229,000	28,196,000	22,816,000
Income tax recorded to stockholders' equity	-1,100,000	7,000,000	-100,000
Deferred tax assets [Abstract]
Allowance for loan and lease losses	25,689,000	26,729,000
Deferred compensation	8,744,000	7,931,000
Postretirement benefit obligation	2,377,000	2,596,000
Unrealized losses on securities available for sale	0	5,900,000
Accrued liabilities	1,778,000	3,265,000
Stock-based compensation expense	6,457,000	7,862,000
Equipment leasing	1,416,000	1,661,000
Other	1,325,000	2,125,000
Total deferred tax assets	47,786,000	58,069,000
Deferred tax liabilities [Abstract]
Pension and executive retirement	12,192,000	17,417,000
Fair value adjustments from acquisitions	1,243,000	2,070,000
Unrealized gains on securities available for sale	1,331,000	0
Premises and equipment, primarily due to accelerated depreciation	2,491,000	2,270,000
Deferred loan costs	1,460,000	1,624,000
Intangible amortization	14,162,000	12,007,000
Other	390,000	892,000
Total deferred tax liabilities	33,269,000	36,280,000
Net deferred tax asset at year-end	14,517,000	21,789,000	11,115,000
Net deferred tax asset (liability) at beginning of year	21,789,000	11,115,000
Increase in net deferred tax asset	-7,272,000	10,674,000
Reduction in unrecognized tax benefits resulting from expiration of statute of limitations of prior years' tax filings			-900,000
Decrease in tax expense			-800,000
Federal statutory income tax rate (in hundredths)	35.00%
Income tax reconciliation [Abstract]
Federal income tax at statutory rate	39,306,000	31,482,000	27,081,000
Tax exempt income	-2,250,000	-2,433,000	-2,536,000
Net increase in CSV of life insurance	-1,734,000	-1,166,000	-908,000
Low income housing tax credits	-880,000	-819,000	-629,000
State taxes, net of federal tax benefit	2,939,000	1,512,000	1,182,000
Other, net	-152,000	-380,000	-1,374,000
Total income tax expense	$37,229,000	$28,196,000	$22,816,000

Employee_Benefit_Plans_Details

Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Adjustment of accumulated other comprehensive income	$2,400,000
Transition obligation period of recognition	20 years
Net actuarial loss that will be amortized from Accumulated other comprehensive income (loss) in next fiscal year	2,400,000
Prior service credit that will be amortized from Accumulated other comprehensive income (loss) in next fiscal year	200,000
Assumptions used to determine benefit obligations [Abstract]
Discount rate (in hundredths)			3.50%
Expected long-term return on plan assets (in hundredths)	7.50%	7.50%	7.50%
Rate of compensation increase (in hundredths)		3.00%	3.00%
Assumptions used to determine net periodic pension cost [Abstract]
Discount rate (in hundredths)		3.50%	4.10%
Expected long-term return on plan assets (in hundredths)	7.50%	7.50%	7.50%
Rate of compensation increase (in hundredths)		3.00%	3.00%
Other changes in plan assets and benefit obligation recognized in other comprehensive income (pre-tax) [Abstract]
Amortization of prior service cost	-75,000	-2,790,000	-3,593,000
Amortization of unrecognized net gain	-19,245,000	21,923,000	-24,000
Estimate future benefit payments [Abstract]
Annual rates of increase in the per capita cost of covered medical and prescription drug benefits, minimum (in hundredths)	7.00%
Annual rates of increase in the per capita cost of covered medical and prescription drug benefits, maximum (in hundredths)	9.00%
Ultimate health care cost trend rate (in hundredths)	3.90%
Actual plan asset allocations [Abstract]
Actual plan asset allocations (in hundredths)	100.00%	100.00%
Employer contributions to 401 (k) plan	2,200,000	2,100,000	1,800,000
Effect of one-percentage point change in assumed health care cost trend rates [Abstract]
One-percentage point Increase on total service and interest cost components	39,000
One-percentage point (decrease) on total service and interest cost components	-33,000
One-percentage point Increase on postretirement accumulated benefit obligation	895,000
One-percentage point (decrease) on postretirement accumulated benefit obligation	-764,000
Minimum [Member]
Assumptions used to determine benefit obligations [Abstract]
Discount rate (in hundredths)	4.19%	4.90%
Rate of compensation increase (in hundredths)	3.00%
Assumptions used to determine net periodic pension cost [Abstract]
Discount rate (in hundredths)	4.90%
Rate of compensation increase (in hundredths)	3.00%
Maximum [Member]
Assumptions used to determine benefit obligations [Abstract]
Discount rate (in hundredths)	4.30%	5.05%
Rate of compensation increase (in hundredths)	3.75%
Assumptions used to determine net periodic pension cost [Abstract]
Discount rate (in hundredths)	5.05%
Rate of compensation increase (in hundredths)	3.75%
Pension Benefits [Member]
Accumulated other comprehensive income (loss), before tax [Abstract]
Net actuarial loss	28,767,000	11,286,000
Prior service cost	97,000	118,000
Total amounts recognized in accumulated other comprehensive loss (pre-tax)	28,864,000	11,404,000
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of period	85,667,000	85,130,000
Service cost	2,290,000	2,493,000	3,122,000
Interest cost	4,142,000	3,223,000	3,145,000
Plan participants' contributions	0	0
Actuarial(gain) loss	12,501,000	-10,853,000
Amendments	0	0
Acquisition	0	10,958,000
Benefits paid	-6,044,000	-5,284,000
Projected benefit obligation at end of period	98,556,000	85,667,000	85,130,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of period	118,574,000	99,705,000
Actual return on plan assets	3,950,000	18,451,000
Acquisition	0	4,994,000
Employer contributions	752,000	708,000
Plan participants' contributions	0	0
Benefits paid	-6,044,000	-5,284,000
Fair value of plan assets at end of period	117,232,000	118,574,000	99,705,000
Funded status	18,676,000	32,907,000
Accumulated benefit obligation	98,600,000	85,700,000
Amounts recognized in Balance Sheet [Abstract]
Other assets	39,044,000	48,189,000
Other liabilities	-20,368,000	-15,282,000
Funded status	18,676,000	32,907,000
Components of net periodic benefit cost [Abstract]
Service cost	2,290,000	2,493,000	3,122,000
Interest cost	4,142,000	3,223,000	3,145,000
Expected return on plan assets	-8,681,000	-7,804,000	-6,686,000
Amortization of prior service cost	23,000	23,000	283,000
Amortization of unrecognized net loss	79,000	2,692,000	3,330,000
Net periodic pension cost	-2,147,000	627,000	3,194,000
Other changes in plan assets and benefit obligation recognized in other comprehensive income (pre-tax) [Abstract]
Net loss (gain)	17,233,000	-21,500,000	894,000
Prior service cost	0	0	-1,006,000
Amortization of prior service cost	-23,000	-23,000	-283,000
Amortization of unrecognized net gain	-79,000	-2,692,000	-3,330,000
Total recognized in other comprehensive loss (income)	17,131,000	-24,215,000	-3,725,000
Total recognized in net periodic benefit cost and other comprehensive income (loss) - pre-tax	14,984,000	-23,588,000	-531,000
Estimate future benefit payments [Abstract]
2014	6,011,000
2015	6,221,000
2016	9,473,000
2017	7,100,000
2018	6,953,000
2019 - 2022	40,351,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	117,232,000	118,574,000	99,705,000
Pension Benefits [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	72,722,000	86,711,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	72,722,000	86,711,000
Pension Benefits [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	44,510,000	31,863,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	44,510,000	31,863,000
Pension Benefits [Member] | Cash and Cash Equivalents [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of period	7,533,000
Fair value of plan assets at end of period	4,423,000
Target asset allocations [Abstract]
Target allocation percentage of assets, range minimum (in hundredths)	0.00%
Target allocation percentage of assets, range maximum (in hundredths)	20.00%
Actual plan asset allocations [Abstract]
Actual plan asset allocations (in hundredths)	4.00%	6.00%
Fair value of plan assets	4,423,000
Pension Benefits [Member] | Cash and Cash Equivalents [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	4,423,000	7,533,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	4,423,000	7,533,000
Pension Benefits [Member] | Cash and Cash Equivalents [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	0	0
Actual plan asset allocations [Abstract]
Fair value of plan assets	0	0
Pension Benefits [Member] | Fixed Income Securities [Member]
Target asset allocations [Abstract]
Target allocation percentage of assets, range minimum (in hundredths)	20.00%
Target allocation percentage of assets, range maximum (in hundredths)	40.00%
Actual plan asset allocations [Abstract]
Actual plan asset allocations (in hundredths)	38.00%	27.00%
Pension Benefits [Member] | Equity [Member]
Target asset allocations [Abstract]
Target allocation percentage of assets, range minimum (in hundredths)	40.00%
Target allocation percentage of assets, range maximum (in hundredths)	80.00%
Actual plan asset allocations [Abstract]
Actual plan asset allocations (in hundredths)	58.00%	67.00%
Pension Benefits [Member] | Foreign Equity Mutual Funds [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	38,581,000	15,653,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	38,581,000	15,653,000
Pension Benefits [Member] | Foreign Equity Mutual Funds [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	38,581,000	15,653,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	38,581,000	15,653,000
Pension Benefits [Member] | Foreign Equity Mutual Funds [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	0	0
Actual plan asset allocations [Abstract]
Fair value of plan assets	0	0
Pension Benefits [Member] | Equity Mutual Funds [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	29,718,000	16,727,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	29,718,000	16,727,000
Pension Benefits [Member] | Equity Mutual Funds [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	29,718,000	16,727,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	29,718,000	16,727,000
Pension Benefits [Member] | Equity Mutual Funds [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	0	0
Actual plan asset allocations [Abstract]
Fair value of plan assets	0	0
Pension Benefits [Member] | US Government Bonds [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	4,420,000	9,355,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	4,420,000	9,355,000
Pension Benefits [Member] | US Government Bonds [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	0	0
Actual plan asset allocations [Abstract]
Fair value of plan assets	0	0
Pension Benefits [Member] | US Government Bonds [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	4,420,000	9,355,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	4,420,000	9,355,000
Pension Benefits [Member] | Corporate Bonds [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	40,090,000	19,665,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	40,090,000	19,665,000
Pension Benefits [Member] | Corporate Bonds [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	0	0
Actual plan asset allocations [Abstract]
Fair value of plan assets	0	0
Pension Benefits [Member] | Corporate Bonds [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period	40,090,000	19,665,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	40,090,000	19,665,000
Pension Benefits [Member] | Common Stock [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		44,532,000
Actual plan asset allocations [Abstract]
Fair value of plan assets		44,532,000
Pension Benefits [Member] | Common Stock [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		44,532,000
Actual plan asset allocations [Abstract]
Fair value of plan assets		44,532,000
Pension Benefits [Member] | Common Stock [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		0
Actual plan asset allocations [Abstract]
Fair value of plan assets		0
Pension Benefits [Member] | Municipal Bonds and Notes [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		1,451,000
Actual plan asset allocations [Abstract]
Fair value of plan assets		1,451,000
Pension Benefits [Member] | Municipal Bonds and Notes [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		0
Actual plan asset allocations [Abstract]
Fair value of plan assets		0
Pension Benefits [Member] | Municipal Bonds and Notes [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		1,451,000
Actual plan asset allocations [Abstract]
Fair value of plan assets		1,451,000
Pension Benefits [Member] | Foreign Bonds and Notes [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		1,392,000
Actual plan asset allocations [Abstract]
Fair value of plan assets		1,392,000
Pension Benefits [Member] | Foreign Bonds and Notes [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		0
Actual plan asset allocations [Abstract]
Fair value of plan assets		0
Pension Benefits [Member] | Foreign Bonds and Notes [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		1,392,000
Actual plan asset allocations [Abstract]
Fair value of plan assets		1,392,000
Pension Benefits [Member] | Foreign Equity [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		2,266,000
Actual plan asset allocations [Abstract]
Fair value of plan assets		2,266,000
Pension Benefits [Member] | Foreign Equity [Member] | Level 1 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		2,266,000
Actual plan asset allocations [Abstract]
Fair value of plan assets		2,266,000
Pension Benefits [Member] | Foreign Equity [Member] | Level 2 [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at end of period		0
Actual plan asset allocations [Abstract]
Fair value of plan assets		0
Other Benefits [Member]
Accumulated other comprehensive income (loss), before tax [Abstract]
Net actuarial loss	2,929,000	1,628,000
Prior service cost	-314,000	-521,000
Total amounts recognized in accumulated other comprehensive loss (pre-tax)	2,615,000	1,107,000
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of period	7,428,000	4,071,000
Service cost	16,000	23,000	20,000
Interest cost	347,000	286,000	155,000
Plan participants' contributions	266,000	269,000
Actuarial(gain) loss	1,452,000	-369,000
Amendments	0	-54,000
Acquisition	0	3,928,000
Benefits paid	-799,000	-726,000
Projected benefit obligation at end of period	8,710,000	7,428,000	4,071,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of period	0	0
Actual return on plan assets	0	0
Acquisition	0	0
Employer contributions	533,000	457,000
Plan participants' contributions	266,000	269,000
Benefits paid	-799,000	-726,000
Fair value of plan assets at end of period	0	0	0
Funded status	-8,710,000	-7,428,000
Accumulated benefit obligation	8,700,000	7,400,000
Amounts recognized in Balance Sheet [Abstract]
Other assets	0	0
Other liabilities	-8,710,000	-7,428,000
Funded status	-8,710,000	-7,428,000
Components of net periodic benefit cost [Abstract]
Service cost	16,000	23,000	20,000
Interest cost	347,000	286,000	155,000
Expected return on plan assets	0	0	0
Amortization of prior service cost	-206,000	-205,000	-202,000
Amortization of unrecognized net loss	151,000	280,000	182,000
Net periodic pension cost	308,000	384,000	155,000
Other changes in plan assets and benefit obligation recognized in other comprehensive income (pre-tax) [Abstract]
Net loss (gain)	1,452,000	-369,000	136,000
Prior service cost	0	-54,000	0
Amortization of prior service cost	206,000	205,000	202,000
Amortization of unrecognized net gain	-151,000	-280,000	-182,000
Total recognized in other comprehensive loss (income)	1,507,000	-498,000	156,000
Total recognized in net periodic benefit cost and other comprehensive income (loss) - pre-tax	1,815,000	-114,000	311,000
Estimate future benefit payments [Abstract]
2014	538,000
2015	549,000
2016	571,000
2017	592,000
2018	578,000
2019 - 2022	2,881,000
Actual plan asset allocations [Abstract]
Fair value of plan assets	$0	$0	$0

StockBased_Compensation_Detail

Stock-Based Compensation (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock options additional disclosures [Abstract]
Stock-based compensation expense	$3,521,000	$4,305,000	$4,364,000
Restricted stock and restricted stock units, weighted average grant date fair value [Abstract]
Number of shares available for future grant (in shares)	3,800,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	4 years
Stock awards termination period	10 years
Stock options [Roll Forward]
Outstanding, beginning of period (in shares)	1,341,500
Granted (in shares)	3,296
Exercised (in shares)	-290,243
Forfeited (in shares)	-105
Expired (in shares)	-16,106
Outstanding, end of period (in shares)	1,038,342	1,341,500
Exercisable, end of period (in shares)	1,031,726
Expected to vest (in shares)	5,249
Stock options, weighted average exercise price [Abstract]
Outstanding, beginning of period (in dollars per share)	$22.98
Granted (in dollars per share)	$24.80
Exercised (in dollars per share)	$22.58
Forfeited (in dollars per share)	$20.19
Expired (in dollars per share)	$22.36
Outstanding, end of period (in dollars per share)	$23.10	$22.98
Exercisable, end of period (in dollars per share)	$23.09
Expected to vest (in dollars per share)	$24.50
Stock options additional disclosures [Abstract]
Weighted average remaining contractual term, outstanding, end of period (in years)	3 years 4 months 24 days
Weighted average remaining contractual term, exercisable, end of period (in years)	3 years 4 months 13 days
Weighted average remaining contractual term, expected to vest (in years)	7 years 3 months 25 days
Aggregate intrinsic value, outstanding, end of period	3,353,951
Aggregate intrinsic value, exercisable, end of period	3,342,258
Aggregate intrinsic value, expected to vest	9,354
Stock-based compensation expense	100,000	200,000	500,000
Proceeds from stock options exercised	6,554,000	7,927,000	1,908,000
Tax benefits related to stock options exercised	313,000	178,000	8,000
Intrinsic value of stock options exercised	789,000	905,000	498,000
Fair value of shares vested during the year	393,000	766,000	1,656,000
Restricted Stock [Member]
Stock options additional disclosures [Abstract]
Unrecognized compensation cost	4,400,000
Unrecognized compensation cost, weighted average period of recognition (in years)	1 year 8 months 12 days
Restricted stock and restricted stock units [Roll Forward]
Unvested, beginning of period (in shares)	66,650
Forfeited (in shares)	0
Vested (in shares)	-14,650
Unvested, end of period (in shares)	52,000
Restricted stock and restricted stock units, weighted average grant date fair value [Abstract]
Unvested, beginning of period (in dollars per share)	$23.15
Forfeited (in dollars per share)	$0
Vested (in dollars per share)	$22.16
Unvested, end of period (in dollars per share)	$23.43
Restricted Stock [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	5 years
Restricted Stock [Member] | Non-employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period	3 years
Restricted Stock Units (RSUs) [Member]
Restricted stock and restricted stock units [Roll Forward]
Unvested, beginning of period (in shares)	539,850
Forfeited (in shares)	-5,090
Vested (in shares)	-105,013
Granted (in shares)	209,228
Unvested, end of period (in shares)	638,975
Restricted stock and restricted stock units, weighted average grant date fair value [Abstract]
Unvested, beginning of period (in dollars per share)	$27.36
Forfeited (in dollars per share)	$0
Vested (in dollars per share)	$0
Granted (in dollars per share)	$24.11
Unvested, end of period (in dollars per share)	$31.01
Restricted and Deferred Stock Awards [Member]
Stock options additional disclosures [Abstract]
Stock-based compensation expense	4,200,000	3,800,000	3,700,000
Tax benefit from compensation expense	$2,900,000	$2,400,000	$1,500,000

Stockholders_Equity_Details

Stockholders Equity (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 27, 2014
Stockholders Equity [Abstract]
Unrecognized prior service cost and net actuarial loss on pension plans	($19,181,000)	($7,785,000)
Unrealized net holding (losses) gains on available for sale securities	2,154,000	-8,980,000
Accumulated other comprehensive loss	-17,027,000	-16,765,000
Class of Warrant or Right [Line Items]
Future dividend payment restrictions	The approval of the Office of Comptroller of the Currency (OCC) is required to pay dividends when a bank fails to meet certain minimum regulatory capital standards or when such dividends are in excess of a subsidiary bank's earnings retained in the current year plus retained net profits for the preceding two years as specified in applicable OCC regulations.
Preceding period of retained net profits for approval of Office of Comptroller of the Currency (in years)	2 years
Statutory amount available for dividend payments	88,700,000
Common stock repurchased during period (in shares)	3,288	584,925	769,568
Common stock repurchased during period	$100,000
Treasury Stock Acquired, Average Cost Per Share	$22.02
Stock Repurchase Program, Number Of Additional Shares Authorized To Be Repurchased				1,000,000

Regulatory_Capital_Requirement2

Regulatory Capital Requirements (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Total Capital (to risk weighted assets) [Abstract]
Total capital to risk weighted assets	$777,651	$723,580
Total capital to risk weighted assets (in hundredths)	13.50%	12.99%
Minimum capital required for capital adequacy to risk weighted assets (in hundredths)	8.00%	8.00%
Capital required for classification as well capitalized to risk weighted assets (in hundredths)	10.00%	10.00%
Tier I Capital (to risk weighted assets) [Abstract]
Tier I capital to risk weighted assets	709,965	653,950
Tier I capital to risk weighted assets (in hundredths)	12.32%	11.74%
Minimum Tier one capital required for capital adequacy to risk weighted assets(in hundredths)	4.00%	4.00%
Tier one capital required for classification as well capitalized to risk weighted assets (in hundredths)	6.00%	6.00%
Tier I Capital (to average assets) [Abstract]
Tier I capital to average assets	709,965	653,950
Tier I capital to average assets (in hundredths)	9.39%	8.93%
Minimum Tier I leverage capital required for capital adequacy to average assets (in hundredths)	4.00%	4.00%
Tier I leverage capital required for classification as well capitalized to average assets (in hundredths)	5.00%	5.00%
NBT Bank [Member]
Total Capital (to risk weighted assets) [Abstract]
Total capital to risk weighted assets	727,771	686,194
Total capital to risk weighted assets (in hundredths)	12.72%	12.41%
Minimum capital required for capital adequacy to risk weighted assets (in hundredths)	8.00%	8.00%
Capital required for classification as well capitalized to risk weighted assets (in hundredths)	10.00%	10.00%
Tier I Capital (to risk weighted assets) [Abstract]
Tier I capital to risk weighted assets	660,086	617,038
Tier I capital to risk weighted assets (in hundredths)	11.54%	11.16%
Minimum Tier one capital required for capital adequacy to risk weighted assets(in hundredths)	4.00%	4.00%
Tier one capital required for classification as well capitalized to risk weighted assets (in hundredths)	6.00%	6.00%
Tier I Capital (to average assets) [Abstract]
Tier I capital to average assets	$660,086	$617,038
Tier I capital to average assets (in hundredths)	8.79%	8.47%
Minimum Tier I leverage capital required for capital adequacy to average assets (in hundredths)	4.00%	4.00%
Tier I leverage capital required for classification as well capitalized to average assets (in hundredths)	5.00%	5.00%

Earnings_Per_Share_Details

Earnings Per Share (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Basic earnings per share [Abstract]
Net income available to common shareholders	$75,074	$61,747	$54,558
Weighted average common shares, basic (in shares)	43,877,000	41,930,000	33,379,000
Basic EPS (in dollars per share)	$1.71	$1.47	$1.63
Diluted earnings per share [Abstract]
Net income available to common shareholders	$75,074	$61,747	$54,558
Dilutive effect of stock based compensation (in shares)	518,000	420,000	340,000
Weighted average common shares, diluted (in shares)	44,395,000	42,350,000	33,719,000
Diluted EPS (in dollars per share)	$1.69	$1.46	$1.62
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options excluded from calculation of diluted EPS (in shares)	493,000	1,048,000	1,193,000

Reclassification_Adjustments_O2

Reclassification Adjustments Out of Other Comprehensive (Loss) Income (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains	($92)	($1,426)	($599)
Interest income	-251,878	-238,079	-204,203
Salaries and employee benefits	119,667	113,580	104,815
Income tax expense	37,229	28,196	22,816
Net Income	75,074	61,747	54,558
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	200	565
Total reclassification during the period, net of tax	-267	740
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income	-313	-861
Gains on Available for Sale Securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains	-92	-1,426
Amortization of Unrealized Gains and Losses Related to Securities Transfer [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	-421	0
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax expense	29	1,189
Net Income	46	1,601
Amortization of Net Gains [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	94	2,972
Amortization of Prior Service Costs [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits	($19)	($182)

Commitments_and_Contingent_Lia2

Commitments and Contingent Liabilities (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 24, 2014
Commitments and Contingent Liabilities [Abstract]
Percentage of the Company's loans secured by real estate (in hundredths)	59.00%
Guarantor Obligations [Line Items]
Loans serviced by the Company for unrelated third parties	$626,000,000	$685,600,000
Mortgage servicing rights	1,500,000	2,200,000
Federal Reserve Bank Requirement [Abstract]
Federal Reserve Bank maintenance period	14 days
Average reserve at Federal Reserve Bank for maintenance period			46,900,000
Unused lines of Credit [Member]
Guarantor Obligations [Line Items]
Commitments - maximum potential obligation	214,175,000	216,658,000
Commitment to Extend Credits [Member]
Guarantor Obligations [Line Items]
Commitments - maximum potential obligation	972,912,000	849,092,000
Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Commitments - maximum potential obligation	35,244,000	36,837,000
Obligation instrument term		5 years
Commercial Letters of Credit [Member]
Guarantor Obligations [Line Items]
Commitments - maximum potential obligation	22,486,000	41,263,000
Loans Sold with Recourse [Member]
Guarantor Obligations [Line Items]
Commitments - maximum potential obligation	$23,351,000	$15,741,000

Fair_Values_of_Financial_Instr2

Fair Values of Financial Instruments (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Financial assets [Abstract]
Securities held to maturity	$454,994,000	$113,276,000
Financial liabilities [Abstract]
Time deposits	1,043,823,000	1,021,142,000
Long-term debt	130,945,000	308,823,000
Junior subordinated debt	101,196,000	101,196,000
Securities Available for Sale [Abstract]
Total Securities Available for Sale	1,013,171,000	1,364,881,000
Trading Securities	7,793,000	5,779,000
Liabilities [Abstract]
Collateral dependent impaired financing receivable with specific reserves	5,800,000
Allowance for loan and lease losses collateral dependent impaired loans with specific reserves	1,100,000
Liquidation expense ratio on impaired collateral minimum (in hundredths)	10.00%
Liquidation expense ratio on impaired collateral maximum (in hundredths)	35.00%
Recurring Basis [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	23,111,000	43,616,000
Federal Agency	329,914,000	278,915,000
State & municipal	37,570,000	113,665,000
Mortgage-backed	364,727,000	364,164,000
Collateralized mortgage obligations	242,129,000	549,528,000
Other securities	15,720,000	14,993,000
Total Securities Available for Sale	1,013,171,000	1,364,881,000
Trading Securities	7,793,000	5,779,000
Interest Rate Swaps	4,707,000	281,000
Total	1,025,671,000	1,370,941,000
Liabilities [Abstract]
Interest Rate Swaps	4,707,000	281,000
Total	4,707,000	281,000
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Recurring Basis [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	23,111,000	43,616,000
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	7,612,000	6,796,000
Total Securities Available for Sale	30,723,000	50,412,000
Trading Securities	7,793,000	5,779,000
Interest Rate Swaps	0	0
Total	38,516,000	56,191,000
Liabilities [Abstract]
Interest Rate Swaps	0	0
Total	0	0
Significant Other Observable Inputs (Level 2) [Member] | Recurring Basis [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	0	0
Federal Agency	329,914,000	278,915,000
State & municipal	37,570,000	113,665,000
Mortgage-backed	364,727,000	364,164,000
Collateralized mortgage obligations	242,129,000	549,528,000
Other securities	8,108,000	8,197,000
Total Securities Available for Sale	982,448,000	1,314,469,000
Trading Securities	0	0
Interest Rate Swaps	4,707,000	281,000
Total	987,155,000	1,314,750,000
Liabilities [Abstract]
Interest Rate Swaps	4,707,000	281,000
Total	4,707,000	281,000
Significant Unobservable Inputs (Level 3) [Member] | Recurring Basis [Member]
Securities Available for Sale [Abstract]
U.S. Treasury	0	0
Federal Agency	0	0
State & municipal	0	0
Mortgage-backed	0	0
Collateralized mortgage obligations	0	0
Other securities	0	0
Total Securities Available for Sale	0	0
Trading Securities	0	0
Interest Rate Swaps	0	0
Total	0	0
Liabilities [Abstract]
Interest Rate Swaps	0	0
Total	0	0
Carrying Amount [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Securities held to maturity	454,361,000	117,283,000
Financial liabilities [Abstract]
Time deposits	1,043,823,000	1,021,142,000
Long-term debt	130,945,000	308,823,000
Junior subordinated debt	101,196,000	101,196,000
Carrying Amount [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Net Loans	5,528,912,000	5,337,361,000
Estimated Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Financial assets [Abstract]
Securities held to maturity	454,994,000	113,276,000
Financial liabilities [Abstract]
Time deposits	1,038,877,000	1,023,982,000
Long-term debt	132,562,000	325,195,000
Junior subordinated debt	103,770,000	105,121,000
Estimated Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member]
Financial assets [Abstract]
Net Loans	$5,584,777,000	$5,386,520,000

Sale_of_Equity_Investment_Deta

Sale of Equity Investment (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Sale of Equity Investment [Abstract]
Date of disposal		17-Apr-14
Percentage of ownership interest sold (in hundredths)	20.00%	20.00%	20.00%
Book value	$3,000,000	$3,000,000	$3,000,000
Total sale price of investment	140,000,000	140,000,000	140,000,000
Gain on sale of equity investments	19,401,000		19,401,000	0	0
Proceeds of sale held in escrow	$5,200,000	$5,200,000	$5,200,000

Parent_Company_Financial_Infor2

Parent Company Financial Information (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets [Abstract]
Cash and cash equivalents	$146,636	$158,926	$163,668
Securities available for sale, at estimated fair value	1,013,171	1,364,881
Trading securities	7,793	5,779
Other assets	126,967	127,234
Total assets	7,797,926	7,652,175
Liabilities and Stockholders' Equity [Abstract]
Total liabilities	6,933,745	6,835,606
Stockholders' equity	864,181	816,569	582,273	538,110
Total liabilities and stockholders' equity	7,797,926	7,652,175
Condensed Income Statements [Abstract]
Securities gains (losses)	92	1,426	599
Interest, dividend and other income	275,081	268,723	239,397
Income before income tax benefit and equity in undistributed income of subsidiaries	112,303	89,943	77,374
Income tax (expense) benefit	-37,229	-28,196	-22,816
Net income	75,074	61,747	54,558
Operating activities [Abstract]
Net income	75,074	61,747	54,558
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Stock-based compensation	3,521	4,305	4,364
Gain (Loss) on sales of available-for-sale securities	-49	-1,283	-442
Net change in other liabilities	5,286	-5,219	-128
Net change in other assets	-27,949	20,463	6,804
Net cash provided by operating activities	87,811	119,298	88,854
Investing activities [Abstract]
Purchases of available-for-sale securities	-197,652	-353,714	-483,858
Sales and maturities of available-for-sale securities	236,133	376,509	573,828
Purchases of premises and equipment	-9,003	-5,766	-6,994
Net cash used in investing activities	-143,741	-183,754	-126,850
Financing activities [Abstract]
Payments on long-term debt	-315,831	-163,595	-3,354
Purchases of treasury shares	72	12,459	15,490
Cash dividends and payments for fractional shares	-36,905	-33,518	-26,712
Net cash provided by financing activities	43,640	59,714	72,283
Net (decrease) increase in cash and cash equivalents	-12,290	-4,742	34,287
Cash and cash equivalents at beginning of year	158,926	163,668	129,381
Cash and cash equivalents at end of year	146,636	158,926	163,668
NBT Bancorp Inc [Member]
Assets [Abstract]
Cash and cash equivalents	3,586	3,741	23,095
Securities available for sale, at estimated fair value	11,649	11,008
Trading securities	6,761	4,742
Investment in subsidiaries, on equity basis	947,880	896,479
Other assets	61,829	49,530
Total assets	1,031,705	965,500
Liabilities and Stockholders' Equity [Abstract]
Total liabilities	167,524	148,931
Stockholders' equity	864,181	816,569
Total liabilities and stockholders' equity	1,031,705	965,500
Condensed Income Statements [Abstract]
Dividends from subsidiaries	35,400	13,500	79,175
Management fee from subsidiaries	87,116	84,778	78,665
Securities gains (losses)	49	1,273	442
Interest, dividend and other income	800	636	720
Total revenue	123,365	100,187	159,002
Operating expense	89,834	83,679	79,015
Income before income tax benefit and equity in undistributed income of subsidiaries	33,531	16,508	79,987
Income tax (expense) benefit	631	-1,046	-284
Dividends in excess of income (equity in undistributed income) of subsidiaries	40,912	46,285	-25,145
Net income	75,074	61,747	54,558
Operating activities [Abstract]
Net income	75,074	61,747	54,558
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Stock-based compensation	3,521	4,305	4,364
Gain (Loss) on sales of available-for-sale securities	49	1,273	442
Equity in undistributed income	-75,824	-59,785	-54,030
Cash dividend from subsidiaries	35,400	13,500	79,175
Net change in other liabilities	18,594	-18,077	-3,181
Net change in other assets	-25,151	14,928	2,030
Net cash provided by operating activities	31,663	17,891	83,358
Investing activities [Abstract]
Purchases of available-for-sale securities	-597	0	-4,163
Sales and maturities of available-for-sale securities	140	1,948	1,445
Net cash used in acquisitions	0	2,232	-14,612
Purchases of premises and equipment	-640	-782	-1,240
Net cash used in investing activities	-1,097	3,398	-18,570
Financing activities [Abstract]
Proceeds from the issuance of shares to employee benefit plans and other stock plans	5,943	5,512	1,387
Payments on long-term debt	0	0	-3,340
Purchases of treasury shares	-72	-12,459	-15,490
Cash dividends and payments for fractional shares	-36,905	-33,518	-26,712
Excess tax benefit from exercise of stock options	313	-178	8
Net cash provided by financing activities	-30,721	-40,643	-44,147
Net (decrease) increase in cash and cash equivalents	-155	-19,354	20,641
Cash and cash equivalents at beginning of year	3,741	23,095	2,454
Cash and cash equivalents at end of year	$3,586	$3,741	$23,095