Allowance for Loan Losses and Credit Quality of Loans, Allowance for Loan Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan portfolio segments			3
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	$ 70,734	$ 70,484	$ 71,334	$ 71,234
Charge-offs	(5,830)	(5,265)	(17,052)	(18,131)
Recoveries	1,075	940	3,123	3,070
Provision	4,755	5,175	13,329	15,161
Balance as of End of Period	70,734	71,334	70,734	71,334
Allowance for loan losses
Allowance for loan losses	70,734	71,334	70,734	71,334
Allowance for loans individually evaluated for impairment	2,720		2,720		175
Allowance for loans collectively evaluated for impairment	68,014		68,014		71,159
Ending balance of loans	4,251,119		4,251,119		3,800,203
Ending balance of loans individually evaluated for impairment	13,017		13,017		6,219
Ending balance of loans and leases collectively evaluated for impairment	4,238,102		4,238,102		3,793,984
Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	37,495	39,147	38,831	40,101
Charge-offs	(1,904)	(1,694)	(4,685)	(7,153)
Recoveries	492	367	1,180	1,262
Provision	1,734	1,073	2,491	4,683
Balance as of End of Period	37,817	38,893	37,817	38,893
Allowance for loan losses
Allowance for loan losses	37,817	38,893	37,817	38,893
Allowance for loans individually evaluated for impairment	2,720		2,720		175
Allowance for loans collectively evaluated for impairment	35,097		35,097		38,656
Ending balance of loans	1,992,891		1,992,891		1,702,577
Ending balance of loans individually evaluated for impairment	13,017		13,017		6,219
Ending balance of loans and leases collectively evaluated for impairment	1,979,874		1,979,874		1,696,358
Commercial Loans [Member] \| Commercial [Member]
Allowance for loan losses
Ending balance of loans	602,546		602,546		511,074
Commercial Loans [Member] \| 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%		80.00%
Allowance for loan losses
Ending balance of loans	1,020,720		1,020,720		834,899
Commercial Loans [Member] \| Agricultural [Member]
Allowance for loan losses
Ending balance of loans	66,774		66,774		66,537
Commercial Loans [Member] \| 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%		75.00%
Allowance for loan losses
Ending balance of loans	36,543		36,543		33,926
Commercial Loans [Member] \| Business Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Business Banking Loans, maximum amount	350		350
Allowance for loan losses
Ending balance of loans	266,308		266,308		256,141
Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	27,235	25,718	26,049	26,126
Charge-offs	(3,446)	(3,526)	(11,237)	(10,420)
Recoveries	574	571	1,918	1,803
Provision	2,213	3,533	9,846	8,787
Balance as of End of Period	26,576	26,296	26,576	26,296
Allowance for loan losses
Allowance for loan losses	26,576	26,296	26,576	26,296
Allowance for loans individually evaluated for impairment	0		0		0
Allowance for loans collectively evaluated for impairment	26,576		26,576		26,049
Ending balance of loans	1,607,780		1,607,780		1,516,115
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans and leases collectively evaluated for impairment	1,607,780		1,607,780		1,516,115
Consumer Loans [Member] \| Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of automobile financing to indirect relationships with dealers (in hundredths)	70.00%		70.00%
Principal repayment term of loan, minimum (in years)			3 years
Principal repayment term of loan, maximum (in years)			6 years
Allowance for loan losses
Ending balance of loans	962,619		962,619		873,103
Consumer Loans [Member] \| 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%		85.00%
Allowance for loan losses
Ending balance of loans	576,208		576,208		569,645
Consumer Loans [Member] \| Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal repayment term of loan, minimum (in years)			1 year
Principal repayment term of loan, maximum (in years)			10 years
Allowance for loan losses
Ending balance of loans	68,953		68,953		73,367
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%		85.00%
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	5,943	5,373	6,249	4,627
Charge-offs	(480)	(45)	(1,130)	(558)
Recoveries	9	2	25	5
Provision	809	588	1,137	1,844
Balance as of End of Period	6,281	5,918	6,281	5,918
Allowance for loan losses
Allowance for loan losses	6,281	5,918	6,281	5,918
Allowance for loans individually evaluated for impairment	0		0		0
Allowance for loans collectively evaluated for impairment	6,281		6,281		6,249
Ending balance of loans	650,448		650,448		581,511
Ending balance of loans individually evaluated for impairment	0		0		0
Ending balance of loans and leases collectively evaluated for impairment	650,448		650,448		581,511
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance as of Beginning of Period	61	246	205	380
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	(1)	(19)	(145)	(153)
Balance as of End of Period	60	227	60	227
Allowance for loan losses
Allowance for loan losses	60	227	60	227
Allowance for loans collectively evaluated for impairment	$ 60		$ 60		$ 205

Represents the maximum repayment term of the debt instrument.

No definition available.

Name:	nbtb_DebtInstrumentRepaymentTermMaximum
Namespace Prefix:	nbtb_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the minimum repayment term of the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	nbtb_
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- Definition

This element represents the maximum percentage of the equity in home , for the originated amounts of home equity loans.

+ References

No definition available.

+ Details

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Namespace Prefix:	nbtb_
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- Definition

This element represents the maximum percentage of the appraised value or purchase price of a property, for the originated amounts of real estate loans.

+ References

No definition available.

+ Details

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- Definition

This element represents the number of portfolio segments within the loan portfolio.

+ References

No definition available.

+ Details

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- Definition

Represents the percentage of automobile financing to indirect relationships the Company maintains with dealers.

+ References

No definition available.

+ Details

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Namespace Prefix:	nbtb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the maximum loan amount available for small business customers.

+ References

No definition available.

+ Details

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Namespace Prefix:	nbtb_
Data Type:	xbrli:monetaryItemType
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- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 11B

-URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953423-111524

-Subparagraph (c)(1)

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Period Type:	instant

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

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Balance Type:	credit
Period Type:	instant

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

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Period Type:	instant

- Definition

Charge to expense for financing receivables that are expected to be uncollectible.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reduction to the allowance for credit losses related to collections on financing receivables which have been partially or fully charged off as bad debts.

+ References

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- Definition

Reduction to the allowance for credit losses related to financing receivables deemed uncollectible.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

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- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

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- Definition

Reflects the aggregate gross carrying amount of all categories of loans and leases held in portfolio, after deducting deferred income, but before deducting the allowance for losses on loans and leases.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6965416&loc=d3e5074-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6375948&loc=d3e4428-111522

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-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Chapter 8

-Paragraph 116

-IssueDate 2006-05-01

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Chapter V

-Section 563c.102

-Paragraph 8

-Subparagraph e

-Subsection I

-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

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