Allowance for Loan and Lease Losses and Credit Quality of Loans and Leases (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2011	Dec. 31, 2010
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	$ 16,414	$ 23,116
61 - 90 Days Past Due Accruing	4,107	5,563
Greater Than 91 Days Past Due Accruing	4,525	2,325
Total Past Due Accruing	25,046	31,004
Non-Accrual	39,752	42,467
Current	3,643,292	3,536,535
Recorded Total Loans and Leases	3,708,090	3,610,006
Home Equity Loan amount, Percentage of Equity in Home, Maximum (in hundredths)	85.00%
Residential Real Estate Loan amount, percentage of appraised value or purchase price of the property, maximum (in hundredths)	85.00%
Troubled Debt Restructured Loans Amount	4,600	1,000
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	2,240	4,140
61 - 90 Days Past Due Accruing	996	1,330
Greater Than 91 Days Past Due Accruing	239	94
Total Past Due Accruing	3,475	5,564
Non-Accrual	20,453	25,051
Current	1,623,806	1,549,756
Recorded Total Loans and Leases	1,647,734	1,580,371
Commercial Portfolio Segment [Member] \| Commercial Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	169	136
61 - 90 Days Past Due Accruing	233	55
Greater Than 91 Days Past Due Accruing	44	94
Total Past Due Accruing	446	285
Non-Accrual	2,044	5,837
Current	506,716	461,633
Recorded Total Loans and Leases	509,206	467,755
Commercial Portfolio Segment [Member] \| Commercial Real Estate Other Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	277	1,263
61 - 90 Days Past Due Accruing	391	0
Greater Than 91 Days Past Due Accruing	195	0
Total Past Due Accruing	863	1,263
Non-Accrual	5,324	5,687
Current	782,378	730,285
Recorded Total Loans and Leases	788,565	737,235
Commercial Portfolio Segment [Member] \| Agricultural Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	64	63
61 - 90 Days Past Due Accruing	13	92
Greater Than 91 Days Past Due Accruing	0	0
Total Past Due Accruing	77	155
Non-Accrual	3,467	4,065
Current	61,050	63,336
Recorded Total Loans and Leases	64,594	67,556
Commercial Portfolio Segment [Member] \| Agricultural Real Estate Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	0	108
61 - 90 Days Past Due Accruing	0	0
Greater Than 91 Days Past Due Accruing	0	0
Total Past Due Accruing	0	108
Non-Accrual	1,890	2,429
Current	31,116	33,400
Recorded Total Loans and Leases	33,006	35,937
Commercial Portfolio Segment [Member] \| Small Business Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,730	2,570
61 - 90 Days Past Due Accruing	359	1,183
Greater Than 91 Days Past Due Accruing	0	0
Total Past Due Accruing	2,089	3,753
Non-Accrual	7,728	7,033
Current	242,547	261,102
Recorded Total Loans and Leases	252,364	271,888
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	12,825	15,974
61 - 90 Days Past Due Accruing	2,861	4,107
Greater Than 91 Days Past Due Accruing	2,652	1,312
Total Past Due Accruing	18,338	21,393
Non-Accrual	10,071	8,765
Current	1,461,499	1,451,083
Recorded Total Loans and Leases	1,489,908	1,481,241
Consumer Portfolio Segment [Member] \| Indirect Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	7,904	9,307
61 - 90 Days Past Due Accruing	1,780	2,193
Greater Than 91 Days Past Due Accruing	1,427	862
Total Past Due Accruing	11,111	12,362
Non-Accrual	1,323	1,971
Current	851,111	814,594
Recorded Total Loans and Leases	863,545	828,927
Consumer Portfolio Segment [Member] \| Home Equity Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	4,249	5,740
61 - 90 Days Past Due Accruing	887	1,756
Greater Than 91 Days Past Due Accruing	1,050	396
Total Past Due Accruing	6,186	7,892
Non-Accrual	8,352	6,395
Current	538,387	561,391
Recorded Total Loans and Leases	552,925	575,678
Consumer Portfolio Segment [Member] \| Direct Financing Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	672	927
61 - 90 Days Past Due Accruing	194	158
Greater Than 91 Days Past Due Accruing	175	54
Total Past Due Accruing	1,041	1,139
Non-Accrual	396	399
Current	72,002	75,098
Recorded Total Loans and Leases	73,439	76,636
Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Abstract]
31 - 60 Days Past Due Accruing	1,349	3,002
61 - 90 Days Past Due Accruing	250	126
Greater Than 91 Days Past Due Accruing	1,634	919
Total Past Due Accruing	3,233	4,047
Non-Accrual	9,228	8,651
Current	557,987	535,696
Recorded Total Loans and Leases	$ 570,448	$ 548,394

Financing receivables that are less than 61 days past due but more than 30 days past due.

Name:	nbtb_FinancingReceivableRecordedInvestment31To60DaysPastDue
Namespace Prefix:	nbtb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are less than 91 days past due but more than 60 days past due.

+ Details

Name:	nbtb_FinancingReceivableRecordedInvestment61To90DaysPastDue
Namespace Prefix:	nbtb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are greater than 91 days past due.

+ Details

Name:	nbtb_FinancingReceivableRecordedInvestmentGreaterThan91DaysPastDue
Namespace Prefix:	nbtb
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ Details

Name:	nbtb_HomeEquityLoanOriginationAmountPercentageOfEuityInHomeMaximum
Namespace Prefix:	nbtb
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ Details

Name:	nbtb_ResidentialRealEstateLoanOriginationAmountPercentageOfAppraisedValueOrPurchasePriceOfPropertyMaximum
Namespace Prefix:	nbtb
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings after the financing receivable has been modified.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 32

-URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953670-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are current.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

-URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953401-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentCurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6965416&loc=d3e5111-111524

-Subparagraph (d)

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentPastDue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentPastDueAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-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.

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant