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Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) (USD $) | 12 Months Ended
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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 us-gaap_DividendsPayableAmountPerShare | $ 0.81 us-gaap_DividendsPayableAmountPerShare | $ 0.80 us-gaap_DividendsPayableAmountPerShare
Purchase of treasury shares (in shares) | 3,288 us-gaap_StockRepurchasedDuringPeriodShares | 584,925 us-gaap_StockRepurchasedDuringPeriodShares | 769,568 us-gaap_StockRepurchasedDuringPeriodShares
Net issuance of shares for acquisition (in shares) | 0 us-gaap_StockIssuedDuringPeriodSharesAcquisitions | 10,346,363 us-gaap_StockIssuedDuringPeriodSharesAcquisitions | 1,269,592 us-gaap_StockIssuedDuringPeriodSharesAcquisitions
Treasury stock reissued in acquisition of Alliance (in shares) | 0 us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued | 408,957 us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued | 0 us-gaap_StockIssuedDuringPeriodSharesTreasuryStockReissued
Net issuance of shares to employee stock plans, including tax benefit (in shares) | 386,692 nbtb_StockIssuedDuringPeriodSharesEmployeeBenefitPlansAndOtherStockPlans | 385,219 nbtb_StockIssuedDuringPeriodSharesEmployeeBenefitPlansAndOtherStockPlans | 118,616 nbtb_StockIssuedDuringPeriodSharesEmployeeBenefitPlansAndOtherStockPlans

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- Definition Number of shares issued during the period to an employee benefit plans and other stock plans. + References No definition available. + Details
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- Definition The per share amount of a dividend declared, but not paid, as of the financial reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 + Details
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- Definition Number of shares of stock issued during the period pursuant to acquisitions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.28,29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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- Definition Number of treasury shares (units) reissued during the period, excluding reissuance of shares (units) held in treasury used to satisfy equity-based compensation obligations exercised by the holders of such rights. Upon reissuance of shares (units) from treasury, either the common or preferred stock (unit) reissued is outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 + Details
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- Definition Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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