Regulatory Capital Requirements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Total Capital (to risk weighted assets) [Abstract]
Total capital to risk weighted assets	$ 777,651us-gaap_Capital	$ 723,580us-gaap_Capital
Total capital to risk weighted assets (in hundredths)	13.50%us-gaap_CapitalToRiskWeightedAssets	12.99%us-gaap_CapitalToRiskWeightedAssets
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	709,965us-gaap_TierOneRiskBasedCapital	653,950us-gaap_TierOneRiskBasedCapital
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	709,965us-gaap_TierOneLeverageCapital	653,950us-gaap_TierOneLeverageCapital
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%

The amount of total capital as defined in the regulations.

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-Name Accounting Standards Codification

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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The minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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