Regulatory Capital Requirements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Total Capital (to risk weighted assets) [Abstract]
Total capital to risk weighted assets	$ 528,674	$ 537,305
Total capital to risk weighted assets (in hundredths)	12.81%	13.70%
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	476,837	487,994
Tier I capital to risk weighted assets (in hundredths)	11.56%	12.44%
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	476,837	487,994
Tier I capital to average assets (in hundredths)	8.74%	9.16%
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	506,246	510,196
Total capital to risk weighted assets (in hundredths)	12.28%	13.03%
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	454,476	460,969
Tier I capital to risk weighted assets (in hundredths)	11.03%	11.77%
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	$ 454,476	$ 460,969
Tier I capital to average assets (in hundredths)	8.35%	8.67%
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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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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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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Tier 1 capital divided by risk weighted assets as defined by regulations.

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