Regulatory Capital Requirements (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Total Capital (to risk weighted assets) [Abstract]
Total capital to risk weighted assets	$ 839,152	$ 809,685
Total capital to risk weighted assets ratio	12.39%	12.74%
Minimum capital required for capital adequacy to risk weighted assets	8.00%	8.00%
Capital required for classification as well capitalized to risk weighted assets	10.00%	10.00%
Tier I Capital (to risk weighted assets) [Abstract]
Tier I capital to risk weighted assets	$ 773,111	$ 745,341
Tier I capital to risk weighted assets ratio	11.42%	11.73%
Minimum Tier I capital required for capital adequacy to risk weighted assets	4.00%	4.00%
Tier I capital required for classification as well capitalized to risk weighted assets	6.00%	6.00%
Tier I Capital (to average assets) [Abstract]
Tier I capital to average assets	$ 773,111	$ 745,341
Tier I capital to average assets ratio	9.11%	9.44%
Minimum Tier I leverage capital required for capital adequacy to average assets	4.00%	4.00%
Tier I leverage capital required for classification as well capitalized to average assets	5.00%	5.00%
Common Equity Tier I Capital [Abstract]
Common equity Tier I capital	$ 676,111	$ 648,341
Common equity Tier I capital ratio	9.98%	10.20%
Minimum Tier I capital required for capital adequacy	4.50%	4.50%
Tier I capital required for classification as well capitalized	6.50%	6.50%
NBT Bank [Member]
Total Capital (to risk weighted assets) [Abstract]
Total capital to risk weighted assets	$ 790,034	$ 724,238
Total capital to risk weighted assets ratio	11.75%	11.47%
Minimum capital required for capital adequacy to risk weighted assets	8.00%	8.00%
Capital required for classification as well capitalized to risk weighted assets	10.00%	10.00%
Tier I Capital (to risk weighted assets) [Abstract]
Tier I capital to risk weighted assets	$ 723,992	$ 659,894
Tier I capital to risk weighted assets ratio	10.76%	10.45%
Minimum Tier I capital required for capital adequacy to risk weighted assets	4.00%	4.00%
Tier I capital required for classification as well capitalized to risk weighted assets	6.00%	6.00%
Tier I Capital (to average assets) [Abstract]
Tier I capital to average assets	$ 723,992	$ 659,894
Tier I capital to average assets ratio	8.59%	8.41%
Minimum Tier I leverage capital required for capital adequacy to average assets	4.00%	4.00%
Tier I leverage capital required for classification as well capitalized to average assets	5.00%	5.00%
Common Equity Tier I Capital [Abstract]
Common equity Tier I capital	$ 723,992	$ 659,894
Common equity Tier I capital ratio	10.76%	10.45%
Minimum Tier I capital required for capital adequacy	4.50%	4.50%
Tier I capital required for classification as well capitalized	6.50%	6.50%

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The Common Equity Tier 1 Risk-weighted Capital ratio (Common Equity Tier 1 Capital divided by Risk-weighted Assets) as defined in the regulations.

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Common Equity Tier 1 Risk-based capital as defined in the regulations.

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The minimum Common Equity Tier 1 Capital ratio (Common Equity Tier 1 Capital divided by Risk-based Assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The Common Equity Tier 1 Capital ratio (Common Equity Tier 1 Capital divided by Risk-based Assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

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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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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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