Minimum Regulatory Capital Requirement (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
NBI Consolidated [Member]
Actual amount [Abstract]
Total capital (to risk weighted assets)	$ 151,824	$ 140,228
Tier 1 capital (to risk weighted assets)	143,472	132,160
Tier 1 capital (to average assets)	143,472	132,160
Actual Ratio [Abstract]
Total capital (to risk weighted assets) (in hundredths)	22.40%	20.90%
Tier 1 capital (to risk weighted assets) (in hundredths)	21.20%	19.70%
Tier 1 capital (to average assets) (in hundredths)	13.30%	12.70%
Minimum capital requirement amount [Abstract]
Total capital (to risk weighted assets)	54,225	53,615
Tier 1 capital (to risk weighted assets)	27,113	26,807
Tier 1 capital (to average assets)	43,010	41,598
Minimum capital requirement ratio [Abstract]
Total capital (to risk weighted assets) (in hundredths)	8.00%	8.00%
Tier 1 capital (to risk weighted assets) (in hundredths)	4.00%	4.00%
Tier 1 capital (to average assets) (in hundredths)	4.00%	4.00%
NBB [Member]
Actual amount [Abstract]
Total capital (to risk weighted assets)	148,684	136,932
Tier 1 capital (to risk weighted assets)	140,335	128,864
Tier 1 capital (to average assets)	140,335	128,864
Actual Ratio [Abstract]
Total capital (to risk weighted assets) (in hundredths)	22.00%	20.50%
Tier 1 capital (to risk weighted assets) (in hundredths)	20.80%	19.30%
Tier 1 capital (to average assets) (in hundredths)	13.10%	12.50%
Minimum capital requirement amount [Abstract]
Total capital (to risk weighted assets)	53,984	53,348
Tier 1 capital (to risk weighted assets)	26,992	26,674
Tier 1 capital (to average assets)	42,973	41,293
Minimum capital requirement ratio [Abstract]
Total capital (to risk weighted assets) (in hundredths)	8.00%	8.00%
Tier 1 capital (to risk weighted assets) (in hundredths)	4.00%	4.00%
Tier 1 capital (to average assets) (in hundredths)	4.00%	4.00%
Minimum to be well capitalized under prompt corrective action provisions, amount [Abstract
Total capital (to risk weighted assets)	67,481	66,684
Tier 1 capital (to risk weighted assets)	40,488	40,011
Tier 1 capital (to average assets)	$ 53,716	$ 51,617
Minimum to be well capitalized under prompt corrective action provisions, ratio [Abstract]
Total capital (to risk weighted assets) (in hundredths)	10.00%	10.00%
Tier 1 capital (to risk weighted assets) (in hundredths)	6.00%	6.00%
Tier 1 capital (to average assets) (in hundredths)	5.00%	5.00%

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The amount of total capital as defined in the regulations.

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The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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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 amount of Total Capital required to be categorized as well as capitalized 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 required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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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 under the regulatory framework for prompt corrective action.

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Tier 1 Risk Based Capital as defined in the regulations.

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The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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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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