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Securities, Temporarily impaired securities (Details) (USD $) In Thousands, unless otherwise specified | 9 Months Ended |
--- | --- | ---
Sep. 30, 2012 | Dec. 31, 2011
Temporarily Impaired Securities [Abstract] |  |
Less Than 12 Months, Fair Value | $ 52,096 | $ 14,673
Less Than 12 Months, Unrealized Loss | 877 | 136
12 Months or More, Fair Value | 2,648 | 1,123
12 Months or More, Unrealized Loss | 195 | 188
Number of temporarily impaired securities | 62 |
Fair Value of temporarily impaired securities | 54,744 |
Unrealized loss on securities | 1,072 |
Number of securities that were temporarily impaired in a continuous loss position for twelve months or more | 5 |
Securities In Unrealized Loss Positions 12 Months Or Longer Fair Value | 2,648 |
Securities In Unrealized Loss Positions 12 Months Or Longer Unrealized Loss | 196 |
U.S. Government agencies and corporations [Member] |  |
Temporarily Impaired Securities [Abstract] |  |
Less Than 12 Months, Fair Value | 41,282 | 6,230
Less Than 12 Months, Unrealized Loss | 709 | 20
12 Months or More, Fair Value | 0 | 0
12 Months or More, Unrealized Loss | 0 | 0
States and political subdivisions [Member] |  |
Temporarily Impaired Securities [Abstract] |  |
Less Than 12 Months, Fair Value | 10,814 | 3,527
Less Than 12 Months, Unrealized Loss | 168 | 19
12 Months or More, Fair Value | 536 | 981
12 Months or More, Unrealized Loss | 3 | 26
Corporate debt securities [Member] |  |
Temporarily Impaired Securities [Abstract] |  |
Less Than 12 Months, Fair Value | 0 | 4,916
Less Than 12 Months, Unrealized Loss | 0 | 97
12 Months or More, Fair Value | 1,979 | 0
12 Months or More, Unrealized Loss | 21 | 0
Other [Member] |  |
Temporarily Impaired Securities [Abstract] |  |
Less Than 12 Months, Fair Value | 0 | 0
Less Than 12 Months, Unrealized Loss | 0 | 0
12 Months or More, Fair Value | 133 | 142
12 Months or More, Unrealized Loss | $ 171 | $ 162

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized as held-to-maturity and available for sale securities that have been in a continuous unrealized loss position. + References No definition available. + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities that have been in a continuous unrealized loss position for more than twelve months. + References No definition available. + Details
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X
- Definition This item contains disclosure of the number of investment positions for twelve months or longer in the available-for-sale and held-to-maturity investments determined to be temporarily impaired. + References No definition available. + Details
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- Definition Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for more than twelve months for securities. + References No definition available. + Details
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- Definition Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for securities. + References No definition available. + Details
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- Definition Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for securities. + References No definition available. + Details
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Namespace Prefix: | nksh_
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- Definition This item represents the aggregate fair value of investments in debt and equity securities that have been in a continuous unrealized loss position for less than twelve months. + References No definition available. + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities that have been in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
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- Definition This item contains disclosure of the number of investment positions determined to be temporarily impaired. + References No definition available. + Details
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- Definition The increase (decrease), resulting in a loss, in the difference between the fair value and the carrying value, or in the comparative fair values, of securities held at each balance sheet date, that was included in earnings for the period. + References No definition available. + Details
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