| **Consolidated Balance Sheets (Parenthetical) (Unaudited) (USD $)In Thousands, except Share data, unless otherwise specified** | Mar. 31, 2013 | Dec. 31, 2012 |
|--------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| Amortized cost of available-for-sale securities                                                                                | $ 493,631     | $ 558,818     | [1] |
| Fair value of held-to-maturity securities                                                                                      | $ 73,245      |          |  |
| Common stock, no par value                                                                                                     |     |     | [1] |
| Common stock, shares authorized                                                                                                | 2,500,000,000 | 2,500,000,000 | [1] |
| Common stock, shares issued                                                                                                    | 21,698,115    | 21,698,115    | [1] |
| Preferred stock Series A [Member]                                                                                              |          |          |  |
| Preferred stock, par value                                                                                                     | $ 10.00       | $ 10.00       | [1] |
| Preferred stock, shares authorized                                                                                             | 200,000       | 200,000       | [1] |
| Preferred stock, shares issued                                                                                                 | 0             | 0             | [1] |
| Preferred stock, shares outstanding                                                                                            | 0             | 0             | [1] |
| Preferred stock [Member]                                                                                                       |          |          |  |
| Preferred stock, par value                                                                                                     | $ 1.00        | $ 1.00        | [1] |
| Preferred stock, shares authorized                                                                                             | 15,000,000    | 15,000,000    | [1] |
| Preferred stock, shares issued                                                                                                 | 0             | 0             | [1] |
| Preferred stock, shares outstanding                                                                                            | 0             | 0             | [1] |
|                                                                                                                                |
| [1]Derived from audited consolidated financial statements                                                                      |

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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.
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| - Definition
Issuance value per share of no-par value common stock; generally not indicative of the fair market value per share.
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| - Definition
The maximum number of common shares permitted to be issued by an entity's charter and bylaws.
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| - Definition
Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Face amount or stated value per share of nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer); generally not indicative of the fair market value per share.
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| - Definition
The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.
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| - Definition
Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.
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