| **Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $)In Thousands, except Per Share data, unless otherwise specified** | Mar. 31, 2015                                      | Dec. 31, 2014                                      | Mar. 31, 2014                                      |
|------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------|----------------------------------------------------|----------------------------------------------------|
| **Assets**                                                                                                                         |                                               |                                               |                                               |
| Securities to be held to maturity                                                                                                  | $ 267,247us-gaap_HeldToMaturitySecuritiesFairValue | $ 279,704us-gaap_HeldToMaturitySecuritiesFairValue | $ 176,562us-gaap_HeldToMaturitySecuritiesFairValue |
| **Shareholders' equity**                                                                                                           |                                               |                                               |                                               |
| Common stock, par value per share (usd per share)                                                                                  | $ 0.01us-gaap_CommonStockParOrStatedValuePerShare  | $ 0.01us-gaap_CommonStockParOrStatedValuePerShare  | $ 0.01us-gaap_CommonStockParOrStatedValuePerShare  |

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Fair value of investments in debt securities classified as held-to-maturity.
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