| **Investment Securities - Amortized Cost and Approximate Fair Value of Securities (Details) (USD $)In Thousands, unless otherwise specified** | Mar. 31, 2014 | Dec. 31, 2013 |
|-----------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | $ 597,967     | $ 537,848     |
| Gross Unrealized Gains                                                                                                                        | 11,694        | 7,896         |
| Gross Unrealized Losses                                                                                                                       | 4,154         | 9,543         |
| Fair Value                                                                                                                                    | 605,507       | 536,201       |
| Amortized Cost                                                                                                                                | 544,470       | 559,378       |
| Gross Unrealized Gains                                                                                                                        | 8,821         | 5,282         |
| Gross Unrealized Losses                                                                                                                       | 1,670         | 3,813         |
| Fair Value                                                                                                                                    | 551,621       | 560,847       |
| Amortized Cost                                                                                                                                | 1,142,437     | 1,097,226     |
| Gross Unrealized Gains                                                                                                                        | 20,515        | 13,178        |
| Gross Unrealized Losses                                                                                                                       | 5,824         | 13,356        |
| Fair Value                                                                                                                                    | 1,157,128     | 1,097,048     |
| U.S. Treasury                                                                                                                                 |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 15,918        | 15,914        |
| Gross Unrealized Gains                                                                                                                        | 79            | 80            |
| Gross Unrealized Losses                                                                                                                       | 14            | 21            |
| Fair Value                                                                                                                                    | 15,983        | 15,973        |
| U.S. Government-sponsored agency securities                                                                                                   |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 3,355         | 3,550         |
| Gross Unrealized Gains                                                                                                                        | 27            | 12            |
| Gross Unrealized Losses                                                                                                                       |          | 17            |
| Fair Value                                                                                                                                    | 3,382         | 3,545         |
| State and municipal                                                                                                                           |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 244,298       | 231,005       |
| Gross Unrealized Gains                                                                                                                        | 6,291         | 3,878         |
| Gross Unrealized Losses                                                                                                                       | 1,451         | 3,896         |
| Fair Value                                                                                                                                    | 249,138       | 230,987       |
| Amortized Cost                                                                                                                                | 144,787       | 145,941       |
| Gross Unrealized Gains                                                                                                                        | 1,977         | 62            |
| Gross Unrealized Losses                                                                                                                       | 28            | 91            |
| Fair Value                                                                                                                                    | 146,736       | 145,912       |
| U.S. Government-sponsored mortgage-backed securities                                                                                          |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 326,329       | 279,299       |
| Gross Unrealized Gains                                                                                                                        | 4,869         | 3,926         |
| Gross Unrealized Losses                                                                                                                       | 661           | 1,973         |
| Fair Value                                                                                                                                    | 330,537       | 281,252       |
| Amortized Cost                                                                                                                                | 399,683       | 413,437       |
| Gross Unrealized Gains                                                                                                                        | 6,844         | 5,220         |
| Gross Unrealized Losses                                                                                                                       | 1,642         | 3,722         |
| Fair Value                                                                                                                                    | 404,885       | 414,935       |
| Corporate obligations                                                                                                                         |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 6,361         | 6,374         |
| Gross Unrealized Gains                                                                                                                        | 428           |          |
| Gross Unrealized Losses                                                                                                                       | 2,028         | 3,636         |
| Fair Value                                                                                                                                    | 4,761         | 2,738         |
| Equity securities                                                                                                                             |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 1,706         | 1,706         |
| Fair Value                                                                                                                                    | $ 1,706       | $ 1,706       |

| X                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accumulated pre-tax unrealized gain before deducting pre-tax unrealized loss on investments in available-for-sale debt securities impacting investments.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                         |
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| - Definition
Amount of accumulated pre-tax unrealized loss before deducting pre-tax unrealized gain on investments in available-for-sale securities impacting investments.
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No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the excess of amortized cost basis over fair value of securities in a gain position and which are categorized as held-to-maturity.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the excess of amortized cost basis over fair value of securities in a loss position and which are categorized as held-to-maturity.
+ References
No definition available.
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| X                                                                                                                                                                                                                                       |
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Securities, Amortized Cost
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| X                                                                                                                                                                                                                               |
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Securities, Fair Value
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| X                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Securities Gross Unrealized Gains
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| X                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Securities Gross Unrealized Losses
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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
Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value of investments in debt securities classified as held-to-maturity.
+ References
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