| **Investment Securities - Amortized Cost and Approximate Fair Values of Securities (Detail) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2013 | Dec. 31, 2012 |
|-----------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | $ 537,848     | $ 498,104     |
| Gross Unrealized Gains                                                                                                                        | 7,896         | 21,184        |
| Gross Unrealized Losses                                                                                                                       | 9,543         | 5,945         |
| Fair Value                                                                                                                                    | 536,201       | 513,343       |
| Amortized Cost                                                                                                                                | 559,378       | 361,020       |
| Gross Unrealized Gains                                                                                                                        | 5,282         | 17,170        |
| Gross Unrealized Losses                                                                                                                       | 3,813         | 16            |
| Fair Value                                                                                                                                    | 560,847       | 378,174       |
| Amortized Cost                                                                                                                                | 1,097,226     | 859,124       |
| Gross Unrealized Gains                                                                                                                        | 13,178        | 38,354        |
| Gross Unrealized Losses                                                                                                                       | 13,356        | 5,961         |
| Fair Value                                                                                                                                    | 1,097,048     | 891,517       |
| U.S. Treasury                                                                                                                                 |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 15,914        |          |
| Gross Unrealized Gains                                                                                                                        | 80            |          |
| Gross Unrealized Losses                                                                                                                       | 21            |          |
| Fair Value                                                                                                                                    | 15,973        |          |
| Government Agency and Municipal Bonds and Notes                                                                                               |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 3,550         | 4,475         |
| Gross Unrealized Gains                                                                                                                        | 12            | 165           |
| Gross Unrealized Losses                                                                                                                       | 17            |          |
| Fair Value                                                                                                                                    | 3,545         | 4,640         |
| State and municipal                                                                                                                           |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 231,005       | 148,187       |
| Gross Unrealized Gains                                                                                                                        | 3,878         | 10,025        |
| Gross Unrealized Losses                                                                                                                       | 3,896         | 18            |
| Fair Value                                                                                                                                    | 230,987       | 158,194       |
| Amortized Cost                                                                                                                                | 145,941       | 117,227       |
| Gross Unrealized Gains                                                                                                                        | 62            | 5,489         |
| Gross Unrealized Losses                                                                                                                       | 91            | 1             |
| Fair Value                                                                                                                                    | 145,912       | 122,715       |
| U.S. Government-sponsored mortgage-backed securities                                                                                          |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 279,299       | 337,631       |
| Gross Unrealized Gains                                                                                                                        | 3,926         | 10,994        |
| Gross Unrealized Losses                                                                                                                       | 1,973         | 46            |
| Fair Value                                                                                                                                    | 281,252       | 348,579       |
| Amortized Cost                                                                                                                                | 413,437       | 243,793       |
| Gross Unrealized Gains                                                                                                                        | 5,220         | 11,681        |
| Gross Unrealized Losses                                                                                                                       | 3,722         | 15            |
| Fair Value                                                                                                                                    | 414,935       | 255,459       |
| Corporate obligations                                                                                                                         |          |          |
| **Gain (Loss) on Investments [Line Items]**                                                                                                   |          |          |
| Amortized Cost                                                                                                                                | 6,374         | 6,105         |
| Gross Unrealized Losses                                                                                                                       | 3,636         | 5,881         |
| Fair Value                                                                                                                                    | 2,738         | 224           |
| 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                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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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| - Definition
Securities, Amortized Cost
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| X                                                                                                                                                                                                                               |
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| - Definition
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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