| **Fair Values of Assets and Liabilities - Schedule of Assets Measured on Non-Recurring Basis (Detail) - USD ($) $ in Thousands** | Sep. 30, 2015 | Dec. 31, 2014 |
|----------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                 |          |          |
| Total Assets                                                                                                                     | $ 1,125,998   | $ 1,368,052   |
| Fair Value, Measurements, Nonrecurring [Member]                                                                                  |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                 |          |          |
| Impaired loans                                                                                                                   | 36,572        | 45,790        |
| Other real estate owned                                                                                                          | 12,394        | 7,981         |
| Total Assets                                                                                                                     | 48,966        | 53,771        |
| Level 1 [Member]                                                                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                 |          |          |
| Total Assets                                                                                                                     | 0             | 0             |
| Level 1 [Member] | Fair Value, Measurements, Nonrecurring [Member]                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                 |          |          |
| Impaired loans                                                                                                                   | 0             | 0             |
| Other real estate owned                                                                                                          | 0             | 0             |
| Total Assets                                                                                                                     | 0             | 0             |
| Level 2 [Member]                                                                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                 |          |          |
| Total Assets                                                                                                                     | 1,088,299     | 1,337,633     |
| Level 2 [Member] | Fair Value, Measurements, Nonrecurring [Member]                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                 |          |          |
| Impaired loans                                                                                                                   | 26,916        | 34,864        |
| Other real estate owned                                                                                                          | 12,386        | 7,828         |
| Total Assets                                                                                                                     | 39,302        | 42,692        |
| Level 3 [Member]                                                                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                 |          |          |
| Total Assets                                                                                                                     | 37,699        | 30,419        |
| Level 3 [Member] | Fair Value, Measurements, Nonrecurring [Member]                                                               |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                 |          |          |
| Impaired loans                                                                                                                   | 9,656         | 10,926        |
| Other real estate owned                                                                                                          | 8             | 153           |
| Total Assets                                                                                                                     | $ 9,664       | $ 11,079      |

| X                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Impaired loans fair value.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Other real estate owned assets fair value.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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