| **Impairment of Investment Securities - Pooled Trust Preferred Collateralized Debt Obligations (Detail) (USD $)In Thousands, unless otherwise specified** |           |           | 6 Months Ended |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------|-----------|-----------|----------------|
||
| **Impairment Of Investment Securities [Line Items]**                                                                                                      |      |      |           |   |   |   |   |   |   |   |   |   |   |
| Book Value                                                                                                                                                |      |      | $ 41,851       | $ 1,830 | $ 59 | $ 2,691 | $ 1,941 | $ 2,322 | $ 1,438 | $ 5,446 | $ 12,343 | $ 13,344 | $ 437 |
| Securities available for sale, at fair value                                                                                                              | 1,347,611 | 1,318,365 | 28,154         | 1,294 | 109 | 2,626 | 1,281 | 1,380 | 1,497 | 3,289 | 8,103 | 8,196 | 379 |
| Unrealized Gain (Loss)                                                                                                                                    |      |      | $ (13,697)     | $ (536) | $ 50 | $ (65) | $ (660) | $ (942) | $ 59 | $ (2,157) | $ (4,240) | $ (5,148) | $ (58) |
| Debt Instrument, Credit Rating                                                                                                                            |      |      |           | B1/BB | C/- | Ca/- | C/C | Caa1/C | Caa3/C | Caa3/C | Caa3/C | Ca/C | Ca/C |
| Number of Banks (in banks)                                                                                                                                |      |      |           | 6 | 3 | 14 | 30 | 41 | 46 | 66 | 59 | 57 | 11 |
| Deferrals and Defaults as a % of Current Collateral                                                                                                       |      |      |           | 18.05% | 100.00% | 52.23% | 54.77% | 28.47% | 33.74% | 25.87% | 20.68% | 26.73% | 59.24% |
| Excess Subordination as a % of Current Performing Collateral                                                                                              |      |      |           | 55.11% | 0.00% | 0.00% | 0.00% | 10.41% | 0.00% | 0.00% | 12.85% | 38.29% | 34.51% |

| X                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Available for sale securities book value.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Deferrals and defaults as a percentage of current collateral.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Excess subordination as a percentage of current performing collateral.
+ References
No definition available.
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| X                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Pooled trust preferred collateralized debt obligations in number of banks.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unrealized gain (loss) on investments in debt and equity securities classified as available-for-sale securities.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Description of the credit rating indicative of likelihood of repayment of the debt instrument given by a credit rating agency (for example, Standard and Poor's, Moody's, Fitch).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5
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