| **Loans and Allowance for Credit Losses - Additional Information (Detail) (USD $)** | 3 Months Ended |           | 3 Months Ended |           | 3 Months Ended |           | 3 Months Ended |            | 3 Months Ended |
|-------------------------------------------------------------------------------------|----------------|-----------|----------------|-----------|----------------|-----------|----------------|------------|----------------|
||
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                    |           |      |           |      |           |      |           |       |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Increase (decrease) in nonperforming loans                                          |           |      |           |      |           |      |           |       |           |   | $ 3,800,000 | $ 2,700,000 | $ (29,300,000) |   |   | $ (17,200,000) | $ (2,500,000) |   |   |   |   |   |   |
| Charge-offs                                                                         | 10,476,000     | 4,992,000 |           | 5,300,000 | 2,800,000      | 2,500,000 |           |       |           |   |   |   |   |   |   |   |   |   |   | 2,800,000 |   |   |   |
| Nonaccrual loans                                                                    |           |      |           |      |           |      |           |       |           | 1,100,000 |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Decrease in specific allowance for nonperforming loans                              |           |      |           |      |           |      |           |       |           |   |   |   | 5,100,000 |   |   |   |   |   |   |   |   |   |   |
| Unfunded commitments related to nonperforming loans                                 |           |      |           |      |           |      |           |       |           |   |   |   | 1,200,000 |   |   |   |   |   |   |   |   |   |   |
| Off balance sheet reserve to nonperforming loans                                    |           |      |           |      |           |      |           |       |           |   |   |   |   |   | 200,000 |   |   |   |   |   |   |   |   |
| Loans held for sale                                                                 | 0              |      |           |      |           |      |           |       |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Total gains or losses included in earnings                                          | 126,000        | 1,307,000 |           |      |           |      |           |       |           |   |   |   |   |   |   |   |   |   |   |   |   | 126,000 | 1,768,000 |
| Nonaccrual                                                                          | 64,141,000     |      | 94,518,000     |      |           |      |           |       |           |   |   |   | 18,700,000 |   |   |   |   |   |   | 3,500,000 |   |   |   |
| Non Accrual Status Of Loans After Number Of Days Past Due                           |           |      |           |      |           |      | 150 days       |       |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Financing receivable recorded investment nonaccrual status remaining portion        |           |      |           |      |           |      |           |       |           |   |   |   |   |   |   |   |   |   | 44,100,000 |   | 17,300,000 |   |   |
| Principal payment of nonaccrual loans                                               |           |      |           |      |           |      |           |       |           |   |   |   |   |   |   |   |   | 8,000,000 |   |   |   |   |   |
| Nonaccrual loans charge off                                                         |           |      |           |      |           |      |           |       | 3,200,000      |   |   |   |   |   |   |   |   | 15,400,000 |   |   |   |   |   |
| Impaired loans under nonperforming status                                           |           |      |           |      |           |      |           | 20,800,000 |           |   |   |   |   |   |   |   |   |   |   |   | 3,500,000 |   |   |
| Troubled debt restructured loans decreased                                          |           |      |           |      |           |      |           |       |           |   |   |   | 17,300,000 |   |   |   |   |   |   |   |   |   |   |
| Commitments related to troubled debt restructured loans increased                   |           |      |           |      |           |      |           |       |           |   |   |   | (500,000) |   |   |   |   |   |   |   |   |   |   |
| Loans with modifications to rate and payment due to reamortization                  |           |      |           |      |           |      |           |       |           |   |   |   | $ 500,000 | $ 97,000 |   |   |   |   |   |   |   |   |   |

| X                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of Non Accrual Status Loan
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| X                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Decrease in specific allowance for nonperforming loans.
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| X                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing receivable recorded investment nonaccrual status remaining portion.
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| X                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Impaired loans under nonperforming status.
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| X                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Increase (decrease) in nonperforming loans.
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| X                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Increase In Commitments Related To Troubled Debt Restructured Loans
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| X                                                                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans with modifications to rate and payment due to reamortization.
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| X                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Nonaccrual loans charge off.
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| X                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Non Accrual Status Of Loans After Number Of Days Past Due
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| X                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Off balance sheet reserve to nonperforming loans.
+ References
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| X                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Principal payment of nonaccrual loans.
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| X                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Troubled debt restructured loans decreased.
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| X                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Unfunded commitments related to nonperforming loans.
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| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of gain (loss) recognized in earnings, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of direct write-downs of financing receivables charged against the allowance.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The aggregate carrying amount of loans receivable that will be sold to other entities. Includes mortgage and all other loans (collectively, loans) not classified as held for investment. Such loans are stated at the lower of cost or market, or elected fair value. Mortgage loans exclude mortgage-backed securities which are considered a debt security (other loan).
+ References
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