| **Impairment of Investment Securities - Additional Information (Detail) (USD $)**                                      | 12 Months Ended |
|------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Non-credit related gains (losses) on securities                                                                        | $ 9,800,000     |  | $ 2,200,000 |  | $ (400,000) |  |
| Corporate/Mortgage-Backed Securities, Amortized cost                                                                   | 1,350,466,000   |  | 1,169,613,000 |  |   |  |
| Fair Value                                                                                                             | 1,318,365,000   |  | 1,171,303,000 |  |   |  |
| Number of banks and other financial institutions comprising the security                                               | 288             |  |   |  |   |  |
| Number Of Pooled Securities with No Senior Class                                                                       | 4               |  |   |  |   |  |
| Number of Securities with No Excess Subordination                                                                      | 5               |  |   |  |   |  |
| Number of Securities with Excess Subordination                                                                         | 5               |  |   |  |   |  |
| Collateral issued by financial institutions                                                                            | 15,000,000,000  |  |   |  |   |  |
| Fair Value Input Coupon Rates                                                                                          | 10.00%          |  |   |  |   |  |
| Coupon interest rate                                                                                                   | 7.00%           |  |   |  |   |  |
| Estimate of future cash flows prepayment percentage in year three                                                      | 40.00%          |  |   |  |   |  |
| Estimate of future cash flows prepayment percentage thereafter                                                         | 2.00%           |  |   |  |   |  |
| Prepayment rate                                                                                                        | 5.00%           |  |   |  |   |  |
| Probability percentage assigned to default bank subject to market indicators                                           | 10.00%          |  |   |  |   |  |
| Probability of default                                                                                                 | 100.00%         |  |   |  |   |  |
| Probability percentage assigned to default bank                                                                        | 100.00%         |  |   |  |   |  |
| Projected recovery rate                                                                                                | 0.00%           |  |   |  |   |  |
| Net securities (losses) gains                                                                                          | (1,158,000)     |  | 192,000 |  | 2,185,000 |  |
| Other investments                                                                                                      | 35,444,000      |  | 28,228,000 |  |   |  |
| Percentage of Excess Stock to be Purchased                                                                             | 100.00%         |  |   |  |   |  |
| Maximum percentage of stock to be purchased                                                                            | 5.00%           |  |   |  |   |  |
| Proceeds from the redemption of FHLB stock                                                                             | 10,904,000      |  | 11,568,000 |  | 9,063,000 |  |
| Available for sale securities book value                                                                               | 42,040,000      |  |   |  |   |  |
| Excess recognized as an adjustment to yield                                                                            | (2,375,000)     | [1] | (1,462,000) | [1] | (114,000) | [1] |
| Other than-temporary impairment charge                                                                                 | 13,356,000      |  | 0 |  | 0 |  |
| Minimum [Member]                                                                                                       |            |  |   |  |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Subordinated tranches range                                                                                            | 7.00%           |  |   |  |   |  |
| Total principal amount of the respective securities                                                                    | 5.00%           |  |   |  |   |  |
| Excess subordination as a percentage of current performing collateral                                                  | 3.00%           |  |   |  |   |  |
| Collateral issued by financial institutions                                                                            | 15,000,000,000  |  |   |  |   |  |
| Probabilities for performing collateral range                                                                          | 0.33%           |  |   |  |   |  |
| Excess percent value of future cash flows over current book value                                                      | 22.00%          |  |   |  |   |  |
| Maximum [Member]                                                                                                       |            |  |   |  |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Subordinated tranches range                                                                                            | 35.00%          |  |   |  |   |  |
| Excess subordination as a percentage of current performing collateral                                                  | 59.00%          |  |   |  |   |  |
| Collateral issued by financial institutions                                                                            | 2,000,000,000   |  |   |  |   |  |
| Probabilities for performing collateral range                                                                          | 75.00%          |  |   |  |   |  |
| Excess percent value of future cash flows over current book value                                                      | 163.00%         |  |   |  |   |  |
| Over fifteen billion [Member]                                                                                          |            |  |   |  |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Prepayment rate                                                                                                        | 100.00%         |  |   |  |   |  |
| Corporate Securities [Member]                                                                                          |            |  |   |  |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Corporate/Mortgage-Backed Securities, Amortized cost                                                                   | 6,693,000       |  | 6,703,000 |  |   |  |
| Fair Value                                                                                                             | 7,021,000       |  | 6,991,000 |  |   |  |
| Obligations of U.S. Government-Sponsored Enterprises [Member]                                                          |            |  |   |  |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Total unrealized losses                                                                                                | 61.00%          |  |   |  |   |  |
| Pooled Trust Preferred Collateralized Debt Obligations [Member]                                                        |            |  |   |  |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Total unrealized losses                                                                                                | 39.00%          |  |   |  |   |  |
| Corporate/Mortgage-Backed Securities, Amortized cost                                                                   | 42,040,000      |  | 51,866,000 |  |   |  |
| Fair Value                                                                                                             | 23,523,000      |  | 23,373,000 |  |   |  |
| Mm Comm Ix [Member]                                                                                                    |            |  |   |  |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Other than-temporary impairment charge                                                                                 | 13,400,000      |  |   |  |   |  |
| Corporate Securities [Member]                                                                                          |            |  |   |  |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Corporate/Mortgage-Backed Securities, Amortized cost                                                                   | 6,600,000       |  |   |  |   |  |
| Net securities (losses) gains                                                                                          | $ 1,300,000     |  |   |  |   |  |
| Trust preferred collateralized debt obligations [Member]                                                               |            |  |   |  |   |  |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                               |            |  |   |  |   |  |
| Percentage of Current Performing Collateral                                                                            | 0.00%           |  |   |  |   |  |
|                                                                                                                        |
| [1]Represents the increase in cash flows recognized either as principal payments or interest income during the period. |

| X                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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Asset Size Of Financial Institution
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| - Definition
Available for sale securities book value.
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| - Definition
Coupon Interest Rate
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| X                                                                                                                                                                                                                                                                                             |
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| - Definition
Estimate Of Future Cash Flows Percentage In Year One and Two
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| - Definition
Estimate Of Future Cash Flows Prepayment Percentage After Year Two
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| X                                                                                                                                                                                                                                                                                                               |
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| - Definition
Excess present value of future cash flows over our current book value.
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| X                                                                                                                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Excess subordination as a percentage of current performing collateral.
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| X                                                                                                                                                                                                                                     |
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| - Definition
Fair Value Input Coupon Rates
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| X                                                                                                                                                                                                                                                                |
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| - Definition
Maximum percentage of stock to be purchased.
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| - Definition
Non-credit related gains (losses) on securities
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| X                                                                                                                                                                                                                                                                                                                     |
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| - Definition
Number of banks and other financial institutions comprising the security.
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| X                                                                                                                                                                                                                                                                          |
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| - Definition
Number Of Pooled Securities with No Senior Class
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| - Definition
Number of Securities with Excess Subordination
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Number of Securities with No Excess Subordination
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| - Definition
Current performing collateral related to the security.
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| X                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of Excess Stock to be Purchased
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of principal amount in pooled security securities.
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| - Definition
Percentage Of Total Unrealized Losses
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| - Definition
Probabilities for performing collateral range.
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| - Definition
Probability of default.
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| X                                                                                                                                                                                                                                                                         |
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| - Definition
Probability percentage assigned to default bank.
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| - Definition
Probability percentage assigned to default bank subject to market indicators.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Projected recovery rate.
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| X                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Subordinated tranches range.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The net gain (loss) realized from the sale, exchange, redemption, or retirement of securities, not separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held due to increases in cash flows expected to be collected and recognized over the remaining life of the security.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security because of the sale of impaired securities during the period.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The cash inflow associated with the sale of the Federal Reserve Stock (equity interest in Federal Reserve Bank) during the period.
+ References
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