| **Impairment of Investment Securities - Schedule of Unrealized Losses and Estimated Fair Values (Detail) (USD $)**          | 9 Months Ended        |               |               |
|-----------------------------------------------------------------------------------------------------------------------------|-----------------------|---------------|---------------|
||
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                                    |                  |          |          |
| Estimated Fair Value, Less Than 12 Months                                                                                   |                  | $ 765,433,000 | $ 135,599,000 |
| Grous Unrealized Losses Less Than 12 Months                                                                                 |                  | (24,191,000)  | (464,000)     |
| Estimated Fair Value, 12 Months or More                                                                                     |                  | 22,603,000    | 23,350,000    |
| Gross Unrealized Losses 12 Months or More                                                                                   |                  | (23,440,000)  | 28,496,000    |
| Total Estimated Fair Value                                                                                                  |                  | 788,036,000   | 158,949,000   |
| Total Gross Unrealized Losses                                                                                               |                  | (47,631,000)  | 28,960,000    |
| Gross Unrealized Losses Related To Available For Sale Securities                                                            | Less than $1 thousand |          |          |
| US Government Agencies Residential Mortgage-backed Securities [Member]                                                      |                  |          |          |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                                    |                  |          |          |
| Estimated Fair Value, Less Than 12 Months                                                                                   |                  | 2,092,000     | 0             |
| Grous Unrealized Losses Less Than 12 Months                                                                                 |                  | (16,000)      | 0             |
| Estimated Fair Value, 12 Months or More                                                                                     |                  | 0             | 13,000        |
| Gross Unrealized Losses 12 Months or More                                                                                   |                  | 0             | 0             |
| Total Estimated Fair Value                                                                                                  |                  | 2,092,000     | 13,000        |
| Total Gross Unrealized Losses                                                                                               |                  | (16,000)      | 0             |
| Obligations of U.S. Government-Sponsored Enterprises - Mortgage-Backed Securities - Residential [Member]                    |                  |          |          |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                                    |                  |          |          |
| Estimated Fair Value, Less Than 12 Months                                                                                   |                  | 580,232,000   | 76,296,000    |
| Grous Unrealized Losses Less Than 12 Months                                                                                 |                  | (22,258,000)  | (392,000)     |
| Estimated Fair Value, 12 Months or More                                                                                     |                  | 0             | 21,000        |
| Gross Unrealized Losses 12 Months or More                                                                                   |                  | 0             | 0             |
| Total Estimated Fair Value                                                                                                  |                  | 580,232,000   | 76,317,000    |
| Total Gross Unrealized Losses                                                                                               |                  | (22,258,000)  | (392,000)     |
| Obligations of U.S. Government-Sponsored Enterprises - Other Government-Sponsored Enterprises [Member]                      |                  |          |          |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                                    |                  |          |          |
| Estimated Fair Value, Less Than 12 Months                                                                                   |                  | 183,075,000   | 59,303,000    |
| Grous Unrealized Losses Less Than 12 Months                                                                                 |                  | (1,894,000)   | (72,000)      |
| Estimated Fair Value, 12 Months or More                                                                                     |                  | 0             | 0             |
| Gross Unrealized Losses 12 Months or More                                                                                   |                  | 0             | 0             |
| Total Estimated Fair Value                                                                                                  |                  | 183,075,000   | 59,303,000    |
| Total Gross Unrealized Losses                                                                                               |                  | (1,894,000)   | (72,000)      |
| Pooled Trust Preferred Collateralized Debt Obligations [Member]                                                             |                  |          |          |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                                    |                  |          |          |
| Estimated Fair Value, Less Than 12 Months                                                                                   |                  | 34,000        | 0             |
| Grous Unrealized Losses Less Than 12 Months                                                                                 |                  | (23,000)      | 0             |
| Estimated Fair Value, 12 Months or More                                                                                     |                  | 22,603,000    | 23,316,000    |
| Gross Unrealized Losses 12 Months or More                                                                                   |                  | (23,440,000)  | (28,496,000)  |
| Total Estimated Fair Value                                                                                                  |                  | 22,637,000    | 23,316,000    |
| Total Gross Unrealized Losses                                                                                               |                  | (23,463,000)  | (28,496,000)  |
| Debt Securities [Member]                                                                                                    |                  |          |          |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                                    |                  |          |          |
| Estimated Fair Value, Less Than 12 Months                                                                                   |                  | 765,433,000   |          |
| Grous Unrealized Losses Less Than 12 Months                                                                                 |                  | (24,191,000)  |          |
| Estimated Fair Value, 12 Months or More                                                                                     |                  | 22,603,000    |          |
| Gross Unrealized Losses 12 Months or More                                                                                   |                  | (23,440,000)  |          |
| Total Estimated Fair Value                                                                                                  |                  | 788,036,000   |          |
| Total Gross Unrealized Losses                                                                                               |                  | (47,631,000)  |          |
| Equity Securities [Member]                                                                                                  |                  |          |          |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                                    |                  |          |          |
| Estimated Fair Value, Less Than 12 Months                                                                                   |                  | 0             |          |
| Grous Unrealized Losses Less Than 12 Months                                                                                 |                  | 0             |          |
| Estimated Fair Value, 12 Months or More                                                                                     |                  | 0             |          |
| Gross Unrealized Losses 12 Months or More                                                                                   |                  | 0             |          |
| Total Estimated Fair Value                                                                                                  | 0                     | 0             |          |
| Total Gross Unrealized Losses                                                                                               |                  | 0             |          |
| Maximum [Member] | Obligations of U.S. Government-Sponsored Enterprises - Mortgage-Backed Securities - Residential [Member] |                  |          |          |
| **Schedule of Trading Securities and Other Trading Assets [Line Items]**                                                    |                  |          |          |
| Available-for-sale Securities, Gross Unrealized Gain (Loss)                                                                 | $ 1,000               |          |          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Available-for-sale securities continuous unrealized income (loss) position less than twelve months aggregate gain (losses).
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Gross unrealized losses related to available for sale securities.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for securities which are categorized neither as held-to-maturity nor trading securities.
+ References
No definition available.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of the excess of amortized cost basis over fair value of securities in a loss position and categorized neither as held-to-maturity nor trading securities.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for securities categorized neither as held-to-maturity nor trading securities.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27337-111563Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 17 -Subparagraph a(1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 03-1 -Paragraph 21 -Subparagraph a(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The net amount of gross unrealized gains (losses) for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.
+ References
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| X                                                                                                                                                                                             |
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