| **Allowance for Credit Losses and Loan Portfolio by Loan Segment (Detail) (USD $)In Thousands, unless otherwise specified** | Mar. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2012 | Dec. 31, 2011 |
|-----------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|---------------|
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | $ 3,508       | $ 4,243       |          |          |
| Collectively evaluated for impairment                                                                                       | 64,915        | 65,123        |          |          |
| Loans acquired with deteriorated credit quality                                                                             | 114           |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 68,537        | 69,366        | 70,369        | 70,898        |
| Individually evaluated for impairment                                                                                       | 57,987        | 68,099        |          |          |
| Collectively evaluated for impairment                                                                                       | 2,810,125     | 2,821,358     |          |          |
| Loans acquired with deteriorated credit quality                                                                             | 11,430        | 12,752        |          |          |
| Loans                                                                                                                       | 2,879,542     | 2,902,209     |          |          |
| Commercial                                                                                                                  |          |          |          |          |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | 838           | 1,628         |          |          |
| Collectively evaluated for impairment                                                                                       | 24,533        | 24,285        |          |          |
| Total Allowance for Loan Losses                                                                                             | 25,371        | 25,913        | 15,574        | 17,731        |
| Individually evaluated for impairment                                                                                       | 11,057        | 14,190        |          |          |
| Collectively evaluated for impairment                                                                                       | 766,238       | 765,707       |          |          |
| Loans acquired with deteriorated credit quality                                                                             | 1,037         | 1,710         |          |          |
| Loans                                                                                                                       | 778,332       | 781,607       |          |          |
| Commercial Real Estate                                                                                                      |          |          |          |          |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | 2,373         | 2,565         |          |          |
| Collectively evaluated for impairment                                                                                       | 22,508        | 24,138        |          |          |
| Loans acquired with deteriorated credit quality                                                                             | 97            |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 24,978        | 26,703        | 37,907        | 37,919        |
| Individually evaluated for impairment                                                                                       | 39,154        | 45,394        |          |          |
| Collectively evaluated for impairment                                                                                       | 1,307,663     | 1,309,912     |          |          |
| Loans acquired with deteriorated credit quality                                                                             | 9,669         | 10,015        |          |          |
| Loans                                                                                                                       | 1,356,486     | 1,365,321     |          |          |
| Consumer                                                                                                                    |          |          |          |          |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                          |          |          |          |          |
| Collectively evaluated for impairment                                                                                       | 2,689         | 2,593         |          |          |
| Total Allowance for Loan Losses                                                                                             | 2,689         | 2,593         | 2,805         | 2,902         |
| Collectively evaluated for impairment                                                                                       | 73,314        | 75,748        |          |          |
| Loans acquired with deteriorated credit quality                                                                             |     |     |          |          |
| Loans                                                                                                                       | 73,314        | 75,748        |          |          |
| Residential                                                                                                                 |          |          |          |          |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                          |          |          |          |          |
| Individually evaluated for impairment                                                                                       | 297           | 50            |          |          |
| Collectively evaluated for impairment                                                                                       | 15,165        | 14,107        |          |          |
| Loans acquired with deteriorated credit quality                                                                             | 17            |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 15,479        | 14,157        | 14,083        | 12,343        |
| Individually evaluated for impairment                                                                                       | 7,776         | 8,515         |          |          |
| Collectively evaluated for impairment                                                                                       | 660,897       | 667,401       |          |          |
| Loans acquired with deteriorated credit quality                                                                             | 724           | 1,027         |          |          |
| Loans                                                                                                                       | 669,397       | 676,943       |          |          |
| Finance Lease                                                                                                               |          |          |          |          |
| **Financing Receivable, Allowance for Credit Losses [Line Items]**                                                          |          |          |          |          |
| Collectively evaluated for impairment                                                                                       | 20            |          |          |          |
| Total Allowance for Loan Losses                                                                                             | 20            |          | 0             | 3             |
| Collectively evaluated for impairment                                                                                       | 2,013         | 2,590         |          |          |
| Loans acquired with deteriorated credit quality                                                                             |     |     |          |          |
| Loans                                                                                                                       | $ 2,013       | $ 2,590       |          |          |

| X                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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| - Definition
The balance of financing receivables that were acquired with deteriorated credit quality.
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| - Definition
The valuation allowance for financing receivables acquired with deteriorated credit quality.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.
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| - Definition
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| - Definition
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.
+ References
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