| **Loans and Allowance - Summary of Non-Accrual Loans by Loan Class (Detail) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2012 | Dec. 31, 2011 |
|-------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                              |          |          |
| Non-accrual loans                                                                                                             | $ 53,399      | $ 69,592      |
| Commercial and industrial                                                                                                     |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                              |          |          |
| Non-accrual loans                                                                                                             | 12,195        | 12,246        |
| Construction                                                                                                                  |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                              |          |          |
| Non-accrual loans                                                                                                             | 4,814         | 8,990         |
| Commercial and farm land                                                                                                      |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                              |          |          |
| Non-accrual loans                                                                                                             | 22,612        | 31,093        |
| Residential                                                                                                                   |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                              |          |          |
| Non-accrual loans                                                                                                             | 11,476        | 14,805        |
| Home Equity                                                                                                                   |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                              |          |          |
| Non-accrual loans                                                                                                             | 1,997         | 1,896         |
| Consumer                                                                                                                      |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                              |          |          |
| Non-accrual loans                                                                                                             |          | 1             |
| Finance Leases                                                                                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                              |          |          |
| Non-accrual loans                                                                                                             | 301           |     |
| Other Loans                                                                                                                   |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                              |          |          |
| Non-accrual loans                                                                                                             | $ 4           | $ 561         |

| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5111-111524
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |