Summary of Non-Accrual Loans by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 56,999	$ 69,592
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	12,507	12,246
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	5,440	8,990
Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	24,501	31,093
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	12,444	14,805
Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,761	1,896
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	3	1
Finance Lease
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	337
Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 6	$ 561