Summary of Non-Accrual Loans by Loan Class (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 63,127	$ 69,592
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	13,723	12,246
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	7,630	8,990
Commercial and farm land
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	26,838	31,093
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	12,583	14,805
Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,855	1,896
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	146	1
Finance Lease
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	345
Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 7	$ 561