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