Allowance for Loan Losses - Summary of Nonaccrual Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	$ 27,817	$ 29,855
Commercial & Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	2,771	2,869
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	13,732	16,250
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	10,555	9,701
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	723	958
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	$ 36	$ 77