Allowance for Loan Losses - Summary of Nonaccrual Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	$ 13,582	$ 13,558
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	1,274	1,264
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	4,507	3,403
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	1,994	2,134
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	5,735	6,674
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	32	41
Consumer and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Total, Non-Accrual Status	$ 40	$ 42