Loans and Allowance for Loan Losses - Schedule of Loans Modified and Considered Troubled Debt Restructuring (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 SecurityLoan	Dec. 31, 2013 SecurityLoan
Financing Receivable, Modifications [Line Items]
Number	16	22
Pre-Modification Recorded Investment	$ 1,348	$ 4,373
Post-Modification Recorded Investment	1,348	4,373
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number	7	4
Pre-Modification Recorded Investment	668	253
Post-Modification Recorded Investment	668	253
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number	3	6
Pre-Modification Recorded Investment	11	138
Post-Modification Recorded Investment	11	138
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number	1	1
Pre-Modification Recorded Investment	39	24
Post-Modification Recorded Investment	39	24
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number	5	11
Pre-Modification Recorded Investment	630	3,958
Post-Modification Recorded Investment	$ 630	$ 3,958