Loans and Allowance for Loan Losses - Schedule of Loans Modified and Considered Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) SecurityLoan	Sep. 30, 2014 USD ($) SecurityLoan	Sep. 30, 2015 USD ($) SecurityLoan	Sep. 30, 2014 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	4	2	13	15
Pre-Modification Recorded Investment	$ 247	$ 198	$ 556	$ 1,237
Post-Modification Recorded Investment	$ 247	$ 198	$ 556	$ 1,237
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	1	1	3	6
Pre-Modification Recorded Investment	$ 66	$ 158	$ 139	$ 557
Post-Modification Recorded Investment	$ 66	$ 158	$ 139	$ 557
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan			3	1
Pre-Modification Recorded Investment			$ 129	$ 39
Post-Modification Recorded Investment			$ 129	$ 39
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	1	1	2	5
Pre-Modification Recorded Investment	$ 149	$ 40	$ 228	$ 630
Post-Modification Recorded Investment	$ 149	$ 40	$ 228	$ 630
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number | SecurityLoan	2		5	3
Pre-Modification Recorded Investment	$ 32		$ 60	$ 11
Post-Modification Recorded Investment	$ 32		$ 60	$ 11