Loans and Allowance for Loan Losses - Schedule of How Loans Were Modified as Troubled Debt Restructured Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Modifications [Line Items]
Adjusted Interest Rate	$ 0	$ 0	$ 0	$ 0
Extended Maturity	247	158	453	381
Combined Rate and Maturity		40	103	856
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Adjusted Interest Rate	0	0	0	0
Extended Maturity	66	158	139	255
Combined Rate and Maturity				302
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Adjusted Interest Rate	0	0	0	0
Extended Maturity			129
Combined Rate and Maturity				39
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Adjusted Interest Rate	0	0	0	0
Extended Maturity	149		149	118
Combined Rate and Maturity		40	79	512
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Adjusted Interest Rate	0	$ 0	0	0
Extended Maturity	$ 32		36	8
Combined Rate and Maturity			$ 24	$ 3