Loans and Allowance for Loan Losses - Schedule of How Loans Were Modified as Troubled Debt Restructured Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Modifications [Line Items]
Adjusted Interest Rate		$ 420
Extended Maturity	492	809
Combined Rate and Maturity	856	3,144
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Extended Maturity	366	218
Combined Rate and Maturity	302	35
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Extended Maturity		24
Combined Rate and Maturity	39
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Adjusted Interest Rate		420
Extended Maturity	118	433
Combined Rate and Maturity	512	3,105
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Extended Maturity	8	134
Combined Rate and Maturity	$ 3	$ 4