Loans and Allowance for Loan Losses - Schedule of How Loans Were Modified as Troubled Debt Restructured Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 4,857	$ 1,428
Adjusted Interest Rate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		15
Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	2,928	516
Combined Rate and Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	1,929	897
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	3,208	447
Commercial [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	2,560	182
Commercial [Member] | Combined Rate and Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	648	265
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		128
Agriculture [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		128
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	1,460	598
Real Estate [Member] | Adjusted Interest Rate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		15
Real Estate [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	298	150
Real Estate [Member] | Combined Rate and Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	1,162	433
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	189	255
Consumer [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	70	56
Consumer [Member] | Combined Rate and Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 119	$ 199