Loans - (Additional Information Related to Accruing TDR's) (Detail) - Accruing TDR [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Loans [Line Items]
Recorded investment	$ 8,436	$ 19,275
Average year-to- date recorded investment	8,594	19,020
Unpaid principal balance	8,485	19,318
Unfunded commitments to fund TDRs	165	377
Commercial [Member]
Loans [Line Items]
Recorded investment	5,790	13,249
Average year-to- date recorded investment	5,866	12,496
Unpaid principal balance	5,831	13,249
Unfunded commitments to fund TDRs	163	375
Agriculture [Member]
Loans [Line Items]
Recorded investment	84	2,711
Average year-to- date recorded investment	85	3,110
Unpaid principal balance	87	2,715
Commercial Real Estate [Member]
Loans [Line Items]
Recorded investment	388	610
Average year-to- date recorded investment	394	627
Unpaid principal balance	389	622
Residential Real Estate Segment [Member]
Loans [Line Items]
Recorded investment	2,162	2,687
Average year-to- date recorded investment	2,234	2,767
Unpaid principal balance	2,166	2,714
Unfunded commitments to fund TDRs	2	2
Consumer [Member]
Loans [Line Items]
Recorded investment	12	18
Average year-to- date recorded investment	15	20
Unpaid principal balance	$ 12	$ 18