Loans and Allowance for Loan Losses - Schedule of Risk Category of Loans by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 2,556,652	$ 2,575,408
Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,491,065	2,489,353
Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	65,587	86,055
Commercial Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,158,022	1,251,992
Commercial Real Estate [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,146,696	1,215,015
Commercial Real Estate [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	11,326	36,977
Commercial and Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	592,052	582,527
Commercial and Industrial [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	560,282	553,045
Commercial and Industrial [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	31,770	29,482
Residential Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	503,439	444,540
Residential Real Estate [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	495,418	439,184
Residential Real Estate [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,021	5,356
Agricultural Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	141,868	139,332
Agricultural Real Estate [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	132,065	129,285
Agricultural Real Estate [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	9,803	10,047
Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	68,378	62,894
Consumer [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	67,997	61,976
Consumer [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	381	918
Agricultural [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	92,893	94,123
Agricultural [Member] | Unclassified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	88,607	90,848
Agricultural [Member] | Classified [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 4,286	$ 3,275