Loans - Contractual Aging of Recorded Investment in Past Due Loans by Portfolio Classification of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 3,727	$ 1,139
Current	1,299,263	1,217,860
Loans after net deferred loan fees and costs	1,302,990	1,218,999
Recorded Investment > 90 Days and Accruing	0	0
30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	322	688
60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	941	451
Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,464
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,492	425
Current	173,824	164,266
Loans after net deferred loan fees and costs	175,316	164,691
Consumer Real Estate [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	269	355
Consumer Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	191	70
Consumer Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,032
Agricultural Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	88	107
Current	188,738	198,752
Loans after net deferred loan fees and costs	188,826	198,859
Agricultural Real Estate [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		107
Agricultural Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	88
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	176	85
Current	94,314	111,864
Loans after net deferred loan fees and costs	94,490	111,949
Agricultural [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		78
Agricultural [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		7
Agricultural [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	176
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	185
Current	587,469	550,082
Loans after net deferred loan fees and costs	587,654	550,082
Commercial Real Estate [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	185
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,733	468
Current	202,310	143,541
Loans after net deferred loan fees and costs	204,043	144,009
Commercial and Industrial [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		201
Commercial and Industrial [Member] | 60 to 89 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	750	267
Commercial and Industrial [Member] | Greater Than 90 Days [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	983
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	53	54
Current	52,608	49,355
Loans after net deferred loan fees and costs	52,661	49,409
Consumer [Member] | 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 53	$ 54