Loans - Analysis of Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
ALLOWANCE FOR CREDIT LOSSES:
Balance at beginning of year				$ 21,575				$ 17,283	$ 21,575	$ 17,283
Charge Offs									(990)	(827)
Recoveries									439	298
Provision for credit losses - loans	$ 278	$ 460	$ 143	817	$ 755	$ 1,637	$ 1,628	580	1,698	4,600	$ 3,444
Provision for credit losses-Off balance sheet credit exposures	189	$ (76)	$ (129)	62					46
Other Non-interest expense related to unfunded										221
Balance at ending of year					21,575					21,575	17,283
Ending balance: individually evaluated for impairment					1,996					1,996
Ending balance: collectively evaluated for impairment					19,579					19,579
Ending balance: loans acquired with deteriorated credit quality					0					0
FINANCING RECEIVABLES:
Ending balance	2,578,472				2,356,387				$ 2,578,472	2,356,387
Ending balance: individually evaluated for impairment					8,857					8,857
Ending balance: collectively evaluated for impairment					2,346,871					2,346,871
Ending balance: loans acquired with deteriorated credit quality					659					659
Cumulative Effect, Period of Adoption, Adjustment [Member]
ALLOWANCE FOR CREDIT LOSSES:
Accounting Standards Update [Extensible Enumeration]									Accounting Standards Update 2016-13 [Member]
Consumer Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Balance at beginning of year				998				857	$ 998	857
Charge Offs										0
Recoveries									35	20
Provision for credit losses - loans									(326)	121
Balance at ending of year					998					998	857
Ending balance: individually evaluated for impairment					6					6
Ending balance: collectively evaluated for impairment					992					992
Ending balance: loans acquired with deteriorated credit quality					0					0
FINANCING RECEIVABLES:
Ending balance	521,908				494,423				521,908	494,423
Ending balance: individually evaluated for impairment					569					569
Ending balance: collectively evaluated for impairment					493,449					493,449
Ending balance: loans acquired with deteriorated credit quality					405					405
Agricultural Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Balance at beginning of year				349				1,040	349	1,040
Charge Offs										0
Recoveries									105
Provision for credit losses - loans									24	(691)
Balance at ending of year					349					349	1,040
Ending balance: individually evaluated for impairment					0					0
Ending balance: collectively evaluated for impairment					349					349
Ending balance: loans acquired with deteriorated credit quality					0					0
FINANCING RECEIVABLES:
Ending balance	223,479				220,514				223,479	220,514
Ending balance: individually evaluated for impairment					2,280					2,280
Ending balance: collectively evaluated for impairment					218,039					218,039
Ending balance: loans acquired with deteriorated credit quality					195					195
Agricultural [Member]
ALLOWANCE FOR CREDIT LOSSES:
Balance at beginning of year				751				709	751	709
Charge Offs										0
Recoveries									10	7
Provision for credit losses - loans									225	35
Balance at ending of year					751					751	709
Ending balance: individually evaluated for impairment					0					0
Ending balance: collectively evaluated for impairment					751					751
Ending balance: loans acquired with deteriorated credit quality					0					0
FINANCING RECEIVABLES:
Ending balance	132,763				128,926				132,763	128,926
Ending balance: individually evaluated for impairment					152					152
Ending balance: collectively evaluated for impairment					128,774					128,774
Commercial Real Estate [Member]
ALLOWANCE FOR CREDIT LOSSES:
Balance at beginning of year				11,924				9,130	11,924	9,130
Recoveries									8	9
Provision for credit losses - loans									1,967	2,785
Balance at ending of year					11,924					11,924	9,130
Ending balance: individually evaluated for impairment					438					438
Ending balance: collectively evaluated for impairment					11,486					11,486
Ending balance: loans acquired with deteriorated credit quality					0					0
FINANCING RECEIVABLES:
Ending balance	1,335,075				1,150,511				1,335,075	1,150,511
Ending balance: individually evaluated for impairment					4,108					4,108
Ending balance: collectively evaluated for impairment					1,146,389					1,146,389
Ending balance: loans acquired with deteriorated credit quality					14					14
Commercial and Industrial [Member]
ALLOWANCE FOR CREDIT LOSSES:
Balance at beginning of year				5,382				3,847	5,382	3,847
Charge Offs									(565)	(418)
Recoveries									84	93
Provision for credit losses - loans									(643)	1,860
Balance at ending of year					5,382					5,382	3,847
Ending balance: individually evaluated for impairment					1,551					1,551
Ending balance: collectively evaluated for impairment					3,831					3,831
Ending balance: loans acquired with deteriorated credit quality					0					0
FINANCING RECEIVABLES:
Ending balance	284,894				272,119				284,894	272,119
Ending balance: individually evaluated for impairment					1,581					1,581
Ending balance: collectively evaluated for impairment					270,493					270,493
Ending balance: loans acquired with deteriorated credit quality					45					45
Consumer [Member]
ALLOWANCE FOR CREDIT LOSSES:
Balance at beginning of year				891				625	891	625
Charge Offs									(425)	(409)
Recoveries									197	169
Provision for credit losses - loans									451	506
Balance at ending of year					891					891	625
Ending balance: individually evaluated for impairment					1					1
Ending balance: collectively evaluated for impairment					890					890
Ending balance: loans acquired with deteriorated credit quality					0					0
FINANCING RECEIVABLES:
Ending balance	80,353				89,894				80,353	89,894
Ending balance: individually evaluated for impairment					167					167
Ending balance: collectively evaluated for impairment					89,727					89,727
Unallocated [Member]
ALLOWANCE FOR CREDIT LOSSES:
Balance at beginning of year				18				34	18	34
Provision for credit losses - loans										(16)
Balance at ending of year					18					18	34
Ending balance: collectively evaluated for impairment					18					18
Ending balance: loans acquired with deteriorated credit quality					0					0
Unfunded Loan Commitment & Letters of Credit [Member]
ALLOWANCE FOR CREDIT LOSSES:
Balance at beginning of year				$ 1,262				$ 1,041	1,262	1,041
Provision for credit losses-Off balance sheet credit exposures									46
Other Non-interest expense related to unfunded										221
Balance at ending of year	2,212				1,262				2,212	1,262	$ 1,041
Ending balance: collectively evaluated for impairment					1,262					1,262
Ending balance: loans acquired with deteriorated credit quality					$ 0					$ 0
Unfunded Loan Commitment & Letters of Credit [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
ALLOWANCE FOR CREDIT LOSSES:
Balance at ending of year	$ 904								$ 904