Allowance for Loan Losses - Changes in the Allowance for Loan Losses and Loan Balances Outstanding (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 14,433	$ 14,315	$ 14,361	$ 14,268
Charge-offs	(230)	(305)	(356)	(890)
Recoveries	1,644	297	1,842	529
Provision	(1,300)	400	(1,300)	800
Ending Balance	14,547	14,707	14,547	14,707
Commercial and Agriculture [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	1,446	1,795	1,478	1,819
Charge-offs	(20)		(42)
Recoveries	30	12	35	31
Provision	101	(412)	86	(455)
Ending Balance	1,557	1,395	1,557	1,395
Commercial Real Estate Non Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	4,711	4,926	4,657	4,334
Charge-offs		(55)		(64)
Recoveries	1,319	76	1,359	90
Provision	(1,061)	(1,794)	(1,047)	(1,207)
Ending Balance	4,969	3,153	4,969	3,153
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	4,114	3,666	4,086	3,747
Charge-offs	(129)	(213)	(225)	(541)
Recoveries	272	34	361	165
Provision	(358)	(17)	(323)	99
Ending Balance	3,899	3,470	3,899	3,470
Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	408	498	371	428
Recoveries	1	2	2	3
Provision	(43)	(66)	(7)	3
Ending Balance	366	434	366	434
Farm Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	496	799	538	822
Recoveries				51
Provision	(20)	(215)	(62)	(289)
Ending Balance	476	584	476	584
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	358	190	382	200
Charge-offs	(39)	(37)	(47)	(87)
Recoveries	19	16	33	30
Provision	20	21	(10)	47
Ending Balance	358	190	358	190
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	2,372	1,808	2,467	2,221
Charge-offs	(42)		(42)	(198)
Recoveries	3	157	52	159
Provision	60	3,108	(84)	2,891
Ending Balance	2,393	5,073	2,393	5,073
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	528	633	382	697
Provision	1	(225)	147	(289)
Ending Balance	$ 529	$ 408	$ 529	$ 408