Allowance for Loan Losses - Ending Allocation of Allowance for Loan Losses and Loan Balances Outstanding (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Jan. 04, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	$ 348		$ 188
Collectively evaluated for impairment	12,544		12,942
Total	13,047	$ 13,300	13,305	$ 14,547	$ 14,433	$ 14,361
Individually evaluated for impairment	5,733		6,539
Collectively evaluated for impairment	1,094,846		1,048,711
Total	1,100,817		1,055,506
Receivables Acquired with Deteriorated Credit Quality [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with credit deterioration	155		175
Loan balance of loans acquired with credit deterioration	238		256
Commercial and Agriculture [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	235		82
Collectively evaluated for impairment	1,291		1,850
Total	1,608	1,569	2,018	1,557	1,446	1,478
Individually evaluated for impairment	1,562		1,983
Collectively evaluated for impairment	142,059		133,391
Total	143,708		135,462
Commercial and Agriculture [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with credit deterioration	82		86
Loan balance of loans acquired with credit deterioration	87		88
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	4		4
Collectively evaluated for impairment	2,006		2,167
Total	2,010	2,259	2,171	2,393	2,372	2,467
Individually evaluated for impairment	1,715		1,896
Collectively evaluated for impairment	170,547		159,468
Total	172,262		161,364
Commercial Real Estate Non Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	4,739		4,606
Total	4,739	4,543	4,606	4,969	4,711	4,657
Individually evaluated for impairment	355		359
Collectively evaluated for impairment	405,521		395,572
Total	405,876		395,931
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	103		102
Collectively evaluated for impairment	2,500		2,898
Total	2,676	3,022	3,089	3,899	4,114	4,086
Individually evaluated for impairment	1,487		1,686
Collectively evaluated for impairment	256,942		245,454
Total	258,580		247,308
Residential Real Estate [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired with credit deterioration	73		89
Loan balance of loans acquired with credit deterioration	151		168
Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	482		420
Total	482	413	420	366	408	371
Collectively evaluated for impairment	63,538		56,293
Total	63,538		56,293
Farm Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Individually evaluated for impairment	6
Collectively evaluated for impairment	419		442
Total	425	407	442	476	496	538
Individually evaluated for impairment	614		614
Collectively evaluated for impairment	38,455		40,556
Total	39,069		41,170
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	324		314
Total	324	354	314	358	358	382
Individually evaluated for impairment			1
Collectively evaluated for impairment	17,784		17,977
Total	17,784		17,978
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collectively evaluated for impairment	783		245
Total	$ 783	$ 733	$ 245	$ 529	$ 528	$ 382