Allowance for Loan Losses - Credit Exposures by Internally Assigned Grades (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	$ 1,629,052	$ 1,301,919
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	1,599,711	1,276,090
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	14,687	11,103
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	14,654	14,726
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	442,444	203,110
Commercial and Agriculture [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	437,923	199,649
Commercial and Agriculture [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	2,526	2,236
Commercial and Agriculture [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	1,995	1,225
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	252,914	245,606
Commercial Real Estate Owner Occupied [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	241,144	237,171
Commercial Real Estate Owner Occupied [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	8,867	5,617
Commercial Real Estate Owner Occupied [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	2,903	2,818
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	646,792	592,222
Commercial Real Estate Non Owner Occupied [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	643,612	588,633
Commercial Real Estate Non Owner Occupied [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	1,773	2,155
Commercial Real Estate Non Owner Occupied [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	1,407	1,434
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	84,245	80,312
Residential Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	78,028	73,289
Residential Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	486	528
Residential Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	5,731	6,495
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	166,171	145,260
Real Estate Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	165,678	145,251
Real Estate Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	485
Real Estate Construction [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	8	9
Farm Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	35,441	34,114
Farm Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	32,302	30,808
Farm Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	550	567
Farm Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	2,589	2,739
Consumer and Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	1,045	1,295
Consumer and Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	1,024	1,289
Consumer and Other [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans with credit exposures as assigned an internal risk grade	$ 21	$ 6