Loans - Schedule of Loans Not Rated by Class of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	$ 171,663	$ 164,028
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	817	951
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	518	911
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	150,803	144,098
Construction & Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	3,352	4,760
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	16,173	13,308
Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	171,125	163,333
Performing [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	817	951
Performing [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	518	911
Performing [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	150,295	143,440
Performing [Member] | Construction & Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	3,352	4,760
Performing [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	16,143	13,271
Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	538	695
Nonperforming [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	508	658
Nonperforming [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans not rated by class of loans	$ 30	$ 37