Loans - Summary of Impaired Loans by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Unpaid Principal Balance
With no allowance recorded	$ 1,883	$ 5,495
With an allowance recorded	25,160	167
Total	27,043	5,662
Impaired Financing Receivable, Recorded Investment [Abstract]
With no allowance recorded	1,875	5,487
With an allowance recorded	25,160	167
Total	27,035	5,654
Allowance for Loan Losses Allocated	20,771	17
Construction and Land Development
Unpaid Principal Balance
With no allowance recorded	30	2,298
Impaired Financing Receivable, Recorded Investment [Abstract]
With no allowance recorded	30	2,298
Residential Real Estate | Closed-end 1-4 family
Unpaid Principal Balance
With no allowance recorded	319	1,280
With an allowance recorded	643
Impaired Financing Receivable, Recorded Investment [Abstract]
With no allowance recorded	311	1,272
With an allowance recorded	643
Allowance for Loan Losses Allocated	17
Residential Real Estate | Other
Unpaid Principal Balance
With no allowance recorded	1,523	1,917
Impaired Financing Receivable, Recorded Investment [Abstract]
With no allowance recorded	1,523	1,917
Commercial and Industrial
Unpaid Principal Balance
With no allowance recorded	11
With an allowance recorded	24,517	167
Impaired Financing Receivable, Recorded Investment [Abstract]
With no allowance recorded	11
With an allowance recorded	24,517	167
Allowance for Loan Losses Allocated	$ 20,754	$ 17