Loans Held for Investment and Allowance for Loan Losses - Schedule of How Loans Were Modified as Troubled Debt Restructured Loans (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 1,304	$ 2,150
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	212	361
Commercial [Member] | C&I [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	212	361
Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	68	68
Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	993	1,690
Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	200	200
Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	548	1,047
Real Estate [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	245	443
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	31	31
Consumer [Member] | Auto [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	31	31
Maturity Extended [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	725	725
Maturity Extended [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	212	212
Maturity Extended [Member] | Commercial [Member] | C&I [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	212	212
Maturity Extended [Member] | Agriculture [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	68	68
Maturity Extended [Member] | Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	445	445
Maturity Extended [Member] | Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	200	200
Maturity Extended [Member] | Real Estate [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	245	245
Combined Rate and Maturity [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	579	1,425
Combined Rate and Maturity [Member] | Commercial [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		149
Combined Rate and Maturity [Member] | Commercial [Member] | C&I [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		149
Combined Rate and Maturity [Member] | Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	548	1,245
Combined Rate and Maturity [Member] | Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	548	1,047
Combined Rate and Maturity [Member] | Real Estate [Member] | Residential [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans		198
Combined Rate and Maturity [Member] | Consumer [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	31	31
Combined Rate and Maturity [Member] | Consumer [Member] | Auto [Member]
Financing Receivable, Modifications [Line Items]
Troubled Debt Restructured Loans	$ 31	$ 31