Allowance for Credit Losses - Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($) investmentSecurity	Jun. 30, 2020 USD ($) investmentSecurity	Jun. 30, 2021 USD ($) investmentSecurity	Jun. 30, 2020 USD ($) investmentSecurity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	3,000	0	8	6,000
Pre-mod outstanding principal balance	$ 2,706	$ 0	$ 4,079	$ 680
Post-mod outstanding principal balance	2,706	0	4,070	738
Financial impact due to TDR taken as additional provision	$ 999	$ 0	$ 2,365	$ 21
Number that defaulted during the period (in investment securities) | investmentSecurity	0	1,000	4	2,000
Recorded investment of TDRs that defaulted during the period	$ 0	$ 735	$ 1,094	$ 1,037
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	1,000	0	3	3,000
Pre-mod outstanding principal balance	$ 706	$ 0	$ 1,763	$ 487
Post-mod outstanding principal balance	706	0	1,760	549
Financial impact due to TDR taken as additional provision	$ 706	$ 0	$ 1,762	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	3	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 847	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	2,000
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 172
Post-mod outstanding principal balance	0	0	0	169
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	1,000	0	2,000
Recorded investment of TDRs that defaulted during the period	$ 0	$ 735	$ 0	$ 1,037
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	2,000	0	5	1,000
Pre-mod outstanding principal balance	$ 2,000	$ 0	$ 2,316	$ 21
Post-mod outstanding principal balance	2,000	0	2,310	20
Financial impact due to TDR taken as additional provision	$ 293	$ 0	$ 603	$ 21
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	1	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 247	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
Construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	0
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 0
Post-mod outstanding principal balance	0	0	0	0
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	0	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 0	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
Agriculture production
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	0
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 0
Post-mod outstanding principal balance	0	0	0	0
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	0	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 0	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
Leases
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	0
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 0
Post-mod outstanding principal balance	0	0	0	0
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	0	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 0	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
CRE non-owner occupied | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	1,000	0	2	1,000
Pre-mod outstanding principal balance	$ 706	$ 0	$ 1,023	$ 257
Post-mod outstanding principal balance	706	0	1,018	251
Financial impact due to TDR taken as additional provision	$ 706	$ 0	$ 1,020	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	0	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 0	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
CRE owner occupied | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	1	0
Pre-mod outstanding principal balance	$ 0	$ 0	$ 740	$ 0
Post-mod outstanding principal balance	0	0	742	0
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 742	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	0	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 0	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
Multifamily | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	0
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 0
Post-mod outstanding principal balance	0	0	0	0
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	0	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 0	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
Farmland | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	2,000
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 230
Post-mod outstanding principal balance	0	0	0	298
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	3	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 847	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
SFR 1-4 1st DT liens | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	0
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 0
Post-mod outstanding principal balance	0	0	0	0
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	1,000	0	2,000
Recorded investment of TDRs that defaulted during the period	$ 0	$ 735	$ 0	$ 1,037
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
SFR HELOCs and junior liens | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	2,000
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 172
Post-mod outstanding principal balance	0	0	0	169
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	0	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 0	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0
Other | Consumer
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	0
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 0
Post-mod outstanding principal balance	0	0	0	0
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	0	0	0	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 0	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ 0	$ 0	$ 0	$ 0