Allowance for Credit Losses - Troubled Debt Restructurings (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) investmentSecurity	Sep. 30, 2020 USD ($) investmentSecurity	Sep. 30, 2021 USD ($) investmentSecurity	Sep. 30, 2020 USD ($) investmentSecurity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	6,000	6,000	14	12,000
Pre-mod outstanding principal balance	$ 4,153	$ 2,741	$ 8,232	$ 3,420
Post-mod outstanding principal balance	4,147	2,655	8,217	3,393
Financial impact due to TDR taken as additional provision	$ 156	$ 381	$ 2,521	$ 402
Number that defaulted during the period (in investment securities) | investmentSecurity	1,000	4,000	5	5,000
Recorded investment of TDRs that defaulted during the period	$ 13	$ 1,685	$ 1,107	$ 2,579
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ (5)	$ 0	$ (5)	$ 0
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	4,000	6,000	7	9,000
Pre-mod outstanding principal balance	$ 3,993	$ 2,741	$ 5,756	$ 3,227
Post-mod outstanding principal balance	3,988	2,655	5,748	3,204
Financial impact due to TDR taken as additional provision	$ 50	$ 381	$ 1,812	$ 381
Number that defaulted during the period (in investment securities) | investmentSecurity	0	3,000	3	3,000
Recorded investment of TDRs that defaulted during the period	$ 0	$ 1,542	$ 847	$ 1,542
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	$ 143	$ 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	7	0
Pre-mod outstanding principal balance	$ 160	$ 0	$ 2,476	$ 0
Post-mod outstanding principal balance	159	0	2,469	0
Financial impact due to TDR taken as additional provision	$ 106	$ 0	$ 709	$ 0
Number that defaulted during the period (in investment securities) | investmentSecurity	1,000	0	2	0
Recorded investment of TDRs that defaulted during the period	$ 13	$ 0	$ 260	$ 0
Financial impact due to the default of previous TDR taken as charge- offs or additional provisions	$ (5)	$ 0	$ (5)	$ 0
Construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number (in investment securities) | investmentSecurity	0	0	0	1,000
Pre-mod outstanding principal balance	$ 0	$ 0	$ 0	$ 21
Post-mod outstanding principal balance	0	0	0	20
Financial impact due to TDR taken as additional provision	$ 0	$ 0	$ 0	$ 21
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	3,000	1,000	5	2,000
Pre-mod outstanding principal balance	$ 3,943	$ 319	$ 4,966	$ 576
Post-mod outstanding principal balance	3,938	314	4,956	565
Financial impact due to TDR taken as additional provision	$ 0	$ 314	$ 1,020	$ 314
Number that defaulted during the period (in investment securities) | investmentSecurity	0	1,000	0	1,000
Recorded investment of TDRs that defaulted during the period	$ 0	$ 141	$ 0	$ 141
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	5,000	1	5,000
Pre-mod outstanding principal balance	$ 0	$ 2,422	$ 740	$ 2,422
Post-mod outstanding principal balance	0	2,341	742	2,341
Financial impact due to TDR taken as additional provision	$ 0	$ 67	$ 742	$ 67
Number that defaulted during the period (in investment securities) | investmentSecurity	0	2,000	0	2,000
Recorded investment of TDRs that defaulted during the period	$ 0	$ 1,401	$ 0	$ 1,401
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	1,000	0	1	2,000
Pre-mod outstanding principal balance	$ 50	$ 0	$ 50	$ 229
Post-mod outstanding principal balance	50	0	50	298
Financial impact due to TDR taken as additional provision	$ 50	$ 0	$ 50	$ 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	0	0	2,000
Recorded investment of TDRs that defaulted during the period	$ 0	$ 0	$ 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	1,000	0	0
Recorded investment of TDRs that defaulted during the period	$ 0	$ 143	$ 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