Allowance for Credit Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 30,616	$ 32,582	$ 30,323
Charge-offs	(1,755)	(3,639)	(2,364)
Recoveries	1,885	3,363	2,040
Provision (benefit)	42,188	(1,690)	2,583
Ending balance	91,847	30,616	32,582
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	2,775	2,575
Charge-offs	0	0	0
Recoveries	0	0	0
Provision	625	200
Ending balance	3,400	2,775	2,575
Credit Loss [Roll Forward]
Beginning balance	33,391
Charge-offs	(1,755)
Recoveries	1,885
Provision	42,813
Ending balance	95,247	33,391
Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	18,913
Ending balance		18,913
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	0
Ending balance		0
Credit Loss [Roll Forward]
Beginning balance	18,913
Ending balance		18,913
Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	11,995	12,944	11,441
Charge-offs	(182)	(746)	(15)
Recoveries	226	1,528	67
Provision (benefit)	29,806	(1,731)	1,451
Ending balance	53,693	11,995	12,944
Commercial real estate \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	11,848
Ending balance		11,848
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	10,084	11,051	10,544
Charge-offs	(799)	(770)	(1,161)
Recoveries	1,067	1,310	1,431
Provision (benefit)	6,512	(1,507)	237
Ending balance	25,148	10,084	11,051
Consumer \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	8,284
Ending balance		8,284
Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,867	5,610	5,757
Charge-offs	(774)	(2,104)	(1,103)
Recoveries	568	513	445
Provision (benefit)	1,552	848	511
Ending balance	4,252	4,867	5,610
Commercial and industrial \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	(1,961)
Ending balance		(1,961)
Construction
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,388	2,497	1,826
Charge-offs	0	0	0
Recoveries	0	0	0
Provision (benefit)	3,219	891	671
Ending balance	7,540	3,388	2,497
Construction \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	933
Ending balance		933
Agriculture production
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	261	480	755
Charge-offs	0	(19)	(85)
Recoveries	24	12	97
Provision (benefit)	1,103	(212)	(287)
Ending balance	1,209	261	480
Agriculture production \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	(179)
Ending balance		(179)
Leases
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	21	0	0
Charge-offs	0	0	0
Recoveries	0	0	0
Provision (benefit)	(4)	21	0
Ending balance	5	21	0
Leases \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	(12)
Ending balance		(12)
Mortgage Loans on Real Estate \| Commercial loans
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance			3,164
Provision			(589)
CRE non-owner occupied \| Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	5,948	7,401	6,693
Charge-offs	0	0	(15)
Recoveries	198	1,486	47
Provision (benefit)	16,533	(2,939)	676
Ending balance	29,380	5,948	7,401
CRE non-owner occupied \| Commercial real estate \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	6,701
Ending balance		6,701
CRE owner occupied \| Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,027	2,711	2,686
Charge-offs	0	(746)	0
Recoveries	28	42	20
Provision (benefit)	6,525	20	5
Ending balance	10,861	2,027	2,711
CRE owner occupied \| Commercial real estate \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,281
Ending balance		2,281
Multifamily \| Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	3,352	2,429	1,491
Charge-offs	0	0	0
Recoveries	0	0	0
Provision (benefit)	5,839	923	938
Ending balance	11,472	3,352	2,429
Multifamily \| Commercial real estate \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,281
Ending balance		2,281
Farmland \| Commercial real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	668	403	571
Charge-offs	(182)	0	0
Recoveries	0	0	0
Provision (benefit)	909	265	(168)
Ending balance	1,980	668	403
Farmland \| Commercial real estate \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	585
Ending balance		585
SFR 1-4 1st DT liens \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,306	2,676	2,317
Charge-offs	(13)	(2)	(77)
Recoveries	416	54	0
Provision (benefit)	4,733	(422)	436
Ending balance	10,117	2,306	2,676
SFR 1-4 1st DT liens \| Consumer \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	2,675
Ending balance		2,675
SFR HELOCs and junior liens \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	6,183	7,582	7,641
Charge-offs	(116)	(3)	(301)
Recoveries	304	935	1,143
Provision (benefit)	762	(2,331)	(901)
Ending balance	11,771	6,183	7,582
SFR HELOCs and junior liens \| Consumer \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,638
Ending balance		4,638
Other \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,595	793	586
Charge-offs	(670)	(765)	(783)
Recoveries	347	321	288
Provision (benefit)	1,017	1,246	702
Ending balance	3,260	1,595	$ 793
Other \| Consumer \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 971
Ending balance		$ 971

Credit Loss, Allowance For Credit Loss

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Credit Loss, Allowance For Credit Loss, Recovery

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

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Amount of expense (reversal of expense) for expected credit loss for off-balance sheet credit exposure. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

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