Loans - Summary of Loan Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Total	$ 4,887,496		$ 4,763,127
Total principal balance of loans owed, net of charge-offs	4,928,842		4,805,596
Unamortized net deferred loan fees	(17,218)		(16,984)
Deferred Discounts, Finance Charges and Interest Included in Receivables	(17,984)
Discounts to principal balance of loans owed, net of charge-offs	4,893,640		(25,485)
Allowance for credit losses on loans	(84,306)	$ (86,062)	(91,847)	$ (87,575)	$ (79,739)	$ (30,616)
Commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Total	3,222,737		2,951,902
Allowance for credit losses on loans	(50,729)	(51,637)	(53,693)	(50,294)	(44,850)	(11,995)
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	1,053,653		952,108
Allowance for credit losses on loans	(23,491)	(23,950)	(25,148)	(24,007)	(23,165)	(10,084)
Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total	345,027		526,327
Allowance for credit losses on loans	(3,427)	(4,511)	(4,252)	(4,534)	(4,018)	(4,867)
Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	216,680		284,842
Allowance for credit losses on loans	(5,528)	(4,951)	(7,540)	(7,640)	(6,775)	(3,388)
Agriculture production
Loans and Leases Receivable Disclosure [Line Items]
Total	44,410		44,164
Allowance for credit losses on loans	(1,119)	(1,007)	(1,209)	(1,093)	(919)	(261)
Leases
Loans and Leases Receivable Disclosure [Line Items]
Total	4,989		3,784
Allowance for credit losses on loans	(12)	(6)	(5)	(7)	(12)	(21)
CRE non-owner occupied | Commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Total	1,526,030		1,535,555
Allowance for credit losses on loans	(25,221)	(26,028)	(29,380)	(28,847)	(26,091)	(5,948)
CRE owner occupied | Commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Total	701,041		624,375
Allowance for credit losses on loans	(10,730)	(10,463)	(10,861)	(9,625)	(8,710)	(2,027)
Multifamily | Commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Total	829,644		639,480
Allowance for credit losses on loans	(12,876)	(13,196)	(11,472)	(10,032)	(8,581)	(3,352)
Farmland | Commercial real estate
Loans and Leases Receivable Disclosure [Line Items]
Total	166,022		152,492
Allowance for credit losses on loans	(1,902)	(1,950)	(1,980)	(1,790)	(1,468)	(668)
SFR 1-4 1st DT liens | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	662,343		546,592
SFR HELOCs and junior liens | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	323,258		327,484
Allowance for credit losses on loans	(10,431)	(10,701)	(11,771)	(11,676)	(12,108)	(6,183)
Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	68,052		78,032
Allowance for credit losses on loans	$ (2,442)	$ (2,620)	$ (3,260)	$ (3,394)	$ (3,042)	$ (1,595)