Loans Held for Investment and Allowance for Loan Losses - Schedule of loans that are individually evaluated for credit losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	$ 53,284
Recorded Investment With No Allowance	11,120
Recorded Investment With Allowance	28,106
Total Recorded Investment	39,226	$ 190,416	$ 197,451
Related Allowance	3,386	18,573	20,637
Average Recorded Investment	44,634
Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		21,964	21,439
Recorded Investment With Allowance		17,369	21,180
Related Allowance		2,952	3,419
Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		151,083	154,832
Related Allowance		15,621	17,218
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	7,300
Recorded Investment With No Allowance	992
Recorded Investment With Allowance	4,628
Total Recorded Investment	5,620	29,066	40,083
Related Allowance	1,271	5,417	6,826
Average Recorded Investment	6,409
Commercial [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		1,806	1,544
Recorded Investment With Allowance		2,903	3,471
Related Allowance		777	799
Commercial [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		24,357	35,068
Related Allowance		4,640	6,027
Commercial [Member] | C&I [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		19,289	30,644
Related Allowance		3,881	5,391
Commercial [Member] | C&I [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		1,806	1,544
Recorded Investment With Allowance		2,903	3,471
Related Allowance		777	799
Commercial [Member] | C&I [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		14,580	25,629
Related Allowance		3,104	4,592
Commercial [Member] | Municipal [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		9,777	9,439
Related Allowance		1,536	1,435
Commercial [Member] | Municipal [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		9,777	9,439
Related Allowance		1,536	1,435
Agriculture [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	1,340
Recorded Investment With No Allowance	632
Recorded Investment With Allowance	496
Total Recorded Investment	1,128	6,859	6,648
Related Allowance	98	1,790	982
Average Recorded Investment	1,200
Agriculture [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		457	470
Recorded Investment With Allowance		612	606
Related Allowance		170	96
Agriculture [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		5,790	5,572
Related Allowance		1,620	886
Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	44,208
Recorded Investment With No Allowance	9,496
Recorded Investment With Allowance	22,660
Total Recorded Investment	32,156	152,324	148,256
Related Allowance	2,016	11,359	12,821
Average Recorded Investment	36,683
Real Estate [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		19,701	19,425
Recorded Investment With Allowance		13,462	16,602
Related Allowance		2,004	2,522
Real Estate [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		119,161	112,229
Related Allowance		9,355	10,299
Real Estate [Member] | Construction & Development [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		12,497	15,205
Related Allowance		880	652
Real Estate [Member] | Construction & Development [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		1,124	1,176
Recorded Investment With Allowance		171	2,661
Related Allowance		12	35
Real Estate [Member] | Construction & Development [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		11,202	11,368
Related Allowance		868	617
Real Estate [Member] | Farm [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		10,295	10,648
Related Allowance		671	1,312
Real Estate [Member] | Farm [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		2,241	2,614
Recorded Investment With Allowance		4,618	4,685
Related Allowance		590	654
Real Estate [Member] | Farm [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		3,436	3,349
Related Allowance		81	658
Real Estate [Member] | Non-Owner Occupied CRE [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		39,387	22,626
Related Allowance		3,335	1,921
Real Estate [Member] | Non-Owner Occupied CRE [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		6,045	4,009
Recorded Investment With Allowance		1,043	1,234
Related Allowance		226	500
Real Estate [Member] | Non-Owner Occupied CRE [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		32,299	17,383
Related Allowance		3,109	1,421
Real Estate [Member] | Owner Occupied CRE [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		55,450	62,730
Related Allowance		3,599	5,829
Real Estate [Member] | Owner Occupied CRE [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		6,081	7,279
Recorded Investment With Allowance		3,476	3,518
Related Allowance		599	657
Real Estate [Member] | Owner Occupied CRE [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		45,893	51,933
Related Allowance		3,000	5,172
Real Estate [Member] | Residential [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		34,695	37,047
Related Allowance		2,874	3,107
Real Estate [Member] | Residential [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With No Allowance		4,210	4,347
Recorded Investment With Allowance		4,154	4,504
Related Allowance		577	676
Real Estate [Member] | Residential [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		26,331	28,196
Related Allowance		2,297	2,431
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Contractual Principal Balance	436
Recorded Investment With Allowance	322
Total Recorded Investment	322	2,167	2,464
Related Allowance	1	7	8
Average Recorded Investment	$ 342
Consumer [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With Allowance		392	501
Related Allowance		1	2
Consumer [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		1,775	1,963
Related Allowance		6	6
Consumer [Member] | Auto [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		1,716	1,930
Related Allowance		5	6
Consumer [Member] | Auto [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With Allowance		317	407
Related Allowance		1	1
Consumer [Member] | Auto [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		1,399	1,523
Related Allowance		4	5
Consumer [Member] | Non-Auto [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		451	534
Related Allowance		2	2
Consumer [Member] | Non-Auto [Member] | Collateral Pledged [Member]
Financing Receivable, Impaired [Line Items]
Recorded Investment With Allowance		75	94
Related Allowance			1
Consumer [Member] | Non-Auto [Member] | Uncollateralized [Member]
Financing Receivable, Impaired [Line Items]
Total Recorded Investment		376	440
Related Allowance		$ 2	$ 1