Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Change in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period			$ 117,306
PCL	$ (3,991)	$ 18,185	(14,492)	$ 38,766
Balance at end of period	104,032		104,032
Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	109,191	100,564	117,306	84,277
Loans charged-off	(4,828)	(1,870)	(6,073)	(7,415)
Recoveries	3,660	2,309	7,291	4,777
Net (charge-offs) recoveries	(1,168)	439	1,218	(2,638)
PCL	(3,991)	18,185	(14,492)	38,766
Balance at end of period	104,032	119,188	104,032	119,188
Allowance for Credit Losses, ACL [Member] | Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	5,058	9,079	6,854	6,371
Loans charged-off		(7)		(7)
Recoveries	313	92	1,079	186
PCL	(261)	2,776	(2,823)	5,578
Balance at end of period	5,110	11,940	5,110	11,940
Allowance for Credit Losses, ACL [Member] | Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	8,667	11,711	9,928	5,888
Loans charged-off	(58)	(36)	(84)	(100)
Recoveries	181	83	252	146
PCL	1,609	958	303	2,594
Balance at end of period	10,399	12,716	10,399	12,716
Allowance for Credit Losses, ACL [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
PCL	1,600
Allowance for Credit Losses, ACL [Member] | Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	3,753	8,042	5,143	3,044
Loans charged-off	(4)		(4)	(19)
Recoveries	8	13	108	106
PCL	(847)	2,844	(2,337)	4,877
Balance at end of period	2,910	10,899	2,910	10,899
Allowance for Credit Losses, ACL [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	46,438	28,127	48,523	26,158
Loans charged-off	(79)		(79)	(2,448)
Recoveries	1,027	445	1,057	506
PCL	(2,970)	7,845	(5,085)	20,380
Balance at end of period	44,416	36,417	44,416	36,417
Allowance for Credit Losses, ACL [Member] | Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	5,770	5,273	7,382	4,024
Loans charged-off				(8)
Recoveries	5	12	11	18
PCL	(464)	2,315	(2,082)	4,331
Balance at end of period	5,311	7,600	5,311	7,600
Allowance for Credit Losses, ACL [Member] | Commercial and Industrial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	20,166	14,564	14,851	25,992
Loans charged-off	(3,674)	(297)	(3,697)	(1,279)
Recoveries	652	191	1,939	733
PCL	(3,171)	(1,908)	880	(3,932)
Balance at end of period	13,973	12,550	13,973	12,550
Allowance for Credit Losses, ACL [Member] | Other Construction [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
PCL	1,400
Allowance for Credit Losses, ACL [Member] | Other Construction [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	5,124	7,711	8,158	1,889
Recoveries	43	21	44	40
PCL	1,363	3,071	(1,672)	5,672
Balance at end of period	6,530	10,803	6,530	10,803
Allowance for Credit Losses, ACL [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	4,750	6,596	5,838	3,379
Loans charged-off	(391)	(671)	(833)	(1,361)
Recoveries	387	468	749	941
PCL	130	4	(878)	1,379
Balance at end of period	4,876	6,397	4,876	6,397
Allowance for Credit Losses, ACL [Member] | State and Other Political Subdivision Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	3,015	3,441	3,190	2,229
PCL	218	(27)	43	(1,270)
Balance at end of period	3,233	3,414	3,233	3,414
Allowance for Credit Losses, ACL [Member] | Other Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	6,450	6,020	7,439	5,303
Loans charged-off	(622)	(859)	(1,376)	(2,193)
Recoveries	1,044	984	2,052	2,101
PCL	402	307	(841)	(843)
Balance at end of period	$ 7,274	$ 6,452	$ 7,274	6,452
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
LHFI				(3,039)
Allowance for loan losses, acquired loans transfer				815
Acquired loans ACL adjustment				1,007
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				(1,217)
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				(188)
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				4,188
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				2,891
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				(8,179)
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				(765)
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Commercial and Industrial Loans [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				(8,964)
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Other Construction [Member] | Other Loans Secured by Real Estate [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				3,202
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Consumer Loans [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				2,059
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | State and Other Political Subdivision Loans [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				2,455
Allowance for Credit Losses, ACL [Member] | ASU 2016-13 [Member] | Other Commercial Loans [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				$ 2,084