Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Change in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 117,306
PCL	(10,501)	$ 20,581
Balance at end of period	109,191
Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	117,306	84,277
Loans charged-off	(1,245)	(5,545)
Recoveries	3,631	2,468
Net (charge-offs) recoveries	2,386	(3,077)
PCL	(10,501)	20,581
Balance at end of period	109,191	100,564
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	6,854	6,371
Recoveries	766	94
PCL	(2,562)	2,802
Balance at end of period	5,058	9,079
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	9,928	5,888
Loans charged-off	(26)	(64)
Recoveries	71	63
PCL	(1,306)	1,636
Balance at end of period	8,667	11,711
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	5,143	3,044
Loans charged-off		(19)
Recoveries	100	93
PCL	(1,490)	2,033
Balance at end of period	3,753	8,042
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	48,523	26,158
Loans charged-off		(2,448)
Recoveries	30	61
PCL	(2,115)	12,535
Balance at end of period	46,438	28,127
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	7,382	4,024
Loans charged-off		(8)
Recoveries	6	6
PCL	(1,618)	2,016
Balance at end of period	5,770	5,273
Allowance for Credit Losses, ACL [Member] | Commercial and Industrial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	14,851	25,992
Loans charged-off	(23)	(982)
Recoveries	1,287	542
PCL	4,051	(2,024)
Balance at end of period	20,166	14,564
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	8,158	1,889
Recoveries	1	19
PCL	(3,035)	2,601
Balance at end of period	5,124	7,711
Allowance for Credit Losses, ACL [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	5,838	3,379
Loans charged-off	(442)	(690)
Recoveries	362	473
PCL	(1,008)	1,375
Balance at end of period	4,750	6,596
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	3,190	2,229
PCL	(175)	(1,243)
Balance at end of period	3,015	3,441
Allowance for Credit Losses, ACL [Member] | Other Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	7,439	5,303
Loans charged-off	(754)	(1,334)
Recoveries	1,008	1,117
PCL	(1,243)	(1,150)
Balance at end of period	$ 6,450	6,020
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