Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Summary of Balance in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Total	$ 104,032		$ 117,306
Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	4,249		4,379
Collectively Evaluated for Credit Loss	99,783		112,927
Total	104,032	$ 109,191	117,306	$ 119,188	$ 100,564	$ 84,277
Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	32,878		43,409
Collectively Evaluated for Credit Loss	10,119,991		9,781,115
Total	10,152,869		9,824,524
Commercial and Industrial Loans [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	577		579
Collectively Evaluated for Credit Loss	13,396		14,272
Total	13,973	20,166	14,851	12,550	14,564	25,992
Commercial and Industrial Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	4,474		14,076
Collectively Evaluated for Credit Loss	1,322,131		1,295,002
Total	1,326,605		1,309,078
Consumer Loans [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively Evaluated for Credit Loss	4,876		5,838
Total	4,876	4,750	5,838	6,397	6,596	3,379
Consumer Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively Evaluated for Credit Loss	156,075		164,386
Total	156,075		164,386
State and Other Political Subdivision Loans [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	1,584		1,700
Collectively Evaluated for Credit Loss	1,649		1,490
Total	3,233	3,015	3,190	3,414	3,441	2,229
State and Other Political Subdivision Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	3,854		3,970
Collectively Evaluated for Credit Loss	1,132,910		996,806
Total	1,136,764		1,000,776
Other Commercial Loans [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	2,088		2,100
Collectively Evaluated for Credit Loss	5,186		5,339
Total	7,274	6,450	7,439	6,452	6,020	5,303
Other Commercial Loans [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	5,451		5,615
Collectively Evaluated for Credit Loss	458,992		519,508
Total	464,443		525,123
Loans Secured by Real Estate [Member] | Construction, Land Development and Other Land [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively Evaluated for Credit Loss	5,110		6,854
Total	5,110	5,058	6,854	11,940	9,079	6,371
Loans Secured by Real Estate [Member] | Construction, Land Development and Other Land [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	5,903		5,756
Collectively Evaluated for Credit Loss	526,734		508,300
Total	532,637		514,056
Loans Secured by Real Estate [Member] | Other Secured by 1-4 Family Residential Properties [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively Evaluated for Credit Loss	10,399		9,928
Total	10,399	8,667	9,928	12,716	11,711	5,888
Loans Secured by Real Estate [Member] | Other Secured by 1-4 Family Residential Properties [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss			454
Collectively Evaluated for Credit Loss	507,733		524,278
Total	507,733		524,732
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively Evaluated for Credit Loss	44,416		48,523
Total	44,416	46,438	48,523	36,417	28,127	26,158
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	11,763		12,037
Collectively Evaluated for Credit Loss	2,807,899		2,696,989
Total	2,819,662		2,709,026
Loans Secured by Real Estate [Member] | Other Real Estate Secured [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively Evaluated for Credit Loss	5,311		7,382
Total	5,311	5,770	7,382	7,600	5,273	4,024
Loans Secured by Real Estate [Member] | Other Real Estate Secured [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	57		60
Collectively Evaluated for Credit Loss	1,078,565		1,065,904
Total	1,078,622		1,065,964
Other Loans Secured by Real Estate [Member] | Other Construction [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively Evaluated for Credit Loss	6,530		8,158
Total	6,530	5,124	8,158	10,803	7,711	1,889
Other Loans Secured by Real Estate [Member] | Other Construction [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively Evaluated for Credit Loss	827,665		794,983
Total	827,665		794,983
Other Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Collectively Evaluated for Credit Loss	2,910		5,143
Total	2,910	$ 3,753	5,143	$ 10,899	$ 8,042	$ 3,044
Other Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member] | Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually Evaluated for Credit Loss	1,376		1,441
Collectively Evaluated for Credit Loss	1,301,287		1,214,959
Total	$ 1,302,663		$ 1,216,400