Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Loan Portfolio Held for Investment (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Loan Portfolio [Abstract]
Total LHFI	$ 10,152,869	$ 9,824,524
Less allowance for credit losses (ACL), LHFI	104,032	117,306
Net LHFI	10,048,837	9,707,218
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	532,637	514,056
Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	1,302,663	1,216,400
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	507,733	524,732
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	1,078,622	1,065,964
Other Construction [Member] | Other Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	827,665	794,983
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	2,819,662	2,709,026
Commercial and Industrial Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	1,326,605	1,309,078
Consumer Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	156,075	164,386
State and Other Political Subdivision Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	1,136,764	1,000,776
Other Commercial Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	$ 464,443	$ 525,123