Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Aging Analysis of Past Due and Nonaccrual LHFI by Loan Type (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		$ 12,627	$ 17,691
Nonaccrual		53,226	61,624
Current Loans		9,269,775	8,756,553
Total LHFI		9,335,628	8,835,868
Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		10,393	14,383
Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		1,592	2,452
Past Due 90 Days or More [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due	[1]	642	856
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		636	284
Nonaccrual		897	2,218
Current Loans		1,161,258	1,054,099
Total LHFI		1,162,791	1,056,601
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		380	284
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		256
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		6,405	10,869
Nonaccrual		16,810	14,718
Current Loans		1,832,698	1,799,905
Total LHFI		1,855,913	1,825,492
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		5,254	8,600
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		940	1,700
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 90 Days or More [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due	[1]	211	569
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		1,698	1,887
Nonaccrual		7,700	9,621
Current Loans		2,465,847	2,209,406
Total LHFI		2,475,245	2,220,914
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		1,698	1,887
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		8	296
Nonaccrual		1,032	927
Current Loans		723,440	542,597
Total LHFI		724,480	543,820
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		8	197
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due			99
Commercial and Industrial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		668	1,646
Nonaccrual		21,775	23,938
Current Loans		1,455,453	1,513,131
Total LHFI		1,477,896	1,538,715
Commercial and Industrial Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		617	1,346
Commercial and Industrial Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		12	300
Commercial and Industrial Loans [Member] | Past Due 90 Days or More [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due	[1]	39
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		2,980	2,440
Nonaccrual		108	205
Current Loans		172,650	179,803
Total LHFI		175,738	182,448
Consumer Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		2,208	1,800
Consumer Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		380	353
Consumer Loans [Member] | Past Due 90 Days or More [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due	[1]	392	287
State and Other Political Subdivision Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		76	186
Nonaccrual		4,079	8,595
Current Loans		963,789	965,037
Total LHFI		967,944	973,818
State and Other Political Subdivision Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		76	186
Other Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		156	83
Nonaccrual		825	1,402
Current Loans		494,640	492,575
Total LHFI		495,621	494,060
Other Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		152	$ 83
Other Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due		$ 4

[1] Past due 90 days or more but still accruing interest.