Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Change in Allowance for Loan Losses (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		$ 79,290
Provision for loan losses, LHFI		10,797	$ 17,993	$ 15,094
Balance at end of period		84,277	79,290
Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		79,290	76,733	71,265
Transfers	[1]		1,554
Loans charged-off		(14,481)	(29,489)	(21,147)
Recoveries		8,671	12,499	11,521
Net (charge-offs) recoveries		(5,810)	(16,990)	(9,626)
Provision for loan losses, LHFI		10,797	17,993	15,094
Balance at end of period		84,277	79,290	76,733
Allowance for Loan Losses, LHFI [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		7,390	7,865
Transfers	[1]		584
Loans charged-off		(40)	(123)
Recoveries		894	1,124
Provision for loan losses, LHFI		16	(2,060)
Balance at end of period		8,260	7,390	7,865
Allowance for Loan Losses, LHFI [Member] | 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		8,641	10,874
Transfers	[1]		182
Loans charged-off		(531)	(1,629)
Recoveries		666	646
Provision for loan losses, LHFI		156	(1,432)
Balance at end of period		8,932	8,641	10,874
Allowance for Loan Losses, LHFI [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		22,376	23,428
Transfers	[1]		446
Loans charged-off		(322)	(1,184)
Recoveries		472	133
Provision for loan losses, LHFI		3,632	(447)
Balance at end of period		26,158	22,376	23,428
Allowance for Loan Losses, LHFI [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		3,450	2,790
Transfers	[1]		291
Recoveries		29	23
Provision for loan losses, LHFI		545	346
Balance at end of period		4,024	3,450	2,790
Allowance for Loan Losses, LHFI [Member] | Commercial and Industrial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		27,359	22,851
Transfers	[1]		46
Loans charged-off		(5,344)	(18,823)
Recoveries		1,257	5,410
Provision for loan losses, LHFI		2,720	17,875
Balance at end of period		25,992	27,359	22,851
Allowance for Loan Losses, LHFI [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		2,890	3,470
Transfers	[1]		5
Loans charged-off		(2,278)	(2,089)
Recoveries		1,829	2,019
Provision for loan losses, LHFI		938	(515)
Balance at end of period		3,379	2,890	3,470
Allowance for Loan Losses, LHFI [Member] | State and Other Political Subdivision Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		990	789
Provision for loan losses, LHFI		1,239	201
Balance at end of period		2,229	990	789
Allowance for Loan Losses, LHFI [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		6,194	4,666
Loans charged-off		(5,966)	(5,641)
Recoveries		3,524	3,144
Provision for loan losses, LHFI		1,551	4,025
Balance at end of period		$ 5,303	$ 6,194	$ 4,666

[1] The allowance for loan losses balance related to the remaining loans acquired in the Bay Bank, Heritage and Reliance acquisitions, which were transferred from acquired impaired loans to LHFI during 2018.