LHFI and Allowance for Loan Losses, LHFI - Change in Allowance for Loan Losses (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		$ 76,733
Provision for loan losses, LHFI		17,993	$ 15,094	$ 10,957
Balance at end of period		79,290	76,733
Allowance for Loan Losses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		76,733	71,265	67,619
Transfers	[1]	1,554
Loans charged-off		(29,489)	(21,147)	(18,930)
Recoveries		12,499	11,521	11,619
Net (charge-offs) recoveries		(16,990)	(9,626)	(7,311)
Provision for loan losses, LHFI		17,993	15,094	10,957
Balance at end of period		79,290	76,733	71,265
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		7,865	9,085
Transfers	[1]	584
Loans charged-off		(123)	(79)
Recoveries		1,124	1,428
Provision for loan losses, LHFI		(2,060)	(2,569)
Balance at end of period		7,390	7,865	9,085
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		10,874	10,347
Transfers	[1]	182
Loans charged-off		(1,629)	(950)
Recoveries		646	1,833
Provision for loan losses, LHFI		(1,432)	(356)
Balance at end of period		8,641	10,874	10,347
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		23,428	20,967
Transfers	[1]	446
Loans charged-off		(1,184)	(4,231)
Recoveries		133	396
Provision for loan losses, LHFI		(447)	6,296
Balance at end of period		22,376	23,428	20,967
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		2,790	2,263
Transfers	[1]	291
Loans charged-off			(5)
Recoveries		23	69
Provision for loan losses, LHFI		346	463
Balance at end of period		3,450	2,790	2,263
Allowance for Loan Losses, LHFI [Member] | Commercial and Industrial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		22,851	22,011
Transfers	[1]	46
Loans charged-off		(18,823)	(8,286)
Recoveries		5,410	2,578
Provision for loan losses, LHFI		17,875	6,548
Balance at end of period		27,359	22,851	22,011
Allowance for Loan Losses, LHFI [Member] | Consumer Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		3,470	3,241
Transfers	[1]	5
Loans charged-off		(2,089)	(2,546)
Recoveries		2,019	1,938
Provision for loan losses, LHFI		(515)	837
Balance at end of period		2,890	3,470	3,241
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		789	859
Provision for loan losses, LHFI		201	(70)
Balance at end of period		990	789	859
Allowance for Loan Losses, LHFI [Member] | Other Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		4,666	2,492
Loans charged-off		(5,641)	(5,050)
Recoveries		3,144	3,279
Provision for loan losses, LHFI		4,025	3,945
Balance at end of period		$ 6,194	$ 4,666	$ 2,492

[1] The allowance for loan losses balance related to the remaining loans acquired in the Heritage acquisition on April 15, 2011, the Bay Bank merger on March 16, 2012 and the Reliance merger on April 7, 2017, which were transferred from acquired impaired loans to LHFI during 2018.