Allowance for Loan Losses - Roll Forward Of the Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Allowance for loan losses:
Beginning balance	$ 47,355	$ 44,149	$ 46,211	$ 42,737
Charge-offs	(1,340)	(2,216)	(4,986)	(5,228)
Recoveries	345	448	1,575	1,622
Net (charge-offs) recoveries	(995)	(1,768)	(3,411)	(3,606)
Provision for loan losses charged to operations	2,250	2,150	5,810	5,400
Ending balance	48,610	44,531	48,610	44,531
Individually evaluated for impairment	1,280	2,928	1,280	2,928
Collectively evaluated for impairment	44,502	39,678	44,502	39,678
Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	2,828	1,925	2,828	1,925
Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance	7,146	5,092	5,542	5,486
Charge-offs	(511)	(974)	(1,627)	(2,110)
Recoveries	24	137	373	258
Net (charge-offs) recoveries	(487)	(837)	(1,254)	(1,852)
Provision for loan losses charged to operations	1,448	938	3,819	1,559
Ending balance	8,107	5,193	8,107	5,193
Individually evaluated for impairment	421	96	421	96
Collectively evaluated for impairment	7,326	4,772	7,326	4,772
Commercial, financial, agricultural | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	360	325	360	325
Real estate – construction
Allowance for loan losses:
Beginning balance	4,702	2,580	3,428	2,380
Charge-offs	0	0	0	0
Recoveries	3	67	10	101
Net (charge-offs) recoveries	3	67	10	101
Provision for loan losses charged to operations	8	161	1,275	327
Ending balance	4,713	2,808	4,713	2,808
Individually evaluated for impairment	70	9	70	9
Collectively evaluated for impairment	4,643	2,799	4,643	2,799
Real estate – construction | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	0	0	0	0
Real estate – 1-4 family mortgage
Allowance for loan losses:
Beginning balance	11,657	12,104	12,009	14,294
Charge-offs	(211)	(575)	(1,861)	(1,401)
Recoveries	119	145	335	291
Net (charge-offs) recoveries	(92)	(430)	(1,526)	(1,110)
Provision for loan losses charged to operations	(1,497)	439	(415)	(1,071)
Ending balance	10,068	12,113	10,068	12,113
Individually evaluated for impairment	70	855	70	855
Collectively evaluated for impairment	9,493	10,644	9,493	10,644
Real estate – 1-4 family mortgage | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	505	614	505	614
Real estate – commercial mortgage
Allowance for loan losses:
Beginning balance	22,450	22,600	23,384	19,059
Charge-offs	(216)	(543)	(875)	(1,204)
Recoveries	152	72	756	884
Net (charge-offs) recoveries	(64)	(471)	(119)	(320)
Provision for loan losses charged to operations	2,041	481	1,162	3,871
Ending balance	24,427	22,610	24,427	22,610
Individually evaluated for impairment	715	1,963	715	1,963
Collectively evaluated for impairment	21,751	19,662	21,751	19,662
Real estate – commercial mortgage | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	1,961	985	1,961	985
Installment loans to individuals
Allowance for loan losses:
Beginning balance	1,400	1,773	1,848	1,518
Charge-offs	(402)	(124)	(623)	(513)
Recoveries	47	27	101	88
Net (charge-offs) recoveries	(355)	(97)	(522)	(425)
Provision for loan losses charged to operations	250	131	(31)	714
Ending balance	1,295	1,807	1,295	1,807
Individually evaluated for impairment	4	5	4	5
Collectively evaluated for impairment	1,289	1,801	1,289	1,801
Installment loans to individuals | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	$ 2	$ 1	$ 2	$ 1