Allowance for Loan Losses - Roll Forward Of the Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Allowance for loan losses:
Beginning balance	$ 46,401	$ 42,923	$ 46,211	$ 42,737
Charge-offs	(1,581)	(1,414)	(3,646)	(3,012)
Recoveries	725	890	1,230	1,174
Net (charge-offs) recoveries	(856)	(524)	(2,416)	(1,838)
Provision for loan losses charged to operations	1,810	1,750	3,560	3,250
Ending balance	47,355	44,149	47,355	44,149
Individually evaluated for impairment	1,515	3,208	1,515	3,208
Collectively evaluated for impairment	43,584	38,781	43,584	38,781
Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	2,256	2,160	2,256	2,160
Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance	7,071	5,112	5,542	5,486
Charge-offs	(457)	(304)	(1,116)	(1,136)
Recoveries	114	64	349	121
Net (charge-offs) recoveries	(343)	(240)	(767)	(1,015)
Provision for loan losses charged to operations	418	220	2,371	621
Ending balance	7,146	5,092	7,146	5,092
Individually evaluated for impairment	417	166	417	166
Collectively evaluated for impairment	6,404	4,587	6,404	4,587
Commercial, financial, agricultural | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	325	339	325	339
Real estate – construction
Allowance for loan losses:
Beginning balance	4,198	2,119	3,428	2,380
Charge-offs	0	0	0	0
Recoveries	3	3	7	34
Net (charge-offs) recoveries	3	3	7	34
Provision for loan losses charged to operations	501	458	1,267	166
Ending balance	4,702	2,580	4,702	2,580
Individually evaluated for impairment	0	2	0	2
Collectively evaluated for impairment	4,702	2,578	4,702	2,578
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	11,404	12,162	12,009	14,294
Charge-offs	(979)	(551)	(1,650)	(826)
Recoveries	83	64	216	146
Net (charge-offs) recoveries	(896)	(487)	(1,434)	(680)
Provision for loan losses charged to operations	1,149	429	1,082	(1,510)
Ending balance	11,657	12,104	11,657	12,104
Individually evaluated for impairment	76	878	76	878
Collectively evaluated for impairment	11,053	10,534	11,053	10,534
Real estate – 1-4 family mortgage | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	528	692	528	692
Real estate – commercial mortgage
Allowance for loan losses:
Beginning balance	21,914	22,073	23,384	19,059
Charge-offs	(46)	(434)	(659)	(661)
Recoveries	496	717	604	812
Net (charge-offs) recoveries	450	283	(55)	151
Provision for loan losses charged to operations	86	244	(879)	3,390
Ending balance	22,450	22,600	22,450	22,600
Individually evaluated for impairment	1,014	2,159	1,014	2,159
Collectively evaluated for impairment	20,036	19,313	20,036	19,313
Real estate – commercial mortgage | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	1,400	1,128	1,400	1,128
Installment loans to individuals
Allowance for loan losses:
Beginning balance	1,814	1,457	1,848	1,518
Charge-offs	(99)	(125)	(221)	(389)
Recoveries	29	42	54	61
Net (charge-offs) recoveries	(70)	(83)	(167)	(328)
Provision for loan losses charged to operations	(344)	399	(281)	583
Ending balance	1,400	1,773	1,400	1,773
Individually evaluated for impairment	8	3	8	3
Collectively evaluated for impairment	1,389	1,769	1,389	1,769
Installment loans to individuals | Receivables Acquired with Deteriorated Credit Quality
Allowance for loan losses:
Ending balance	$ 3	$ 1	$ 3	$ 1