Allowance for Loan Losses - Roll Forward Of the Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Rollforward of the allowance for loan losses
Beginning balance	$ 46,211	$ 42,737
Charge-offs	(2,065)	(1,598)
Recoveries	505	284
Net (charge-offs) recoveries	(1,560)	(1,314)
Provision for loan losses	1,750	1,500
Ending balance	46,401	42,923
Period-End Amount Allocated to:
Individually evaluated for impairment			$ 1,472	$ 3,977
Collectively evaluated for impairment			43,112	36,227
Purchased with deteriorated credit quality	46,211	42,737	46,401	42,923
Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	1,817	2,719
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	1,817	2,719	1,817	2,719
Commercial, financial, agricultural
Rollforward of the allowance for loan losses
Beginning balance	5,542	5,486
Charge-offs	(659)	(832)
Recoveries	235	57
Net (charge-offs) recoveries	(424)	(775)
Provision for loan losses	1,953	401
Ending balance	7,071	5,112
Period-End Amount Allocated to:
Individually evaluated for impairment			272	165
Collectively evaluated for impairment			6,494	4,569
Purchased with deteriorated credit quality	5,542	5,486	7,071	5,112
Commercial, financial, agricultural | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	305	378
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	305	378	305	378
Real estate – construction
Rollforward of the allowance for loan losses
Beginning balance	3,428	2,380
Charge-offs	0	0
Recoveries	4	31
Net (charge-offs) recoveries	4	31
Provision for loan losses	766	(292)
Ending balance	4,198	2,119
Period-End Amount Allocated to:
Individually evaluated for impairment			1	0
Collectively evaluated for impairment			4,197	2,119
Purchased with deteriorated credit quality	3,428	2,380	4,198	2,119
Real estate – construction | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	0	0
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	0	0	0	0
Real estate – 1-4 family mortgage
Rollforward of the allowance for loan losses
Beginning balance	12,009	14,294
Charge-offs	(671)	(275)
Recoveries	133	82
Net (charge-offs) recoveries	(538)	(193)
Provision for loan losses	(67)	(1,939)
Ending balance	11,404	12,162
Period-End Amount Allocated to:
Individually evaluated for impairment			168	1,139
Collectively evaluated for impairment			10,750	10,256
Purchased with deteriorated credit quality	12,009	14,294	11,404	12,162
Real estate – 1-4 family mortgage | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	486	767
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	486	767	486	767
Real estate – commercial mortgage
Rollforward of the allowance for loan losses
Beginning balance	23,384	19,059
Charge-offs	(613)	(227)
Recoveries	108	95
Net (charge-offs) recoveries	(505)	(132)
Provision for loan losses	(965)	3,146
Ending balance	21,914	22,073
Period-End Amount Allocated to:
Individually evaluated for impairment			1,026	2,670
Collectively evaluated for impairment			19,865	17,830
Purchased with deteriorated credit quality	23,384	19,059	21,914	22,073
Real estate – commercial mortgage | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	1,023	1,573
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	1,023	1,573	1,023	1,573
Installment loans to individuals
Rollforward of the allowance for loan losses
Beginning balance	1,848	1,518
Charge-offs	(122)	(264)
Recoveries	25	19
Net (charge-offs) recoveries	(97)	(245)
Provision for loan losses	63	184
Ending balance	1,814	1,457
Period-End Amount Allocated to:
Individually evaluated for impairment			5	3
Collectively evaluated for impairment			1,806	1,453
Purchased with deteriorated credit quality	1,848	1,518	1,814	1,457
Installment loans to individuals | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	3	1
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	$ 3	$ 1	$ 3	$ 1