Allowance for Loan Losses - Changes in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Rollforward of the allowance for loan losses
Beginning balance				$ 46,211				$ 42,737	$ 46,211	$ 42,737	$ 42,437
Charge-offs									(6,428)	(7,008)	(9,471)
Recoveries									2,433	2,932	2,241
Net charge-offs									(3,995)	(4,076)	(7,230)
Provision for loan losses										7,550	6,604
Benefit attributable to FDIC loss share agreements											(265)
Recoveries payable to FDIC											1,191
Provision for loan losses charged to operations	$ 1,000	$ 2,250	$ 1,810	1,750	$ 2,150	$ 2,150	$ 1,750	1,500	6,810	7,550	7,530
Ending balance	49,026				46,211				49,026	46,211	42,737
Period-End Amount Allocated to:
Individually evaluated for impairment												$ 1,514	$ 2,674	$ 4,141
Collectively evaluated for impairment												44,960	41,760	35,776
Purchased with deteriorated credit quality	49,026			46,211	46,211			42,737	46,211	42,737	42,437	49,026	46,211	42,737
Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Beginning balance				1,777				2,820	1,777	2,820
Ending balance	2,552				1,777				2,552	1,777	2,820
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	2,552			1,777	1,777			2,820	1,777	2,820	2,820	2,552	1,777	2,820
Commercial, financial, agricultural
Rollforward of the allowance for loan losses
Beginning balance				5,542				5,486	5,542	5,486	4,186
Charge-offs									(2,415)	(2,874)	(2,725)
Recoveries									618	422	331
Net charge-offs									(1,797)	(2,452)	(2,394)
Provision for loan losses										2,508	3,716
Benefit attributable to FDIC loss share agreements											(61)
Recoveries payable to FDIC											39
Provision for loan losses charged to operations									4,524		3,694
Ending balance	8,269				5,542				8,269	5,542	5,486
Period-End Amount Allocated to:
Individually evaluated for impairment												336	190	446
Collectively evaluated for impairment												7,772	5,040	4,668
Purchased with deteriorated credit quality	8,269			5,542	5,542			5,486	5,542	5,486	4,186	8,269	5,542	5,486
Commercial, financial, agricultural | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Beginning balance				312				372	312	372
Ending balance	161				312				161	312	372
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	161			312	312			372	312	372	372	161	312	372
Real estate – construction
Rollforward of the allowance for loan losses
Beginning balance				3,428				2,380	3,428	2,380	1,852
Charge-offs									(51)	0	0
Recoveries									13	105	47
Net charge-offs									(38)	105	47
Provision for loan losses										943	364
Benefit attributable to FDIC loss share agreements											0
Recoveries payable to FDIC											117
Provision for loan losses charged to operations									1,365		481
Ending balance	4,755				3,428				4,755	3,428	2,380
Period-End Amount Allocated to:
Individually evaluated for impairment												68	4	1
Collectively evaluated for impairment												4,687	3,424	2,379
Purchased with deteriorated credit quality	4,755			3,428	3,428			2,380	3,428	2,380	1,852	4,755	3,428	2,380
Real estate – construction | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Beginning balance				0				0	0	0
Ending balance	0				0				0	0	0
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	0			0	0			0	0	0	0	0	0	0
Real estate – 1-4 family mortgage
Rollforward of the allowance for loan losses
Beginning balance				12,009				14,294	12,009	14,294	13,908
Charge-offs									(2,023)	(1,713)	(3,906)
Recoveries									573	733	997
Net charge-offs									(1,450)	(980)	(2,909)
Provision for loan losses										(1,305)	2,616
Benefit attributable to FDIC loss share agreements											(115)
Recoveries payable to FDIC											794
Provision for loan losses charged to operations									(420)		3,295
Ending balance	10,139				12,009				10,139	12,009	14,294
Period-End Amount Allocated to:
Individually evaluated for impairment												79	606	1,134
Collectively evaluated for impairment												9,572	10,831	12,319
Purchased with deteriorated credit quality	10,139			12,009	12,009			14,294	12,009	14,294	13,908	10,139	12,009	14,294
Real estate – 1-4 family mortgage | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Beginning balance				572				841	572	841
Ending balance	488				572				488	572	841
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	488			572	572			841	572	841	841	488	572	841
Real estate – commercial mortgage
Rollforward of the allowance for loan losses
Beginning balance				23,384				19,059	23,384	19,059	21,111
Charge-offs									(1,197)	(1,791)	(2,123)
Recoveries									1,108	1,565	757
Net charge-offs									(89)	(226)	(1,366)
Provision for loan losses										4,551	(879)
Benefit attributable to FDIC loss share agreements											(48)
Recoveries payable to FDIC											241
Provision for loan losses charged to operations									1,197		(686)
Ending balance	24,492				23,384				24,492	23,384	19,059
Period-End Amount Allocated to:
Individually evaluated for impairment												1,027	1,867	2,445
Collectively evaluated for impairment												21,564	20,625	15,008
Purchased with deteriorated credit quality	24,492			23,384	23,384			19,059	23,384	19,059	21,111	24,492	23,384	19,059
Real estate – commercial mortgage | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Beginning balance				892				1,606	892	1,606
Ending balance	1,901				892				1,901	892	1,606
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	1,901			892	892			1,606	892	1,606	1,606	1,901	892	1,606
Installment and Other
Rollforward of the allowance for loan losses
Beginning balance				1,848				1,518	1,848	1,518	1,380
Charge-offs									(742)	(630)	(717)
Recoveries									121	107	109
Net charge-offs									(621)	(523)	(608)
Provision for loan losses										853	787
Benefit attributable to FDIC loss share agreements											(41)
Recoveries payable to FDIC											0
Provision for loan losses charged to operations									144		746
Ending balance	1,371				1,848				1,371	1,848	1,518
Period-End Amount Allocated to:
Individually evaluated for impairment												4	7	115
Collectively evaluated for impairment												1,365	1,840	1,402
Purchased with deteriorated credit quality	1,371			1,848	1,848			1,518	1,848	1,518	1,380	1,371	1,848	1,518
Installment and Other | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Beginning balance				1				1	1	1
Ending balance	2				1				2	1	1
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	$ 2			$ 1	$ 1			$ 1	$ 1	$ 1	$ 1	$ 2	$ 1	$ 1