Allowance for Loan Losses - Roll Forward Of the Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Rollforward of the allowance for loan losses
Beginning balance	$ 44,149	$ 44,098	$ 42,737	$ 42,437
Charge-offs	(2,216)	(1,303)	(5,228)	(4,070)
Recoveries	448	479	1,622	1,677
Net (charge-offs) recoveries	(1,768)	(824)	(3,606)	(2,393)
Provision for loan losses		2,676		5,619
Benefit attributable to FDIC loss-share agreements		(149)		(265)
Recoveries payable to FDIC		123		526
Provision for loan losses charged to operations	2,150	2,650	5,400	5,880
Ending balance	44,531	45,924	44,531	45,924
Period-End Amount Allocated to:
Individually evaluated for impairment					$ 2,928	$ 8,899
Collectively evaluated for impairment					39,678	33,607
Purchased with deteriorated credit quality	44,149	44,098	42,737	42,437	44,531	45,924
Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	1,925	3,418	1,925	3,418
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	1,925	3,418	1,925	3,418	1,925	3,418
Commercial, financial, agricultural
Rollforward of the allowance for loan losses
Beginning balance	5,092	4,512	5,486	4,186
Charge-offs	(974)	(394)	(2,110)	(1,099)
Recoveries	137	85	258	243
Net (charge-offs) recoveries	(837)	(309)	(1,852)	(856)
Provision for loan losses		1,308		2,174
Benefit attributable to FDIC loss-share agreements		(61)		(61)
Recoveries payable to FDIC		4		11
Provision for loan losses charged to operations	938	1,251	1,559	2,124
Ending balance	5,193	5,454	5,193	5,454
Period-End Amount Allocated to:
Individually evaluated for impairment					96	1,004
Collectively evaluated for impairment					4,772	4,002
Purchased with deteriorated credit quality	5,092	4,512	5,486	4,186	5,193	5,454
Commercial, financial, agricultural | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	325	448	325	448
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	325	448	325	448	325	448
Real estate – construction
Rollforward of the allowance for loan losses
Beginning balance	2,580	2,269	2,380	1,852
Charge-offs		0	0	0
Recoveries	67	4	101	15
Net (charge-offs) recoveries	67	4	101	15
Provision for loan losses		(52)		348
Benefit attributable to FDIC loss-share agreements		0		0
Recoveries payable to FDIC		2		8
Provision for loan losses charged to operations	161	(50)	327	356
Ending balance	2,808	2,223	2,808	2,223
Period-End Amount Allocated to:
Individually evaluated for impairment					9	2
Collectively evaluated for impairment					2,799	2,221
Purchased with deteriorated credit quality	2,580	2,269	2,380	1,852	2,808	2,223
Real estate – construction | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	0	0	0	0
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	0	0	0	0	0	0
Real estate – 1-4 family mortgage
Rollforward of the allowance for loan losses
Beginning balance	12,104	14,219	14,294	13,908
Charge-offs	(575)	(242)	(1,401)	(745)
Recoveries	145	188	291	753
Net (charge-offs) recoveries	(430)	(54)	(1,110)	8
Provision for loan losses		1,154		1,333
Benefit attributable to FDIC loss-share agreements		0		(115)
Recoveries payable to FDIC		93		278
Provision for loan losses charged to operations	439	1,247	(1,071)	1,496
Ending balance	12,113	15,412	12,113	15,412
Period-End Amount Allocated to:
Individually evaluated for impairment					855	5,144
Collectively evaluated for impairment					10,644	9,542
Purchased with deteriorated credit quality	12,104	14,219	14,294	13,908	12,113	15,412
Real estate – 1-4 family mortgage | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	614	726	614	726
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	614	726	614	726	614	726
Real estate – commercial mortgage
Rollforward of the allowance for loan losses
Beginning balance	22,600	21,683	19,059	21,111
Charge-offs	(543)	(466)	(1,204)	(1,653)
Recoveries	72	181	884	582
Net (charge-offs) recoveries	(471)	(285)	(320)	(1,071)
Provision for loan losses		(87)		1,067
Benefit attributable to FDIC loss-share agreements		(47)		(48)
Recoveries payable to FDIC		24		229
Provision for loan losses charged to operations	481	(110)	3,871	1,248
Ending balance	22,610	21,288	22,610	21,288
Period-End Amount Allocated to:
Individually evaluated for impairment					1,963	2,635
Collectively evaluated for impairment					19,662	16,410
Purchased with deteriorated credit quality	22,600	21,683	19,059	21,111	22,610	21,288
Real estate – commercial mortgage | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	985	2,243	985	2,243
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	985	2,243	985	2,243	985	2,243
Installment loans to individuals
Rollforward of the allowance for loan losses
Beginning balance	1,773	1,415	1,518	1,380
Charge-offs	(124)	(201)	(513)	(573)
Recoveries	27	21	88	84
Net (charge-offs) recoveries	(97)	(180)	(425)	(489)
Provision for loan losses		353		697
Benefit attributable to FDIC loss-share agreements		(41)		(41)
Recoveries payable to FDIC		0		0
Provision for loan losses charged to operations	131	312	714	656
Ending balance	1,807	1,547	1,807	1,547
Period-End Amount Allocated to:
Individually evaluated for impairment					5	114
Collectively evaluated for impairment					1,801	1,432
Purchased with deteriorated credit quality	1,773	1,415	1,518	1,380	1,807	1,547
Installment loans to individuals | Receivables Acquired with Deteriorated Credit Quality
Rollforward of the allowance for loan losses
Ending balance	1	1	1	1
Period-End Amount Allocated to:
Purchased with deteriorated credit quality	$ 1	$ 1	$ 1	$ 1	$ 1	$ 1