Allowance for Loan Losses - Investment in Loans, Net of Unearned Income on Impairment Methodology (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	$ 40,530	$ 35,278
Collectively evaluated for impairment	8,822,779	8,825,597
Loans, net of unearned income	9,054,654	9,083,129
Receivables Acquired with Deteriorated Credit Quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	191,345	222,254
Commercial, financial, agricultural
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	6,675	2,445
Collectively evaluated for impairment	1,274,775	1,264,324
Loans, net of unearned income	1,305,076	1,295,912
Commercial, financial, agricultural \| Receivables Acquired with Deteriorated Credit Quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	23,626	29,143
Real estate – construction
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	9,565	10,043
Collectively evaluated for impairment	771,966	730,625
Loans, net of unearned income	781,531	740,668
Real estate – construction \| Receivables Acquired with Deteriorated Credit Quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	0	0
Real estate – 1-4 family mortgage
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	15,976	14,238
Collectively evaluated for impairment	2,706,816	2,732,862
Loans, net of unearned income	2,765,472	2,795,343
Real estate – 1-4 family mortgage \| Receivables Acquired with Deteriorated Credit Quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	42,680	48,243
Real estate – commercial mortgage
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	7,789	8,059
Collectively evaluated for impairment	3,888,483	3,903,012
Loans, net of unearned income	4,017,969	4,051,509
Real estate – commercial mortgage \| Receivables Acquired with Deteriorated Credit Quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	121,697	140,438
Installment loans to individuals
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	525	493
Collectively evaluated for impairment	180,739	194,774
Loans, net of unearned income	184,606	199,697
Installment loans to individuals \| Receivables Acquired with Deteriorated Credit Quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	$ 3,342	$ 4,430

Investment in loans, net of unearned income on impairment methodology.

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

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-Publisher FASB
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-Topic 310
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The balance of financing receivables that were individually evaluated for impairment.

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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