Allowance for Loan Losses - Investment in Loans, Net of Unearned Income on Impairment Methodology (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	$ 38,606	$ 35,278
Collectively evaluated for impairment	8,840,841	8,825,597
Loans, net of unearned income	9,088,293	9,083,129
Receivables Acquired with Deteriorated Credit Quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	208,846	222,254
Commercial, financial, agricultural
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	5,809	2,445
Collectively evaluated for impairment	1,277,801	1,264,324
Loans, net of unearned income	1,308,457	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	24,847	29,143
Real estate – construction
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	8,805	10,043
Collectively evaluated for impairment	732,268	730,625
Loans, net of unearned income	741,073	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	13,952	14,238
Collectively evaluated for impairment	2,711,397	2,732,862
Loans, net of unearned income	2,769,173	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	43,824	48,243
Real estate – commercial mortgage
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	9,442	8,059
Collectively evaluated for impairment	3,937,908	3,903,012
Loans, net of unearned income	4,083,632	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	136,282	140,438
Installment loans to individuals
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	598	493
Collectively evaluated for impairment	181,467	194,774
Loans, net of unearned income	185,958	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	$ 3,893	$ 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
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The balance of financing receivables that were individually evaluated for impairment.

+ References

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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

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-Publisher FASB
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-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

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Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

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-Name Accounting Standards Codification
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-SubTopic 10
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