Allowance for Loan Losses - Investment in Loans, Net of Unearned Income on Impairment Methodology (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	$ 26,747	$ 27,992
Collectively evaluated for impairment	7,176,982	5,902,959
Loans, net of unearned income	7,448,608	6,202,709
Receivables Acquired with Deteriorated Credit Quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	244,879	271,758
Commercial, financial, agricultural
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	2,291	1,886
Collectively evaluated for impairment	989,185	703,610
Loans, net of unearned income	1,008,935	717,490
Commercial, financial, agricultural \| Receivables Acquired with Deteriorated Credit Quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	17,459	11,994
Real estate – construction
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	2,730	662
Collectively evaluated for impairment	574,990	551,177
Loans, net of unearned income	577,720	552,679
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	840
Real estate – 1-4 family mortgage
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	13,347	12,088
Collectively evaluated for impairment	2,222,736	1,794,137
Loans, net of unearned income	2,295,852	1,878,177
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	59,769	71,952
Real estate – commercial mortgage
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	8,078	13,079
Collectively evaluated for impairment	3,216,345	2,700,829
Loans, net of unearned income	3,390,389	2,898,895
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	165,966	184,987
Installment loans to individuals
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	301	277
Collectively evaluated for impairment	173,726	153,206
Loans, net of unearned income	175,712	155,468
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	$ 1,685	$ 1,985

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

No definition available.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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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://www.xbrl.org/2003/role/presentationRef
-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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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