Loans and Allowance for Loan Losses - Classified as troubled debt restructurings (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) Contract	Mar. 31, 2017 USD ($) Contract
Financing Receivable, Modifications [Line Items]
Number of contracts, covered \| Contract	0	2
Post modification outstanding recorded investment, covered \| $	$ 0	$ 103
Number of subsequent default contracts, covered \| Contract	0	0
Recorded investment at subsequent default, covered \| $	$ 0	$ 0
Commercial, Financial and Agricultural
Financing Receivable, Modifications [Line Items]
Number of Contracts \| Contract	2	10
Post-Modification Outstanding Recorded Investment \| $	$ 490	$ 80,790
Number of subsequent default contracts \| Contract	0	0
Recorded investment at subsequent default \| $	$ 0	$ 0
Commercial Real Estate \| Real estate – construction
Financing Receivable, Modifications [Line Items]
Number of Contracts \| Contract	1	0
Post-Modification Outstanding Recorded Investment \| $	$ 32	$ 0
Number of subsequent default contracts \| Contract	0	0
Recorded investment at subsequent default \| $	$ 0	$ 0
Commercial Real Estate \| Commercial real estate – mortgage
Financing Receivable, Modifications [Line Items]
Number of Contracts \| Contract	1	0
Post-Modification Outstanding Recorded Investment \| $	$ 1,383	$ 0
Number of subsequent default contracts \| Contract	0	0
Recorded investment at subsequent default \| $	$ 0	$ 0
Residential Real Estate \| Residential real estate – mortgage
Financing Receivable, Modifications [Line Items]
Number of Contracts \| Contract	17	13
Post-Modification Outstanding Recorded Investment \| $	$ 4,119	$ 2,772
Number of subsequent default contracts \| Contract	1	1
Recorded investment at subsequent default \| $	$ 80	$ 505
Residential Real Estate \| Equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts \| Contract	0	17
Post-Modification Outstanding Recorded Investment \| $	$ 0	$ 546
Number of subsequent default contracts \| Contract	0	0
Recorded investment at subsequent default \| $	$ 0	$ 0
Residential Real Estate \| Equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts \| Contract	7	10
Post-Modification Outstanding Recorded Investment \| $	$ 1,271	$ 408
Number of subsequent default contracts \| Contract	2	0
Recorded investment at subsequent default \| $	$ 132	$ 0
Consumer \| Credit card
Financing Receivable, Modifications [Line Items]
Number of Contracts \| Contract	0	0
Post-Modification Outstanding Recorded Investment \| $	$ 0	$ 0
Number of subsequent default contracts \| Contract	0	0
Recorded investment at subsequent default \| $	$ 0	$ 0
Consumer \| Consumer direct
Financing Receivable, Modifications [Line Items]
Number of Contracts \| Contract	0	0
Post-Modification Outstanding Recorded Investment \| $	$ 0	$ 0
Number of subsequent default contracts \| Contract	0	0
Recorded investment at subsequent default \| $	$ 0	$ 0
Consumer \| Consumer indirect
Financing Receivable, Modifications [Line Items]
Number of Contracts \| Contract	0	10
Post-Modification Outstanding Recorded Investment \| $	$ 0	$ 168
Number of subsequent default contracts \| Contract	0	1
Recorded investment at subsequent default \| $	$ 0	$ 22

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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