Note 17 - Derivative Financial Instruments - Outstanding Undesignated Interest Rate Swap Contracts (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Receiving [Member]
Notional amount	$ 60,872	$ 54,964
Weighted average maturity (Year)	8 years 109 days	8 years 255 days
Fair value	$ 1,879	$ 259
Paying [Member]
Notional amount	$ 60,872	$ 54,964
Weighted average maturity (Year)	8 years 109 days	8 years 255 days
Fair value	$ 1,913	$ 283

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

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Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageRemainingMaturity1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=sybt_ReceivingMember
Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
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