Note 4 - Loans and Allowance for Credit Losses on Loans - Loans Individually Evaluated for Impairment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2019
Loans with no related allowance recorded, recorded investment			$ 3,468
Loans with no related allowance recorded, unpaid principal balance			3,926
Loans with no related allowance recorded, average recorded investment	$ 2,872	$ 2,908
Loans with no related allowance recorded, interest income recognized	0	0
Loans with an allowance recorded, recorded investment			8,062
Loans with an allowance recorded, unpaid principal balance			8,062
Related allowance			1,163
Loans with an allowance recorded, average recorded investment	42	41
Loans with an allowance recorded, interest income recognized	0	0
Recorded investment			11,530
Unpaid principal balance			11,988
Average recorded investment	2,914	2,949
Interest income recognized	0	0
Commercial and Industrial Portfolio Segment [Member]
Loans with no related allowance recorded, recorded investment			174
Loans with no related allowance recorded, unpaid principal balance			174
Loans with no related allowance recorded, average recorded investment	136	164
Loans with no related allowance recorded, interest income recognized	0	0
Loans with an allowance recorded, recorded investment			8,049
Loans with an allowance recorded, unpaid principal balance			8,049
Related allowance			1,150
Loans with an allowance recorded, average recorded investment	28	27
Loans with an allowance recorded, interest income recognized	0	0
Recorded investment			8,223
Unpaid principal balance			8,223
Average recorded investment	164	191
Interest income recognized	0	0
Construction and Development Excluding Undeveloped Land Portfolio Segment [Member]
Loans with no related allowance recorded, recorded investment			0
Loans with no related allowance recorded, unpaid principal balance			0
Loans with no related allowance recorded, average recorded investment	0	80
Loans with no related allowance recorded, interest income recognized	0	0
Related allowance			0
Recorded investment			0
Unpaid principal balance			0
Average recorded investment	0	80
Interest income recognized	0	0
Undevelopment Land Portfolio Segment [Member]
Loans with no related allowance recorded, recorded investment			0
Loans with no related allowance recorded, unpaid principal balance			0
Loans with no related allowance recorded, average recorded investment	0	119
Loans with no related allowance recorded, interest income recognized	0	0
Related allowance			0
Recorded investment			0
Unpaid principal balance			0
Average recorded investment	0	119
Interest income recognized	0	0
Real Estate Mortgage Portfolio Segment [Member]
Loans with no related allowance recorded, recorded investment			3,294
Loans with no related allowance recorded, unpaid principal balance			3,752
Loans with no related allowance recorded, average recorded investment	2,736	2,545
Loans with no related allowance recorded, interest income recognized	0	0
Loans with an allowance recorded, recorded investment			13
Loans with an allowance recorded, unpaid principal balance			13
Related allowance			13
Loans with an allowance recorded, average recorded investment	14	14
Loans with an allowance recorded, interest income recognized	0	0
Recorded investment			3,307
Unpaid principal balance			3,765
Average recorded investment	2,750	2,559
Interest income recognized	0	0
Real Estate Mortgage Portfolio Segment [Member] \| Commercial Investment [Member]
Loans with no related allowance recorded, recorded investment			741
Loans with no related allowance recorded, unpaid principal balance			741
Loans with no related allowance recorded, average recorded investment	524	376
Loans with no related allowance recorded, interest income recognized	0	0
Related allowance			0
Recorded investment			741
Unpaid principal balance			741
Average recorded investment	524	376
Interest income recognized	0	0
Real Estate Mortgage Portfolio Segment [Member] \| Owner Occupied Commercial [Member]
Loans with no related allowance recorded, recorded investment			2,278
Loans with no related allowance recorded, unpaid principal balance			2,736
Loans with no related allowance recorded, average recorded investment	1,427	1,226
Loans with no related allowance recorded, interest income recognized	0	0
Related allowance			0
Recorded investment			2,278
Unpaid principal balance			2,736
Average recorded investment	1,427	1,226
Interest income recognized	0	0
Real Estate Mortgage Portfolio Segment [Member] \| One to Four Family Residential [Member]
Loans with no related allowance recorded, recorded investment			124
Loans with no related allowance recorded, unpaid principal balance			124
Loans with no related allowance recorded, average recorded investment	426	614
Loans with no related allowance recorded, interest income recognized	0	0
Loans with an allowance recorded, recorded investment			13
Loans with an allowance recorded, unpaid principal balance			13
Related allowance			13
Loans with an allowance recorded, average recorded investment	14	14
Loans with an allowance recorded, interest income recognized	0	0
Recorded investment			137
Unpaid principal balance			137
Average recorded investment	440	628
Interest income recognized	0	0
Real Estate Mortgage Portfolio Segment [Member] \| Home Equity Junior Lien [Member]
Loans with no related allowance recorded, recorded investment			151
Loans with no related allowance recorded, unpaid principal balance			151
Loans with no related allowance recorded, average recorded investment	359	329
Loans with no related allowance recorded, interest income recognized	0	0
Related allowance			0
Recorded investment			151
Unpaid principal balance			$ 151
Average recorded investment	359	329
Interest income recognized	$ 0	$ 0

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5258-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953550-111524

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRelatedAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5258-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=sybt_CommercialAndIndustrialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=sybt_ConstructionAndDevelopmentExcludingUndevelopedLandPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=sybt_UndevelopmentLandPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=sybt_RealEstateMortgagePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sybt_CommercialInvestmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sybt_OwnerOccupiedCommercialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sybt_OneToFourFamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sybt_HomeEquityJuniorLienMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: