Note 5 - Loans - Loans Individually Evaluated for Impairment (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loans with no related allowance recorded, recorded investment	$ 3,468	$ 2,611	$ 7,332
Loans with no related allowance recorded, unpaid principal balance	3,926	3,766	9,072
Loans with no related allowance recorded, average recorded investment	3,019	3,948	4,304
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	8,062	42	48
Loans with an allowance recorded, unpaid principal balance	8,062	42	48
Related allowance	1,163	42	48
Loans with an allowance recorded, average recorded investment	1,644	2,786	1,981
Loans with an allowance recorded, interest income recognized	0	3	78
Recorded investment	11,530	2,653	7,380
Unpaid principal balance	11,988	3,808	9,120
Average recorded investment	4,663	6,734	6,285
Interest income recognized	0	3	78
Commercial and Industrial Portfolio Segment [Member]
Loans with no related allowance recorded, recorded investment	174	192	1,142
Loans with no related allowance recorded, unpaid principal balance	174	707	2,202
Loans with no related allowance recorded, average recorded investment	166	161	411
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	8,049	28	34
Loans with an allowance recorded, unpaid principal balance	8,049	28	34
Related allowance	1,150	28	34
Loans with an allowance recorded, average recorded investment	1,631	1,851	1,882
Loans with an allowance recorded, interest income recognized	0	2	78
Recorded investment	8,223	220	1,176
Unpaid principal balance	8,223	735	2,236
Average recorded investment	1,797	2,012	2,293
Interest income recognized	0	2	78
Construction and Development Excluding Undeveloped Land Portfolio Segment [Member]
Loans with no related allowance recorded, recorded investment	0	318	664
Loans with no related allowance recorded, unpaid principal balance	0	489	834
Loans with no related allowance recorded, average recorded investment	64	437	559
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	0	0	0
Loans with an allowance recorded, unpaid principal balance	0	0	0
Related allowance	0	0	0
Loans with an allowance recorded, average recorded investment	0	0	0
Loans with an allowance recorded, interest income recognized	0	0	0
Recorded investment	0	318	664
Unpaid principal balance	0	489	834
Average recorded investment	64	437	559
Interest income recognized	0	0	0
Undevelopment Land Portfolio Segment [Member]
Loans with no related allowance recorded, recorded investment	0	474	474
Loans with no related allowance recorded, unpaid principal balance	0	506	506
Loans with no related allowance recorded, average recorded investment	95	474	425
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	0	0	0
Loans with an allowance recorded, unpaid principal balance	0	0	0
Related allowance	0	0	0
Loans with an allowance recorded, average recorded investment	0	24	48
Loans with an allowance recorded, interest income recognized	0	0	0
Recorded investment	0	474	474
Unpaid principal balance	0	506	506
Average recorded investment	95	498	473
Interest income recognized	0	0	0
Real Estate Mortgage Portfolio Segment [Member]
Loans with no related allowance recorded, recorded investment	3,294	1,627	5,052
Loans with no related allowance recorded, unpaid principal balance	3,752	2,064	5,530
Loans with no related allowance recorded, average recorded investment	2,694	2,853	2,909
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	13	14	14
Loans with an allowance recorded, unpaid principal balance	13	14	14
Related allowance	13	14	14
Loans with an allowance recorded, average recorded investment	13	911	5
Loans with an allowance recorded, interest income recognized	0	1	0
Recorded investment	3,307	1,641	5,066
Unpaid principal balance	3,765	2,078	5,544
Average recorded investment	2,707	3,764	2,914
Interest income recognized	0	1	0
Real Estate Mortgage Portfolio Segment [Member] \| Commercial Investment [Member]
Loans with no related allowance recorded, recorded investment	741	138	52
Loans with no related allowance recorded, unpaid principal balance	741	138	53
Loans with no related allowance recorded, average recorded investment	448	35	110
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	0	0	0
Loans with an allowance recorded, unpaid principal balance	0	0	0
Related allowance	0	0	0
Loans with an allowance recorded, average recorded investment	0	0	0
Loans with an allowance recorded, interest income recognized	0	0	0
Recorded investment	741	138	52
Unpaid principal balance	741	138	53
Average recorded investment	448	35	110
Interest income recognized	0	0	0
Real Estate Mortgage Portfolio Segment [Member] \| Owner Occupied Commercial [Member]
Loans with no related allowance recorded, recorded investment	2,278	586	3,332
Loans with no related allowance recorded, unpaid principal balance	2,736	1,023	3,789
Loans with no related allowance recorded, average recorded investment	1,437	1,503	1,678
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	0	0	0
Loans with an allowance recorded, unpaid principal balance	0	0	0
Related allowance	0	0	0
Loans with an allowance recorded, average recorded investment	0	897	0
Loans with an allowance recorded, interest income recognized	0	0	0
Recorded investment	2,278	586	3,332
Unpaid principal balance	2,736	1,023	3,789
Average recorded investment	1,437	2,400	1,678
Interest income recognized	0	0	0
Real Estate Mortgage Portfolio Segment [Member] \| One to Four Family Residential [Member]
Loans with no related allowance recorded, recorded investment	124	760	1,637
Loans with no related allowance recorded, unpaid principal balance	124	760	1,657
Loans with no related allowance recorded, average recorded investment	516	1,242	935
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	13	14	14
Loans with an allowance recorded, unpaid principal balance	13	14	14
Related allowance	13	14	14
Loans with an allowance recorded, average recorded investment	13	14	5
Loans with an allowance recorded, interest income recognized	0	1	0
Recorded investment	137	774	1,651
Unpaid principal balance	137	774	1,671
Average recorded investment	529	1,256	940
Interest income recognized	0	1	0
Real Estate Mortgage Portfolio Segment [Member] \| Home Equity First Lien [Member]
Loans with no related allowance recorded, recorded investment	0	0	0
Loans with no related allowance recorded, unpaid principal balance	0	0	0
Loans with no related allowance recorded, average recorded investment	0	0	0
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	0	0	0
Loans with an allowance recorded, unpaid principal balance	0	0	0
Related allowance	0	0	0
Loans with an allowance recorded, average recorded investment	0	0	0
Loans with an allowance recorded, interest income recognized	0	0	0
Recorded investment	0	0	0
Unpaid principal balance	0	0	0
Average recorded investment	0	0	0
Interest income recognized	0	0	0
Real Estate Mortgage Portfolio Segment [Member] \| Home Equity Junior Lien [Member]
Loans with no related allowance recorded, recorded investment	151	143	31
Loans with no related allowance recorded, unpaid principal balance	151	143	31
Loans with no related allowance recorded, average recorded investment	293	73	186
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	0	0	0
Loans with an allowance recorded, unpaid principal balance	0	0	0
Related allowance	0	0	0
Loans with an allowance recorded, average recorded investment	0	0	0
Loans with an allowance recorded, interest income recognized	0	0	0
Recorded investment	151	143	31
Unpaid principal balance	151	143	31
Average recorded investment	293	73	186
Interest income recognized	0	0	0
Consumer Portfolio Segment [Member]
Loans with no related allowance recorded, recorded investment	0	0	0
Loans with no related allowance recorded, unpaid principal balance	0	0	0
Loans with no related allowance recorded, average recorded investment	0	23	0
Loans with no related allowance recorded, interest income recognized	0	0	0
Loans with an allowance recorded, recorded investment	0	0	0
Loans with an allowance recorded, unpaid principal balance	0	0	0
Related allowance	0	0	0
Loans with an allowance recorded, average recorded investment	0	0	46
Loans with an allowance recorded, interest income recognized	0	0	0
Recorded investment	0	0	0
Unpaid principal balance	0	0	0
Average recorded investment	0	23	46
Interest income recognized	$ 0	$ 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=118936363&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=118936363&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=118936363&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=118936363&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=118936363&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_HomeEquityFirstLienMember
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:

- Details

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