Goodwill And Other Intangible Assets (Summary Of Other Intangible Assets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Unidentifiable intangible assets [Abstract]
Gross carrying amount	$ 2,268	$ 2,267
Less: accumulated amortization	2,268	2,216
Net carrying amount	0smmf_IndefiniteLivedIntangibleAssetsNet	51smmf_IndefiniteLivedIntangibleAssetsNet
Identifiable intangible assets [Abstract]
Gross carrying amount	3,000	3,000
Less: accumulated amortization	1,500	1,300
Net carrying amount	1,500us-gaap_FiniteLivedIntangibleAssetsNet	1,700us-gaap_FiniteLivedIntangibleAssetsNet
Community Banking [Member]
Unidentifiable intangible assets [Abstract]
Gross carrying amount	2,268	2,267
Less: accumulated amortization	2,268	2,216
Net carrying amount	0	51
Identifiable intangible assets [Abstract]
Gross carrying amount	0	0
Less: accumulated amortization	0	0
Net carrying amount	0	0
Insurance Services [Member]
Unidentifiable intangible assets [Abstract]
Gross carrying amount	0	0
Less: accumulated amortization	0	0
Net carrying amount	0	0
Identifiable intangible assets [Abstract]
Gross carrying amount	3,000	3,000
Less: accumulated amortization	1,500	1,300
Net carrying amount	$ 1,500	$ 1,700

Name:	smmf_IdentifiableintangibleassetsAbstract
Namespace Prefix:	smmf_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Indefinite-Lived Intangible Assets, Accumulated Amortization

+ References

No definition available.

+ Details

Name:	smmf_IndefiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix:	smmf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Indefinite-Lived Intangible Assets, Net

+ References

No definition available.

+ Details

Name:	smmf_IndefiniteLivedIntangibleAssetsNet
Namespace Prefix:	smmf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	smmf_UnidentifiableintangibleassetsAbstract
Namespace Prefix:	smmf_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

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

- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

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

- Definition

Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

+ Details

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

- Definition

Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

+ Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=smmf_CommunityBankingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=smmf_InsuranceServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: