Goodwill And Other Intangible Assets (Summary Of Goodwill Activity) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2015 USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 6,198
Acquired goodwill, net	0
Ending balance	6,198
Community Banking [Member]
Goodwill [Roll Forward]
Beginning balance	1,488
Acquired goodwill, net	0
Ending balance	1,488
Insurance Services [Member]
Goodwill [Roll Forward]
Beginning balance	4,710
Acquired goodwill, net	0
Ending balance	$ 4,710

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

+ Details

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

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=smmf_CommunityBankingMember
Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
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Period Type: