Number of Unrelated Parties

No definition available.

Name:	smmf_NumberofUnrelatedParties
Namespace Prefix:	smmf_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Subordinated borrowing, not pre-payable within number of years.

+ References

No definition available.

+ Details

Name:	smmf_SubordinatedBorrowingNotPrePayableWithinNumberOfYears
Namespace Prefix:	smmf_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Subordinated borrowing, term

+ References

No definition available.

+ Details

Name:	smmf_SubordinatedBorrowingTerm
Namespace Prefix:	smmf_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Subordinated debt amount qualifying as tier two capital reduced by percent each year until maturity.

+ References

No definition available.

+ Details

Name:	smmf_SubordinatedDebtAmountQualifyingAsTierTwoCapitalReducedByPercentEachYearUntilMaturity
Namespace Prefix:	smmf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Subordinated Debt, Number of Issuances

+ References

No definition available.

+ Details

Name:	smmf_SubordinatedDebtNumberofIssuances
Namespace Prefix:	smmf_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Subordinated debt qualifies as tier two capital under federal reserve board guidelines, debt maturity

+ References

No definition available.

+ Details

Name:	smmf_SubordinatedDebtQualifiesAsTierTwoCapitalUnderFederalReserveBoardGuidelinesDebtMaturityDate
Namespace Prefix:	smmf_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow from the repayment of long-term borrowing where a lender is placed in a lien position behind debt having a higher priority of repayment (senior) in case of liquidation of the entity's assets before its maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

+ Details

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

- Definition

Stated interest rate of the subordinated debt.

+ References

No definition available.

+ Details

Name:	us-gaap_SubordinatedBorrowingInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of subordinated debt (with initial maturities beyond one year or beyond the operating cycle if longer). Subordinated debt places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Article 5
-Subsection 19, 20, 22

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 10
-Section F

+ Details

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

- Details

Name:	smmf_RelatedAndUnrelatedPartiesAxis=us-gaap_DirectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	smmf_RelatedAndUnrelatedPartiesAxis=smmf_UnrelatedPartyOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	smmf_RelatedAndUnrelatedPartiesAxis=smmf_UnrelatedPartyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Borrowed Funds Borrowed Funds (Subordinated Debentures) (Narrative) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2009 USD ($) loan party	Dec. 31, 2008 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Subordinated debentures	$ 0	$ 6,800,000	$ 10,000,000	$ 16,800,000
Tier 2 capital	5 years
Tier 2 capital decrease each year until maturity	20.00%
Number of unrelated parties \| party		2
Number of issuances \| loan		3
Interest rate		10.00%
Number of years subordinated borrowing is not pre-payable		5 years
Term of subordinated borrowing		10 years	7 years 6 months
Basis spread on variable rate	0.50%		2.75%
Prepaid subordinated debt	$ 16,800,000
Director [Member]
Debt Instrument [Line Items]
Subordinated debentures		$ 5,000,000
Unrelated Party One [Member]
Debt Instrument [Line Items]
Subordinated debentures		1,000,000
Unrelated Party Two [Member]
Debt Instrument [Line Items]
Subordinated debentures		$ 800,000