Securities (Narrative) (Details)	3 Months Ended
Mar. 31, 2013 security
Securities [Abstract]
Available for sale securities, number of securities	61

Number of available-for-sale (AFS) securities with other-than- temporary impairment in which a portion of the impairment remains in other comprehensive income having an unrealized loss at the reporting date.

No definition available.

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