Securities (Narrative) (Details) - Jun. 30, 2015	security state
Available-for-sale Securities [Abstract]
Number of states with highest volume of state and political subdivision securities \| state	5
Securities held with an unrealized loss position	83

State and Political Subdivisions Securities, Number of States with Highest Volume

No definition available.

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