Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net unrealized gain (loss) on cashflow hedge	$ (3,714)smmf_CashflowHedge	$ 803smmf_CashflowHedge	$ 0smmf_CashflowHedge
Net unrealized gain (loss) on cashflow hedge, deferred taxes	(1,374)	297	0
Non-credit related other-than-temporary impairment on available for sale debt securities	0	37	857
Non-credit related other-than-temporary impairment on available for sale debt securities, deferred taxes	0	14	326
Net unrealized gain (loss) on available for sale debt securities	7,037	(8,527)	2,550
Net unrealized gain (loss) on available for sale debt securities, deferred taxes	2,604	(3,155)	969
Reclassification adjustment for net realized gains (losses) included in net income	$ 213	$ 240	$ 2,348

Cash flow Hedge

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Net unrealized (loss) on cashflow hedge, deferred tax.

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Amount after tax of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

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Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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Amount of tax expense (benefit) before reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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Amount before tax of other than temporary impairment (OTTI) on investment in available-for-sale debt security, recognized in other comprehensive loss.

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