Deposits - Schedule of Maturities for Time Deposits (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Scheduled remaining maturity:
2018	$ 717,851
2019	140,680
2020	34,264
2021	23,878
2022	7,138
Thereafter	335
Total time deposits	$ 924,146

Time Deposit And Brokered Deposits, Maturities, Next Twelve Months

No definition available.

Name:	lion_TimeDepositAndBrokeredDepositsMaturitiesNextTwelveMonths
Namespace Prefix:	lion_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant