v3.26.1
DERIVATIVE INSTRUMENTS - Schedule of Derivative Instruments Not Designated as Accounting Hedge (Details) - Not Designated as Hedging Instrument - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Derivative Instruments, Gain (Loss) [Line Items]        
Total gain (loss) on derivative instruments not designated as accounting hedges $ (120) $ (11) $ 89 $ 59
Interest Rate Contract | Income Statement Location [Axis]: msbi:FeesAndCommissionsMortgageBankingAndServicingAndOtherResidential        
Derivative Instruments, Gain (Loss) [Line Items]        
Total gain (loss) on derivative instruments not designated as accounting hedges $ (120) $ (11) $ 89 $ 59