v3.26.1
DERIVATIVE INSTRUMENTS - Schedule of Derivative Instruments (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Derivative Instruments and Hedging Activities Disclosures [Line Items]        
Gain (loss) recognized in income on derivative $ (517) $ 223 $ (166) $ 1,087
Gain (loss) reclassified from AOCI into income (194) (642) (541) (1,479)
Interest Rate Contract | Income Statement Location [Axis]: us-gaap:InterestExpenseOperating        
Derivative Instruments and Hedging Activities Disclosures [Line Items]        
Gain (loss) recognized in income on derivative 372 (86) 1,022 (785)
Gain (loss) reclassified from AOCI into income (30) 104 (60) 245
Interest Rate Contract | Income Statement Location [Axis]: us-gaap:InterestIncomeSecuritiesTaxable        
Derivative Instruments and Hedging Activities Disclosures [Line Items]        
Gain (loss) recognized in income on derivative (336) 71 (431) 517
Gain (loss) reclassified from AOCI into income (54) (5) (108) 82
Interest Rate Contract | Income Statement Location [Axis]: us-gaap:NoninterestExpense        
Derivative Instruments and Hedging Activities Disclosures [Line Items]        
Gain (loss) recognized in income on derivative     (154) 0
Gain (loss) reclassified from AOCI into income     (154) 0
Interest Rate Contract | Income Statement Location [Axis]: msbi:InterestAndFeeIncomeLoansAndLeasesTaxable        
Derivative Instruments and Hedging Activities Disclosures [Line Items]        
Gain (loss) recognized in income on derivative (553) 238 (603) 1,355
Gain (loss) reclassified from AOCI into income $ (110) $ (741) $ (219) $ (1,806)