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FHLB ADVANCES - Summary of FHLB Advances (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
FHLB ADVANCES AND OTHER BORROWINGS    
Total FHLB advances $ 258,000 $ 293,000
FHLB advances, collateral for mortgage and home equity line of credit loans 2,580,000 2,870,000
Line of credit facility, maximum borrowing capacity 770,000  
Midland States Bank | Fixed rate fixed term maturing October 2029    
FHLB ADVANCES AND OTHER BORROWINGS    
Total FHLB advances $ 108,000 $ 168,000
Interest rate 3.93% 4.08%
Midland States Bank | Putable fixed rate maturing July 2034    
FHLB ADVANCES AND OTHER BORROWINGS    
Total FHLB advances $ 150,000 $ 125,000
Interest rate 3.56% 4.00%