Quarterly report [Sections 13 or 15(d)]

GOODWILL AND INTANGIBLE ASSETS (Narrative) (Details)

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GOODWILL AND INTANGIBLE ASSETS (Narrative) (Details) - USD ($)
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Apr. 01, 2025
Dec. 31, 2024
Finite-Lived Intangible Assets [Line Items]            
Goodwill $ 1,726,386,000   $ 1,726,386,000     $ 1,214,053,000
Intangible Assets 333,236,000   333,236,000     84,563,000
Impairment of goodwill or intangible assets     0      
Intangible assets, amortization expense $ 18,145,000 $ 5,804,000 $ 41,976,000 $ 13,693,000    
Core Deposits [Member] | Maximum [Member]            
Finite-Lived Intangible Assets [Line Items]            
Intangible assets, amortization period (years) 10 years   10 years      
Other Intangible Assets [Member] | Minimum [Member]            
Finite-Lived Intangible Assets [Line Items]            
Intangible assets, amortization period (years) 5 months   5 months      
Other Intangible Assets [Member] | Maximum [Member]            
Finite-Lived Intangible Assets [Line Items]            
Intangible assets, amortization period (years) 16 years   16 years      
American National            
Finite-Lived Intangible Assets [Line Items]            
Goodwill           $ 288,842,000
Sandy Spring            
Finite-Lived Intangible Assets [Line Items]            
Goodwill $ 512,333,000   $ 512,333,000   $ 512,333,000  
Goodwill, measurement period adjustments 15,400,000          
Sandy Spring | Wholesale Banking            
Finite-Lived Intangible Assets [Line Items]            
Goodwill 399,600,000   399,600,000      
Sandy Spring | Consumer Banking            
Finite-Lived Intangible Assets [Line Items]            
Goodwill $ 112,700,000   $ 112,700,000