Quarterly report [Sections 13 or 15(d)]

GOODWILL AND INTANGIBLE ASSETS (Narrative) (Details)

v3.26.1
GOODWILL AND INTANGIBLE ASSETS (Narrative) (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Dec. 31, 2025
Apr. 01, 2025
Finite-Lived Intangible Assets [Line Items]          
Goodwill $ 1,754,875,000   $ 1,754,875,000 $ 1,733,287,000  
Intangible Assets 300,099,000   $ 300,099,000 315,544,000  
Impairment of goodwill or intangible assets 0        
Intangible assets, amortization expense $ 15,446,000 $ 5,398,000      
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) 3 years   3 years    
Other Intangible Assets [Member] | Maximum [Member]          
Finite-Lived Intangible Assets [Line Items]          
Intangible assets, amortization period (years) 16 years   16 years    
Operating segments | Wholesale Banking          
Finite-Lived Intangible Assets [Line Items]          
Goodwill $ 1,281,726,000   $ 1,281,726,000 1,254,979,000  
Intangible Assets 49,719,000   49,719,000 50,916,000  
Operating segments | Consumer Banking          
Finite-Lived Intangible Assets [Line Items]          
Goodwill 473,149,000   473,149,000 478,308,000  
Intangible Assets 598,000   598,000 621,000  
Corporate Other          
Finite-Lived Intangible Assets [Line Items]          
Goodwill 0   0 0  
Intangible Assets 249,782,000   249,782,000 $ 264,007,000  
Sandy Spring          
Finite-Lived Intangible Assets [Line Items]          
Goodwill 540,800,000   540,800,000   $ 540,821,000
Goodwill, measurement period adjustments     44,000,000    
Sandy Spring | Wholesale Banking          
Finite-Lived Intangible Assets [Line Items]          
Goodwill 431,700,000   431,700,000    
Sandy Spring | Consumer Banking          
Finite-Lived Intangible Assets [Line Items]          
Goodwill 109,100,000   $ 109,100,000    
Sandy Spring | Operating segments | Wholesale Banking          
Finite-Lived Intangible Assets [Line Items]          
Goodwill, measurement period adjustments 26,700,000        
Sandy Spring | Operating segments | Consumer Banking          
Finite-Lived Intangible Assets [Line Items]          
Goodwill, measurement period adjustments $ (5,200,000)