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ACQUISITION OF WASHINGTONFIRST BANKSHARES, INC (Details) - Subsequent Event [Member]
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
Banks
shares
Jan. 01, 2018
USD ($)
$ / shares
Sandy Spring Bank [Member]    
Business Acquisition [Line Items]    
Number of shares issued by the company, pursuant to acquisition | shares 11,446,441  
Weighted average [Member] | Sandy Spring Bank [Member]    
Business Acquisition [Line Items]    
Share Price | $ / shares   $ 39.5051
Business acquistion, WashingtonFirst Bank    
Business Acquisition [Line Items]    
Effective Date of Acquisition Jan. 01, 2018  
Transaction value, business combination $ 452  
Number of Banking Offices | Banks 19  
Assets of new acquisition   $ 2,100
Provisional amount of goodwill recognized   $ 264
Business acquistion, WashingtonFirst Bank | Sandy Spring Shareholders    
Business Acquisition [Line Items]    
Percentage of voting interests acquired, combined co.   67.70%
Business acquistion, WashingtonFirst Bank | WashingtonFirst Shareholders    
Business Acquisition [Line Items]    
Percentage of voting interests acquired, combined co.   32.30%