STOCKHOLDERS EQUITY (Additional Information) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2015	Dec. 31, 2018	Jul. 01, 2011	May 01, 2004
Stockholders Equity Note [Line Items]
Common Stock, Shares Authorized	100,000,000		100,000,000
Common Stock, Par or Stated Value Per Share	$ 1.00		$ 1
Dividend Reinvestment Plan [Member]
Dividend Reinvestment Plan [Abstract]
Dividend Reinvestment Plan, Description	The Company has a dividend reinvestment plan that is sponsored and administered by Computershare Shareholder Services as independent agent, which enables current shareholders as well as first-time buyers to purchase and sell common stock of Sandy Spring Bancorp, Inc. directly through Computershare at low commissions. Participants may reinvest cash dividends and make periodic supplemental cash payments to purchase additional shares.
Dividend Reinvestment Plan, Additional Dividends Potential Payment	$ 167,300,000
Loans due to related parties	$ 0		$ 0
Common Stock | Director Plan [Member]
Stockholders Equity Note [Line Items]
Common Stock, Shares Authorized					45,000
Shares available for issuance	24,424
Common Stock | Director Plan [Member] | Minimum [Member]
Dividend Reinvestment Plan [Abstract]
Percentage of fee of annual retainer fee to purchase shares	50.00%
Common Stock | Employee Stock Purchase Plan [Member]
Stockholders Equity Note [Line Items]
Shares authorized but unissued				300,000
Shares available for issuance	72,490
Share Exercise Price Description	Shares are purchased at 85% of the fair market value on the exercise date through monthly payroll deductions of not less than 1% or more than 10% of cash compensation paid in the month.
Dividend Reinvestment Plan [Abstract]
Percentage of fair market value of share price	85.00%
Common Stock | Employee Stock Purchase Plan [Member] | Minimum [Member]
Dividend Reinvestment Plan [Abstract]
Percentage of cash compensation paid through payroll deductions	1.00%
Common Stock | Employee Stock Purchase Plan [Member] | Maximum [Member]
Dividend Reinvestment Plan [Abstract]
Percentage of cash compensation paid through payroll deductions	10.00%
Common Stock | 2015 stock repurchase plan [Member] | Current Repurchase Program [Member]
Stockholders Equity Note [Line Items]
Share Repurchase Program Shares Authorized To Acquire Outstanding Common Stock Percentage		5.00%
Repurchase of outstanding shares of common stock under Stock Repurchase Program		1,200,000
Stock Repurchased During Period, Shares		736,139
Stock Repurchased During Period, Value		$ 19,200,000
stock Repurchase Program Expiration Date		Aug. 31, 2017
Common Stock | 2018 stock repurchase plan [Member]
Stockholders Equity Note [Line Items]
Shares available for issuance	1,800,000
Stock Repurchased During Period, Shares	668,191
Stock Repurchased During Period, Value	$ 24,300,000