STOCKHOLDERS EQUITY (Additional Information) (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2015	Dec. 31, 2017	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		$ 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	$ 94.6
Common Stock | Current Repurchase Program [Member]
Stockholders Equity Note [Line Items]
Share Repurchase Program Shares Authorized To Acquire Outstanding Common Stock Percentage	5.00%
Common Stock | Director Plan [Member]
Stockholders Equity Note [Line Items]
Shares authorized but unissued					45,000
Shares available for issuance	25,291
Common Stock | Employee Stock Purchase Plan [Member]
Stockholders Equity Note [Line Items]
Shares authorized but unissued				300,000
Shares available for issuance	109,571
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
Common Stock | 2015 stock repurchase plan [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		$ 19.2
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