PENDING ACQUISITION (Details) $ / shares in Units, $ in Millions		9 Months Ended
	May 15, 2017 USD ($) Banks $ / shares	Sep. 30, 2017
Business Acquisition [Line Items]
Common stock ratio of Parent and Acquiree stock	0.8713
The combined entity name		Maryland corporation
Expected period to close acquisition transaction		The transaction, which is expected to close in the fourth quarter of 2017
Contingent Consideration Arrangements Description		Under the terms of the agreement, WashingtonFirst shareholders are expected to receive 0.8713 shares of Company common stock for each share owned of WashingtonFirst common stock, subject to adjustment if the Company’s average stock price during a specified measurement period prior to closing is more than $50.15 or less than $37.07 per share.
Sandy Spring Bank [Member]
Business Acquisition [Line Items]
Share Price	$ 42.72
Percentage of Voting Interests Acquired	67.80%
Maximum [Member] | Sandy Spring Bank [Member]
Business Acquisition [Line Items]
Share Price	$ 50.15
Minimum [Member] | Sandy Spring Bank [Member]
Business Acquisition [Line Items]
Share Price	$ 37.07
WashingtonFirst Bank [Member]
Business Acquisition [Line Items]
Estimated Amount of Payment to Acquire Business, Gross | $	$ 498
Percentage of Voting Interests Acquired	32.20%
Assets of new acquisition | $	$ 2,100
Number of Banking Offices | Banks	19