ACQUISITION OF WASHINGTONFIRST BANKSHARES INC -acquired assets liabilities (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Jan. 31, 2018	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Purchase price:
Fair value of common share issue (11,446,197 shares), based on Sandy Spring's share price of $39.02	$ 446,640	$ 446,640
Cash for fractional shares	10
Total purchase price	$ 446,650
Identifiable assets and liabilities:
Cash and cash equivalents			$ 32,497
Residential mortgage loans held for sale			25,789
Investment securities			302,321
Loans			1,680,278
Premises and equipment			4,602
Other Real Estate Owned			497
Accrued Interest Receivable			6,648
Other Intangible assets			11,370
Other Assets			33,764
Total identifiable assets			2,097,766	$ 2,100,000
Deposits			1,610,327
Other Liabilities			283,808
Borrowings			17,525
Total identifiable liabilities			1,911,660
Provisional fair value of net assets acquired including identifiable intangible assets			186,106
Provisional resulting goodwill			$ 260,544