ACQUISITION OF REVERE BANK - Provisional fair values of acquired identifiable assets and liabilities assumed (Details) - USD ($) $ / shares in Units, $ in Thousands		9 Months Ended
	Apr. 01, 2020	Sep. 30, 2020
Purchase price:
Fair value of common shares issued (12,768,949 shares) based on Sandy Spring's share price of $22.64	$ 289,089	$ 289,089
Fair value of Revere stock options converted to Sandy Spring stock options	3,611
Cash paid for cashed-out Revere stock options	291
Cash for fractional shares	11
Total purchase price	293,002
Identifiable assets:
Cash and cash equivalents	80,768
Investments available-for-sale	180,752
Loans	2,502,244
Premises and equipment	3,443
Accrued interest receivable	7,651
Core deposit intangible asset	18,360
Other assets	52,812
Total identifiable assets	2,846,030
Identifiable liabilities:
Deposits	2,322,422
Borrowings	205,514
Other liabilities	25,933
Total identifiable liabilities	2,553,869
Provisional fair value of net assets acquired including identifiable intangible assets	292,161
Provisional resulting goodwill	$ 841
Stock issued during period (in shares)	12,768,949	12,768,949
Closing price (in dollars per share)	$ 22.64