INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 1,475				$ 916				$ 1,475	$ 916
Income tax expense (benefit)	18,227	$ 14,292	$ (5,348)	$ 300	$ 8,614	$ 9,531	$ 8,945	$ 9,338	27,471	$ 36,428	$ 31,824
Operating Loss Carryover [Member]
Operating Loss Carryforwards [Line Items]
Valuation allowance	19,900								19,900
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 23,000								23,000
WashingtonFirst Bankshares Inc | CARES Act
Operating Loss Carryforwards [Line Items]
Income tax expense (benefit)									$ (1,800)