PROPERTY AND EQUIPMENT - Property and Equipment (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 28,955	$ 26,235
Less: accumulated depreciation	(9,637)	(5,568)
Property and equipment, net	19,318	20,667
Office and computer equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 12,822	10,383
Office and computer equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated Life (in years)	3
Office and computer equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated Life (in years)	8
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 10,503	10,572
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated Life (in years)	10
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 3,794	3,794
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated Life (in years)	2
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated Life (in years)	8
Software
Property, Plant and Equipment [Line Items]
Estimated Life (in years)	3 years
Property, plant and equipment, gross	$ 1,836	$ 1,486