PROPERTY AND EQUIPMENT, NET - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 494,231	$ 461,641
Less: Accumulated depreciation and amortization	(248,529)	(228,121)
Property and equipment, net	245,702	233,520
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	182,885	168,125
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	143,962	139,174
Capitalized software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	127,971	119,452
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 39,413	$ 34,890