STOCKHOLDERS' EQUITY - Effects of Share-Based Compensation on Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 77,303	$ 61,088
Cost of revenue
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	76	21
Product development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	57,400	42,649
Sales and marketing
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	6,407	6,202
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-based compensation expense	$ 13,420	$ 12,216