STOCK-BASED COMPENSATION - Schedule of non-cash compensation expense related to equity awards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total non-cash compensation	$ 68,555	$ 53,733	$ 52,167
Cost of revenue
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total non-cash compensation	1,639	1,319	755
Selling and marketing expense
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total non-cash compensation	7,480	6,240	5,785
General and administrative expense
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total non-cash compensation	50,989	39,650	39,177
Product development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total non-cash compensation	$ 8,447	$ 6,524	$ 6,450