LEASES - Lease Cost (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Fixed lease cost	$ 18,557
Variable lease cost	2,901
Net lease cost	21,458
Short-term Lease, Cost	600
Sublease Income	1,400
Cost of revenue
Lessee, Lease, Description [Line Items]
Fixed lease cost	207
Variable lease cost	0
Selling and marketing expense
Lessee, Lease, Description [Line Items]
Fixed lease cost	9,277
Variable lease cost	1,572
General and administrative expense
Lessee, Lease, Description [Line Items]
Fixed lease cost	7,617
Variable lease cost	1,021
Product development expense
Lessee, Lease, Description [Line Items]
Fixed lease cost	1,456
Variable lease cost	$ 308