LEASES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessor, Lease, Description [Line Items]
Term of contract	11 years
Operating lease, cost	$ 34,300
Variable lease, cost	400
Short term lease, cost	900
Sublease income	100
Operating lease, expense		$ 11,700	$ 7,400
Operating lease, payments	12,700	10,800
Right of use assets obtained in exchange for operating lease liability	39,800	57,900
Reduction in right of use assets	28,300	2,900
Amortization of right of use asset	$ 23,744	$ 11,940	$ 0
Remaining lease term	6 years 6 months	4 years 6 months
Weighted average discount (in percent)	9.10%	7.20%
San Francisco Office
Lessor, Lease, Description [Line Items]
Reduction in right of use assets	$ 28,100
Amortization of right of use asset	$ 12,500
Remaining lease term	1 year
Early termination fees	$ 5,200