LEASES - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Feb. 29, 2020	Apr. 30, 2019
Lessee, Lease, Description [Line Items]
Remeasurement adjustment	$ 500		$ 500		$ 7,000
ROU asset	6,912		6,912
Lease liability	8,268		8,268
Lease incentive receivable	1,983		1,983
Future minimum lease payments	13,372		13,372
Operating lease expense	$ 200	$ 0	$ 600	$ 1,300
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent		us-gaap:OtherAssetsNoncurrent
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent		us-gaap:OtherLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent		us-gaap:OtherLiabilitiesNoncurrent
3611 Valley Centre Drive, San Diego, California
Lessee, Lease, Description [Line Items]
Remaining lease term						7 years 7 months
Operating lease extension term						5 years
Future minimum lease payments	$ 49,500		$ 49,500
New Lease Space Delivered In Advance Of Lease Commencement
Lessee, Lease, Description [Line Items]
Operating lease discount rate	6.70%		6.70%
ROU asset	$ 8,900		$ 8,900
Lease liability	8,800		8,800
Future minimum lease payments	13,000		13,000
New Lease Space Not Yet Delivered
Lessee, Lease, Description [Line Items]
Lease incentive receivable	2,000		2,000
Future minimum lease payments	$ 36,500		$ 36,500