COMMITMENTS AND CONTINGENCIES - Operating and Finance Leases Narrative (Details) $ in Thousands	1 Months Ended		3 Months Ended
	Jul. 31, 2019 USD ($) ft² renewal_option	Dec. 31, 2018 ft² renewal_option	Mar. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease renewal term			5 years
Operating lease option to terminate term			1 year
Leased area of office space executed but not yet commenced (in sq ft) | ft²	226,158
Lease executed but not yet commenced, term	15 years 6 months
Lease executed but not yet commenced, number of renewal options | renewal_option	2
Lease executed but not yet commenced renewal term	5 years
Lease executed but not yet commenced | $	$ 42,700		$ 82,692
Minimum
Lessee, Lease, Description [Line Items]
Operating lease term			1 year
Maximum
Lessee, Lease, Description [Line Items]
Operating lease term			12 years
Lease executed but not yet commenced, option to terminate leased space (up to)	50.00%
Equipment
Lessee, Lease, Description [Line Items]
Finance lease, remaining lease term			9 months 18 days
Oakland, California | Building
Lessee, Lease, Description [Line Items]
Operating lease term		12 years
Operating lease renewal term		5 years
Leased area of office space (in sq ft) | ft²		355,762
Operating lease, number of renewal options | renewal_option		2