COMMITMENTS AND CONTINGENCIES - Narrative (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Jul. 31, 2019 USD ($) ft² renewal_option	Dec. 31, 2018 USD ($) ft² renewal_option	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease renewal term			5 years
Operating lease option to terminate term			1 year
Total lease payments over term			$ 534,778
Leased area of office space executed but not yet commenced (in sq ft) | ft²	226,258
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		383,669
Total rental expenses for operating leases			39,319
Total rental expenses for operating leases			$ 32,500	$ 23,300	$ 12,900
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			2 years
Oakland, California | Building
Lessee, Lease, Description [Line Items]
Operating lease term		12 years		12 years
Operating lease renewal term		5 years		5 years
Leased area of office space (in sq ft) | ft²		355,762
Operating lease, number of renewal options | renewal_option		2
Total lease payments over term		$ 276,000		$ 276,000