LEASES - Narrative (Details) ft² in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2020 USD ($) ft²	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	May 31, 2015 ft²	Feb. 28, 2015 ft²
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 3,814	$ 3,814		$ 4,850
Right-of-use assets	2,202	2,202		4,048
Deferred rent					$ 800
Impairment of right-of-use lease asset		$ 939
San Jose California Facility
Lessee, Lease, Description [Line Items]
Impairment of right-of-use lease asset	$ 900
Forecast | Administrative and Headquarters Facility
Lessee, Lease, Description [Line Items]
Right-of-use assets			$ 600
Area | ft²			5
Lease agreements | San Jose California Facility
Lessee, Lease, Description [Line Items]
Area | ft²						33	42
ASU 2016-02
Lessee, Lease, Description [Line Items]
Operating lease liabilities				$ 4,900
Operating lease, borrowing rate				3.25%
Right-of-use assets				$ 4,000