Balance Sheet Components - Intangible assets (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Intangible assets
Impairment	$ 0	$ 0
Finite-lived intangible assets, net	25,602,000		$ 26,024,000
Total intangible assets, net	25,602,000		26,024,000
Amortization expense	422,000	$ 422,000
Developed technology
Intangible assets
Total intangible assets	25,000,000		25,000,000
Accumulated amortization	(4,444,000)		(4,028,000)
Finite-lived intangible assets, net	20,556,000		20,972,000
In process research and development
Intangible assets
Total intangible assets	4,800,000		8,800,000
Impairment			(4,000,000)
Finite-lived intangible assets, net	4,800,000		4,800,000
Trademarks
Intangible assets
Total intangible assets	300,000		300,000
Accumulated amortization	(54,000)		(48,000)
Finite-lived intangible assets, net	$ 246,000		$ 252,000