Balance Sheet Components - Intangible assets (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Intangible assets
Finite-lived intangible assets, net	$ 31,288,889		$ 31,710,556
Impairment	0
Total intangible assets, net	31,288,889		31,710,556
Impairment	0
Amortization expense	421,667	$ 421,667
Developed technology
Intangible assets
Total intangible assets	25,000,000		25,000,000
Accumulated amortization	(2,777,778)		(2,361,111)
Finite-lived intangible assets, net	22,222,222		22,638,889
In process research and development
Intangible assets
Total intangible assets	8,800,000		8,800,000
Trademarks
Intangible assets
Total intangible assets	300,000		300,000
Accumulated amortization	(33,333)		(28,333)
Finite-lived intangible assets, net	$ 266,667		$ 271,667