Balance Sheet Components - Intangible assets (Details) - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Intangible assets
Impairment		$ (2,300,000)				$ (2,300,000)
Total intangible assets, net	$ 32,132,222	33,397,222		$ 32,132,222		33,397,222
Amortization expense	421,667		$ 281,111	1,265,000	$ 281,111
Developed technology
Intangible assets
Total intangible assets	25,000,000	25,000,000		25,000,000		25,000,000
Accumulated amortization	(1,944,445)	(694,445)		(1,944,445)		(694,445)
Total intangible assets, net	23,055,555	24,305,555		23,055,555		24,305,555
In process research and development
Intangible assets
Total intangible assets	8,800,000	11,100,000		8,800,000		11,100,000
Impairment						(2,300,000)
Total intangible assets, net	8,800,000	8,800,000		8,800,000		8,800,000
Trademarks
Intangible assets
Total intangible assets	300,000	300,000		300,000		300,000
Accumulated amortization	(23,333)	(8,333)		(23,333)		(8,333)
Total intangible assets, net	$ 276,667	$ 291,667		$ 276,667		$ 291,667