Balance Sheet Components - Intangible assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Intangible assets
Impairment	$ 0	$ (2,300,000)
Total intangible assets, net	31,710,556	33,397,222
Impairment	$ 0	2,300,000
Estimated useful life	15 years
Amortization expense	$ 1,686,657	702,778
Developed technology
Intangible assets
Total intangible assets	25,000,000	25,000,000
Accumulated amortization	(2,361,111)	(694,445)
Total intangible assets, net	22,638,889	24,305,555
In process research and development
Intangible assets
Total intangible assets	8,800,000	11,100,000
Impairment		(2,300,000)
Total intangible assets, net	8,800,000	8,800,000
Impairment		2,300,000
Trademarks
Intangible assets
Total intangible assets	300,000	300,000
Accumulated amortization	(28,333)	(8,333)
Total intangible assets, net	$ 271,667	$ 291,667