Balance Sheet Components - Intangible assets (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Intangible assets
Impairment	$ (4,000,000)	$ 0	$ (4,000,000)	$ 0
Finite-lived intangible assets, net	26,867,222		26,867,222		$ 31,710,556
Total intangible assets, net	26,867,222		26,867,222		31,710,556
Amortization expense	421,667	$ 843,334	421,667	$ 843,334
Developed technology
Intangible assets
Total intangible assets	25,000,000		25,000,000		25,000,000
Accumulated amortization	(3,194,445)		(3,194,445)		(2,361,111)
Finite-lived intangible assets, net	21,805,555		21,805,555		22,638,889
In process research and development
Intangible assets
Total intangible assets	8,800,000		8,800,000		8,800,000
Impairment			(4,000,000)
Finite-lived intangible assets, net	4,800,000		4,800,000		8,800,000
Trademarks
Intangible assets
Total intangible assets	300,000		300,000		300,000
Accumulated amortization	(38,333)		(38,333)		(28,333)
Finite-lived intangible assets, net	$ 261,667		$ 261,667		$ 271,667