Income Taxes - Schedule of reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax benefit using U.S. federal statutory rate	$ (27,918,000)	$ (46,464,000)	$ (86,426,000)
State income taxes, net of federal benefit	(5,486,000)	(6,694,000)	(5,570,000)
Stock-based compensation	4,379,000	(12,000)	(5,909,000)
Research and development tax credits	(2,491,000)	(3,743,000)	(2,468,000)
Effect of federal tax law change	0	0	86,035,000
Other adjustments - ASU 2016-09 adoption	0	0	6,135,000
Change in the valuation allowance	26,918,000	49,550,000	(39,045,000)
Convertible note	(128,000)	(128,000)	47,016,000
Permanent items	457,000	883,000	543,000
Foreign rate differential	3,414,000	2,649,000	0
Uncertain Tax Positions	0	0	3,056,000
Other	855,000	3,959,000	(3,367,000)
Income tax expense	$ 0	$ 0	$ 0