Stockholders' Equity - Summary of Restricted Stock Award Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Shares, Unvested Issued		675,000
Restricted Stock Awards [Member]
Number of Shares, Restricted stock awards outstanding, Unvested at beginning	2,391,665	6,309,874
Number of Shares, Unvested Issued	562,500	833,333
Number of Shares, Unvested Vested	(2,237,500)	(3,926,542)
Number of Shares, Restricted stock awards subject to repurchase
Number of Shares, Unvested Forfeited	(399,998)	(825,000)
Number of Shares Restricted stock awards outstanding, Unvested at ending	316,667	2,391,665
Number of Shares Common stock options, outstanding at Beginning balance	14,008,076	10,484,046
Number of Shares, Issued
Number of Shares, Vested	2,237,500	3,926,542
Number of Shares, Restricted stock awards subject to repurchase	(1,064,549)
Number of Shares, Forfeited	(746,813)	(402,512)
Number of Shares Common stock options, outstanding at Ending balance	14,434,214	14,008,076
Weighted Average Grant-Fair Value Date, Beginning balance	$ 0.56	$ 0.50
Weighted Average Grant-Fair Value Date, Issued	0.18	0.48
Weighted Average Grant-Fair Value Date, Vested
Weighted Average Grant-Fair Value Date, Forfeited
Weighted Average Grant-Fair Value Date, Ending balance	$ 0.42	$ 0.56