Net Loss Per Share - Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	15,480,421	17,015,005	55,007,222
Convertible preferred stock
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding			43,933,006
Warrants to purchase convertible preferred stock
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding			135,567
Restricted Common Stock
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	376,514	2,230,235	6,277,014
Stock options
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	15,103,907	14,784,770	4,661,635
Series A redeemable convertible preferred stock
Diluted net loss per share attributable to common stockholders
Percentage of cumulative dividends per year	8.00%