Net Loss Per Share - Antidilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	16,246,836	17,345,706
Restricted Common Stock
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	397,252	2,644,423
Stock options
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	15,849,584	14,701,283