Net Loss per Share - Anti-dilution (Details) - shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	4,848,698	2,995,952
Options to Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	4,315,942	2,773,066
Restricted Stock Unit Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from the calculation of diluted net loss per share attributable to common stockholders	532,756	222,886