Net Loss Per Common Share - Schedule of Potentially Dilutive Securities Excluded from Diluted Net Loss Per Common Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities
Potentially dilutive securities excluded from diluted net loss per common share	1,747,718	1,653,958	3,902,602
Redeemable Convertible Preferred Stock
Antidilutive Securities
Potentially dilutive securities excluded from diluted net loss per common share			2,486,199
Options to Purchase Common Stock
Antidilutive Securities
Potentially dilutive securities excluded from diluted net loss per common share	1,593,195	1,414,730	927,175
RSU
Antidilutive Securities
Potentially dilutive securities excluded from diluted net loss per common share	30,680
Common Stock Subject to Repurchase
Antidilutive Securities
Potentially dilutive securities excluded from diluted net loss per common share	96,153	211,538	461,538
Redeemable Convertible Preferred Stock Warrants
Antidilutive Securities
Potentially dilutive securities excluded from diluted net loss per common share			27,690
Common Stock Warrants
Antidilutive Securities
Potentially dilutive securities excluded from diluted net loss per common share	27,690	27,690