Net Loss per Share - Schedule of Anti-dilutive Shares Outstanding Excluded in Calculation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	1,809,718	6,499,921	6,308,030
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	1,294,128	1,130,141	938,250
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	47,312
The March 2017 Preferred stock warrant or common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total	468,278	680,027	680,027
Series B-1 Convertible Preferred Stock (as-converted)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total		3,848,023	3,848,023
Series A-2 Convertible Preferred Stock (as-converted)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Total		841,730	841,730