Net Loss Per Share - Common Stock Underlying Potentially Dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock dilutive securities	781,230	760,416
Convertible redeemable preferred stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock dilutive securities		638,416
Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock dilutive securities	317,630
Options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock dilutive securities	463,600	122,000