Net Loss Per Share - Common Stock Underlying Potentially Dilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock dilutive securities	838,526	1,919,247
Convertible Promissory Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock dilutive securities		188,593
Convertible redeemable preferred stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock dilutive securities		1,608,654
Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock dilutive securities	312,426
Options to purchase common stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock dilutive securities	526,100	122,000