Net loss per share (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Schedule of Potentially Dilutive Securities Outstanding Excluded from Computations of Diluted Weighted-Average Shares Outstanding

The following potentially dilutive securities outstanding have been excluded from the computations of diluted weighted-average shares outstanding because such securities have an antidilutive impact due to losses reported (in common stock equivalent shares).

	As of December 31,
	2018		2017
Convertible preferred stock		—		914,200
Warrants issued to 2010/2012 convertible note holders to    purchase common stock		102,070		102,070
Options to purchase common stock		1,667,153		1,026,987
Warrants issued in 2009 to purchase common stock		1,851		1,851
Warrants issued to underwriter to purchase common stock		16,500		16,500
Series A warrants to purchase common stock		485,121		485,121
Series C warrants to purchase common stock		118,083		118,083
Series D warrants to purchase common stock		586,162		586,162
2017 PIPE warrants		6,024,425		6,024,425
2018 PIPE warrants		513,617		—
Total		9,514,982		9,275,399