Net loss per share (Tables)

12 Months Ended

Dec. 31, 2019

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,
	2019		2018
Warrants issued to 2010/2012 convertible note    holders to purchase common stock		102,070		102,070
Options to purchase common stock		2,123,117		1,667,153
Warrants issued in 2009 to purchase common stock		—		1,851
Warrants issued to underwriter to purchase common    stock		16,500		16,500
Series A warrants to purchase common stock		—		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		513,617
Total		9,483,974		9,514,982