Net loss per share - Computation of diluted net loss per share attributable to common stockholders (Details) - shares
3 Months Ended 9 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Diluted net loss per share attributable to common stockholders        
Antidilutive securities excluded from computation of diluted weighted average shares outstanding 5,413,746 4,170,879 5,413,746 4,170,879
Options to purchase common stock        
Diluted net loss per share attributable to common stockholders        
Antidilutive securities excluded from computation of diluted weighted average shares outstanding 4,916,402 3,673,535 4,916,402 3,673,535
Warrant liability        
Diluted net loss per share attributable to common stockholders        
Antidilutive securities excluded from computation of diluted weighted average shares outstanding 497,344 497,344 497,344 497,344