Stock Based Compensation - Classification of expense (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Share-Based Compensation        
Stock-based compensation expense $ 2,344 $ 880 $ 5,935 $ 1,823
Total unrecognized compensation cost 18,483   $ 18,483  
Expenses expected to be recognized over a weighted average remaining period     2 years 8 months 12 days  
Research and development expenses        
Share-Based Compensation        
Stock-based compensation expense 1,318 473 $ 2,974 989
General and administrative expenses        
Share-Based Compensation        
Stock-based compensation expense $ 1,026 $ 407 $ 2,961 $ 834