Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Summary of Stock Option Activity (Details)

v3.20.1
Stockholders' Equity - Summary of Stock Option Activity (Details) - USD ($)
9 Months Ended
Jan. 31, 2020
Apr. 30, 2019
Jan. 31, 2020
Number of Shares      
Balance Outstanding, January 31, 2019 (in shares) 2,776,778   2,776,778
Exercisable, January 31, 2019 (in shares) 1,824,684   1,824,684
Stock Incentive Plan and Stock Option Grants to Employees and Directors      
Number of Shares      
Balance Outstanding, April 30, 2019 (in shares)     3,408,154
Options granted (in shares)     150,000
Exercised (in shares)     (580,901)
Forfeited (in shares)     (200,475)
Balance Outstanding, January 31, 2019 (in shares) 2,776,778 3,408,154 2,776,778
Exercisable, January 31, 2019 (in shares) 1,824,684   1,824,684
Weighted Average Exercise Price      
Balance Outstanding, April 30, 2019 (in dollars per share)     $ 4.44
Granted (in dollars per share)     5.21
Exercised (in dollars per share)     2.72
Forfeited (in dollars per share)     7.44
Balance Outstanding, January 31, 2019 (in dollars per share) $ 4.61 $ 4.44 4.61
Exercisable, January 31, 2019 (in dollars per share) $ 3.77   $ 3.77
Stock Option Activity, Additional Disclosures      
Options outstanding, weighted average remaining contractual term 2 years 2 months 15 days 2 years 10 months 24 days  
Options outstanding, aggregate intrinsic value $ 14,302,102 $ 6,880,644 $ 14,302,102
Options exercisable, weighted average remaining contractual term 1 year 7 months 28 days    
Options exercisable, aggregate intrinsic value $ 11,808,246   $ 11,808,246