Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Summary of Warrant Activity (Details)

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Stockholders' Equity - Summary of Warrant Activity (Details) - Warrant - USD ($)
6 Months Ended
Oct. 31, 2019
Apr. 30, 2019
Oct. 31, 2019
Number of Shares      
Balance Outstanding, April 30, 2019 (in shares)     731,152
Granted (in shares)     0
Exercised (in shares)     (164,929)
Surrendered (in shares)     0
Expired (in shares)     0
Balance Outstanding, October 31, 2019 (in shares) 566,223 731,152 566,223
Exercisable, October 31, 2019 (in shares) 516,223   516,223
Weighted Average Exercise Price      
Balance Outstanding, April 30, 2019 (in dollars per share)     $ 5.28
Granted (in dollars per share)     0
Exercised (in dollars per share)     2.05
Surrendered (in dollars per share)     0
Expired (in dollars per share)     0
Balance Outstanding, October 31, 2019 (in dollars per share) $ 6.22 $ 5.28 6.22
Exercisable, October 31, 2019 (in dollars per share) $ 6.35   $ 6.35
Weighted Average Remaining Contractual Term      
Weighted Average Remaining Contractual Term 3 years 7 months 28 days 3 years 3 months 14 days  
Weighted Average Remaining Contractual Term, Exercisable 3 years 7 months 2 days    
Aggregate Intrinsic Value      
Average Intrinsic Value $ 154,820 $ 413,296 $ 154,820
Aggregate Intrinsic Value, Exercisable $ 86,820   $ 86,820