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Stock-based Payments - Stock Purchase Warrants Activity (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Apr. 30, 2019
Apr. 30, 2018
Apr. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]      
Aggregate Intrinsic Value, Exercised $ 905    
Aggregate Intrinsic Value, Forfeited $ 388    
Warrant      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Number of Shares, Beginning Balance 2,004,284 2,004,284  
Number of Shares, Granted 0 0  
Number of Shares, Exercised (247,468) 0  
Number of Shares, Forfeited (85,376) 0  
Number of Shares, Expired 0 0  
Number of Shares, Ending Balance 1,671,440 2,004,284 2,004,284
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]      
Weighted Average Exercise Price, Beginning Balance (in usd per share) $ 5.57 $ 5.57  
Weighted Average Exercise Price, Granted (in usd per share) 0.00 0.00  
Weighted Average Exercise Price, Exercised (in usd per share) 5.28 0  
Weighted Average Exercise Price, Forfeited (in usd per share) 4.80 0  
Weighted Average Exercise Price, Expired (in usd per share) 0.00 0.00  
Weighted Average Exercise Price, Ending Balance (in usd per share) $ 6.20 $ 5.57 $ 5.57
Weighted Average Remaining Contractual Life (Years), Balance 10 months 25 days 1 year 9 months 18 days 2 years 9 months 18 days
Aggregate Intrinsic Value, Beginning Balance $ 0 $ 0  
Aggregate Intrinsic Value, Granted 0 0  
Aggregate Intrinsic Value, Ending Balance $ 5,730 $ 0 $ 0