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Stock-based Payments - Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 12, 2013
Feb. 18, 2011
Apr. 30, 2021
Apr. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation expense     $ 598 $ 600
Stock options award shares to purchase common stock (in shares) 16,667      
Grants in period, weighted average grant date fair value (in dollars per share)     $ 5.11 $ 5.33
Warrants outstanding (in shares)     0 0
Proceeds from warrant exercises     $ 3,900  
Stock issued during period shares stock options and warrants exercised (in shares)     161,000  
Equity Incentive Plan 2010        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expiration term of awards     10 years  
Strike price as percent of market value     100.00%  
Equity Incentive Plan 2010 | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares granted, net of forfeitures (in shares)   30,000,000    
2008 Equity Incentive Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expiration term of awards     10 years  
Director Compensation Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock options award shares to purchase common stock (in shares) 8,333      
Stock option award shares to purchase unregistered common stock (in shares) 1,667      
Vested percent 25.00%      
Director Compensation Plan | Board of Directors Chairman        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Term of option to purchase     5 years