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Stock-Based Compensation Narrative (Details) - USD ($)
$ in Thousands
12 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2015
Stock-Based Compensation      
Stock based compensation expense $ 3,709 $ 4,562 $ 3,768
Restated 2006 Plan      
Stock-Based Compensation      
Maximum number of shares that may be granted to one participant during any twelve month period 2,000,000    
Maximum amount that may be paid in cash as a performance-based award to one participant during any twelve month period $ 5,000    
Restated 2006 Plan | Maximum      
Stock-Based Compensation      
Number of shares authorized to be issued pursuant to awards 4,884,157    
Restated 2006 Plan | Incentive stock options | Minimum      
Stock-Based Compensation      
Percentage of the fair market value on date of grant 100.00%    
2002 Plan | Stock options      
Stock-Based Compensation      
Exercisable period from grant date 5 years    
Number of awards that may be granted 0    
1992 Plan | Stock options      
Stock-Based Compensation      
Exercisable period from grant date 5 years