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Income Taxes - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Jan. 18, 2011
Income Taxes [Line Items]      
Income tax settlement amount $ 800    
Tax paid for income tax settlement 430    
Interest paid for income tax settlement 370    
Aggregate finance asserting liability total     3,852
Taxation payable     2,220
Penalties and interest payable     1,632
Potential cumulative liability 8.00%    
Net operating loss carryforwards 71,965    
Net operating loss carryforwards expiry period 2024 through 2033    
State net operating loss carryforwards expiry period 85,304    
Net operating loss carryforwards benefit recorded additional paid-in capital 383    
Alternative minimum tax credit carryforwards 3,330 3,330  
General business tax credit carryforwards 2,095 1,438  
General business tax credit carryforwards expiration date 2023 through 2033    
Valuation allowance 19,652    
Settlements (430)    
Unrecognized tax benefit net of federal benefit on state issue 0 0  
Deferred tax assets unrecognized tax benefits subject to valuation allowance 398    
Uncertain tax positions, accrued interest 76 34  
Uncertain tax positions, penalties 9 9  
Accrued income tax expense 41 (95)  
Business Acquisition [Member]
      
Income Taxes [Line Items]      
Increase (decrease) in valuation allowance $ (5,084)    
State [Member]
      
Income Taxes [Line Items]      
Net operating loss carryforwards expiry period 2014 through 2033