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Stock-based Compensation (Details 2) (Stock options, USD $)
Share data in Thousands, except Per Share data, unless otherwise specified
 12 Months Ended
Aug. 31, 2012
Aug. 31, 2011
Aug. 31, 2010
Aug. 31, 2009
Weighted-average assumptions for grants of stock options        
Dividend rate (as a percent)   0.00% 0.00%  
Risk-free interest rate (as a percent)   2.20% 2.70%  
Expected term (in years)   6 years 3 months 18 days 6 years 2 months 12 days  
Expected volatility (as a percent)   48.10% 69.30%  
Other information on stock options        
Weighted-average grant date fair value of stock options granted (in dollars per share)   $ 6.85 $ 6.86  
Number of Stock Options Outstanding        
Outstanding at the beginning of the period (in shares) 775 507 950  
Granted (in shares)   453 138  
Forfeited (in shares) (118) (85) (25)  
Exercised (in shares) (81) (100) (556)  
Outstanding at the end of the period (in shares) 576 775 507 950
Vested and expected to vest at the end of the period (in shares) 521      
Exercisable at the end of the period (in shares) 235      
Weighted-Average Exercise Price        
Outstanding at the beginning of the period (in dollars per share) $ 8.20 $ 1.12 $ 0.56  
Granted (in dollars per share)   $ 14.31 $ 1.68  
Forfeited (in dollars per share) $ 11.64 $ 6.95 $ 0.84  
Exercised (in dollars per share) $ 0.86 $ 0.78 $ 0.42  
Outstanding at the end of the period (in dollars per share)per $ 8.54 $ 8.20 $ 1.12 $ 0.56
Vested and expected to vest at the end of the period (in dollars per share) $ 8.23      
Exercisable at the end of the period (in dollars per share) $ 5.74      
Weighted-Average Remaining Contractual Life        
Outstanding at the beginning of the period 7 years 7 months 6 days 8 years 6 months 8 years 1 month 6 days 7 years 7 months 6 days
Outstanding at the end of the period 7 years 7 months 6 days 8 years 6 months 8 years 1 month 6 days 7 years 7 months 6 days
Vested and expected to vest at the end of the period 7 years 6 months      
Exercisable at the end of the period 6 years 9 months 18 days      
Aggregate Intrinsic Value        
Outstanding at the beginning of the period $ 1,456,000 $ 4,766,000 $ 41,000  
Outstanding at the end of the period 263,000 1,456,000 4,766,000 41,000
Vested and expected to vest at the end of the period 257,000      
Exercisable at the end of the period 173,000      
Additional information on stock options        
Aggregate intrinsic value of options exercised 300,000 800,000 3,000,000  
Unrecognized compensation cost related to unvested stock options 1,300,000 2,000,000    
Weighted-average remaining period over which expense will be recognized 2 years 3 months 18 days 3 years 3 months 18 days    
Employees
        
Other information on stock options        
Aggregate grant date fair value of stock options granted to employees   $ 3,100,000 $ 874,000  
Number of Stock Options Outstanding        
Granted (in shares)   453