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Accounting for Stock-Based Compensation (Details) (USD $)
In Millions, except Share data, unless otherwise specified
1 Months Ended 3 Months Ended 9 Months Ended
Jul. 31, 2012
Feb. 28, 2013
Feb. 29, 2012
Feb. 28, 2013
Y
Feb. 29, 2012
Y
Stock options
         
Share-Based Compensation          
Granted (in shares) 958,180        
Granted (in dollars per share) $ 12.90        
Fair value of stock options granted (in dollars) $ 4.6        
Assumptions used in the Black-Scholes option pricing models to estimate the fair value of each stock option grant          
Risk-free interest rate (as a percent)       0.60% 1.50%
Expected volatility of common stock (as a percent)       51.00% 46.00%
Dividend yield (as a percent)       2.30% 1.00%
Expected option term (in years)       5.4 5.7
Stock options, additional disclosures          
Total intrinsic value of stock options exercised       0.3 3.3
Compensation expense   1.0 1.1 2.6 3.3
Restricted stock
         
Stock options, additional disclosures          
Compensation expense   $ 2.3 $ 2.7 $ 5.4 $ 6.6
Granted (in shares) 65,780        
Granted (in dollars per share) $ 12.90        
Restricted stock | Board of Directors
         
Stock options, additional disclosures          
Granted (in shares) 45,000        
Granted (in dollars per share) $ 11.56        
Performance-based restricted stock
         
Stock options, additional disclosures          
Granted (in shares) 53,280        
Granted (in dollars per share) $ 12.90