Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans (Details)

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Employee Benefit Plans (Details) (USD $)
In Millions, unless otherwise specified
4 Months Ended 12 Months Ended
May 31, 2012
May 31, 2012
Jan. 31, 2012
May 31, 2011
Employee Benefit Plans (Textual) [Abstract]        
Maximum percentage of salary deferral under incentive retirement plan   50.00%    
Percentage of employee pay eligible for employer matching contribution 6.00%   4.00%  
Percentage of eligible pay that is matched by the employer 50.00%   50.00%  
Company contributions to the Plan   $ 10.3   $ 3.5
Deferred compensation plans contribution   Eligible employees can defer up to 50% of their annual base salary and bonus and outside directors can defer 100% of their Board cash compensation    
Percentage of annual base salary that eligible employees can defer   50.00%    
Percentage of board cash compensation that may be deferred   100.00%    
Amounts accrued under deferred compensation plans $ 9.2 $ 9.2   $ 8.9