Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies (Details Textual)

v2.4.0.8
Commitments and Contingencies (Details Textual) (USD $)
3 Months Ended
Aug. 31, 2014
May 31, 2014
Commitments and Contingencies (Textual)    
Commitments to purchase capital assets $ 5,600,000 $ 16,000,000
Line of Credit [Member]
   
Line of Credit Facility [Line Items]    
Amount outstanding 0  
Revolving Credit Facility [Member]
   
Line of Credit Facility [Line Items]    
Amount outstanding 0  
Maximum amount outstanding during period 100,000,000  
Interest rate on amount borrowed 3.25%  
Maximum borrowing capacity 750,000,000  
Expiration date Jun. 21, 2018  
Standby Letters of Credit [Member]
   
Line of Credit Facility [Line Items]    
Amount available 43,000,000 43,000,000
Expiration date range of letters of credit December 2014 and July 2015  
Irrevocable stand by letters of credit amount outstanding $ 0