Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies (Details Textual)

v3.3.1.900
Commitments and Contingencies (Details Textual) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
May. 31, 2016
Feb. 29, 2016
May. 31, 2015
Mar. 17, 2016
Commitments and Contingencies (Textual)        
Commitments to purchase capital assets   $ 5,800,000 $ 9,500,000  
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    
Line of credit facility, initial term   5 years    
Maximum borrowing capacity   $ 1,000,000,000 $ 750,000,000  
Expiration date   Aug. 05, 2020 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   April 2016 and December 2016    
Irrevocable stand by letters of credit amount outstanding   $ 0    
PNC credit facility [Member]        
Line of Credit Facility [Line Items]        
Subsequent Event, Date Mar. 17, 2016      
Maximum borrowing capacity       $ 150,000,000