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Share-Based Compensation - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended
Nov. 30, 2015
Nov. 30, 2014
Nov. 30, 2015
Nov. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Awards outstanding to officers, directors and key employees 800,000   800,000  
Total number of shares cumulatively authorized to be issued under our stock incentive plans 7,120,000   7,120,000  
Share-based compensation $ 1,800,000 $ 1,500,000 $ 3,000,000 $ 2,500,000
Employee service share-based compensation, nonvested awards, compensation not yet recognized, share-based awards other than options $ 15,000,000   $ 15,000,000  
Remaining weighted-average period     2 years 10 months 24 days  
Tax benefit related to share-based compensation     $ 400,000 1,500,000
Weighted-average remaining contractual life of options exercisable     1 year 7 months 6 days  
Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation     $ 0 0
Award vesting period     4 years  
Stock option year term     10 years  
Long Term Performance Stock Unit Awards [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation     $ 200,000 0
Performance Period     3 years  
Service Period     3 years  
Settlement period     20 days  
Long Term Performance Stock Unit Awards [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Possible payouts     0.00%  
Long Term Performance Stock Unit Awards [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Possible payouts     300.00%  
Stock and Stock Units [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation     $ 2,500,000 $ 2,100,000
Stock and Stock Units [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period     2 years  
Stock and Stock Units [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Award vesting period       4 years
Performance Shares [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation     $ 200,000 $ 300,000
Award vesting period     4 years