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Share Repurchase Plans (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 15 Months Ended
Nov. 30, 2017
Nov. 30, 2016
Nov. 30, 2017
Sep. 01, 2016
Equity, Class of Treasury Stock [Line Items]        
Total cost of repurchased shares $ 3,893 $ 12,156    
2016 To 2018 Share Repurchase Program [Member]        
Equity, Class of Treasury Stock [Line Items]        
Share buy-back plan, amount authorized       $ 75,000
Share buy-back plan, number of shares repurchased 35,250   325,823  
Average price of shares repurchased $ 110.42      
Total cost of repurchased shares $ 3,900   $ 35,000