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Share Repurchase Plans (Narrative) (Details) - USD ($)
$ in Thousands
12 Months Ended
Aug. 31, 2017
Aug. 31, 2016
Aug. 31, 2015
Equity, Class of Treasury Stock [Line Items]      
Total cost of repurchased shares $ 31,109 $ 32,131 $ 30,259
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 290,573    
Total cost of repurchased shares $ 31,100