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Retirement Plans (Narrative) (Details) - USD ($)
3 Months Ended 6 Months Ended 12 Months Ended
Nov. 30, 2017
Aug. 31, 2017
Aug. 31, 2016
Aug. 31, 2017
Aug. 31, 2016
Feb. 28, 2017
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plan, Amortization of Gain (Loss)   $ (500,000) $ (400,000) $ (900,000) $ (800,000)  
Contributions to pension plan       0    
Anticipated contribution during remainder of fiscal year   $ 0   $ 0    
Expected rate of return on plan assets           7.75%
Subsequent Event [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Contributions to pension plan $ 6,000,000