Retirement Plans (Narrative) (Details) $ in Thousands	12 Months Ended
	Aug. 31, 2017 USD ($) item	Aug. 31, 2016 USD ($)	Aug. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 1,700	$ 1,500	$ 1,200
Number of former executives | item	5
Number of highest compensation years | item	3
Actuarial loss	$ 287	$ (576)
Discount rate, liability	3.70%	3.30%
Discount Rate, net periodic benefit cost	3.30%	4.10%	4.00%
Supplemental Employee Retirement Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Actuarial loss	$ 200