Fair Value Of Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	Nov. 30, 2017	Aug. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents carried at cost	$ 70.9	$ 73.9
2016 and 2013 Fixed Rate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, carrying value, including accrued interest	578.2	578.2
2016 and 2013 Fixed Rate Notes [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	578.2	578.2
2016 Variable Rate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, carrying value, including accrued interest	98.2	60.1
2016 Variable Rate Notes [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 98.2	$ 60.1