Fair Value Of Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	Feb. 28, 2018	Aug. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents carried at cost	$ 69.4	$ 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
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
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	0.0	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	0.0	$ 60.1
2013, 2016, and 2018 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	720.7
2013, 2016, and 2018 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	$ 720.7