Fair Value Of Financial Instruments (Narrative) (Details) - USD ($)	Aug. 31, 2018	Aug. 31, 2017
Cash equivalents carried at cost	$ 58,000,000	$ 73,900,000
2018, 2016 and 2013 Fixed Rate Notes [Member]
Long-term debt, fair value	718,200,000	578,200,000
Long-term debt, carrying value, including accrued interest	718,200,000	578,200,000
2016 Variable Funding Notes [Member]
Long-term debt, fair value	0	60,100,000
Long-term debt, carrying value, including accrued interest	$ 0	$ 60,100,000