Fair Value Of Financial Instruments (Narrative) (Details) - USD ($)	Aug. 31, 2017	Aug. 31, 2016
Cash equivalents carried at cost	$ 73,900,000	$ 59,200,000
2016 and 2013 Fixed Rate Notes [Member]
Long-term debt, fair value	578,200,000	579,600,000
Long-term debt, carrying value, including accrued interest	578,200,000	579,600,000
2016 Variable Funding Notes [Member]
Long-term debt, fair value	60,100,000	0
Long-term debt, carrying value, including accrued interest	$ 60,100,000	$ 0