Interim Financial Statements - Additional Information (Detail)	3 Months Ended	6 Months Ended
	Feb. 28, 2018 USD ($) shares	Feb. 28, 2018 USD ($) shares
Share Repurchase Program - 2014
Equity, Class of Treasury Stock [Line Items]
Stock repurchased during period, shares | shares	0	0
Stock repurchase program total cost of repurchased shares		$ 137,000,000
Repurchase of common stock, shares | shares		3,206,226
Remaining authorized repurchase amount	$ 88,000,000	$ 88,000,000
Maximum | Share Repurchase Program - 2013
Equity, Class of Treasury Stock [Line Items]
Amount authorized for repurchase	$ 225,000,000	$ 225,000,000