Principal Payments on Notes Payable (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
2018 Senior Notes
Debt Instrument [Line Items]
Convertible senior notes	$ 119,063	$ 119,063
Debt instrument, redemption, description	The repayment of the $119.1 million of Convertible senior notes due 2018 is assumed to occur in stock at the scheduled maturity in 2018 instead of assuming an earlier conversion by the holders.
2024 Convertible Senior Notes
Debt Instrument [Line Items]
Convertible senior notes	$ 275,000
Debt instrument, redemption, description	The repayment of the $275.0 million of Convertible senior notes due 2024 is assumed to occur at the scheduled maturity in 2024 instead of assuming an earlier conversion by the holders.