Long-term Debt - Summary of 4 1/16% Debentures Repurchased (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2015	May. 31, 2014	Aug. 31, 2014
Debt Instrument [Line Items]
Principal amount repurchased		$ 45.7		$ 50.2
Cash repurchase price		(91.4)		(100.8)
Loss on 4 1/16% Debentures repurchased	$ (0.5)	$ (45.9)	$ (0.7)	(50.8)	$ (60.6)
4 1/16% Convertible Subordinated Debentures [Member]
Debt Instrument [Line Items]
Principal amount repurchased				50.2
Cash repurchase price				(100.8)
Write-off of deferred financing costs				(0.2)
Loss on 4 1/16% Debentures repurchased				$ (50.8)