Income (Loss) Per Share of Common Stock - Summary of Reconciliation of Numerator and Denominator Used to Calculate Basic and Diluted Loss Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended		9 Months Ended
	May. 31, 2015	Aug. 31, 2014	May. 31, 2014	Feb. 28, 2014	May. 31, 2015	May. 31, 2014	Aug. 31, 2014
Numerator:
Income (loss) from continuing operations	$ 18.4	$ (10.1)	$ (50.1)	$ (2.3)	$ 14.3	$ (52.4)
(Loss) income from discontinued operations, net of income taxes	0.0	0.2	(0.8)	0.0	0.2	(0.8)	$ (0.6)
Net income (loss)	18.4	$ (9.9)	(50.9)	$ (2.3)	14.5	(53.2)	$ (63.1)
Income allocated to participating securities	(0.5)		0.0		(0.4)	0.0
Net income (loss) for basic earnings per share	17.9		(50.9)		14.1	(53.2)
Interest on convertible subordinated debentures	1.0		0.0		2.2	0.0
Net income (loss) for diluted earnings per share	$ 18.9		$ (50.9)		$ 16.3	$ (53.2)
Denominator:
Basic weighted average shares (in shares)	61.2		57.9		59.9	58.7
Effect of:
4 1/16% Convertible Subordinated Debentures (“4 1/16% Debentures”) (in shares)	10.9		0.0		12.0	0.0
Employee stock options and stock purchase plan (in shares)	0.2		0.0		0.3	0.0
Diluted weighted average shares (in shares)	72.3		57.9		72.2	58.7
Basic
Income (loss) per share from continuing operations (in USD per share)	$ 0.29	$ (0.18)	$ (0.87)	$ (0.04)	$ 0.23	$ (0.90)
Loss per share from discontinued operations, net of income taxes (in USD per share)	0.00	0.00	(0.01)	0.00	0.00	(0.01)
Net income (loss) per share (in USD per share)	0.29	$ (0.18)	(0.88)	$ (0.04)	0.23	(0.91)
Diluted
Income (loss) per share from continuing operations (in USD per share)	0.26		(0.87)		0.22	(0.90)
Loss per share from discontinued operations, net of income taxes (in USD per share)	0.00		(0.01)		0.00	(0.01)
Net income (loss) per share (in USD per share)	$ 0.26		$ (0.88)		$ 0.22	$ (0.91)