Common Stock and Related Matters - Earnings per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Basic Earnings per Share from Continuing Operations:
Income from continuing operations	$ 116.3	$ 105.5	$ 79.0
Less: Income attributable to participating securities	(2.2)	(1.9)	(1.4)
Income from continuing operations available to common shareholders	114.1	103.6	77.6
Basic weighted average shares outstanding	41,400,000	42,200,000	42,500,000
Basic earnings per share from continuing operations	$ 2.75	$ 2.46	$ 1.83
Diluted Earnings per Share from Continuing Operations:
Income from continuing operations	116.3	105.5	79.0
Less: Income attributable to participating securities	(2.2)	(1.9)	(1.4)
Income from continuing operations available to common shareholders	114.1	103.6	77.6
Basic weighted average shares outstanding	41,400,000	42,200,000	42,500,000
Common stock equivalents	500,000	600,000	800,000
Diluted weighted average shares outstanding	41,900,000	42,800,000	43,300,000
Diluted earnings per share from continuing operations	$ 2.72	$ 2.42	$ 1.79
Basic Earnings per Share from Discontinued Operations:
Income (Loss) from Discontinued Operations	0	0	0.6
Basic weighted average shares outstanding	41,400,000	42,200,000	42,500,000
Basic earnings (loss) per share from discontinued operations	$ 0.00	$ 0.00	$ 0.01
Diluted Earnings per Share from Discontinued Operations:
Income (Loss) from Discontinued Operations	$ 0	$ 0	$ 0.6
Basic weighted average shares outstanding	41,400,000	42,200,000	42,500,000
Common stock equivalents	500,000	600,000	800,000
Diluted weighted average shares outstanding	41,900,000	42,800,000	43,300,000
Diluted earnings (loss) per share from discontinued operations	$ 0.00	$ 0.00	$ 0.01
Stock Options
Earnings per Share, Basic and Diluted [Line Items]
Stock options excluded from diluted earnings per share (in shares)	180,000	135,000