Income Taxes - Provision for Income Taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012	Aug. 31, 2011
Income Tax Disclosure [Abstract]
Provision for current federal taxes	$ 48.4	$ 47.9	$ 36.9
Provision for current state taxes	6.9	5.4	3.9
Provision for current foreign taxes	4.2	3.7	2.3
Provision for deferred taxes	6.2	5.7	9.0
Total provision for income taxes	$ 65.7	$ 62.7	$ 52.1