Stock-Based Compensation - Summary of Stock-Based Compensation Expense by Type of Award (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
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2.0	$ 1.6	$ 7.3	$ 3.0	$ 4.5
Stock Appreciation Rights [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1.3	(0.4)	3.8	(0.5)
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	0.2	0.1	0.3	0.1
Restricted Shares, Service Based [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	0.9	1.3	2.6	2.2
Restricted Shares, Performance Based [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ (0.4)	$ 0.6	$ 0.6	$ 1.2